JP3347644B2 - Laser light source device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light source device for stabilizing the wavelength of a laser light source such as a semiconductor laser used for optical communication or the like and oscillating.

[0002]

2. Description of the Related Art At present, in optical communication, wavelength multiplexing communication in which light of a large number of wavelengths is multiplexed on an optical fiber and communication is performed, thereby greatly increasing the transmission amount as compared with the case of using light of a single wavelength. A method is being considered. In order to realize wavelength division multiplexing communication, laser light of many wavelengths is transmitted at intervals of, for example, 1 nm or less within a relatively narrow wavelength band where the optical signal can be amplified as it is, so that the wavelength of the laser light source is sufficiently stabilized. You need to keep it. Further, in optical information processing and optical measurement, stabilization of the wavelength of a laser light source is an important issue in order to increase the density of information and increase the accuracy of measurement.

In order to stabilize the emission wavelength of a laser light source, for example, an element having a reference wavelength characteristic is used, an error from the emission wavelength is detected by some method, and the error is fed back to the laser light source. For this reason, conventionally, a device that stabilizes the wavelength based on the absorption of atoms or molecules using the absorption of atoms or molecules, or the wavelength of the reference light or light source using holography, grating or Mach-Zehnder interferometer or Fabry-Perot interferometer, is determined by dithering. A method of modulating and adjusting the wavelength is known. Dithering is to slightly oscillate the wavelength of light by some method. The dither is used to determine the difference and the direction from the reference wavelength and feed back to the laser light source to stabilize the emission wavelength. In addition, a method of stabilizing the emission wavelength of a laser light source by using a multi-layered interference light filter, an etalon, or the like as a wavelength reference and using a wavelength reference is also used.

In Japanese Patent Application Laid-Open No. 60-74687, light from a semiconductor laser is separated without dithering, and two filters having slightly different wavelengths are used. A method has been proposed in which the light is detected by a conversion element and fed back to a semiconductor laser so that the light intensity ratio is constant.

[0005]

However, in such a conventional method, the light source is slightly changed by dither to change the emission wavelength, the direction is electrically determined, and the change with respect to the reference is detected. Since the feedback is made to the semiconductor laser as the light source, the light of the light source is modulated. For this reason, there is a possibility that the signal may overlap with the modulated signal as information, and there is a drawback that an electric filter such as a low-pass filter or the like is required to eliminate the influence of dither. In addition, since dither is used, the control system becomes complicated. When the dither has a movable part, there is a problem that reliability is low and life is shortened. In the method of JP-A-60-74687,
A beam splitter or the like is required to split light, but the beam splitter is affected by the polarization of the light, and the spectral ratio tends to change depending on the temperature. There was a drawback that it was difficult to make. Also, there is a disadvantage that it is difficult to manufacture two optical filters having slightly different transmission wavelengths.

In order to use the stabilized light, a part of the laser light is added to a wavelength stabilizing device using a beam splitter for splitting the laser light, and the other part is used as a stabilized laser light. Therefore, there is a disadvantage that a beam splitter is required separately from the wavelength stabilizing device.

The present invention has been made in view of such a conventional problem. A beam splitter and a wavelength stabilizing device are integrated with each other to achieve a highly accurate wavelength stabilization with an extremely simple configuration. It is an object to provide a laser light source device that can emit laser light.

[0008]

