JPH0758820B2 - Semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention is an external resonator in which a quarter-wave plate is inserted in one of the external resonators and a birefringent material is inserted in the other to obtain two orthogonal polarizations with different frequencies. Type semiconductor laser device is characterized.

[Industrial application field]

The present invention relates to a semiconductor laser device used as a two-frequency light source, and more particularly to an external resonator type semiconductor laser device capable of reducing the number of constituent parts and having a variable frequency difference between the two-frequency light.

With the development of optical application technology, devices with new functions are being rapidly developed. Also in the field of optical measurement, there is a demand for a method of measuring various physical quantities using laser light. In order to perform highly accurate measurement using one of them, the optical heterodyne method, it is necessary to stably obtain two laser beams having frequencies close to each other. Also, due to the demand for miniaturization of measuring instruments, it is necessary to use a semiconductor laser in place of the gas laser that has been used conventionally.

[Conventional technology]

Recently, the number of optical measurement devices that use laser light is increasing in the field of measurement such as distance measurement and velocity measurement. To perform such measurement efficiently by using the optical heterodyne method, two laser light with stable frequency difference are used. He-Ne lasers using the Zeeman effect are often used as dual-frequency light sources. In addition, as another light source, there is an example in which a birefringent material is obtained by inserting a birefringent substance into the cavity of a gas laser (Walter M. doyle et al. APPLIED PHYSICS LETTERS Vol.5,
Number 10 1964). In addition, the laser light is divided into two and one frequency is slightly changed by using an acousto-optic device.
There is also a method of obtaining frequency light. 2 using a semiconductor laser
As a frequency laser light source, there is an external resonator structure (Japanese Patent Application No. 58-177233) filed previously by the applicant of the present application, but none has been put into practical use.

[Problems to be solved by the invention]

When a semiconductor laser is used to obtain dual-frequency light having different polarization planes, a large phase difference occurs between polarization modes due to the anisotropy of the propagation constant due to the waveguide structure inside the semiconductor laser. Therefore, there is a problem that the effective cavity lengths are greatly different between the polarization modes, and it is very difficult to simultaneously oscillate two lights having extremely close frequencies and different polarization modes. The same problem also remains unsolved in a semiconductor laser device having an external cavity structure.

[Means for solving problems]

The present inventors have found that the problems caused by the internal structure of the semiconductor laser described above eliminate laser oscillation due to reflection at the end face of the semiconductor laser, and rotate the polarization plane of the return light from the reflecting mirror by 90 degrees in the external resonator configuration. Therefore, in order to solve the above-mentioned problems, an external resonator type semiconductor laser device in which at least the semiconductor laser (1) is located at the center and the reflecting mirrors (3) are arranged on both sides thereof is realized. There is a TE polarization plane (11) of the semiconductor laser in which the axis direction is centered on the 1/4 wavelength plate (4) in the optical path (21) on one side.
And the optical path on the other side (2
2) A semiconductor laser device characterized in that a birefringent substance (5) is inserted therein to obtain two orthogonally polarized lights having different frequencies.

[Action]

In the present invention, the anisotropy of the semiconductor laser can be canceled by the combination of the semiconductor laser and the quarter-wave plate, and an isotropic semiconductor laser medium for various deflection components can be realized. Then, by inserting a birefringent substance into the resonator, the effective resonator length for two polarized lights changes.
A frequency light source can be realized.

〔Example〕

FIG. 1 is an embodiment diagram showing the overall structure of a semiconductor laser device according to the present invention, FIG. 2 is a perspective view of the semiconductor laser device according to the present invention in which a part of FIG. 1 is taken out, and FIG. FIG. 1 is a diagram showing the rotation state of the polarization plane in the device, FIG. 4 is a diagram showing the variability of the oscillation frequency in the first device, FIG. 5 (a)
(B) is an embodiment of a semiconductor laser device in which a resonator is integrated as a modification of the present invention.

