JPH03144424A - Optical monostable multivibrator - Google Patents

Abstract

PURPOSE:To apply the optical monostable multivibrator to applications such as the generation of a slow light clock or the expansion of the duty factor of a light pulse, etc., by feeding back a response signal for a photoelectric current in a load circuit to a current bias, and setting a bistable semiconductor laser at an on-state by inputting an input light pulse at an off-state. CONSTITUTION:When the bistable semiconductor laser 1 starts laser oscillation, a photodiode 3 receives part of the beam of the laser and the photoelectric current is generated, and the photoelectric current flows in the load circuit 5. When the photoelectric current flows in the load circuit 5, the response signal for the photoelectric current is fed back to the current bias of the bistable semiconductor laser 1. The bistable semiconductor laser 1 comes off a bistable region, and the bistable semiconductor laser 1 set at the on-state by the input of the input light pulse is reset to the off-state. Therefore, the light pulse with desired pulse width can be obtained corresponding to the response signal from the load circuit 5. Thereby, it is possible to obtain the optical monostable multivibrator used in the application such as the one to generate the slow light clock or the one to expand the duty factor of the light pulse, etc.

Description

[Detailed Description of the Invention] Table of Contents Overview Industrial Application Fields Prior Art (Fig. 11) Means for Solving Problems to be Solved by the Invention (Fig. 1) Functional Examples ゛ (Fig. Figures 2 to 1O) Effects of the invention Optical monostable device used for generating a low-speed optical clock based on an optical frame extracted from a required optical signal train, increasing the duty ratio of optical pulses, etc. Regarding multivibrators, the purpose of providing such a novel optical monostable multivibrator is to provide an output optical pulse having a pulse width larger than the pulse width of the input optical pulse when an input optical pulse is input to a bistable semiconductor laser. is an optical monostable multivibrator outputted from the bistable semiconductor laser, the bistable semiconductor laser having two stable states including an on state and an off state; a variable voltage source or a variable current source that applies a current bias to the semiconductor laser; a photodiode that receives a portion of the output light of the bistable semiconductor laser; a voltage source that applies a reverse bias to the photodiode; and a load circuit through which the generated photocurrent flows, and a response signal to the photocurrent in the load circuit is fed back to the current bias to turn off the bistable semiconductor laser that was turned on by inputting the input optical pulse. Squeeze horizontally as shown.

INDUSTRIAL APPLICATION FIELD The present invention relates to an optical monostable multivibrator used for generating a low-speed optical clock based on an optical frame extracted from an optical signal train, increasing the duty ratio of optical pulses, and the like.

BACKGROUND OF THE INVENTION With the development of optical communication networks and the increase in capacity and speed of transmission lines, optical signal processing technology that processes optical signals in their optical state without converting them into electrical signals is attracting attention. Among these, synchronous optical signal processing technology, in which optical signals multiplexed on the time axis are processed in synchronization with data frames or clocks, is being researched in various places as a highly practical technology. In this type of synchronous optical signal processing, it is necessary to extract a frame signal or a clock signal from an optical signal sequence multiplexed on the time axis and supply it to a signal processing section.

Conventional technology In conventional signal processing technology, processing is performed using electrical signals without using optical signal frames or clocks, so there is no specific example of extracting frames or clocks in the form of optical signals. . Further, even when synchronization processing is performed within a transmission processing node placed on an optical transmission path, all such signal processing is performed by processing electrical signals. A general conceptual diagram of signal processing using this electrical signal is shown in FIG.

Optical signal train 102 input from optical transmission line (input section) 101
is converted into an electrical signal in the optical/electrical conversion circuit 103, and the signal frame and clock are extracted in the electrical signal processing section 104. When a transmission processing node performs signal branching processing to an optical terminal such as an optical subscriber, after further processing is performed to create a low-speed clock for sending the signal to the optical terminal, this clock and the signal are combined. is converted into an optical signal again in the electrical/optical conversion circuit 105 and then output to the optical transmission line (output section) 106.

Problems to be Solved by the Invention Therefore, for example, it is possible to handle ultra-high-speed optical signals such as optical frame lines,
In order to realize drop/add processing for connection to multi-channel optical terminals, an ultra-high-speed, multi-channel optical/electrical conversion section and an electrical signal processing section are required for electrical signal processing as shown in Figure 11. In response to an increase in the capacity of signals that are required and handled, there is a problem in that the processing device becomes larger or more complex in the case of multi-channel processing, or a problem arises in terms of processing speed.

