JP3167967B2 - Tunable semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source used for optical communication and the like, and more particularly to a tunable wavelength semiconductor laser device having an improved wavelength control circuit of a multi-electrode distributed reflection type semiconductor laser used for optical wavelength division multiplexing transmission.

[0002]

2. Description of the Related Art With the advance of optical fiber amplifiers, wavelength division multiplexing (wavelength division multiplexing) is performed at a high density within the band of the amplifier.
Research on ion multiplexing (WDM) transmission schemes and transparent lightwave networks using the WDM schemes has been actively conducted.

In such a lightwave network,
By dynamically changing the transmission wavelength, the network can be made flexible. Such a wavelength tunable light source is a distributed Bragg reflection type semiconductor laser device (DBR-L) in terms of mass productivity, reliability, and high-speed response.
D) is promising.

A DBR-LD includes an active region, a phase adjustment region, and a distributed Bragg reflector (DBR) region, and applies an injection current to the active region to change a current injected into the phase adjustment region and the DBR region. Thus, the light source can change the oscillation wavelength.

FIG. 8 shows a conventional example of a wavelength control circuit of the DBR-LD. 8, 100 is a distributed Bragg reflection type semiconductor laser device (DBR-LD), 110 is a wavelength reference device, 120 is a wavelength detector, 130 is an error signal detector, 160 is a beam splitter, 200 is a current source, 21
0 is a phase adjustment region injection current control unit, and 213 is a DBR region injection current control unit.

[0006] Among these, the DBR-LD 100 is a semiconductor laser light source as a wavelength variable light source in optical transmission. As shown in FIG. 8, the DBR-LD 100 has an active region 101 and a phase adjustment region 102 as element structures. And a distributed Bragg reflector (DBR) region 103.
The active region 101, the phase adjustment region 102, and the DBR region 10 are provided in the device body of the DBR-LD 100.
Electrodes 105a, 105b, and 105c for separately applying currents to the respective regions are provided corresponding to the three regions. The electrode 105a is for the active region,
b is for the phase adjustment region, and the electrode 105c is for the DBR region.

The beam splitter 160 is a DBR-LD1
A part of the light LBf from the wavelength
And, for example, a half mirror. The wavelength reference device 110 is for passing a component in a predetermined wavelength range of the branched light, and the wavelength detection unit 120 detects the wavelength of the light passing through the wavelength reference device 110. And outputs a signal corresponding to the detection wavelength.

The error signal detector 130 receives the output signal from the wavelength detector 120 and the wavelength switching signal, and converts the output signal from the wavelength detector 120 to a wavelength determined by the signal content of the wavelength switching signal. The phase adjustment region injection current control section 210 detects the error (wavelength difference) and outputs the error signal as an error signal. The DBR-LD 100
The magnitude of the current injected into the phase adjustment region 102 is controlled. This phase adjustment region injection current control unit 210
Is output from the phase adjustment region 1 via the electrode 105b.
02.

The DBR region injection current control unit 213 controls the magnitude of the current injected into the DBR region 103 of the DBR-LD 100 in response to the wavelength switching signal, and is controlled by the DBR region injection current control unit 213. Is output to the DBR region 103 via the electrode 105c.

The current source 200 is a DBR-LD 100
This is a current source for applying a constant active region injection current to the active region 101 of FIG. 1, and the current from the current source 200 is injected into the active region 101 via the electrode 105a.

The DBR-LD 100 used here is called a multi-electrode distributed-reflection type semiconductor laser device because it has a plurality of electrodes such as 105a, 105b and 105c. The multi-electrode DBR-LD 100 has a DBR region. The Bragg wavelength is controlled by the injection current to 103, and single mode oscillation is performed at a longitudinal mode wavelength near the Bragg wavelength.
Since this longitudinal mode wavelength is mainly controlled by the injection current into the phase adjustment region 102, this point is satisfactorily used for wavelength control.

The operation of the conventional device having such a configuration will be described.

First, a constant active region injection current is applied to the active region 101 from a current source 200. In addition, a wavelength switching signal corresponding to the wavelength to be oscillated is externally provided to the DBR region injection current control unit 213 and the error signal detection unit 130, so that the DBR region 103 is provided in the DBR region based on the given wavelength switching signal. DB from current control unit 213
An R region injection current is provided.

Active region 10 in DBR-LD 100
A part of the output light LBf from the first side is partially branched by a beam splitter 160 such as a half mirror, and
Input to 0. Then, light of a component in a predetermined wavelength region is selected by the wavelength reference device 110 and the light is selected by the wavelength detector 12.
Input to 0.

In the wavelength detector 120, the wavelength reference device 110
Detecting the oscillation wavelength of the DBR-LD based on the output from
A signal corresponding to the detected wavelength is output to error signal detection section 130. Then, the error signal detection unit 130 detects an error signal corresponding to a difference between the desired wavelength determined based on the wavelength switching signal and the detected wavelength, and outputs the error signal to the phase adjustment region injection current control unit 210. .

