JPH06224517A - Variable-wavelength semiconductor laser device - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser the wavelength of which can be changed in a wide range at a high speed. CONSTITUTION:Active semiconductor layers 1 are formed in such a way that the layers 1 are arranged in parallel with each other in the light guiding direction of the optical wave guide of a laser resonator and electric field impression upon semiconductor light absorption changing layers which are integrated on the same semiconductor substrate 8, generate optical gains when currents are injected, and are changed in light absorbing amount when electric fields are impressed is performed independently from the current injection into the layers 1. A distributed diffraction grating 5 which changes the refractive index of the layers 1 by changing the light absorption of the layers 1 by impressing electric fields and, in addition, performs distributed optical feedback for giving wavelength selecting properties to the layer 1 is provided in the light guiding direction inside the laser resonator and in parallel with the layers 1 and 2.

Description

Detailed Description of the Invention

[0001]

This invention relates to optical communication, optical information processing,
The present invention relates to a wavelength tunable semiconductor laser device that can be used as a small light source in the field of optical measurement and the like, and to a semiconductor laser device that can perform wavelength tunable control continuously and at high speed over a wide wavelength range.

[0002]

2. Description of the Related Art Next, an example of the structure of a conventional tunable wavelength semiconductor laser device is shown in FIGS. FIG. 2 shows a distributed reflection (DBR) type wavelength tunable semiconductor laser device, which includes an active waveguide region 21 that produces an optical gain, a phase adjusting waveguide region 22 that controls the phase of propagating light, and a wavelength tunable control of laser light. The wavelength control waveguide region 23 is arranged in series in the optical waveguide direction.

In the device of FIG. 2, the currents IB and IC are injected into the phase adjustment waveguide region 22 and the wavelength control waveguide region 23 independently of the injection current IA into the active waveguide region 21 for laser oscillation. As a result, the refractive index of the phase adjustment waveguide region 22 and the wavelength control waveguide region 23 directly changes due to the plasma effect. Therefore, the injection current I in each of the phase adjustment waveguide region 22 and the wavelength control waveguide region 23 is
By independently controlling B and IC, the equivalent refractive index neq of the laser resonator changes, and the Bragg wavelength λb = determined by the uneven period Λ of the diffraction grating 23A in the wavelength control waveguide region 23.
The phase of the propagating light changes to 2neq × Λ, and the oscillation wavelength changes continuously.

Further, in this type of similar laser device, an electric field is applied to the phase adjusting waveguide region 22 to obtain the Franz-
A laser device has also been proposed in which the refractive index of the phase adjustment waveguide region 22 is directly changed by utilizing the refractive index change of the Keldysh effect or the quantum confined Stark effect to change the oscillation wavelength. For these laser devices, see, for example, K. Kobayashi et al., Lightwabe Technolog.
y vol.6, No.11, pp1623-pp1633,1988 and U.Koren et al., a
ppl.Phys.Lett., Vol.53, No.22, pp2132-pp2134, 1988.

Next, FIG. 3 shows an example of the structure of a double waveguide type wavelength tunable semiconductor laser device. In FIG. 3, an active region 31 that produces an optical gain and a wavelength control region 32 that variably controls the wavelength of laser light are arranged in the optical waveguide of the laser resonator in parallel with each other in the optical waveguide direction.

In FIG. 3, the active region 31 for laser oscillation is shown.
By injecting a current into the wavelength control region 32 independently of the injection current into the wavelength control region 32, the carrier density of the wavelength control region 32 changes, and the refractive index of the wavelength control region 32 directly changes due to the plasma effect. Therefore, the equivalent refractive index neq of the laser resonator changes, the Bragg wavelength λb determined by the uneven period Λ of the diffraction grating 33 formed in the resonator changes, and the oscillation wavelength changes continuously. This laser device is described in detail, for example, in Japanese Patent Laid-Open No. 3-87086.

