JPS606553B2 - semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wavelength tunable semiconductor light emitting device in which a laser oscillation wavelength is changed by electrical control.

A common double hetero type semiconductor laser has a structure shown in FIG. In this figure, 1 and 2 are strip line electrodes, 3 to 6 are semiconductor layers sandwiched between the electrodes, for example, 3 is a p-type GaAs layer, 4 is a p-type GaAI melon layer, 5 is an n-type CanAs layer, 6 is an n-type Ga carrier layer. FIG. 2 shows this semiconductor element viewed from above, that is, from the electrode 1 side.
In order to cause laser oscillation, a forward bias is applied, that is, a more positive potential is applied to electrode 1 than to electrode 2, a forward current is caused to flow through the pn junction consisting of layers 4 and 5, and fractional carriers are injected. In this way, electron-hole pairs are generated and light is emitted due to their recombination. At this time, electrode 1 has the role of allowing current to flow with a width W toward electrode 2, and at the same time, light is also confined below this electrode. I'm doing a lot of work. In other words, the light is confined within the W of the layer 4 and performs laser oscillation. This laser device uses the cleavage planes of surfaces 7 and 8 at both ends as reflecting mirrors, and these two reflecting mirrors constitute a resonator. Then, the output light is extracted from the surface 7 or the surface 8, or from both the surfaces 7 and 8. The longitudinal mode of this ordinary laser has a spectrum shown in FIG. 3, which is related to the distance L between the surfaces 7 and 8 as shown in the following equation.

q trench = L--Lateral △^ = Rust △ q... Small ■ q = 1, 2, 3''''... Here, q is the number of longitudinal modes, ^ is the oscillation wavelength, and n is the refractive index of the waveguide. be.

The spectral interval △^ is inversely proportional to the resonator length L, as shown by the equation (2). Furthermore, it can be seen that if the refractive index n changes, the oscillation wavelength ^ changes from equation {1}, and the spectral interval Δin changes from equation {2}. Using this fact, a wavelength tunable laser can be constructed. The present invention focuses on the above point, and its feature is that a common electrode is attached to one surface parallel to the pn junction surface of a semiconductor having a pn junction, and a pair of electrodes are attached to the other surface, and these electrodes are connected to each other. A pair of parallel strip line-shaped optical transmission paths are formed between common electrodes, and the distances between semiconductor cleavage planes at both ends of these optical transmission paths are unequal, and the lengths of the pair of optical transmission paths are optically coupled. By applying a voltage between the electrodes to cause laser oscillation in one optical transmission line, and electrically controlling the refractive index of the other optical transmission line, the wavelength of the output light is changed. It is at the point where it becomes.

This will be explained in detail below with reference to Examples. Fourth
The figures show an embodiment of the invention in longitudinal section, and FIG. 5 shows a plan view thereof.

As shown in these figures, this device has two parallel strip-line electrodes 9, ID, which correspond to the haze electrodes shown in FIG.
and the electrode for electrode 2 is Hironaka's common electrode 11,
Between these electrodes there is a p-type Ga pseudolayer 18, a p-type GaAI
As layer 15, n-type GaAI melon layer 16, n-type Ga layer 17
interpose a semiconductor consisting of In this way, for the reason mentioned above, the inside of the electrodes 9 and 10 W, , W2 and the length L, , L
A laser device is obtained in which two laser elements each consisting of a semiconductor region W3 and electrodes at both ends are arranged side by side with a semiconductor region W3 in between. Note that in this example, L<L2, W,=W2. In the present invention, one of them, for example, the side having the electrode 9, is forward-biased to operate as a laser element, and the other electrode 1
The side having 0 is reverse biased so that it does not operate as a laser element and serves as a mere optical transmission line.

The middle semiconductor region W3 interposed between both elements serves as a light guide that couples the optical transmission paths of both elements. and electrodes 9,1
Since the applied voltages are different, in order to prevent short circuits, the layer 18 is separated into two parts with a gap between them, and the layer 15 is
In the middle W3, the layer 15 is made into an insulator (intrinsic semiconductor) by ion implantation to a depth that penetrates the layer 15 and reaches the layer 16. In this device, a positive potential is applied to electrode 9 with respect to electrode 11, and electrode 1 is applied with a positive potential relative to electrode 11.
0' When a negative potential is applied to the electrode 11, the layer 15
In the middle W, the part 12 consists of layers 15 and 16.
A forward current flows through the n-junction (layer 15 may be made of n-type CanAs and a pn junction may be formed with layers 18 and 15), causing laser oscillation, while in the portion W2 inside layer 15, layer 15
, 16 (or layers 18, 15) is biased in the opposite direction, and by appropriately selecting the impurity concentration in the semiconductor, the depletion layer formed by the p-n junction becomes a light guide layer in the portion 13. It grows to.

