JPS6017717A - Semiconductor optical modulating element - Google Patents

Abstract

PURPOSE:To obtain a modulating output containing no excessive spectrum width, and also to form an optical modulating element which takes largely a percentage modulation and an extinction ratio, also is remarkably short in element length, and manufactured easily, by varying a waveguide function by using a current injection and modulating light. CONSTITUTION:When a modulating current as an arrow 13 of a broken line is made to flow, a carrier is closed up in an InGaAsP optical waveguide layer 7, a refractive index of a part to which the current has been injected by a plasma vibration effect drops, and a refractive index distribution becomes that which has a waveguide function whose center part is high and whose circumference is low as a broken line. Accordingly, input light is scarcely attenuated, and can be wave-guided to the output end. In this way, a waveguide function of a semiconductor is varied by utilizing a fact that a refractive index in the X axis direction of the InGaAsP optical waveguide layer 7 is varied depending on whether a modulating current flowing in a zinc diffusion area 12 exists or not, or it is large or small, with respect to input light having an electric power of a prescribed value. In this way, the magnitude of output light in the output end is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a light modulation device, and more particularly to a semiconductor light modulation device that can have a sufficient extinction ratio and is easy to manufacture.

(Background Art) Semiconductor lasers are being put into practical use as light sources for optical fiber communications. Advantages of semiconductor lasers include small size, high reliability, and direct modulation. That is, by modulating the injected current, a corresponding optical output can be directly obtained. However, this direct modulation has one essential drawback. That is, since carriers such as electrons or holes in the region where light is generated fluctuate, the refractive index also fluctuates due to the plasma oscillation effect, and as a result, the wavelength of the emitted light fluctuates greatly.

Therefore, the spectral width of a directly modulated semiconductor laser is 1, which is abnormally large compared to the band of the modulation signal.

In this way, excessive spectral width causes signal deterioration in optical fiber transmission and significantly reduces performance. Therefore, in order to eliminate these inconveniences, it is necessary to modulate the output of the semiconductor laser while keeping it constant and keeping the spectral width very narrow. To do this, it is necessary to use a separate optical modulation element. .

Typical conventional optical modulation elements include the directional coupling type shown in FIG. 1 and the Matsuhatsu Ender interferometer type shown in FIG. 2.

Both FIG. 1 and FIG. 2 show plan views, in which optical waveguides 1 and 2 are fabricated on crystals such as Z, ISBO 3, etc., electrodes 3 and 4 are provided, and input light is controlled by a modulation signal 5. The output light is obtained by controlling the

Although there are some improved versions and other examples of these optical modulators, most of them utilize the electro-optic effect, that is, the small change in the refractive index of the rAybo, crystal or optical waveguide 2 caused by a control electric field, to achieve propagation. It controls the phase of the light being transmitted and the optical coupling between the two waveguides.

However, since the change in refractive index due to the electro-optic effect is very small, this type of light modulation element has an element length of several nanometers.
The disadvantage is that it is several meters long. In addition, as shown in Figs. 1 and 2, in the type using two waveguides], 2, the two waveguides are required to be almost completely identical, and the cross section and length of the waveguides are Production was extremely difficult due to severe restrictions on the relationship between the two.

(Problems to be solved by the invention) In order to solve the drawbacks of the conventional optical modulation elements, the present invention provides an optical modulation element that has a sufficient modulation rate and extinction ratio, has few manufacturing restrictions, and can be miniaturized. The purpose is to The present invention will be described in detail below using the drawings.

(Structure and operation of the invention) FIG. 3(α) shows an embodiment of the invention, and shows a cross-sectional view of a semiconductor optical modulation element viewed from the front.

In the following description, Jnl-, GCLOcAs, , Pl-, C, and X, which are substantially lattice-matched to the InP substrate, are used.

An example using an optical waveguide region made of a compound semiconductor (with y omitted) will be described.

The input light is incident on the region surrounded by the broken line, that is, in the X-axis direction (longitudinal direction of the semiconductor) of the optical waveguide region.

6 is an n-type InP substrate, 7 is I<(LA8P optical waveguide layer, 8 is P-type 1nl), 9 is n-type Ink (LAMP cap layer, 10 and 11 are electrodes, and 12 is a zinc diffusion region. InG (LA8P optical waveguide layer 7 is 6 and 8
Because it has a higher refractive index than InP in the Y-axis (vertical) direction, it has a waveguide function, that is, a function to confine input light in the optical waveguide layer 7, but in the X-axis (horizontal) direction, it has a waveguide function (in the same figure). b)
As shown by the solid line in the refractive index distribution, the refractive index is constant, so it does not have a waveguide function. Therefore, the input light is gradually radiated to the surroundings, and the output light becomes extremely small at the other output end in the X-axis direction.

However, when a modulation current as shown by the broken arrow 13 is applied, the carriers are confined in the IfLG (LA8P optical waveguide layer 7) and the refractive index of the part where the current is injected decreases due to the plasma oscillation effect. As shown by the broken line, the distribution has a waveguide function where the center is high and the periphery is low.Therefore, the input light can be guided to the output end with almost no attenuation.