According to a first aspect of the present invention, there is provided a laser light source capable of continuously changing the wavelength of light, and a transmission wavelength of an optical filter as a cutoff wavelength.
A cut filter, and a beam splitter that receives the laser light from the laser light source, splits the incident laser light into branched light and transmitted light at a predetermined branching ratio of 1: N, and emits the transmitted light as a laser light output. When the incident beam splitter branched light transmits light of a predetermined wavelength, said optical filter and said optical filter to be incident again on the beam splitter by reflecting other, the branched by the beam splitter branched light A slide adjustment mechanism for continuously changing the incident position on the optical axis with respect to the predetermined direction, a first light receiving element for receiving the transmitted light of the optical filter, and the beam of the branched light reflected by the optical filter A second light receiving element for receiving light transmitted through the splitter, and an amplifier for compensating by amplifying an output of the second light receiving element in accordance with the branching ratio N Wherein the output ratio calculating means for calculating a normalized output ratio of the first light receiving element and the amplifying element is provided in the vicinity of the optical filter, the temperature detection for detecting the temperature in the vicinity of said optical filter Temperature compensating means for compensating for a change in characteristics due to a temperature change of the interference light filter based on an output of the temperature detecting means by correcting a target value of an output ratio output from the output ratio calculating means. Wavelength control means for controlling an emission wavelength of the light source so that a target value of an output ratio output by the temperature compensation means becomes a predetermined value, wherein the optical filter has a wavelength λ with respect to a transmission wavelength λ. Low-refractive-index films and high-refractive-index films having an optical thickness of / 4 are alternately stacked in multiple layers, and the transmission wavelength λ is continuous in a predetermined direction of the substrate at least within the emission range of the laser light source. Target Characterized in that the optical thickness to vary is obtained continuously changed.

[0009]

[0010]

[0011]

According to a second aspect of the present invention, in the laser light source device according to the first aspect, the wavelength control means detects a difference between the output ratio calculated by the output ratio calculation means and a predetermined reference value. Error detection means, reference value setting means for setting a reference value to the error detection means, and light source driving means for controlling the emission wavelength of the laser light source so that the error value detected by the error detection means becomes zero. And the following.

[0013]

[0014]

According to the present invention having such features,
The laser light source is caused to emit light, and the laser light is incident on the beam splitter. The beam splitter transmits a part of the light and branches the other light, and makes the branched laser light incident on the optical filter. The optical filter transmits light of a predetermined wavelength and reflects others. The light transmitted through the optical filter and the light reflected and transmitted again through the beam splitter are received by the first and second light receiving elements, respectively, and the output of the second light receiving element is compensated according to the branching ratio. The output ratio is calculated by the output ratio calculating means. Then, by controlling the emission wavelength of the laser light source so that the output ratio becomes a predetermined value, laser light of a predetermined wavelength can be emitted. Further, the optical filter is realized by an interference light filter of a multilayer film, and a wavelength variable interference light filter configured so that the transmission wavelength continuously changes in a predetermined direction is used, and its light receiving position is changed. Then, the emission wavelength of the laser light source can be changed. Also, a cutoff between the light source and the optical filter
By providing a filter, one of the characteristics of the optical filter
To define only one slope as a lock point
It was done. In the present invention, the reference value is set by the reference value setting means, and the difference between the output ratio calculated by the output ratio calculation means and the reference value is detected by the error detection means as an error. By controlling the laser light source so that the error becomes zero by the light source driving unit, the emission wavelength of the laser light source can be finely adjusted.

[0016]

FIG. 1 is a block diagram showing the overall configuration of a laser light source device according to a first embodiment of the present invention. In this figure, the laser light source uses a distributed feedback laser diode (LD) 1 in this embodiment, and emits laser light having one line spectrum. The emission wavelength of the laser light source can be externally controlled by current or temperature control, for example, within a range of 2 to 3 nm.
This laser light is guided to the optical fiber 2.

At the other end of the optical fiber 2, there are provided a lens 3 for converting a laser beam incident from the optical fiber 2 into parallel light and a cut filter 4 for shielding a part of the incident light. The transmitted light is provided to the beam splitter 5. The beam splitter 5 is a light splitting unit that splits light by, for example, depositing a metal film or a multi-layered dielectric film on a glass substrate, and transmits part of incident light and reflects the other. The transmitted light enters the optical fiber 7 via the lens 6. The other end of the optical fiber 7 is connected to a measuring device, an optical communication device, or the like using stabilized laser light as a light source.
The light split by the beam splitter 5 is provided to the optical bandpass filter 8. The optical bandpass filter 8 is arranged perpendicular to the split laser beam and has a constant transmission wavelength. The photodiode PD1, which is the first light receiving element, is disposed at a position where the light passes through the optical bandpass filter 8, and a position symmetrical to the photodiode PD1, that is, a position where the reflected light of the optical bandpass filter 8 is received beyond the beam splitter 5 , A photodiode PD2 as a second light receiving element is disposed. The outputs of the photodiodes PD1 and PD2 are provided to an output ratio calculating means 9. The output ratio calculation means 9 calculates the output ratio of the two input signals and outputs a monitor signal, and the output is given to the wavelength control means 10. The wavelength controller 10 controls the emission wavelength of the laser light source so that the output ratio of the output ratio calculator 9 becomes a predetermined value. The emission wavelength of the laser light source is adjusted by changing the drive current of the laser diode 1 or changing the ambient temperature.

