JPH0644739B2 - Optical transmitter - Google Patents

Description

The present invention relates to an optical transmitter used in an optical communication device. In particular, it relates to improvements in devices that transmit light intensity modulated signals.

〔Overview〕

In an optical transmitter that inputs a modulated signal as an electrical signal and outputs an intensity-modulated optical signal, the modulated signal undergoes logical addition and logical conversion in an electrical circuit, and a phase-modulated optical signal is generated according to the electrical circuit output. Then, the optical signal is subjected to differential logic conversion corresponding to the above-mentioned summation / logical conversion in the optical signal circuit to obtain an optical signal which is intensity-modulated at high speed at high speed.

[Conventional technology]

2. Description of the Related Art Conventionally, a transmission device that gives a modulated signal as an electric signal and outputs an intensity-modulated optical signal has been widely used in an optical communication device, but a light emitting element such as a light emitting diode or a semiconductor laser is used for the light source, The drive current is intensity-modulated by a modulation signal. Therefore, a switching circuit is required to control the switching of the drive current.

[Problems to be solved by the invention]

In such a conventional circuit, in order to increase the level of output light, it is necessary to open and close a large drive current in accordance with the modulation signal, which has a drawback that the element of the open / close circuit becomes large. Further, the light emitting element also has a drawback that stable output light cannot be obtained because of a change in parameters such as a change in temperature and a change in refractive index according to a modulation signal. In particular,
This drawback is remarkable as the speed of the modulation signal increases,
It is known that the switching element serves as an element that limits the speeding up and causes inconveniences such as widening of the spectral width of the output light.

An object of the present invention is to improve this, and an object thereof is to provide an optical transmitter which does not require an opening / closing element and is capable of generating stable output light having a high level of light intensity modulation at a high speed.

[Means for solving problems]

The present invention inputs an input signal terminal for inputting a modulated signal as a binary digital electric signal, an exclusive OR circuit in which this input signal terminal is connected to one input, and an output signal of this exclusive OR circuit. And a delay circuit that gives a delay of 1 bit and a continuous output light that is phase-modulated such that the output signal of the exclusive OR circuit is a modulation input and the phase is substantially different by π according to the modulation input. A light source to be generated, an optical branch circuit for branching output light of the light source, an optical delay circuit for passing one output of the optical branch circuit to give a 1-bit delay, an output of the optical delay circuit and the optical branch And an optical multiplexing circuit for multiplexing the outputs of the circuits.

Furthermore, the second invention of the present invention is a photodetector that detects the intensity of output light of the optical multiplexing circuit, and an error detection circuit that detects an error between the detection output of the photodetector and the intensity of the modulation signal. A control circuit for controlling a bias voltage applied to the modulation input of the light source by the output of the error detection circuit is provided.

[Action]

In the device of the present invention, the light source can emit continuous light,
The output light is phase-modulated. On the modulation input side of the light source, an add / drop logic conversion circuit of an electric circuit is provided to perform logic conversion on the modulation signal, and on the output side of the light source, differential logic conversion is performed by an optical circuit. Therefore, in this optical circuit, a high level optical pulse is output at the timing when two optical signals having the same phase are combined, and a low level (or zero level) is output at the timing when two signals having different phases are combined. An optical pulse is output, and as a result, an optical signal intensity-modulated by the input modulation signal can be obtained. In this device, since the light source emits light continuously, there is no need for a switching circuit for the drive current, and since there is no change in the drive current of the light emitting element, there is no change in the parameters of the light emitting element and stable output light can be obtained. You can

According to the present invention, since the light source operates continuously, various negative feedback circuits are provided to stabilize the operation of the light source, and a device of high quality can be practically obtained.

〔Example〕

FIG. 1 is a block diagram of the apparatus of the embodiment of the present invention. The modulation signal is input to the input signal terminal 1 as an electric signal.
This electric signal is logically processed by the electric circuit means 2 and given to the modulation input of the light source 3. The light source 3 is a device that generates optical signals having different phases according to its modulation input, and in this example, 0 for the logical value "0" of the modulation signal.
The optical signal of the phase is generated, and the optical signal of the π phase is generated with respect to the logical value “1” of the modulation signal. This optical signal is logically processed by the optical circuit means 4 and transmitted from the output signal terminal 5 as an optical signal.

