JPS6332986A - Integrated semiconductor laser - Google Patents

Abstract

PURPOSE:To generate laser oscillation on respective quantum levels, by forming an active layer in multiple quantum-wells having barrier width narrowed and electronic states combined and besides by composing plural semiconductor laser elements, which have the similar resonator lengths and the regions where carriers different in size can be injected, on the similar substrate. CONSTITUTION:Cleavage planes 12 and 13 compose a Fabry-Perot resonator. Diffused p-type dopants form a striped waveguide, which runs in parallel with the axis of the resonator, in quantum-well layers. This stripe width is made small because light through the waveguide is more absorbed by free carriers in the diffusion region in the vicinity of the guided-wave path. The lengths LA,LB, and LC in the resonator-length directions of electrodes 4A, 4B, and 4C, become small in the order of them, and LA is equal to the resonator length. If the lengths LA, LB,and LC of the respective electrodes are set up to be ones in which laser oscillation on the respective levels can be generated, laser beams with respective different wavelengths can be oscillated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an integrated semiconductor laser used in wavelength multiplexed optical communications and the like.

[Conventional technology]

Figure 3 (al is for example Applied Physics Letters, Vol. 29, p. 506, 1976 (Appl, Phys.
s, Lett.

Vol, 29. p. 506. (1976)) is a diagram showing the configuration of a conventional integrated semiconductor laser for wavelength multiplexed optical communication.

In the figure, 3 is the n-side electrode, 4 is the p4@ electrode, and 5 is the n-side electrode.
GaAs substrate, 6 is NA 16. s G ao
, qAs, 11 is Zn diffusion front, 14 is p-Ga
As, 15 is pA 1o, z Gao, a A 3%
16 is pA 1 o, oyG ao, 93A S
, 17 are periodic irregularities.

This laser oscillates through distributed feedback due to the periodic unevenness. Assuming that the period of concavities and convexities is A, the oscillation wavelength λ is as follows.

n is the effective refractive index of the waveguide, and m is an integer. Since Δ is very small and it is difficult to process unevenness, m=3 is usually used.

As shown in FIG. 3, if 8 is slightly changed in some of the four wave paths, light of different wavelengths can be obtained according to equation (1).

However, manufacturing such an integrated laser requires many difficult steps, such as forming unevenness in each waveguide with a slightly different number of eight, and epitaxial growth being performed twice, which makes the unevenness easy to collapse. It's bad.

[Problem that the invention seeks to solve]

Conventional light sources for wavelength-multiplexed optical communication are constructed as described above and are difficult to manufacture and therefore expensive.

This invention was made to solve the above-mentioned problems, and its purpose is to obtain an integrated semiconductor laser in which semiconductor lasers whose oscillation wavelengths are systematically varied can be integrated by one crystal growth. .

[Means for solving problems]

The integrated semiconductor laser according to the present invention uses a multi-quantum well in which electronic states are combined by narrowing the barrier width as an active layer, has the same cavity length, and can inject carriers of different sizes. A plurality of semiconductor lasers each having a region are formed on the same substrate.

[Function] Since the semiconductor laser of the present invention has a narrow barrier width, coupling of electronic states between well layers occurs and the quantum level of one quantum well layer is separated into multiple quantum levels. By making the size of the current injection region of each laser different in the resonator axis direction in correspondence with the value of each quantum level, each of the lasers is caused to oscillate at each of the separated quantum levels. Can be done.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is the negative current terminal, 2A.

2B, 2C are positive current terminals, 3 is n-side electrode, 4A, 4
B, 4C are n side electrodes, 5 is n6-GaAs substrate, 6 is n
-AlGaAs cladding layer, 7 is an active layer consisting of multi-ffl quantum wells, 8 is p-AlGaAs cladding layer, 9A,
9B and 9C are p''-GaAS contact layers, 10 is an insulating film, 11 is a p-type impurity diffusion front, 12, 1.3
is the open side of the arm.

The armature viewing surfaces 12 and 13 constitute Fabry-Perot resonators. The diffused p-type dopants form striped waveguides in the quantum well layer parallel to the axis of the cavity. Here, this stripe width is determined by the width of the stripe in the diffusion region near the waveguide.
It is narrowed to increase the absorption of guided light by free carriers. Further, the lengths La, Lm, and Lc of the electrodes 4A, 4B, and 4C in the resonator length direction are successively shorter, and LA is the same as the length of the resonator.

