JPH09162477A - Wavelength stabilizing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a desired oscillation wavelength of a semiconductor laser by detecting the optical intensity of the reflection output from an air-gap etalon, discriminated in wavelength with variation in wavelength due to variation in the refractive index of air taken into account, by means of an optical intensity detector. SOLUTION: Part of laser light output from an LD 12 is separated by a beam splitter 15, and is passed through a beam splitter 16. Laser light that is reflected by an air-gap etalon 17 and is not directed into a corner cube 19 is reflected by the beam splitter 16, and its intensity is detected with a PD 20. When the wavelength of length-measuring light deviates from a reference wavelength λ0 due to the refractive index of air, and the output of the PD 20 deviates from a set value or peak value, an LD injection current control unit 21 increases or decreases the amount of injection current supplied to the LD 12 as required. Since the oscillation wavelength of the LD 12 is controlled using laser light propagated through a dead path section and using the reference length L of the air-gap etalon 17 as a reference, therefore, the wavelength of length-measuring light is kept stabilized even if the refractive index of air varies.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength stabilizing device used for a light source such as a laser length measuring machine.

[0002]

2. Description of the Related Art Conventionally, a laser length measuring machine for measuring a moving displacement of an object with a wavelength of a laser beam as a length measuring standard has been widely known, and recently, an attempt to use a semiconductor laser as a light source of the laser length measuring machine. Has been done.

FIG. 4 illustrates the characteristics of the oscillation wavelength corresponding to the injection current into this semiconductor laser (hereinafter abbreviated as "LD") at temperatures T1 [° C] and T2 [° C] (T1 <T2). Therefore, it can be seen that the oscillation wavelength depends on the injection current and the temperature as shown in FIG. Therefore, in order to stabilize the oscillation wavelength that is the length measurement reference to the reference wavelength λ0 in FIG. 4, the temperature of the LD is controlled so that it is always T1 [° C.], and the current injected into the LD is i1. The constant current control may be performed so that

FIG. 5 exemplifies the configuration of a wavelength stabilization device capable of further stabilizing the oscillation wavelength of the LD. That is, in the figure, 1 is a light source unit, 2 in the light source unit 1 is an LD, and the temperature of the LD 2 is detected by a thermistor 3 in the light source unit 1. The temperature information detected by the thermistor 3 is sent to the LD temperature control unit 4, where a temperature control signal is generated so that the temperature of the LD 2 becomes equal to the preset temperature. Is sent to the Peltier element 5 of the light source unit 1 and heats or absorbs heat to control the temperature of the LD 2 so as to maintain the set temperature.

A part of the laser light output from the LD 2 of the light source unit 1 is used as a length measuring light and is incident on the etalon 6 which transmits or absorbs only a specific wavelength component of the laser light.

Generally, the etalon 6 has a periodic wavelength discrimination characteristic as shown in FIG. 6, and the transmitted light amount of the etalon 6 having such a characteristic is determined by a photodiode (hereinafter referred to as "P").
Abbreviated as "D") 7, and the information of the detected light amount is L
By sending it to the D injection current control unit 8, the LD injection current control unit 8 controls the amount of injection current supplied to the LD 2 so that the information on the light amount reaches a certain set value or peak value.

However, in reality, the LD temperature control unit 4 is set to L
The temperature is controlled so that the temperature of D2 is always T1 [° C], and when it becomes T1 [° C] and is almost stable, a control start signal is sent from the LD temperature controller 4 to the LD injection current controller 8. To be done. The LD injection current control unit 8 first supplies the injection current i1 of the light source unit 1 according to this control start signal, and thereafter performs feedback control in accordance with the light amount information from the PD 7. With the above operation, the oscillation wavelength of the LD 2 is stabilized at the reference wavelength λ 0 peculiar to the etalon 6.

[0008]

However, in the laser length measuring machine, air exists between the light source and the moving object, and the refractive index n of the air changes depending on the temperature and the atmospheric pressure at that time. The wavelength of the length measuring light changes according to the change of the refractive index of air, and as a result, an error occurs in the movement displacement.

