JPH098391A - Laser output light controller - Google Patents

Abstract

PURPOSE: To obtain a laser output light controller in which the output light from a variable wavelength laser light source operating in a single longitudinal mode can be stabilized upon variation of wavelength. CONSTITUTION: An external resonator type variable wavelength LD light source comprises an LD(laser diode) 1 and a diffraction grating 2. Laser light emitted from an end face of the LD 1 is amplified through a TWA(traveling wave optical amplifier) 16 and branched through an optical branch unit 8 before one branched light is outputted. The other branched light is converted through a light receiving circuit 10 into an optical output signal being fed to one input terminal of a comparator circuit 11 having the other input terminal being fed with a reference signal from a reference circuit 12. The comparator circuit 11 compares two input signals and delivers the comparison results to a TWA drive circuit 17 which controls current supply to the TWA 16 thus controlling the optical amplification factor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light output controller for controlling and stabilizing the fluctuation of output light in a laser light source having a variable wavelength.

[0002]

2. Description of the Related Art Conventionally, a reflection mirror is provided outside an LD (laser diode), and a resonator is constituted by the external reflection mirror and the end face of the LD to stabilize the oscillation wavelength of the LD. A laser has been devised. This external resonator type laser operates in the longitudinal single mode in both the steady state and the transient state of the LD. Therefore, this external resonator type laser is an indispensable element in the field of optical measurement technology that requires a tunable wavelength and a stable longitudinal single mode. FIG. 3 is a configuration diagram showing an example of the configuration of a laser light output control device for an external resonator type laser according to the prior art. Reference numeral 1 is an LD having one end surface 1a coated with an AR coating (non-reflection coating). Reference numeral 2 denotes a diffraction grating provided outside the end face 1a side of the LD 1, and through the collimator lens 3, LD
The other end face 1b of 1 and the diffraction grating 2 constitute a resonator. The diffraction grating 2 is for selectively oscillating the LD 1 in a specific longitudinal single mode. The laser light has a variable wavelength range of approximately 1480 to 1580 nm and is emitted from the end face (hereinafter referred to as the emission end face) 1b of the LD1.

The diffraction grating 2 described above is controlled by an angle adjustment drive circuit 4 and a phase adjustment drive circuit 5. The angle adjustment drive circuit 4 adjusts the angle of the diffraction grating 2 with respect to the emission end facet 1b of the LD1 to change the oscillation wavelength of the LD1. The phase adjustment drive circuit 5 satisfies the resonance condition by setting the resonator length to be an integral multiple of 1/2 of the wavelength with respect to the wavelength selected by the angle adjustment drive circuit 4 described above. .

Reference numeral 6 denotes an LD drive circuit, which controls the current injected into the LD1 to control the output intensity of the laser light emitted from the LD1. The laser light emitted from the emission end face 1 b is collimated through the collimator lens 3 and enters the optical isolator 7. The optical isolator 7 allows light to pass through in only one direction, and prevents the laser light emitted from the emission end face 1b from entering the LD 1 again due to reflection or the like. The laser light passing through the optical isolator 7 enters the optical branching device 8, and is reflected and transmitted. The optical branching device 8 transmits the incident light in the same direction as the incident direction and reflects it in the direction perpendicular to the incident direction, and the transmitted laser light is used as output light. The reflected light is condensed by the lens 9 and enters the light receiving circuit 10. The light receiving circuit 10 detects the power of incident light and outputs a light output signal, and the light output signal is input to one input end of the comparison circuit 11.

Reference numeral 12 is a reference circuit for outputting a reference signal of the output light, and the output reference signal is input to the other input terminal of the comparison circuit 11. The comparator circuit 11 compares the two input signals described above to detect a difference, and outputs a deviation signal corresponding to the difference to the LD drive circuit 6.
Then, based on this deviation signal, the LD drive circuit 6 described above controls the current injected into the LD 1 to control the output light.

