JPS6320892A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser device having high yield and stable single mode selectivity by forming a grating giving the change of a refractive index at least two kinds of periods to propagated beams in a waveguide. CONSTITUTION:A grating 9 has a period slightly different from a grating 8, and is formed at a position where the intensity of wave-guided beams is increased sufficiently. Since the periods of the gratings 8, 9 slightly differ, the wavelength distribution of reflectivity differs from that in case of a single grating and is shaped asymmetrically. Consequently, wavelength-gain characteristics are also formed asymmetrically, and the degeneracy of the maximum gains is released. Since laser oscillation is generated at the resonance mode of the maximum gains, laser oscillation is unified, thus acquiring single mode oscillation. Accordingly, a semiconductor laser device, which can be manufactured easily through an easy manufacturing process, yield of which is improved and which oscillates at a stable single mode, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device that oscillates at a single wavelength.

[Conventional technology]

FIG. 2(a) is a diagram showing the structure of a semiconductor laser device known as a minute 1tj feedback type laser. In this figure, 1 and 2 are p and n electrons, respectively, 3 is an active layer that becomes a laser medium by carrier injection, 4 is an n-type optical guide layer, and 6 and 7 are p-type and n-type cladding layers, respectively. It is made of a material with a lower refractive index than the active layer 3 and the light guide layer 4 at .degree.

8 is a grating.

In this semiconductor laser device, the active layer is 3°, the optical guide layer is 4°
A slab-type waveguide is composed of four layers, cladding layers 6 and 7, and light is propagated while being confined in the vicinity of the central active layer 3 and optical guide layer 4.

Now, the main feature of a distributed feedback laser is the grating 8, which is formed by providing periodic irregularities on the interface between the light guide layer 4 and the cladding layer 7. The essence lies in the fact that a refractive index change is provided.The period A of the groove 8 is set to 8-T(λ/n) ・m, where the wavelength of the propagating light is ^. Here, n is the equivalent refractive index - the propagation constant β of C1 light, n=βλ72π m is a positive integer.

It is.

Next, the operation will be explained.

When light propagates along a waveguide, it undergoes periodic refractive index fluctuations and is diffracted in a specific direction (angle). Under the condition that the wavelength of the light satisfies the period of the grating 8 and the above formula (this wavelength is called the Bragg wavelength), 180
'It is diffracted backwards.

In other words, a reflection occurs. Therefore, laser oscillation is generated by applying positive feedback using this reflection, but it is not due to reflection from a specific surface (reflection occurs in a distributed manner, so it is called a distributed feedback laser. Since it only reflects light, the selectivity of the oscillation wavelength is good, and development as a single wavelength oscillation laser is progressing.

However, in reality, there is a slight width in the wavelength of the reflected light, and for this reason, the laser gain also has a width. Figure 2 (b) shows the resonance mode within the gain width. The resonant modes are located symmetrically on both sides of the gain peak (Bragg wavelength). There is no problem because the mode with low gain does not oscillate, but having two modes with the maximum gain is a big deal, and oscillation usually occurs in one or both of these two modes.

[Problem that the invention seeks to solve]

In the conventional semiconductor laser device as described above, in order to select one of the two modes with the maximum gain, the reflectance at the left and right end faces is changed to make the wavelength-gain 7FJ characteristic asymmetrical, or the phase of the grating 8 is changed midway. A method has been considered in which the resonance mode is shifted to the gain peak by changing only π. However, the method of changing the reflectance at the left and right end faces does not always provide sufficient mode selectivity and lacks stability. Also, the phase of grating 8 is changed to π
The method of changing only π requires advanced technology to change the phase itself, and it is difficult to change exactly π, which has the problem of low yield and not necessarily being able to select a single mode stably.

This invention was made to solve these problems, and it can be manufactured using an easy manufacturing process, has a high yield, and
It is an object of the present invention to obtain a semiconductor laser device having stable single mode selectivity.

[Means for solving problems]

The semiconductor laser device according to the present invention is provided with a grating in a waveguide that provides a small change in refractive index (with two types of periods) to propagating light.

[Effect]

In this invention, each grating provides a gain at a respective Bragg wavelength, and when these gratings overlap, the wavelength-gain distribution becomes asymmetric.

