JP3031976B2 - Semiconductor laser device - Google Patents

Description

The present invention relates to a semiconductor laser device used for optical information processing, optical measurement, optical communication, and the like, and in particular, stabilizes a beam emission angle and a wavelength. And a semiconductor laser device.

(Prior Art) In recent years, for the purpose of application to optical information processing apparatuses such as optical disk systems and optical scanners, or optical measurement and optical communication,
Various semiconductor lasers have been developed. These semiconductor lasers have various requirements for transverse mode characteristics, optical spectrum characteristics, noise characteristics, and the like, depending on the application. In particular,
In applications such as a light source for an optical disk system, it is required to oscillate in a stable transverse mode even in a high output operation.

Semiconductor lasers having various transverse mode control structures have been developed for such purposes, but all have a complicated device structure for stabilizing the transverse mode, and the fabrication process is also complicated. In high-power operation, the mode tends to be unstable due to refractive index fluctuation due to heat generation and spatial hole burning of carriers, and it is difficult to realize stable transverse mode oscillation. Also, as a means of increasing the output,
Although array lasers have been developed, it is difficult to synchronize the phase of each array with an array laser, and even if phase synchronization is achieved, the 180 ° mode is usually more stable than the 0 ° mode, so a far-field image is simple. Instead of a peak shape, it becomes a bimodal shape.

On the other hand, as a method of controlling the mode from outside the semiconductor laser, a phase-locked laser using an external resonator as shown in FIG. 12 has been reported (Technical Digest, 10th IEEE).
International Semiconductor Laser Conference, Kana
zawa, F-4 (1986)). In the figure, 1 is a semiconductor laser device, 2
Is a slit, and 3 is a spherical mirror. The light emitted from the laser element 1 is applied to the spherical mirror 3 through the slit 2, and the reflected light is fed back to the laser element 1 through the slit 2.

However, in this method, since the slit is used as the spatial filter, the control of the oscillation mode is incomplete. That is, since the slit is a binary filter, the near-field image on the LD end face as a Fourier transform is a pattern having side lobes. Therefore, for example, when this is applied to a single mode stripe laser, a higher-order mode corresponding to a side lobe easily oscillates, and light emitted from such a laser cannot be focused on a single spot.

Further, when used in a hologram scanner or the like, it is required that the waveform change due to temperature or the like is small. As means for realizing such a wavelength-stabilized laser, various complex resonator structures provided with an external resonator have been developed. For example,
As shown in FIG. 13, a composite resonator can be formed by providing a lens 4 and a reflecting mirror 5 behind the semiconductor laser device 1 and returning the light emitted from the rear surface to the semiconductor laser device 1. However, in this structure, the wavelength selectivity due to the composite resonator effect is used, so that, for example, wavelength stability cannot be always obtained in a wide range with respect to temperature fluctuation. Further, in this structure, the wavelength cannot be made variable because the external resonator structure is fixed.

(Problems to be Solved by the Invention) As described above, in the conventional external resonator structure using slits or the like, the control of the oscillation mode is incomplete, and it has been difficult to obtain stable transverse mode oscillation. In addition, it is difficult to obtain wavelength stability with respect to a wide range of temperature fluctuations in the complex resonator structure using the conventional reflecting mirror, and further, there is a problem that the wavelength cannot be controlled from the outside.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor laser device that oscillates in a stable fundamental transverse mode even in a high-output operation.

Another object of the present invention is to provide a semiconductor laser device capable of stabilizing the wavelength over a wide temperature range and controlling the wavelength from the outside.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to provide an optical feedback optical system including a beam emission angle selection element, a wavelength selection element, and the like in order to solve the above-described problem. is there.

That is, the present invention relates to a semiconductor laser device having an external resonator structure, a semiconductor laser element, an optical system for returning a part of light emitted from the laser element to a light emitting end face of the laser element, A beam exit angle selection element arranged in the optical path of the system and having a higher transmittance as the incident angle is smaller is provided.