In the above configuration, when changing the oscillation frequency of the LD 1, the operator first inputs a desired frequency value to the angle adjustment drive circuit 4. Based on this input information,
The angle adjustment drive circuit 4 changes the angle of the diffraction grating 2 with respect to the emission end facet 1b of the LD1, and changes the wavelength of the diffracted light that is incident on the LD1 again. Next, the phase adjustment drive circuit 5 adjusts the resonator length so that the diffracted light satisfies the resonance condition, and causes laser oscillation in the resonator. The laser light emitted from the emission end face 1b is collimated through the collimator lens 3, passes through the optical isolator 7, and then is transmitted and reflected by the optical branching device 8. The laser light transmitted through the optical branching device 8 becomes output light, and the reflected light is condensed by the lens 9 and enters the light receiving circuit 10. After that, the light receiving circuit 1
0, the comparison circuit 11, and the LD drive circuit 6 feed back the LD1 to stabilize the output light of the wavelength selected in the diffraction grating 2.

As another laser light output control device,
A laser light output control device using a variable optical attenuator shown in FIG. 4 has been devised. FIG. 4 is a configuration diagram showing a configuration example of a laser light output control device using a variable optical attenuator. The same parts as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 4, reference numeral 13 denotes a variable wavelength LD light source, which is similar to the external resonator type LD light source described above, but the LD which is a constituent element of the LD light source 13 is driven by a constant current. Reference numeral 14 is a variable attenuator that attenuates incident light, and is composed of optical components such as an ND filter,
The attenuation of incident light is changed by mechanically moving the ND filter or the like. Reference numeral 15 mechanically moves an ND filter, which is one component of the variable attenuator 14, to control the amount of attenuation of light propagating in the variable attenuator 14.

The laser light emitted from the LD light source 13 enters the variable attenuator 14 and is attenuated while propagating. Then, the light is transmitted and reflected by the optical branching device 8, and the transmitted light becomes output light. Further, the reflected laser light is condensed by the lens 9, its power is detected by the light receiving circuit 10, and an optical output signal is output. This optical output signal is input to the comparison circuit 11 and compared with the reference signal input from the reference circuit 12 to the comparison circuit 11. The comparison circuit 11 outputs a deviation signal according to the comparison result to the attenuator drive circuit 15, and the attenuator drive circuit 15 outputs the variable attenuator 14 based on the deviation signal.
Is controlled so that the output light becomes constant.

[0009]

By the way, in the laser light output control device shown in FIG. 3, when wavelength sweeping is performed, the above operation is repeated continuously.
Of the laser light emitted from the emission end face 1b is periodically changed due to a change in the reflection characteristics and the oscillation phase condition or a change in the oscillation condition due to the residual reflectance of the end face 1a of the LD1. In order to control this fluctuation, the light receiving circuit 10 and the comparison circuit 1
1, and LD drive 6 feeds back to LD1,
The current injected into LD1 is controlled. But LD1
When the current injected into the LD1 changes, the carrier density in the LD1 changes, and the refractive index in the LD1 also changes with the change in the carrier density. Therefore, the effective optical length changes,
There is a problem that the oscillation frequency of the laser beam changes due to deviation from the oscillation conditions, making it impossible to set the oscillation frequency precisely.

Further, in the laser light output control apparatus using the optical attenuator shown in FIG. 4, since the LD 1 which is a problem in the configuration of FIG. 3 is not directly driven, the resonator due to the change in carrier density is used. There is no problem of oscillation wavelength change due to change in length. However, since the laser light is attenuated and the amount of this attenuation is controlled to stabilize the output light, there is a problem that it cannot be used when the output intensity of the LD light source 13 is weak. Also, when controlling the attenuation of the laser light,
Since the ND filter, which is one component of the variable attenuator 14, is mechanically moved, there is a problem that the control time is several tens of msec and the optical output control with high-speed response cannot be performed.

Further, recently, an apparatus for stabilizing the output light by using an optical fiber amplifier in a saturated state has been devised, and a dummy LD light source, a pump LD light source for pumping, a fiber coupler, and a fiber which constitute this apparatus have been devised. The amplifier and the like are very expensive, and there is a problem that the manufacturing cost of the device increases. In addition, a current of several hundred mA is required to drive the pumping LD light source for excitation, which is one of the components of the above-mentioned device, and there is a problem that power consumption increases.
Furthermore, the variable wavelength range of the output light by this device is 15
It is 30 nm to 1570 nm, which is narrower than the variable wavelength range of LD1 in FIG.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a laser light output control device capable of obtaining stable output light with a simple structure and obtaining output light without noise. To aim.

