WO2014103231A1

WO2014103231A1 - Mach-zehnder optical modulator, optical communication system, and control method for mach-zehnder optical modulator

Info

Publication number: WO2014103231A1
Application number: PCT/JP2013/007363
Authority: WO
Inventors: 峰斗佐藤
Original assignee: 日本電気株式会社
Priority date: 2012-12-25
Filing date: 2013-12-16
Publication date: 2014-07-03
Also published as: JPWO2014103231A1

Abstract

Timing among a plurality of electrical drive signals cannot be controlled with higher precision; therefore, this Mach-Zehnder optical modulator has: a splitting means for splitting light that is input; first and second waveguides that guide the waves of each split input light; a multiplexing means for multiplexing and outputting each input light that has been guided in the first and second waveguides; a signal generating circuit for generating a signal for transmission; a plurality of electrodes disposed along either or both of the first and second waveguides for modulating the input light according to the signal; a drive means that applies the signal to each of the plurality of electrodes according to the signal generated by the signal generating circuit; a detection means for detecting the intensity of output light that the multiplexing means outputs; and a control means for controlling the timing for applying the signal to each of the plurality of electrodes on the basis of the intensity of the output light detected by the detection means.

Description

Mach-Zehnder optical modulator, optical communication system, and control method for Mach-Zehnder optical modulator

The present invention relates to a Mach-Zehnder optical modulator, an optical communication system, and a control method for the Mach-Zehnder optical modulator.

The demand for broadband multimedia communication services such as the Internet and video distribution has increased explosively. Along with this, the introduction of high-density, wavelength-multiplexed optical fiber communication systems capable of longer-distance transmission, higher capacity, and higher reliability in the trunk line system and the metro system has been advanced. In a communication system using such an optical fiber, it is required to increase the transmission band utilization efficiency per optical fiber. In order to increase the transmission band utilization efficiency per optical fiber, it is necessary to increase the data symbol frequency or increase the multi-value number.

In order to operate with the data symbol frequency increased, the band of the element is an important factor. Taking an optical element (for example, an optical modulator) generally used in an optical fiber communication system as an example, the band is limited mainly due to the CR time constant limitation due to the influence of the resistance component R and the capacitance C of the element. . Since these optical elements utilize the interaction between light and electricity, the required voltage and the capacity of the element are determined by the electric field strength and the interaction length. In general, when the interaction length is long, the electric field intensity per unit length is small, but conversely, the capacitance of the element increases. Therefore, for example, in an optical modulator, power consumption, extinction characteristics, and bandwidth are in a trade-off relationship. Therefore, in such an optical element, an eclectic design in consideration of the trade-off relationship described above has to be performed.

On the other hand, a method for solving the trade-off relationship has been proposed. For example, Patent Document 1 proposes a structure including a plurality of electrodes for applying a voltage for modulating one or both of input light guided through a waveguide along the waveguide. Thereby, long electrodes can be electrically separated and driven independently, and the capacitance of the element can be reduced.

In such an electrode division structure, a drive unit is provided, and the drive unit applies a voltage to each of the plurality of electrodes in accordance with an electric signal input thereto. Here, in order to appropriately match the timing at which the voltage is applied to each of the plurality of electrodes, it is necessary to control the timing at which each of the plurality of electrical signals is input to the driving unit with high accuracy. Hereinafter, for the sake of simplicity, an electric signal input to the driving unit is referred to as a driving electric signal.

For example, when a modulation signal of about 10 Gb / s is output by an electrode division structure having an interval of about several hundred μm, a unit UI of 10 Gb / s is obtained from several ps which is a propagation time when propagating through a waveguide of about several hundred μm. ) Within a range of 100 ps or less, it is necessary to control the timing at which each of the plurality of electrical signals is input to the drive unit. Such timing control in the ps order is realized by a general circuit in which a phase interpolator circuit and a D-flip flop circuit are combined, for example.

In Patent Document 2, there is a general method for detecting a phase difference between driving electric signals input to a plurality of Mach-Zehnder type modulators in a lithium niobate (hereinafter referred to as LN) modulator. It is disclosed. In this method, an electrode or element is driven with a signal on which a low-frequency signal (several kHz to MHz) having a predetermined phase is superimposed, and a component of the optical output that responds to the low-frequency signal is monitored. The phase difference between the drive electrical signals input to each of the plurality of Mach-Zehnder type modulators is controlled based on the monitored result.

Further, Patent Document 3 includes a Mach-Zehnder type modulator, and a Mach-Zehnder so that the monitor light at a position away from the spectrum center wavelength of the CS-RZ (Carrier-suppressed Return-to-Zero) signal light by a predetermined frequency is minimized. The phase shift between the signals of the drive system input to each type modulator is controlled.

International Publication No. 2011/043079 JP 2010-20689 A JP 2003-279912 A

However, the related technique has a problem that the timing between a plurality of drive electric signals cannot be controlled with high accuracy. In the method described in Patent Document 2, only a slow change due to a temperature change or a change with time of a component can be detected. For this reason, the timing between a plurality of drive electric signals cannot be controlled with an accuracy within a range of several ps to 100 ps. The method described in Patent Document 3 uses a phenomenon peculiar to the CS-RZ modulation method and cannot be applied to timing control between a plurality of drive electric signals in the electrode division structure.

An object of the present invention is to provide a Mach-Zehnder type optical modulator, an optical communication system, and a control method for the Mach-Zehnder type optical modulator that control timing between a plurality of drive electric signals with higher accuracy.

A Mach-Zehnder optical modulator according to the present invention includes a demultiplexing unit that demultiplexes input light, first and second waveguides that guide each demultiplexed input light, and first and second waveguides. Multiplexing means for multiplexing and outputting each input light guided through the waveguide, a signal generation circuit for generating a signal, and one of the first and second waveguides for modulating the input light according to the signal Alternatively, a plurality of electrodes arranged along both sides, a driving unit that applies a signal to each of the plurality of electrodes according to a signal generated by the signal generation circuit, and an intensity of output light output from the multiplexing unit are detected. Detection means, and control means for controlling the timing of applying the signal to each of the plurality of electrodes based on the intensity of the output light detected by the detection means.

The method for controlling a Mach-Zehnder optical modulator according to the present invention demultiplexes input light, guides each input light demultiplexed by the first and second waveguides, and first and second waveguides. Each of the input light guided by the first and second waveguides is combined and output as output light, and the first and second waveguides are guided by a plurality of electrodes provided along one or both of the first and second waveguides. A voltage for modulating one or both of the input lights to be waved is applied, and the timing of applying a signal to each of the plurality of electrodes is controlled according to the intensity of the output light.

