JP3490476B2 - Wavelength stabilizer - Google Patents

Description

Description: 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. 2. Description of the Related Art Conventionally, there has been known a laser length measuring machine which measures a displacement of an object using a wavelength of a laser beam as a length measurement reference. Recently, attempts have been made to use a semiconductor laser as a light source of a laser length measuring machine. Semiconductor laser (hereinafter referred to as
As shown in FIG. 6, the oscillation wavelength of the LD depends on the injection current and the temperature. In order to stabilize the wavelength that is the length measurement standard to λo in FIG. 6, the temperature of the LD may be controlled to T1 (° C.), and the injection current of the LD may be controlled to be constant at i1. Further, according to the wavelength stabilizing device configured as shown in FIG. 4, the oscillation wavelength of the LD can be stabilized with higher accuracy. In this wavelength stabilizing device, L
The temperature of D2 is detected by the thermistor 3, and the detected temperature is input to the LD temperature controller 4. LD temperature controller 4
Controls the Peltier element 5 provided in the light source unit 1 so that the temperature of the LD 2 is equal to a preset temperature. The laser beam output from the LD 2 is incident on a wavelength discriminating element (hereinafter, described as an etalon) 6 which transmits or absorbs a specific wavelength of the laser beam. Generally, the etalon 6 has a periodic wavelength discrimination characteristic as shown in FIG. The amount of transmitted light of the etalon 6 having such characteristics is detected by a photodiode (hereinafter, referred to as PD) 8,
The LD injection current control section 9 controls the injection current supplied to the LD 2 so that the detected light amount becomes a certain set value or a peak value. [0005] Actually, the LD temperature controller 4 is
Is controlled to be T1 (° C.).
When the temperature is almost stabilized at (° C.), the LD temperature controller 4 sends a control start signal to the LD injection current controller 9. When receiving the control start signal, the LD injection current control unit 9 first sets the injection current i1.
After that, feedback control is performed while observing the output of PD8. As a result, the oscillation wavelength of the LD 2 is stabilized at λo. By the way, in the above wavelength stabilizing device,
The temperature control needs to be performed near the set temperature T1 (° C.), and the current control needs to be performed near the set current value i1. Since the wavelength discrimination characteristic of the etalon 6 has a peak even at a wavelength (λ1, λ2, etc.) other than the wavelength λo as shown in FIG. 5, the LD injection current control unit 9 which only looks at the output value of the PD 8 has This is because there is a possibility of locking to a wavelength (λ1, λ2, etc.) other than the wavelength λo by mistake. [0007] However, the oscillation wavelength of the LD changes over time as shown in FIG. 7 (OPTRONICS (1992) No. 11
HOYA Co., Ltd. Yamaura, Lime, Hirano) That is, the straight line shown in FIG.
Even if the temperature of 2 is T1 (° C.) and the injection current of the LD is i1, the oscillation wavelength of the LD deviates from λo. As a result, L
Even if the temperature of D and the injection current of LD are set to predetermined values, a desired oscillation wavelength cannot be obtained, and there is a possibility that the wavelength is locked to a different wavelength. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a wavelength stabilizing apparatus which can always stabilize a desired wavelength even when an LD or the like changes with time and has improved reliability. And In order to achieve the above object, a semiconductor laser, a wavelength discriminating element for discriminating a wavelength of a laser beam output from the semiconductor laser, and an output light of the wavelength discriminating element are provided. A photodetector for detecting the intensity, a first storage unit for updating and storing the temperature of the semiconductor laser according to a temporal change during operation, and a temperature control when the wavelength stabilizing device is operated from the beginning. Sometimes, a temperature control unit that starts temperature control using the temperature of the semiconductor laser finally stored in the first storage unit, and updates an injection current value of the semiconductor laser according to a temporal change during operation. And a second storage unit for storing and storing the injection current value of the semiconductor laser finally stored in the second storage unit when controlling the injection current when the wavelength stabilizing device is operated from the beginning. An injection current control unit for starting control, wherein the temperature control unit, when the injection current value supplied to the semiconductor laser from the injection current control unit fluctuates beyond a certain value, the temperature of the injection current A temperature change corresponding to the variation is calculated, and the set temperature of the semiconductor laser is changed using the calculation result. The temperature controller of the wavelength stabilizing device according to the first aspect controls the temperature so that the temperature of the LD becomes the set temperature. Is stored in the first storage unit. When starting the temperature control when the wavelength stabilizing device is operated from the beginning, the control is finally performed using the temperature of the LD stored in the first storage unit as the set temperature. When the value of the injection current supplied from the injection current control unit to the LD fluctuates beyond a certain value, a temperature change corresponding to the fluctuation of the injection current is calculated, and the calculation result is used to calculate the temperature of the LD. Change the set temperature. Here, the set temperature is changed by the temperature control unit in accordance with a change in the injection current of the LD. Embodiments of the present invention will be described below. FIG. 1 is a configuration diagram of a wavelength stabilizing device according to a first embodiment of the present invention. As shown in FIG.