Further, the present invention is a semiconductor laser device comprising: a semiconductor laser element; and an optical system for returning a part of light emitted from the laser element to a light emitting end face of the laser element, wherein the optical system includes: It is characterized in that an optical filter and a rectangular prism are formed integrally with each other so that the wavelength at which the transmittance increases according to the incident angle, and the reflectance is increased at a specific wavelength.

Further, the present invention is a semiconductor laser device comprising: a semiconductor laser element; and an optical system for returning a part of light emitted from the laser element to a light emitting end face of the laser element, wherein the optical system includes: It is characterized by having a semiconductor multilayer structure in which a plurality of semiconductor layers having different compositions are stacked, and having a high reflectance for a specific wavelength.

(Operation) According to the present invention, by providing an optical feedback optical system including a beam emission angle selection element, only a beam having a small emission angle can be returned to the light emission end face of the laser element, thereby achieving high output operation. Also, stable oscillation in the basic transverse mode can be achieved.

Further, according to the present invention, by providing an optical field-back optical system including a wavelength selection element and the like, only a specific wavelength can be returned to the light emitting end face of the laser element, thereby stabilizing the wavelength in a wide range. It becomes possible. In addition, by changing the inclination of the wavelength selection element with respect to the optical path, the wavelength can be controlled from the outside.

Furthermore, by providing an optical feedback optical system including both a beam emission angle selection element and a wavelength selection element,
It is possible to stabilize the wavelength in a wide range together with stable oscillation in the fundamental transverse mode in high-power operation.

(Examples) Hereinafter, details of the present invention will be described with reference to the illustrated examples.

FIG. 1 is a schematic configuration diagram showing a semiconductor laser device according to a first embodiment of the present invention. In the figure, 10 is a semiconductor laser element, 11 is an optical filter (beam emission angle selection element), 12 is a lens, and 13 is a half mirror. In this figure, light emitted from a semiconductor laser device 10 passes through an optical filter 11 and is collimated by a lens 12 to form a half mirror.
It is incident on 13. A part of this light is reflected by the half mirror 13 and focused again by the lens 12, and the optical filter 11
And returns to the semiconductor laser device 10. Half mirror 13
, The light is fed back, so that an external resonator is constituted as a whole.

The feature of this embodiment lies in that an optical filter 11 is arranged as a beam emission angle selection element in this external resonator.
The optical filter 11 has an angle selectivity with respect to incident light, and the transmittance increases as the incident angle decreases.
Therefore, by arranging the optical filter 11 in the optical path, a component having a smaller beam divergence angle of the light emitted from the laser element 10 transmits through the optical filter 11 better.
That is, the resonator loss is reduced for a mode having an output beam component having a small beam divergence angle, whereby stable transverse mode oscillation is obtained.

As the optical filter 11 in FIG. 1, for example, a band-pass filter made of a dielectric multilayer film can be used.
FIG. 2 shows an example of the structure of a band-pass filter. In the figure, 20 is a glass substrate, 21 is a multilayer film composed of alternating layers of a high refractive index layer (indicated by hatching) and a low refractive index layer, and 22 is an antireflection film. As a configuration of the multilayer film 21, for example, HLHL ... HL (2H)
Configurations such as LH ... LHLH or HLHL ... LH (2L) HL ... LHLH can be used. Here, H and L are optical thickness λ _{0/4 (0} λ is the central wavelength) represents a high refractive index layer and a low refractive index layer.

FIG. 3 shows the incident angle dependence of the transmittance of such a band-pass filter. Here, the substrate is made of BK7 glass (refractive index 1.51), the high refractive index layer is TiO ₂ (refractive index n _H = 2.3), and the low refractive index layer is SiO ₂ (refractive index n _L = 1.45). The transmittance in the case of 9 to 23 layers is shown. As can be seen from the figure, the incident angle dependency becomes steeper as the number of layers increases. Therefore, various beam output angle selectivities can be provided according to the purpose.

