JPH05300096A - Optical transmitter and optical receiver for optical parallel transmission and optical parallel transmitting system provided with them - Google Patents

Abstract

(57) [Abstract] [Object] The present invention relates to an optical transmitter and an optical receiver for optical parallel transmission, and an optical parallel transmission system including them, and enables stable operation without significantly increasing power consumption. With the goal. In an optical transmitter for optical parallel transmission including an LD array 111 including a plurality of LDs, one specific LD 11
APC is performed only on No. 3 and each intensity-modulated light is transmitted to the optical receiver 130 by the optical fiber array 120. In the optical receiver 130, the LD 113 for which APC is performed is performed.
A clock is extracted on the basis of the optical signal from and the identification operation of each channel is performed based on this clock.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter and an optical receiver for optical parallel transmission, and an optical parallel transmission system including them.

With the development of optical communication technology, the broadband property of optical fibers has been applied not only to the trunk line system but also to high-speed data transmission between or within communication devices such as transmission terminal equipment and switching equipment, or between computers or within computers. Applying the utilized optical transmission technology has been noticed and studied. In such an optical transmission interface,
An optical parallel transmission system that transmits many signals in parallel is effective. The optical parallel transmission system has characteristics that it is superior in characteristics such as transmission speed, transmission distance, and electromagnetic induction noise, etc., as compared with the electrical parallel transmission system, and research and development in various fields are underway. ..

As a light source on the transmission side in the optical parallel transmission system, a light emitting element array formed by integrally integrating a plurality of light emitting elements is used. As a practical light emitting element,
Although a light emitting diode (LED) and a semiconductor laser (laser diode: LD) are known, the semiconductor laser is more excellent from the viewpoint of high speed and high output.

Generally, in a semiconductor laser, characteristics such as an oscillation threshold value and light emission efficiency (differential quantum efficiency) greatly change depending on the ambient temperature as compared with a light emitting diode, so that it is stable against temperature change and the like. It is required to realize various operations.

On the other hand, when the light emitting element array is mounted on the optical transmitter or when the light receiving element array is mounted on the optical receiver, the mounting area can be reduced as compared with the case where a plurality of single elements are used. Therefore, the device can be downsized. In order to effectively reduce the size of such a device,
It is effective to accommodate a circuit for driving each element in a substrate or a package having a small area, and it is required to reduce the power consumption of such a drive circuit.

[0006]

2. Description of the Related Art Conventionally, as a method of driving a single-element semiconductor laser, a modulation current pulse is superimposed on a bias current fixed near the laser oscillation threshold and supplied to the semiconductor laser. It is known that a semiconductor laser having a relatively small laser oscillation threshold is used and a bias current is set to zero to directly supply a modulation current pulse.

However, according to these methods, stable operation of the semiconductor laser may become difficult due to variations in the laser oscillation threshold of the semiconductor laser due to temperature and the like.

On the other hand, there is automatic light output intensity control (APC) as a technique that enables stable operation of a semiconductor laser against temperature fluctuations.

[0009]

When the former conventional technique for fixing the bias current to zero or a predetermined value is applied to all channel elements (semiconductor laser unit) of the semiconductor laser array, the circuit scale can be reduced. Therefore, the power consumption can be reduced, but there is a problem that the operation of the semiconductor laser units of all channels becomes unstable due to temperature fluctuations and the like.

On the other hand, when the latter prior art (APC) is applied to the semiconductor laser units of all the channels of the semiconductor laser array, stable operation of all the channels becomes possible. Since an alternative means is required, there has been a problem that the circuit scale increases and the power consumption increases as the number of channels increases. As a technique related to this, JP-A-63-1
There is one disclosed in Japanese Patent No. 44653.

An object of the present invention is to provide an optical transmitter and an optical receiver for optical parallel transmission, which can realize stable operation without increasing the power consumption so much, and an optical parallel transmission system including them. That is.

[0012]

FIG. 1 is a claim correspondence diagram. The optical transmitter for optical parallel transmission of the present invention is a semiconductor laser array 12 including a plurality of semiconductor laser units 11.
A plurality of driving means 13 for respectively driving the plurality of semiconductor laser units 11 based on input data; and a part of light output from one specific semiconductor laser unit selected from the plurality of semiconductor laser units 11. , A light intensity detecting means 1 for outputting an electric signal according to the light intensity
4 and the electric signal from the light intensity detecting means 14, and feedback means 1 for feeding back to the driving means for driving the specific semiconductor laser unit so that the average level becomes constant.
5 and.