Therefore, in order to accurately measure the moving displacement with the laser length measuring machine using the wavelength stabilizing device shown in FIG. 5, an air sensor or the like is installed in the vicinity of the optical path to measure the temperature and atmospheric pressure during the length measurement. It is necessary to measure and obtain the refractive index n of the air at that time, and correct the moving displacement measured by the oscillation wavelength of the LD 2 and the correction coefficient calculated from the obtained refractive index n of the air.

This is particularly noticeable in the case of measuring a minute distance with high resolution in a fine shape measuring apparatus. For example, the measuring distance is about 1 [mm], whereas a physical optical element is used. Due to the arrangement of the light source, the area (hereinafter abbreviated as "dead path") not used for length measurement between the light source and the moving object is
It may be about 0 [cm].

In this case, no matter how the oscillation wavelength of the LD 2 is stabilized, fluctuations in the refractive index of air in the dead path portion greatly affect the overall length measurement error. Further, although the air sensor may be used as described above, since the optical path is configured as short as possible for the above reason, it is practically difficult to arrange the air sensor near the optical path.

The present invention has been made in view of the above situation, and an object thereof is to stabilize the oscillation wavelength of a semiconductor laser at a desired wavelength including a change in the refractive index of air in the dead path portion. It is to provide a wavelength stabilization device capable of performing the above.

[0013]

According to the first aspect of the present invention,
A semiconductor laser that receives a supply of injection current and outputs laser light, and is mounted between the semiconductor laser and a moving object,
An air gap etalon that discriminates the wavelength of the laser light output from the semiconductor laser including a change in wavelength due to a change in the refractive index of air, and a light intensity detector that detects the intensity of reflected light from the air gap etalon, An injection current control means for controlling the injection current amount to the semiconductor laser so that the output of the light intensity detector has a predetermined value, and a temperature control means for performing temperature control so that the semiconductor laser has a set temperature. I am preparing to have it.

As a result, according to the invention of claim 1,
Laser light is output from the semiconductor laser that has been supplied with the injection current. The output laser light is incident on the air gap etalon arranged in the dead path portion and having the wavelength discrimination characteristic. Then, the reflected output light intensity from the air gap etalon, which is wavelength-discriminated including the change of the wavelength due to the change of the refractive index of air, is detected by the light intensity detector, and the detection result is fed back to the injection current control means. The injection current control means controls the injection current amount supplied to the semiconductor laser so that the output of the light intensity detector becomes a predetermined value.

According to a second aspect of the present invention, a semiconductor laser which outputs a laser beam by receiving an injection current, and a laser beam which is mounted between the semiconductor laser and a moving object and is output from the semiconductor laser are provided. The air gap etalon that discriminates the wavelength by including the wavelength change due to the change of the refractive index of air, the light intensity detector that detects the intensity of the transmitted light from this air gap etalon, and the output of this light intensity detector An injection current control means for controlling the injection current amount to the semiconductor laser so that the value becomes a value and a temperature control means for controlling the temperature so that the semiconductor laser reaches a set temperature are provided.

As a result, according to the invention of claim 2,
Laser light is output from the semiconductor laser that has been supplied with the injection current. The output laser light is incident on the air gap etalon arranged in the dead path portion and having the wavelength discrimination characteristic. Then, the transmitted output light intensity from the air gap etalon, which has been wavelength-discriminated including the change of the wavelength due to the change of the refractive index of air, is detected by the light intensity detector, and the detection result is fed back to the injection current control means. The injection current control means controls the injection current amount supplied to the semiconductor laser so that the output of the light intensity detector becomes a predetermined value.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows a schematic configuration of a wavelength stabilizing device according to a first embodiment of the present invention.

In the figure, 11 is a light source section, 12 is an LD, and 13
Is a thermistor for detecting the temperature of the LD 12, and 14 is a Peltier element that heats / absorbs heat so that the LD 12 reaches a preset temperature based on the temperature detected by the thermistor 13. The LD 12, the thermistor 13 and the Peltier element 14 serve as a light source. The part 11 is configured.

A part of the laser light emitted from the LD 12 is separated by a beam splitter 15 arranged in the optical path, passes through a beam splitter 16, and passes through an air gap etalon 17 arranged in a dead path portion. Then
The light is reflected by a corner cube 19 attached to a moving object (not shown) to be measured and reaches the interference system 18. The laser beam split by the beam splitter 15 is also incident on the interference system 18 as reference light.