The electric circuit means 2 will be described. An exclusive OR circuit 21 which receives the signal from the circuit terminal 1 as one input, and an output of the exclusive OR circuit 21 which is branched to give a delay of one bit of the modulation signal to the exclusive OR circuit. The delay circuit 22 is provided to the other input of the circuit 21, and the output of the exclusive OR circuit 21 is provided to the light source 3 as a modulation input. The electric circuit means 2 is a well-known 1-bit sum / division logic conversion circuit.

Explaining the optical circuit means 4, the output light of the light source 3 is branched into two optical signals by an optical branching circuit 41, one of which passes through an optical delay circuit 42 and the other directly, of an optical multiplexing circuit 43. Combined into two inputs. The optical delay circuit 42 is a circuit that delays the optical signal by one bit as described above. Optical multiplexing circuit
The output of 43 is coupled to the output signal terminal 5. The optical circuit means 4 is a 1-bit differential logic conversion circuit composed of an optical circuit.

To explain the operation of this device, FIGS. 2 (a) to (g) are signal time charts of points (a) to (g) shown in FIG. That is, when the signal of FIG. 2 (a) is given to the terminal 1, the exclusive OR circuit 21 and the delay circuit 22 carry out the addition / conversion logic conversion to obtain the signal shown in FIG. 2 (c). . This serves as a modulation signal for the light source 3 to generate a phase-modulated optical signal as shown in FIG. 2 (d). This optical signal is an optical branch circuit
It is split into two at 41, and one of them is split by the optical delay circuit 42
When a bit delay is given, the signal shown in FIG. When these two signals (d) and (e) are combined by the optical combining circuit 43, the output light is canceled and becomes zero at the timing when the 0-phase and π-phase signals are combined, and the 0-phase and 0-phase are combined. Phase or π
At the timing when the phase and the π phase are multiplexed, they are emphasized and the output light becomes “1”. Therefore, the optical signal shown in FIG. 2 (g) is transmitted to the terminal 5. This optical signal (g) is a signal having the same logic as the logic of the input modulation signal (a) given to the terminal 1 and having a delay of 1 bit.

That is, if the logical value of the i-th time slot of the input signal of the electric circuit means 2 for performing the logical sum conversion is X _i and the logical value of the i-th time slot of the output signal is Y _i , then Y _i = X _i Y _{i -1} (1). On the other hand, since the logic value of the i-th time slot of the input signal of the optical circuit means 4 for performing the differential logic conversion is Y _i ,
If the logical value of the i-th time slot of the output signal is Z _i , then Z _i = Y _i Y _i-1 (2). Therefore, from the above formulas (1) and (2), Z _i = X _i (3) is obtained.

In this device, since the light source 3 only needs to be phase-modulated, it is not necessary to open and close the drive current, and continuous operation is possible. Therefore, a switching circuit for switching the drive current is not needed. It is possible to adapt to a high speed modulation signal by eliminating the switching circuit, which is a factor that mainly limits the speedup. Further, since the switching circuit for switching a large drive current is eliminated, the device can be downsized. Further, since the drive current of the light source 3 is not intermittent, changes in parameters such as temperature and refractive index of the light emitting element used for the light source 3 are eliminated, and stable output light can be obtained.

FIG. 3 is a block diagram of a practical apparatus according to the present invention. This example is an embodiment of the second invention of the present invention. At this position, a semiconductor laser is used for the phase modulation light source 3, and an optical hybrid circuit is used for each of the optical branching circuit 41 and the optical multiplexing circuit 43. The feature of this device is that two negative feedback control circuits are provided in order to stabilize the light emission state of the light source 3. That is, the first control circuit receives the opposite output light of the light source 3 by the photodetector 32, and controls the value of the bias current given to the semiconductor laser by the bias circuit 31 according to the detected output. The second control circuit is provided with a photodetector 33 at the output of the optical multiplexing circuit 43, compares this detection output with the logic of the input modulation signal at the terminal 1 by the error amplifier 35, and outputs the error amplifier 35.
According to the output of, the level of the modulation signal given to the light source 3 is stabilized. The output light of the optical transmitter is remarkably stabilized by these two control circuits. Such a control circuit cannot be provided in the conventional circuit in which the drive current of the light emitting element is intermittent, and can be provided only when the light source 3 emits continuous light.