[0013]

According to the first aspect of the present invention,
A reference circuit for outputting a reference signal indicating the power of output light to be obtained, and a traveling wave type optical amplifier for amplifying the laser light emitted from the external resonator type wavelength tunable LD light source with an amplification factor according to the injection current. An optical branching device that splits the laser light emitted from the traveling wave type optical amplifier in two directions and outputs one of the branched lights as an output light, and the other branched light of the optical branching device is received and converted into an electric signal. A light receiving circuit that outputs as a light output signal, a comparison circuit that compares the light output signal and the reference signal and outputs a comparison result, and a traveling wave that controls the injected current based on the comparison result of the comparison circuit Type optical amplifier drive circuit, and a laser light output control device. Claim 2
In the laser light output control device according to claim 1, the invention described in claim 1 is based on only the wavelength of the laser light emitted from the external resonator type wavelength tunable LD light source into which the one branch light is incident. It is characterized in that the following output light is emitted.

[0014]

In the laser light output control device of the present invention, the laser light emitted from the external resonator type wavelength tunable LD light source is amplified by the traveling wave type optical amplifier, and the amplified laser light is branched in two directions. Of the branched light as an output light, the other branched light is converted into an electric signal to obtain an optical output signal, and the optical output signal is compared with a reference signal representing the power of the target output light, and the comparison result is Based on this, the amplification factor of the traveling wave optical amplifier is controlled. Thereby, even when the laser light emitted from the external resonator type wavelength tunable LD light source changes,
Stable output light can be obtained. Further, in the laser light output control device of the present invention, since the output light is made incident on the reflector having wavelength selectivity and the reflected light is obtained as the output light, the laser light passes through the traveling wave type optical amplifier. It is possible to remove spontaneous emission light that is mixed in at that time, and obtain output light without noise.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a block diagram showing the arrangement of a laser light output control apparatus according to the first embodiment of the present invention. In this figure, parts common to those in FIGS. The description is omitted. In FIG. 1, 16 is TWA
(Traveling-wave type optical amplification element) having a double hetero structure including an active layer and two clad layers sandwiching the active layer, similar to the LD (laser diode) 1, and gain amplification thereof. The operating current is a dozen mA to several tens mA. TW
A16 has a current injected from the TWA drive circuit 17, and when light passes through the active layer of the TWA16, optical amplification is performed by stimulated emission. Further, both end surfaces of the TWA 16 are AR-coated (non-reflective coating), which prevents the both end surfaces from forming a resonator and performing optical amplification only for wavelengths satisfying the resonance condition. It is a thing. Therefore, the wavelength of the light incident on the TWA 16 is TWA 1
Within the gain range of 6, the incident light will be amplified. The TWA 16 may have a structure in which a window structure is incorporated in the end surface or a structure in which light is obliquely incident on the end surface.

The TWA drive circuit 17 controls the current injected into the TWA 16 based on the signal output from the comparison circuit 17. The apparatus shown in FIG. 1 is obtained by reconfiguring the apparatus shown in FIG. 3 as follows. First, the LD drive circuit 6 is separated from the comparison circuit 11 to be independent. Next, between the optical isolator 7 and the optical branching device 8, the collimator lens 3, the TWA 16, the collimator lens 3 and the optical isolator 7 are arranged in this order from the emission end side of the optical isolator 7 to the original optical axis (hereinafter, this optical axis). The axis is referred to as the first optical axis). The output of the comparison circuit 11 is input to the TWA drive circuit 17, and the output of the TWA drive circuit 17 is input to the TWA 16.