The air gap etalon 17 disposed in the dead path portion has a pair of parallel flat plate mirrors 17b, 1 on both ends of a low thermal expansion coefficient material plate 17a as shown in FIG.
The laser light passes through the apertures formed in the parallel plate mirrors 17b and 17c, and the parallel plate mirrors 7c and 7c face each other.
The distance between them becomes the reference length L, and the low thermal expansion coefficient material plate 1
Due to the material of 7a, the reference length L is maintained regardless of the outside air temperature.

Further, the beam splitter 16 reflects the laser light reflected by the air gap etalon 17 to generate P
The light amount information obtained by the PD 20 is sent to the LD injection current control unit 21 so that the LD injection current control unit 21 has a certain set value or peak value. The amount of injection current supplied to the LD 12 is controlled.

The thermistor 13 detects the temperature of the LD 12 and sends the obtained temperature information to the LD temperature control section 22. LD
The temperature control unit 22 creates a temperature control signal such that the temperature of the LD 12 becomes equal to a preset temperature, and sends the temperature control signal to the Peltier element 14 of the light source unit 11 to cause heat generation or heat absorption to cause the temperature of the LD 12 to rise. Controls so as to maintain the set temperature.

The operation in the case of stabilizing the wavelength of the length-measuring light to be the reference value λ0 in the above-mentioned configuration will be described. First, the LD 12 is controlled by the LD temperature control unit 22 to control the driving of the Peltier element 14 to a constant temperature T1 [° C.], while the LD injection current control unit 21 sets the injection current to the LD 12 to i1.
The oscillation wavelength of 2 is λ0. The laser light output from the LD 12 is first partially separated by the beam splitter 15, then passes through the beam splitter 16, and enters the air gap etalon 17. Here, the laser light separated by the beam splitter 15 is incident on the interference system 18 as reference light.

In the air gap etalon 17, as shown in FIG.
With the configuration as shown in FIG.
The laser light that has passed through the aperture formed in 7c is reflected by the corner cube 19 attached to the moving object, and enters the interference system 18 as the length measurement light.

On the other hand, the laser light reflected by the air gap etalon 17 and not incident on the corner cube 19 is reflected by the beam splitter 16 and then P
It is incident on D20 and its intensity (light amount) is detected.

Here, when the wavelength of the length measuring light changes from the reference wavelength λ 0 due to the refractive index of air and the output of the PD 20 is no longer a preset value or peak value, L
The D-injection current control unit 21 always sets the LD1 so that the output of the PD 20 is always at a preset value or peak value.
The amount of injection current supplied to 2 is controlled.

By continuing such an operation, L
Since the oscillation wavelength of D12 is controlled with the reference length L of the air gap etalon 17 using the laser light that has propagated through the dead path portion, the wavelength of the measurement light is always set even if the refractive index n of air changes. It can be stabilized at λ 0, and it is not necessary to correct the movement displacement.

In such a wavelength stabilizer, the wavelength itself of the length measuring light can be stabilized by removing the influence of the change in the refractive index of air in the measurement environment, so that it is possible to use an air sensor or the like as in the conventional case. It is not necessary to measure the air temperature and atmospheric pressure to obtain the refractive index n of air, and to perform the operation of correcting the movement displacement based on the oscillation wavelength of the LD and the wavelength of the length measuring light obtained from the refractive index n of air. Therefore, an air sensor, a correction calculation circuit, an etalon temperature control device, and the like are unnecessary, and the configuration and processing can be simplified.

Further, even when performing high-resolution length measurement at a minute distance, the influence of air fluctuations due to dead paths is eliminated, and the length measurement reproducibility is improved. (Second Embodiment) FIG. 3 shows a schematic structure of a wavelength stabilizing device according to a second embodiment of the present invention, and is basically the same as that shown in FIG. The same parts are designated by the same reference numerals and the description thereof will be omitted.