The optical receiver for optical parallel transmission of the present invention receives a plurality of optical signals transmitted in parallel, and outputs a plurality of light receiving means 31 for outputting electric signals corresponding to the optical intensities thereof.
A clock generating means 32 for generating an identification clock based on an electrical signal from one specific light receiving means selected from a plurality of light receiving means 31, and based on the clock from the clock generating means 32, the light receiving means 31 And an identification unit 33 that identifies the electric signal.

The optical parallel transmission system of the present invention comprises an optical transmitter 10 for optical parallel transmission according to the present invention and a parallel optical transmission line 20 for transmitting a plurality of optical signals from the semiconductor laser array 12 in the optical transmitter 10. And an optical receiver 30 for optical parallel transmission according to the present invention, which receives a plurality of optical signals transmitted by the parallel optical transmission line 20. The specific light receiving means in the optical receiver 30 receives the optical signal from the specific semiconductor laser unit in the optical transmitter 10.

[0015]

In optical parallel transmission, the greatest influence of unstable operation of the semiconductor laser array due to temperature fluctuation is reproduction or extraction of timing information such as a clock on the receiving side. The present invention focuses on the point that if accurate timing information is obtained for only one channel on the receiving side, the identification operation for all channels can be performed based on this timing information.

That is, by performing APC on only one specific semiconductor laser unit on the transmitting side to stabilize its operation, the specific semiconductor laser unit accurately transmits the reference timing information, and the specific semiconductor laser unit is transmitted. Even when the operation of the semiconductor laser unit other than the unit fluctuates due to temperature fluctuation or the like, stable identification operation on the receiving side is possible.

[0017]

EXAMPLES Examples of the present invention will be described below. FIG. 2 is a block diagram of an optical parallel transmission system showing an embodiment of the present invention. This system uses an optical transmitter 110 that outputs a plurality of channels of optical signals in parallel, an optical fiber array 120 that includes a plurality of optical fibers that separately transmits optical signals from the optical transmitter 110, and an optical fiber array 120 that transmits the optical signals. The optical receiver 130 receives the generated optical signal for each channel. The configuration and operation of the optical receiver 130 will be described later.

The optical transmitter 110 includes a semiconductor laser array in which a plurality of semiconductor laser units are integrated together. Hereinafter, this array is referred to as an LD array, and each unit is referred to as an LD.

The LD array 111 includes n (n is a natural number) LDs 112 (# 1 to #n) not subjected to APC and A
It is provided with one LD 113 which is a PC. LD
The reference numeral 112 and the LD 113 are the same as the components of the integrated LD array, and the reference numerals are different for the convenience of description.

Each of the LDs 112 (# 1 to #n) is provided with a corresponding one of the drive circuits 114 (# 1 to #n).
n), and the LD 113 is driven by the drive circuit 115. The input data D _in (# 1 to #n) is input to the drive circuits 114 (# 1 to #n), and the input data D _in ′ is input to the drive circuit 115. The input data D _in (# 1 to #n) is transmission data, and the input data D _in ′ is transmission data or a periodic signal such as a clock.

Each LD 112 (# 1 to #n) and 113
Are driven by the drive currents supplied from the respective drive circuits to output intensity-modulated light. Reference numeral 116 is an LD
A photodiode for receiving a part of the light output from 113 and detecting the light intensity thereof is shown. As this photodiode 116, in this embodiment, an electric signal corresponding to the average level of the detected light intensity is used. In order to output
A photodiode having a response frequency sufficiently lower than the frequency corresponding to the bit rate of the input data D _in ′ used for driving the LD 113 is used.

The feedback circuit 117 includes the photodiode 11
Receiving the electric signal from 6, the feedback is applied to the drive circuit 115 so that the detection light intensity in the photodiode 116 becomes constant. Drive circuits 114 (# 1 to #n) and 11
5 and a specific configuration example of the feedback circuit 117 will be described later.