Next, FIG. 4 shows the configuration of a distributed feedback (DFB) type wavelength tunable semiconductor laser device. In FIG. 4, the upper electrode of the DFB laser is divided into a plurality of parts. Figure 4
When the current injected from the upper electrode 41 and the electrode 42 is controlled independently, the gain in the resonator partially changes, and the carrier density in the active region changes. Therefore, the refractive index of the active region changes due to the plasma effect, so that the Bragg wavelength of distributed feedback changes, and the oscillation wavelength continuously changes.
Regarding this laser device, for example, Y. Yoshikuni et a
l., Electron. Lett., Vol. 22, No. 22, pp1153-pp1154, 1986
Are described in detail in.

[0008]

However, FIG. 2 and FIG.
In the wavelength tunable semiconductor laser device shown in Fig. 5, the wavelength tunable mechanism is based on the change in carrier density in the wavelength control region due to the current injection in the wavelength control region, so the maximum changing speed is the carrier lifetime in the wavelength control region. Limited, 1-3
It is about ns.

Further, in the wavelength tunable semiconductor laser device by applying an electric field in the phase adjustment waveguide region 22 of FIG. 2, the wavelength tunable mechanism is the Franz-Keldish effect or the quantum confined Stark effect to change the refractive index of the phase adjustment waveguide region. It is possible to tune the wavelength at a high speed of about 0.1 ps, but since the amount of change in the refractive index is small and the refractive index in the wavelength control region cannot be changed, the wavelength can be tuned over a wide wavelength range. Have difficulty.

In the wavelength tunable semiconductor laser device of FIG. 4, the wavelength tunable mechanism is based on a change in carrier density in the active region. The maximum rate of change depends on the carrier life of the active region and the photon life of the laser light, and changes relatively fast at about 20 to 50 ps. However, since the amount of change in carrier density in the active region is relatively small, the change in refractive index is small and it is difficult to change the wavelength over a wide wavelength range.

[0011]

In order to achieve this object, according to the present invention, they are formed in an optical waveguide of a laser resonator so as to be arranged close to each other in parallel with each other in the waveguide direction, and are formed on a common semiconductor substrate 8. The semiconductor light absorption change layer 2 includes a semiconductor active layer 1 which is integrated and produces an optical gain by current injection, and a semiconductor light absorption change layer 2 whose light absorption amount is changed by application of an electric field.
The electric field is applied independently of the current injection into the semiconductor active layer 1, and the refractive index of the semiconductor active layer 1 is changed due to the change in light absorption due to the applied electric field. Further, a distributed diffraction grating 5 for performing distributed light feedback for providing wavelength selectivity is provided in parallel with the semiconductor active layer 1 and the semiconductor light absorption change layer 2 in the optical waveguide direction in the laser resonator.

[0012]

The wavelength tunable mechanism of the present invention can be described as follows. First, the absorption change due to the Franz-Keldish effect or the quantum confined Stark effect is used to change the optical absorption in the semiconductor optical absorption change region, and the loss in the laser resonator is changed accordingly. Therefore,
The semiconductor carrier cavity threshold carrier density changes.

Since the carrier density of the semiconductor active region is kept at the threshold carrier density in the laser oscillation state, the threshold carrier density changes due to the loss change, and thus the carrier density of the semiconductor active region also changes. The plasma effect changes the refractive index of the semiconductor active region. Therefore, the equivalent refractive index of the laser resonator changes, and the oscillation wavelength changes.

