JPH09129982A - External resonator type ld light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of the places to be adjusted in angle of optical parts for optical resonance reflection by forming the external reflector of an optical resonance reflector structure of a diffraction grating, a beam splitter which transmits and splits reflected light, corner-cube prism which changes the optical path of the reflected light in parallel, etc. SOLUTION: The light emitted from a semiconductor laser 24 is made incident to an optical fiber 34 through a lens 28, etc., and becomes output light. On the other hand, the light which is converted in optical path in parallel is made incident to an external reflector composed of a beam splitter 14, a diffraction grating 16, and a corner-cube prism (prism) 12 and, after wavelength selection, only the light having the Bragg wavelength is inputted to the light emitting position of the prism 12. The light which is again passed through the prism 12 is made incident to the beam splitter 14 and most of the incident light is made incident to the diffraction grating 16 through the beam splitter, while the light equal to the reflectivity returns to the laser 24 side. Since the incident angle of the incident light to the grating 16 is the same, the incident light is reflected to the splitter 14 side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LD light source, and more specifically to an external resonator type LD light source applied to the field of optical measurement technology.

[0002]

2. Description of the Related Art In order to use an LD light source such as a semiconductor laser in an optical measurement technique, a single mode oscillation LD light source capable of tunable wavelength, having a narrow spectral line width and good wavelength stability is required. The structure of the single mode oscillation LD light source is a monolithic type L in which a diffraction grating is formed in the waveguide inside the LD element.
It can be roughly classified into a D structure and an external resonator type LD structure in which a reflector such as a diffraction grating is arranged outside the LD element.

FIG. 4 shows the structure of such an external resonator type LD light source in the prior art. Here, a diffraction grating 46 is provided outside the LD 24 having a non-reflective film on one end face.
The structure when seen from the side of the external resonator type LD light source in which is arranged. With this structure, the diffraction grating 46 is the LD 24.
It is arranged in a Littrow arrangement with respect to the emitted light. The wavelength selected by the diffraction grating 46 and reflected by the LD 24 is called the Bragg wavelength. Since the Bragg wavelength is changed by rotating the diffraction grating 46, the wavelength can be tuned by rotating the diffraction grating 46.

However, in order to change the wavelength over a wide range, the diffraction grating 4 with respect to the rotation axis of the diffraction grating 46 shown in FIG.
It is important to adjust the two angles of the parallelism of 6 (θ1) and the incident angle (θ2) of the LD output light to the rotation axis of the diffraction grating. The adjustment accuracy may be about 0.01 degree, and the optical axis adjustment is easy.

[0005]

However, in the external resonator type LD light source having only the diffraction grating 46 of this kind, sufficient performance cannot be obtained in the spectral line width and the wavelength stability. Therefore, a high-performance L that satisfies such requirements
As a D light source, for example, in Japanese Patent Laid-Open No. 6-112583, an optical resonance reflector (ROR) is used.
An LD light source incorporating an or) structure is disclosed. Specifically, there is an external resonator type LD light source in which an ROR structure is formed from the diffraction grating 46, the beam splitter 14 and the total reflection mirror 38, and is arranged as an external reflector of the LD 24 having a non-reflection film on one end surface. . When the ROR structure is incorporated in the external resonator type LD light source, a narrow spectral line width can be obtained without lengthening the external resonator due to the steep reflection characteristic having wavelength dependence using the resonance characteristic of light.

However, in order to form the ROR structure from the optical components of the diffraction grating 46, the beam splitter 14 and the total reflection mirror 38, it is necessary to create a resonance characteristic with spatial light, and it is very difficult to adjust the optical axis. That is, the diffraction grating 4
6. In order to use the ROR structure formed by the beam splitter 14 and the total reflection mirror 38 in the LD light source, at least 5 positions are required as the angle adjusting parts of the optical component including the LD part 24. Since the adjustment accuracy is about 0.001 degree, which is about 10 times as high as that when only the diffraction grating 46 is used, it is very difficult to adjust the optical axis. Also,
When the angle adjustment is changed on the optical axis due to temperature change or the like, there is a problem that the ROR resonance characteristic is changed and the reproducibility and stability are deteriorated. Therefore, even if an external cavity type LD light source having an ROR structure is manufactured, it takes a lot of time to adjust the optical axis, and there are problems of reproducibility and stability, and it is very difficult to commercialize the product.

In the conventional ROR structure in which the parallel light from the LD 24 shown in FIG. 3 is reflected by the beam splitter 14 toward the total reflection mirror side, when the ROR resonance characteristic is weak, no reflection occurs between the total reflection mirror and the LD. The Fabry-Perot (FP) resonator formed on the end face without the film also causes a problem of FP mode oscillation.

The present invention reduces the number of angle adjustment points of the optical component for ROR resonance, facilitates the adjustment, shortens the adjustment time, and improves the reproducibility and stability of the external resonator type LD light source. A type LD light source is provided.