Therefore, the present invention aims to provide a novel optical monostable multivibrator that can be used in applications such as generating a low-speed optical clock based on an optical frame extracted from an optical signal train and expanding the duty ratio of optical pulses. The purpose is

Means for Solving the Problems FIG. 1 is a block diagram of the principle of the present invention. In this optical monostable multivibrator, when an input optical pulse is input to the bistable semiconductor laser, an output optical pulse having a pulse width larger than the pulse width of the input optical pulse is outputted from the bistable semiconductor laser. It is something.

1 is a bistable semiconductor laser. Reference numeral 2 denotes a variable voltage source or variable current source, which applies a current bias to the bistable semiconductor laser 1 so that the bistable semiconductor laser 1 can take two stable states consisting of an on state and an off state. 3 is a photodiode that receives part of the output light of the bistable semiconductor laser 1.

4 is a voltage source that applies a reverse bias to the photodiode 3. 5 is a load circuit through which the photocurrent generated in the photodiode 3 flows.

A response signal to the photocurrent in the load circuit 5 is fed back to the current bias to turn off the bistable semiconductor laser 1 which has been turned on by inputting the input optical pulse.

Function: The bistable semiconductor radar 1 has a variable voltage source or a variable current source 2.
It is possible to take two stable states consisting of an on state and an off state.

When a light pulse such as an optical frame is input to the bistable semiconductor laser 1 which has been reset to the off state, the bistable semiconductor laser 1 is turned on and starts laser oscillation. When the bistable semiconductor laser 1 starts laser oscillation, the photodiode 3 receives a part of the light, and the photodiode 3
A photocurrent is generated, and this photocurrent flows through the load circuit 5.

When a photocurrent flows through the load circuit 5, a response signal to the photocurrent is fed back to the current bias of the bistable semiconductor laser 1, and the bistable semiconductor laser 1 moves out of the bistable region and is turned on by the input optical pulse. The bistable semiconductor laser 1 that is in the OFF state is reset to the OFF state. Therefore, an optical pulse with a desired pulse width can be obtained according to the response signal of the load circuit 5, and an optical monostable multivibrator that is triggered by the input optical pulse is provided.

According to a preferred embodiment of the present invention, the load circuit 5 includes a load resistance and a load capacitance through which a photocurrent flows, and the pulse width of the output optical pulse is determined by the values of the load resistance and load capacitance.

According to another preferred embodiment of the present invention, the load circuit 5 includes a first load resistor through which a photocurrent flows, and the voltage across the first load resistor is amplified by a transistor. There is.

Example Embodiments of the present invention will be described below based on the drawings.

Fig. 2 is a circuit diagram of an optical monostable multivibrator showing a preferred embodiment of the present invention, Fig. 3 is a block diagram of a bistable semiconductor laser which is a component thereof, and Fig. 4 is an explanatory diagram of bistable property. .

First, as shown in FIGS. 3 and 4, the bistable semiconductor laser 11
The configuration and operation of this will be explained. As shown in FIG. 3, the bistable semiconductor laser 11 has electrodes 23 and 24 divided in the longitudinal direction of the active layer 22 and the optical axis direction, and a common electrode on the back side of these electrodes. A ground electrode 25 is formed. Current bias I supplied to electrodes 23 and 24, 1.
By setting P to an appropriate value, the optical output P changes in response to a change in the optical input PIN or a change in the current bias 11 or I2. U changes with hysteresis, resulting in bistability.

FIG. 4 is a diagram for explaining this bistability, and the vertical axis is the optical output P. UT 1 horizontal axis is one current bias I2
The other current bias 11 is shown when is constant at an appropriate value. When the current bias L is gradually increased in the OFF state 31 where light is slightly emitted spontaneously, the ON state (laser emission state) 32 is reached at the set threshold value 1108.
The threshold voltage resets once it reaches the ON state 32. , P(<I+o*). That is, in the current bias 11 such that rlOFF<I+<I+ow, the bistable semiconductor laser 11 has a property that it can stably take an off state 31 where the optical output is small and an on state 32 where the optical output is large. The above hysteresis characteristic of the optical output is with respect to the current bias (injected current), but if the current bias is fixed in the bistable region, optical memory operation is possible. That is, in FIG. 4, the bistable region (1+o□~
When the current bias h is fixed to I+ox) and a sufficiently strong optical pulse is injected from the outside into the bistable semiconductor radar in the OFF state, this optical pulse changes it from the OFF state 31 to the ON state! 332 and the optical pulse is interrupted, the on state 32 is maintained as it is until the current bias It becomes smaller than Il0FF, and a memory operation for optical input can be performed. In the following explanation, when the bistable semiconductor laser is in the off state 31, the spontaneous emission light output is ignored and the light output is zero.