Next, the operation will be explained.

In the multiple quantum well of this example, since the barrier layer has a narrow width, the width of the barrier layer is narrow.
Coupling of electronic states occurs between the two quantum wells, and as a result, the fundamental quantum level of this multiple quantum well is split into three as shown in Figure 2, with only the level involving heavy holes (h h). When looking at this, three absorption peaks are observed.<1i Focusing on light emission involving only small holes is equivalent to considering only the TE mode). It is well known that the density of states of these quantum levels increases stepwise as the energy increases, so if the injected carrier density is made sufficiently high to cause band filling, the amplification gain of the high energy quantum levels will increase. It is being

Next, a semiconductor laser with a cavity length LA and a length Lll (L
Consider injecting current only into the region l < t, a'J. An amplification gain g8 is obtained in the region where the current is injected. If the waveguide loss due to absorption, scattering, etc. is α, laser oscillation occurs when the following conditions are met.

Here, R is the reflectance of the arm opening surface 12.13. As is clear from equation (2), as L becomes smaller, the right side of the inequality increases, so unless g is high, oscillation will not occur. From this, it can be seen that if , is made smaller one after another, oscillations due to the three levels described above can be obtained in the order of the longer wavelengths.

Therefore, the length LA of each electrode in the device of this embodiment shown in FIG.
By setting L, , Lc to lengths that allow oscillation by each level, laser beams of different wavelengths are oscillated from each integrated semiconductor laser.

As described above, in this example, a plurality of semiconductor lasers with the same cavity length are configured on the same substrate, with the active layer being a multi-quantum well layer having a barrier layer thin enough to combine electronic states,
By changing the length of each electrode, the internal loss of the resonator is made different, and each oscillates at a different quantum level, making it possible to oscillate at different wavelengths, making this a semiconductor that can be used for wavelength multiplexing communications. Laser is obtained.

Furthermore, since this semiconductor laser does not require the production of a diffraction grating, it can be produced by one epitaxial growth process, making it both inexpensive.

In addition, in the semiconductor laser according to the present invention, in order to increase the optical propagation loss, the energy of the injected carriers is relaxed, and the occupation rate of higher-order quantum levels is increased. It is desirable that the layer thickness of the quantum well active layer is 300 Å or less, and the stripe width of the optical waveguide due to lateral confinement is 3 microns or less.

Furthermore, in the above embodiment, the case where GaAs/AlGaAs was used as the semiconductor was explained, but this is InP/InG.
aAsP may also be used.

〔Effect of the invention〕

As described above, according to the present invention, in an integrated semiconductor laser, by narrowing the barrier width, a multiple quantum well in which electronic states are combined is used as an active layer, and a multi-quantum well with the same resonator length and different sizes is used as an active layer. Since a plurality of semiconductor lasers each having a region into which carriers can be injected are formed on the same substrate, an integrated semiconductor laser for wavelength multiplexed optical communication that oscillates at different wavelengths can be obtained at a low cost.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the structure of an integrated semiconductor laser according to the present invention, Figure 2 is a diagram showing the absorption spectrum of three quantum wells with coupling, and Figure 3 (a) is a diagram showing the conventional multi-wavelength oscillation. FIG. 3(b) is a cross-sectional view showing the structure of a semiconductor laser, and is a perspective view showing a conventional semiconductor laser that oscillates at multiple wavelengths. In the figure, 1 is the negative current terminal, 2 is the positive current terminal,
3 is an n-side electrode, 4 is a p-side electrode, 5 is an n-GaAs substrate, 6 is an nAlGaAs cladding layer, 7 is an active layer consisting of a multiple quantum well, 8 is a p-AtGaAs cladding layer, 9 is p-GaAs: ] contact layer, 10 is an insulating film, 11 is a diffusion front, and 12° and 13 are open faces.

Claims (1)

[Claims] (1) In an integrated semiconductor laser in which a plurality of semiconductor lasers having the same cavity length are configured on the same substrate, each of the plurality of semiconductor lasers is separated by a narrow barrier that connects the electronic states of adjacent quantum wells. 1. An integrated semiconductor laser comprising: an active layer having a multi-quantum well structure having a width; and a carrier injection region having a size different from that of other lasers.