JPH0555701A - Tunable semiconductor laser device - Google Patents

Abstract

(57) [Summary] [Object] To obtain a wavelength tunable semiconductor laser device having a large wavelength tunable width in proportion to the amount of change in the injected carrier concentration by making it possible to increase the amount of change in the injected carrier concentration. A quantum well structure is used as an active layer, electrodes are separated into front and rear in a resonator direction, and a second conductivity type region is diffused and formed in a first conductivity type layer existing between the separated electrodes. A reverse voltage is applied to the active layer from one of the divided electrodes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable semiconductor laser device.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view showing a conventional wavelength tunable semiconductor laser device. 1 is an n-side first ohmic electrode,
2 is an n-side second ohmic electrode, 3 is an n-type cladding layer, 4
Is a diffraction grating, 6 is a p-type cladding layer, 7 is a p-type ohmic electrode, 9 is an n-type contact layer, and 10 is an active layer.

Next, the operation will be described. Since the ohmic electrode for injecting a current into the laser active layer is divided into the first n-side electrode 1 and the second n-side electrode 2, the currents injected into the front side and the rear side of the laser resonator are independently controlled. can do. Laser gain is represented by the multiplication of photon density and current density in the cavity. Generally, since the photon density in the resonator is non-uniformly distributed, a high laser gain can be obtained efficiently by increasing the current density in the high photon density region, and conversely, the current in the low photon density region can be increased. The higher the density, the lower the laser gain.

From the above, when the ratio of the injection currents on the front surface and the rear surface is variously changed, the laser gain changes, and as a result, the threshold current density changes. Wavelength tunable amount Δλ,
The relationship of the threshold carrier density change amount ΔN is given by the following equation. Δλ = (λ / n) Γ (dn / dN) ΔN where n is the refractive index, λ is the wavelength, dn / dN is the differential efficiency of the refractive index with respect to the carrier density, and Γ is the ratio of laser light confined in the active layer. Show. When ΔN is changed from the above equation, Δλ increases accordingly. That is, the wavelength can be changed.

[0005]

The wavelength tunable amount Δλ in the wavelength tunable semiconductor laser device having the above-mentioned configuration is substantially determined by the threshold carrier concentration change amount ΔN and the optical confinement coefficient Γ. It However, since these values depend on the structure and cannot be made too large, there is a problem that Δλ is also relatively small.

The present invention has been made to solve the above problems, and an object thereof is to obtain a wavelength tunable semiconductor laser device having a large wavelength tunable amount Δλ.

[0007]

A wavelength tunable semiconductor laser device according to the present invention comprises an active layer, a first conductivity type cladding layer and a second conductivity type cladding layer sandwiching the active layer, and a first conductivity side. In a semiconductor laser device including an electrode and a second conductive side electrode, the active layer has a quantum well structure, and the first conductive side electrode is formed by dividing the active layer in the front-rear direction in a front-rear direction. , The second conductivity type region is diffused and formed to reach the active layer with respect to the first conductivity type layer existing between the isolated electrodes, and the active region is formed from one of the divided electrodes. The voltage is applied in the opposite direction to the layer.

[0008]

According to the present invention, the active layer has a quantum well structure, and the first conductive side electrode is divided into front and rear portions with respect to the resonator direction, and is formed separately. A first conductivity type layer existing in the first conductivity type layer is diffused until it reaches the active layer, and a voltage is applied from one of the divided electrodes in the opposite direction to the active layer. The absorption coefficient of the quantum well active layer increases in proportion to the voltage. Therefore, the loss in the resonator increases, and in order to compensate for this, the amount of injected carriers must be increased. As a result, the amount of change in ΔN increases, and the amount of wavelength variation Δλ increases.

[0009]

1 is a sectional view showing a wavelength tunable semiconductor laser device according to an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 3 denote the same or corresponding portions, 5 is a quantum well active layer, and 8 is a p-type diffusion region.

When a reverse voltage is applied to the quantum well layer, the absorption coefficient on the long wavelength side increases due to the quantum Stark effect.
FIG. 2 shows experimental values of the applied voltage dependence of the absorption spectrum. For example, focusing on the wavelength of 1.55 μm, the absorption coefficient increases as the applied voltage increases. Here, considering the laser oscillation conditions, the relationship between the gain and the loss is expressed by the following equation. G (N) = α _i + α _M

The left side is a gain G which is a function of the carrier concentration N.
(N), the right side is represented by the sum of the internal absorption loss α _i and the resonator loss α _M. It is considered that the effect of increasing the absorption loss due to the reverse application voltage is structurally manifested as an increase in α _M. Therefore, in order to satisfy the laser oscillation condition, G
(N) must be increased, and for that purpose the injected carrier concentration N must be changed. As a result,
Since the change amount ΔN of the injected carrier concentration can be increased, the wavelength variable width Δλ proportional to ΔN also increases.

In such a semiconductor device of this embodiment, the active layer has a quantum well structure, the electrodes are separated into front and rear, and the second conductivity type impurities are present in the first conductivity type layer existing between the electrodes before and after the electrode. Since the second conductivity type region is formed by diffusion until reaching the active layer, and a reverse voltage is applied to either one of the electrodes with respect to the active layer, the amount of change in injected carrier concentration can be changed by applying this voltage. Can be bigger,
The wavelength tunable width can be increased in proportion to the amount of change in the injected carrier concentration.

[0013]

As described above, according to the present invention, the active layer has the quantum well structure, and the electrodes are separated into the front and rear,
A second conductivity type impurity is diffused into the first conductivity type layer existing between the electrodes before and after the electrode until it reaches the active layer to form a second conductivity type region, and one of the electrodes is opposite to the active layer. Since the directional voltage is applied, it is possible to increase the amount of change in the injected carrier concentration by applying this voltage, and to increase the wavelength tunable width in proportion to the amount of change in the injected carrier concentration. ..

[Brief description of drawings]

FIG. 1 is a sectional view showing a wavelength tunable semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the applied voltage dependence of the absorption spectrum of the device of the above-mentioned embodiment.

FIG. 3 is a sectional view of a conventional wavelength tunable semiconductor laser device.

[Explanation of symbols]

 1 n-side first ohmic electrode 2 n-side second ohmic electrode 3 n-type clad layer 4 diffraction grating 5 quantum well type active layer 6 p-type clad layer 7 p-type ohmic electrode 8 p-type diffusion region 9 n-type contact layer 10 active layer

Claims (1)

[Claims] 1. A semiconductor laser device comprising an active layer, a first conductivity type clad layer and a second conductivity type clad layer sandwiching the active layer, a first conductivity side electrode and a second conductivity side electrode, wherein: The active layer has a quantum well structure, and the first conductive-side electrode is divided into front and rear portions with respect to the resonator direction and is formed so as to be separated from each other.
The second conductivity type region is diffused and formed to reach the active layer with respect to the conductivity type layer, and a voltage may be applied to the active layer in the opposite direction from one of the divided electrodes. Characteristic tunable semiconductor laser device.