JPS60224289A - External resonator type laser diode - Google Patents

Abstract

PURPOSE:To obtain a laser diode, in which a compound mode is hard to occur, the mode is stabilized and a far view image pattern is of circular shape, by inclining the light input and output end surfaces of a semiconductor light emitting element with respect to its light axis. CONSTITUTION:The light input and output end surfaces of a semiconductor light emitting element 100 are inclined with respect to its light axis. When a current is supplied to such a semiconductor light emitting element 100, light is emitted in the direction of A and A'. The residual light of about 2% is reflected in the direction B but is not reflected in a stripe region 9. The reflected light is inputted to the outer surface of the light emitting element 100. Since a reflection preventing film is formed on the outer surface, the light is transmitted to the outside of the light emitting element 100 and is not inputted into the light emitting elememt 100 again. Therefore a compound mode is not generated by the residual light, which is yielded at the light input and output end surfaces of the light emitting element 100. Thus the mode is stabilized. Since the slant angle is selected so that it is larger than the angle of diffraction, the far view image pattern becomes approximately circular.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an external cavity type laser diode. In particular, the present invention relates to improvements that prevent the generation of complex modes and stabilize the modes of external cavity laser diodes.

(2) Background of the technology An external cavity laser diode is a laser diode in which the resonator, which is essential for functioning as a laser, is provided outside the semiconductor light emitting device, rather than on the light input/output end face of the semiconductor light emitting device. This external cavity type laser diode, which is referred to as a diode, has a semiconductor light emitting element l and an optical axis 12 facing the light input/output end face 11 of the semiconductor light emitting element l, as shown in FIG. It is composed of a pair of optical systems (lenses in the figure) 2 and light reflecting means (reflecting mirrors in the figure) 3 arranged orthogonally to each other. Since other optical elements can be placed in between, various new functions can be added.

As mentioned above, laser diodes generally use semiconductor light-emitting elements, so due to their structure, it is not always easy to make the near-field pattern circular. However, if you somehow find a way to make the far-field pattern circular. If you do, it will be advantageous. This is because the coupling efficiency with the optical system can be increased.

(3) In the C1 external cavity laser diode, which has a problem with the prior art, it is necessary that the reflection of light at the light input/output end face of the semiconductor light emitting element be as small as possible. Otherwise, a composite resonator will be constructed due to the residual reflection at the light input/output end face, and a composite mode will be generated due to the return light at the light input/output end face, resulting in the mode becoming unstable. Because there is. In order to eliminate this drawback as much as possible, in conventional external cavity laser diodes, it is common to form an antireflection film made of aluminum oxide or the like on the light input/output end facets. is 98
%, and it is difficult to avoid residual reflected light of about 2%, and it is difficult to admit that it is necessarily an acceptable level.Therefore, it is necessary to reduce the residual reflection, reduce the degree of composite mode generation, and make the mode more stable. It has been desired to develop an external cavity type laser diode with an L/climb. Further, as mentioned above, since it is desirable for a laser diode to have a circular far-field pattern, it has been desired to develop an external cavity type laser diode having a circular far-field pattern.

(4) Purpose of the invention The purpose of the present invention is to meet these demands,
An object of the present invention is to provide an external cavity type laser diode in which a complex mode is generated and the mode is stable. A further object of the present invention is to provide an external cavity laser diode in which complex modes are less likely to occur, the mode is stable, and the far-field pattern is circular.

(5) Structure of the Invention The structure of the present invention includes a semiconductor light emitting device, a pair of optical systems and a light reflecting means disposed facing the light input/output end face of the semiconductor light emitting device and perpendicular to the optical axis. The external cavity type laser diode is characterized in that the light input/output end face of the semiconductor light emitting element is inclined with respect to its optical axis.

The present invention utilizes the natural law that if the residual reflected light, that is, the return light at the light input/output end face of a semiconductor light emitting element is emitted to the outside of the waveguide layer of the semiconductor light emitting element, a composite mode will not occur.

Also, once the light emitted outside the waveguide layer is reflected on the inner surface of the semiconductor light emitting element, the reflected light may enter the waveguide layer again and cause a complex mode. If a light absorption film such as Ge is formed on the surface, or an antireflection film made of a material with an appropriate difference in refractive index from the material of the semiconductor light emitting element is formed,
The effect is significant. When the material of the semiconductor light emitting device is indium phosphide, it has been experimentally confirmed that when a layer of titanium dioxide is formed on the outer peripheral surface of the device, the residual reflectance is improved to about 0.2%.

Since a laser diode is constructed with a stack of semiconductor layers, the waveguide layer generally has a rectangular shape at the light input/output end face. As a result, the near-field image has an elliptical shape (more precisely, a rectangular shape).

It is known that the diffraction angle in the long sleeve direction of an ellipse is smaller than the diffraction angle in the short axis direction. Therefore, it is most advantageous for the above-mentioned direction of inclination to be the same direction as the direction in which this optical diffraction angle is minimized.

Similarly to the above, when the material of the semiconductor light emitting device is indium phosphide, if a layer of titanium dioxide is formed on the outer circumferential surface and the inclination direction is selected to be the same direction as the direction in which the light diffraction angle is the minimum, It has been experimentally confirmed that the residual reflectance was improved to about 0.1%.

Furthermore, as mentioned above, it is desirable that the far-field pattern be close to a circle, so if the tilt direction is the above-mentioned direction and the tilt angle is greater than or equal to the prior diffraction angle in this tilt direction, the desired purpose can be achieved. most convenient for

(6) Embodiments of the Invention Hereinafter, with reference to the drawings, the main manufacturing process of an external cavity laser diode according to an embodiment of the present invention will be explained to further clarify the structure and unique effects of the present invention. Make it.