In Figure 2, 16.17 is a bistable semiconductor laser film.
The bistable semiconductor laser 1 is a variable voltage source or a variable current source that applies a current bias to the bistable semiconductor laser 1 so that it can assume two stable states consisting of an on state and an off state, that is, it is in a bistable region. For the bistable semiconductor laser 11,
Since optical coupling is possible on both end surfaces of the active layer, the output light from one side can be transmitted to the photodiode 12.
Let it be incident on . The photodiode 12 is normally reverse biased by a voltage #18, so that when light is incident on the photodiode 12, a photocurrent is generated in the photodiode 12.

The photocurrent iP generated in the photodiode 12 is connected to the load resistance (resistance value is R) 13 and the load capacitance (capacitance value is C> 14)
flows through a load circuit consisting of A response signal to the photocurrent in this load circuit, that is, a voltage signal (high frequency signal) across the load resistor 13 and load capacitor 14 is added to the current bias of the bistable semiconductor laser 11 via the capacitor 15. The reason why the load circuit and the bistable semiconductor laser are connected using the capacitor 15 is to prevent the operating point of the bistable semiconductor laser from changing due to a DC component due to the bias applied to the photodiode 12.

FIG. 5 is an equivalent circuit diagram when a photocurrent ip is generated in the photodiode 12, and FIG. 6 is a waveform diagram of each part of the circuit of FIG. 2. In the waveform diagram, (a) shows the input optical waveform, (b) shows the optical output waveform of the bistable semiconductor laser 11,
(C) is the waveform of the photocurrent generated in the photodiode 12;
(a) is the connection point between the photodiode 12 and the load circuit (
(e) is the waveform of the current bias of the bistable semiconductor laser 11 to which the response signal of the load circuit is added.

When an input optical pulse having an optical power of PIN is input to the bistable semiconductor laser 11 from the outside, the bistable semiconductor laser 11 changes from the off state to the on state and starts laser oscillation. When this light enters the photodiode 12, a photocurrent i begins to flow through the photodiode 12. The response time of this photocurrent ip is in a region where it is sufficiently smaller than the time constant RC determined by the resistance value R of the load resistor 13 and the capacitance value C of the load capacitor 14.
As for the photocurrent flowing in 2, there is no essential contradiction in approximately representing it as a step function as shown in FIG. 6(C). In this case, the photodiode 12 generating the photocurrent IP can be regarded as a constant current source, so the photodiode 12, load resistance 13, and load capacitance 1
An equivalent circuit diagram of a circuit in which 4 and 4 are connected is shown in FIG. In the figure, 41 is a constant current source, and this constant current source 41 has a step current i (t) given by the following equation.
flow.

1(t)=ip−u(t)·(1) Here, u(t) represents a step function. At this time, the potential difference V(1) generated across the resistor R and capacitor C is expressed as follows.

v(t)=ip・R・(1-exp(-t/RC)
) u(t) = 12) Therefore, under these assumptions, when the bistable semiconductor laser 11 starts oscillating and the photocurrent i starts flowing through the photodiode 12, the potential at point A in FIG. , according to the function shown in equation (2),
It begins to decrease as shown in FIG. 6(d).

By the way, the relationship between current and voltage in a bistable semiconductor laser is as in the case of a general semiconductor laser,
The state is as shown in FIG. 7(a). If this current-voltage characteristic curve is at the bias point before starting oscillation, the current 11 will change to (C) as the potential decreases as shown in ('b) in the figure. ). The amplitude of the voltage signal at this time can be determined by the photocurrent l and the load resistance value R, so if this voltage amplitude is set to a sufficiently large value, the current generator will stop oscillating after a certain period of time. It becomes smaller than the threshold value 11OFF (point ■ in the figure).At this time, the bistable semiconductor laser 11 stops oscillating, and at the same time the photocurrent flowing through the photodiode 12 also becomes zero (see the waveform diagram in Figure 6). Along with this, the potential at point A in Figure 2 returns to its initial value (point ■ in Figures 6 and 7) according to the equation (2) with the opposite sign. The stable semiconductor laser 11 remains in the off state and stops oscillating until the next input optical pulse is input.In this way, the pulse width of the input optical pulse is changed from point ■ to ■■ in FIG. It is possible to expand the pulse width to correspond to the time taken to reach the point and extract it as the output of the bistable semiconductor laser 11.As mentioned above, the optical output of the bistable semiconductor laser 11 is transmitted from the active layer to each other. Since the light is output in two opposite directions, even if one of the lights is made incident on the photodiode 12,
Optical output with an expanded pulse width can be extracted from the opposite direction.