From this, the maximum rate of wavelength change is determined by the rate of change of carrier density in the semiconductor active region.
High speed can be obtained similarly to the wavelength tunable semiconductor laser device. Further, the maximum wavelength tunable amount is determined by the loss variation amount in the laser resonator and the carrier density-gain characteristic of the semiconductor active region. Therefore, a relatively large wavelength tunable amount can be achieved by using a medium (for example, multiple quantum well) in which the semiconductor light absorption change region has a large absorption change and the semiconductor active region has a large gain dependency of carrier density.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, FIG. 1 shows the configuration of an embodiment of a wavelength tunable semiconductor laser device according to the present invention. FIG. 1 is a perspective view of a wavelength tunable semiconductor laser device, with a part cut away to show the internal structure. In FIG. 1, the clad layer 11 is formed on the semiconductor substrate 8. The semiconductor substrate 8 is made of, for example, InP, and the cladding layer 11 is also made of InP. In the clad layer 11, a current blocking layer 7 made of InP having a conductivity type different from that of the clad layer 11 or an insulating property is formed except for a region serving as an optical waveguide portion.

A distributed diffraction grating 5 for providing wavelength selectivity is formed on the clad layer 11 by the optical waveguide layer 4 in the laser light propagation direction. The optical waveguide layer 4 is made of, for example, InGa.
It is composed of AsP. On the optical waveguide layer 4, the active layer 1, the intermediate separation layer 3, the light absorption change layer 2 and the cladding layer 9 are laminated in this order. The active layer 1 is, for example, InGaAs / InGaA.
The band gap energy of the multi-quantum well structure is Eg, which is composed of a multilayer thin film of sP. Intermediate separation layer 3
Is transparent, for example, composed of InP. The light absorption change layer 2 is composed of, for example, a multi-quantum well structure composed of InGaAs / InGaAsP multilayer thin films. The cladding layer 9 is made of, for example, InP.

In this laminated semiconductor, only the central portion forming the laser resonator is left in the propagation direction of the laser light, the upper layer portion is removed to the upper portion of the cladding layer 11, and the common electrode extraction layer 6 is laminated. The common electrode extraction layer 6 uses a semiconductor such as InP having a bandgap energy larger than that of the active layer 1 and the light absorption change layer 2 of the same conductivity type as the intermediate separation layer 3.

Further, a clad layer 10 having the same composition as the clad layer 9 is laminated on the clad layer 9 with the same width or wider than the clad layer 9 on the left and right sides. Next, the electrode forming low resistance layer 12 for lowering the ohmic resistance is laminated on the cladding layer 10. The electrode forming low resistance layer 12 is formed of, for example, InGaAs. In this state, the laser driving electrode 13 is formed below the semiconductor substrate 8, and the electric field applying electrode 15 for changing the light absorption is formed above the electrode forming low resistance layer 12. Further, the common electrodes 16 are formed on the common electrode extraction layer 6 so as to face each other.

In FIG. 1, an insulating layer 14 of, for example, SiO ₂ is provided in order to reduce the element capacitance and facilitate the separation of the electric field applying electrode 15 and the common electrode 16. The positional relationship between the active layer 1 and the light absorption change layer 2 may be reversed upside down around the intermediate separation layer 3.

The active region portion which produces optical gain and the absorption change region portion which produces optical absorption change must be semiconductor PN junctions for efficient current injection or electric field application. When the layer 10 and the electrode-forming low resistance layer 12 are P-type semiconductors, the intermediate separation layer 3 and the common electrode extraction layer 6 must be N-type semiconductors. The layer 11 must be a P-type semiconductor and the current blocking layer 7 must be an N-type semiconductor or an insulating semiconductor.

In this state, a current is injected from the laser driving electrode 13 into the path of the current injected into the active layer 1, passes through the semiconductor substrate 8 and the clad layer 11, and passes through the current blocking layer 7 in the vicinity of the active layer 1. Flow in the order of the active layer 1, the intermediate separation layer 3, and the common electrode extraction layer 6,
It is taken out by the common electrode 16. At this time, radiative recombination occurs in the active layer 1 having the PN junction, and laser oscillation occurs when the optical gain in the laser resonator is balanced with the optical loss.

