JP5885297B2 - Apparatus and method for generating optical signals of various modulation formats - Google Patents

Description

  The present invention relates to an apparatus and a method for generating optical signals of various modulation formats used in an optical communication system including an optical communication apparatus and an optical fiber link.

  Conventionally, there are two methods for generating an 8 quadrature amplitude modulation (8 QAM) optical signal having an optimal arrangement.

  One method is to use a combined transmitter comprising a π / 4 bias dual parallel Mach-Zehnder modulator DP-MZM (comprising two sub-MZMs integrated with a main MZ interferometer) and a phase modulator ( Non-patent document 1). The π / 4 bias DP-MZM is used to generate a four amplitude and phase modulated signal, each MZM being driven by a binary electrical signal with a different drive voltage. After [0,2π] phase modulation, an 8QAM signal is generated by using a phase modulator.

  Another method uses a single π / 4 bias DP-MZM together with a high-speed arbitrary waveform generator (AWG) or a digital-to-analog converter (DAC) (Non-patent Document 2). With the use of AWG or DAC, the in-phase and quadrature components of the 8QAM signal are each modulated with two independent MZMs of DP-MZM.

In order to efficiently use spectrum resources in a dynamically reconfigurable wavelength division multiplexing (WDM) network, an optical communication device can provide flexibility (that is, the modulation format of an optical signal can be flexibly changed). desired. For this reason, several techniques are proposed. Among these, a new type of transmission device in which a silica planar lightwave circuit (PLC) and a LiNbO ₃ phase modulator are hybridly integrated has been proposed (Non-patent Document 3).

J. Yu, et al., "High-Speed PDM-RZ-8QAM DWDM Transmission (160x114 Gb / s) Over 640 km of Standard Single-Mode Fiber" IEEE PTL, vol.21, no. 18, pp. 1299- 1301, 2009 N. Kikuchi, et al., "Highly Sensitive Optical Multilevel Transmission of Arbitrary Quadrature-Amplitude Modulation (QAM) Signals With Direct Detection" JLT, vol. 28, no. 1, pp. 123-130, 2010 H. Takara, et al., "Experimental Demonstration of 400 Gb / s Multi-flow, Multirate, Multi-reach Optical Transmitter for Efficient Elastic Spectral Routing" ECOC2011, paper Tu.5.A.4

  However, the transmission apparatus configurations of Non-Patent Documents 1 and 2 have a problem of requiring a very expensive device such as a feedback circuit and / or AWG for controlling the bias point of DP-MZM.

  Further, in order to generate an optical signal using the transmission device of Non-Patent Document 3, many control parameters such as a tuning coupler, a phase shifter, and a bias controller are required. As a result, there has been a problem that these transmission devices become complicated and cost increases.

  Therefore, an object of the present invention is to provide an apparatus and a method for generating optical signals of various modulation formats with a simpler configuration and reducing the cost of a transmission apparatus.

Apparatus for generating an optical signal at a different modulation format of the present invention for solving the above problems, according to the drive signal and bias voltage is input, a dual-drive Mach-Zehnder modulator operating the optical signal amplitude and phase, are input according multilevel drive signal that includes the dual-drive Mach-Zehnder optical signals that have been manipulated by the modulator and the phase modulator for multiple phase modulation, the drive signal and bias voltage, and a driving means to generate the multilevel drive signal The drive means can change the amplitude and bias voltage of the drive signal and the multi-level of the multi-level drive signal corresponding to various modulation formats, thereby changing the optical signals of various modulation formats. It can be generated.

The drive signal is formed Rukoto from the inverted signal of the first driving signal and the first driving signal is preferred.

Further, the driving means changes a set of the amplitude A ₁ of the first driving signal, the amplitude A ₂ of the inverted signal of the first driving signal, and the bias voltage v _b in accordance with various modulation formats. It is also preferable.