Next, the output ratio calculating means 9 and the wavelength control means 1
0 will be described with reference to FIG. Outputs from the first and second photodiodes PD1 and PD2 are provided to I / V converters 11a and 11b in the output ratio calculating means 9 and are converted into voltage signals. The output of the I / V converter 11b is given to an amplifier 12 having a gain corresponding to a branching ratio of the beam splitter 5, which will be described later, to compensate for the output level of the photodiode PD2. I / V converter 11a and amplifier 1
The output of 2 is provided to an adder 13 and a subtractor 14, and the respective outputs are added and subtracted and provided to a divider 15.
The divider 15 normalizes the light received by the photodiodes PD1 and PD2, and detects the wavelength of the input light based on the output ratio. Here, the I / V converter 11
a, 1b, an amplifier 12, an adder 13, a subtractor 14, and a divider 15 constitute an output ratio calculating means 9 for detecting the wavelength of the laser beam based on the output ratio of the first and second light receiving elements.
The output is provided to an error detector 16. Error detector 1
A reference voltage is applied to the other input terminal of the reference numeral 6. This reference voltage is set between + V _CC and −V _DD by reference value setting means 17,
For example, it is configured to be adjustable by the variable resistor VR1. The error amplifier 16 detects a difference between the reference voltage and the input voltage as an error signal, and outputs the error signal to a PID control unit 18.
Give to. The PID control section 18 performs PID control so that the error signal becomes 0, and the output is fed back to the laser diode 1 via the laser diode drive section 19. The laser diode drive unit 19 controls the current flowing through the laser diode 1 or the temperature of the laser diode 1 so as to control the emission wavelength of the laser diode 1 so as to change within a range of, for example, 2 to 3 nm or less. is there. Here, the error detector 16 and the variable resistors VR1 and PI that apply a reference voltage to the error detector 16 are used.
The D control unit 18 and the laser diode driving unit 19 constitute a wavelength control unit 10 that controls the emission wavelength of the laser light source so that the output ratio of the output ratio calculation unit 9 becomes a predetermined value.

The optical bandpass filter 8 uses a multilayer optical interference filter in which high refractive index films and low refractive films having an optical thickness of λ / 4 with respect to the transmission wavelength λ are alternately laminated. By providing a cavity layer having an optical film thickness of λ / 2 at the intermediate portion, the optical fiber is configured to have an optical band-pass filter characteristic for transmitting light of a certain wavelength.

Next, the operation of the laser light source device according to this embodiment will be described. Laser light oscillated by the laser diode 1 enters the cut filter 4 via the optical fiber 2 and the lens 3. FIG. 3A shows a cut filter 4.
3 (b) and 3 (c) are graphs showing transmittance and reflectance characteristics of the optical bandpass filter 8. FIG. The cut filter 4 selects a characteristic that transmits light having a longer wavelength and cuts light having a shorter wavelength by using the center wavelength λ1 of the optical bandpass filter 8 as a cutoff wavelength in advance. The light that has passed through the cut filter 4 enters the beam splitter 5. Here, the branching / transmission ratio of the beam splitter 5 is set to 1: N. The laser light transmitted through the beam splitter 5 enters the optical fiber 7 via the lens 6. On the other hand, the split light reflected by the beam splitter 5 enters the optical bandpass filter 8. Then, only a part of the light passes through the optical bandpass filter 8 and enters the photodiode PD1. As shown in FIGS. 3B and 3C, the optical bandpass filter 8 has a characteristic of transmitting light of a predetermined wavelength λ1 and reflecting other light. Therefore, the light reflected by the optical band-pass filter 8 enters the beam splitter 5 again, is branched at a ratio of 1: N, and the transmitted light enters the photodiode PD2. At this time, the light outputs obtained by the photodiodes PD1 and PD2 with respect to the emission wavelength λ of the laser diode 1 are as shown in FIGS. 3D and 3E, respectively. Amplifier 1
Numeral 2 compensates for a decrease in the output level due to the light branching of the photodiode PD2 at this time. This way I
The outputs obtained from the / V converter 11a and the amplifier 12 correspond to the transmittance in FIG. 3B and the reflectance in FIG. 3C, respectively.

