JPS5861692A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To realize stable single wavelength oscillation by disposing the convergent lens which outputs the parallel light and the optical waveguide material which has the diffraction grating at the inclined end surface. CONSTITUTION:An output beam of laser 9 is converted to the parallel beam by the convergent lens 11. The parallel beam advances in parallel within the optical waveguide rod 12 and reflected by the diffraction grating 8. Only the light beam which satisfies the wavelength relation determined by the refractive index of rod 12, period of grating 8 and incident angle is reflected in the same direction as the incident beam and then returned to the laser 9. Therefore, when observed from the laser element, the reflectivity is large only for such wavelength and the oscillation threshold level becomes small and thereby single wavelength operation in the vicinity of such wavelength can be realized. Moreover, further excellent efficiency can be obtained by providing the reflection film 15 to the grating 8 while mounting the reflection preventing films 13, 14 to the end of laser 9, lens 11 and rod 12, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to stabilizing the oscillation wavelength of a semiconductor laser.

Semiconductor lasers are widely used as light emitting sources in the fields of optical information processing and optical fiber communication. Currently, in these applications, only the so-called intensity of light is used, and the original characteristic of light, that is, its ultra-broadband nature, is not utilized. The reason for this is that the frequency of light emitted from a normal semiconductor laser is extremely unstable. In particular, instability is significant when high-speed pulse operation is performed for communication purposes or the like.

This instability in the oscillation wavelength is caused by the fact that normal semiconvoluted lasers use a pair of cleavage planes in the crystal as a resonator.
This is due to the fact that this resonator does not have any wavelength selectivity. Therefore, in order to stabilize the oscillation wavelength, it is necessary to impart wavelength selectivity to the resonator by some method.

For this purpose, lasers with a double resonator structure and lasers with a structure incorporating a diffraction grating have been proposed, and prototypes are being produced.

Among these, the dual resonator structure requires detailed wavelength setting and inherently has the possibility of multi-wavelength oscillation.

On the other hand, when a diffraction grating is applied internally or externally, since the diffraction grating has a fairly sharp wavelength selectivity, complete single wavelength oscillation is possible and its stability is extremely high.

As examples of attaching a diffraction grating inside a laser, a distributed feedback laser as shown in Fig. 1al and a distributed reflection laser as shown in FBL have been experimentally produced, and high wavelength stability has been obtained. . In FIGS. 1al and lbl, 1 is a light-emitting layer or active layer such as InGaAsP, 2, 3.4 is a cladding layer such as InP, and 5 is a cladding layer such as InP.
is an output extraction layer such as InGaAsP, 6.7 is an electrode, and 8 is a diffraction grating. However, such lasers are difficult to manufacture and may pose problems in terms of structural reliability.

On the other hand, when providing a diffraction grating externally, conventionally it is quite large-scale as it requires a lens etc. as shown in Figure 2.
Not only will the optical system become unstable, but the compact feature of semiconductor lasers will no longer be utilized. In FIG. 2, 8 is a diffraction grating, and 9 is, for example, InGaAsP/
In a semiconductor laser such as an InP laser, IO is a lens.

The present invention is a semiconductor laser device designed to solve the above-mentioned difficulties of the prior art.

The present invention will be explained in detail below.

FIG. 3 shows an example of the present invention. In FIG. 3, 8 is a diffraction grating, 9 is a semiconductor laser, 11 is a cylindrical or prismatic focusing lens, 12 is an optical waveguide such as a cylindrical or prismatic optical waveguide rod, 13 and 14 are antireflection films,
15 is a reflective film. The cylindrical or prismatic focusing lens 11 has a pitch of about 1/4 in this example, so that the output light of the laser 9 at a certain angle is converted into parallel light. Here, not necessarily 1 +
1.

Even if it is not about - hit, about m + ahi, chi (m ” O
Parallel light can also be obtained with r1.2, 3...). The waveguide 12, which is made of glass or quartz and has no focusing property, travels in parallel as it is, and the diffraction grating r8
reflected by. The element reflected by the diffraction grating 8 is λ in an ideal case, where the refractive index of the original waveguide 12 is n1, the period of the diffraction grating 8 is 71, and the angle of incidence is θ. -2n A sin
Only those that satisfy the wavelength relationship θ are reflected in the same direction as the incident light and returned into the laser 9.

Therefore, when viewed from the laser, the reflectance is large only for this wavelength, and therefore the oscillation threshold is also small, realizing single wavelength operation around this wavelength. On the other hand, in terms of size, both the focusing lens 11 and the optical waveguide rod 12 are sufficient in length, so it is quite possible to reduce the size of the three parts as a whole to 10W or less. Therefore, packaging can also be performed. Further, as shown in the figure, a reflective film 15 is formed on the diffraction grating 8 by vapor deposition of gold or the like.
If antireflection coatings 13 and 14 are applied to the end face of the laser 9, the focusing lens 11, the waveguide rod 12, etc., the effect will be even more effective.

Furthermore, since the semiconductor laser of the present invention utilizes a normal cleavage plane, there is no problem of impairing reliability.

As described above, according to the present invention, it is possible to obtain a semiconductor laser device that performs stable single wavelength oscillation, which is also excellent in reliability, and maintains the compact characteristics of the semiconductor laser. Therefore, the laser of the present invention is extremely promising as a light-emitting layer for low-loss optical fiber communications, and is highly useful for realizing long-distance and wide-band original fiber communications.

[Brief explanation of the drawing]

1al, (bl is a vertical cross-sectional view showing an example of a conventional semiconductor laser equipped with an internal diffraction grating; FIG. 2 is a schematic side view showing a conventional example of a laser with an external diffraction grating that combines a lens and a diffraction grating; Fig. 3 is a schematic side view showing one embodiment of the present invention. 1... Emitting layer or active layer (for example, InGaAsP/
For InP-based lasers, InGaAsP), 2,
3, 4-... cladding layer (e.g. InP), 5...
Output extraction layer (e.g. InGaAa P), 6, 7
...electrode, 8...diffraction grating, 9...semiconductor laser (e.g. InGaAsP/Inp laser), 1
0・V7zu, 11... Cylindrical or prismatic focusing lens, 12... Cylindrical or prismatic optical waveguide rod, 13.14... Anti-reflection film, 15... Reflective film.

Claims (3)

[Claims] (1) A semiconductor laser, a focusing lens that outputs parallel light, and an optical waveguide whose one end surface is inclined with respect to the optical axis and which has a diffraction grating on the inclined end surface are sequentially arranged so that the optical axis is #
Semiconductor laser devices arranged close to each other or bonded to each other so as to coincide with each other. (2) The semiconductor laser device according to claim 1, further comprising a reflective film on the end face having the diffraction grating. (3) An antireflection film is provided on the end faces of the semiconductor laser, the focusing lens, and the optical waveguide that are close to each other or bonded to each other. The semiconductor laser device described.