See Figure 2 (front view) A semiconductor light emitting device made of a stack of semiconductor layers is manufactured.

A typical example of the main manufacturing process is shown below. Using a liquid phase epitaxial growth method, for example, a layer containing Sn at about 1017 cm-3 and having a thickness of 1.51 Lm is formed on the n-InP substrate 4.
A lower cladding layer 5 made of an n-type InP layer of about 5 cm is formed, and a p-I n Ga A layer containing cd of about 5 x 1016 cm-3 and having a thickness of about 0.1 final layer is formed.
An active layer 6 made of an S P layer is formed, and C is applied.
Contains Cd to about 1017c fat -3 and has a thickness of 1.5 1
Form an upper cladding layer 7 of approximately
A contact layer 8 having a thickness of about 1pm and a thickness of about 18c+m-'' is formed.

3 (plan view) and FIG. 4 (side view), as is clear from FIG. Leaving an extending striped region 9, S is applied to the left and right regions thereof to a depth reaching the lower cladding layer 5 (see FIG. 4 (side view)).
The contact layer 8, upper cladding layer 7, and active layer 6 are converted into n-type regions 8', 7', and 6° by ion implantation of n. As a result, when a voltage is applied from top to bottom in FIG. 4, current flows only through the striped region 9.

Refer to FIG. 5 (front view) A triple layer of Ti/Pt/Au is applied to the upper and lower surfaces (the upper surface of the contact layer 8 and the lower surface of the substrate 4) of the laminate manufactured in the above manner using an electron beam deposition method or the like. The layers are formed to form positive and negative electrodes 10 and lOo, respectively.

Refer to FIG. 6 (plan view) The striped region 9 is sliced at an angle of about 2O2, and a titanium dioxide layer is sputtered on the outer peripheral surface of the semiconductor light emitting device 100 to a thickness of 2.000 to 3.00OA. to form an antireflection coating (not shown).

Refer to FIG. 7 (plan view) In the semiconductor light emitting device 100 manufactured through the above steps,
When a current is supplied to emit light, the light is emitted in the directions indicated by A and A' in the figure, but about 2% of the residual reflected light is reflected in the direction indicated by B in the figure, and is reflected in the striped area 9 (
It does not reflect into the liquid conducting layer). Then, the semiconductor light emitting device 1
However, since an anti-reflection film (not shown) is formed on this outer circumferential surface, the light is transmitted to the outside of the semiconductor light emitting device 100 without being reflected, and then enters the semiconductor light emitting device 100 again. Therefore, no composite mode is generated due to residual light generated at the light input/output end face of the semiconductor light emitting device 100.

Refer to FIG. 8 (plan view) A set of an optical system (lens in the figure) 2 and a light reflecting means (reflector in the figure) 3 is arranged in the optical paths A and A' of the semiconductor light emitting device 10G. Completes external cavity type laser diode.

An external cavity laser diode with a visible structure is not affected by returned light, so no compound mode is generated.
mode becomes stable. Furthermore, the above-mentioned inclination angle is chosen to be larger than the diffraction angle, so that the far-field pattern is approximately circular.

(7) As described in detail, according to the present invention, it is possible to provide an external cavity laser diode in which complex modes are less likely to occur and the mode is stable. Furthermore, it is an object of the present invention to provide an external cavity laser diode in which complex modes are less likely to occur, the mode is stable, and the far-field pattern is circular.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of an example of an external cavity type laser diode. 2 to 6 are front views (views seen from a direction perpendicular to the optical axis) showing the main manufacturing steps of a semiconductor light emitting device constituting an external cavity laser diode according to an embodiment of the present invention; They are a plan view, a side view (view from the optical axis direction), a front view, and a plan view. FIG. 7 is an explanatory diagram for explaining the present invention in detail, and is a plan view of a semiconductor light emitting device. FIG. 8 is a conceptual configuration diagram (plan view) of an external cavity type laser diode according to an embodiment of the present invention. l...Semiconductor light emitting element, 11...Light input/output end surface,
12-Reining optical axis, 2-fight-optical system, 3... Light reflecting means, 4... Substrate, 5.q. Lower cladding layer, 6
...Active layer, 6°...Fist n-InGaAsP layer,
7... Upper cladding layer, 8... Contact layer,
7°, 8゛ Φ・*n-InP layer, 9... Striped region, 100... Semiconductor light emitting device, 10.10'
-... Positive and negative electrodes, A, A''... Optical path of emitted light,
Figure 1 Figure 2 Figure 3

Claims (5)

[Claims] (1) An external resonator consisting of a semiconductor light emitting device, and a pair of optical systems and light reflecting means disposed facing the light input/output end faces of the semiconductor light emitting device and perpendicular to the optical axis. 1. An external cavity type laser diode, characterized in that a light input/output end face of the semiconductor light emitting element is inclined with respect to its optical axis. (2) The external cavity laser diode according to claim 1, wherein a light absorption film is formed on the outer peripheral surface of the semiconductor light emitting element. (3) The external cavity laser diode according to claim 1, wherein an antireflection film is formed on the outer peripheral surface of the semiconductor light emitting element. (4) The external resonator according to claim 1, 2, or 3, wherein the direction of inclination of the optical axis is the same as the direction in which the light diffraction angle at the light input/output end face is minimum. type laser diode. (5) The external cavity laser diode according to claim 4, wherein the inclination angle of the optical axis is larger than the optical diffraction angle.