The LD 12 having the characteristic shown by the symbol is provided. An injection current i1 held at a constant value is supplied from the LD injection current control unit 13 to the LD12. LD12
Is split by a beam splitter 15 and one light is incident on an etalon 14 as a wavelength discriminating element. The other laser beam is guided to a length measuring optical system (not shown) as length measuring light. The transmitted light of the etalon 14 is incident on a PD 16 as a photodetector, and the output of the PD 16 is input to an LD temperature controller 17. The temperature of the LD 12 is detected by a thermistor 18 and input to the LD temperature control unit 17. A storage unit 20 in which an initial set temperature is stored is connected to the LD temperature control unit 17. The LD temperature control unit 17 performs temperature control at the start of the temperature control using the initial set temperature of the storage unit 20 so that the temperature of the LD becomes the initial set temperature.
Using the 16 outputs, the temperature control is performed so that the PD output has a predetermined set value or always has a peak value. Next, the operation in the case of stabilizing the oscillation wavelength of the LD 12 at λo in this embodiment having the above-described configuration will be described. The LD injection current control section 13 always performs constant current control so that the injection current of the LD 12 becomes i1. The LD temperature controller 17 reads the initial set temperature from the storage unit 20 and controls the current of the Peltier element 19 so that the temperature detected by the thermistor 18 becomes the initial set temperature. Thereafter, when the detected temperature of the thermistor 18 becomes substantially equal to the initial set temperature, the LD temperature control unit 17 performs the temperature control according to the output of the PD 16 instead of the initial set temperature. If the transmission characteristic of the etalon 14 is as shown in FIG. 5, the output of the PD 16 has a peak value when the oscillation wavelength of the LD 12 is λo. Therefore,
The LD temperature control unit 17 may control the temperature of the LD 12 so that the output of the PD 16 always has a peak value. At this time, the temperature of the LD 12 deviates from T1 (° C.) with time . Therefore, the detected temperature of the thermistor 18 when the LD temperature control unit controls the temperature using the output of the PD 16 is stored in the storage unit 20 as an initial set temperature when the temperature control is next started, and is updated. To go. Next, when the temperature control is started, the updated value in the storage unit 20 is controlled as the initial set temperature. That is, the storage unit 20 stores the oscillation wavelength of the LD
The optimum temperature of the LD 12 to be set to o is stored. As described above, according to the present embodiment, even if the oscillation wavelength of the LD with respect to the temperature T1 (° C.) and the injection current i1 deviates from λo due to the aging of the LD 12, the LD for obtaining the desired oscillation wavelength λo. Is stored in the storage unit 20,
Since this is updated, the optimal initial temperature corresponding to the current change with time can be immediately set at the start of the next control, and the desired oscillation wavelength λo can always be stabilized. FIG. 2 is a configuration diagram of a wavelength stabilizing device according to a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals. This embodiment is an example in which the temperature of the LD is controlled to be constant, the injection current of the LD is changed according to the temporal change of the LD, and stored in the storage unit. In the wavelength stabilizing device of this embodiment, a storage unit 20 'storing an injection current value is connected to an injection current control unit 13', and the output of the PD 16 is input to the injection current control unit 13 '. The injection current value stored in the storage unit 20 'is a value that can obtain a desired oscillation wavelength λo with respect to the current change with time of the LD 12, similarly to the temperature of the LD of the first embodiment. Here, it is assumed that the LD 12 has the characteristics as shown in FIG. 6, as in the first embodiment. The LD temperature control section 17 'sets a preset temperature in advance, and controls the temperature of the LD 12 detected by the thermistor 18 to be the preset temperature. An operation in the case where the oscillation wavelength of the LD 12 is stabilized at λo in the above configuration will be described. In this embodiment, the LD 12 is controlled to a constant temperature T1 (° C.) by the LD temperature controller 13 '. Then, the LD injection current control unit 13 ′ reads the initial injection current value from the storage unit 20 ′ and supplies it to the LD 12. The LD injection current control section 13 'controls the injection current so that the output of the PD 16 always has a peak value. At this time, the injection current value of the LD should be near i1, but as the LD 12 changes over time, i1