The phase adjustment region injection current control section 210 having received the error signal corrects the current value based on the input error signal, and supplies the corrected current to the phase adjustment region 102. Thus, the oscillation wavelength of the DBR-LD 100 is controlled to a desired wavelength determined based on the wavelength switching signal.

[0017]

As described above, the DBR-
In the laser light source using the LD, a wavelength switching signal corresponding to a target wavelength to be oscillated is externally supplied to the DBR region injection current control unit 213 and the error signal detection unit 130, and the DBR region injection current control unit 213 controls the DBR of the DBR-LD 100. By controlling the value of the current injected into the region 103 in accordance with the wavelength switching signal, a laser beam near the target wavelength can be output, and the wavelength of the emitted laser beam is detected and given by the wavelength switching signal. The error signal from the target wavelength is detected by the error signal detection unit 130, and the correction corresponding to the error is performed by the phase adjustment region injection current control unit 210, and the value of the current injected into the phase adjustment region 102 is feedback controlled. By doing so, it becomes possible to output laser light of a target wavelength.

As described above, this apparatus obtains an error signal corresponding to the difference between the wavelength of the output laser beam and the desired wavelength which is a comparison reference given by the wavelength switching signal. The wavelength is set to a desired wavelength by controlling the injection current into the phase adjustment region 102 of the LD 100, and the wavelength is switched based on a wavelength switching signal.
This is performed by the wavelength switching control unit controlling the injection current into the DBR region 103.

That is, by "adjusting the injection current into the DBR region 103", "coarse adjustment of the wavelength can be performed, and fine adjustment of the wavelength can be performed by the injection current into the phase adjustment region 102."

However, the wavelength tunable characteristic of the DBR-LD 100 is accompanied by a mode jump, and hysteresis exists near the mode jump. In the hysteresis region, it can be seen that the laser can oscillate at any wavelength depending on how the current is set, that is, the oscillation state is unstable.

In such an unstable region, the wavelength is unstable due to factors such as disturbance such as temperature change and deterioration of the laser, and there has been a problem that the control system itself may fail in some cases.

Therefore, an object of the present invention is to detect an unstable state due to hysteresis and avoid it.
An object of the present invention is to provide a variable wavelength semiconductor laser device that enables stable wavelength control of a multi-electrode DBR-LD. Still another object of the present invention is to provide a semiconductor laser wavelength control device capable of reducing power consumption and cost.

[0023]

In order to achieve the above object, a tunable semiconductor laser device according to the present invention comprises a multi-electrode semiconductor laser device having an active region, a phase adjustment region and a distributed Bragg reflector region; Wavelength discriminating means for discriminating the wavelength of the forward output light of the semiconductor laser element, and the desired wavelength determined from a desired wavelength determined by a wavelength switching signal for instructing switching to a desired wavelength and a wavelength based on the output of the wavelength discriminating means, Error detecting means for detecting an amount of wavelength error with respect to, first control means for controlling an injection current to the phase adjustment region based on an output from the error detecting means, and the Bragg reflector based on the wavelength switching signal a first intensity detecting means for detecting a second control means that controls the current injected into the region, the intensity of the backward output light of the semiconductor laser element,
Wherein the first intensity detecting means comprises:
And the Bragg
After mode jump when the injection current to the reflector area is reduced
The output from the first intensity detecting means is Vf
Can, said second control means before Symbol first intensity detecting means
Output is in the range of 0.35Vf to 0.8Vf
Controlling the injection current into the distributed Bragg reflector region.
It is characterized by that.

Further, while reducing power consumption and cost,
In addition, in order to enable stable wavelength control, the tunable semiconductor laser device according to the present invention includes a multi-electrode semiconductor laser device including an active region, a phase adjustment region, and a distributed Bragg reflector region (DBR region); Wavelength discriminating means for discriminating the wavelength of the output light of the semiconductor laser element, and a wavelength based on the output of the wavelength discriminating means and a desired wavelength determined by a wavelength switching signal for instructing a switch to a desired wavelength, for the desired wavelength Error detection means for detecting a wavelength error, third control means for controlling an injection current to the phase adjustment area based on an output from the error detection means, and control of an injection current to the distributed Bragg reflector area comprising a fourth control means for said third control means, be configured to include a current limiter to provide the upper and lower limits of the current injected into the phase control region And it features.

The multi-electrode semiconductor laser device of the present invention having such a configuration controls the Bragg wavelength by the injection current into the DBR region, and oscillates in a single mode at a longitudinal mode wavelength near the Bragg wavelength. This longitudinal mode wavelength is controlled mainly by the injection current into the phase adjustment region. Here, the DBR region has the highest reflectance near the Bragg wavelength, and the reflectance decreases as the wavelength deviates from the Bragg wavelength. That is, the intensity of light transmitted through the DBR region increases as the wavelength deviates from the Bragg wavelength. Therefore, by detecting the output light intensity from the DBR region side (rear), the degree of coincidence between the Bragg wavelength and the longitudinal mode wavelength, that is, the stability of the oscillation state can be determined.