The level of the transmitted light incident on the photodiode PD2 is determined by the branching ratio 1: N of the beam splitter 5. For example, if the emission wavelength is set to be fixed when the transmission and reflection ratio of the optical bandpass filter 8 is 1: 1, the branching ratio of the beam splitter 5 is 1: 1.
In the case of 1, PD2 with respect to PD1 as shown in FIG.
Is fixed at 0.5. Similarly, when the branching ratio of the beam splitter 5 is 1:10,
The light receiving ratio of PD2 is 0.9, and when the branching ratio is 1: 100, the light receiving ratio is 0.99. By increasing the branching ratio N in this manner, the light receiving levels of PD1 and PD2 can be reduced as shown in FIG.
As shown in FIG. Therefore, if the branching ratio N is sufficiently large, the gain of the amplifier 12 may be 1, and
The amplifier 12 may be eliminated.

Accordingly, assuming that the outputs of the I / V converter 11a and the amplifier 12 are A and B, these are added and subtracted, and the result is divided by the divider 15 to calculate (AB) / (A + B). The level normalized by the division is as shown in FIG. As described above, the wavelength monitor signal changes continuously according to the emission wavelength of the laser light source. The difference value between the level of the wavelength monitor signal and the reference voltage of the error detector 16 is used as an error signal, and the error signal is controlled to be zero so that the error signal matches the reference voltage set in the error detector 16. The wavelength of the laser diode 1 can be controlled. For example, if the reference voltage is 0 V, the I / V converter 11
When the wavelength a2 and the output level of the amplifier 12 are equal, the error signal becomes 0, and the emission wavelength of the laser diode can be controlled to λ2. Fig. 5
, The wavelength is locked to λ4 on the short wavelength side. By changing the reference voltage of the error detector 16 in this manner, the emission wavelength can be finely adjusted within the wavelength range of λ1 to λ3 shown in FIGS.

Here, the beam splitter 5 for splitting the laser beam uses a beam splitter having a predetermined splitting ratio, but the splitting ratio varies within a certain range depending on the temperature, the polarization plane, and the like.
When the branching ratio N changes depending on such a change in temperature or polarization plane, the level of light received by the two photodiodes PD1 and PD2 changes. However, as the branching ratio N of the beam splitter 5 increases, the ratio of the amount of fluctuation received by the two photodiodes PD1 and PD2 decreases as shown in FIG. In FIG. 6, the variation of the branch ratio is ± 0.
For three beam splitters 5 of 1%, ± 1%, and ± 10%, curves A, B, and C show the ratios of the fluctuation amounts of PD1 and PD2, respectively. If the branching ratio N of the beam splitter 5 is increased in this manner, even if a beam splitter having a large fluctuation in the branching ratio is used, the ratio of the fluctuation amount is small and almost 0%. The wavelength can be fixed.

FIG. 7 is a perspective view showing a state in which a branch / wavelength lock portion other than the laser light source of the laser light source device according to the first embodiment is housed in the case 21 as one module. In this embodiment, a part of the laser light enters via the optical fiber 2, and the light transmitted through the beam splitter is output from the optical fiber 7. In this case, a power supply line and a monitor output line are provided. The case 21 is provided with a knob 22 for finely adjusting the emission wavelength by adjusting the resistance value of the variable resistor VR1 of the reference value adjusting means. Further, the case may be configured to be airtight without exposing such a knob to the outside.