[0009]

To achieve this object, according to the present invention, one end face is provided with a non-reflective film, and the light emitted from the non-reflective end face is parallel to the LD 24 driven by the semiconductor laser drive circuit. An external resonator type LD light source that includes a lens 22 that converts light into light and an external reflector that selects and reflects the emitted light that has been converted into parallel light and that uses the light emitted from the other end face as output light is The beam splitter 14 that reflects and splits the light emitted from the non-reflection film side of the LD 24 and transmits and splits the reflected light from the diffraction grating 16 and the corner cube prism 12, and the reflected light from the beam splitter 14 and the diffraction grating 16 in parallel. It has a corner cube prism 12 for changing the optical path, and a diffraction grating 16 for wavelength-selecting and reflecting the reflected light from the corner cube prism 12, External reflector optical resonant reflector structure is formed by over-cube prism 12 and the diffraction grating 16.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of an external resonator type LD light source according to the present invention will be described with reference to FIGS. FIG. 1 shows the structure of the external resonator type LD light source seen from the light source upper surface, and FIG. 2 shows the side view seen from the LD side. In FIGS. 1 and 2, 10 is a phase adjustment drive circuit, 12 is a corner cube prism, 13 is a parallel moving mechanism, 14 is a beam splitter with low reflectance, 16
Is a diffraction grating, 18 is a variable wavelength driving circuit, 20 is a rotation adjusting mechanism, 22, 28 and 32 are lenses, 24 is an LD element which is a semiconductor laser having a non-reflective film on one end face, and 26 is L.
D drive circuit, 30 is an optical isolator, and 34 is an output fiber.

Referring to FIG. 1, an LD element 24 used in an external resonator type LD light source has an antireflection film on one end face and an antireflection film on the other end face. It is an element. The LD drive circuit 26 injects a current into the LD element 24 to emit light. That is,
When a current is injected into the LD element 24 by the LD drive circuit 26, the light emitted from the end face on which the antireflection film is not applied passes through the lens 28, the optical isolator 30 and the lens 30, and is incident on the optical fiber 34, and is output. Become light. on the other hand,
The light emitted from the end surface of the non-reflection film is converted into parallel light by the lens 22 and input to the external reflector of the ROR structure formed by the diffraction grating 16, the beam splitter 14, and the corner cube prism 12.

The beam splitter 14 is a beam splitter having a reflectance of 10% to 30%, and the parallel light from the lens 22 is converted into a light path by the corner cube prism 12. The corner cube prism 12 has a function of reflecting the reflected light in parallel with the incident light itself and in the opposite direction even when the incident light is incident at an angle. Therefore, the collimated light that has entered the corner cube prism 12 is 18 degrees from the incident position of the corner cube prism 12.
The light is emitted from the position of 0 ° axial rotation target, and its emission optical path is incident on the diffraction grating 16 in parallel with the incident optical path. Therefore, it is not necessary to adjust the angle, and the parallelism with the rotation axis of the diffraction grating 16 and the incident angle of the parallel light with respect to the rotation axis of the diffraction grating 16 are adjusted as in the external resonator type LD light source using only the diffraction grating 16. It suffices to adjust the angles of the two locations with high accuracy.

The diffraction grating 16 is provided with a rotation adjusting mechanism 20, and the corner cube prism 12 is provided with a parallel moving mechanism 13. Further, the rotation adjusting mechanism 20 has a variable wavelength driving circuit 18 for driving the rotation adjusting mechanism 20,
3 includes a phase adjustment drive circuit 10. The rotation of the diffraction grating 16 is adjusted by a control signal from the wavelength tunable drive circuit 18, whereby the wavelength of the external resonator type LD light source is tuned. Further, the movement adjustment of the parallel moving mechanism 13 is performed by the control signal from the phase adjustment drive circuit 10, and thus the phase adjustment of the external resonator type LD light source is performed. If the phase adjustment drive circuit 10 and the wavelength tunable drive circuit 18 simultaneously rotate the diffraction grating 16 and move the parallel movement of the corner cube prism 12 while maintaining the phase matching condition at the time of laser oscillation, continuous operation without mode hopping is performed. The wavelength can be changed.

The light incident on the diffraction grating 16 is reflected by the diffraction grating 1
Only the Bragg wavelength selected in 6 is reflected again to the corner cube prism 12 side, passes through the same optical path, and enters the exit position of the corner cube prism 12. The parallel light that has passed through the corner cube prism 12 again is
The light is again incident on the beam splitter 14, and the light corresponding to the reflectance returns to the LD 24 side. However, most of the incident light (90% ~ 7
0%) is transmitted through the beam splitter 14 and is incident on the position of the diffraction grating 16 different from the above as shown in FIG. Then, the wavelength is again selected by the diffraction grating 16, but since the incident angle to the diffraction grating 16 is the same as the above, the incident light becomes the reflected light as it is and is reflected to the beam splitter 14 side.