In the present invention, the multi-electrode semiconductor laser
The element (multi-electrode DBR-LD) is arranged separately from the first element.
Out of the multi-electrode DBR-LD
Detect the intensity of the force light. And the note to the DBR area
The first intensity after mode jump when the input current is reduced
When the output from the detection means is Vf, the second control
The output from the first intensity detecting means is 0.35V.
f and 0.8 Vf.
To control the injection current to The wavelength tunable characteristic of the multi-electrode DBR-LD involves mode jumps, and hysteresis exists near the mode jumps. In such a state, since the oscillation wavelength is unstable, there is a problem that the wavelength control becomes unstable due to disturbance or the like, but as described above, the degree of coincidence between the Bragg wavelength and the longitudinal mode wavelength, that is, , The stability of the oscillation state depends on the output light intensity from the DBR region (rear output light
Intensity) and control the injection current in the DBR region.
Control the rear output light by controlling
Therefore, in order to ensure stability, the detected value of the rear light intensity is set to 0.
What is necessary is just to make it in the range of 35 Vf to 0.8 Vf.
Therefore, taking advantage of this fact, the first intensity detecting means
The detected value of the backward light intensity is set so as to fall within the above range.
The second control means controls the injection current in the DBR region.
And, as it can be solved instability problems of the wavelength control
Become .

The same wavelength of the oscillation wavelength of the DBR-LD periodically appears around the Bragg wavelength with respect to the current injected into the phase adjustment region. The change in wavelength with respect to the change in injection current into the phase adjustment region decreases as the current increases. Further, as the injection current into the phase adjustment region increases, the optical loss in the phase adjustment region also increases. For the above reasons, in order to obtain the same wavelength variable width, it is advantageous that the current value is smaller in terms of power consumption and loss. On the other hand, if the current value is too small, the amount of change in wavelength with respect to the current becomes large, and it is necessary to control the current value with excessively high accuracy. Therefore,
By giving appropriate upper and lower limits to the current value, the power consumption of the control circuit can be reduced, and the cost can be reduced because excessively accurate current control becomes unnecessary.

[0028]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
1 shows a wavelength control circuit according to the embodiment. In FIG.
100 is a multi-electrode distributed Bragg reflection semiconductor laser device (DBR-LD), 110 is a wavelength reference device, 120 is a wavelength detector, 130 is an error signal detector, 140 is a backward light intensity detector, 160 is a beam splitter, 200 Is the current source,
210 is a phase adjustment region injection current control unit, and 212 is a DBR
This is a region injection current control unit. LBf is DBR-LD10
0, LBr of the forward output light of the emitted laser beam
Is the rear output light of the laser beam emitted by the DBR-LD 100.

The DBR-LD 100 is a semiconductor laser light source as a wavelength variable light source in optical transmission. As shown in FIG. 1, the DBR-LD 100 has an active region 101, a phase adjusting region 102, a distributed Bragg reflection There is a container region (DBR region) 103. Also, DB
In the element body of the R-LD 100, these active regions 10
1. Electrodes 105a, 105b, and 105c for separately applying current to the respective regions are provided corresponding to the phase adjustment region 102 and the DBR region 103.
The electrode 105a is for the active region, the electrode 105b is for the phase adjustment region, and the electrode 105c is for the DBR region.

The current source 200 is a current source for applying a constant active region injection current Ia to the active region 101, and is configured to apply the current to the active region 101 via the electrode 105a. The beam splitter 160 is a DBR-LD10
0 is arranged in the optical path of the output light (forward output light) LBf from the active region 101 side to branch a part of the output light LB to the wavelength reference device 110.
This is based on a half mirror or the like.

The wavelength reference unit 110 is for passing a component within a predetermined wavelength range of the split and provided light, and the wavelength detection unit 120 is provided with the wavelength reference unit 1.
It detects the wavelength of the light passing through 10, and outputs a signal corresponding to the detected wavelength.

The error signal detecting section 130 receives the output signal from the wavelength detecting section 120 and the wavelength switching signal, and outputs the output signal from the wavelength detecting section 120 with respect to the wavelength determined by the signal content of the wavelength switching signal. The rear light intensity detector 140 detects an error (wavelength difference) and outputs the error signal as an error signal. The rear light intensity detector 140 outputs a laser beam (rear output) emitted from an end of the element body of the DBR-LD 100 on the side of the DBR region 103. (Light) The light intensity of LBr is detected and a detection signal corresponding to the intensity is output.

The phase adjustment region injection current control unit 210
Controls the amount of current injected into the phase adjustment region 102 of the DBR-LD 100 in accordance with the error signal output from the error signal detector 130. The output current from the phase adjustment region injection current control unit 210 is
To the phase adjustment region 102 via the.