The time from when the bistable semiconductor laser 11 starts oscillating to when it stops oscillating is determined by the time constant RC determined by the resistance value R of the load resistor 13 and the capacitance value C of the load capacitor 14, and the voltage of the bistable semiconductor laser 11. - It is determined by the current characteristics and the current bias conditions, but is essentially controlled by the above time constant RC, so generally, by determining the values of the load resistance and load capacitance, It is possible to determine the time from the start of oscillation to the stop of oscillation, that is, the pulse width of the expanded optical pulse.

In this way, according to this embodiment, the operation as an optically stable multivibrator that turns on when a light pulse is input and maintains that state for a period of time determined by the time constant RC can be realized in the state of an optical signal. . In other words,
It becomes possible to generate a low-speed optical clock from an optical frame and expand the duty ratio of optical pulses without performing electrical synchronization control.

The magnitude of the voltage signal fed back to the bistable semiconductor laser 11 is determined by the product of the photocurrent l and the load resistance value R, but when the photocurrent i is small and it is difficult to obtain a sufficient voltage signal, The circuit configuration is as shown in FIG. In this example, the photocurrent generated in the photodiode 12 is made to flow through the first load resistor 51, and as the photocurrent flows through the first load resistor 51, a photocurrent generated between both ends of the first load resistor 51 is generated. Transistor (field effect transistor) 5
2 is used to amplify the signal. The voltage signal is input to the gate (G) of the transistor 52, and the voltage signal is input to the gate (G) of the transistor 52.
A bias voltage -V is applied to the drain (D>) of the transistor 52.The output signal (response signal) of the load circuit including this transistor 52 is taken out from the source (S) of the transistor 52, and is shown in FIG. In the same way as in the circuit shown in 1, the current bias of the bistable semiconductor laser is fed back through a capacitor (not shown).

A second transistor is connected between the source (S) of the transistor 52 and the ground.
Load resistance (resistance value is R) 53 and load capacitance (capacitance value is C)
) 54 are connected. In this configuration, the second
The pulse width of the output optical pulse can be determined by the values of the load resistance 53 and load capacitance 54. Furthermore, since the amplitude of the response signal fed back to the current bias of the bistable semiconductor laser corresponds to the product of the amplified source current and the second load resistance R, the photocurrent 1 generated in the photodiode 12
Even when , is small, a sufficiently large amplitude of the response signal can be obtained. In this case, compared to the case where the amplitude of the response signal is increased by increasing the value of the load resistance without amplifying the photocurrent, it is possible to prevent deterioration of the high-speed characteristics. In other words, when the value of the load resistance is increased, the time constant represented by RC also increases, and the pulse width that can be created is limited to a large one. However, when amplifying the photocurrent In order to obtain a predetermined response signal amplitude, the value of the load resistance may be small, so the pulse width that can be produced is not limited to a large one.

FIG. 9 is a diagram showing an example of an embodiment of the present invention, in which the present invention is applied to an optical direct branching device in an optical drop/add node device for horizontal optical transmission.

61 is an optical clock generation circuit constructed using the optical monostable multivibrator of the present invention, and when an optical frame pulse is input to this circuit, the pulse width is expanded and a low-speed optical clock is output. . Optical couplers 62 and 65 divide the power of optical data transmitted through the optical transmission line 69 into two. Reference numeral 63 denotes an optical frame extraction circuit, which extracts an optical frame from which a signal is generated for the optical clock generation circuit 61 from previous data.

A part of the optical data string transmitted through the optical transmission line 69 is input to an optical frame extraction circuit 63 by the optical coupler 62, and an optical frame is extracted. This optical frame is sent to the optical clock generation circuit 61 after its timing is adjusted in accordance with the desired data bits on the optical transmission line 69 by the optical timing adjustment circuit 64. The optical clock generation circuit 61 generates a low-speed optical clock based on the optical frame whose timing has been adjusted. The optical frame and optical clock thus generated are sent to an optical threshold element 66 and an optical bistable element 67, respectively.