Resonance characteristics are obtained by repeating these, and since the corner cube prism 12 is used, an ROR type resonator having diffraction gratings on both end surfaces is formed, and L
It functions as an external reflector on the non-reflection film side of D24.

The angle adjustment of the optical components in the external resonator type LD light source of the ROR structure using the corner cube prism 12 is performed by adjusting the angle of the external resonator type LD light source using only the diffraction grating 16 shown in FIG. And the parallelism of the diffraction grating 16 with respect to the rotation axis of the diffraction grating 16 and L
There are two positions of the incident angle of the D emission light on the rotation axis of the diffraction grating. However, even if the corner cube prism 12 is used, since the resonance characteristic is obtained, the adjustment accuracy is about 10 times severer as in the conventional ROR structure. The angle adjustment of the corner cube prism 12 is not necessary, but the position adjustment is necessary in order to match the optical paths of the incident light and the reflected light on the rotation axis of the diffraction grating 16, but the strict accuracy like the angle adjustment is not necessary. .

As a result, the number of angle adjustment points is small and the optical axis adjustment becomes easy, and the adjustment time can be shortened and the reproducibility and stability of the LD light source can be improved.

In the conventional ROR structure in which the parallel light from the LD is reflected by the beam splitter 14 toward the total reflection mirror side, when the ROR resonance characteristic is weak, the total reflection mirror and the non-reflection film of the LD 24 are applied. There is also a problem that a Fabry-Perot (FP) resonator formed by an end face which is not formed oscillates in the FP mode. However, in the ROR structure of the present embodiment, the diffraction grating 16 has a structure of both end faces, Only the wavelength selected in 16 will oscillate, and RO
Stable single-mode oscillation can be obtained even when the R resonance characteristic is weakened.

As described above, the optical component for forming the ROR structure has a wavelength-selective diffraction grating and a reflectance of 10
% -30%, transmittance 90% -70%, and a corner cube prism that has a function of making incident light and reflected light parallel at all times independent of the angle of optical components. The ROR structure is used as an external reflector on the non-reflection film side of the LD. Therefore, the only angle adjustment points of the optical component that can be adjusted with high accuracy are the angle adjustments of two points, the parallelism of the diffraction grating with respect to the rotation axis of the diffraction grating and the incident angle of the parallel light to the rotation axis of the diffraction grating. Becomes Although it is necessary to adjust the position of the corner cube prism, adjustment accuracy such as angle adjustment of optical components is not necessary, and only position adjustment in the horizontal direction with respect to the rotation axis of the diffraction grating is required.

[0020]

As described above, according to the present invention, since the number of angle adjusting points of the optical component for ROR resonance is small, the optical axis adjustment is greatly simplified, and the adjustment time can be shortened and the manufacturing reproducibility can be improved. . Further, in the conventional ROR structure, when the emitted light from the LD is reflected to the total reflection mirror side, the FP mode oscillation that occurs when the ROR characteristic is weak is eliminated, and a stable single mode oscillation is obtained. Reproducibility and stability are improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of an external resonator type LD light source according to the present invention.

FIG. 2 is a side view of the external resonator type LD light source shown in FIG. 1 when viewed from the LD side.

FIG. 3 is a schematic diagram of a conventional external cavity LD light source having a ROR structure.

FIG. 4 is a schematic side view of an external resonator type LD light source including only a conventional diffraction grating.

[Explanation of symbols]

 10 Phase Adjustment Driving Circuit 12 Corner Cube Prism 13 Parallel Moving Mechanism 14 Beam Splitter 16 Diffraction Grating 18 Wavelength Tunable Driving Circuit 20 Rotation Adjustment Mechanism 22 ・ 28 ・ 32 Lens 24 Semiconductor Laser (LD) 30 Optical Isolator 34 Output Fiber

Claims (1)

[Claims] 1. A semiconductor laser (24) provided with a non-reflection film on one end face thereof and driven by a semiconductor laser drive circuit, and a lens (22) for converting light emitted from the non-reflection end face into parallel light.
And an external reflector that includes an external reflector that wavelength-selects and reflects the emitted light converted into parallel light, and uses the emitted light from the other end face as the output light. A beam splitter (14) that reflects and splits the light emitted from the non-reflective film side and transmits and splits the reflected light from the diffraction grating (16) and the corner cube prism (12), the beam splitter (14) and the diffraction grating (16). )) Has a corner cube prism (12) for converting the reflected light from the parallel path to a parallel path, and a diffraction grating (16) for selecting and reflecting the reflected light from the corner cube prism (12). ), Corner cube prism (12)
An external resonator type LD light source, characterized in that an external reflector having an optical resonance reflector structure is formed by the diffraction grating (16).