In FIGS. 1 and 2, 1 is a semiconductor laser having antireflection films formed on both end surfaces for use as an active medium, 2 is a microlens for collimation for collimating emitted light from the semiconductor laser, 3 Is a reflecting mirror for returning light to the laser, and 4 is a birefringence axis azimuth of 45 degrees with respect to the TE polarization plane 11 of the semiconductor laser 1 [in the figure, the axis azimuth is shown by an arrow 41, and the axis azimuth is Rotation angle θ from the virtual line corresponding to TE polarization plane 11
1 is 45 degrees] made of crystal etc. arranged at an angle
The 1/4 wave plate, 5 has a birefringence axis azimuth of (45 + α) degrees with respect to the TE polarization plane 11 of the semiconductor laser 1 [in the figure, the axis azimuth is shown by an arrow 51, and the axis azimuth is the TE polarization plane]. The rotation angle θ2 is 45 degrees + α degrees from the corresponding phantom line of 11] 1/4 wavelength plate made of birefringent material such as quartz crystal, 21 and 22 arranged at an angle
Shows the optical path in the resonator.

The α degree is in the range of 0 ° <α <45 °, 5 ° to 10 °
Is suitable.

In the semiconductor laser device configured as described above, the light in the optical path 21 emitted from the laser 1 to the (A) side is collimated by the lens 2, passes through the 1/4 wavelength plate 4, and is reflected by the mirror 3 again. The light passes through the quarter-wave plate 4, is condensed by the lens 2, and enters the inside of the laser 1.

Similarly, the light in the optical path 22 emitted from the laser 1 to the (B) side is collimated by the lens 2 and passes through the 1/4 wavelength plate 5, and then is reflected by the mirror 3 and is again reflected by the 1/4 wavelength plate 5.
Through the lens 2 and is condensed by the lens 2 to enter the inside of the laser 1.

Therefore, the light emitted from the laser 1 with TE polarization on the left side is initially
By passing back and forth (twice) through the quarter-wave plate 4, it is returned to TM polarized light that is orthogonal to TE polarized light. On the contrary, TM polarized light is converted into TE polarized light.

At this time, the dotted line a including the laser 1 inside the resonator ...
In the part (A) on the left side of a ', the anisotropy of the plane of polarization is canceled by the 1/4 wavelength plate 4 by reciprocating.

However, in the (B) part on the right side of the resonator, in the optical path 22,
1/4, which is a birefringent substance whose axis direction is slightly deviated from 45 degrees
Since the wave plate 5 is inserted, the effective resonator lengths for two orthogonal polarizations can be slightly different.

As a result, two orthogonal polarizations TE, T with slightly different frequencies
M will oscillate.

At this time, the axis direction of the 1/4 wavelength plate 5 placed in the optical path 22 is (4
5 + α) degrees, two oscillating linearly polarized light TE,
The direction of TM is rotated by an angle α from the TE and TM axes as shown in Fig. 3, and when the resonator length is 20 cm, the oscillation frequency difference between the two polarizations is linear according to the rotation angle α as shown in Fig. 4. Change.

In this embodiment, the case where the quarter-wave plate 4 is inserted in the optical path 21 has been described, but it has the same polarization plane conversion effect, for example, it does not hinder the application of the electro-optical effect element. .

Further, as the quarter-wave plate 5, a quarter-wave plate whose axis azimuth is slightly deviated from 45 degrees was used as the quarter-wave plate 5, but this has the same axis azimuth as the quarter-wave plate 4 of 45 degrees. Even if the thicknesses are different and the 1/8 wavelength plate is used, the same function is exhibited.

FIGS. 5 (a) and 5 (b) are a side view and a sectional view of a semiconductor laser device according to the present invention in which optical elements are integrated.