Next, a second embodiment of the present invention will be described with reference to FIGS. In this embodiment, the wavelength of the laser light of the light to be locked can be adjusted from outside. The same parts as those in the above-described first embodiment are denoted by the same reference numerals, and detailed description is omitted. In this embodiment, an interference light filter 30 is used instead of the optical bandpass filter 8.
The wavelength of the transmitted light can be continuously changed depending on the incident position in the longitudinal direction (X axis) of the substrate. The slide mechanism 31 mechanically slides the interference light filter 30 by a small distance in the X-axis direction while keeping the interference light filter 30 perpendicular to the laser beam to change the incident position. Other configurations are the same as those of the first embodiment.

Next, this interference light filter is disclosed in Japanese Patent Publication No. 7-92530.
This will be described next with reference to FIG.
Tunable interference light filter 30 according to the present embodiment
Is formed by depositing a multi-layer of a substance on a substrate 41 such as glass or silicon. The substrate 41 is made of a material having a high light transmittance in a wavelength range to be used, and a dielectric or a semiconductor is used. In this embodiment, quartz glass is used. Then, on the upper portion of the substrate 41, a multilayer film 42 of a deposition material, a dielectric, a semiconductor, or the like having a high light transmittance at a wavelength to be used is deposited. Here, it is assumed that the multilayer film 42 is formed from a lower multilayer film 43, a cavity layer 44, and an upper multilayer film 45 as shown. On the lower surface of the substrate 41, an antireflection film 46 is formed by vapor deposition.

[0027] Here, the multilayer film 42, the material used as the deposition material of the antireflection film 46, for example Si O ₂ (refractive index _{n = 1.46), Ta 2 O} 5 (n = 2.15), Si (n = 3.46)
And Al ₂ O ₃ , Si ₂ N ₄ , MgF and the like are used. In this embodiment, the multilayer films 43 and 45 are formed by alternately stacking low-refractive-index films and high-refractive-index films. Here, the thickness d, the transmission wavelength λ, and the refractive index n are set to have the following relationship. λ = 4nd (1) That is, each layer has an optical thickness nd of λ / 4. By alternately stacking low-refractive-index films and high-refractive-index films, the full width at half maximum (FWHM) of the transmittance peak is reduced. The thickness d _c of the cavity layer 44 is the transmission wavelength λ,
The following relationship is established with the refractive index n. λ = 2nd _c (2) That is, the optical thickness nd _c of the cavity layer 44 is λ / 2.

The interference light filter 3 according to the present embodiment will now be described.
In the case of 0, since the transmission wavelength and the film thickness have the relationship of the formulas (1) and (2), the substrate 41 is an elongated plate-like substrate, the refractive index of the multilayer film 42 is constant, and the film thickness is continuous. The transmission wavelength λ is changed by changing the transmission wavelength λ. The transmission wavelength of the tunable interference light filter 30 is set to λ
_{a to} λ _c (λ _a <λ _c ), and the center point (x = x _b )
Let λ _{b be} the transmission wavelength at. Upper and lower multilayer films 43 and 45
Is formed by alternately laminating a first deposited material film having a first refractive index n _{1 and} a second deposited material film having a second refractive index n ₂ having a lower refractive index. That is, as shown in FIG. 9 (c), an enlarged view of the circular portion in FIG. 9 (a), each film thickness is continuously changed. In FIG. 9C, the low refractive index film of the lower multilayer film 43 is 43L, the high refractive index film is 43H, the high refractive index film of the upper multilayer film 45 is 45H, and the low refractive index film is 45L. And with respect to the transmission wavelength lambda _a end x _a on the X-axis of the filter of FIG. 9 (a), respectively a low refractive index film and a high refractive index film in the above equation (1), holds true (2) Set as follows. The x _b, the transmission wavelength lambda _b at x _c, with respect to lambda _c, the wavelength lambda _b, wherein at lambda _c (1), and sets the film thickness so that holds true (2). The film thickness between them is also set such that the change in wavelength changes linearly. Therefore, each film thickness of the multilayer film is set at positions x _a to x on the x-axis as shown in the figure.
It changes continuously with _c , and the film thickness increases in the positive direction of the X-axis.

