JP2002016317A - Semiconductor laser light source and measuring apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a semiconductor light source in which influence of mode jump is prevented by simple constitution, and a measuring apparatus using the light source. SOLUTION: In this invention, a semiconductor laser light source for obtaining optical output from a semiconductor laser is improved. This equipment has a control part which detects, on the basis of optical output of the semiconductor laser, that a mode jump current value has entered a prescribed current range, and executes at least one from among alarm output and change of value of a driving current in the semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser light source for outputting light with a semiconductor laser, and more particularly to a semiconductor laser light source having a simple structure for preventing the influence of a mode jump and a measuring instrument using the same. is there.

[0002]

2. Description of the Related Art A semiconductor laser oscillating in a single mode (single wavelength) has a mode jump in which the oscillation wavelength changes discontinuously. For example, a DBR oscillating in a single mode
(Distributed Bragg reflection)
FIG. 7 shows the drive current versus light output characteristics of the semiconductor laser. The oscillation wavelength changes discontinuously before and after the mode jump current values Ik1 and Ik2 shown in FIG. When a DBR semiconductor laser having such characteristics is used for a measuring instrument, Iop, which is an intermediate point between the mode jump current values Ik1 and Ik2, is set as a drive current while avoiding the mode jump current values Ik1 and Ik2.

Generally, mode jump current values Ik1, Ik
Since k2 drifts with time, the oscillation wavelength changes discontinuously when the mode jump current value has drifted to the drive current value Iop, which may cause a problem in measurement. In order to avoid this, feedback control is performed such that the drive current value Iop is always substantially at the center of the mode jump current values Ik1 and Ik2. Such devices are, for example, "Wavelength stabilisation of a three-elect
rode distributed Bragg reflector laser withlongitu
dinal mode control ", ELECTRONICS LETTERS 13th March
1997 Vol.33 No.6 pp.494-495. Hereinafter, this will be described with reference to FIG.

[0004] In FIG. 8, a DBR semiconductor laser 1 comprises:
It comprises an active region 11, a phase adjustment region 12, and a DBR region 13.

The active region 11 generates a laser beam when a current is injected. The phase adjustment area 12 is a pn
By flowing a current perpendicular to the junction or flowing a current through the thin film heater, the refractive index of the waveguide is changed, the phase of laser light in the semiconductor laser is adjusted, and the oscillation wavelength is changed. The DBR region 13 receives a laser beam from the active region 11 through the phase adjustment region 12 and causes a current to flow perpendicular to the pn junction or a current to the thin-film heater to reduce the refractive index of the waveguide. The oscillation wavelength is changed by adjusting the reflection characteristics of the diffraction grating.

The current sources I1 to I3 are respectively connected to the active region 1
1. Apply current to the phase adjustment region 12 and the DBR region 13,
Control of each area is performed.

The optical coupler OC1 branches the output of the DBR semiconductor laser 1 to optical fibers 102 and 103 via the optical fiber 101. The optical coupler OC2 converts the light from the optical fiber 103 into the optical fibers 104 and 10.
Branch to 5.

[0008] The photodiode PD 1 receives light from the optical fiber 104. Oscillator OSC is 10KH
The sine wave current of z is output and given to the DBR region 13. The lock-in amplifier A1 receives the output of the photodiode PD1 and the output of the oscillator OSC, and supplies a current to the phase adjustment region 12.

The filter F is a filter having two different center wavelengths, and receives light from the optical fiber 105,
The light passing through the respective filters is output to the photodiodes PD2 and PD3. The differential amplifier A2 inputs the output of the photodiode PD2 to an inverting input terminal, inputs the output of the photodiode PD3 to a non-inverting input terminal,
The output is connected to the BR area 13.