This is because the substrate 7 on which the laser 1 is mounted is formed of a birefringent material such as quartz, a recess 71 for embedding the laser 1 in the surface of the substrate 7, and reflecting mirrors 74 and 75 on both end faces thereof. The external resonator type semiconductor laser device is provided by mounting the substrate 7 on the heat sink substrate 8.

At this time, in the recess 71, the region 72 between the laser 1 and the reflecting mirror 74 and the region 73 between the laser 1 and the reflecting mirror 75 on the substrate 7 have different thicknesses (length between the laser 1 and the reflecting mirror 74 or 75). Is formed on the surface of the substrate 7 so that
The optical axis in the cross section of the regions 72 and 73 is 45 degrees with respect to the TE polarization plane of the laser 1 as shown by an arrow 76.

Due to such a difference in the thickness dimension, the region 72 has the same function as that of the quarter-wave plate 4, and the region 73 has the same function as that of the quarter-wave plate 5 with an inclined axis.

At this time, the length I of the area 72 is determined by the following equation.

No is the refractive index of the substrate 7 for ordinary rays, and ne is the refractive index of the substrate 7 for extraordinary rays.

Further, the length of the region 73 can be changed according to the required frequency difference within a range that does not satisfy the above formula (I).

〔The invention's effect〕

As described above, according to the present invention, not only a dual-frequency light source can be easily realized by using a semiconductor laser, but also
The frequency difference between frequencies becomes variable, and the effect that contributed to expanding the applicable range of heterodyne measurement using light is remarkable.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a perspective view according to the present invention in which a part of FIG. 1 is taken out, and FIG. Fig. 4 shows the rotation of the polarization plane with respect to the set angle α of the wave plate 5, and Fig. 4 shows the set angle α of the 1/4 wave plate 5 when the cavity length is 20 cm.
And FIG. 5 (a) and FIG. 5 (b) are side views and cross sections showing a semiconductor laser device in which optical elements according to another embodiment of the present invention are integrated. It is a figure. [Explanation of reference numerals] In these figures, 1 is a semiconductor laser with an antireflection film, 3, 74, 75
Is a reflecting mirror, 4 is a left quarter wave plate, 5 is a right quarter wave plate, 7 is a substrate, and 72 and 73 are polarization propagation regions of the substrate 7 having different polarization plane conversion effects.

Claims (5)

[Claims] 1. An external resonator type semiconductor laser device in which at least a semiconductor laser (1) is provided as a center and reflecting mirrors (3) are arranged on both sides thereof, and a 1/4 optical path is provided in a one-side optical path (21).
The wave plate (4) is arranged so that its axial direction is 45 degrees with respect to the TE polarization plane (11) of the semiconductor laser centered on it.
A semiconductor laser device characterized in that a birefringent substance (5) is inserted into the optical path (22) on the other side to obtain two orthogonal polarizations having different frequencies. 2. The birefringent material (5) according to claim 1, wherein the birefringent substance (5) is a quarter-wave plate, and its axis direction is slightly deviated from 45 degrees with respect to the TE polarization plane of the semiconductor laser. A semiconductor laser device characterized in that 3. A semiconductor laser device according to claim 1, wherein the birefringent material (5) is a wave plate having a thickness different from that of the quarter wave plate (4). . 4. A semiconductor laser device according to claim 3, wherein the birefringent substance (5) is a 1/8 wavelength plate. 5. The birefringent material (5) according to claim 1 is provided as a substrate (7) on which the semiconductor laser (1) is mounted, and the substrate (7) is provided on the surface thereof. The semiconductor laser (1) is embedded in the formed recess (71), and reflecting mirrors (74) and (75) are provided on both side end surfaces of the semiconductor laser (1) to form an external resonator type semiconductor laser device. The concave portion (71) is a region (7) between the semiconductor laser (1) and the reflecting mirror (74) on the substrate (7).
2) and the region (73) between the semiconductor laser (1) and the reflecting mirror (75) are formed on the substrate (7) so as to have different thickness dimensions. Laser device.