As described above, by continuously changing the film thickness, when the multilayer film 42 is formed on the substrate 41 by vapor deposition, the substrate is so formed as to continuously change the distance from the vapor deposition source. This can be realized by arranging them at an angle.

Although the thickness of the interference light filter 30 is continuously changed, each thickness is fixed, and the refractive indexes n ₁ and n ₂ of the multilayer film 42 are continuously changed in the X-axis direction. The optical thickness may be varied continuously by changing the optical thickness.

The interference light filter 3 constructed as described above
0 has a narrow band characteristic, and has a sufficiently stable characteristic against a temperature change or the like. Therefore, the interference light filter 30
By mechanically moving the position where light is incident in the X-axis direction using the slide adjustment mechanism 31, the transmission wavelength itself can be continuously changed. In this case, the branched light is converted by the slide adjusting mechanism 31 into the photodiode P.
The wavelength incident on D1 changes, and the locking wavelength can be changed.

FIG. 10A is a perspective view showing a state in which a branch / wavelength lock portion other than the laser light source of the laser light source device according to the second embodiment is housed in the case 32 as one module. In this embodiment, in order to greatly change the emission wavelength of the laser diode 1, the adjustment knob 33 of the slide adjustment mechanism 31 is rotated to change the incident position of the incident light on the interference light filter 30. In this way, the transmission wavelength λ1 of the interference light filter 20 shown in FIGS. 3B and 3C can be changed. In this case, it is necessary to use a filter having characteristics corresponding to the cut filter 4. In this way, the wavelength at which light can be emitted can be greatly changed. Therefore, if the emission wavelength is roughly adjusted by the incident position on the interference light filter 30 and the fine adjustment of the wavelength is adjusted by changing the reference voltage of the reference value setting means 17, the user can set the wavelength to an arbitrary one. It becomes possible.

In the above-described second embodiment, the slide adjusting mechanism 31 and the knobs 33 and 34 of the variable resistor VR1 are used.
Can be adjusted from outside the case.
As shown in FIG. 0 (b), the wavelength may be changed only by the knob 33 of the slide adjustment mechanism 31 without providing the reference value setting means by the variable resistor VR1. FIG. 1
As shown in FIG. 0 (c), the laser light is set to a wavelength required at the time of manufacture, and the knob 33 of the slide adjustment mechanism 31 and the knob 34 of the variable resistor VR1 for fine adjustment are not exposed to the outside of the case. The emission wavelength of the light source may not be adjusted. This makes it possible to realize a stabilizing device in which the emission wavelength of the laser light source is stabilized with an extremely simple configuration without the need for the user to adjust the wavelength one by one, and hermetic sealing becomes easy. Also, without exposing the knob 33 of the slide adjusting mechanism 31 to the outside of the case 32, FIG.
As shown in (d), only the knob 34 of the variable resistor VR1 for fine adjustment may be adjustable. In this case, the user can fine-tune the emission wavelength within a predetermined range of the set wavelength by setting the required wavelength by the slide adjustment mechanism 31 at the time of manufacture.

Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, the beam splitter 5 is not a beam splitter in which metal or a dielectric multilayer film is deposited on glass, but is formed by fusing two optical fibers. In this embodiment, the laser light emitted from the laser diode 1 is guided to the optical fiber 51 via the lens 3 and the cut filter 4. Optical fiber 5
1 is directly connected to a measuring device or an optical communication device. Then, another optical fiber 52 is closely arranged on a part of the optical fiber 51, and a part thereof is fused. A part of the laser beam transmitted through the optical fiber 51 is fused by the fusion portion 53 into the optical fiber 52.
The light is guided to the photodiode PD1, which is the first light receiving element, via the optical bandpass filter 8 as described above. In order to receive the light reflected by the optical bandpass filter 8, a photodiode PD2 as a second light receiving element is provided at the other end of the optical fiber 52. In this way, a part of the reflected light from the optical bandpass filter 8 can be received by the photodiode PD2. Other configurations are the same as those of the first embodiment. Further, as in the second embodiment, an interference light filter 30 may be used instead of the optical bandpass filter 8 to shift the incident position in the X-axis direction. In this case, since the beam splitter 5 using a glass substrate is unnecessary and the number of lenses can be reduced, the optical branching / wavelength lock module can be made extremely small. Also, the number of parts is reduced, and the cost can be reduced.