FIG. 7 shows this state, where 13a is a portion that becomes a depletion layer of the optical transmission line 13, and 13b is a normal portion that does not become a depletion layer. These regions 12, 13 are optically coupled by the insulating region 14 of the layer 15, which serves as a light guide, so that this laser device has two optical transmission paths 12, 13 with distributed coupling. This results in a composite resonator laser having two resonators whose lengths L, , - are different, and therefore whose resonance frequencies are different. Therefore, the longitudinal mode of this laser device is as shown in FIG.

In FIG. 6, a shows the spectral characteristics of the laser element on the region 12 side, and b shows the spectral characteristics of the laser element on the region 13 side. The dot spacing A in 2 is different, and when L.<L2, △ in,
>△ entered 2. A semiconductor laser device with two resonators oscillates at a frequency where the two resonance frequencies match.
As shown in Fig. 6, if the resonant frequencies of the two resonators match at wavelength ^a, the wavelength of the output light of this laser device will be ^, . (=^2,).

This laser device can electrically change the oscillation wavelength. Next, a method for changing this oscillation wavelength will be described. When a reverse voltage is applied to the electrode 1 of region 13 in FIG.
, 13M, and as the voltage is increased, this part 13
a expands. The refractive index changes depending on the number of carriers, so if the direction of the crystal is selected appropriately, the refractive index n,' of the part 13a where the depletion layer is expanded will be the same as the part 13 that is not a depletion layer.
The refractive index n of b becomes larger. Therefore, the refractive index changes for the light propagating in the optical transmission line 13, so the above '1}
, '2 - As is clear from equation 2, the wavelength input of the spectrum is 2,
, input 22... and the interval △ input 2 change. the result"
^,. What was oscillating at (= input 2,) is now input a, input 2
2, ^ scales and input 24 all move toward the long wavelength side, and the interval between them also changes, resulting in input, .mi input, and with an appropriate reverse voltage, ^, 2 = input 22. Therefore, this laser Ha^
, 2 wavelengths. When the voltage is further increased, the voltage turns on at an appropriate voltage, 3=^23 or ^,4=^24, and the oscillation wavelength shifts one after another as the voltage changes.
In this way, the oscillation wavelength of this semiconductor laser is not changed by changing the resonance conditions of one resonator, but by oscillating at the same resonant frequency of two resonators, and changing the oscillation wavelength of one resonator. The feature is that by changing the resonance conditions, the matching resonance frequencies are changed discontinuously one after another.

In conventional single-resonator lasers, the oscillation wavelength is rarely changed by the laser device itself, and it is common practice to change the wavelength externally if necessary. Furthermore, when the oscillation wavelength is changed in the laser device itself, the range of change is very small; for example, when changing the refractive index, the change is only about 0.7A. In this respect, in the present invention, the spectral interval is approximately △^(3
The wavelength can be changed in steps of ~10A), allowing for a wider wavelength change range than conventional semiconductor lasers, and compared to methods that change the wavelength using an external mechanism, it is a 4-inch device and operates at low voltage and power. In terms of being forced to
Very advantageous. In this laser device, the oscillation wavelength can be stabilized by detecting the output and adding feedback from one electrode.

Further, by changing the voltage applied to the electrode 10 and changing the oscillation wavelength, time division multiplex communication can be easily performed.
In the illustrated embodiment, the portion 9 that operates as a laser element,
Portions 10, 11, 15 to 18 forming one side of the composite resonator are provided only on the negative side of 11, 15 to 18; may be provided.

Further, although the depletion layer is used to change the refractive index, other electrical means of carrier injection may also be used.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a conventional semiconductor laser, Fig. 2 is a plan view thereof, Fig. 3 is a spectral characteristic diagram, Fig. 4 is a schematic cross-sectional view showing an example of Honsomei's semiconductor laser, and Fig. 5 6 is a spectral characteristic diagram, and FIG. 7 is a schematic partial sectional view for explaining the operation. In the drawing, 12 and 13 are optical transmission lines, 11 is a common electrode, and 9 and 1
0 is a pair of strip line electrodes, and 14 is an electrically insulating layer that is part of an optical conductor layer. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1. Attach a common electrode to one surface parallel to the pn junction surface of a semiconductor having a pn junction and a pair of electrodes to the other surface to form a pair of parallel strip line-shaped optical transmission paths between these electrodes and the common electrode. The distances between the semiconductor cleavage planes at both ends of these optical transmission lines are made unequal, the lengths of the pair of optical transmission lines to be optically coupled are made different, and a voltage is applied between the electrodes to cause one of the optical A wavelength tunable semiconductor light emitting device characterized in that the wavelength of output light is changed by generating laser oscillation in a transmission path and electrically controlling the refractive index of the other optical transmission path.