The drive means can generate a set of drive signal and bias voltage of A ₁ = A ₂ = v _b = V _π ( where V _π is a switching voltage of the dual drive Mach-Zehnder modulator) . , thereby, as one of various modulation formats of the optical signals, M is also preferably capable of generating optical signals of M phase-shift keying format is even.

In addition, the drive means sets a combination of a drive signal and a bias voltage of A ₁ = A ₂ = v _b = 2V _π / 3 (where V _π is a switching voltage of the dual drive Mach-Zehnder modulator). generation can, thereby, as one of various modulation formats of the optical signals, is also preferred Rukoto can generate optical signals 6 quadrature amplitude modulation format.

The driving _{means, A 1 = A 2/2} = V π / 2 and _v b = 0.58V _{π (here,} the V _[pi, which is the switching voltage of the dual-drive Mach-Zehnder modulator.) Driving the It can generate a set of signals and the bias voltage, thereby, as one of various modulation formats of the optical signals, Rukoto is preferable to generate an optical signal of 8 quadrature amplitude modulation format.

Further, the multi-level drive signal is obtained by adding the drive signal and the drive signal amplitude G ₂ of amplitude G _1, G ₁ and G ₂ are to change the multilevel supports various modulation formats it is also preferable to change, et al. are.

Further, the multi-level drive signal, a G 1 _{= G} 2 = _0, thereby, as one of various modulation formats of the optical signals, also Rukoto can generate optical signals of binary modulation format preferred.

Further, the multi-level drive signal _(here, the V _[pi, the a switching voltage of a dual drive Mach-Zehnder _{modulator.) G} 1 = V π and _G 2 = 0 is, thus, a variety of modulation formats as one of the optical signals, Rukoto is preferable to generate an optical signal of 4-level modulation format.

Further, the multi-level drive _{signal, G 1 = G 2 = 2V} π / 3 ( where the V _[pi, the a switching voltage of a dual drive Mach-Zehnder modulator.), And thereby, various modulation formats as one of the optical signals, Rukoto is preferable to generate an optical signal of 6 values modulation format.

Further, the multi-level drive _{signal, G 1 = G 2/2} = V π ( here, the V _[pi, the a switching voltage of a dual drive Mach-Zehnder modulator.), And thereby, various modulation formats as one of the optical signals, Rukoto is preferable to generate an optical signal of 8-level modulation format.

In order to solve the above problems, a method for generating an optical signal in various modulation formats according to the present invention is such that a dual drive Mach-Zehnder modulator manipulates the amplitude and phase of an optical signal according to an input drive signal and a bias voltage. A step of phase-modulating the optical signal operated by the dual drive Mach-Zehnder modulator according to an input multi-level drive signal, and a driving means comprising the drive signal and bias voltage, and see containing and generating the multi-level drive signals, and the step of generating the amplitude and the bias voltage of the drive signal, and the multi-level of the multilevel drive signal, changing in response to various modulation formats Accordingly, optical signals of various modulation formats can be generated .

As described above, equipment of the present invention is composed only of dual-drive Mach-Zehnder modulator and a phase modulator. For this reason, only one feedback control circuit is required for bias control of the dual drive Mach-Zehnder modulator. As a result, the structure of equipment is simplified, the cost is greatly reduced. Further, the bottom area of the equipment also reduces.

1 shows a configuration of an apparatus for generating an optical signal in various modulation formats according to the present invention. The transfer curve characteristic of DD-MZM for conventional (D) BPSK signal modulation is shown. The arrangement | positioning figure of the (D ) xPSK optical signal produced | generated by this transmitter is shown. The transfer curve characteristic of DD-MZM for 6QAM signal modulation is shown. An arrangement diagram of an optical signal at an output of DD-MZM and an arrangement diagram of a 6QAM optical signal generated by the transmission apparatus are shown. The transfer curve characteristic of DD-MZM for 8QAM signal modulation is shown. FIG. 2 shows an arrangement diagram of optical signals at the output of DD-MZM and an arrangement diagram of 8QAM optical signals generated by the transmission apparatus.

