JPH03105992A - Optical semiconductor element - Google Patents

Abstract

PURPOSE:To change a refractive index of a light guide layer independently and to change a transmission central wavelength or an oscillation wavelength while an intensity of a transmitted light of an oscillated light is kept definite by a method wherein a separate layer is formed between an active layer and the light guide layer and an electric current is made to flow to the light guide layer independently of the active layer. CONSTITUTION:A prescribed voltage is applied to a first electrode 20; an electric current Ia is injected into an InGaAsP active layer; a wavelength-variable filter is set to a state that it is immediately prior to a laser oscillation. Thereby, a resonance wavelength of the wavelength-variable filter, i.e. a transmission central wavelength, is first decided. Then, an electric current ls is injected, independently of the InGaAsP active layer 10, from a second electrode 22 formed on the bottom of a p-type InP substrate 2 into an InGaAsP light guide layer 6 which is separated electrically from the InGaAsP active layer 10 by an n-type InP separate layer 8. When the electric current Is is controlled, it is possible to largely change the transmission central wavelength of the wavelength-variable filter. Thereby, a tunable laser or the wavelength-varaible filter whose variable wavelength width is large is realized.

Description

[Detailed Description of the Invention] [IR Required] Related to optical semiconductor devices, in particular, a wavelength tunable filter that extracts an optical signal of a certain wavelength from a wavelength-multiplexed optical signal, or a wavelength tunable filter that selectively extracts an optical signal of a plurality of wavelengths. The present invention relates to a wavelength tunable laser that oscillates in a wavelength tunable laser, and the purpose of the present invention is to provide an optical semiconductor device that can greatly change the resonant wavelength while keeping the intensity of transmitted light or oscillated light constant, and can increase the wavelength multiplicity of an optical network. a semiconductor substrate of a first conductivity type, a light guide layer formed on the semiconductor substrate, and a second conductivity type semiconductor substrate formed on the light guide layer.
a conductive type separate layer, an active layer electrically separated from the light guide layer by the separate layer, and a second conductive type formed on both sides of the light guide layer, the separate layer, and the active layer. a buried layer; a first electrode formed on the active layer via a cladding layer of a first conductivity type; a second electrode formed on the bottom surface of the semiconductor substrate; and a third electrode formed by the light guide layer, and is configured to change the resonant wavelength by passing current through the light guide layer and the active layer, respectively, independently. [Industrial Application Field] The present invention relates to an optical semiconductor device, and in particular to a wavelength tunable filter that extracts an optical signal of a certain wavelength from a wavelength multiplexed optical signal or a wavelength tunable filter that selectively extracts an optical signal of a plurality of wavelengths. Concerning oscillating wavelength tunable lasers. In recent years, with the commercialization of long-distance, large-capacity optical communication systems, the usefulness of optical networks that utilize optical wavelength multiplexing has increased. In order to improve the performance of this optical network, it is necessary to increase the number of wavelength multiplexed channels. Therefore, there is a need to expand the tunable wavelength width of a tunable filter, which is an important element for configuring an optical network. Similarly, there is also a demand for expanding the tunable wavelength width of wavelength tunable lasers.

[Conventional technology] A conventional wavelength tunable filter is shown in FIG.