FIG. 3 shows L in the optical transmitter 110 of FIG.
FIG. 6 is a perspective view for explaining an arrangement example of each constituent member near the D array 111. The LD array 111 is fixed to the edge of the heat sink 201 for the purpose of heat dissipation and the like. Each L
Each of D112 and 113 has a light emitting point on each of the two cleavage surfaces facing each other. Hereinafter, the light emitted from one light emitting point of the LD and coupled to the optical transmission line is referred to as front light, and the light emitted from the other one light emitting point is referred to as rear light.

In this embodiment, each LD 112 and 113 is
The light emitting points of the front light are positioned on the same straight line at equal intervals, and the respective front lights are incident on the plurality of optical fibers 203 forming the parallel optical transmission line 120. LD 112 and 113
As an optical coupling structure between the optical fiber 203 and the optical fiber 203, a coupling structure in which the core end surface of the optical fiber 203 is located close to the light emitting points of the LDs 112 and 113 can be used.

Such direct coupling between the optical fiber and the LD is performed by using the fiber holder 204 in which V-grooves parallel to each other and having a pitch equal to the pitch of the light emitting points of the LD are formed, and near the end of each optical fiber 203. Is seated in the V groove, and the fiber holder 204 and the LD array 111 are seated.
This can be easily performed by adjusting the relative positional relationship of

Regarding the photodiode 116 for receiving a part of the light output from the LD 113, the photodiode 116 is mounted on the heat sink 201 so that the light receiving portion of the photodiode 116 faces the light emitting point of the rear light of the LD 113. You can fix it to. In addition, each LD112
, 113 are grounded via the heat sink 201, and the other electrode is supplied with a drive current from the drive circuit via the bonding wire 202.

FIG. 4A shows the driving circuits 114 and 115.
4B is a diagram showing an example of the configuration of FIG.
It is a figure which shows the other structural example. The drive circuit of FIG. 4A outputs the pulse current I _m according to the input data to the LD 112.
It includes a modulation circuit 301 for supplying (113) and a bias circuit 302 for supplying a DC bias current I _b to the LD 112 (113). The modulation circuit 301 includes a transistor Tr1 and a resistor R1, and the bias circuit 302 includes a transistor Tr2 and a resistor R2.

The anode of the LD 112 (113) is grounded, and the cathode is connected to the connectors of the transistors Tr1 and Tr2. The input data D _in (D _in ′) is input to the base of the transistor Tr1 and the transistor Tr2
A bias control signal (in the case of the drive circuit 115) or a fixed constant current (in the case of the drive circuit 114) from a feedback circuit described later is input to the base of the. Transistor Tr
The emitter of 1 is connected to one end of the resistor R1, and the other end of the resistor R1 is connected to the power supply terminal -V1. Transistor Tr
The emitter of 2 is connected to one end of the resistor R2, and the other end of the resistor R2 is connected to the power supply terminal -V2.

On the other hand, the drive circuit shown in FIG.
It has a configuration in which the bias circuit 302 is removed from the drive circuit of (A). That is, this drive circuit is the modulation circuit 3
It consists of 01 only.

In the following description, a method of inputting a bias control signal to the bias circuit 302 to drive the LD using the drive circuit of FIG. 4A is called an APC type drive method,
The bias circuit 302 using the drive circuit of FIG.
A method of inputting a fixed current to the LD to drive the LD is called a fixed bias driving method, and the LD is driven by using the driving circuit of FIG.
The method of driving the is called a biasless driving method.

FIG. 5 is a diagram for explaining the principle of LD intensity modulation when the drive circuit of FIG. 4A is used, that is, when the APC drive method or the fixed bias drive method is used.
Reference numeral 401 represents the IL characteristic of the LD, and the vertical axis represents L.
The light intensity of the D output and the horizontal axis represent the current supplied to the LD. Reference numeral 402 represents the drive current waveform corresponding to the time change of the current value supplied to the LD in association with the IL characteristic 401. Reference numeral 403 denotes the intensity-modulated optical waveform corresponding to the temporal change of the light intensity, which is also the IL characteristic 401.
It corresponds to.

As is clear from the IL characteristic 401, L
D has a characteristic that the laser intensity is started at the laser oscillation threshold value I _th and the light intensity increases as the current increases in the region of the current larger than the threshold value I _th .