〔Example〕

FIG. 1(a) is a diagram showing the structure of an embodiment of a semiconductor laser device of the present invention. In this figure, Figure 2 (,)
The same reference numerals indicate the same parts, 5 is a p-type light guide layer, 9 is a grating whose period is slightly different from that of the grating 8, and the shape of the unevenness to be formed may be a sine shape, a rectangle, or any other arbitrary shape. However, it is necessary to form it at a position where the intensity of the guided light is sufficiently strong.

As is clear from Fig. 1(a), this device is as shown in Fig. 2(a).
Since the structure is such that the grating 9 is newly added to the semiconductor laser device shown in a), there is no particular difficulty in the manufacturing process, and there is no factor that would reduce the yield.

Next, the operation will be explained.

When a voltage is applied to the p and n electrodes 1 and 2 and a current is caused to flow, carriers are injected into the active layer 3, which becomes a laser medium. Active layer 3. The waveguide formed by the optical guide layers 4, 5 and the clad RFI 6, 7 layers due to the difference in refractive index transmits light to the active layer 3 in the center and the optical guide Ji! It propagates in the horizontal direction of the page while being confined in the vicinity of f4,5. At this time, the propagating light is simultaneously subjected to periodic refractive index changes of the grating 8 at the boundary between the light guide F14 and the cladding layer 7 and the grating 9 at the boundary between the light guide layer 5 and the cladding layer 6.

The period of the grating 9 is ・~÷+−(λ/n) ・m with respect to the wavelength of the propagation destination, and the light at the Bragg wavelength is reflected backward in a distributed manner, providing positive feedback for laser oscillation. You can get 1. Tat!
Since the periods of the gratings 8 and 9 are slightly different, the wavelength distribution of reflectance becomes asymmetrical unlike in the case of a single grating.

Therefore, as shown in FIG. 1(b), the wavelength-gain characteristics also become asymmetrical, and the degeneracy of the maximum gain is resolved.

Since laser oscillation occurs in the resonance mode with the maximum gain, single mode oscillation is achieved by 1'J by combining them into one.

In the above embodiment, the gratings 8 and 9 are located on both sides of the active layer 3, but they may be located anywhere within the light distribution. Alternatively, a single grating having refractive index changes in two types of periods may be used.

For example, if a single-period grating is represented by a;a oX Slnω,x, then a=aosin ωox+alsin IJJI! A similar effect can be obtained with a single grating having unevenness.

In addition, in the above embodiment, for convenience, the case where the gouging 8°9 extends over the entire waveguide is described, but this is not necessarily limited to this, and the same effect can be obtained even if the gouging is formed in a part of the waveguide. There is no need for the two gratings 8 and 9 to overlap and face each other.

Furthermore, there is no need to limit the period to the ZPfi class (it is clear from the asymmetry point of view that the same effect can be obtained even if there are three or more types.

〔Effect of the invention〕

As explained above, this invention is equipped with a grating in the waveguide that changes the refractive index at two different periods for the propagating light, so it can be manufactured through an easy manufacturing process and has a high yield. , and a semiconductor laser device that oscillates in a stable single mode can be obtained.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are diagrams showing the structure of an embodiment of the semiconductor laser device of the present invention and diagrams showing its wavelength-gain characteristics. FIGS. FIG. 1 is a diagram showing the structure of a laser device and a diagram showing its wavelength-gain characteristics. In the figure, 1 is a p-electrode, 2 is a Ti electrode, 3 is an active layer, 4 and 5 are optical guide layers, 6 and 7 are cladding layers, 8.9
is a grating. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa (2 others) Figure 1 (b) □ Wavelength Figure 2 (a) Written amendment to the procedure (spontaneous) 1. Indication of the case Patent application No. 1-166181 2. Invention Name Semiconductor radar device 3, relationship to the case of the person making the amendment Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Moriya Shiki, representative of Mitsubishi Electric Corporation 4, agent residence Address: 2-2-3-5 Marunouchi, Chiyoda-ku, Tokyo
, ? Column 6 of the detailed description of the invention in the 1O positive subject specification, ? 1O positive details! rn=βλ72π on page 3, lines 2 and 3 of IIV3 is a positive integer. It is. ”, as below? to correct. "n=βλ/2π. Also, m is a positive integer."

Claims (1)

[Scope of Claims] A semiconductor laser device having a waveguide including an active layer, characterized in that a grating that changes the refractive index of propagating light in at least two types of periods is provided in the waveguide. Semiconductor laser equipment. (2) The semiconductor laser device according to claim (1), wherein the grating that changes the refractive index with at least two types of periods includes two gratings with different periods sandwiching the active layer. .