The DBR region injection current control section 212 responds to the wavelength switching signal by using the DBR region 1 of the DBR-LD 100.
The current controlled and output by the DBR region injection current control section 212 is supplied to the DBR region 10 via the electrode 105c.
3 is injected. Furthermore, the DBR region injection current control unit 212 receives a voltage corresponding to the intensity of the output light (rear output light LBr) from the DBR region 103 side of the DBR-LD 100 detected and output by the rear light intensity detection unit 140. Then, it has a function of judging whether or not the output voltage is within an allowable range, and, if the output voltage is out of the allowable range, correcting the injection current IDBR into the DBR region 103 in accordance with the degree of deviation.

The current source 200 is a DBR-LD 100
This is a current source for applying a constant active region injection current to the active region 101 of FIG. 1, and the current from the current source 200 is injected into the active region 101 via the electrode 105a.

Since the DBR-LD 100 used here has a plurality of electrodes as described above, the multi-electrode DBR-L
D, the multi-electrode DBR-LD 100
The Bragg wavelength is controlled by the injection current into the BR region 103, and single mode oscillation is performed at a longitudinal mode wavelength near the Bragg wavelength. Since this longitudinal mode wavelength is mainly controlled by the injection current into the phase adjustment region 102, this point is basically the same as in the prior art in that it is used for wavelength control, but in the present invention, DBR in addition to the conventional control method
-Detecting the rear output light of the LD 100 and determining whether the output voltage is within an allowable range according to the detection level of the light intensity, and if the output voltage is out of the allowable range, a DBR area corresponding to the degree of departure is determined. The basic feature of the present invention is that the injection current IDBR to 103 is corrected.

Next, the operation of the present apparatus having such a configuration will be described.

First, the active region 10 of the DBR-LD 100
1 is supplied with a constant active region injection current Ia from the current source 200. In addition, a wavelength switching signal corresponding to a wavelength to be oscillated is externally provided to the DBR region injection current control unit 212 and the error signal detection unit 130, so that the DBR region 103 is provided in the DBR region based on the given wavelength switching signal. The DBR region injection current IDBR is supplied from the current control unit 212.

As a result, the wavelength of the laser beam output from the DBR-LD 100 is set near the desired wavelength.

When a constant active region injection current Iact is supplied from the current source 200, the DBR-LD 100 enters a laser oscillation state, and laser light is emitted outward from the active region 101 side of the DBR-LD 100. (This is referred to as front output light LBf to distinguish it from output light (rear output light) from the DBR region 103 side in the DBR-LD 100).

A part of the output light (forward output light LBf) from the active region 101 side of the DBR-LD 100 is partly branched by a beam splitter 160 such as a half mirror and input to the wavelength reference device 110. Wavelength reference 1
In 10, light of a wavelength range component within a predetermined range is transmitted and input to the wavelength detection unit 120.

In the wavelength detector 120, the wavelength reference device 110
By detecting the wavelength of the light obtained from the
And outputs a detection signal corresponding to the detected wavelength. This detection signal is sent to the error signal detection unit 13.
0 is given.

The error signal detecting section 130 detects an error signal corresponding to the difference between the desired wavelength determined based on the wavelength switching signal and the detected wavelength, and outputs this error signal to the phase adjustment area injection current control section 210. I do.

Receiving the error signal, the phase adjustment region injection current control section 210 corrects the current value based on the error signal, and supplies the corrected current to the phase adjustment region 102 as the current Ipc. Thereby, the DBR-LD10
A wavelength of 0 is set for the wavelength switching signal.

On the other hand, the rear light intensity detector 140
The intensity of output light (rear output light LBr) from the DBR region 103 side of the R-LD 100 is detected, and a voltage corresponding to the detected light intensity is output to the DBR region injection current control unit 212.

The DBR region injection current control section 212 determines whether or not the output voltage from the rear light intensity detection section 140 is within a predetermined allowable range P, and determines only if the output voltage is out of the allowable range P. The correction is made to the injection current IDBR into the DBR region 103 according to the relationship described below so that the detection output voltage value of the rear light intensity detection unit 140 indicates a value within the allowable range P.

FIG. 2 shows an injection current I to the DBR region 103.
The output voltage from the rear light intensity detection unit 140 with respect to DBR is shown. Note that white circles in the figure indicate the characteristics when the current is increased, and Δ indicates the characteristics when the current is decreased.
In FIG. 2, (a) is a characteristic diagram showing the relationship between the DBR region injection current and the output wavelength, and (b) is a characteristic diagram showing the relationship between the DBR region injection current and the output of the backward light intensity detector. In the DBR region injection current-output wavelength characteristic diagram of FIG. 2A, Ais indicated with an upward arrow and a downward arrow
Is the unstable region where mode jump with hysteresis characteristics is unavoidable.In this period, even if the injection current value is the same, the wavelength of the oscillating laser light may be completely different depending on the setting method. You can see that there is.

The unstable area Ais is shown in FIG.
In the relationship between the injection current of the DBR region and the output characteristic of the rear light intensity detector, the relationship between the output Vup from the rear light intensity detector and Vlo
w is outside the unstable region Ais,
Therefore, the output of the backward light intensity detector 140 changes from Vup to Vlow.
Within this range, it can be confirmed that there is no danger of unstable operation.