As described above, according to the present embodiment, since the optical filter 11 as the beam emission angle selection element is arranged in the optical path of the optical system that feeds back a part of the emission light from the laser element 10, Only the beam with a small emission angle of the emitted light can be returned to the light emission end face of the laser element 10. Therefore, the laser element 10 can oscillate in a stable basic transverse mode even in a high-power operation.

FIGS. 4 (a) to 4 (c) are schematic diagrams showing a second embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the example of FIG. 4A, a grating lens 14 is used in place of the lens 12. In this case, since the grating lens 14 can be used by being bonded to the optical filter 11, the size of the optical system can be reduced, and the filter position can be easily adjusted. In this example, the case where the grating lens 14 and the optical filter 11 are bonded and used is shown, but a multilayer film may be formed directly on the back surface of the grating lens 14. At this time, the side on which the multilayer film is formed only has to face the semiconductor laser device 10 side.

In the example of FIG. 4B, the half mirror 13 and the grating lens 14 are formed integrally. That is, behind the optical filter 11 with respect to the semiconductor laser element 10, the semi-transparent mirror 15 composed of a grating lens is arranged. In this case, the light emitted from the laser element 10 passes through the optical filter 11, is partially reflected by the semi-transparent mirror 15, passes through the optical filter 11 again, and returns to the laser element 10. Since a part of the light incident on the semi-transparent mirror 15 passes through as it is, this light can be used as the laser emission light.

The example of FIG. 4C is an improvement of the conventional example shown in FIG. 12, and an optical filter 11 is used instead of the slit of the conventional example.
Is provided. In the figure, reference numeral 16 denotes a spherical mirror. As described above, since the slit is a binary filter, the mode selectivity is not perfect. However, in this embodiment, a filter in which the transmittance continuously changes with the angle as shown in FIG. , A good basic lateral mode is selected.

The semiconductor laser element shown in the above example can be basically of any structure. That is, a refractive index guided laser having a single stripe structure, a gain guided laser, or a wide stripe laser or an array laser may be used. In the case of a single stripe laser,
Even in a high-power operation, fundamental transverse mode oscillation is stably obtained. In the case of a wide stripe laser or an array laser, an output beam having a unimodal far-field image profile is obtained. Further, if an antireflection film is formed on the emission end face of the semiconductor laser device in the above example, the effect of the external resonator can be obtained more.

FIG. 5 is a schematic configuration diagram showing a third embodiment of the present invention. In the figure, 10 is a semiconductor laser element, 12 is a lens, 31 is an optical filter (wavelength selection element), and 13 is a half mirror.
In this figure, light emitted from a semiconductor laser device 10 is collimated by a lens 12, passes through an optical filter 31, and enters a half mirror 13. A part of this light is reflected by the half mirror 13, passes through the optical filter 31 again, returns to the semiconductor laser device 10, and the light is fed back by the half mirror 13, so that an external resonator is constituted as a whole.

The feature of this embodiment lies in that an optical filter 31 is arranged as a wavelength selection element in this external resonator. That is, since the resonator loss is reduced for a certain wavelength due to the wavelength selectivity of the optical filter 31, a semiconductor laser oscillating stably at that wavelength can be obtained. Although mode hopping due to temperature fluctuation may occur in the example of FIG. 13, the present embodiment can stabilize the wavelength over a wide range.

As the optical filter 31, a band-pass filter made of a dielectric multilayer film can be used as in the first embodiment. FIG. 6 shows the wavelength characteristics of such a band-pass filter. Here, the substrate is made of BK7 glass (refractive index
1.51), the high refractive index layer is TiO ₂ (refractive index n _H = 2.3), and the low refractive index layer is SiO ₂ (refractive index n _L = 1.45).
The transmittance in the case of layers 19 to 19 was shown. The horizontal axis is the wavelength normalized by the center wavelength λ ₀ of the filter. The incident angle is 25
The case of a filter designed as ゜ is shown. FIG. 6A shows TE polarized light, that is, when the polarization direction is parallel to an incident plane formed by the normal line of the optical filter and the optical axis,
(B) shows the case of TM polarized light, which is a polarization direction perpendicular to that.