For example, on an n-type InP substrate 32, an n-type! nGaAsP optical guide layer 36, non-doped I nGaAsP active layer 38, p-type InP cladding layer 4
0 and p-type 1 nGaAsP contact layers 42 are formed in order. And the mesa-shaped p-type I
nGaAsP contact layer 42, p-type InP cladding layer 40, InGaAsP active layer 38, and InGaAs
An n-type InP buried layer 44 is formed on the surface of the P light guide layer 36.
is formed. For example, three @poles 46, 48.5 are placed on the p-type InGaAsP contact NJ42.
0 is arranged in the direction of light propagation, that is, in the direction of the resonator, and an electrode 52 is formed on the bottom surface of the n-type InP substrate 32. In this way, a horizontal variable wavelength filter similar to a multi-electrode DFB (distributed feedback) laser is formed. Next, we will explain the operation. Usually, the oscillation wavelength of a DFB laser is determined by the pitch of a diffraction grating formed inside. That is, the oscillation wavelength λ of the DFB laser is given by λ''=2N-A-n.tt. Here, N is the order of the diffraction grating, A is the pitch of the diffraction grating, and n ar+ is the amount of light propagating through the active layer. This is the equivalent refractive index. N-type InP substrate 32 of the DFB laser with the same structure as in Fig. 2
When the electrode 52 on the bottom surface is grounded and a predetermined voltage is applied to the three electrodes 4648.50 on the p-type 1nGaAsP contact layer 42 to uniformly inject a driving current, laser oscillation is performed at a predetermined wavelength. In contrast, three electricity [! 46
, 48. When a current with a value close to the driving current is uniformly injected from 50 to create a state immediately before laser oscillation, and optical signals with various wavelengths are input from the outside, only the light corresponding to the laser oscillation wavelength is generated. is selectively amplified and output. That is, an optical filter is configured that passes only an optical signal of a specific wavelength corresponding to the oscillation wavelength of the DFB laser. Furthermore, when the amount of current injected from the three t-poles 46, 48, 50 is changed, the number of carriers in the InGaAsP active layer 38 changes due to the plasma effect, and the equivalent refractive index of light is n.
, , changes. This allows the oscillation wavelength of the DFB laser to be changed. Therefore, when this DFB laser is used as a filter, the transmission center wavelength during filter operation can be changed in response to changes in the oscillation wavelength, thus constructing a wavelength tunable filter. However, in this wavelength tunable DFB laser, the amount of current injection is changed in order to change the oscillation wavelength, which causes the InGaA
sP life I1! ．． The gain of the layer 38 changes, and the amplification factor of the light changes. Similarly, in the case of a wavelength tunable filter, by changing the amount of current injection to change the transmission center wavelength, the gain of the InGaAsP active layer 38 changes, and the amplification factor of the transmitted light changes. Moreover, when the ratio of the current injected from the three electrodes 46, 48, 50 is changed, the refractive index distribution in the cavity direction becomes non-uniform due to the change in the number of carriers in the InGaAsP active layer 38, and the equivalent refractive index of light n @yt changes. Therefore, as shown in the graph of FIG. 3 showing the relationship between the oscillation wavelength and gain of a wavelength tunable DFB laser, InGaAs
The oscillation wavelength of the DFB laser changes while keeping the gain of the P active layer 38 constant. Therefore, when this wavelength tunable DFB laser is used as a filter, the transmission center wavelength during filter operation can be changed in response to changes in the oscillation wavelength while keeping the optical amplification factor constant. However, in this wavelength tunable DFB laser, the range in which the ratio of current injected from the three electrodes 46, 48, 50 can be adjusted is limited, and when the optical amplification factor is kept constant, the oscillation wavelength cannot be changed too much. Therefore, in a wavelength tunable filter as well, the transmission center wavelength cannot be changed significantly if the optical amplification factor is kept constant. [Problems to be Solved by the Invention] As described above, in the conventional wavelength tunable filter or wavelength tunable DFB laser, when the amount of current injection is changed in order to change the transmission center wavelength or the oscillation wavelength, the gain of the active layer changes. The amplification factor of the transmitted light changes. Even if a method is used to adjust the ratio of current flowing from multiple electrodes to the active layer so that the optical amplification factor remains constant, the range of adjustment is limited, so the optical amplification factor is kept constant. In this state, the transmission center wavelength or oscillation wavelength cannot be changed too much. For this reason, when configuring a system using a wavelength tunable filter or a wavelength tunable laser, there is a problem that the resonant wavelength variable range is narrow and it is not possible to increase the wavelength multiplicity. Therefore, an object of the present invention is to provide an optical semiconductor device that can greatly change the resonance wavelength while keeping the intensity of transmitted light or oscillated light constant, and can increase the wavelength multiplicity of an optical network. [Means for Solving the Problems] The above-mentioned problems include a semi-dedicated substrate of a first conductivity type, a light guide layer formed on the semiconductor substrate, and a second conductivity type formed on the light guide layer. a separate layer, an active layer electrically separated from the light guide layer by the separate layer, and a second conductivity type embedding formed on both sides of the light guide layer, the separate layer, and the active layer. a first conductivity type cladding layer formed on the active layer through a cladding layer of a first conductivity type.
a second electrode formed on the bottom surface of the semiconductor substrate, and a third electrode formed on the buried waste, and a current is applied to the light guide layer and the active layer respectively independently. This is accomplished by an optical semiconductor device that is characterized by changing the resonant wavelength by changing the resonant wavelength. [Function] That is, according to the present invention, the refractive index of the light guide layer can be changed independently by passing a current through the light guide layer which is electrically separated from the active layer by the separate layer. Therefore, the resonance wavelength can be changed significantly while keeping the gain of the active layer constant.