An optical communication system according to the present invention includes an optical transmitter that outputs an optical signal modulated by a Mach-Zehnder optical modulator, a transmission path through which the optical signal propagates, and an optical receiver that receives a previous signal via the transmission path The Mach-Zehnder optical modulator includes: a demultiplexing unit that demultiplexes the input light; first and second waveguides that guide the demultiplexed input light; and the first and second waveguides Multiplexing means for multiplexing and outputting each input light guided through the waveguide, a signal generation circuit for generating a signal, and the first and second waveguides for modulating the input light according to the signal A plurality of electrodes arranged along one or both, a driving means for applying a signal to each of the plurality of electrodes according to a signal generated by the signal generation circuit, and detecting the intensity of output light output from the multiplexing means Based on the intensity of the output light detected by the detection means detected by the detection means. A control means for controlling the timing of applying a signal to each of the.

A Mach-Zehnder type optical modulator according to the present invention includes a demultiplexing unit that demultiplexes input light into two, first and second waveguides that guide the demultiplexed input light, and first and second waveguides. A multiplexing means for multiplexing and outputting each input light guided through two waveguides, and a voltage for modulating one or both of the respective input lights guided through the first and second waveguides Electrodes for branching, branching means for branching the output light output from the multiplexing means, detection means for detecting the intensity of one of the output lights branched by the branching means, and a signal generation circuit for generating a plurality of electrical signals Driving means for applying a predetermined voltage to the electrodes connected to the electrodes according to a plurality of electrical signals, and timing for inputting a plurality of signals to the driving means based on the intensity of the output light detected by the detecting means And control means for controlling.

According to the control method of the Mach-Zehnder optical modulator according to the present invention, the input light is demultiplexed into two, the input light demultiplexed by the first and second waveguides is guided, and the first and second The first and second waveguides are combined by the electrodes provided along one or both of the first and second waveguides. A voltage for modulating one or both of the input lights that are guided in the light is applied, and the timing at which at least one of a plurality of signals applied to the electrodes is applied to the electrodes according to the intensity of the output light is controlled. .

According to the present invention, it is possible to provide a Mach-Zehnder optical modulator, an optical communication system, and a control method for the Mach-Zehnder optical modulator that control timings between a plurality of drive electrical signals with higher accuracy.

1 is a functional block diagram showing a Mach-Zehnder optical modulator according to a first embodiment. FIG. 6 is a constellation diagram illustrating a relationship between a phase difference in a state where a plurality of drive electrical signals are in phase and output light amplitude. FIG. 6 is a constellation diagram illustrating a relationship between a phase difference in a state where a plurality of drive electric signals are out of phase and output light amplitude. It is a figure which shows the relationship between a drive electrical signal and the intensity | strength of output light. 3 is a flowchart showing the operation of the Mach-Zehnder optical modulator according to the first embodiment. It is a figure which shows the example of a pattern of a drive electrical signal. FIG. 5 is a diagram showing the relationship between the time average of output light intensity and the phase difference between driving electric signals for each signal type when the delay time is 0 to 2T _baud . In the delay time is 0 ± 0.5 T _baud, the relationship between the phase difference between the time average and the driving electric signal of the output light intensity is a diagram illustrating each type of signal. 6 is a flowchart showing the operation of the Mach-Zehnder optical modulator according to the second embodiment. It is a functional block diagram showing a Mach-Zehnder type optical modulator according to a third embodiment. 10 is a flowchart showing the operation of the Mach-Zehnder optical modulator according to the third embodiment. 10 is a flowchart showing the operation of the Mach-Zehnder optical modulator according to the third embodiment. It is a functional block diagram showing a Mach-Zehnder type optical modulator according to a fourth embodiment. It is a flowchart which shows operation | movement of the Mach-Zehnder type | mold optical modulator which concerns on 4th Embodiment. FIG. 10 is a functional block diagram illustrating a Mach-Zehnder optical modulator according to a fifth embodiment. 5 is a diagram for explaining a control method of a Mach-Zehnder optical modulator 4000. FIG. 5 is a diagram for explaining an example of a control method of a Mach-Zehnder optical modulator 4000. FIG. 5 is a diagram for explaining an example of a control method of a Mach-Zehnder optical modulator 4000. FIG. It is a functional block diagram which shows the optical transmitter which concerns on 6th Embodiment. It is a functional block diagram which shows the optical communication system which concerns on 7th Embodiment.

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary.

First, the configuration of the Mach-Zehnder optical modulator 1000 according to the first embodiment will be described. A Mach-Zehnder optical modulator 1000 according to the first embodiment shown in FIG. 1 includes a modulation unit 100, a branching unit 200, a detection unit 300, drive

units

401 and 402, a control unit 500, and a signal generation circuit. 600. The modulation unit 100 further includes a demultiplexing unit 110, a plurality of

electrodes

121 and 122, a multiplexing unit 130, and

waveguides

141 and 142.

The demultiplexing unit 110 demultiplexes the input light. For example, the demultiplexing unit 110 branches light introduced from the outside, and gives a predetermined phase difference to the other light with respect to the branched light. Specifically, the demultiplexing unit 110 is connected to the

waveguides

141 and 142, one light output from the demultiplexing unit 110 is introduced into the waveguide 141, and the other light is introduced into the waveguide 142. . Here, the predetermined phase difference can be set to π / 2, for example. The demultiplexing unit 110 can be realized by, for example, an MMI (Multi-Mode Interference). Alternatively, it can be realized with a Y branch.

The

waveguides

141 and 142 guide the light introduced from the demultiplexing unit 110 to the multiplexing unit 130.

The

electrodes

121 and 122 are disposed along one or both of the first and

second waveguides

141 and 142 in order to modulate the input light according to the signal generated by the signal generation circuit 600. For example, the

electrodes

121 and 122 are connected to the

corresponding drive units

401 and 402, respectively, and the

waveguides

141 and 142 are input according to the drive electric signal input when the input light passes through the vicinity of the

electrodes

121 and 122, respectively. Apply voltage to As a result, the refractive indexes of the

waveguides

141 and 142 change, and the phase of the input light passing therethrough is modulated. In the present embodiment, the electrodes are described as two

electrodes

121 and 122, but the number of electrodes may be three or more.

The multiplexing unit 130 multiplexes and outputs each input light guided through the first and

second waveguides

141 and 142. For example, the multiplexing unit 130 introduces two lights, and gives a predetermined phase difference to the other light with respect to one of the introduced lights. Next, the one light and the other light are combined, and the combined light is output to the outside. The multiplexing unit 130 has its input connected to the

waveguides

141 and 142 and its output connected to the branching unit 200. Then, the light guided through the waveguide 141 is introduced into the multiplexing unit 130 as one light, and the light guided through the waveguide 142 is introduced into the multiplexing unit 130 as the other light. Here, the predetermined phase difference can be set to π / 2, for example. However, the predetermined phase difference in the demultiplexing unit 110 and the multiplexing unit 130 is not limited to π / 2. The multiplexing unit 130 can be realized by, for example, an MMI (Multi-Mode Interface).

