JP3006822B2 - Laser wavelength controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser wavelength control device for controlling the wavelength of a laser beam output from a laser diode, and more particularly to a laser wavelength control device for preventing temperature fluctuation of the oscillation center wavelength. About.

[0002]

2. Description of the Related Art The characteristics of laser light output from a laser diode fluctuate due to a temperature change in a module (hereinafter abbreviated as "LD module") accommodating the laser diode. Therefore, when an LD module is used in a device in which such fluctuation is not preferable, an element for controlling the temperature is incorporated in the module to prevent fluctuation of the oscillation center wavelength.

In Japanese Patent Application Laid-Open No. 58-96794, the temperature of a laser diode is sensed by a thermal element, and a signal representing the temperature is amplified and then input to a temperature control circuit. The temperature control circuit controls the electronic cooler according to the sensed temperature so as to keep the output of the laser diode constant.

In Japanese Patent Application Laid-Open No. 3-119776, a monitor circuit for monitoring the distortion characteristics of a laser diode is provided, and the operating temperature of the laser diode is changed according to the output signal of the monitor circuit. This makes it possible to obtain a device that can maintain stable light output characteristics for a long period of time.

FIG. 4 shows a general configuration of a circuit for controlling the temperature of such an LD module. In the LD module 11, the laser diode 1
2, a thermistor 13 and a Peltier effect element 14 as an electronic cooler are arranged adjacent thereto. LD
A comparator 15 is arranged outside the module 11.
The temperature of the laser diode 12 in the LD module 11 is detected by the thermistor 13 and its detection output 1
6 is input to one end of the comparator 15. The other end of the comparator 15 receives a reference signal of a designated potential. The comparison result 18 output from the comparator 15 is input to the Peltier effect element 14 and temperature control for keeping the laser diode 12 at desired characteristics is performed.

The above is a technique for keeping the output of laser light constant or maintaining low distortion characteristics. There is also a problem that the oscillation center wavelength shifts when the temperature in the LD module fluctuates, and this point is disclosed in Japanese Patent Application No. 4-032675 filed on January 23, 1992.

FIG. 5 shows the configuration of the laser wavelength control device disclosed in this publication. LD module 21
, A laser diode (LD) 22 and a Peltier effect element 23 are arranged. The laser beam 24 output from the laser diode 22 is incident on an optical narrow band filter 25,
The output light 26 is received by a photodiode (PD) 27. The detection output 28 of the photodiode 27 is input to a temperature adjustment circuit 29, from which the laser diode 22
Control signal 3 for preventing temperature fluctuation of oscillation center wavelength
1 is output. The control signal 31 is supplied to the Peltier effect element 23 to control the temperature of the LD module 21.

FIG. 6 shows the principle of temperature control of the laser wavelength control device. In the drawing, the curve on the left side shows the waveform (optical output power) of the laser beam 24L when the oscillation center wavelength is the desired wavelength λ. The curve on the right shows the waveform of the laser beam 26H when the temperature is higher by a predetermined temperature than this. The oscillation center wavelength at this time is λ ′ longer than λ. Further, the wavelength region 35 indicated by oblique lines in FIG.
Shows the range of wavelengths transmitted by the optical narrow band filter 25.

The temperature adjusting circuit 29 shown in FIG. 5 controls the temperature in the LD module 21 so that the light receiving output of the laser beam 24 in the wavelength region 35 becomes the maximum value, thereby controlling the oscillation center wavelength of the laser diode 22. Is kept at λ.

[0010]

However, in the conventional laser wavelength control device shown in FIG.
Since only one was used, if the oscillation center wavelength of the laser beam 24 was greatly shifted when the temperature changed abruptly or when the apparatus was started, the detection output itself of the photodiode 27 could not be obtained. Peltier effect element 2
There is a problem that it is difficult to control whether to control the direction of cooling 3 or the direction of generating heat, and it takes time to control or malfunctions. Further, if the optical output power near the oscillation center wavelength of the laser beam 24 has a flat characteristic, there is a problem that it is difficult to accurately set the oscillation center wavelength to a desired wavelength λ.

