JPH07231132A - Semiconductor optical device - Google Patents

Abstract

PURPOSE:To obtain a device which enables high speed operation with excellent stability of oscillation wavelength by providing a common active layer formed on a semiconductor substrate and three regions of a light emitting element, an optical modulator and a semiconductor optical amplifier which are optically coupled sequentially. CONSTITUTION:A common active layer 1 to 3 formed on a semiconductor substrate 5, and three regions of a light emitting element I, an optical modulator II and a semiconductor amplifier III which are optically coupled sequentially are provided. For example, a common semiconductor layer (active layer) 1 to 3 having a small band gap consisting of InGaAsP is formed and a P-type InP layer 4 is formed thereon. A diffraction grating 6 is formed on a semiconductor layer 2 of the semiconductor laser to form a distribution feedback type laser. The electrodes 7 to 9 isolated to the resions I to III are respectively formed on the upper surface of the P-type InP layer 4, a common electrode 10 is formed at the rear surface of the substrate 5 and the regions I to III are coupled optically but is isolated electrically.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical device, and more particularly to a semiconductor optical device as a light source which can operate at high speed and has excellent stability of oscillation wavelength.

[0002]

2. Description of the Related Art FIG. 4 is a diagram for explaining optical modulation of a laser using a conventional electroabsorption type optical modulator. This laser is a so-called modulator-equipped semiconductor laser, I is a semiconductor distributed feedback laser, and II is an electroabsorption optical modulator.
The semiconductor distributed feedback laser and the electro-absorption optical modulator are formed on the same n-type semiconductor substrate 5 and are optically coupled but electrically insulated. Ie modulator (I
The active layer 1 of I) and the active layer 2 of the laser (I) are composed of a common semiconductor layer, a diffraction grating is formed in the active layer 2 of the laser, and a modulator is formed on the p-type semiconductor layer 4 which is a clad layer. An electrode 7 for applying the electric field and an electrode 8 for injecting a current into the laser are separately formed. A common ground electrode 10 is provided on the back surface of the substrate 5. A constant light output can be obtained by injecting a constant current in the forward direction in the semiconductor distributed feedback laser of I. A coded optical output is obtained by applying a coded voltage in the opposite direction to the electroabsorption optical modulator of II.

[0003]

It is known that in the optical modulation of a laser using an electro-absorption optical modulator, the wavelength variation of output light is smaller than that in the method of directly modulating the laser current. However, it is known that even in the modulator, since the refractive index changes with the application of voltage, phase modulation occurs and the wavelength changes. At the time of high-speed modulation, this wavelength variation is a factor that limits the extension of optical communication over long distances. SUMMARY OF THE INVENTION It is an object of the present invention to solve such conventional problems and to provide a semiconductor optical device capable of high-speed operation and excellent in stability of oscillation wavelength.

[0004]

In order to achieve the above object, according to a first aspect of the semiconductor optical device of the present invention, the semiconductor optical device has a common active layer portion formed on a semiconductor substrate and has a sequential optical structure. It has three regions, that is, a light emitting device, a light modulator, and a semiconductor optical amplifier, which are coupled to each other.

According to the second aspect of the present invention, a semiconductor optical device including a light emitting element, an optical modulator, and a semiconductor optical amplifier which share an active layer portion in which semiconductor multi-layered films formed on a semiconductor substrate are shared. In the optical modulator, the light emission output from the light emitting element is subjected to electro-optical absorption modulation, and the semiconductor optical amplifier performs phase modulation opposite to the phase modulation of the light emission output in the modulator. .

In any of the above-mentioned devices, the light emitting element is a laser having a diffraction grating, and the optical modulator is an electro-optical absorption type modulator that controls an optical absorption coefficient by an electric field applied in the opposite direction, In addition, it is preferable that the semiconductor optical amplifier is set to a gain saturation level by injecting a current in the forward direction. Further, the common active layer may be composed of a semiconductor multilayer film having a quantum well structure.

Further, a semiconductor optical waveguide may be provided on the active layer portion of the optical modulator and the active layer portion of the semiconductor optical amplifier, and may be provided directly or at an end portion of the light emitting element opposite to the optical modulator. A light receiving element may be provided via an optical waveguide formed on the semiconductor substrate, and the band gap of the active layer portion of the optical modulator is the band gap of the active layer portion of the light emitting element and the semiconductor optical amplifier. May be larger.