In the first and second embodiments described above,
Although the adder, the subtractor, and the divider for calculating the output ratio are provided as the signal processing circuit, the ratio of the output of the I / V converter 11a to the output of the amplifier 12 may be directly calculated. Not even. Alternatively, the lock point may be set at two positions on the slope of the transmission / reflection characteristics as shown in FIGS. 3B and 3C without providing the cut filter 4. In this case, the emission wavelength can be fixed to one of the two lock points depending on the moving direction of the error signal.

Although a laser diode is used as a laser light source in the above-described embodiment, other laser light sources may be used. In the above-described first and second embodiments, the beam splitter 5 is a beam splitter in which a metal or a dielectric multilayer film is deposited on glass, and in the third embodiment, one of the two optical fibers is used. Although the part is a beam splitter fused, it is possible to use other various light branching elements as long as they are configured as a two-input two-output light branching element by using an optical planar waveguide and crossing or coupling. It goes without saying that you can do it.

In the above-described embodiment, the amplifier 1 amplifies the output of the I / V converter 11b in the output ratio calculating means.
2, the emission wavelength may be fixed in a state where the output level of the photodiode PD2 is reduced due to the branching ratio of the beam splitter 5. Beam splitter 5
If the branching ratio N is sufficiently large, the photodiode PD1,
Since the output laser of PD2 becomes almost equal, the amplifier 12
There is no need to provide

Next, a laser light source device according to a fourth embodiment of the present invention will be described. In this embodiment, since the optical filters according to the first and second embodiments have a temperature dependency, it is possible to compensate for the temperature and output a light source having a constant wavelength regardless of the ambient temperature. It was made. FIG. 12 shows a configuration of the temperature compensating means 60 for temperature compensating the output ratio calculated by the output ratio calculating means. The temperature compensating means 60 is calibrated including the temperature detecting means 61 and the adder 62. The temperature detecting means 61 detects the ambient temperature of the optical bandpass filter 8, and its output is given to the adder 62. The adder 62 adds the temperature detection signal such that the output from the output ratio calculating means 9 has a substantially linear temperature characteristic with respect to the temperature as shown by the curve A in FIG. In this case, the temperature can be corrected very easily.
As shown by the curve B, there is obtained an effect that a laser beam having a substantially constant wavelength characteristic can be output regardless of the ambient temperature.

[0039]

As described in detail above, the claims of the present application are described below.
According to the inventions of the first and second aspects, the emission wavelength of the light source is controlled based on the ratio between the transmitted light and the reflected light of the optical filter by using the beam splitter and the optical filter. Therefore, a beam splitter can be built in, and by increasing the branching ratio of the optical branching means, it is possible to obtain high-precision wavelength accuracy without being affected by the branching ratio of the beam splitter and the wavelength dependency. it can. Further, by controlling the position of incidence on the interference light filter, the effect that the emission wavelength can be controlled within a wide range can be obtained. Further, by detecting the ambient temperature and compensating for the output of the output ratio calculating means, it is possible to obtain an effect that a laser beam having a constant wavelength can be output without being affected by the ambient temperature. Also cutoff
Lock points can be limited to one using filters
Therefore, it is possible to simplify the configuration of the wavelength control means.
The above effect can be obtained. According to the second aspect of the present invention, it is possible to finely adjust the emission frequency of the laser light source by changing the reference value set by the reference value setting means.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a laser light source device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an output ratio calculation unit and a wavelength control unit of the laser light source device according to the first embodiment of the present invention.

FIG. 3 is a graph showing changes in characteristics of the cut filter, the interference light filter, and the photodiodes PD1 and PD2 with respect to the emission wavelength.

FIG. 4 is a diagram showing an output ratio of a photodiode with respect to a branching ratio of a beam splitter.

FIG. 5 is a graph showing a change in an error signal with respect to a wavelength.

FIG. 6 is a graph showing a change in the amount of change in the output of the photodiodes PD1 and PD2 with respect to the branching ratio of the beam splitter.