When the laser wavelength controller is constructed using a general circuit device as shown in FIG. 4, it is necessary to calculate the comparison result 18 outputted from the comparator 15 so as to obtain the set wavelength. Alternatively, there is a problem that the control of the Peltier effect element 14 needs to be controlled by a control unit according to the experiment result using a lookup table (not shown), and the configuration of the device becomes complicated. Further, since the thermistor 13 is used, it is difficult to perform control with high accuracy using its output characteristics. Further, since individual laser diodes have different oscillation wavelengths even at the same temperature, individual laser wavelengths are different. There is a problem that fine adjustment of the control device is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser wavelength control device which does not require any special adjustment and can reliably maintain the oscillation center wavelength of laser light at a desired value.

[0013]

According to the present invention, there is provided a laser wavelength control device for outputting a laser beam, a laser beam output from the laser beam output device, and a laser beam output from the laser beam output device. The long-wavelength filter and the short-wavelength filter that transmit light at wavelengths slightly shifted by the same wavelength on the long-wavelength side and the short-wavelength side, and the intensity of the laser light that has passed through these long-wavelength and short-wavelength filters increases. Temperature control means for controlling the temperature of the laser light output means so as to be equal.

That is, a long-wavelength filter and a short-wavelength filter that transmit light at wavelength positions slightly shifted from the predetermined oscillation center wavelength by the same wavelength on the long wavelength side and the short wavelength side are prepared. By controlling the temperature of the laser light output means so that the intensities of the laser light transmitted through the filter become equal, the oscillation center wavelength of the laser light is set to a predetermined oscillation center wavelength.

Further, the laser wavelength control device of the present invention comprises: a laser light output means for outputting a laser light; and a laser light output from the laser light output means. The long-wavelength filter and the short-wavelength filter, which transmit light at wavelengths slightly shifted by an arbitrary wavelength to the short-wavelength side and the short-wavelength side, respectively. And a temperature control means for controlling the temperature of the laser light output means so as to have a predetermined ratio determined by the relationship between the output wavelength characteristic and the filters set on the long wavelength side and the short wavelength side.

That is, in the above configuration, the long-wavelength filter and the short-wavelength filter that transmit light at wavelength positions slightly shifted by an arbitrary wavelength from the predetermined oscillation center wavelength to the long wavelength side and the short wavelength side, respectively, are provided. Have it ready
The temperature control of the laser light output means is performed so that the intensity of the laser light transmitted through these filters has a predetermined ratio determined by the relationship between the output wavelength characteristics of the laser light and the filters set on the long wavelength side and the short wavelength side. By doing so, the oscillation center wavelength of the laser beam is set to a predetermined oscillation center wavelength.

Further, the laser wavelength control device of the present invention
A laser light output unit that outputs laser light, an oscillation center wavelength setting unit that sets an oscillation center wavelength of the laser light output from the laser light output unit, and an oscillation center wavelength that is set by the oscillation center wavelength setting unit. A long-wavelength filter and a short-wavelength filter that transmit light at wavelengths slightly shifted by an arbitrary wavelength to the long-wavelength side and a short-wavelength side as the center, and a laser beam that has passed through the long-wavelength filter and the short-wavelength filter. Temperature control means for controlling the temperature of the laser light output means so that the intensity becomes a predetermined ratio determined by the relation between the output wavelength characteristic of the laser light and the filters set on the long wavelength side and the short wavelength side. It is characterized by:

That is, in the laser wavelength control apparatus of the present invention, the oscillation center wavelength of the laser beam is set by the oscillation center wavelength setting means, and the oscillation center wavelength set by the oscillation center wavelength setting means is centered on the long wavelength side. Using the long-wavelength filter and the short-wavelength filter that transmit light at wavelengths slightly shifted by an arbitrary wavelength to the short-wavelength side, the intensity of the laser light that has passed through these filters is determined by the output wavelength characteristics of the laser light and the length. By controlling the temperature of the laser light output means so as to have a predetermined ratio determined by the relationship between the filter set on the wavelength side and the filter set on the short wavelength side, the oscillation center wavelength of the laser light is set to an arbitrary oscillation center wavelength. That is.