The best mode for carrying out the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a configuration of an apparatus for generating an optical signal in various modulation formats according to the present invention. This transmission apparatus includes a laser light source 1 and an optical phase modulation unit 2, and the optical phase modulation unit 2 includes a dual drive Mach-Zehnder modulator 21 (DD-MZM), a phase modulator 22 (PM), and an encoder 23.

The optical phase modulation unit 2 performs optical phase modulation on the continuous light from the laser light source 1 based on the data v ₁ (t) and v ₂ (t) of the input electrical signal, and outputs the phase modulated optical signal to the optical transmission line. .

によって駆動される。もし、データとその反転データの振幅が一致（つまり、Ａ_１＝Ａ_２）する場合、この変調器はプッシュプルモードで動作するため、チャープ無しの光信号を得ることができる。しかしながら、駆動信号の振幅が異なった状態（Ａ_１≠Ａ_２）で、バイアス電圧ｖ_ｂを変化させることで、光信号のチャープを調整できる。ＤＤ−ＭＺＭ２１の分岐／合成比を同じにすると、ＤＤ−ＭＺＭの伝達関数は、

で表される。ここで、Ｖ_πはＤＤ−ＭＺＭ２１のスイッチング電圧である。したがって、３つのパラメータ（Ａ_１，Ａ_２、ｖ_ｂ）を調節することによって、光信号の振幅と位相を操作することができる。 The DD-MZM 21 includes two Mach-Zehnder modulators (MZM), and the continuous light is branched into two, and after the amplitude and phase are manipulated by the drive signal in each MZM, they are combined and output. Since the chirp of the optical signal can be controlled by adjusting the magnitude of the drive signal, the amplitude and phase of the optical signal can be manipulated. DD-MZM21 is a set of electrical signals,

Driven by. If the amplitude of the data and its inverted data match (that is, A ₁ = A ₂ ), this modulator operates in the push-pull mode, so that an optical signal without chirp can be obtained. However, with the amplitude of the drive signal is different (A ₁ ≠ A _2), by changing the bias voltage v _b, can be adjusted chirp of the optical signal. When the branch / synthesis ratio of DD-MZM21 is the same, the transfer function of DD-MZM is

It is represented by Here, the V _[pi is the switching voltage of the DD-MZM21. Therefore, the amplitude and phase of the optical signal can be manipulated by adjusting the three parameters (A ₁ , A ₂ , v _b ).

The phase modulator 22 performs binary, ternary, or quaternary phase modulation by sending a multi-level electrical signal v ₂ (t), and an optical signal of QPSK, 6PSK / 6QAM, or 8PSK / 8QAM modulation format. Can be modulated.

The encoder 23 drives the DD-MZM 21 using the data signal v ₁ (t) and its inverted data as drive signals. Further, the phase modulator 22 is driven using the data signal v ₂ (t) as a drive signal. At this time, the encoder 23 outputs two drive signals whose amplitudes are adjusted in order to modulate the phase of the optical signal, and drives the phase modulator 22 with the data signal v ₂ (t) obtained by adding them.

  As described above, the transmission apparatus of the present invention can be used to flexibly modulate an optical signal with various modulation formats (BPSK, QPSK, 6PSK / 6QAM, and 8PSK / 8QAM).

Hereinafter, some examples of modulation formats of an apparatus for generating an optical signal in various modulation formats according to the present invention will be described.