The branching unit 200 is connected to the output of the multiplexing unit 130 and branches the light output from the multiplexing unit 130 into two. Then, the branching unit 200 outputs one of the branched lights to the detection unit 300 and the other to the outside. The branch unit 200 can be realized by an MMI, a Y branch, a directional coupler, or the like. However, the Mach-Zehnder optical modulator 1000 does not necessarily include the branching unit 200.

The detection unit 300 detects the intensity of the output light output from the multiplexing unit 130. The detection unit 300 has an input connected to the output of the branch unit 200 and an output connected to the control unit 500. Then, the detection unit 300 detects one intensity of the light branched by the branch unit 200. Next, the detection unit 300 converts the detected light intensity into an electric signal, and outputs the converted electric signal to the control unit 500. The detection unit 300 can be realized by, for example, a PD (Photo Detector) and an ADC (Analog-to-Digital Converter). In this case, the light into which the PD is introduced is converted into an electric signal, and the converted electric signal is input to the ADC. The ADC converts the amplitude of the input electrical signal into a digital signal, and outputs the converted digital signal to the control unit 500.

The output of the signal generation circuit 600 is connected to the drive unit 401 and the control unit 500. The signal generation circuit 600 receives an external input signal (not shown) and generates a drive electric signal in accordance with the input signal. Next, the generated drive electric signal is output to the drive unit 401 and the control unit 500.

The input of the control unit 500 is connected to the detection unit 300 and the signal generation circuit 600, and the output is connected to the drive unit 402. Then, the control unit 500 controls the timing of applying a signal to each of the plurality of

electrodes

121 and 122 based on the intensity of the signal light detected by the detection unit 300. FIG. 1 shows an example in which the timing at which a signal is applied to each of the plurality of

electrodes

121 and 122 is controlled by controlling the timing at which a plurality of drive electrical signals are input to each of the plurality of

drive units

401 and 402. As an example of controlling the timing, at least one of a plurality of drive electrical signals output from the signal generation circuit 600 is input to the control unit 500, and the control unit 500 detects the phase of the input drive electrical signal. You may make it shift according to the intensity | strength of light. In this case, the control unit 500 outputs a drive electric signal whose phase is shifted to the drive unit 402.

The

drive units

401 and 402 are provided corresponding to the plurality of

electrodes

121 and 122, respectively, and outputs thereof are connected to the plurality of

electrodes

121 and 122, respectively. The input of the drive unit 401 is connected to the output of the signal generation unit 600, and the input of the drive unit 402 is connected to the output of the control unit 500. Each of the

drive units

401 and 402 applies a signal to each of the plurality of

electrodes

121 and 122 in accordance with the signal generated by the signal generation circuit 600. In FIG. 1, as an example, each of the

drive units

401 and 402 applies a predetermined voltage to the

electrodes

121 and 122 to be connected in accordance with a drive electrical signal input from the signal generation circuit 600 and the control unit 500. Here, one drive electric signal is input to the drive unit 401, but two or more drive electric signals may be input to one drive unit.

For example, by using a drive electric signal as a differential output, the

electrodes

121 and 122 can be push-pull driven by the drive electric signal. In this way, the

electrodes

121 and 122 change the electric field strength of a part of the

waveguides

141 and 142. The configuration of the Mach-Zehnder optical modulator 1000 has been described above.

The operation of the Mach-Zehnder optical modulator 1000 according to the first embodiment will be described with reference to FIG. First, light is input to the demultiplexing unit 110. The demultiplexing unit 110 demultiplexes the input light (S1). The

waveguides

141 and 142 guide the demultiplexed input light (S2). The combining unit 130 combines the input light guided through the

waveguides

141 and 142, and outputs the combined light as output light (S3). Then, a voltage for modulating one or both of the input lights guided through the first and second waveguides is applied (S4). Next, the controller 500 controls the timing of applying a signal to each of the plurality of

electrodes

121 and 122 according to the intensity of the output light (S5). For example, the control unit 500 shifts the phase of the driving electric signal input according to the intensity of the output light, and outputs the shifted driving electric signal to the driving unit 402.

Next, using the case where the

drive units

401 and 402 push-pull drive the

electrodes

121 and 122 as an example, the phase of the drive electrical signal output from the signal generation circuit 600, the intensity of the light output from the multiplexing unit 130, The relationship will be described. Here, of m electrodes (m is an arbitrary integer equal to or greater than 1), the propagation time for light to propagate between the kth electrode and the (k + 1) th electrode along the light traveling direction. Is Δtk. In addition, the total time during which light propagates between the electrode 121 and the electrode 122 is Δt1, the driving electric signal output by the driving unit 401 is the driving electric signal SG1, and the driving electric signal output by the driving unit 402 is the driving electric signal SG2. And In this case, when the drive electrical signal SG1 and the drive electrical signal SG2 are in phase, the drive electrical signal SG2 waveform has the same phase pattern as the drive electrical signal SG1 and the phase is delayed by the delay time Δt1. To do. Hereinafter, a state where the phase difference Δt between the drive electric signal (k) and the drive electric signal (k + 1) input to each electrode is equal to the propagation time Δtk is referred to as a “phase-matched state”.

With reference to FIG. 2A, output light from the multiplexing unit 130 when the Mach-Zehnder optical modulator 1000 is operated in a state where the phases are matched (Δt1−Δt = 0) will be described. Here, as an example, it is assumed that the lengths of the two

electrodes

121 and 122 are equal, the drive electric signals SG1 and SG2 have the same waveform pattern, and the amplitude and offset are equal. It is assumed that the length of the electrode and the amplitude and offset of the drive electric signal are adjusted so that the amount of phase change in each of the

electrodes

121 and 122 is 0 to π / 2. In this case, the amount of phase change provided by the

electrodes

121 and 122, that is, the entire Mach-Zehnder optical modulator 1000 is 0 to π. This is based on the principle that the phases of the light changed by the electrode 121 and the electrode 122 are added in a state where the phases of the driving electric signal SG1 and the driving electric signal SG2 are matched.

Push-pull drive of the

drive units

401 and 402 changes the phase of light passing through the

waveguides

141 and 142. That is, the symbol of light passing through the waveguide 141 moves from the first quadrant to the second quadrant in FIG. 2A. On the other hand, the symbol of light passing through the waveguide 142 moves from the fourth quadrant of FIG. 2A to the third quadrant. Due to such a phase change, the intensity and phase of the light combined by the combining unit 130 are modulated. For this reason, the symbol of the light combined by the combining unit 130 appears as a change on the I axis in FIG. 2A. That is, the modulator operates so that the symbol of the output light travels between +1 (0) and −1 (π) on the I axis in accordance with the pattern of the drive electric signal.