The operation of such a device will be described below.
Current is supplied to the active region 11, the phase adjustment region 12, and the DBR region 13 by the current sources I1 to I3. This gives D
The BR semiconductor laser 1 outputs light to the optical fiber 101. This optical output is based on the optical coupler OC1, optical fiber 1
03, input to the filter F via the optical coupler OC2 and the optical fiber 105. Then, light passes through the filter F at two different center wavelengths, and is detected by the photodiodes PD2 and PD3, respectively. The difference between the outputs of the photodiodes PD2 and PD3 is determined by the differential amplifier A
In step 2, the data is output to the DBR area 13. Since the output of the differential amplifier A2 indicates a deviation from the wavelength at which the outputs of the two filters become the same, the wavelength of the optical output of the DBR semiconductor laser 1 is adjusted to the center of two different center wavelengths of the filter F. .

Then, the oscillator OSC oscillates and gives a current to the DBR region 13. Thereby, the optical output of the DBR semiconductor laser 1 is modulated. This optical output is input to the photodiode PD1 via the optical fiber 101, the optical coupler OC1, the optical fiber 103, the optical coupler OC2, and the optical fiber 104. Photodiode PD
The light output is converted into a current at 1 and input to the lock-in amplifier A1. Then, the lock-in amplifier A1 performs synchronous detection of the output of the photodiode PD1 based on the signal of the oscillator OSC, and outputs the output to the phase adjustment region 12. D
Since the optical output of the BR semiconductor laser 1 becomes maximum when the operating point is substantially at the center of the mode jump current value, the output of the lock-in amplifier A1 indicates a deviation from the center of the mode jump current value. As a result, the operating point is controlled at the center of the mode jump current value.

[0012]

In such a device,
In order to prevent the influence of the mode jump, a wavelength reference using a feedback control system and a filter F is required, and thus the configuration is complicated.

Accordingly, an object of the present invention is to provide a simple configuration,
An object of the present invention is to realize a semiconductor laser light source that prevents the influence of a mode jump and a measuring device using the same.

[0014]

According to the present invention, there is provided a semiconductor laser light source for outputting light with a semiconductor laser, wherein a mode jump current value falls within a predetermined current range based on the light output of the semiconductor laser. A control unit for detecting and performing at least one of an alarm output and a change of a drive current value of the semiconductor laser is provided.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention. Here, the same DBR semiconductor laser 1 as in FIG.
Are denoted by the same reference numerals and description thereof is omitted.

In FIG. 1, a half mirror 2 has a DBR
Transmits and reflects the output light of the semiconductor laser 1. The light receiving circuit (photodiode) 3 receives the reflected light from the half mirror 2 and converts it into an electric signal. The signal processing circuit 4 inputs the electric signal of the light receiving circuit 3 and converts it into a digital signal.
The memory (storage unit) 5 stores a current value used in the active region of the DBR semiconductor laser 1 and a warning current value. The control unit 6
The operating current value of the memory 5 is output as a driving current value, and at the same time, the driving current value is changed to determine the amount of increase in optical output. Stop output or device. The drive circuit 7 receives the current value of the control unit 6 and
A current is applied to the semiconductor laser 1. Here, the current to the phase adjustment region and the DBR region is provided from the drive circuit 7, but the current value is constant, and the description thereof will be omitted.

The operation of such a device is described below.
FIG. 2 is a diagram for explaining the operation of the device shown in FIG. 1, and shows the drive current versus optical output and oscillation wavelength characteristics of the DBR semiconductor laser 1. (A) shows the initial state, and (b) shows the state after the mode jump current value has drifted low. Here, the memory 5 stores the used current value I3, the warning current values I1, I2, I
4, I5 are stored.

As shown in FIG. 2A, the optical power increases with the current, but the optical power changes discontinuously before and after the mode jump current value. This is shown as a characteristic as shown in FIG. In FIG. 3, a is the optical power, and b is the amount of increase in the optical power at every 0.1 mA obtained from the optical power characteristics. As is clear from FIG. 3, except for the mode jump current value, the optical output increase amount is about 0.05 mW, but the mode jump current value is about 0.4 mW, which is about one digit larger. Therefore, the amount of increase in the optical power for each constant current is measured, and if this increase is larger than a predetermined value, it is understood that the increase is the mode jump current value.