The first embodiment shows a (differential) M phase shift keying format ((D) × PSK). Here, (differential) indicates that the M phase shift keying format may be a differential M phase shift keying format. Further, ((D) × PSK) is a notation in a (differential) M phase shift keying format, and this notation will be used below. Where M = 2 (denoted by B) , 4 (denoted by Q) , 6 and 8. FIG. 2 shows a transfer curve characteristic of DD-MZM for conventional (D) BPSK signal modulation. By setting A ₁ = A ₂ = v _b = V _π , a conventional (D) BPSK signal can be obtained at the output of DD-MZM. Thereafter, nothing input to the phase modulator, i.e. _{v 2 (t) = 0 (} G 1 = G 2 = 0) case, equipment of the present invention can produce a (D) BPSK optical signal. 2 value _G 1 = V _[pi and _G 2 = 0 to the phase modulator ([0, π / 2] phase _{modulation) v} By entering 2 (t), equipment of the present invention (D) QPSK light A signal can be generated. Similarly, by inputting ternary ([0, π / 3, 2π / 3]) phase modulation v ₂ (t) with G ₁ = G ₂ = 2V _π / 3 to the phase modulator, (D) 6PSK light signals, four values in _{G 1 = G 2/2 =} V π to the phase modulator ([0, π / 4, π / 2,3π / 4] phase _{modulation) v} 2 can be entered in the (t) ( D) An 8PSK optical signal can be generated. Figure 3 shows a layout of the generated by This equipment (D) x PSK optical signal.

In the second embodiment, 6 quadrature amplitude modulation format (6QAM) is shown. This equipment, for generating a 6QAM signal with optimal placement of the right view in FIG. 5, DD-MZM operates in push-pull mode, but the amplitude and the bias voltage of the drive signal in the first embodiment Slightly different. FIG. 4 shows the transfer curve characteristics of DD-MZM for 6QAM signal modulation. By setting A ₁ = A ₂ = v _b = 2V _π / 3, the optical signal is modulated with a phase difference between the two symbols of π and an amplitude ratio of 1: 2. The left diagram in FIG. 5 shows an arrangement diagram of optical signals at the output of the DD-MZM. Thereafter, 3 values _{G 1 = G 2 = 2V π} / 3 to the phase modulator _{(amplitude v} 2 (t) is 0,2V π _/ 3,4V π / 3) By inputting the electrical signal , equipment of the present invention can generate 6QAM optical signal. Right view in FIG. 5 shows a layout of 6QAM optical signal generated by This equipment.

In the third embodiment, 8 quadrature amplitude modulation format (8QAM) is shown. This equipment can also be used to generate an 8QAM signal in an optimal arrangement as shown in the right diagram of FIG. In the case of 8QAM modulation, the amplitude of the drive signal of DD-MZM needs to be different. FIG. 6 shows the transfer curve characteristics of DD-MZM for 8QAM signal modulation. By the _{A 1 = A 2/2 =} V π / 2 and _{v b} ≒ 0.58V _π, the phase difference between two symbols 3 [pi] / 4, amplitude ratio (1 + √3): in √2 The optical signal is modulated. The left diagram in FIG. 7 shows an arrangement diagram of optical signals at the output of the DD-MZM. Thereafter, the phase modulator _{G 1 = G 2/2 =} V 4 values _{[pi (amplitude v} 2 (t) is _{0, V π / 2, V} π, and a 3V _π / 2) the electrical signal by entering, equipment of the present invention can generate 8QAM optical signal. Right view in FIG. 7 shows a layout of 8QAM optical signal generated by This equipment.

  In DD-MZM, the phase difference between two symbols is π / 4, the amplitude ratio is (1 + √3): √2, and it is also possible to generate an 8QAM optical signal by modulating the optical signal. It is.