Next, the output light from the multiplexing unit 130 when the phase is not matched using FIG. 2B will be described. Here, as an example, a case where the drive electrical signal SG1 and the drive electrical signal SG2 are shifted by 1/2 bit will be described. That is, the case where Δt1−Δt = 0.5 UI is assumed with 1 UI as a phase for one bit.

FIG. 2B shows a case of 0.5 UI, that is, a ½ bit shift, so that the timing is correct for the drive electrical signals SG1 and SG2 for half of one bit. Therefore, the symbol of the output light of the multiplexing unit 130 operates so as to go back and forth between +1 (0) and −1 (π) on the I axis. However, the remaining half of the time is given by the electrode 122 to the phase given by the electrode 121 because the timing at which light passes through the electrode 122 and the timing at which voltage is applied to the electrode 122 do not match. The phase is not added. In this example, since the drive electrical signal SG2 is delayed by 1/2 bit with respect to the drive electrical signal SG1, the timing at which the phase is given by the electrode 122 is not the moment when the phase of π / 2 is turned by the electrode 121, but by π / 4 When it comes back. As a result, the phase imparted by the

electrodes

121 and 122 to the light passing through the waveguide 141 is 3π / 4 in total.

Further, when the phase change by the electrode 122 returns to 0, the application of the phase by the electrode 121 does not return to 0. That is, since the phase of the drive electrical signal SG1 is ½ bit earlier than the phase of the drive electrical signal SG2, the phase applied by the electrode 121 is π / 4. As a result, the phase imparted by the

electrodes

121 and 122 to the light passing through the waveguide 141 is π / 4 in total. In this way, symbols whose output light amplitudes are + 1 / √2 and −1 / √2 are generated as errors.

Next, the relationship between the drive electrical signal (voltage (V)) and the output light intensity (arbitrary unit, au: arbitrary unit) from the multiplexing unit 130 will be described with reference to FIG. As conditions, the amplitudes and offsets of the drive electric signals SG1 and SG2 were made equal, and a PRBS (Pseudorandom Binary Bit Sequence) pattern was input. The baud rate is 10G, and the phase shift between the drive electrical signal SG1 and the drive electrical signal SG2 is 0 and 0.5 UI. Here, in FIG. 3, the propagation time Δt1 is set to 0 and the drive electric signal SG2 is relative to the drive electric signal SG1 (ns (ns ()) so that the correspondence between the waveforms becomes clear between the drive electric signal SG1 and the drive electric signal SG2. Nanosecond)). That is, the state in which the phase of the drive electrical signal SG2 and the phase of the drive electrical signal SG1 are in agreement is defined as the state in which the phase is in agreement, and in the state in which the phase is not in agreement, only the phase deviation from the desired state is displayed. Yes. In practice, the drive electrical signal SG2 is input to the electrode 122 with a delay of Δt1 from the timing shown in FIG. That is, the phase of the drive electrical signal SG2 is delayed by Δt1 from the drive electrical signal SG1.

From this result, when the difference between the phase of the drive electrical signal SG1 and the phase of the drive electrical signal SG2 is different from the propagation time of the light (a state where the phases are not matched), it is not originally generated in the output light of the multiplexing unit 130. It can be seen that an expected intermediate value occurs.

As described above, the Mach-Zehnder optical modulator 1000 includes a detection unit 300 that detects the intensity of output light output from the multiplexing unit 130, and a plurality of

electrodes

141 and 142 based on the intensity of output light detected by the detection unit 300, respectively. And a control unit 500 that controls the timing of applying a signal to. As a result, the intensity of the output light output from the multiplexing unit 130 changes even when the phase between the drive electrical signals does not match with an accuracy of 100 ps or less as shown in FIG. Thus, it is possible to detect the timing deviation between the drive electric signals and control the timing between the plurality of drive electric signals with higher accuracy than in the prior art.

In addition, the time difference from the location where the drive electrical signal is input to the drive unit to the electrode affects the intensity of the output light. Based on the intensity of the output light output from the multiplexing unit 130, the control unit 500 controls the timing at which a plurality of drive electrical signals are input to the plurality of

drive units

401 and 402, respectively. If it is assumed that the timings of the drive electrical signals are matched, the timing shift between the signals generated from the location where the drive electrical signal is input to the drive unit to the electrode can be detected. That is, by controlling the timing at which a plurality of drive electrical signals are input to each of the plurality of drive units based on the light intensity detected by the detection unit 300, an electrical propagation delay corresponding to the path from the drive unit to the electrode is included. Thus, the timing between the plurality of drive electrical signals corresponding to each of the plurality of electrodes can be controlled.

One of the plurality of drive electric signals is input to the control unit 500, but this is not the only case. Two or more driving electric signals may be input to the controller 500. In this case, the control unit 500 performs control based on the detected light intensity when two or more input drive electric signals are input to the drive unit 402. For example, the phase of each of the two or more drive electric signals input to the control unit 500 is shifted based on the output light intensity, and then the shifted drive electric signal is output to the drive unit 402.

In the first embodiment, the case of two electrodes has been described. However, three or more electrodes may be provided. In that case, a plurality of drive units connected to each of the plurality of electrodes are also provided.

Next, a second embodiment will be described. The configuration of the Mach-Zehnder optical modulator according to the second embodiment is the configuration described in the first embodiment shown in FIG. 1, and the operations of the signal generation circuit and the control unit are different from those of the first embodiment. The second embodiment will be described with reference to FIG.

The signal generation circuit 600 according to the second embodiment receives a predetermined bit string (not shown) and generates a plurality of drive electric signals corresponding to the input predetermined bit string.

In addition, the control unit 500 controls the timing at which the drive electrical signal is input to the drive unit 402 so that the time average of the light intensity detected by the detection unit 300 is maximized.

Hereinafter, the control of the control unit 500 will be described in detail.

First, FIG. 5 shows an example of the time change of the amplitude of the drive electric signal. Here, as an example, a 4-bit drive electric signal will be described. That is, when one pulse width of the _baud rate is set to T _baud , the cycle is repeated at a period of T _patt = 4T _baud . Although the data pattern in FIG. 5 is 1000, patterns such as 1100, 1010, and 1110 can be expressed.

Next, FIGS. 6A and 6B show the relationship between the time average of the output light intensity from the multiplexing unit 130 detected by the detection unit 300 and the phase difference between the phase of the drive electrical signal SG1 and the phase of the drive electrical signal SG2. It explains using. Here, 1000, 1010, and PRBS, which are characterized by changes in the intensity of output light, are exemplified as predetermined bit strings as signal types. Further, as an example, the output light intensity (au) sampled at about 533 MHz, which is 1/10 or less with respect to a data baud rate of 10 GHz, is plotted on the vertical axis. For this reason, in this embodiment, the output light intensity which the detection part 300 detects is a time average. 6A and 6B show the difference (hereinafter referred to as delay time) from the ideal phase difference of the drive electrical signal SG2 with respect to the drive electrical signal SG1. For example, when the difference is 0, the difference between the phase of the drive electrical signal SG1 and the phase of the drive electrical signal SG2, that is, the delay time of the drive electrical signal SG2 with respect to the drive electrical signal SG1 is the same as the light propagation time. Indicates.