According to the third aspect of the present invention, the first and the first optically coupled layers formed on the same semiconductor substrate
A semiconductor device having second and third semiconductor elements, each semiconductor element having a junction in which a semiconductor layer having a small band gap is sandwiched between a p-type semiconductor and an n-type semiconductor,
The semiconductor layer having a small band gap is divided into three regions corresponding to the three semiconductor elements along the traveling direction of light, the band gap of the central region is larger than the band gaps of the end regions, and the first and A diffraction grating is formed in a semiconductor layer having a small band gap in any one of the third semiconductor devices.

Further, according to a fourth aspect of the present invention, there is provided a semiconductor optical device in which first and second semiconductor elements having a common active layer portion formed on a semiconductor substrate are combined, wherein Is a light modulator that modulates the input light by electro-optical absorption, and the second semiconductor device is a semiconductor optical amplifier that performs a phase modulation of the light emission output of the modulator and a phase opposite thereto. And

[0010]

It is known that in a semiconductor amplifier, when a certain amount of light or more is input, gain saturation occurs and carriers are reduced. At this time, since the refractive index increases due to the plasma effect as the number of carriers decreases, the phase is modulated and frequency fluctuation, that is, wavelength fluctuation occurs. This effect has the opposite phase to the phase modulation that occurs in the electro-absorption optical modulator,
To cancel the frequency fluctuation due to the phase modulation of the modulator and further increase the injection current of the laser to increase the optical output, or to increase the injection current of the semiconductor amplifier and increase the gain saturation to generate the antiphase phase modulation. You can also

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a schematic cross section of a semiconductor optical device of the present invention. Three regions of a semiconductor laser (I), an optical modulator (II) and a semiconductor optical amplifier (III) are formed on the same n-type semiconductor substrate 5 (for example, an n-InP substrate).
The respective regions are common semiconductor layers (active layers) 1, 2 and 3 formed on the substrate 5 and made of, for example, InGaAsP and having a small band gap, and the p-type semiconductor layer 4 on the semiconductor layers.
(For example, p-InP). That is, a common semiconductor layer having a small band gap is sandwiched between an n-type semiconductor layer and a p-type semiconductor layer. A diffraction grating 6 is formed on the semiconductor layer 2 of the semiconductor laser to form a distributed feedback laser.
Separated electrodes 7, 8 and 9 are formed on the upper surface of the p-type semiconductor layer 4, while a common electrode 10 is formed on the rear surface of the substrate 5. Thus, the regions I, II and III are optically coupled and electrically insulated. Such a structure can be produced by a normal crystal growth method or a lithography method.

A constant optical output can be obtained by injecting a constant current in the forward direction to the semiconductor distributed feedback laser of I. II
When an electric field is applied to the electro-absorption type optical modulator, the absorptance of the semiconductor layer 1 changes, and the input light can be modulated. For example, the encoded light output is obtained by applying the encoded voltage in the opposite direction. Here, in order to increase the transparency in the absence of an electric field, the band gap of the semiconductor layer 1 in the region (II) may be made larger than the band gaps of the semiconductor layers 2 and 3 in the regions (I, III) at both ends. For example, the semiconductor layer 1 is made of InGaAsP having a composition of 1.55 μm, and the semiconductor layers 2 and 3 are made of 1.48 μm.
The composition is InGaAsP. A constant current is injected into the semiconductor amplifier of III. A large optical output can be obtained by increasing the current of the semiconductor distributed feedback laser of I. III
In the semiconductor amplifier of, when light above a certain level is input, gain saturation occurs, carriers decrease and the refractive index increases due to the plasma effect, which causes phase modulation. This effect is similar to the phase modulation that occurs in an electroabsorption optical modulator. Since is the opposite phase, it is possible to cancel the phase modulation and further generate the opposite phase modulation. FIG. 2 is a diagram for explaining it, and (a) shows an example of the output waveform of the optical modulator (II). (B) is the frequency variation of light in the optical modulator (∂φ _II
An example of time change of / ∂t) is shown. The refractive index fluctuates when the electric field applied to the optical modulator rises and falls, so that phase modulation occurs, which causes frequency fluctuations. (C) shows an example of frequency fluctuation (∂φ _III / ∂t) in the semiconductor optical amplifier (III). In a semiconductor amplifier, when a certain amount of light or more is input, gain saturation occurs and carriers are reduced. At this time, as shown in FIG. 2C, the phase is modulated due to the increase in the refractive index due to the plasma effect as the carriers decrease, and the frequency fluctuation (∂φ _III / ∂t)
That is, wavelength variation occurs. As shown in the figure, this effect has a phase opposite to that of the phase modulation that occurs in the electro-absorption optical modulator shown in FIG. 2B, and therefore frequency fluctuations due to the phase modulation of the modulator (∂φ _III / ∂t ) Is further canceled and the injection current of the laser is increased to increase the optical output, or the injection current of the semiconductor amplifier is decreased to decrease the saturation power, so that the opposite phase modulation can be generated.