The drive current waveform 402 is a waveform in which the pulse current I _m corresponding to the data input is superimposed on the DC bias current I _b . When the fixed bias driving method is applied, the bias current I _b is approximately equal to the lasing threshold I _th. When the APC driving method is applied, as will be described later, as a result of APC, the bias current I _b is always larger than the laser oscillation threshold I _th .

When such a driving current is supplied to the LD, the light intensity of the LD output changes according to the IL characteristic 401, and intensity modulated light is obtained. The drive current waveform 402 is I-
It is reflected in the intensity modulation waveform 403 via the L characteristic.

FIG. 6 is an explanatory view of the principle of the intensity modulation of the LD when the drive circuit of FIG. 4B is used, that is, when the bias-free drive method is used. In this case, the bias current becomes zero and only the pulse current I _m corresponding to the input data is supplied to the LD as the drive current. The drive current waveform is reflected in the intensity-modulated light waveform as in the case of FIG.

In the case of the non-bias drive method,
When the drive current value transits between the high level and the low level (zero level), the laser oscillation threshold value I _th is always passed. The effect will be described later.

FIG. 7 is a diagram showing a specific configuration example of the feedback circuit 117 of FIG. This feedback circuit detects a current-voltage converter (resistor 501 and amplifier 502) that converts the photocurrent generated in the photodiode 116 into a voltage value, and an error value between the voltage value converted by this converter and the reference voltage. The error value is calculated by using the drive circuit 115 of FIG. 2 (specifically, FIG. 4A).
Operational amplifier 503 for feedback to the bias circuit 302)
Including and

The cathode of the photodiode 116 is grounded, and the anode is connected to the power supply terminal -V via the resistor 501. When a part of light from the LD 113 (see FIG. 2 and FIG. 3) is input to the photodiode with the reverse bias applied to the photodiode 116, a photocurrent corresponding to the intensity of the input light is generated in the photodiode. 11
6 and resistor 501. In the present embodiment, the response frequency of the photodiode 116 is sufficiently lower than the frequency corresponding to the bit rate of the input data, so the magnitude of the photocurrent depends on the average light intensity of the intensity-modulated light input to the photodiode 116. Will be things.

The change in the photocurrent generated in the photodiode 116 is taken out as a potential change at the connection point between the photodiode 116 and the resistor 501 and amplified by the amplifier 502. The output voltage V _a of the amplifier 502 is input to the first input port of the operational amplifier 503 as a component corresponding to the average value of the light intensity, and a predetermined reference voltage V a is input to the second input port of the operational amplifier 503. _ref is entered.

The operational amplifier 503 proportionally amplifies the difference component of the two input voltage values and outputs it as an error signal. This error signal is fed back to the bias circuit 302 of FIG. 4A through a buffer circuit or an inverting circuit (not shown) that is used as appropriate.

LD using the feedback circuit of FIG.
The operating principle of APC for 113 (see FIG. 2) is shown in FIG.
Will be explained. In FIG. 8, reference numeral 601 is the lowest temperature T _{min in} the operating temperature range of the LD array 111 (see FIG. 2).
Represents the IL characteristics of the LD 113 at, and reference numerals 602 and 603 denote LD 11 at temperatures T ₁ and T _2, respectively.
3 represents the I-L characteristic (T _min <T ₁ <T ₂ ).

[0042] Now, a bias current and a pulse current to the LD113 as the average value of the light intensity when the at temperatures T ₁ input error of the operational amplifier 503 in FIG. 7 (V _a -V _ref) is zero becomes P ₀ Assume that the amplitude of is set. In LD, as the temperature rises, I
As the laser oscillation threshold in the -L characteristic increases, the differential coefficient of the characteristic curve decreases.

In this state, when the temperature of the LD 113 rises from T ₁ to T ₂ , the I-L characteristic represented by reference numeral 602 changes to the I-L characteristic represented by reference numeral 603, so that the light intensity is changed. It decreases from P ₀ to P ₁ smaller than this.

The light intensity is reduced and the photodiode of FIG.
When the photocurrent flowing through 116 decreases, the operational amplifier 503
Error input (V_a-V_ref) Is negative and this error input
The output signal of the operational amplifier 503 corresponding to is shown in FIG.
Current I in the drive circuit of_bIncrease. Reverse
And the temperature of LD113 is T₁When it becomes lower than
Is the error input of the operational amplifier 503 (V_a-V_ref) Is positive
And the bias current I _bIs reduced.