First, the control unit 6 drives the DBR semiconductor laser 1 with a drive current I3 to the drive circuit 7. Then, after a lapse of a predetermined time (a time when the drift amount is not large), the control unit 6 changes the drive current every 0.1 mA, and drives the drive circuit 7 to drive the DBR semiconductor laser 1. The output light of the DBR semiconductor laser 1 is transmitted through a half mirror 2 to a light receiving circuit 3.
Is input to The output light is converted into an electric signal by the light receiving circuit 3 and is converted into a digital signal by the signal processing circuit 4.

As a result, as shown in FIG. 3B, the control unit 6 obtains the optical power increase amount every 0.1 mA. Then, the control unit 6 obtains a current value (mode jump current value) where the optical power increase amount is 0.3 mW or more, and obtains a portion of the warning current value. Between I1 and I2, or I
When the mode jump current value enters between 4 and I5,
The control unit 6 outputs an alarm. When a mode jump current value enters between I2 and I3 or between I3 and I4, the control unit 6 outputs an alarm and stops the drive circuit 7.

For example, as shown in FIG. 2B, when the drift occurs, the amount of increase in the optical power between I4 and I5 is 0.
It becomes 3 mW or more, and an alarm is output.

As described above, the control unit 6 sets the
Obtain the optical power increment for every 0.1 mA,
The mode jump current value is obtained, and an alarm is output depending on the position. This alarm causes the DBR
The operating conditions of the semiconductor laser 1 can be changed or stopped, or the operating conditions can be changed at the next maintenance. That is, with a simple configuration, it is possible to prevent the influence of the mode jump.

Next, another embodiment, an embodiment using a length measuring device (measuring device) will be described with reference to FIG. Here, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

In FIG. 4, the half mirror 21 has a DB
The output light from the R semiconductor laser 1 enters and is split into signal light and reference light. The fixed mirror 22 reflects the reference light from the half mirror 21 to the half mirror 21. The movable mirror 23 is attached to an object to be measured (not shown) that moves, and transfers the signal light from the half mirror 21 to the half mirror 2.
Reflects to 1.

The light receiving circuit 31 receives the interference light from the half mirror 21, converts the light into an electric signal, and inputs the electric signal to the signal processing circuit 4. The memory (storage unit) 51 includes an initial current value Iop1, an alarm current value I1,
I2, wavelength λ at use current Iop1, warning current I1, I
The two wavelengths λ1 and λ2 are stored. The control unit 61 is connected to the signal processing circuit 4 and the memory 51, and controls the DBR semiconductor laser 1
Is driven by the drive circuit 7 to determine the change in the wavelength of the DBR semiconductor laser 1 from the digital signal of the signal processing circuit 4 and detect that the mode jump current value falls within the predetermined current range (within the warning current range). , The use current Iop and the warning current values I1 and I2 of the DBR semiconductor laser 1 are changed.

The operation of such a device will be described below.
FIG. 5 is a flowchart showing the operation of the device shown in FIG. FIG. 6 is a diagram for explaining the operation of the device shown in FIG. 4, and shows the drive current versus optical power and oscillation wavelength characteristics of the DBR semiconductor laser 1, as in FIG. (A) is an initial state,
(B) shows the state after drift. Here, FIG.
For example, as shown in FIG.
0 mA, and the wavelength jump is 0.1 nm. Therefore, the warning current is set to I1 = Iop-5 mA and I2 = Iop + 5 mA.

As shown in FIG. 6A, the oscillation wavelength gradually increases with the current, and discontinuously decreases with the mode jump current value. By utilizing this, the position of the mode jump current value can be detected.

