JP2004247327A - External resonator wavelength variable light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an external resonator wavelength variable light source which is capable of outputting the light whose wavelength can be changed over a wide range. <P>SOLUTION: The external resonator wavelength variable light source is equipped with a wavelength selection reflector 4 structure arranged outside an optical amplifier 1 and capable of changing its output light in wavelength by the wavelength selection reflector 4 structure. The optical amplifier 1 is a semiconductor laser having a structure wherein the band gap energy is changed stepwise or continuously in the lengthwise direction of a resonator. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an external resonator type wavelength tunable light source device used in the field of optical communication and optical measurement technology, and more particularly to a wavelength tunable light source capable of widely changing a wavelength range.
[0002]
[Prior art]
As a light source for measuring the wavelength characteristics of optical component parts for optical communication, a light source that has single-mode oscillation with a narrow spectral line width, good wavelength stability, and tunable wavelength is required. An external resonator type wavelength tunable light source using a diffraction grating 4A having a selection function is used.
[0003]
2. Description of the Related Art In recent years, with the spread of WDM (Wavelength Division Multiplexing), the measurement range of wavelength characteristics of optical component parts to be used has been expanded, and it has become necessary to cope with a wider band of C band + L band + S band. I have.
[0004]
FIG. 4 is a block diagram showing a configuration example of a conventional external resonator type wavelength tunable light source. In FIG. 4, 1 is an optical amplifier, 2 is an optical amplifier drive circuit, 3A to 3C are lenses, 4A is a diffraction grating, 4B is a reflector, 6 is an optical isolator, 5B is a rotation control means, and 5A is a rotation control drive circuit. is there. The wavelength selection reflector 4 is constituted by the diffraction grating 4A and the reflector 4B, and the wavelength selection drive circuit 5 is constituted by the rotation control means 5B and the rotation control drive circuit 5A. The wavelength selection reflector 4 and the wavelength selection drive circuit 5 are wavelength variable means.
[0005]
Next, the operation of FIG. 4 will be described. The optical amplifier 1 is a Fabry-Perot type semiconductor laser (LD), which is provided with a non-reflective film 1A on one emission surface, and emits light from both emission surfaces according to an injection current from the optical amplifier drive circuit 2.
[0006]
The LD element serving as the optical amplifier 1 amplifies light in a wavelength region corresponding to the band gap energy of the active layer, and the band cap energy here is constant in the longitudinal direction of the resonator.
[0007]
The lens 3A is disposed on the emission optical axis of the optical amplifier 1 on the side of the non-reflection film 1A, and converts the light emitted from the exit surface of the optical amplifier 1 on the side of the non-reflection film 1A into parallel light. The outgoing light converted into parallel light is incident on the wavelength selective reflector 4.
[0008]
The diffraction grating 4A is fixed to an optical base table (not shown), and reflects light having a specific wavelength represented by Expression (1) depending on the incident angle among incident parallel lights.
λB = d / N × [sin (α) + sin (β)] (1)
Here, λB is the Bragg wavelength selected by the diffraction grating 4A, d is the groove interval of the diffraction grating 4A, N is the order of the diffracted light (usually N = 1), α is the normal of the diffraction grating 4A and the optical amplifier 1 The angle from the emission optical axis (the angle of incidence on the diffraction grating 4A), and β is the angle between the normal to the diffraction grating 4A and the diffraction optical axis of the light diffracted by the diffraction grating 4A (the diffraction angle from the diffraction grating 4A), respectively. Is shown.
[0009]
That is, the diffraction grating 4A is arranged at a position where the outgoing light is incident at an incident angle α on the outgoing optical axis from the outgoing surface of the optical amplifier 1 on the antireflection film 1A side, and is incident from the optical amplifier 1 at an incident angle α. Of the parallel light, the light having the wavelength represented by the above-described formula (1) is diffracted at an angle β as the first-order diffracted light, and the light that is not diffracted by the light having the wavelength represented by the formula (1) is changed to the normal line of the diffraction grating 4A. On the other hand, the light is reflected as 0th-order diffracted light at an angle symmetrical to the incident angle α.
[0010]
The reflector 4B is disposed on the rotating mechanism 7, and reflects only light having a wavelength perpendicularly incident on the reflector 4B out of the diffracted light from the diffraction grating 4A obtained by the equation (1) into the same optical path as the incident optical path. To the optical amplifier 1. Light having a wavelength not perpendicularly incident on the reflector 4B is reflected on an optical path different from the incident optical path, and therefore does not return to the optical amplifier 1.