According to FIG. 6A, until the delay time of SG2 reaches 1T _baud , the time average of the output light intensity from the multiplexing unit 130 detected by the detection unit 300 decreases monotonously as the delay time increases for each signal pattern. I understand that. However, when the delay time exceeds 1T _baud , the time average of the output light intensity detected by the detection unit 300 first converges to about ½ when the phase is matched in 1000 patterns.

The reason for this is as follows. That is, the drive electrical signal input to the drive unit in 1000 patterns is 1100 when the timings of the drive electrical signal SG1 and the drive electrical signal SG2 are shifted by 1T _baud . In addition, when there is a shift of 2T _{baud, the} drive electric signal input to the drive unit is 1010. Thus, the probability of occurrence of 1 and 0 in the drive electric signal is halved. For this reason, the time average of the output light intensity is about ½ of the intensity when the phase is matched.

Since PRBS has patterns of various lengths, the appearance probability of 1 and 0 varies in the vicinity of ½. On the other hand, if the pattern 1010 is shifted by 1T _baud , the relationship between the drive electric signals SG1 and SG2 is completely in phase. For this reason, the intensity of the output light from the multiplexing unit 130 becomes 0, and returns to the original intensity when shifted by 1T _baud .

As described above, as shown in FIG. 6A, it is understood that the time average of the output light intensity detected by the detection unit 300 has a single maximum value with respect to the change in the delay time. Therefore, by using a pattern such as PRBS or 1000, the control unit 500 controls the timing at which a plurality of drive electrical signals are input to the drive unit 402 so that the time average of the light intensity detected by the detection unit 300 is maximized. The timing between the drive electric signals SG1 and SG2 can be an ideal phase difference. As an example of controlling the timing of the drive electrical signal, the control unit 500 may shift the phase of the drive electrical signal input and output the phase-shifted drive electrical signal to the drive unit 402.

On the other hand, FIG. 6B also shows the relationship between the time average of the output light intensity from the multiplexing unit 130 detected by the detection unit 300 and the phase difference between the phase of the drive electrical signal SG1 and the phase of the drive electrical signal SG2. As an example, the difference (delay time) from the ideal phase difference of SG2 is shifted by ± 0.5T _{baud in the} vicinity of 0 with respect to the drive electrical signal SG1.

As can be seen from FIG. 6B, the 1010 pattern has a greater attenuation of light intensity with respect to the delay time than the 1000 pattern and the PRBS pattern. This is because, when a rectangular pulse is expanded in a Fourier series, the 1010 pattern includes many frequency components with the fastest speed, and is highly sensitive to a difference from an ideal phase difference. For this reason, the delay time corresponding to a minute change in output light intensity is the smallest in 1010 patterns. That is, the change in the output light intensity with respect to the change in the delay time at 1010 as the predetermined bit string is large. Using this, the control unit 500 can control the difference between the ideal phase difference related to the drive electrical signal SG2 with respect to the drive electrical signal SG1 and the current phase difference with high accuracy.

Also, a bit string including a lower frequency component than 1010 can be used as the bit string. As shown in FIG. 6B, in such a bit string, the change in the delay time corresponding to the change in the output light intensity is relatively large. For this reason, the dynamic range of the phase difference between the drive electrical signals SG1 and SG2 that can be controlled by the control unit 500 is increased by using a bit string including a low frequency component. Examples of a bit string including a low frequency component include PRBS having a mark ratio of about 1/2 and 1000 patterns.

Although the case where the drive electric signals SG1 and SG2 are 4-bit pulse signals has been described here, the waveform is merely an example of the waveform, and the drive electric signal waveform applicable to the present embodiment is not limited to this.

The operation of the Mach-Zehnder optical modulator 1000 according to the second embodiment will be described with reference to FIG. The description of the same operation as that of the Mach-Zehnder optical modulator 1000 according to the first embodiment is omitted. The operation up to applying a voltage for modulating one or both of the input lights guided through the first and second waveguides (S4) is the same. Thereafter, the timing of applying a signal to each of the plurality of electrodes is controlled so that the time average of the intensity of the output light is maximized (S6). Here, the signal applied to each of the plurality of electrodes may be a signal in which a signal having a predetermined amplitude and a signal having an amplitude higher than the predetermined amplitude are alternately repeated.

In the case where there is a phase shift as shown in FIG. 3, in order to detect the phase difference between the drive electrical signal SG1 (solid line) and the drive electrical signal SG2 (broken line), a high speed capable of monitoring a signal having a frequency equal to or higher than the baud rate. An oscilloscope is required. However, as shown in FIGS. 6A and 6B, even if the output light intensity of the multiplexing unit 130 is sampled at a frequency lower than the baud rate and is time-averaged, the current phase difference between the drive electrical signals SG1 and SG2 The difference from the ideal phase difference appears as a change in the intensity of the output light. Thus, the timing at which the control unit 500 inputs a plurality of drive electric signals to each of the plurality of drive units is controlled so that the time average of the intensity of the output light from the multiplexing unit 130 detected by the detection unit 300 is maximized. To do. This makes it possible to make the timing between the drive electrical signals SG1 and SG2 equal to the light propagation time. As a result, a high-speed and large-scale detection device such as a high-speed oscilloscope is not required.

Further, as in the 1010 pattern, for example, the drive electric signal can be a signal that alternately repeats a signal having a predetermined amplitude and a signal having a higher amplitude than the predetermined amplitude. This makes it possible to take advantage of the fact that the change in the intensity of the output light with respect to the difference between the current phase difference and the ideal phase difference between the drive electrical signals is greater than when no such signal is used, It is possible to control the difference between the accurate phase difference and the phase difference between the drive electrical signals with high accuracy.

A third embodiment will be described. A Mach-Zehnder optical modulator 2000 according to the third embodiment shown in FIG. 8 is different from the Mach-Zehnder optical modulator 1000 according to the second embodiment in that it further includes a switching unit 700.

In addition, at least the first driving electric signal and the second driving electric signal including a higher frequency component than the first driving electric signal are set in the driving electric signal output from the signal generation circuit 600. The first driving electric signal is a driving electric signal corresponding to PRBS having a predetermined bit string of 1000 or a mark ratio of 1/2, and the second driving electric signal is a driving electric signal corresponding to a predetermined bit string of 1010. .