[Example] The present invention will be specifically described below based on an illustrative example. FIG. 1 (a> and (b>) are a perspective view and a sectional view, respectively, showing a wavelength tunable filter according to an embodiment of the present invention. For example, (10
0) Pitch 240 nm, depth 3 on p-type 1nP substrate 2
A non-doped InGaAs film with a photoluminescence wavelength of 1.4 μm and a thickness of 1.2 μm is passed through a 0 nm diffraction grating 4.
The P light guide layer 6 is formed by a normal liquid phase growth method. Further, on this InGaAsP optical guide layer 6, an n layer with a carrier concentration n=2×10"cm- and a thickness of 1.2 μm is formed.
Non-doped InG with a photoluminescence wavelength of 1.55 μm and a thickness of 0.1 μm is passed through the InP type separate layer 8.
The aAsP active layer 10 is formed by liquid phase growth. Therefore, this n-type InP separate layer 8 allows I
The nGaAsP light guide layer 6 and the InGaAsP active layer 10 are electrically isolated from each other. Further, on this InGaAsP active layer 10, there is a p-type I layer with a carrier concentration P=5×10”cm− and a thickness of 1.5 μm.
nP cladding layer 12 and photoluminescence wavelength 1.3
μm, carrier concentration p=1×10”am, thickness 0.4
, um p-type InGaAsP contact layers 14 are sequentially formed by liquid phase growth. Then, a P-type InGaAsP contact layer 14 having a mesa shape, a P-type I
nP cladding layer 12, In nGaAsP active layer 10,n
An n-type InP buried layer 16 is formed on the surface of the InP type separate layer 8 and the InGaAsP light guide layer 6 by liquid phase growth. A current flows through the InGaAsP active layer 10 on the Zn diffusion region 18 formed by diffusing Zn on the surface of the P-type InGaAsP contact 114. A first electrode 20 for injecting a is formed. Further, on the bottom surface of the p-type InP substrate 2, a second electrode 22 for injecting a current Is into the InGaAsP optical guide layer 6 is formed. Furthermore, a third electrode 24 grounded is formed on the n-type InP buried layer 16. Next, we will explain the operation. Apply a predetermined voltage to the first voltage [i20 to
A current Ia is injected into the P active layer 10 to bring the wavelength tunable filter into a state immediately before laser oscillation. As a result, the resonant wavelength of the wavelength tunable filter, that is, the transmission center wavelength, is first determined.
Next, by applying a predetermined voltage to the second electrode 22, I n
When a current Is is injected into the GaAsP light guide layer 6, the equivalent refractive index naff of the InGaAsP light guide layer 6 becomes smaller due to the plasma effect. As a result, the transmission center wavelength is shifted to shorter wavelengths. And at this time, I
Since the current Ia flowing through the nGaAsP active layer 10 does not change, the optical amplification factor does not change. In this way, according to this embodiment, the n-type 1nP separate layer 8 allows the InGaAs
InGaAsP electrically isolated from the P active layer 10
A current Is is injected into the light guide layer 6 from the second electrode (i22) provided on the bottom surface of the p-type InP substrate 2 independently of the InGaAsP active layer 1o, and by controlling this current Is, the wavelength tunable filter is The transmission center wavelength can be changed significantly. In the above embodiment, the case of a wavelength tunable filter has been described, but a tunable wavelength laser can be formed with a structure equivalent to the structure shown in FIG. Also in this tunable wavelength laser, the laser oscillation wavelength can be changed significantly by controlling the injection of current Is into the optical guide layer independently of the active layer, in the same way as in the case of the wavelength tunable filter according to the above embodiment.

[Effects of the Invention] As described above, according to the present invention, by providing a separate layer between the active layer and the light guide layer and passing a current through the light guide layer independently of the active layer, the refraction of the light guide layer can be improved. By independently changing the ratio, the transmission center wavelength or oscillation wavelength can be greatly changed while keeping the intensity of the transmitted light or oscillation light constant.

Thereby, it is possible to realize a wavelength tunable laser or a wavelength tunable filter with a large tunable wavelength width, and increase the wavelength multiplexing degree of the optical network.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a wavelength tunable filter according to an example of the present invention, FIG. 2 is a diagram showing a conventional wavelength tunable filter, and FIG. 3 is a diagram for explaining the operation of the wavelength tunable filter shown in FIG. It is a graph. In the figure, 2... P-type 1nP substrate, 4.34... Diffraction grating, 6... InGaAsP optical guide layer, 8...
...n-type 1nP separate layer, 1 0.38...-I
nGaAs P active layer, 12.40...p type 1
nP cladding layer, 14.42 p-type 1nGaAsP contact layer, 16.44... n-type InP buried layer,
18...Zn diffusion region, 20, 22. 24.46. 48, 50
．． 52... Electrode, 32... N-type InP substrate, 36... N-type InGaAsP light guide layer.

Claims (1)

[Scope of Claims] A semiconductor substrate of a first conductivity type, a light guide layer formed on the semiconductor substrate, a separate layer of a second conductivity type formed on the light guide layer, and the separate layer. an active layer electrically isolated from the light guide layer; a buried layer of a second conductivity type formed on both sides of the light guide layer, the separate layer, and the active layer; a first electrode formed through a conductive cladding layer; a second electrode formed on the bottom surface of the semiconductor substrate; and a third electrode formed on the buried layer; An optical semiconductor device characterized in that a resonant wavelength is changed by passing current through the optical guide layer and the active layer independently.