[0011]
The reflector 4B forms a resonator including the reflection of the diffraction grating 4A and the exit surface of the optical amplifier 1 on which the non-reflection film 1A is not formed, and the light selected by the reflector 4B and the diffraction grating 4A. Is re-entered into the optical amplifier 1 to cause laser oscillation.
[0012]
The rotation mechanism 7 is configured such that the rotation control drive circuit 5A of the wavelength variable means 5 controls the rotation control means 5B to rotate about the rotation axis. With the rotation of the rotation mechanism 7, the change in the angle of the reflector 4B and the change in the cavity length are simultaneously performed, and the wavelength of laser oscillation changes. As a result, the wavelength can be changed within the optical gain range of the optical amplifier 1.
[0013]
The lens 3B is disposed on the emission optical axis of the optical amplifier 1 on the side where the antireflection film 1A is not applied, and converts light emitted from the emission surface of the optical amplifier 1 into parallel light. The emitted light converted into parallel light is incident on the optical isolator 6.
[0014]
The optical isolator 6 is for preventing the reflected light from the output fiber 10 from returning to the optical amplifier 1. The light transmitted through the optical isolator 6 is condensed by the lens 3C and is incident on the output fiber 10 as output light. Is done.
[0015]
[Patent Document 1]
JP 2000-389178 A
Patent Document 1 discloses the configuration shown in FIG.
[0017]
[Problems to be solved by the invention]
The optical amplifier 1 is manufactured by growing an active layer on a substrate by epitaxial growth. The active layer has a quantum well structure (including a strained quantum well structure) to improve luminous efficiency and the like, and has a quantum well width of the active layer. By changing the bandgap energy by changing the composition and the composition, the optical gain wavelength range is changed.
[0018]
However, in the normal epitaxial growth, since the uniform growth is performed in the substrate, the optical gain wavelength range is about 100 nm to 150 nm in the active layer having a single composition. Therefore, although the wavelength selection range of the wavelength selective reflector 4 (the diffraction grating 4A and the reflector 4B) used for the external resonator type wavelength tunable light source is as wide as several hundred nm, the external resonator type wavelength tunable light source is used. Is 100 nm to 150 nm, which is the same as the optical gain wavelength range of the optical amplifier 1.
[0019]
That is, in the conventional configuration shown in FIG. 4, the wavelength variable range is determined by the optical gain range of the optical amplifier 1 even if the wavelength variable range of the external resonator type wavelength variable light source is to be widened. An object of the present invention is to provide a wavelength tunable light source having a wide wavelength tunable width.
[0020]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides
An optical amplifier 1 having an antireflection film 1A at one end;
An optical amplifier driving circuit 2 for driving the optical amplifier 1;
A lens 3A disposed on the emission optical axis of the optical amplifier 1 on the side of the non-reflection film 1A and converting the emission light from the emission surface of the optical amplifier 1 on the side of the non-reflection film 1A into parallel light;
An external resonator type wavelength tunable light source comprising: a wavelength selection reflector 4 for tuning the wavelength of parallel light incident from the lens 3A;
The optical amplifier 1 is a semiconductor laser having a structure in which the band gap energy changes stepwise or continuously in the cavity length direction of the optical amplifier 1.
[0021]
The optical amplifier 1 is a semiconductor laser having an active layer in which quantum wells having different band gap energies are stacked in the layer structure direction.
[0022]
Further, the wavelength selective reflector is
A diffraction grating that reflects light of a specific wavelength determined by the angle of incidence of the incident parallel light,
And a reflector that reflects only light having a vertically incident wavelength out of the reflected light of the diffraction grating.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the external resonator type wavelength tunable light source according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of an external resonator type wavelength tunable light source according to the present invention.
[0024]
In FIG. 1, an optical amplifier 1 is a Fabry-Perot type semiconductor laser, and has an antireflection film on one end surface. The optical amplifier 1 is connected to the optical amplifier drive circuit 2 and emits light from both emission surfaces according to the injection current from the optical amplifier drive circuit 2.