The switching unit 700 switches the drive electrical signal output from the signal generation circuit 600. For example, the switching unit 700 controls the signal generation circuit 600 to switch the drive electrical signal output from the signal generation circuit 600 to either the first drive electrical signal or the second drive electrical signal. Can do. Thereby, the switching unit 700 switches the signal input to the plurality of

electrodes

121 and 122 to a voltage corresponding to one of the first driving electric signal and the second driving electric signal.

Next, the operation of the Mach-Zehnder optical modulator 2000 according to the third embodiment will be described with reference to FIG. The operation until the control unit 500 controls the timing of applying a signal to each of the plurality of

electrodes

121 and 122 according to the intensity of the output light (S5) is the same as that of the Mach-Zehnder optical modulator 1000 according to the first embodiment. It is. Thereafter, the control unit 500 controls the timing of applying the signal to each of the plurality of

electrodes

121 and 122 using a signal that includes a higher frequency component than the signal (S7).

The operations of S4, S5, and S7 in FIG. 9 will be described in more detail with reference to FIG. Here, as an example, the case where the switching unit 700 controls the signal generation circuit 600 based on the time average of the intensity of the output light from the multiplexing unit 130 detected by the detection unit 300 will be described. After the operation of S3, the signal generation circuit 600 outputs the first drive electric signal (S8). Then, the controller 500 controls the timing of applying signals to each of the plurality of

electrodes

121 and 122 according to the intensity of the output light (S9).

Thereafter, the switching unit 700 switches the drive electrical signal output from the signal generation circuit 600 to the second drive electrical signal (S10). It is desirable to switch the drive electrical signal output from the signal generation circuit 600 to the second drive electrical signal in accordance with the time average of the intensity of the output light from the multiplexing unit 130 detected by the detection unit 300. Here, for example, a threshold is set in advance for the time average of the intensity of the output light, and when the time average of the intensity of the output light detected by the detection unit 300 exceeds the threshold, the switching unit 700 switches the drive electrical signal. be able to. The threshold value may be determined as 75% of the maximum intensity, for example. Next, the control unit 500 controls the timing of applying a signal to each of the plurality of

electrodes

121 and 122 according to the intensity of the output light (S11).

As described in the second embodiment, the signal generation circuit 600 outputs the second driving electric signal, whereby the timing between the driving electric signals can be controlled with high accuracy. Further, when the signal generation circuit 600 outputs the first drive electric signal, the dynamic range of the phase difference between the drive electric signals that can be controlled can be increased. Here, the Mach-Zehnder optical modulator 2000 according to the third embodiment includes a switching unit 700 that switches the drive electric signal output from the signal generation circuit 600 based on the time average of the intensity of the output light detected by the detection unit 300. Thus, it is possible to perform control according to the phase difference between the drive electrical signals in consideration of the advantages of using the first drive electrical signal and using the second drive electrical signal. For example, since the time average of the intensity of the output light represents the phase difference between the driving electric signals, the phase difference between the driving electric signals is roughly set by using the first driving electric signal, and then the set phase difference is set. By finding the maximum value of the intensity of the output light using the second drive electric signal in the vicinity of, the phase difference between the drive electric signals SG1 and SG2 can be set quickly.

A fourth embodiment will be described with reference to FIG.

The Mach-Zehnder type optical modulator 3000 according to the fourth embodiment includes a pair of Mach-Zehnder type interferometers, and includes an electrode 150 and a drive unit 800. Different from the vessel 1000.

In the present embodiment, the signal generation circuit 600 receives a predetermined bit string (not shown) and outputs a plurality of drive electric signals corresponding to the predetermined bit string to the drive unit 800 and the control unit 500.

The electrode 150 applies a voltage for modulating one or both of the input light guided through the

waveguides

141 and 142. A plurality of electrodes 150 may be provided along the

waveguides

141 and 142 as in the Mach-Zehnder type optical modulator 1000, but in the present embodiment, it will be described as one for convenience.

The drive unit 800 is connected to the electrode 150 and the signal generation circuit 600, and a drive electric signal from the signal generation circuit 600 is input thereto. Then, a predetermined voltage is applied to the electrode 150 connected in accordance with the drive electric signal output from the signal generation circuit 600.

In the Mach-Zehnder optical modulator 1000, the phase change is applied to the

electrodes

121 and 122, whereas in the Mach-Zehnder optical modulator 3000, a plurality of drive electric signals are added by the drive unit 800. Next, the driving unit 800 applies a voltage corresponding to the added driving electric signal to the electrode 150.

The input of the control unit 500 is connected to the detection unit 300 and the signal generation circuit 600, and the output of the control unit 500 is connected to the drive unit 800. Then, the control unit 500 controls the timing of inputting a plurality of drive electric signals to the drive unit 800 based on the intensity of the signal light detected by the detection unit 300.

The operation of the Mach-Zehnder optical modulator 3000 will be described with reference to FIG. First, light is input to the demultiplexing unit 110. The demultiplexing unit 110 demultiplexes the input light into two (S21). The

waveguides

141 and 142 guide the demultiplexed input light (S22). The combining unit 130 combines the input light guided through the

waveguides

141 and 142, and outputs the combined light as output light (S23). Then, a voltage for modulating one or both of the input lights guided through the first and second waveguides is applied (S24). Next, the controller 500 controls the timing of applying at least one signal among the plurality of signals applied to the electrode 150 according to the intensity of the output light (S25).

Here, the relationship between the plurality of drive electric signals input to the drive unit 800 and the light intensity output from the multiplexing unit 130 is the same as in the case of the Mach-Zehnder type optical modulator 1000. Therefore, also in the Mach-Zehnder optical modulator 3000, the control unit 500 drives at least one signal among a plurality of drive electric signals input to the drive unit 800 based on the intensity of the output light detected by the detection unit 300. By controlling the timing input to the unit 800, it is possible to adjust the deviation of the other driving electrical signal from the ideal timing with respect to one driving electrical signal. In the Mach-Zehnder optical modulator 3000, a plurality of drive electric signals are added by the drive unit 800, so that the deviation from the ideal timing of the other drive electric signal with respect to one drive electric signal is from the signal generation circuit 600. This is caused by a delay due to the electrical wiring and circuits to the driving unit 800. Therefore, the control unit 500 controls the timing at which at least one of the plurality of drive electric signals is input to the drive unit 800 based on the light intensity detected by the detection unit 300, so that the drive unit It is possible to control the timing between the drive electrical signals so as to compensate for the delay caused by up to 800 electrical wirings and circuits.

In this embodiment, an example in which two drive electric signals are multiplexed and applied to a pair of electrodes in one Mach-Zehnder interferometer has been described. However, the number of drive electric signals to be multiplexed, wiring, etc. are limited to this example. I can't. When three or more drive electrical signals are multiplexed, the above-described principle is similarly established between any two signals. Moreover, although the description has been given assuming that the number of control units 500 is one, a plurality of control units 500 may be provided according to the number of drive electric signals.