FIG. 4 is a block diagram of the apparatus of another embodiment of the present invention. This example is characterized by the configuration of the electric circuit means 2.
That is, in this circuit, in order to perform the 1-bit sum / logic conversion, the 2-bit sum / logic conversion is performed once, and the 1-bit differential logic conversion is performed on the output. This may be advantageous if the signal is very fast. Other configurations are similar to those of the embodiment shown in FIG.

Note that the differential logic conversion circuit shown in FIG. 4, that is, the delay circuit 24 and the exclusive logic circuit 25, perform communication even if they are arranged on the receiving side through which the optical signal passes through the transmission path. be able to.

〔The invention's effect〕

As described above, according to the present invention, even though the output light is an intensity-modulated optical signal, it is not necessary to open / close the drive current of the light emitting element of the light source, which is a main factor limiting speedup. Some switching circuits can be omitted. Therefore, the device can be applied with high speed signals and
The device can be made compact. Further, since the drive current of the light emitting element is not intermittent, the parameters of the light emitting element do not change and stable output light can be obtained. Further, since the light source operates continuously, it is possible to provide a negative feedback control circuit for stabilizing the output of the light source, and there is an advantage that the device can be operated more stably.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is a time chart for explaining the operation of the apparatus of the embodiment. FIG. 3 is a block diagram of a practical device of the present invention. FIG. 4 is a block diagram of an apparatus according to the second embodiment of the present invention. 1 ... Input signal terminal (electrical signal), 2 ... electrical circuit means for performing sum / logic conversion, 3 ... phase modulation light source, 4 ... optical circuit means for differential logic conversion, 5 ... output signal terminal ( Optical signal).

Claims (2)

[Claims] 1. An input signal terminal (1) to which a modulation signal is inputted as a binary digital electric signal, an exclusive OR circuit (21) having this input signal terminal connected to one input, and an exclusive OR circuit (21). A delay circuit (22) which receives the output signal of the summing circuit as an input and delays it by one bit and connects it to the other input of the exclusive ORing circuit, and the output signal of the exclusive ORing circuit as a modulation input and the modulation thereof. A light source (3) that generates continuous output light that is phase-modulated so that the phase is substantially different by π according to the input, an optical branch circuit (41) that branches the output light of the light source, and this light An optical delay circuit (42) for passing one output of the branch circuit to give a 1-bit delay, and an optical multiplexing circuit for multiplexing the output of the optical delay circuit and the output of the optical branch circuit and giving them to an output optical signal terminal. (43) and an optical transmitter equipped with Place 2. An input signal terminal (1) for inputting a modulated signal as a binary digital electric signal, an exclusive OR circuit (21) having this input signal terminal connected to one input, and an exclusive logic circuit (21). A delay circuit (22) which receives the output signal of the summing circuit as an input and delays it by one bit and connects it to the other input of the exclusive ORing circuit, and the output signal of the exclusive ORing circuit as a modulation input and the modulation thereof. A light source (3) that generates continuous output light that is phase-modulated so that the phase is substantially different by π according to the input, an optical branch circuit (41) that branches the output light of the light source, and this light An optical delay circuit (42) for passing one output of the branch circuit to give a 1-bit delay, and an optical multiplexing circuit for multiplexing the output of the optical delay circuit and the output of the optical branch circuit and giving them to an output optical signal terminal. (43) and, and this optical multiplexing circuit A photodetector (33) for detecting the intensity of output light, an error detection circuit for detecting an error between the detection output of the photodetector and the intensity of the modulation signal, and the modulation of the light source by the output of the error detection circuit. An optical transmitter comprising: a control circuit that controls a bias voltage applied to an input.