The optical threshold element 66 connects the optical transmission line 69 with the optical coupler 65.
An optical frame is superimposed on a desired bit (for example, data "l") in the optical data string separated from the optical data string, and only the data of the desired bit is extracted by threshold processing. In addition, the optical bistable element 67 superimposes a low-speed optical clock on the data extracted by the optical threshold element 66, expands the duty ratio of the data, and transfers this data to the optical subscriber terminal 6.
Send to 8. Note that the internal configurations of the optical frame extraction circuit 63 and the optical timing adjustment circuit 64 are configured as usual.

In this way, when the present invention is applied to operate the node device 81, there is no need for synchronization processing using electrical signals.

As a result, when the capacity of the signals to be handled increases, it is possible to prevent the device from becoming larger or more complex, and it is also possible to prevent the processing speed from being limited due to the increase in capacity.

In the example shown in Fig. 9, an optical monostable multivibrator is used as an optical clock generation circuit in the node device.
As shown in FIG. 0, an optical monostable multivibrator may be used as the duty ratio expansion circuit 71.

That is, the optical data with a narrow pulse width extracted by the optical frame in the optical threshold element 66 is directly input to the duty expansion circuit 71, the pulse width (duty ratio) of the optical data is expanded, and the optical data is transmitted to the optical subscriber terminal 72. With this configuration, a low-speed optical clock is not generated, so this configuration is useful for simplifying the device configuration when the optical subscriber terminal 72 does not require a low-speed optical clock. It is valid.

As described in detail, the present invention can be used in applications such as generating a low-speed optical clock based on an optical frame extracted from an optical signal train and expanding the duty ratio of optical pulses. This has the effect of making it possible to provide a novel optical monostable multivibrator. Therefore, the present invention greatly contributes to the realization of an all-optical processing type transmission processing node that can process optical signals without converting them into electrical signals.

[Brief explanation of the drawings] Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is an embodiment circuit diagram, Fig. 3 is a diagram showing the configuration of a bistable semiconductor laser, and Fig. 4 is an explanation of bistability. Figure 5 is an equivalent circuit diagram when a photocurrent is generated in the photodiode, Figure 6 is a waveform diagram of the circuit in Figure 2, Figure 7 is an explanatory diagram of the operation of the embodiment, and Figure 8 is another implementation. FIG. 9 is a diagram showing an example of an embodiment of the present invention; FIG. 10 is a diagram of another embodiment of the present invention; FIG. 11 is an explanatory diagram of a prior art. 1.11... Bistable semiconductor laser, 2.16.17... Variable voltage source or variable current source, 3.
12... Photodiode, 4.18... Voltage source, 5... Load circuit.

Claims (5)

[Claims] (1) An optical monostable multivibrator in which, when an input optical pulse is input to the bistable semiconductor laser, an output optical pulse having a pulse width larger than the pulse width of the input optical pulse is output from the bistable semiconductor laser, , a bistable semiconductor laser (1), and a variable voltage source that applies a current bias to the bistable semiconductor laser (1) so that the bistable semiconductor laser (1) can take two stable states consisting of an on state and an off state. A voltage source or variable current source (2), a photodiode (3) that receives a portion of the output light of the bistable semiconductor laser (1), and a voltage source (4) that applies a reverse bias to the photodiode (3). ), and a load circuit (5) through which the photocurrent generated in the photodiode (3) flows, and a response signal to the photocurrent in the load circuit (5) is fed back to the current bias to generate an input optical pulse. An optical monostable multivibrator, characterized in that the above-mentioned bistable semiconductor laser (1), which has been turned on, is turned off by an input of the above. (2) The load circuit (5) is equipped with a load resistance (13) and a load capacitance (14) through which the photocurrent flows, and the output optical pulse is determined by the values of the load resistance (13) and load capacitance (14). Optical monostable multivibrator according to claim 1, characterized in that the pulse width is determined. (3) The load circuit (5) is a first circuit through which the photocurrent flows.
2. The optical monostable according to claim 1, further comprising: a load resistor (51), and a voltage across the first load resistor (51) is amplified by a transistor (52). Multivibrator. (4) A second load resistor (53) and a load capacitor (54) are connected to the output of the transistor (52),
4. The optical monostable multivibrator according to claim 3, wherein the pulse width of the output optical pulse is determined by the values of the second load resistance (53) and the load capacitance (54). (5) The optical monostable multivibrator according to any one of claims 2 to 4, wherein the feedback of the response signal to the current bias is performed via a capacitor (15).