A Mach-Zehnder optical modulator 4000 according to a fifth embodiment will be described with reference to the drawings. FIG. 13 is a block diagram schematically illustrating a configuration of an optical modulator 4000 according to the fifth embodiment.

The Mach-Zehnder type optical modulator 4000 according to the present embodiment includes a demultiplexing unit 110,

waveguides

141 and 142, m (m is an integer of 2 or more) electrodes 161, electrodes 162,. A wave portion 130 is included. Further, the Mach-Zehnder optical modulator 4000 includes a branching unit 200, detection units 300, m × n control units 5011, 5012,... 501n, 5021, 5022,. 502n, 50m1, 50m2, ..., 50mn, a signal generation circuit 600, m drive

units

801, 802, ... 80m. Hereinafter, the description of the same configuration as the Mach-Zehnder optical modulator 1000 is omitted.

m (m is an integer of 2 or more) electrodes 161, electrodes 162,..., 16 m are provided along the

waveguides

141 and 142. These electrodes apply a voltage for modulating one or both of the input lights guided through the

waveguides

141 and 142.

Each of the n control units 5011, 5012,..., 501n has an input connected to the signal generation circuit 600 and an output connected to the drive unit 801. The control units 5011, 5012,..., 501n each receive the drive electric signal output from the signal generation circuit 600, and drive a plurality of drive electric signals based on the light intensity detected by the detection unit 300. The timing input to the unit 801 is controlled. Next, the drive electric signal whose timing is controlled is output to the connected drive unit 801. The other control units (m−1) × n are the same as the control units 5011, 5012,. As an example of controlling the timing, the control unit 500 shifts the phase of the drive electrical signal and outputs the drive electrical signal with the phase shifted to the drive unit 801.

Note that the number of drive electric signals input to each of the

drive units

801, 802,..., 80m may be different for each drive unit. In this case, the number of control units can be changed in accordance with the number of drive electrical signals.

The drive unit 801 is connected to the signal generation circuit 600 and the control units 5011, 5012, ..., 501n. The drive unit 801 multiplexes a plurality of drive electrical signals input from the signal generation circuit 600 and the control units 5011, 5012,..., 501n, and a voltage corresponding to the multiplexed drive electrical signal is applied to the electrode 161. Apply. The operations of the other m−1 drive units 802,..., 80m are the same as those of the drive unit 801.

The signal generation circuit 600 includes

drive units

801, 802,..., 80m and m × n control units 5011, 5012,... 501n, 5021, 5021,. ..Up to m × n driving electric signals are supplied to 50 mn.

In the present embodiment, the first to third embodiments in which the number m of electrodes is an integer of 2 or more, and the fourth embodiment in which the number n of drive electric signals multiplexed for one electrode is 2 or more. Embodiments.

In this embodiment, the number of electrodes and the number of drive electric signals to be multiplexed are generalized, but the same applies to the number of Mach-Zehnder optical modulators. In particular, the present invention can be applied even when two sets of Mach-Zehnder optical modulators known as general IQ modulator configurations are provided. As described above, when the number of modulators, electrodes, and drive electric signals is plural, the principle described in the first to fourth embodiments is similarly established between any two signals, and any two Phase adjustment between two signals is possible.

FIG. 14 illustrates a method for controlling the Mach-Zehnder optical modulator 4000. Here, the following two examples will be described.

First, the “A. Sequential detection” method shown in FIG. 14 will be described. As an example, the timing of one of the drive electrical signals input to the drive unit 801 among the maximum of m × n drive electrical signals composed of m electrodes and n drive electrical signals is used as a reference. m × n control units 5011, 5012,... 501n, 5021, 5022,... 502n,..., 50m1, ... 50mn are one of drive electric signals input to the drive unit 801. As a reference, a deviation from an ideal phase difference with respect to this reference is sequentially detected, and an optimum delay time is set. The operation of setting the delay time is the same as that of the Mach-Zehnder type optical modulator 1000.

This is shown in a graph in which the horizontal axis of FIG. 15 is the electrode number of the Mach-Zehnder optical modulator 4000 and the vertical axis is the propagation delay time (ps (picosecond)) from the reference timing. Here, as an example, m = 7. As shown in FIG. 15, the timing at which the voltage corresponding to the drive electrical signal is applied to each of the plurality of electrodes 161, electrodes 162,... 167 can be matched to the light propagation delay time in order.

In FIG. 15, the example in which the drive electric signal is applied in order from the electrode with the smallest electrode number is described according to an example in which the timing is matched with the light propagation delay time, but the present invention is not limited to this. In other words, the timing at which the drive electrical signal is input to the drive unit can be matched with the light propagation delay time from any source other than the reference drive electrical signal.

Next, a second method “B. Linear interpolation” shown in FIG. 14 will be described. As an example, the timing of one of the drive electrical signals input to the drive unit 801 among the maximum of m × n drive electrical signals composed of m electrodes and n drive electrical signals is used as a reference.

For example, one of the drive electric signals applied to the electrodes provided on the most downstream side in the light traveling direction along the

waveguides

141 and 142 is defined as a drive electric signal SG in FIG. First, any one of the control units 50m1, 50m2,..., 50mn corresponding to the drive electrical signal SG controls the phase of the drive electrical signal SG. Next, by linearly interpolating based on the delay time between the two points, the delay time with respect to the reference corresponding to each of the plurality of electrodes sandwiched between the two points is calculated, and each drive electric signal is driven by the drive unit. The input timing is set. This is shown in a graph in which the horizontal axis of FIG. 16 is the electrode number of the Mach-Zehnder optical modulator 4000 and the vertical axis is the propagation delay time (ps) from the reference timing. Here, as an example, m = 7. In the graph, as an example, the timing of the drive electrical signal input to the drive unit 801 is used as a reference, and the timing of the drive electrical signal SG input to the drive unit 807 is linearly interpolated. This method has the advantage that the detection of the phase shift can be performed only once and the error generated by each detection is included only twice compared with the method of “A. Sequential detection” described above.

Although two types of control methods for the Mach-Zehnder type optical modulator 4000 have been described above, they are merely examples and do not limit the present invention.

An optical transmitter 10000 according to the sixth embodiment will be described with reference to FIG. The optical transmitter 10000 includes a light source 5000 and a Mach-Zehnder optical modulator 6000.

The light source 5000 outputs continuous light. The Mach-Zehnder optical modulator 6000 is connected to the light source 5000, and continuous light from the light source 5000 is introduced. The Mach-Zehnder optical modulator 6000 is any one of the Mach-Zehnder

optical modulators

1000, 2000, 3000, and 4000.