In the above-described structure, when the current is injected from the LD drive circuit 6 and the resonator length is adjusted by the phase adjustment drive circuit 5 so that the resonance condition at the wavelength selected by the diffraction grating 2 is satisfied, the laser is changed. Oscillation occurs. The laser light emitted from the emission end face 1b is collimated by the collimator lens 3
At the end 16 of the TWA 16 which is collimated by the lens 9 and is condensed by the lens 9 after passing through the optical isolator 7.
The light enters from a, undergoes optical amplification, and exits from the other end 16b. The laser light emitted from the TWA 16 becomes parallel in the collimator lens 3, and after passing through the optical isolator 7,
The light is reflected and transmitted by the optical branching device 8. The reflected light is output as output light, and the transmitted light is condensed by the lens 9, and then its power is detected by the light receiving circuit 10, and an optical output signal is output.

This optical output signal is input to the comparison circuit 11, where it is compared with the reference signal input from the reference circuit 12 to detect a difference, and a deviation signal corresponding to this difference is TWA driven from the comparison circuit 11. It is input to the circuit 17. TWA
The drive circuit 17 controls the current injected into the TWA 16 based on this deviation signal. Then, the change in the current injected into the TWA 16 immediately changes the carrier in the TWA 16, and the optical amplification gain in the active layer in the TWA 16 changes, so the optical amplification factor in the TWA 16 is controlled.
In this way, the laser light emitted from the emission end facet 1b of the LD1 is amplified and the optical amplification factor is controlled to stabilize the output light.

[Second Embodiment] FIG. 2 is a block diagram showing the arrangement of a laser light output control apparatus according to the second embodiment of the present invention, which is common to FIGS. 3, 4, and 1. The same reference numerals are given to the parts, and the description thereof will be omitted. FIG.
In the above, reference numeral 18 is a mirror, which functions to reflect incident light. Reference numeral 19 is a diffraction grating similar to the diffraction grating 2 shown in FIGS. The laser light output control device of FIG. 2 differs from that of FIG. 1 in that a mirror 10 is arranged between the optical isolator 7 and the optical branching device 8 so that the first optical axis can be bent at a right angle. Further, the optical branching device 8, the lens 9, and the light receiving circuit 10 are rearranged on the optical axis (hereinafter, this optical axis is referred to as the second optical axis). The optical branching device 8 has a first optical axis and an optical axis formed by the laser light reflected by the branching device 8 (hereinafter referred to as a third optical axis).
It is arranged so that the optical axis becomes parallel and the reflected light enters the diffraction grating 19.

In the above structure, the emitting end face 1b of the LD1
The laser light emitted from the laser beam enters the TWA 16 via the collimating lens 3, the optical isolator 7, and the lens 9. The laser light amplified when passing through the TWA 16 passes through the collimator lens 3 and the optical isolator 7. The laser light emitted from the optical isolator 7 is reflected by the mirror 18, its optical axis is bent at a right angle, enters the optical branching device 8, and is transmitted and reflected. The laser light transmitted through the optical branching device 8 enters the light receiving circuit 10 through the lens 9 and its power is detected. Then, the light receiving circuit 10 outputs this detection signal as an optical output signal, and the optical output signal is fed back. The feedback is the same as that described with reference to FIG. 1, and the description thereof will be omitted.

Further, the laser beam reflected by the optical branching device 8 propagates on the third optical axis, enters the diffraction grating 19 and is diffracted, propagates in the opposite direction on the third optical axis, and again the optical branching device 8 And is reflected and transmitted. The laser light reflected by the optical splitter 8 propagates on the second optical axis, is reflected by the mirror 18, and propagates on the first optical axis in the direction of the TWA 16. However, since the laser light propagating in this direction is cut by the isolator 7, this reflected light is reflected by the TWA 16 and L.
There is no effect on D1. Further, the laser light transmitted through the optical branching device 8 is output as output light.

In the laser light output control device described in the first and second embodiments, LD1 is driven by a constant current,
The output light is controlled by the TWA 16 arranged outside the LD1. Therefore, even when the oscillation frequency is changed, the current injected into the LD1 is constant, and the resonance condition is not changed due to the change of the injection current. Therefore, precise oscillation frequency setting is possible and stable output light is obtained. The effect is that you can. The output light is stabilized by controlling the current injected into the TWA 16 and can be controlled in the order of nsec. Therefore, unlike the conventional case where the parts are mechanically controlled, there is an effect that the light output control can be performed even for a high-speed output light fluctuation of the order of μsec. Further, since the output light is controlled by amplifying the laser light using the TWA 16, there is an effect that the optical loss due to the insertion of the TWA 16 and other optical components can be compensated.