It shifts from. Therefore, the current injection current value of the LD is
Next, the initial injection current value at the time of starting the injection current control is stored in the storage unit 20 'and updated. Next, when starting the injection current control, the updated value in the storage section 20 'is controlled as the initial injection current value. That is, the optimum injection current value of the LD 12 at the point in time at which the oscillation wavelength λo of the LD 12 is stored in the storage unit 20 '. According to this embodiment, the same operation and effect as those of the first embodiment can be obtained. FIG. 3 shows a configuration diagram of a wavelength stabilizing device according to a third embodiment of the present invention. Note that the first and
The same parts as those in the second embodiment are denoted by the same reference numerals. Here, it is also assumed that the LD 12 has characteristics as shown in FIG. In the wavelength stabilizing device of the present embodiment, the LD temperature control unit 23 uses the LD 12 based on the initial set temperature stored in the storage unit 25.
Is started, and thereafter, the operation is performed so that the temperature of the LD becomes the set temperature. The injection current control unit 21 starts supplying the injection current to the LD 12 based on the injection current value stored in the storage unit 22. After setting the injection current value in the storage unit 22 as an initial value, the LD injection current control unit 21 monitors the output of the PD 16 in the same manner as in the above-described second embodiment, and the output of the PD 16 always has a peak value. The value of the injection current is controlled as described above. The storage contents of the storage unit 22 are sequentially updated with the injection current value. On the other hand, the LD injection current control unit 21
Is supplied to the LD temperature control unit 23. The LD temperature control unit 23 changes the set temperature when the injection current value fluctuates beyond a certain width. That is, a change in the temperature of the LD 12 or a direction in which the temperature is changed (corresponding to the same wavelength change) corresponding to the change in the injection current is calculated, and the set temperature is changed. The LD temperature control unit 23 changes the set temperature according to the change of the injection current, and updates the contents stored in the storage unit 25 to the new set temperature. Thereafter, the temperature control is performed at the set temperature after the change. When the wavelength stabilizing device is operated again from the beginning, the wavelength stabilization control is started by using the contents stored in the storage units 22 and 25 in the previous operation as initial setting conditions. As described above, according to the present embodiment, it is possible to always stabilize the oscillation wavelength of the LD at a desired wavelength in response to a temporal change wider than in the first and second embodiments. Also,
Since the operation can be started with the initial setting values (the injection current value of the LD and the set temperature of the LD) according to the current temporal change of the LD 12, the stabilization time can be shortened and the power fluctuation of the laser beam can be reduced. . In the third embodiment, the LD temperature controller 23
Performs constant temperature control with respect to the set temperature, but the effect of the present embodiment is not limited to such a configuration. That is, the same effect can be obtained when both the LD injection current control unit 21 and the LD temperature control unit 23 operate so that the output of the PD 16 becomes a predetermined value. Note that the first and second embodiments described above,
Alternatively, in the combination of the first embodiment and the second embodiment, instead of sequentially updating the storage contents of the storage unit, the initial values of the injection current and the set temperature are always stored, and LD
The injection current control unit and the LD temperature control unit control the injection current value of the LD and the temperature of the LD so that the output of the PD becomes a predetermined value. On the other hand, an alarm unit having a comparison function is provided, and the initial value of the LD injection current and the LD set temperature stored in the storage unit and the current injection current value and L
D, and if the difference exceeds the threshold, LD
An alarm for notifying the change with time is output. According to such a wavelength stabilizing device, the LD
It is very effective to know the replacement time. Also,
In the first, second, and third embodiments, the storage unit
As well as updating the stored contents of
The initial value of the flow and the set temperature are always stored and the comparison function is provided.