Thus, from FIG. 2, the rear light intensity detector 1
It can be seen from the output of 40 that the hysteresis area can be determined. Therefore, the output voltage from the rear light intensity detection unit 140 is, for example, from the rear light intensity detection unit output Vup to V shown in FIG.
The range of low, that is, the allowable range P, is "the output voltage value detected by the rear light intensity detection unit 140 is equal to the allowable range P.
By controlling the injection current into the DBR region 103 as shown in the figure, the hysteresis region can be avoided and stable wavelength control can be realized.

FIG. 2 shows that as the injection current IDBR into the DBR region 103 increases, the rear light intensity detector 14
It can be seen that the output voltage from 0 has decreased. This is because the loss in the DBR region 103 has increased due to the increase in the injection current IDBR into the DBR region 103.

Therefore, a curve Vf obtained by interpolating the output voltage value from the rear light intensity detection unit 140 immediately after the mode jump when the injection current IDBR is decreased with respect to the injection current IDBR into the DBR region 103 is obtained. The upper limit value Vup and the lower limit value Vlow of the range P are set as follows.

Vup = 0.8Vf, Vlow = 0.35V
f By setting the allowable range P in accordance with the value of the current injected into the DBR region 103 as described above, loss fluctuation in the DBR region 103 can be compensated, and stable wavelength control over a wider wavelength range can be performed.

In the present embodiment, the wavelength control is performed by inputting the wavelength switching signal to the error signal detecting section 130. However, the wavelength switching signal is input to the wavelength reference device 110 to change the reference wavelength. May be.

As described above, according to the present invention, when a multi-electrode DBR-LD is used to control the wavelength of laser light generated by varying the injection current value in the phase adjustment region and the DBR region to a desired wavelength, A rear light detecting means for detecting a rear light of the DBR-LD and outputting a voltage signal corresponding to a detection level is provided, and an allowable range P is set according to a current value injected into a DBR region, and the rear light intensity detecting means is provided. Is set to a value within the allowable range P,
By controlling the injection current into the BR region, D
The operation in the hysteresis region where the BR-LD becomes unstable can be avoided, and stable wavelength control can be realized.

In this embodiment, the rear output light of the DBR-LD is detected in order to avoid the operation in the hysteresis region where the DBR-LD becomes unstable, but this detection is performed by the rear light intensity detecting means. The rear output light LBr is directly detected.

However, since the bandgap wavelengths in the phase adjustment region 102 and the DBR region 103 of the DBR-LD 100 are active regions, when the injection current IDBR into these regions increases, oscillation occurs near the bandgap wavelength. become. The light generated by this oscillation becomes the background light with respect to the light in the wavelength band of 1.5 μm, and deteriorates the detection sensitivity of the rear light intensity detection unit 140. This leaves a fear that the operation in the hysteresis region where the DBR-LD becomes unstable may be caused again.

Therefore, it is necessary to take countermeasures.

An example will be described next as a second embodiment.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention.
1 shows a wavelength control circuit according to the embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, in order to remove background light, a DBR that transmits only signal light in a wavelength band of 1.5 μm is used.
-An optical filter 115 is provided between the DBR region 103 side of the LD 100 and the rear light intensity detector 140.

In optical communication using the high-density wavelength division multiplexing transmission system, a wavelength in the 1.5 μm band is normally used. Therefore, an optical filter that transmits only the signal light in the wavelength band of 1.5 μm is used as the optical filter 115. Then, the output light (rear output light) LBr from the DBR region 103 side of the DBR-LD 100 is input to the rear light intensity detector 140 via the optical filter 115 that transmits only signal light in the 1.5 μm band. That is, the rear light intensity detector 140 receives only the signal light in the 1.5 μm wavelength band from the rear output light LBr output from the DBR-LD 100 and generates a voltage signal corresponding to the intensity.

Normally, the phase adjustment region 102 and the DBR region 103 in the DBR-LD 100 have a wavelength of 1.5 μm.
The band gap is set so as not to absorb light in the m band. For this reason, these regions are regarded as passive regions for light in the wavelength band of 1.5 μm.

However, since the bandgap wavelength in the phase adjustment region 102 and the DBR region 103 is an active region, the injection current IP into these regions is
As C and IDBR increase, oscillation occurs near the bandgap wavelength. The light generated by this oscillation becomes the background light with respect to the light in the wavelength band of 1.5 μm, and deteriorates the detection sensitivity of the rear light intensity detection unit 140.

Therefore, as in this embodiment, the wavelength 1.
By using the optical filter 115 that transmits only the signal light in the 5 μm band, even if the injection currents IPC and IDBR to the phase adjustment region 102 and the DBR region 103 increase, stable control without deterioration in detection sensitivity becomes possible. .

Further, by arranging the optical filter 115 at an angle to the rear output light, it is possible to prevent the reflected light from the optical filter 115 from returning to the DBR-LD 100, thereby enabling stable wavelength control. .

Note that, also in the present embodiment, the rear light intensity detector 140
By setting the allowable range for the output voltage from
Loss fluctuations in the BR region can be compensated, and stable wavelength control can be performed over a wider wavelength range.