By thus driving the laser diode 113 based on the drive current obtained by negatively feeding back the bias current, the average intensity of the intensity-modulated light from the LD 113 can be stabilized.

In FIG. 8, reference numeral 604 indicates temperature T ₁
Represents the waveform of the drive current of the LD 113 at,
5 is the LD at the temperature T ₂ obtained as a result of APC
The waveform of the drive current of 113 is shown.

FIG. 9 is a diagram showing another configuration example of the feedback circuit 117 of FIG. This embodiment differs from the embodiment of FIG. 7 in that the reference voltage V _ref ′ input to the operational amplifier 503 is controlled according to the mark ratio of the input data.
Specifically, it is as follows.

The mark ratio monitor circuit 601 is composed of, for example, an integrator provided in the drive circuit 115, and the generation ratio of the logical values “1” and “0” of the input data input to the drive circuit 115, that is, the mark ratio. To detect. The reference voltage setting circuit 602 sets the reference voltage V _ref ′ input to the operational amplifier 503 according to the mark ratio detected by the mark ratio monitor circuit 601.

Now, when the mark rate is, for example, 1/2, that is, when "1" and "0" occur at a ratio of 1: 1 and when the mark rate is, for example, 1/4, that is, "1" and "0". Is 1: 3
The average light intensity of the intensity-modulated light from the LD 113 changes depending on the case. As a result, the operating conditions in the APC described above change.

Therefore, in the present embodiment, the reference voltage setting circuit 602 determines the reference voltage V as a reference according to the mark ratio of the input data notified from the mark ratio monitor circuit 601.
_It changes the value of _ref ′. As a result, the operation of the APC can be stabilized regardless of the change in the mark ratio.

When performing APC on the LD 113, it is desirable that the initial setting value of the bias current supplied to the LD 113 is set to be substantially equal to the laser oscillation threshold value at the lowest temperature of the operating temperature range of the LD array 111. .. By doing so, as is apparent from FIG. 8, the instantaneous value of the drive current supplied to the LD 113 is always larger than the laser oscillation threshold of the LD 113.
The effect of this will be described in detail below.

Now, as shown in FIG.
The current to be applied is time t₀At 0 to I_onTurn into a staircase
It is assumed that it has been converted. In this case, the current value I_onIs LD
Laser oscillation threshold I_thDespite being larger than
Instead, laser oscillation does not start at the same time as the current changes.
Instead, as shown in FIG.₀From finite
Time t_dLaser oscillation is started after a delay. this is,
Electrons in the conduction band injected by current injection become radiative recombination
Finite time τ that is not zero before returning to more valence band _SRequires
Because it does. This time τ_SIs the spontaneous emission carrier lifetime
The value is usually around 2 μs.

Therefore, even if the electrons necessary for laser oscillation are finally injected, a delay will always occur.
This delay t _d is given by the following equation. _{t d = τ S · 1n (} I m / (I m -I th + I b)) where the I _m is a pulse current, I _b is the bias current to be supplied to the modulation or the like. If there is a delay time t _d represented by this equation, the pulse width of the signal obtained by modulating the LD becomes small, and as a result, the effective duty of data is reduced.

This gives the following big problem with respect to skew which is defined as a variation in propagation delay time of data between a large number of channels in parallel transmission. That is, as the duty of data decreases, the transmission bit rate is equivalently increased, and the allowable skew is reduced. As a result, the transmission distance is limited, and the stability and reliability of the entire transmission system are reduced.

Further, in a self-timing type system in which a clock is extracted from a signal transmitted on the receiving side, the delay of the rising edge of data is equivalently taken as an increase in jitter, and accordingly, the jitter of the clock is increased. Also increases, and the identification operation may become unstable.
An increase in jitter in data is schematically shown in FIG. 11A, and an increase in jitter in clock is schematically shown in FIG. 11B.

When the bias-free driving method is implemented by using the driving circuit of FIG. 4B as the driving circuit 114 of the LD 112 of FIG. 2, as is apparent from the operation principle described with reference to FIG. Since the instantaneous value alternately takes a larger current value and a smaller current value than the laser oscillation threshold value I _th , the identification operation may become unstable on the receiving side as described above.