The double hetero structure of TWA16 is basically the same as the double hetero structure of LD1, and optical amplification is possible in a wavelength range of about 100 nm, which is equivalent to the wavelength range in which LD1 can perform laser oscillation. is there. Therefore, the variable wavelength range of the output light is not limited as in the device for stabilizing the output light by using the conventional optical fiber amplifier in the saturated state, and the LD1
There is an effect that the output light can be stabilized in all wavelength bands of the oscillation wavelength. Further, the TWA 16 has a gain amplification operating current of a dozen mA to several tens mA, and an operating current of several hundred mA like a device for stabilizing laser light by using a conventional optical fiber amplifier in a saturated state. Since the pump LD light source for excitation is not required, there is an effect that it can operate with low power. Further, the structure of the present invention is composed of the LD 1, the TWA 16, several optical parts, and several electric circuits, and as in the conventional case, a dummy LD light source, a pump LD light source for pumping, a fiber coupler, a fiber amplifier, etc. There is an effect that an expensive member is not required and an increase in the manufacturing cost of the device can be suppressed.

Further, in the laser light output control apparatus shown in the second embodiment, the laser light emitted from the emitting end face of the LD1 is a longitudinal single mode at the wavelength selected by the diffraction grating 2, but passes through the TWA16. When doing so, noise of spontaneous emission light is mixed. Therefore, the laser light that has passed through the TWA 16 is made incident on the diffraction grating 2 so as to propagate along the third optical axis, and the spontaneous emission light is cut off. Therefore, there is an effect that a vertical single mode output light without noise can be obtained.

[0025]

As described above, according to the laser light output control device of the present invention, stable output light can be obtained with a simple structure. Further, according to the invention described in claim 2, there is an effect that the spontaneous emission light can be removed from the output light, and the output light without noise can be obtained with a simple configuration.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a laser light output control device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a configuration of a laser light output control device according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a configuration of a laser light output control device for an external resonator type laser according to a conventional technique.

FIG. 4 is a configuration diagram showing a configuration example of a laser light output control device using a variable optical attenuator according to a conventional technique.

[Explanation of symbols]

 1 LD (laser diode) 2, 19 Diffraction grating 4 Angle adjustment drive circuit 5 Phase adjustment drive circuit 6 LD drive circuit 8 Optical branching device 10 Light receiving circuit 11 Comparison circuit 12 Reference circuit 16 TWA (traveling wave type optical amplification element) 17 TWA Drive circuit

Claims (2)

[Claims] 1. An LD having an antireflection film on one end surface
(Laser diode) and a reflector having wavelength selectivity on the non-reflection film side of the LD, and the reflector and the LD
An external resonator type wavelength tunable LD light source having a resonator formed with the other end surface of the resonator, and comprising means for adjusting the wavelength of the reflector and means for adjusting the resonator length of the resonator. A laser light output control device for obtaining output light of desired power; a reference circuit for outputting a reference signal representing the power of output light to be obtained; and a laser emitted from the external resonator type wavelength tunable LD light source. A traveling-wave optical amplifier that amplifies light with an amplification factor according to the injection current, and an optical branching device that splits the laser light emitted from the traveling-wave optical amplifier in two directions, and uses one of the branched lights as output light. A light receiving circuit that receives the other branched light of the optical branching device and converts it into an electric signal, and outputs it as an optical output signal; and a comparison circuit that compares the optical output signal with the reference signal and outputs a comparison result. , Based on the comparison result of the comparison circuit Laser output control apparatus comprising a traveling wave type optical amplifier drive circuit for controlling the injection current. 2. The reflector receives the one branched light and emits output light having only the wavelength of the laser light emitted from the external resonator type wavelength tunable LD light source. Item 2. A laser light output control device according to item 1.