Next, a third embodiment will be described.

(Third Embodiment) FIG. 4 shows a wavelength control circuit according to a third embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
In the third embodiment, a forward light intensity detection unit 141 and a computing unit 1 are added to the configuration of the first embodiment shown in FIG.
50, a configuration in which a second beam splitter 161 is provided.

The second beam splitter 161 has a DBR-
Output light on the active region 101 side of the LD 100 (forward output light L
Bf) branches off a part of it and is constituted by a half mirror or the like. The forward light intensity detecting section 141 detects the light intensity of the forward output light split by the second beam splitter 161 and converts it into a voltage signal corresponding to the intensity, and outputs the voltage signal. Intensity detector 14
1 and the output voltage signal of the rear light intensity detection unit 140 as inputs, and the arithmetic unit 150 calculates the output voltage from the rear light intensity detection unit 140 as the output voltage from the front light detection unit 141. The division is performed, and the result is output to the DBR region injection current control unit 212.

In the DBR region injection current control section 212, the output signal from the arithmetic section 150 is set to the allowable range P described in FIG.
Is determined, and if it is out of the allowable range P, the same correction as described in the first embodiment is applied to the injection current IDBR into the DBR region 103.

In such a configuration, the DBR-LD1
A part of the output light of the active region 101 side is split by the second beam splitter 161 and input to the front light intensity detector 141. In the forward light intensity detector 141, the DBR-LD
The output light intensity on the active region 101 side of 100 is detected, and a voltage corresponding to the detected light intensity is output to the arithmetic unit 150.
The arithmetic unit 150 divides the output voltage from the rear light intensity detection unit 140 by the output voltage from the front light detection unit 141, and outputs the result to the DBR region injection current control unit 212.

In the DBR region injection current control unit 212, the output signal from the arithmetic unit 150 is set to the allowable range P described in FIG.
Is determined, and if it is out of the allowable range P, the same correction as described in the first embodiment is added to the injection current IDBR into the DBR region 103.

When the loss inside the laser element increases due to the deterioration of the DBR-LD element or the like, the forward output light intensity decreases as does the rear output light LBr intensity. Therefore, as in the present embodiment, by dividing the output light intensity from the DBR region 103 by the output light intensity from the active region 101 side, the voltage fluctuation from the rear light intensity detection unit 140 due to an increase in the loss inside the laser is reduced. , Can be offset by voltage fluctuations from the front light intensity detection unit 141.

Therefore, since the output from the arithmetic unit 150 always indicates the degree of coincidence between the Bragg wavelength and the longitudinal mode wavelength, stable wavelength control can be realized.

In wavelength multiplex transmission, the transmission light intensity may be adjusted in accordance with the wavelength for reasons such as compensating for the wavelength dependence of the optical fiber amplifier.

In this case, the light intensities of the rear output light LBr and the front output light LBf vary depending on the wavelength. Therefore, by configuring as in the present embodiment, the rear light intensity detecting unit 1 generated by adjusting the transmission light intensity according to the wavelength.
Voltage fluctuation from 40 is compensated, and stable wavelength control can be realized.

In the present embodiment, the output light from the active region 101 side is further branched to separate the forward light intensity detector 141
However, the DC component of the light intensity transmitted through the wavelength reference device may be used as the forward output light intensity.

Also in the present embodiment, by setting the allowable range for the output signal from the arithmetic unit 150 in accordance with the value of the current injected into the DBR region 103, the DBR region 1
03 can be compensated for, and stable wavelength control can be performed over a wider wavelength range.

Further, the injection current into the active region 101 may be controlled so that the output voltage from the front light intensity detecting section 141 becomes constant.

Next, a fourth embodiment will be described.

(Fourth Embodiment) FIG. 5 shows a fourth embodiment of the present invention.
1 shows a wavelength control circuit according to the embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. Also, in FIG. 5, the rear light intensity detection unit 140,
Although the calculation unit 150 and the like are omitted, the object is shown in FIGS.
It can be applied to any of the configurations shown in FIG.

In this embodiment, a current limiter 220 is newly provided as shown in FIG. 5, and the output of the phase adjustment region injection current control section 210 is controlled by the current limiter 22.
It is characterized in that it is provided to the phase adjustment region 103 of the DBR-LD 100 via the “0”. Then, in the current limiter 220, the injection current I
It is set so that a lower limit value Ilow and an upper limit value Iup are given to pc.

In such a configuration, the output current from phase adjustment region injection current control section 210 is equal to current limiter 2
It is provided to the phase adjustment area 102 via 20. In the current limiter 220, the injection current Ipc into the phase adjustment region 102
Is given a lower limit Ilow and an upper limit Iup.

FIG. 6 shows the wavelength characteristics with respect to the current injected into the phase adjustment region 102. As the injection current IPC to the phase adjustment region 102 is changed, it can be seen that the same wavelength periodically appears for the injection current. Then, the lower limit Ilow and the upper limit Iup of the current limiter 220
Is set so as to cover an appropriate range of one cycle of mode jump as shown in FIG. 6, for example.