Initial value and current value of injection current and set temperature by alarm means
And if the difference exceeds a certain threshold, the LD
An alarm to notify time change is output. In this configuration, as described above, the LD
Know the replacement time and remove the effects of LD aging.
The wavelength can be stabilized over a long period of time. Furthermore, in the above description, the main effect is that it can cope with the aging of the LD, but not only that, but also the aging of the temperature sensor of the LD (thermistor in the embodiment) and the temperature sensor peripheral detection system. And so on. In the above description, an etalon has been described as an example of the wavelength discriminating element. However, similar effects can be obtained by using an absorption spectrum of atoms and molecules, a diffraction grating, or the like. The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. As described above, according to the present invention, L
The deviation of the oscillation wavelength can be compensated for in response to the aging of D, and even if the LD or the like changes with time, a desired wavelength can always be stabilized and a wavelength stabilizing device with improved reliability can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a wavelength stabilizing device according to a first embodiment of the present invention. FIG. 2 is a configuration diagram of a wavelength stabilizing device according to a second embodiment of the present invention. FIG. 3 is a configuration diagram of a wavelength stabilizing device according to a third embodiment of the present invention. FIG. 4 is a configuration diagram of a conventional wavelength stabilizing device. FIG. 5 is a diagram showing wavelength discrimination characteristics of an etalon provided in the wavelength stabilizing device. FIG. 6 is a graph showing the relationship between injection current and oscillation wavelength of a laser diode at different temperatures. FIG. 7 is a diagram showing a temporal change of a laser diode. [Description of Signs] 11 ... light source unit, 12 ... laser diode, 13, 21 ...
LD injection current control unit, 14: etalon, 16: photodiode, 17: LD temperature control unit, 20, 22, 25 ...
Storage unit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-318788 (JP, A) JP-A-1-187574 (JP, A) JP-A-63-143888 (JP, A) JP-A-61-1987 264774 (JP, A) JP-A-2-71572 (JP, A) JP-A-62-24822 (JP, A) JP-A-58-21386 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (1)

(57) Claims: 1. A semiconductor laser, a wavelength discriminator for discriminating a wavelength of a laser beam output from the semiconductor laser, and a photodetector for detecting the intensity of the output light of the wavelength discriminator. And a first storage unit for updating and storing the temperature of the semiconductor laser in accordance with a temporal change during operation, and the first storage for temperature control when the wavelength stabilizing device is operated from the beginning. A temperature control unit that starts temperature control using the temperature of the semiconductor laser finally stored in the unit; and a second control unit that updates and stores an injection current value of the semiconductor laser according to a temporal change during operation. A storage unit, and an injection current for starting control using an injection current value of the semiconductor laser finally stored in the second storage unit during injection current control when the wavelength stabilizing device is operated from the beginning. Control unit The temperature control unit, when the injection current value supplied to the semiconductor laser from the injection current control unit fluctuates beyond a certain value, calculates a temperature change corresponding to the fluctuation amount of the injection current. A wavelength stabilizing device for changing a set temperature of the semiconductor laser using the calculation result.