The control section 61 supplies a drive current to the drive circuit 7 as I
op (initially Iop1 of the memory 51)
The semiconductor laser 1 is driven. Output light from the DBR semiconductor laser 1 is divided into signal light and reference light by transmission and reflection at the half mirror 21. The reference light is fixed mirror 2
2 and is returned to the half mirror 21. The signal light is reflected by the moving mirror 23 and returned to the half mirror 21. Then, the half mirror 21 and the fixed mirror 22
The reference light reflected by the light beam and the signal light reflected by the moving mirror 23 interfere with each other, and the interference light is output. The interference light is input to the light receiving circuit 31 and is converted into an electric signal. The electric signal is converted into a digital signal by the signal processing circuit 4 and output to the control unit 61. The controller 61 obtains the moving distance of the moving mirror 23 from the digital signal and the wavelength λ (S1, S2).

Fixed time (time when the drift amount is not large)
After the elapse, the mode jump current value is detected in the following procedure. The control unit 61 drives the DBR semiconductor laser 1 with the drive circuit 7 at the warning current value I1 of the memory 51. The movable mirror 23 is moved manually or automatically by a predetermined distance. Output light from the DBR semiconductor laser 1 is divided into signal light and reference light by transmission and reflection at the half mirror 21. The reference light is reflected by the fixed mirror 22 and returned to the half mirror 21. The signal light is reflected by the moving mirror 23 and returned to the half mirror 21. Then, the reference light reflected by the fixed mirror 22 and the signal light reflected by the movable mirror 23 interfere with each other on the half mirror 21, and the interference light is output. The interference light is input to the light receiving circuit 31 and is converted into an electric signal. The electric signal is converted into a digital signal by the signal processing circuit 4 and output to the control unit 61. The control unit 61 determines the wavelength λ′1 of the warning current value I1 from the digital signal and the predetermined distance.
Ask for. Similarly, the wavelength λ′2 at the warning current I2 is obtained (S2, S3).

Then, the control unit 61 stores the λ
1, λ2 and the measured λ′1, λ′2, Δλ1 =
λ′1−λ1, Δλ2 = λ′2−λ2, and λ1 =
λ′1, λ2 = λ′2 (S4).

| Δλ1 |, | Δλ2 | <0.05 nm
In the case of (FIG. 6A), since the wavelength change is continuously changing, the control unit 61 gives the same drive current value Iop to the drive circuit 7 again to drive the DBR semiconductor laser 1 again. It drives and measures (S1).

| Δλ1 |, | Δλ2 | <0.05 nm
If not (FIG. 6B), the wavelength change is discontinuously changing, so the control unit 61 changes to Iop2 when the used current value Iop1 is Iop1, and changes the used current value Iop to Iop2.
Is Iop2, it is changed to Iop1 (S5). In addition, Iop2 is Iop1 + 15 mA. Due to the change, the warning current value becomes I1 = Iop-5 mA, I2 = Io
Let p + 5 mA. Then, the control unit 61 measures a predetermined distance with the used current value Iop and the warning current values I1 and I2,
Each new wavelength λ, λ1, λ2 is obtained (S
6). Then, again, the control unit 61 supplies a drive current to the drive circuit 7 with Iop, drives the DBR semiconductor laser 1, and
The measurement is performed (S1).

As described above, the control unit 61 measures the predetermined moving distance at predetermined time intervals using the warning current values I1 and I2 as the drive current of the DBR semiconductor laser 1, obtains the wavelength change, and sets the wavelength change within the predetermined range. Since the input of the mode jump current value is detected and the current value Iop used for measurement is changed, the influence of the mode jump and a large error in the measured value can be prevented with a simple configuration.

The present invention is not limited to this, but may be as follows. The device shown in FIG.
Although an example of the alarm output has been described, a configuration may be used in which the current used by the DBR semiconductor laser 1 is changed as in the device shown in FIG. Conversely, the device shown in FIG. 4 may be configured to output an alarm like the device shown in FIG.

In FIG. 1, the configuration in which the optical output is divided by the half mirror 2 is shown. However, as shown in FIG. 8, the optical output may be divided by an optical fiber and an optical coupler. The drive circuit 7 may be included in the control unit 6, or the warning current value may be obtained from the used current value instead of being stored in the memory 5.

Further, the DBR semiconductor laser 1 may be a semiconductor laser that oscillates in a single mode.