Here, the temperature control means can control the temperature by controlling a Peltier effect element arranged near the laser light output means.

The laser light output means uses a laser diode, and the temperature control means converts the laser light output from the laser light output means into an optical narrow band long wavelength filter and a short wavelength filter. The temperature may be controlled using electric signals obtained by photoelectrically converting the light transmitted through the photodiodes with the photodiodes.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a laser wavelength controller according to the present invention will be described in detail with reference to the drawings.

FIG. 1 shows in principle the circuit configuration of a laser wavelength control device in one embodiment of the present invention. The laser wavelength control device of this embodiment is an LD in which a Peltier effect element 41 and a laser diode (LD) 42 are arranged.
Module 43 is used. No thermistor is arranged in the LD module 43. The laser light 45 output from the laser diode 42 is split into two, one of which passes through the optical narrowband high-pass filter 46 and the transmitted light 4
The light 7 enters the first photodiode 48. The other split laser beam 45 passes through the optical narrow-band low-pass filter 51 and enters the second photodiode 53 as transmitted light 52. The first detection output 54 photoelectrically converted and output by the first photodiode 48 and the second detection output 55 photoelectrically converted and output by the second photodiode 53 are output from the comparator 5.
6 and the difference between the two levels is compared in an analog manner. The comparison result 57 is input to the temperature adjustment circuit 58, and the Peltier effect element 41 as an electronic cooler is controlled by the control signal 59 output from the temperature adjustment circuit 58.

FIG. 2 specifically shows a circuit configuration of a main part of the laser wavelength control device. The cathode of the first photodiode 48 that receives the transmitted light 47 of the optical narrowband high-pass filter 46 of FIG. 1 is connected to the other end of the input voltage adjusting resistor 61 having one end of the comparator 56 grounded. The anode is connected to a negative power supply line (not shown) of a potential −V via a current adjusting resistor 62.
Similarly, the cathode of the second photodiode 53 that receives the transmitted light 52 of the optical narrowband low-pass filter 51 is connected to the other end of the input voltage adjusting resistor 63 having one end of the comparator 56 grounded. The anode is connected to the negative power supply line via a current adjusting resistor 64. The resistance values of the two resistors 61 and 63 are equal to each other,
The resistance values of the other two resistors 62 and 64 are also equal to each other.

The comparator 56 includes two transistors 66 and 67 whose emitters are connected to a common constant current source 65. The other end of the constant current source 65 is connected to the aforementioned negative power supply line. The base of the first transistor 66 is connected to the cathode of the first photodiode 48 via the resistor 68. The collector is grounded via a resistor 69 for adjusting the voltage level, and connected to the base of the transistor 72 via a resistor 71 in the temperature adjusting circuit 58. The base of the second transistor 67 is connected to the cathode side of the second photodiode 53 via the resistor 74. The collector is grounded via a voltage level adjusting resistor 75. The emitter of the transistor 72 in the temperature adjustment circuit 58 is connected to the above-mentioned negative power supply line via a current adjustment resistor 77, and the collector is a Peltier effect element 41 having one end grounded.
Is connected to the other end.