As can be seen from this figure, since the pass band can be narrowed by increasing the number of layers, an arbitrary pass bandwidth can be realized as necessary. FIG. 6 (a)
As can be seen from a comparison between (b) and (b), the pass band width is smaller in the case of TE polarized light. Therefore, a narrower bandwidth can be realized with a smaller number of layers by adopting the configuration of TE polarization.

In the configuration of FIG. 5, the optical filter 31 is arranged to be inclined with respect to the optical path. This is to prevent the light reflected by the optical filter 31 from returning to the semiconductor laser device 10.
Further, by changing the tilt angle, it is possible to effectively change the center wavelength of the filter. Therefore, by providing a rotation mechanism in the optical filter 31, the oscillation wavelength can be made variable. FIG. 7 shows the relationship between the incident angle and the effective center wavelength in a bandpass filter having 19 layers. As shown here, by changing the incident angle, the center wavelength can be changed in a wide range.

As described above, according to the present embodiment, since the optical filter 31 as the beam emission angle selection element is arranged in the optical path of the optical system that feeds back a part of the emission light from the laser element 10, Only a specific wavelength component of the emitted light can be returned to the light emitting end face of the laser element 10.
Therefore, the laser element 10 has a stable wavelength in a wide range, and the wavelength can be externally controlled by changing the inclination of the optical filter 31 with respect to the optical path.

FIGS. 8 (a) to 8 (d) are schematic structural views showing a fourth embodiment of the present invention. The same parts as those in FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the example shown in FIG. 5, a feedback optical system including a wavelength selection element is formed in the optical path of the light emitted from the front surface of the semiconductor laser device. However, the feedback optical system may be formed on the rear surface as shown in FIG. In this case, the reflecting mirror 33 is used instead of the half mirror 13.
, All the selected light can be returned to the laser element 10. When a light output monitor is required, the light detector itself may be arranged instead of the reflecting mirror 33.

In the example of FIG. 8B, the beam splitter 36 and the reflecting mirror
An optical feedback optical system is constituted by using 33. That is, the light emitted from the laser element 10 is collimated by the lens 12, and a part of the light is irradiated on the reflecting mirror 33 by the beam splitter 36 through the optical filter 31. And the reflector 33
The light reflected from the optical filter 31 and the beam splitter 3
It returns to the laser element 10 through 6 and the lens 12. In this case, the output of the front emission light can be monitored as needed. For example, it is possible to arrange a photodetector instead of the reflecting mirror 33.

The example of FIG. 8C is an improvement of FIG.
A grating lens 34 is used instead of 12. In this case, the grating lens 34 is connected to the beam splitter 36
The optical system can be miniaturized by sticking the optical system to the optical system. The example of FIG. 8D is an improvement of FIG. 8C, and uses a right-angle prism 37 as a reflecting mirror. In this case, the optical filter 31 is attached to the right-angle prism 37, and the right-angle prism is rotated to change the center wavelength. Therefore, the size of the optical system can be reduced and the filter arrangement can be facilitated.

FIG. 9 is a schematic configuration diagram showing a fifth embodiment of the present invention. The same parts as those in FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. This embodiment is shown in FIG.
In this example, an element 39 in which these elements are integrated is used instead of the optical filter 31 and the reflecting mirror 33.The light split by the beam splitter 36 is focused by a lens 38 and is incident on the integrated element 39. It is supposed to.

The structure of the integrated device 39 is shown in FIG. 40 in the figure is n-GaAs
A substrate, 41 is a reflecting mirror composed of alternating layers of n-GaAlAs having different compositions, 42 is an n-GaAlAs layer, and 43 is two kinds of Ga having different compositions.
A bandpass filter composed of alternating layers of AlAs, 44 is p-GaAl
As layer, 45 indicates an n-side electrode, and 46 indicates a p-side electrode. Although the integrated element 39 itself functions as a wavelength selection element,
By passing a current, it is possible to change the center wavelength of the filter by utilizing a change in the refractive index due to carrier injection. Also, in this example, the case of a GaAlAs-based semiconductor thin film is shown, but depending on the wavelength of the semiconductor laser device to be used, a semiconductor material transparent to the wavelength is selected,
A similar integrated element may be configured.