In addition, FIG. 1 shows a configuration in which the position of the mode jump current is obtained from the amount of increase in the optical output. However, the optical powers P1 and P5 of the warning current values I1 and I5 are stored in the memory 5 for a certain period of time. Later, at the warning current values I1 and I5,
The DBR semiconductor laser 1 is driven, and the optical power P1'P5 '
Ask for. This optical power difference P'1-P1, P'5-P
5, the position of the mode jump current is I1
To I5, and an alarm may be output.

[0038]

According to the present invention, the following effects can be obtained. According to the first aspect, based on the optical output of the semiconductor laser, the control unit detects that the mode jump current value has entered a predetermined current range, and changes the alarm output or the operating current of the semiconductor laser. Therefore, the effect of the mode jump can be prevented with a simple configuration.

According to the second aspect, the control unit changes the drive current of the semiconductor laser to obtain the amount of increase in the optical power, thereby detecting that the mode jump current value falls within the predetermined current range. Since the alarm output or the current used by the semiconductor laser is changed, the influence of the mode jump can be prevented with a simple configuration.

According to the third aspect, the control unit drives the semiconductor laser, obtains a change in the wavelength of the semiconductor laser, detects that a mode jump current value has entered a predetermined current range, and outputs an alarm output or a semiconductor output. Since the current used by the laser is changed, the influence of the mode jump can be prevented with a simple configuration.

According to the fourth aspect, a large error in the measured value can be prevented by changing the alarm output and the current used.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the device shown in FIG.

FIG. 3 is a diagram showing a relationship between optical power characteristics and optical power increase.

FIG. 4 is a configuration diagram showing another embodiment of the present invention.

5 is a flowchart showing the operation of the device shown in FIG.

FIG. 6 is a view for explaining the operation of the apparatus shown in FIG. 4;

FIG. 7 is a diagram showing a drive current versus optical power characteristic of a DBR semiconductor laser.

FIG. 8 is a diagram showing a configuration of a conventional semiconductor laser light source.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DBR semiconductor laser 3, 31 Light receiving circuit 4 Signal processing circuit 6, 61 Control part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Inoue 2-9-132 Nakamachi, Musashino-shi, Tokyo Inside Yokogawa Electric Corporation (72) Inventor Machiko Dobashi 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Corporation (72) Inventor Mamoru Hihara 2-9-32 Nakamachi, Musashino-shi, Tokyo F-term within Yokogawa Electric Corporation (reference) 2G086 EE03 5F073 AA65 BA09 EA03 EA27 FA05 GA02 GA15

Claims (4)

[Claims] 1. A semiconductor laser light source for outputting light by a semiconductor laser, comprising detecting a mode jump current value within a predetermined current range based on an optical output of the semiconductor laser, and outputting an alarm output or a semiconductor laser light. A semiconductor laser light source, comprising: a control unit that performs at least one of changing a current value of a drive current in the semiconductor laser light source. 2. A semiconductor laser light source for outputting light by a semiconductor laser, a light receiving circuit for converting the power of the output light of the semiconductor laser into an electric signal, and a signal processing circuit for converting the electric signal of the light receiving circuit into a digital signal. And changing the drive current of the semiconductor laser to obtain an increase in the optical power of the semiconductor laser from the digital signal of the signal processing circuit, and the mode jump current value falls within a predetermined current range according to the increase in the optical power. A semiconductor laser light source comprising: a control unit that detects the occurrence of an alarm and changes at least one of an alarm output and a current value of a drive current in the semiconductor laser. 3. A semiconductor laser light source that outputs light using a semiconductor laser, wherein: a wavelength measurement system for determining a wavelength of output light of the semiconductor laser; and a wavelength change of the semiconductor laser from the wavelength measurement system by driving the semiconductor laser. A control unit for detecting that a mode jump current value has entered a predetermined current range, and performing at least one of an alarm output and a change in a current value of a drive current in the semiconductor laser. Laser light source. 4. A measuring instrument using the semiconductor laser light source according to claim 1.