The drive circuit 114 of the LD 112 shown in FIG.
As a result, even when the fixed bias driving method is performed using the driving circuit of FIG. 4A, the identification operation may become unstable on the receiving side, though not to the same degree as in the non-bias driving method.

Because, as shown in FIG. 12, LD1
The bias current value in the drive current waveform 701 of _No. 12 is set to be almost equal to the laser oscillation threshold value I _th1 at the temperature T ₁ , and the instantaneous value of the drive current of the LD 112 is always the laser oscillation threshold value I th at the temperature T ₁ . Even if it is set to be larger than _th1, the instantaneous value of the drive current of the LD 112 is higher than the laser oscillation threshold value I _th2 or I _{th3 at the} temperature T ₂ or T ₃ higher than the temperature T _1. This is because even a large value and a small value are taken alternately.

Since the LD 113 of FIG. 2 is subjected to APC, such a problem is unlikely to occur. That is, as described with reference to FIG. 8, when the initial setting value of the bias current supplied to the LD 113 is set to be substantially equal to the laser oscillation threshold value at the lowest temperature of the operating temperature range of the LD array 111, the laser oscillation threshold value is set. The value is always larger than the laser oscillation threshold value at the lowest temperature, and the differential coefficient of the IL characteristic is always smaller than the differential coefficient of the IL characteristic 601 at the minimum temperature, as indicated by reference numerals 602 and 603, for example. Therefore, in the operating temperature range, the instantaneous value of the driving current of the LD 113 is always larger than the laser oscillation threshold value, and the delay of laser oscillation does not occur.

Here, even when the initial setting value of the bias current supplied to the LD 113 is not substantially equal to the laser oscillation threshold value at the lowest temperature of the operating temperature range of the LD array 111, the initial setting value is lower than the threshold value. As long as is large, there is no delay in laser oscillation. In this embodiment, the initial setting value is set to be substantially equal to the threshold value in order to minimize deterioration of the extinction ratio due to temperature rise.

Now, in FIG. 2, if the APC driving method is applied to all the LDs forming the LD array 111, the number of negative feedback loops is required for the number of LDs, so that the structure of the device is extremely complicated. Therefore, a large amount of power consumption is required.

On the other hand, if the non-bias driving method or the fixed bias driving method is applied to all the LDs constituting the LD array 111, the negative feedback control loop and the like are not required, and thus the power consumption can be reduced. As described above, the clock becomes unstable and the identification operation on the receiving side becomes unstable.

In the present invention, attention is paid to the fact that only one clock is required for the stable identification operation on the receiving side. That is, in FIG. 2, if only one LD 113 on the transmission side is subjected to APC, stable identification operation can be performed for all channels based on the clock reproduced by the channel corresponding to the LD 113.
It is possible to simplify the configuration of the device and reduce power consumption.

Next, the structure and operation of an optical receiver for receiving a parallel optical signal transmitted from such an optical transmitter via a parallel optical transmission line will be described. The intensity-modulated light from the LD 113, which is intensity-modulated by the input data (transmission data) D _in ′, is input to the photodiode 8 in the optical receiver 130.
The signal is converted into an electric signal by 01, and this signal is equalized and amplified by the equalizing amplifier 802 and input to the discriminator 803.
The output signal of the equalizing amplifier 802 is also the timing circuit 80.
Enter in 4. The timing circuit 804 generates a clock by self-timedly extracting a predetermined frequency component of the modulation spectrum of the intensity-modulated light received by the photodiode 801.

On the other hand, the intensity-modulated light from each LD 112 (# 1 to #n) is converted into an electric signal by the photodiode 805 (# 1 to #n) in the optical receiver 130, and each electric signal is equalized. Amplifier 806 (# 1 to # 1
#N) is equalized and amplified, and the discriminators 807 (#
1 to #n). Then, the respective discriminators 803 and 8
07 (# 1 to #n) identify the input signal based on the clock from the timing circuit 804 and output output data D _out ′ and D _out (# 1 to #n), respectively. Clock CLK generated by the timing circuit 804
Can be used for purposes other than identification.

According to the present embodiment, the LD 113 outputs intensity-modulated light having a clean waveform without delay in laser oscillation, so that the timing circuit 804 can extract a clock with little jitter, and based on this clock. A stable identification operation can be performed for all channels.