FIG. 3 shows the operation principle of the laser wavelength control device having such a configuration. In the figure, the curve on the left side shows the laser light 45 when the oscillation center wavelength is a desired wavelength λ.
The waveform of L (light output power) is shown. The curve on the right shows the waveform of the laser beam 45H when the temperature rises by a predetermined temperature. The oscillation center wavelength at this time is λ ′ longer than λ. Further, a left wavelength region 81 indicated by oblique lines in the drawing indicates a range of wavelengths transmitted by the optical narrow band high-pass filter 46 (FIG. 1).
The wavelength region 82 on the right is a light narrow band low-pass filter 51.
FIG. 1 shows the range of wavelengths to be transmitted. The center wavelength of the left wavelength region 81 is Δλ more than the wavelength λ.
And the center wavelength of the right wavelength region 82 is longer than the wavelength λ by Δλ. Here, Δλ is a length slightly shifted from the oscillation center wavelength,
More specifically, the amount is such that it is positioned on an inclined portion of the curve indicating the optical power shown in FIG.

When the center wavelength of the laser beam 45 output from the laser diode 42 shown in FIG. 1 is correctly set to the wavelength λ, the laser beam 45H is obtained in FIG. Assuming that the optical power of the laser light 45 is attenuated symmetrically with respect to the oscillation center wavelength, the first and second photodiodes 4 in this state.
8, 53 receive the same amount of light. At this time, the first and second transistors 66 and 67 divide the current flowing through the constant current source 65 into two, and a voltage corresponding to a voltage drop generated by the resistor 69 is input to the temperature adjustment circuit 58 as a comparison result 57 at this time. Is done. The temperature adjusting circuit 58 operates the transistor 72 in response to this, and controls the temperature so that the Peltier effect element 41 maintains the temperature with the collector current.

On the other hand, it is assumed that the temperature inside the LD module 43 changes to a high temperature side due to a change in some situation, and the oscillation center wavelength of the laser beam 45 becomes λ ′. Then, as shown in FIG. 3, the optical power shifts to the right in the figure as a whole, and the two wavelength regions 81 and 82 correspond to the left shoulder portion of the characteristic curve. In this state, the amount of light transmitted through the second wavelength region 82 is larger than the amount of light transmitted through the first wavelength region 81. Therefore, the first photodiode 48
Will receive more light than the second photodiode 53. In this state, the resistance 6 shown in FIG.
1 flows more current than the resistor 63, and the potential difference becomes larger. As a result, the base potential of the first transistor 66 becomes lower than that of the second transistor 67,
The collector current of the first transistor 66 is smaller than that of the second transistor 67. That is, when the center wavelength of the laser beam 45 shifts to the longer wavelength side, the voltage as the comparison result 57 gradually increases to the ground potential side.
In response to this, the collector current of the transistor 72 increases, and the temperature adjustment circuit 58 cools the Peltier effect element 41 more strongly, and shifts the center wavelength of the laser beam 45 from λ ′ to λ.

Conversely, when the temperature in the LD module 43 changes to a lower temperature, temperature control is performed in a direction in which the cooling of the Peltier effect element 41 is weakened, and the center wavelength of the laser beam 45 is set to a desired value. To the wavelength λ.

In the embodiment described above, the Peltier effect element is used as the electronic cooler for controlling the temperature. However, the present invention is not limited to this. Moreover, it is also possible to perform heating control as needed.

Further, in the embodiment, two filters are provided at symmetric wavelength positions from the desired wavelength λ, but it is not always necessary to detect light at the symmetric position. However, in this case, it is necessary to perform temperature control using a relational expression determined by the relation between the characteristic curve of the optical power of the laser light and the arrangement position of each filter. In the embodiment, the laser diode is used as the laser light output means. However, the present invention can be freely applied to other laser light output means. Also,
In the embodiment, the light at the wavelength position where the two filters are fixed is transmitted. However, the wavelength position at which the light is transmitted can be arbitrarily set so that the oscillation center wavelength of the laser light can be freely adjusted. Is also good.

[0031]

As described above, the long-wavelength filter and the short-wavelength filter that transmit light at the wavelength positions slightly shifted by the same wavelength on the long wavelength side and the short wavelength side around the predetermined oscillation center wavelength are used. In advance, the temperature of the laser light output means is controlled so that the intensities of the laser lights transmitted through these filters become equal. Therefore, the oscillation center wavelength of the laser light can be controlled to be constant with a very simple circuit configuration.