Thus, the laser light output from the LD 12 of the light source section 11 is partially separated by the beam splitter 15, passes through the air gap etalon 17 arranged in the dead path section, and then moves as a measurement target. It is reflected by a corner cube 19 attached to an object, separated by a beam splitter 16 ′, and reaches an interference system 18 and a PD 20 interference system 18. The laser beam split by the beam splitter 15 is also incident on the interference system 18 as reference light.

In such a configuration, in the operation for stabilizing the wavelength of the length measuring light to be the reference value λ0, the LD 12 is controlled by the LD temperature control unit 22 to drive the Peltier element 14 first. The LD injection current control unit 21 is controlled to L while the temperature is controlled to a constant temperature T1 [° C.].
The injection current into D12 is set to i1, and the oscillation wavelength of LD12 is set to λ0. The laser light output from the LD 12 first enters the air gap etalon 17 after being partially separated by the beam splitter 15, and the laser light separated by the beam splitter 15 enters the interference system 18 as reference light.

In the air gap etalon 17, as shown in FIG.
With the configuration as shown in FIG.
The laser beam that has passed through the aperture formed in 7c is reflected by the corner cube 19 attached to the moving object, and then part of it is separated by the beam splitter 16 ', and the transmitted laser beam is used as the length measuring light. The separated laser light enters the interference system 18 and enters the PD 20.

Here, when the wavelength of the length measuring light changes from the reference wavelength λ 0 due to the refractive index of air and the output of the PD 20 is no longer a preset value or peak value, L
The D-injection current control unit 21 always sets the LD1 so that the output of the PD 20 is always at a preset value or peak value.
The amount of injection current supplied to 2 is controlled.

By continuing such an operation, L
Since the oscillation wavelength of D12 is controlled with the reference length L of the air gap etalon 17 using the laser light that has propagated through the dead path portion, the wavelength of the measurement light is always set even if the refractive index n of air changes. It can be stabilized at λ 0, and it is not necessary to correct the movement displacement.

In the wavelength stabilizing device according to the second embodiment as described above, as in the wavelength stabilizing device according to the first embodiment, the influence of the change in the refractive index of air in the measurement environment is influenced. Since it is possible to stabilize the wavelength of the length measuring light by itself, the temperature and atmospheric pressure are measured by an air sensor or the like to find the refractive index n of air, and the oscillation wavelength of the LD and the refractive index of air are measured. It is not necessary to perform an operation to correct the moving displacement based on the wavelength of the measuring light obtained from n. Therefore, an air sensor, a correction calculation circuit, an etalon temperature control device, and the like are unnecessary, and the configuration and processing can be simplified.

Further, even when performing high-resolution length measurement at a minute distance, the influence of air fluctuation due to dead path is eliminated, and the length measurement reproducibility is improved. The present invention is not limited to the above-described first and second embodiments, and can be variously modified without departing from the scope of the present invention, for example, the shape of the air gap etalon 17. The configuration does not have to be the one shown in FIG. .

In the above description, the amount of injection current supplied to the LD 12 is variably controlled to stabilize the wavelength while the temperature of the LD 12 is controlled to be constant. However, the injection current amount supplied to the LD 12 is constant. The same effect can be obtained by variably controlling the temperature of the LD 12 in the state of being controlled to.

Although the above description has been given based on the embodiments, the present invention includes the following inventions. (1) A semiconductor laser that outputs a laser beam when supplied with an injection current, and is placed between the semiconductor laser and a moving object, and the laser beam output from the semiconductor laser is generated by changing the refractive index of air. An air gap etalon that discriminates wavelengths including a change in wavelength, a light intensity detector that detects the intensity of reflected light from the air gap etalon, and the semiconductor laser so that the output of this light intensity detector becomes a predetermined value. A wavelength stabilizing device comprising: an injection current control means for controlling the amount of injection current into the semiconductor laser; and a temperature control means for controlling the temperature of the semiconductor laser so as to reach a set temperature.

In this way, the influence of the change in the refractive index of air in the measurement environment can be removed and the wavelength of the length measuring light itself can be stabilized. To obtain the refractive index of air,
It is not necessary to perform an operation to correct the movement displacement based on the oscillation wavelength of the LD and the wavelength of the measuring light obtained from the refractive index of air. Therefore, an air sensor, a correction calculation circuit, an etalon temperature control device, and the like are unnecessary, and the configuration and processing can be simplified.