By the way, when the equalizing amplifier 802 and the timing circuit 804 are connected by DC coupling, the LD113
When the bias current increases considerably above the laser oscillation threshold value as the temperature rises and the extinction ratio of the intensity-modulated light deteriorates, the discriminators 803 and 807 (# 1 to #)
This may affect the identification operation in n). In order to avoid such an influence, the equalizing amplifier 802 and the timing circuit 804 are connected by AC coupling, and the LD 113
The DC component of the received light output of the photodiode 801 that occurs with the increase of the bias current of 1 may be removed.

In this embodiment, the clock is extracted by self-timing extraction based on the intensity-modulated light from the LD 113 which is modulated by the transmission data.
The input data used to drive the above may be used as a clock.
FIG. 13 shows a configuration example of an optical receiver that can be used in this case.

In this embodiment, the LD 113 (see FIG. 2)
Is directly modulated by the clock, the photodetection output of the photodiode 801 has a waveform corresponding to the clock. Therefore, the output signal of the photodiode 801 is amplified to a predetermined level by the amplifier 901 and is input to each of the discriminators 807 (# 1 to #n) as a clock. The clock CLK output from the amplifier 901 can be used for purposes other than identification.

Also in this embodiment, a clock with little jitter can be obtained, so that each discriminator 807 (# 1) can be obtained.
It is possible to stably perform the identification operation in steps # to #n).
When the optical receiver of FIG. 13 is used, the optical transmitter 11
The frequency of the clock input to the drive circuit 115 of 0 is the input data D _in (# 1 to # 1 to the drive circuit 114 (# 1 to #n)).
#N) is set equal to the frequency corresponding to the bit rate.

The drive circuit 11 of the optical transmitter 110 shown in FIG.
The input data D _in 'to 5 is not limited to the transmission data or the clock. That is, since the receiving side may send the timing information for signal identification from the LD 113, the input data D _in ′ to the drive circuit 115 is a signal having a fixed pattern such as a frame signal that repeats periodically. If

[0072]

As described above, according to the present invention,
It becomes possible to stably transmit the reference timing information from the transmitting side to the receiving side without increasing the power consumption of the optical transmitter, and based on this timing information, all channels in the optical receiver are This has the effect of enabling stable identification operation.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a complaint.

FIG. 2 is a block diagram of an optical parallel transmission system showing an embodiment of the present invention.

FIG. 3 is a perspective view near an LD array.

FIG. 4 is a diagram showing a configuration example of a drive circuit.

FIG. 5 is an explanatory diagram of the principle of intensity modulation when the drive circuit of FIG. 4 (A) is used.

FIG. 6 is an explanatory diagram of the principle of intensity modulation when the drive circuit of FIG. 4 (B) is used.

FIG. 7 is a diagram showing a configuration example of a feedback circuit.

FIG. 8 is an explanatory diagram of an operation principle of APC.

FIG. 9 is a diagram showing another configuration example of a feedback circuit.

FIG. 10 is a diagram for explaining a delay in oscillation start in the LD.

FIG. 11 is an explanatory diagram of jitter in data and clock.

FIG. 12 is a diagram for explaining a change in the IL characteristic with a temperature change in the LD.

FIG. 13 is a block diagram showing another embodiment of the optical receiver for optical parallel transmission.

[Explanation of symbols]

 10 optical transmitter 11 semiconductor laser unit 12 semiconductor laser array 13 driving means 14 light intensity detecting means 15 feedback means 20 optical transmission line 30 optical receiver 31 light receiving means 32 clock generating means 33 identifying means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04B 10/02

Claims (16)