As shown in FIG. 3, a semiconductor optical waveguide layer 11 may be formed on the semiconductor layers 2 and 3 of the optical modulator and the semiconductor optical amplifier. This can reduce the transmission loss of light.

Further, in the optical device shown in FIG. 1 or FIG. 3, the semiconductor layer 1, 2, 3 may have a quantum well structure or a multiple quantum well structure, and the same operation can be performed. It is possible to increase the electro-optical absorption effect of the optical modulator. When the quantum well or the multiple quantum well structure is adopted, the band gap of the well of the optical modulator section may be larger than the band gaps on both sides.

It is also possible to connect the light receiving element directly to the end of the distributed feedback laser opposite to the optical modulator or via an optical waveguide layer formed on the same substrate. By doing so, the output of the laser can be monitored and the device can be operated under predetermined oscillation conditions.

[0017]

As described above, in the present invention, in the semiconductor optical amplifier, when a certain amount of light or more is input, gain saturation occurs, carriers are decreased, and the refractive index is increased by the plasma effect, so that phase modulation occurs. To use. Since this effect has a phase opposite to that of the phase modulation that occurs in the electro-absorption optical modulator, it is possible to cancel the phase modulation and generate a phase modulation having an opposite phase. Therefore, according to the present invention, it is possible to realize a semiconductor light source which can operate at high speed and is excellent in stability of oscillation wavelength.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating phase modulation.

FIG. 3 is a schematic cross-sectional view showing another embodiment of the present invention.

FIG. 4 is a schematic sectional view showing a conventional semiconductor laser with a modulator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor layer which comprises an optical modulator 2 Semiconductor layer which comprises a semiconductor laser 3 Semiconductor layer which comprises a semiconductor optical amplifier 4 p-type semiconductor layer 5 n-type semiconductor layer 6 Diffraction grating 7 Modulator electrode 8 Laser electrode 9 Amplifier electrode 10 Common ground electrode 11 Optical waveguide layer

Claims (9)

[Claims] 1. A light emitting device, a light modulator, and a semiconductor optical amplifier, each of which has a common active layer portion formed on a semiconductor substrate and which is optically coupled sequentially. Semiconductor optical device. 2. A semiconductor optical device comprising a composite of a light emitting element, an optical modulator, and a semiconductor optical amplifier, which have a common active layer portion formed by laminating semiconductor multilayer films formed on a semiconductor substrate, wherein the optical modulator A semiconductor optical device characterized in that the light emission output from the light emitting element is subjected to electro-optical absorption modulation, and the semiconductor optical amplifier performs phase modulation opposite to the phase modulation of the light emission output from the modulator. 3. The light emitting element is a laser having a diffraction grating, the optical modulator is an electro-optical absorption type modulator that controls an optical absorption coefficient by an electric field applied in the opposite direction, and the semiconductor optical amplifier. 3. The semiconductor optical device according to claim 1, wherein a current is injected in the forward direction to set the gain saturation level. 4. The common active layer is formed of a semiconductor multilayer film having a quantum well structure.
Or the semiconductor optical device described in 3. 5. The semiconductor optical device according to claim 1, wherein a semiconductor optical waveguide is provided on the active layer portion of the optical modulator and the active layer portion of the semiconductor optical amplifier. apparatus. 6. A light receiving element is provided at an end of the light emitting element opposite to the optical modulator, either directly or through an optical waveguide formed on the semiconductor substrate. 6. The semiconductor optical device according to any one of items 5 to 5. 7. The band gap of the active layer portion of the optical modulator is larger than the band gaps of the active layer portion of the light emitting element and the semiconductor optical amplifier.
7. The semiconductor optical device according to any one of 1 to 6. 8. A semiconductor device having first, second and third semiconductor elements formed on the same semiconductor substrate and optically coupled to each other, each semiconductor element having a small band gap. The semiconductor layer having a junction between layers of a p-type semiconductor and an n-type semiconductor and having a small bandgap is divided into three regions corresponding to the three semiconductor elements along the traveling direction of light, and a central region is formed. Of the semiconductor light having a band gap larger than the band gaps of both end regions and having a small band gap in one of the first and third semiconductor devices. apparatus. 9. A semiconductor optical device in which first and second semiconductor elements having a common active layer portion formed on a semiconductor substrate are combined, wherein the first semiconductor element absorbs input light by electric field light absorption. A semiconductor optical device, which is an optical modulator for modulation, wherein the second semiconductor element is a semiconductor optical amplifier that performs phase modulation of a light emission output of the modulator and a phase opposite thereto.