Further, even when performing high-resolution length measurement at a minute distance, the influence of air fluctuation due to the dead path is eliminated, and the length measurement reproducibility is improved. (2) The invention according to claim 2 is a semiconductor laser which outputs a laser beam upon receiving supply of an injection current, and a laser beam which is mounted between the semiconductor laser and a moving object and is output from the semiconductor laser. The air gap etalon that discriminates the wavelength by including the wavelength change due to the change of the refractive index of air, the light intensity detector that detects the intensity of the transmitted light from this air gap etalon, and the output of this light intensity detector Wavelength stabilization, which is provided with injection current control means for controlling the injection current amount to the semiconductor laser so that the value becomes a value, and temperature control means for controlling the temperature so that the semiconductor laser reaches a set temperature. Device.

By doing so, the wavelength of the length-measuring light itself can be stabilized by removing the influence of the change in the refractive index of the air in the measurement environment, as in the case of the first aspect of the invention. As in the prior art, the temperature and atmospheric pressure are measured with an air sensor or the like to obtain the refractive index of air, and the movement displacement is corrected from the oscillation wavelength of the LD and the wavelength of the measuring light obtained from the refractive index of air. There is no need to do it. Therefore, an air sensor, a correction calculation circuit, an etalon temperature control device, and the like are unnecessary, and the configuration and processing can be simplified. Further, even when high-resolution length measurement is performed at a minute distance, the influence of air fluctuation due to the dead path is eliminated, and the length measurement reproducibility is improved.

[0042]

As described above in detail, according to the present invention, the wavelength stabilizing device capable of always stabilizing the oscillation wavelength of the semiconductor laser to a desired wavelength including the change of the refractive index of air in the dead path portion. Can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration according to a first embodiment of the present invention.

FIG. 2 is a perspective view illustrating a specific configuration shape of the air gap etalon shown in FIG.

FIG. 3 is a block diagram showing a schematic configuration according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a characteristic of a general oscillation wavelength with respect to an injection current of a semiconductor laser.

FIG. 5 is a block diagram illustrating a schematic configuration of a conventional wavelength stabilization device.

FIG. 6 is a diagram illustrating a periodic wavelength discrimination characteristic of a general etalon.

[Explanation of symbols]

 1, 11 ... Light source part 2, 12 ... Semiconductor laser (LD) 3, 13 ... Thermistor 4, 22 ... LD temperature control part 5, 14 ... Peltier element 6 ... Etalon 7, 20 ... Photodiode (PD) 8, 21 ... LD injection current control unit 15, 16, 16 '... Beam splitter 17 ... Air gap etalon 17a ... Low thermal expansion coefficient material plate 17b, 17c ... Parallel flat plate mirror 18 ... Interference system 19 ... Corner cube

Claims (2)

[Claims] 1. A semiconductor laser which outputs a laser beam when supplied with an injection current, and a laser beam which is mounted between the semiconductor laser and a moving object and which is output from the semiconductor laser and has a refractive index of air. The air gap etalon that discriminates the wavelength including the change of the wavelength due to the change, the light intensity detector that detects the intensity of the reflected light from the air gap etalon, and the above-mentioned so that the output of the light intensity detector becomes a predetermined value. A wavelength stabilizing device comprising: an injection current control means for controlling an injection current amount to a semiconductor laser; and a temperature control means for controlling a temperature so that the semiconductor laser has a set temperature. 2. A semiconductor laser which outputs a laser beam when supplied with an injection current, and a laser beam which is mounted between the semiconductor laser and a moving object and which is emitted from the semiconductor laser and has a refractive index of air. The air gap etalon that discriminates the wavelength including the change in the wavelength due to the change, the light intensity detector that detects the intensity of the transmitted light from the air gap etalon, and the above-mentioned so that the output of the light intensity detector becomes a predetermined value. A wavelength stabilizing device comprising: an injection current control means for controlling an injection current amount to a semiconductor laser; and a temperature control means for controlling a temperature so that the semiconductor laser has a set temperature.