Therefore, by doing so, the phase adjustment region 1
The injection current Ipc to 02 is covered for an appropriate range of one cycle of mode jump, and the injection current Ipc having a value outside the range is not given. Therefore, it is not necessary for the phase adjustment region injection current control unit 210 to have a configuration capable of outputting an injection current value that greatly exceeds this cover range. Thus, low power consumption can be achieved.

As described above, according to the present embodiment, the current limiter 220 is provided to set the upper limit value and the lower limit value for the injection current Ipc to the phase adjustment region 102, thereby controlling the control circuit system of the DBR-LD 100. Power consumption, and excessively high-precision current control becomes unnecessary, so that the cost can be reduced.

Next, the power consumption of the control circuit system in the DBR-LD device is reduced, and the cost can be reduced. In addition, the shift of the Bragg wavelength due to the deterioration of the DBR-LD and the like can be achieved. A fifth embodiment will be described as an example in which high performance can always be maintained by coping with a change in the wavelength stabilization characteristic.

(Fifth Embodiment) FIG. 7 shows a wavelength control circuit according to a fifth embodiment of the present invention. The same parts as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted.
In the example shown here, a signal corresponding to its own output current (phase adjustment region injection current) is replaced by the DBR region injection current control unit 21 instead of the phase adjustment region injection current control unit 210 in FIG.
4 and a phase adjustment region injection current control unit 211 having a function of outputting to the DBR region injection current control unit 211. Region injection current control unit 21
It is determined whether or not the output current from 1 is between the upper limit value and the lower limit value of the current limiter 220, and the injection current IDBR to the DBR region 103 is reduced or increased with required characteristics according to the determination result. It is characterized in that a DBR region injection current control unit 214 having a function of controlling as much as possible is used.

The phase adjustment area injection current control section 211 outputs a current (phase adjustment area injection current) to the current limiter 220 based on the output signal from the error signal detection section 130, and outputs an output current (phase adjustment area injection current). Is output to the DBR region injection current control unit 214. Further, the DBR region injection current control unit 214
Then, based on the output signal from the phase adjustment region injection current control unit 211, it is determined whether or not the output current from the phase adjustment region injection current control unit 211 is between the upper limit and the lower limit of the current limiter 220. As a result of the determination, if the upper limit value is exceeded, if the oscillation wavelength of the DBR-LD 100 is on the shorter wavelength side than the desired wavelength that is the set reference, the injection current IDBR into the DBR region 103 is determined. , The Bragg wavelength is shifted to the longer wavelength side, and when the Bragg wavelength is lower than the lower limit value, the reverse is true.
A function is provided to increase the injection current IDBR to the OLED 03 to shift the Bragg wavelength to the shorter wavelength side.

In such a configuration, the phase adjustment region injection current control unit 211 outputs a current to the current limiter 220 based on the output signal from the error signal detection unit 130, and outputs a signal corresponding to the output current to the DBR region. Output to the injection current control unit 213. DBR region injection current control unit 2
In 14, it is determined whether or not the output current from the phase adjustment region injection current control unit 211 is between the upper limit value and the lower limit value of the current limiter 220 based on the output signal from the phase adjustment region injection current control unit 211. .

If the value exceeds the upper limit, D
Since the oscillation wavelength of the BR-LD 100 is on the shorter wavelength side than the desired wavelength which is the set comparison reference, the DBR region 1
03, and the Bragg wavelength is shifted to the longer wavelength side.

On the other hand, when the value is lower than the lower limit value, the current reverse to the DBR region 103 is increased, and the Bragg wavelength is shifted to the shorter wavelength side.

As described above, according to the present embodiment, even if the Bragg wavelength shifts due to the deterioration of the DBR-LD 100 due to aging, the desired wavelength cannot be supplemented by the phase adjustment region 102 alone, the injection into the DBR region 103 is performed. By performing control including the electric current, it is possible to reliably stabilize the wavelength at a desired value.

Therefore, according to this embodiment, it is possible to cope with a change in the wavelength stabilization characteristic due to the shift of the Bragg wavelength due to the degradation of the DBR-LD, as well as energy saving. Can be maintained at all times.

Although various specific examples have been described above, the present invention is not limited to only the above-described embodiments, and can be appropriately modified and implemented without departing from the scope of the invention.

[0096]

As described above, according to the present invention,
Detects the light intensity of the rear output light from the distributed Bragg reflection type semiconductor laser device, and can judge the stability of the oscillation state based on the detected light intensity, so that unstable regions due to hysteresis can be avoided and stable at any wavelength. Wavelength control becomes possible.

Further, by providing an upper limit value and a lower limit value for the injection current into the phase adjustment region, the power consumption of the wavelength control circuit can be reduced, and the current control with excessively high accuracy is not required, so that the cost is reduced. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the present invention, and is a block diagram showing a configuration of a tunable semiconductor laser device according to a first embodiment of the present invention including a wavelength control system.