[0025]
In an InGaAs / InGaAsP semiconductor laser having an MQW (English spelling and Japanese term insertion) structure, LD oscillation in the 1200 nm to 1650 nm band can be achieved by changing the band gap energy. Here, that laser oscillation is possible in the 1200 nm to 1650 nm band means that the composition of InGaAsP is changed. When fixed to a certain composition, the wavelength width of laser oscillation is limited to about 150 nm.
[0026]
Therefore, as the optical amplifier 1 of FIG. 1, an element having a structure in which the band gap energy changes stepwise or continuously in the longitudinal direction of the resonator in the optical amplification region is used. The other configurations and operations in FIG. 1 are the same as those of the wavelength tunable light source in FIG. 4, and a description thereof will be omitted.
[0027]
An element having a structure in which the band gap energy changes stepwise in the longitudinal direction of the resonator is manufactured by a selective growth method. In this selective growth method, a silicon oxide film (SiO2) or the like is formed on an epitaxial growth substrate, the silicon oxide film in a region to be epitaxially grown (optical waveguide which is an optical amplification region) is removed, and then metal organic chemical vapor deposition (MOCVD) is performed. A quantum well structure is grown by the method.
[0028]
In addition, as a technique related to an element having a structure in which the band gap energy changes stepwise or continuously in the longitudinal direction of the resonator of the optical amplification region, it is possible to arbitrarily control the band gap energy. IEICE Transactions Vol. 77-CI No. 5 P250-259, "Quantum level energy control of multiple quantum well structure by selective MOCVD growth and application to optical integrated device", and the manufacturing method is described in JP-A-7-50443.
[0029]
Next, the configuration of the optical amplifier 1 of the external resonator type wavelength tunable light source according to the present invention will be described with reference to FIG. As shown in FIG. 2, the thickness of the quantum well layer grown between the masks changes depending on the mask width of the silicon oxide film and the width between the two masks, and the effect of changing the band gap energy is obtained. As described above, the wavelength range of the optical gain changes.
[0030]
Here, a composition A region where laser oscillation can be performed from 1500 nm to 1650 nm and a composition B region where laser oscillation can be performed from 1400 nm to 1550 nm will be described as examples. The relationship between light amplification (Gain) and light absorption (Loss) is as follows.
[0031]
LD oscillation is possible in a wavelength band where light amplification is larger than light absorption (1500 nm to 1650 nm in the A region and 1400 nm to 1550 nm in the B region). In a wavelength band where light is absorbed and light amplification is small, only spontaneous emission light is obtained. In a wavelength band (long wavelength side) where there is neither light absorption nor optical amplification, the material is transparent, but in a wavelength band where light absorption is present and there is no optical amplification (short wavelength side), only light absorption occurs.
[0032]
In this example, LD oscillation only in the B region is possible at a wavelength shorter than the A region by 100 nm. However, when the A region is integrated, light absorption in the A region is added. Becomes impossible.
[0033]
Therefore, when the composition A and the composition B having different wavelength tunable ranges are integrated in the quantum well layer formed by the selective growth method, the light amplification must be sufficiently larger than the light absorption in order to cause laser oscillation. For this reason, even if the structure of composition C capable of laser oscillation on the shorter wavelength side than composition B is integrated, the light absorption of composition A becomes too large and light amplification cannot be performed.
[0034]
In other words, since the bandgap energy changes stepwise or continuously in the longitudinal direction of the resonator of the optical amplifier 1, the light amplification characteristics with respect to the wavelength in each region are slightly lowered, but light in a wide wavelength range is amplified. It is possible to do. Therefore, the wavelength can be tuned in a wavelength range about 100 nm wider than that of the conventional wavelength tunable light source using a semiconductor laser device having a uniform band gap energy.
[0035]
Next, the wavelength selective reflector structure will be described. The diffraction grating 4A is arranged at a position where the emission light is incident at an incidence angle α on the emission optical axis from the emission surface on the antireflection film 1A side of the optical amplifier 1. The diffraction grating 4A functions as the wavelength selective reflector 4, and diffracts the light of the wavelength represented by the above-mentioned formula (1) at the angle β as the first-order diffracted light, of the parallel light incident from the optical amplifier 1 at the incident angle α. I do. On the other hand, light that is not diffracted by the light having the wavelength represented by the expression (1) is reflected as 0th-order diffracted light at an angle symmetrical to the incident angle α with respect to the normal to the diffraction grating 4A.