A long-wavelength filter and a short-wavelength filter that transmit light at wavelength positions slightly shifted by an arbitrary wavelength from the predetermined oscillation center wavelength to the long wavelength side and the short wavelength side, respectively, are prepared. Temperature control of the laser light output means so that the intensity of the laser light transmitted through these filters has a predetermined ratio determined by the relationship between the output wavelength characteristics of the laser light and the filters set on the long wavelength side and the short wavelength side. Decided to do. Therefore, even when a laser light output means whose optical power characteristics are not symmetrical is used, the oscillation center wavelength of the laser light can be controlled to be constant.

Further, the oscillation center wavelength of the laser beam is set by the oscillation center wavelength setting means, and an arbitrary wavelength is respectively set on the long wavelength side and the short wavelength side around the oscillation center wavelength set by the oscillation center wavelength setting means. Using the long wavelength filter and the short wavelength filter that transmit light at slightly shifted wavelength positions, the intensity of the laser light transmitted through these filters is set to the output wavelength characteristics of the laser light and to the long wavelength side and the short wavelength side. The temperature of the laser light output means is controlled so as to have a predetermined ratio determined by the relationship with the filter. Therefore, the oscillation center wavelength itself of the laser beam can be freely set, and can be maintained at the set oscillation center wavelength.

In the configuration of the present invention, if a Peltier effect element is used for the temperature control means, not only cooling but also heating can be performed, and the temperature control range of the laser wavelength control device can be widened. Can be set.

Further, since a narrow band filter is used,
Temperature control can be performed stably and with high accuracy. Also,
Since temperature control can be performed without using a thermistor, control accuracy can be improved in this respect as well.

[Brief description of the drawings]

FIG. 1 is a principle diagram illustrating a circuit configuration of a laser wavelength controller according to an embodiment of the present invention.

FIG. 2 is a circuit diagram specifically showing a circuit configuration of a main part of the laser wavelength control device of the present embodiment.

FIG. 3 is an explanatory diagram showing an operation principle of the laser wavelength control device of the present embodiment.

FIG. 4 is a block diagram showing a configuration of a conventional temperature control circuit using a general laser diode.

FIG. 5 is a block diagram showing an outline of a circuit configuration of the previously proposed laser wavelength control device.

FIG. 6 is a principle diagram showing an operation principle of the proposed laser wavelength control device.

[Explanation of symbols]

 Reference Signs List 41 Peltier effect element 42 Laser diode 43 LD module 46 Optical narrow band high-pass filter 48 First photodiode 51 Optical narrow band low-pass filter 53 Second photodiode 56 Comparator 58 Temperature adjustment circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01S 3/133 H01S 3/096

Claims (3)

(57) [Claims] 1. A laser light output means for outputting laser light, an oscillation center wavelength setting means for setting an oscillation center wavelength of laser light output from the laser light output means, and an oscillation center wavelength setting means for setting the oscillation center wavelength. A long-wavelength filter and a short-wavelength filter that transmit light at wavelength positions slightly shifted by an arbitrary wavelength to a long-wavelength side and a short-wavelength side with respect to the oscillation center wavelength, and the long-wavelength filter and the short-wavelength side Temperature control of the laser light output means so that the intensity of the laser light transmitted through the filter has a predetermined ratio determined by the relationship between the output wavelength characteristic of the laser light and the filters set on the long wavelength side and the short wavelength side. And a temperature control means for performing the temperature control. 2. The laser wavelength control device according to claim 1, wherein the temperature control means controls the temperature by controlling a Peltier effect element arranged near the laser light output means. 3. The laser light output means is a laser diode, and the temperature control means transmits the laser light output from the laser light output means through an optical narrow band long wavelength filter and a short wavelength filter. 2. The laser wavelength control device according to claim 1, wherein temperature control is performed using an electric signal obtained by photoelectrically converting the light that has been made by the photodiode.