FIG. 2 is a diagram for explaining the present invention, showing a relationship between an output from a rear light intensity detector in a variable wavelength semiconductor laser device of the present invention, a DBR region injection current, and a wavelength of output laser light.

FIG. 3 is a diagram for explaining the present invention, and is a block diagram showing a configuration of a tunable semiconductor laser device according to a second embodiment of the present invention including a wavelength control system.

FIG. 4 is a diagram for explaining the present invention, and is a block diagram showing a configuration of a tunable semiconductor laser device according to a third embodiment of the present invention including a wavelength control system.

FIG. 5 is a diagram for explaining the present invention, and is a block diagram illustrating a configuration of a tunable semiconductor laser device according to a fourth embodiment of the present invention including a wavelength control system.

FIG. 6 is a diagram for explaining the present invention, showing a wavelength characteristic with respect to an injection current to a phase adjustment region in the device of the present invention.

FIG. 7 is a diagram for explaining the present invention, and is a block diagram showing a configuration of a tunable semiconductor laser device according to a fifth embodiment of the present invention including a wavelength control system.

FIG. 8 is a diagram showing a configuration of a conventional wavelength control circuit.

[Explanation of symbols]

100: Multi-electrode distributed Bragg reflection type semiconductor laser (BD
R-LD) 101 Active region 102 Phase adjustment region 103 Distributed Bragg reflector region (BDR region) 105a Active region electrode 105b Phase adjustment region electrode 105c BDR region electrode 110 Wavelength reference Device 115 Optical filter 120 Wavelength detector 130 Error signal detector 140 Rear light intensity detector 141 Front light intensity detector 150 Arithmetic unit 160 Beam splitter 200 Current source 210, 211 Phase injection region injection Current control units 212, 213, 214 ... DBR region injection current control unit 220 ... current limiter LDf ... front output light emitted from BDR-LD LDr ... rear output light emitted from BDR-LD.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-291403 (JP, A) JP-A-8-56030 (JP, A) JP-A-8-190111 (JP, A) IEEE Proceedings-J, vol. 138, no. 2 (1991) pp. 171-177, "Wallength possible DFB and DBR laser for coherent optical fiber communications" (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S5 / 062, H01S 5/125

Claims (6)

(57) [Claims] 1. A multi-electrode semiconductor laser device having an active region, a phase adjustment region and a distributed Bragg reflector region, wavelength discriminating means for discriminating a wavelength of output light forward from the semiconductor laser device, and a switching instruction to a desired wavelength. Error detection means for detecting a wavelength error with respect to the desired wavelength from a desired wavelength determined by a wavelength switching signal for performing the operation and a wavelength based on the output of the wavelength discriminating means; and first control means for controlling the current injected into the phase control region, and a second control means that controls the injection current of on the basis of the wavelength switching signal to said Bragg reflector region, the rear of the semiconductor laser element First intensity detecting means for detecting the intensity of the output light, wherein the first intensity detecting means comprises:
And the Bragg reflector area
The first after the mode jump when the injection current to the
When the output from the intensity detection means is Vf,
Control means outputs from the previous SL first intensity detecting means is zero.
The distribution is set so as to be in the range of 35 Vf to 0.8 Vf.
A tunable semiconductor laser device for controlling an injection current to a Bragg reflector region . 2. The tunable wavelength semiconductor laser device according to claim 1, wherein said first intensity detecting means includes an optical filter that transmits only the 1.5 μm band. 3. The tunable semiconductor laser device according to claim 2, wherein said optical filter is arranged at an angle that is not perpendicular to transmitted light. A second intensity detecting means for detecting the intensity of the forward output light of the semiconductor laser element, and a specific intensity based on an output of the first intensity detecting means and an output of the second intensity detecting means. Computing means for performing computation, wherein the second control means controls an injection current into the distributed Bragg reflector region such that an output from the computing means falls within a preset allowable range. 4. The tunable semiconductor laser device according to claim 1, wherein: 5. A multi-electrode semiconductor laser device having an active region, a phase adjustment region, and a distributed Bragg reflector region, wavelength discriminating means for discriminating a wavelength of output light from the semiconductor laser device, and instructing switching to a desired wavelength. Error detection means for detecting a wavelength error with respect to the desired wavelength from a desired wavelength determined by a wavelength switching signal and a wavelength based on the output of the wavelength discrimination means, and the phase based on an output from the error detection means. A third control unit for controlling an injection current to the adjustment region; and a fourth control unit for controlling an injection current to the distributed Bragg reflector region, wherein the third control unit controls the phase. A tunable wavelength semiconductor laser device having a current limiter for providing an upper limit and a lower limit of an injection current to an adjustment region. 6. The fourth control means monitors an injection current to the phase adjustment area, and when the injection current to the phase adjustment area falls below a lower limit, the fourth control means controls the injection current to the distributed Bragg reflector area. 6. The tunable wavelength semiconductor according to claim 5, wherein the injection current is decreased, and when the injection current to the phase adjustment region becomes larger than an upper limit value, the injection current to the distributed Bragg reflector region is increased. Laser device.