[0036]
The reflector 4B is disposed at a position where the first-order diffracted light having a wavelength that is incident from the optical amplifier 1 on the diffraction grating 4A and diffracted at an angle β is incident, and reflects the first-order diffracted light. At this time, of the diffracted light from the diffraction grating 4A obtained by the expression (1), only light having a wavelength that is perpendicularly incident on the reflector 4B is reflected on the same optical path as the incident optical path, and is fed back to the optical amplifier 1. Light having a wavelength not perpendicularly incident on the reflector 4B is reflected on an optical path different from the incident optical path, and therefore does not return to the optical amplifier 1.
[0037]
In the examples described so far, the structure of the wavelength selective reflector 4 composed of the diffraction grating 4A and the reflector 4B has been described. Obviously, a structure composed of a reflector may be used.
[0038]
[Second embodiment]
In the external resonator type wavelength tunable light source of the second embodiment, the components are the same as those of the first embodiment, but the structure of the optical amplification region of the semiconductor laser as the optical amplifier 1 is different. The semiconductor laser device as the optical amplifier 1 has an active layer structure in which quantum wells having different band gap energies are stacked in the layer structure direction.
[0039]
Also in the LD element having this structure, the effect is equivalent to that of the above-described structure in which the band gap energy changes stepwise or continuously in the cavity length direction, and the optical amplification characteristics with respect to wavelength are slightly lowered. Light can be amplified.
[0040]
As described above, according to the external cavity type wavelength tunable light sources of the first and second embodiments, the wavelength tunable light source using the conventional semiconductor laser device having a multiple quantum well structure having a uniform band gap energy. The wavelength can be changed over a wavelength range as wide as about 100 nm.
[0041]
【The invention's effect】
According to the external cavity type wavelength tunable light source of the present invention, the optical gain wavelength range is wider and the laser oscillation wavelength range is wider than that of a conventional semiconductor laser device having a multiple quantum well structure having a uniform band gap energy. In addition, the wavelength range in which the wavelength can be varied with a small size can be easily widened.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of an external resonator type wavelength tunable light source according to the present invention.
FIG. 2 is a diagram showing a change in thickness of a quantum well layer by a selective growth method.
FIG. 3 is a schematic diagram illustrating optical gain characteristics with respect to wavelength.
FIG. 4 is a block diagram illustrating a configuration example of a conventional external resonator type wavelength tunable light source.
[Explanation of symbols]
1 Optical amplifier 1
1A Non-reflection film 2 Optical amplifier drive circuits 3A, 3B, 3C Lens 4 Wavelength selective reflector 4A Diffraction grating 4B Reflector 5 Wavelength selective drive circuit 5A Rotation control drive circuit 5B Rotation control means 6 Optical isolator 7 Rotation mechanism

Claims (3)

An optical amplifier (1) having an antireflection film (1A) at one end;
An optical amplifier driving circuit (2) for driving the optical amplifier (1);
A lens which is disposed on the emission optical axis on the non-reflection film (1A) side of the optical amplifier (1) and converts the emission light from the emission surface on the non-reflection film (1A) side of the optical amplifier (1) into parallel light ( 3A),
An external resonator type wavelength tunable light source comprising: a wavelength selection reflector (4) for changing the wavelength of parallel light incident from the lens (3A);
The external amplifier type wavelength tunable light source is characterized in that the optical amplifier (1) is a semiconductor laser having a structure in which the band gap energy changes stepwise or continuously in the longitudinal direction of the resonator. An optical amplifier (1) having an antireflection film (1A) at one end;
An optical amplifier driving circuit (2) for driving the optical amplifier (1);
A lens which is disposed on the emission optical axis on the non-reflection film (1A) side of the optical amplifier (1) and converts the emission light from the emission surface on the non-reflection film (1A) side of the optical amplifier (1) into parallel light ( 3A),
An external resonator type wavelength tunable light source comprising: a wavelength selection reflector (4) for changing the wavelength of parallel light incident from the lens (3A);
The optical resonator 1 is a semiconductor laser having a structure in which an active layer is formed by stacking quantum wells having different band gap energies in a layer structure direction. A wavelength-selecting reflector (4) for reflecting light having a specific wavelength determined by an incident angle among incident parallel lights;
The external resonator type wavelength according to claim 1 or 2, wherein the reflector (4B) is configured to reflect only light having a wavelength that is vertically incident among the light reflected by the diffraction grating (4A). Variable light source.

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