JPS63263785A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To improve S/N characteristic of a semiconductor laser without rely ing upon the variation in a returning light ratio by forming a periodic structure for selectively feeding back only a light of wavelength used by diffracting a light generated in an active layer at the upper or lower side of the layer of a laser which is self-oscillated. CONSTITUTION:A guide layer 10 made of In1-pGapP1-qAsq formed between a first upper clad layer 4 and an active layer 4 is formed by a 2-luminous flux interference exposure method and etching, and its periodic structure is so formed as to selectively feed back only a light of wavelength used by operat ing as a secondary diffraction grating. The thickness of the layer 4 is set so that an oscillation spectrum becomes a self-oscillation mode. Since only the light of the wavelength used by the grating of the light generated from the layer 3 is selectively fed back in this manner and the beam width of the spec trum is extended peculiarly for the self-oscillation, S/N characteristic is particu larly preferable to oscillate in a single mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser used as a light source for, for example, optical discs, optical communications, printers, and the like.

[Conventional technology]

FIG. 2 is a perspective view showing the structure of a well-known conventional semiconductor laser chip.

In the figure B, 1 is a substrate made of n-GaAs, 2 is a lower cladding layer made of n-AlxGal-xAs, 3 is an active layer made of undoped AjyGal-yAs, and 4 is a p- A I XG al, A s
5 is a current blocking layer made of n-GaAs; 6 is p A l +tG al-X
A second upper cladding layer made of AS, 7 an electrode contact layer made of p-GaAs, 8 a p-side electrode, and 9 an n-side electrode.

Next, the operation will be explained.

p# electrode f3. When a forward bias is applied between the n-side electrodes 9, an active layer with a narrower energy gap than the lower cladding layer 2 and the first upper cladding layer 4 and a higher refractive index than the lower cladding layer 2 and the first upper cladding layer 4 is formed. Layer 3 contains electrons and
Hole pairs and light are effectively confined.

The above explanation relates to the confinement of electron/hole pairs and light in the vertical direction (up and down direction) in the cross section perpendicular to the stripes.On the other hand, in the horizontal direction, the current blocking layer 5 is connected to the lower cladding 1d2 and the substrate. Since it has a majority carrier different from 1, a current confinement mechanism is formed by a potential wall that prevents carrier conduction, and carriers flow through the groove where there is no current blocking layer 5, and electron/hole pairs are concentrated in the groove. I will do it.

Note that this current blocking layer 5 has a smaller energy gap than the active layer 3, so there is a risk that after carriers are generated by the light generated from the active layer 3, they will be conducted and the height of the potential wall will be reduced. But this problem
This problem can be solved by forming a large number of non-radiative recombination centers in the current blocking layer 5.

In addition, confinement of light in the horizontal direction is caused by a sudden increase in the absorption coefficient of light near the current blocking layer 5 outside the groove, and a decrease in the effective refractive index, which ultimately causes the refractive index inside the groove to decrease, effectively trapping light. It is confined and oscillations are performed efficiently.

Further, the waveguide mechanism that confines light in the horizontal direction and the effective refractive index difference at 17 can be arbitrarily set by controlling the thickness of the first upper cladding layer 4. As this effective refractive index difference increases, that is, as the thickness of the first upper cladding layer 4 decreases, the oscillation spectrum changes from the multimode shown in FIG. 3(11) to that shown in FIG. 3(b). It is known that the mode changes to a self-sustained oscillation mode as shown in Figure 3 (C), and then to a single mode as shown in Figure 3 (C).By setting an appropriate effective refractive index difference, Any oscillation spectrum can be selected.

When a semiconductor laser having the above-mentioned configuration is actually used as a light source for an optical disk, an optical communication device, a printer, etc., its oscillation spectrum characteristics are important.

For example, for use as a light source in a printer, a single mode is required due to the need to suppress sensitivity dispersion. especially,
In high-speed scanning holographic printers, a dynamic single-mode laser with almost no wavelength shift even during high-speed modulation is desired.

Furthermore, a light source for reading optical discs is required to have good S/N characteristics, and as can be seen from the S7N characteristics shown in FIG. 4, single mode lasers are used.

In the case of multimode lasers, the range of return destination vehicles in actual use is currently limited, so an automatic oscillation laser with good S/N characteristics is desired.