  Moreover, all the embodiments described above are illustrative of the present invention and are not intended to limit the present invention, and the present invention can be implemented in other various modifications and changes. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Optical phase modulation part 21 Dual drive Mach-Zehnder modulator 22 Phase modulator 23 Encoder

Claims (12)

A dual drive Mach-Zehnder modulator that manipulates the amplitude and phase of the optical signal according to the input drive signal and bias voltage ;
A phase modulator that multi-phase modulates the optical signal operated by the dual drive Mach-Zehnder modulator according to an input multi-level drive signal ;
A driving means to generate the drive signal and bias voltage, and the multi-level drive signals,
The drive means can change the amplitude and bias voltage of the drive signal, and the multilevel of the multilevel drive signal corresponding to various modulation formats,
Thus, apparatus for generating an optical signal at a different modulation format, wherein Rukoto can generate optical signals of different modulation formats. The drive signal equipment according to claim 1, wherein the formed Rukoto from the inverted signal of the first driving signal and the first drive signal. Said drive means, said amplitude A 1 of the first drive _signal, the amplitude A 2 of the inverted signal of the first driving _signal, and a set of bias voltages v _b, Rukoto varied corresponding to different modulation formats equipment according to claim 2, wherein. It said drive _{means, A 1 = A 2 = v} b = V π ( here, the V _[pi, the a dual drive Mach-Zehnder switching voltage of the modulator.) Of can generate a set of drive signals and bias voltages, this Accordingly, as one of various modulation formats of the optical signals, equipment according to claim 3, M is characterized by Rukoto can generate optical signals of M phase-shift keying format is even. The driving means can generate a set of a driving signal and a bias voltage of A ₁ = A ₂ = v _b = 2V _π / 3 (where V _π is a switching voltage of the dual drive Mach-Zehnder modulator). , thereby, as one of various modulation formats of the optical signals, equipment according to claim 3, characterized in Rukoto can generate optical signals 6 quadrature amplitude modulation format. Said drive _{means, A 1 = A 2/2} = V π / 2 and _v b = 0.58V _{π (here,} the V _[pi, the a dual drive Mach-Zehnder switching voltage of the modulator.) Drive signal and the It can generate a set of bias voltages, thereby, as one of various modulation formats of the optical signals, equipment according to claim 3, characterized in Rukoto can generate optical signals of 8 quadrature amplitude modulation format. The multi-level drive signal is obtained by adding a drive signal having an amplitude G _{1 and} a drive signal having an amplitude G ₂ , and G ₁ and G ₂ are changed to change the multi-level corresponding to various modulation formats. equipment according to claim 1, characterized in that it is. Claim wherein the multi-level drive signal, a G 1 _{= G} 2 = _0, thereby, as one of various modulation formats of the optical signals, characterized by Rukoto can generate optical signals of binary modulation format equipment described in 7. The multi-level drive signal, G 1 ₌ V _[pi and G _{2 =} 0 (where the V _[pi, the a dual drive Mach-Zehnder switching voltage of the modulator.), And thereby, light of various modulation formats one signal, equipment according to claim 7, characterized in Rukoto to generate an optical signal of 4-level modulation format. The multi-level driving signal is G ₁ = G ₂ = 2V _π / 3 (where V _π is a switching voltage of the dual drive Mach-Zehnder modulator) , and thereby, light of various modulation formats. one signal, equipment according to claim 7, characterized in Rukoto to generate an optical signal of 6 values modulation format. The multi-level drive _{signal, G 1 = G 2/2} = V π ( here, the V _[pi, the a dual drive Mach-Zehnder switching voltage of the modulator.), Which allows light of various modulation formats one signal, equipment according to claim 7, characterized in Rukoto can generate optical signals of 8-level modulation format. A dual drive Mach-Zehnder modulator manipulating the amplitude and phase of the optical signal in accordance with the input drive signal and bias voltage ;
A phase modulator multi-phase modulates the optical signal operated by the dual drive Mach-Zehnder modulator according to an input multi-level drive signal ;
Driving means, see contains the steps of: generating the driving signals and the bias voltage, and the multi-level drive signals,
In the generating step, the amplitude and bias voltage of the drive signal and the multilevel of the multilevel drive signal can be changed corresponding to various modulation formats,
Thus, how that generates an optical signal at a different modulation format, characterized in that it can generate optical signals of different modulation formats.

Images