Next, the operation of the optical transmitter 10000 will be described. First, the light source 5000 outputs continuous light. In the Mach-Zehnder type optical modulator 6000, continuous light output from the light source 5000 is introduced as input light. The Mach-Zehnder type optical modulator 6000 modulates the intensity or phase of the input light and outputs the modulated light to the outside.

In the present embodiment, the case where there is one Mach-Zehnder type optical modulator 6000 has been described, but two or more Mach-Zehnder type optical modulators 6000 can be provided, and a plurality of them can be connected in a nested manner.

An optical communication system according to the seventh embodiment will be described with reference to FIG.
The optical communication system is an optical transmission / reception system using the optical transmitter 10000 shown in the sixth embodiment. FIG. 18 shows a configuration of an optical communication system according to the seventh embodiment.

The optical communication system includes an optical transmitter 10000, an optical receiver 20000, an optical fiber 30000 serving as a transmission path, an optical amplifier 40000a, and an optical amplifier 40000b.

The optical transmitter 10000 includes any one of the Mach-Zehnder type

optical modulators

1000, 2000, 3000, and 4000, and is, for example, four-phase shift keying (Quadrature Phase Shift Keying: hereinafter referred to as QPSK) as an optical signal. A QPSK optical signal is output.

An optical fiber 30000 is optically connected between the optical transmitter 10000 and the optical receiver 20000. An optical amplifier 40000a and an optical amplifier 40000b are inserted into the optical fiber 30000 to amplify the propagating optical signal. The optical receiver 20000 demodulates the optical signal into an electrical signal.

With the above configuration, the optical transmission / reception system can transmit an optical signal using the optical transmitter 10000.

The present invention is not limited to the above-described embodiment, and the embodiments may be combined. Further, it goes without saying that various modifications are possible within the scope of the invention described in the claims, and these are also included in the scope of the present invention.

This application claims priority based on Japanese Patent Application No. 2012-281062 filed on Dec. 25, 2012, the entire disclosure of which is incorporated herein.

100 Modulation unit 110

Demultiplexing unit

121, 122, 150, 161, 162 Electrode 130

Multiplexing unit

141, 142 Waveguide 200 Branching unit 300

Detection unit

401, 402, 800, 801, 802

Drive unit

500, 5011, 5012, 5021 , 5022 control unit 600 signal generation circuit 700

switching unit

1000, 2000, 3000, 4000, 6000 Mach-Zehnder type optical modulator 5000 light source 10,000 optical transmitter 20000 optical receiver 30000

fiber

40000a, 40000b optical amplifier

Claims

A demultiplexing means for demultiplexing the input light;
First and second waveguides for guiding each of the demultiplexed input lights;
A multiplexing means for multiplexing and outputting the respective input lights guided through the first and second waveguides;
A signal generation circuit for generating a signal;
A plurality of electrodes disposed along one or both of the first and second waveguides to modulate the input light in response to the signal;
Driving means for applying a signal to each of the plurality of electrodes according to a signal generated by the signal generation circuit;
Detection means for detecting the intensity of the output light output by the multiplexing means;
Control means for controlling the timing of applying the signal to each of the plurality of electrodes based on the intensity of the output light detected by the detection means;
A Mach-Zehnder optical modulator.
The Mach-Zehnder optical modulator according to claim 1, wherein the control unit controls the timing so that a time average of the intensity of the output light is maximized.
The Mach-Zehnder optical modulator according to claim 1, wherein the signal generation circuit generates a signal corresponding to a bit string including 1010.
The signal is composed of at least a first signal and a second signal containing a lot of high frequency components compared to the first signal,
A switching means for switching a signal input to the plurality of electrodes to either the first signal or the second signal;
The Mach-Zehnder optical modulator according to any one of claims 1 to 3.
5. The Mach-Zehnder optical modulator according to claim 4, wherein the switching unit performs the switching based on a time average of the intensity of the output light.
Demultiplex the input light,
Guides each input light demultiplexed by the first and second waveguides,
The input lights guided through the first and second waveguides are combined and output as output light,
A voltage for modulating one or both of the input lights guided through the first and second waveguides by a plurality of electrodes provided along one or both of the first and second waveguides. Applied,
A method for controlling a Mach-Zehnder optical modulator, which controls timing of applying a signal to each of the plurality of electrodes according to the intensity of the output light.
The method of controlling a Mach-Zehnder optical modulator according to claim 6, wherein the timing is controlled so that a time average of the intensity of the output light is maximized.
The control of the Mach-Zehnder optical modulator according to claim 6 or 7, wherein a signal applied to each of the plurality of electrodes is a signal in which a signal having a predetermined amplitude and a signal having an amplitude higher than the predetermined amplitude are alternately repeated. Method.
The method of controlling a Mach-Zehnder modulator according to claim 6, wherein the timing is controlled using a signal including more frequency components higher than frequency components included in the signal after the timing is controlled by the signal.
An optical transmitter that outputs an optical signal modulated by a Mach-Zehnder optical modulator;
A transmission path through which the optical signal propagates, and an optical receiver that receives the optical signal through the transmission path,
The Mach-Zehnder optical modulator is
A demultiplexing means for demultiplexing the input light;
First and second waveguides for guiding each of the demultiplexed input lights;
A multiplexing means for multiplexing and outputting the respective input lights guided through the first and second waveguides;
A signal generation circuit for generating a signal;
A plurality of electrodes disposed along one or both of the first and second waveguides to modulate the input light in response to the signal;
Driving means for applying a signal to each of the plurality of electrodes according to a signal generated by the signal generation circuit;
Detection means for detecting the intensity of the output light output by the multiplexing means;
Control means for controlling the timing of applying the signal to each of the plurality of electrodes based on the intensity of the output light detected by the detection means;
An optical communication system.
A demultiplexing means for demultiplexing the input light into two;
First and second waveguides for guiding each of the demultiplexed input lights;
A multiplexing means for multiplexing and outputting the respective input lights guided through the first and second waveguides;
An electrode for applying a voltage for modulating one or both of each input light guided through the first and second waveguides;
Branching means for branching the output light output by the multiplexing means;
Detecting means for detecting the intensity of one of the output lights branched by the branching means;
A signal generation circuit for generating a plurality of electrical signals;
Driving means connected to the electrodes and applying a predetermined voltage to the electrodes connected in response to the plurality of electrical signals;
Control means for controlling the timing of inputting the plurality of signals to the drive means based on the intensity of the output light detected by the detection means;
A Mach-Zehnder optical modulator.
Split the input light into two,
Guides each input light demultiplexed by the first and second waveguides,
The input lights guided through the first and second waveguides are combined and output as output light,
A voltage for modulating one or both of the input lights guided through the first and second waveguides is applied by an electrode provided along one or both of the first and second waveguides. And
A method for controlling a Mach-Zehnder optical modulator, which controls timing of applying at least one of a plurality of signals applied to the electrode to the electrode according to the intensity of the output light.