Furthermore, as a light source for optical communications, when limited to relatively short-distance applications such as data links, multimode lasers are used to reduce modal noise generated by multimode 7-eye bars.

[Problem that the invention seeks to solve]

As for the conventional semiconductor lasers as described above, there is no structure that can be commonly used for various laser applications, and a structure suitable for each field must be selected to suit the characteristics of each field. For this reason, the manufacturing process for each semiconductor laser becomes complicated and the structure is dispersed, so there is a problem that it is difficult to improve the yield.

This invention was made with the aim of solving these problems, and is a semiconductor laser that has a common structure that can be applied to a wider range of applications, has particularly good S/N characteristics, and oscillates in a single mode.・The first objective is to obtain the

[Means for solving problems]

The semiconductor laser according to the present invention has a periodic structure formed above or below the active layer of an automatically oscillating laser, which diffracts the light generated in the active layer and selectively returns only the light of the wavelength to be used. It is.

[Effect]

In the invention of B, only the light of the wavelength used for one cycle is selectively returned by the back diffraction grating of the light generated in the active layer,
Moreover, the linewidth of the spectrum becomes wide, which is characteristic of automatic oscillation.

〔Example〕

FIG. 1 is a perspective view showing the structure of an embodiment of the semiconductor laser of the present invention.

In this figure, the same symbols as in Fig. 2 indicate the same parts,
10 is the first upper crust I evil 4 and the active 1! Ink-pGa formed between i3, P 1-Q
In the waveguide layer consisting of ASq, 32 of He-Cd+z-
A= ...(+ key) m: Integer, λ. 2. Wavelength to be used, n: pitch of refractive index within the waveguide layer 10.

Further, the thickness of the first upper cladding layer 4 is set so that the oscillation spectrum becomes an automatic oscillation mode as shown in FIG. 3(b).

In addition, all growth is done by MBE method or MOCV l.
) is done by law.

Next, the operation will be explained.

p O-1! When a forward bias is applied between the I electrode 8 and the n-side electrode 9, one line at the back of the spectrum shown in FIG. 3(b) is selected by the diffraction grating formed by the waveguide layer 10. It begins to oscillate with a spectrum as shown in FIG. 3(0). At this time, current injection and confinement into the center of the active layer 3 and light confinement are performed in the lower cladding layer 2 in the same manner as in the conventional example. This is efficiently performed by the first upper cladding layer 4 and the current blocking layer 5.

In other words, although the oscillation mode of the semiconductor laser of this invention is a single mode as shown in FIG. Single automatic oscillation mode. Therefore, as shown in FIG. 4, a high S/N ratio can be maintained regardless of the destination vehicle.

In addition, in the above embodiment, the waveguide layer 10 is I nl-, Ga
.

Although it is made of P , , A sq , it may be made of AjGaAs, or it may be placed below the active layer 3 .

〔Effect of the invention〕

As explained above, the invention of Party B forms a periodic structure above or below the active layer of an automatically oscillating laser that diffracts the light generated in the active layer and selectively returns only the light of the wavelength to be used. Therefore, the S/N characteristic is extremely good irrespective of changes in the destination vehicle, and there is an effect that it can be used for various applications with different usage conditions.

[Brief explanation of drawings]

[Figure] is a perspective view showing the structure of an embodiment of the semiconductor laser of the present invention, Figure 2 is a perspective view showing the structure of a conventional semiconductor laser, and Figure 3 is a diagram for explaining the oscillation mode of the semiconductor laser. , Figure 4 shows the S/D by the oscillation mode of the semiconductor laser.
FIG. 3 is a diagram showing N characteristics. In the figure, 1 is the substrate, 2 is the lower cladding layer, 3 is the active layer, 4 is the first upper cladding layer, 5 is the current blocking layer, 6 is the second upper cladding layer, 7 is the contact layer, 8 is the [1 side] electrode,
9 is an n-side electrode, and 10 is a waveguide layer. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa (2 others) Figure 1 Figure 2

Claims (1)

[Claims] In a self-oscillation laser equipped with a current confinement mechanism for flowing current in a stripe shape in an active layer and a waveguide mechanism having an effective refractive index difference in the lateral direction of the stripe, the above-mentioned A semiconductor laser characterized by forming a periodic structure that diffracts light generated in an active layer and selectively returns only light of a wavelength to be used.