FIG. 11 is a schematic configuration diagram showing a sixth embodiment of the present invention. 1 and 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. In this embodiment, both the emission angle selection element in the first embodiment and the wavelength selection element in the third embodiment are used. Specifically, an optical filter 31 is disposed between the lens 12 and the half mirror 13 in addition to the configuration shown in FIG.

With such a configuration, it goes without saying that good fundamental transverse mode oscillation can be realized by the action of the optical filter 11, and the wavelength can be stabilized over a wide range by the action of the optical filter 31. It is. In addition, by providing a mechanism for rotating the optical filter 31, the oscillation wavelength can be controlled from the outside.

In the case where the feedback optical system is configured using both the emission angle selection element and the wavelength selection element, the present invention is not limited to the example of FIG. 11 at all.
This can be realized by appropriately combining the fifth embodiment. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described above in detail, according to the present invention, by providing an optical feedback optical system including a beam emission angle selection element, a semiconductor laser device that oscillates in a stable fundamental transverse mode even in a high-power operation is provided. Can be realized. Further, by providing the optical feedback optical system including the wavelength selection element, it is possible to realize a semiconductor laser device capable of stabilizing the wavelength in a wide temperature range and controlling the wavelength from the outside.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a semiconductor laser device according to a first embodiment of the present invention, FIG. 2 is a sectional view showing a specific configuration of an optical filter used in the above embodiment, and FIG. FIG. 4 is a characteristic diagram showing a relationship between an incident angle and a transmittance in a filter, FIG. 4 is a schematic configuration diagram showing a second embodiment of the present invention,
FIG. 5 is a schematic structural view showing a third embodiment of the present invention, and FIG.
FIG. 7 is a characteristic diagram showing the relationship between the normalized wavelength and the transmittance in the optical filter used in the above embodiment, FIG. 7 is a characteristic diagram showing the relationship between the incident angle and the center wavelength in the optical filter, and FIG. FIG. 4 is a schematic configuration diagram showing a fourth embodiment of the present invention;
FIG. 9 is a schematic structural diagram showing a fifth embodiment of the present invention, and FIG.
FIG. 11 is a cross-sectional view showing a specific configuration of an integrated device used in the fifth embodiment, FIG. 11 is a schematic configuration diagram showing a sixth embodiment of the present invention, and FIGS. FIG. 11: Optical filter (emission angle selection element), 12, 38: Lens, 13: Half mirror, 14, 34: Grating lens, 15: Semi-transmissive mirror, 16: Spherical mirror, 20: Glass substrate, 21 Multilayer film 22 Antireflection film 31 Optical filter (wavelength selection element) 33 Reflector mirror 36 Beam splitter 37 Right-angle prism 39 Integrated element (wavelength selection element),

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-69987 (JP, A) JP-A-53-58788 (JP, A) JP-A-62-285488 (JP, A) 116992 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00

Claims (3)

(57) [Claims] A semiconductor laser device, an optical system for returning a part of light emitted from the laser device to a light emitting end face of the laser device, and an incident angle arranged in an optical path of the optical system is small. A semiconductor laser device comprising: a beam emission angle selection element having a higher transmittance. 2. A semiconductor laser device comprising: a semiconductor laser element; and an optical system for returning a part of light emitted from the laser element to a light emitting end face of the laser element, wherein the optical system comprises: 1. A semiconductor laser device comprising an optical filter and a rectangular prism integrally formed with an optical filter having a wavelength at which transmittance increases depending on an incident angle, and having a high reflectance at a specific wavelength. 3. A semiconductor laser device comprising: a semiconductor laser device; and an optical system for returning a part of light emitted from the laser device to a light emitting end face of the laser device, wherein the optical system comprises: A semiconductor laser device comprising a semiconductor multilayer structure in which a plurality of semiconductor layers having different compositions are stacked, and having a high reflectance for a specific wavelength.