[Claims] 1. A semiconductor laser array (12) comprising a plurality of semiconductor laser units (11), a plurality of driving means (13) for respectively driving the plurality of semiconductor laser units based on input data, and the plurality of semiconductors. A light intensity detecting means (14) for receiving a part of light output from one specific semiconductor laser unit selected from the laser units and outputting an electric signal according to the light intensity, and a light intensity detecting means (14) from the light intensity detecting means. An optical transmitter for optical parallel transmission, comprising: feedback means (15) for feeding back the driving means for driving the specific semiconductor laser unit so that the average level of the electric signal becomes constant. .. 2. The optical transmitter for optical parallel transmission according to claim 1, wherein the semiconductor laser unit outputs intensity-modulated light whose light intensity changes into a binary value according to the input data. .. 3. A drive circuit for driving the specific semiconductor laser unit, a modulation circuit (301) for supplying a pulse current according to the input data to the specific semiconductor laser unit.
And a bias circuit (302) for supplying a DC bias current to the specific semiconductor laser unit, and the driving means for driving a semiconductor laser unit other than the specific semiconductor laser unit is configured to generate a pulse current according to the input data. The optical transmitter for optical parallel transmission according to claim 2, further comprising a modulation circuit (301) for supplying to a semiconductor laser unit other than the specific semiconductor laser unit. 4. The light receiving means is a photodiode (116).
4. The optical parallel transmission light according to claim 3, wherein the response frequency of the photodiode is sufficiently lower than the frequency corresponding to the bit rate of the input data used for driving the specific semiconductor laser unit. Transmitter. 5. The optical transmitter for optical parallel transmission according to claim 4, wherein the photodiode (116) receives one of front emission light and rear emission light of the specific semiconductor laser unit. 6. The feedback means is the photodiode.
(116) a current-voltage converter that converts the photocurrent generated in (116) into a voltage value, and an error value between the voltage value converted by the converter and the reference voltage is detected and the error value is input to the bias circuit (302). The optical transmitter for optical parallel transmission according to claim 4, further comprising an operational amplifier (503) for feedback. 7. A mark ratio monitor circuit (601) for detecting a mark ratio of input data used for driving the specific semiconductor laser unit, and the operational amplifier according to the mark ratio detected by the mark ratio monitor circuit. The optical transmitter for optical parallel transmission according to claim 6, further comprising a reference voltage setting circuit (602) for setting the reference voltage of (503). 8. A bias circuit (302) for supplying a DC bias current to a semiconductor laser unit other than the specific semiconductor laser unit, the bias current being fixed to a constant value. 3. An optical transmitter for optical parallel transmission according to item 3. 9. The method according to claim 3, wherein the initial setting value of the bias current supplied to the semiconductor laser unit is substantially equal to the laser oscillation threshold value at the lowest temperature of the operating temperature range of the semiconductor laser array. 8. An optical transmitter for optical parallel transmission according to item 8. 10. The optical transmitter for optical parallel transmission according to claim 2, wherein the waveform of the input data used for driving the specific semiconductor laser unit is a fixed pattern that repeats periodically. 11. The bit rate of a plurality of input data used for driving the plurality of semiconductor laser units is the same, and the input data used for driving the specific semiconductor laser unit is a clock. The optical transmitter for optical parallel transmission according to claim 10. 12. A plurality of light receiving means (31) for respectively receiving a plurality of optical signals transmitted in parallel and outputting an electric signal according to the light intensity thereof, and one specification selected from the plurality of light receiving means. Clock generating means (32) for generating a discrimination clock based on an electric signal from the light receiving means, and discrimination means (33) for discriminating the electric signal from the light receiving means based on the clock from the clock generating means. An optical receiver for optical parallel transmission, comprising: 13. The optical signal received by the specific light receiving means is intensity-modulated by transmission information, and the clock generating means regenerates the identifying clock by extracting a predetermined frequency component of the modulation spectrum. The optical receiver for optical parallel transmission according to claim 12, wherein: 14. The optical signal received by the specific light receiving means is intensity-modulated by a clock, and the clock generating means amplifies the electrical signal from the specific light receiving means and directly outputs it as the identifying clock. The optical receiver for optical parallel transmission according to claim 12. 15. An optical transmitter (10) for optical parallel transmission according to claim 1, and a plurality of optical signals transmitted from the semiconductor laser array in the optical transmitter for optical parallel transmission, respectively. Parallel optical transmission line
(20) and the optical receiver (30) for optical parallel transmission according to any one of claims 12 to 14 for receiving a plurality of optical signals transmitted by the parallel optical transmission line, the optical parallel transmission The optical parallel transmission system, wherein the specific light receiving means in the optical receiver for use receives an optical signal from the specific semiconductor laser unit in the optical transmitter for optical parallel transmission. 16. The parallel optical transmission line is an optical fiber array (120) having a plurality of optical fibers, and the optical fiber array is directly coupled to the semiconductor laser array. The optical parallel transmission system described in.