FIG. 7 is a perspective view illustrating a configuration of an optical branching / wavelength lock module according to the first embodiment.

FIG. 8 is a block diagram showing an overall configuration of a laser light source device according to a second embodiment of the present invention.

9A is a cross-sectional view illustrating a configuration of an interference light filter having a single cavity structure according to a second embodiment of the present invention, FIG. 9B is a graph illustrating a change in transmittance on the X axis,
(C) is an enlarged sectional view of the circular portion of (a).

FIG. 10 is a perspective view illustrating a configuration of an optical branching / wavelength lock module according to a second embodiment.

FIG. 11 is a block diagram showing an overall configuration of a laser light source device according to a third embodiment of the present invention.

FIG. 12 is a block diagram showing configurations of an output ratio calculating unit, a temperature compensating unit, and a wavelength controlling unit of a laser light source device according to a fourth embodiment of the present invention.

FIG. 13 is a graph showing a relationship between an ambient temperature and a wavelength before and after temperature compensation.

[Explanation of symbols]

 Reference Signs List 1 laser diode 2, 7, 51, 52 optical fiber 3, 6 lens 4 cut filter 5 beam splitter 8 optical bandpass filter 9 output ratio calculating means 10 wavelength control means 11a, 11b I / V converter 12 amplifier 13 adder 14 Subtractor 15 Divider 16 Error detector 17 Reference value setting means 18 PID control unit 19 Laser diode drive unit 21, 32 Case 22, 33, 34 Knob 30 Interference light filter 31 Slide adjustment mechanism 53 Fused part PD1, PD2 Photo Diode 60 Temperature compensation means 61 Temperature detection means 62 Addition means

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-157780 (JP, A) JP-A-58-97882 (JP, A) JP-A-62-119993 (JP, A) JP-A-6-199983 281812 (JP, A) JP-A-61-72209 (JP, A) JP-A-56-55087 (JP, A)

Claims (2)

(57) [Claims] 1. A laser light source capable of continuously changing the wavelength of light, and a cut-off wavelength having a transmission wavelength of an optical filter as a cut-off wavelength.
A beam splitter that receives the laser light from the laser light source, splits the incident laser light into branched light and transmitted light at a predetermined branching ratio of 1: N, and emits the transmitted light as a laser light output. the incident beam splitter branched light transmits light of a predetermined wavelength, said optical filter to be incident again on the beam splitter by reflecting another, to the optical filter of the split lights split by the beam splitter A slide adjusting mechanism for continuously changing the incident position of the light beam in the predetermined direction; a first light receiving element for receiving light transmitted through the optical filter; and the beam splitter among the branched lights reflected by the optical filter. A second light receiving element for receiving the light transmitted through the second light receiving element, and an amplifier element for compensating by amplifying the output of the second light receiving element in accordance with the branching ratio N. Seen, the first output ratio calculating means for calculating a normalized output ratio of the light receiving element and the amplifying element is provided in the vicinity of the optical filter, a temperature detecting means for detecting the temperature in the vicinity of said optical filter Temperature compensating means for compensating for a change in characteristics due to a temperature change of the interference light filter based on an output of the temperature detecting means by correcting a target value of an output ratio output from the output ratio calculating means, Wavelength control means for controlling an emission wavelength of the light source so that a target value of an output ratio output by the temperature compensation means becomes a predetermined value, wherein the optical filter has a wavelength of λ / A low-refractive-index film and an high-refractive-index film having an optical thickness of 4 are alternately multiplexed, and the transmission wavelength λ is continuous with respect to a predetermined direction of the substrate at least within the emission variable range of the laser light source. Strange A laser light source device characterized in that its optical thickness is continuously changed so as to form a laser. 2. An error detecting means for detecting a difference between an output ratio calculated by the output ratio calculating means and a predetermined reference value, a reference for setting a reference value in the error detecting means. 2. The laser light source according to claim 1, further comprising: a value setting unit; and a light source driving unit that controls an emission wavelength of the laser light source so that an error value detected by the error detection unit becomes zero. apparatus.