On the other hand, when the common electrode 16 is applied with a voltage higher than that of the electric field applying electrode 15, the common electrode take-out layer 6
The intermediate absorption layer 3, the clad layer 9, the clad layer 10, and the electrode-forming low resistance layer 12 are used to interpose P of the light absorption change layer 2.
A reverse bias is applied to the N-junction, and an electric field is applied to the light absorption change layer 2 in a concentrated manner. Further, the laser light generated in the active layer 1 is distributed and guided in the vicinity of the active layer 1, the light absorption change layer 2, and the optical waveguide layer 4, which have a high refractive index.

In the laminated structure semiconductor shown in FIG. 1, the active layer 1 and the light absorption change layer 2 are made of InGaAs / InGaA.
This is an example of the case of using a multiple quantum well structure using a multilayer thin film of sP. The active layer 1 and the light absorption change layer 2 are semiconductors having the same bandgap energy, or the light absorption change layer 2 has a bandgap more than the active layer 1. Another semiconductor layer may be used as long as the semiconductor has a large energy and the band gap energy is smaller than that of the other semiconductor layers. The conductivity type settings of each layer semiconductor may be reversed. further,
Although the optical waveguide layer 4 and the distributed diffraction grating 5 are disposed under the active layer 1, the optical transmission of the laser light such as the upper part of the active layer 1, the upper part of the light absorption change layer 2 or the lower part of the light absorption change layer 2 is performed. It does not matter if they are arranged along the light propagation direction in the region.

[0024]

According to the present invention, since the refractive index of the active region which causes optical gain is changed from the absorption change of the optical absorption change region provided in the laser resonator due to the electric field application, the wavelength can be changed at high speed. It is possible to change the wavelength range of the wide band.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a distributed reflection type wavelength tunable semiconductor laser device according to a conventional technique.

FIG. 3 is a configuration diagram of a double waveguide type wavelength tunable semiconductor laser device according to a conventional technique.

FIG. 4 is a cross-sectional view of a distributed feedback type wavelength tunable semiconductor laser device according to a conventional technique.

[Explanation of symbols]

 1 Active Layer 2 Optical Absorption Change Layer 3 Intermediate Separation Layer 4 Optical Waveguide Layer 5 Distributed Grating 6 Common Electrode Extraction Layer 7 Current Blocking Layer 8 Semiconductor Substrate 9, 10, 11 Clad Layer 12 Low Resistance Layer for Electrode 13 Laser Drive Electrode 14 insulating layer 15 electric field applying electrode 16 common electrode

Claims (2)

[Claims] 1. A semiconductor active layer, which is formed in an optical waveguide of a laser resonator so as to be arranged in parallel and close to each other in the waveguide direction and is integrated on a common semiconductor substrate (8) to generate an optical gain by current injection. (1) and a semiconductor light absorption change layer (2) whose light absorption amount is changed by applying an electric field.The semiconductor light absorption change layer (2) is applied with an electric field independently of the current injection of the semiconductor active layer (1). The wavelength tunable semiconductor laser device is characterized in that the wavelength of the laser light is changed by changing the refractive index of the semiconductor active layer (1) based on the change of light absorption by applying an electric field. 2. A semiconductor active layer, which is formed in an optical waveguide of a laser resonator so as to be arranged in parallel and close to each other in the waveguide direction, integrated on a common semiconductor substrate (8), and which produces an optical gain by current injection. (1) and a semiconductor light absorption change layer (2) whose light absorption amount is changed by applying an electric field.The semiconductor light absorption change layer (2) is applied with an electric field independently of the current injection of the semiconductor active layer (1). Then, the refractive index of the semiconductor active layer (1) is changed from the change of light absorption due to the application of an electric field, and a distributed diffraction grating (5) that performs optical distributed feedback for wavelength selectivity is provided in the laser resonator. A wavelength tunable semiconductor laser device comprising a semiconductor active layer (1) and a semiconductor light absorption change layer (2) arranged in the wave direction in parallel with each other to change the wavelength of laser light.