In this way, this embodiment utilizes the fact that the refractive index of the InGcLA8P optical waveguide layer 7 in the X-axis direction changes depending on the presence or absence or magnitude of the modulation current flowing through the zinc diffusion region 12 for input light having a constant value of power. This is an optical modulation element characterized by changing the magnitude of output light at an output end by changing the waveguide function of a semiconductor.

FIG. 4(α) shows an embodiment of the present invention in which the modulation factor and extinction ratio are improved by further increasing the radiation effect of input light when no current is injected in FIG. 3(α).

That is, the electrode of FIG. 3 (α) is 10.10'.

10"0" is divided into three parts, and the electrodes 10 and 10' are made common.First, a current I is passed through the electrode 10", and the other electrodes io
, io', the third
As explained in the figure, the part of the optical waveguide layer 7 through which the current flowed has a refractive index distribution due to the plasma oscillation effect of the carriers, as shown in Figure 4 (
It becomes small as shown by the solid line in b), and the input light is radiated to the surroundings over a very short distance. That is, the input light is
Almost no output light appears at the output end in the axial direction.

Conversely, if I is set to 20 and a current of I is applied, the refractive index distribution will be high in the center as shown by the broken line in Figure 4(b).
It has a waveguide function for input light, and can be extracted as output light at the output end without being attenuated.

In this way, the waveguide function is changed depending on the presence or absence of current flowing through the three divided electrodes, and no output light appears at the output end9, but it is still possible to extract output light that is almost the same size as the input light. It becomes possible.

In FIG. 5(a), the thickness of the central portion of the I-naaAsp waveguide layer 7 is slightly reduced in order to obtain the same effect as in FIG. 4(a). That is, when the modulation current 13 is absent or small, the refractive index distribution becomes small at the center as shown by the solid line in FIG. does not appear. Conversely, when the modulation current 13 exceeds a certain level, the refractive index distribution is smaller at the periphery than at the center, as shown by the broken line, and the input light is processed as output light at the output end. You can get it out.

As is clear from the above explanation, the basic t of the present invention
The main feature of this method is that modulation is performed by changing the waveguide function of light, that is, whether the light is guided or not, depending on the presence or absence or magnitude of a modulation current, without using the conventional electro-optic effect. The present invention also provides an optical modulation element that can perform modulation without using two waveguides.

In addition, although the above explanation has been about an example in which modulation is performed by injecting a modulation current into the optical waveguide region or its vicinity to change the optical waveguide function, the same effect can be obtained by using modulated light instead of the modulation current. The effect of this can be obtained.

FIG. 6 shows another embodiment of the present invention in which the waveguide function is changed and modulated using modulated light. When modulating light 14 is irradiated using the electrode 10 as a mask, carriers in the peripheral area of the optical waveguide region are excited. However, the same effect as in FIG. 3(G) can be obtained. However, when modulating by light irradiation, the operating principle differs depending on whether the energy hν of the irradiated light is InG (the forbidden band width E (7) of the LASP optical waveguide layer 7 is also large or small). .

If the light energies h and ν are larger than JnG (the forbidden band width E of the LASP optical waveguide layer 7), the current bottoms out to excite carriers in the optical waveguide layer 7 as described above. Similarly, due to the plasma oscillation effect, the refractive index of the part irradiated with the modulating light decreases, and the refractive index distribution becomes one with a waveguide function, with the refractive index being high in the center and low in the periphery.

Conversely, the optical energy Aν is the forbidden band width E of the optical waveguide layer 7.
When g is also small, carriers are not excited and the operation is based on nonlinear effects. In other words, the refractive index of the material changes slightly depending on the light irradiating it, causing dust,
This effect is usually very small, and to increase the nonlinear effect, the intensity of the modulated light must also be increased.

FIG. 7 shows an embodiment of the present invention in which the nonlinear effect can be significantly increased by using a multilayer quantum well structure. In this figure, 15 is a multilayer quantum well layer made of very thin layers of InP and InG (LASP), 16 is an n-type InP, and 17 is a light emitting layer made of InG (LASP).

Therefore, when the current 13 is injected, the InGCLASP layer 17
emits light and the multilayer quantum well layer 15 is irradiated with the light 14, causing a large change in the refractive index of the multilayer quantum well layer 15. Here, if the constant representing the nonlinear effect determined by the material of the multilayer quantum well layer 15 has a positive sign, a waveguide function is generated in the multilayer quantum well layer 15 by current injection, and modulation is also possible.

In this way, in this embodiment, even if modulation light is used, the waveguide function can be changed, and the output light appearing at the output end can also be modulated.

In addition, until now InP substrates and InP substrates have been almost lattice matched,
1-z) Ga, A, 8. The explanation has been given using an example of an optical waveguide region made of Pl, but In (1-x y ) A l x Ga Y which has almost lattice match with the InP substrate
AXl with almost lattice matching with AS or GαAS substrate
It goes without saying that a completely similar light modulation element can be made using a Ga-As compound semiconductor.

(Effects of the Invention) As explained above, the present invention provides a semiconductor optical modulator that performs modulation by changing the waveguide function using current injection or modulating light, and This optical modulation element not only provides a modulated output that does not include width, but also has a sufficiently large modulation factor and extinction ratio compared to conventional ones, and is also much shorter in element length, making it easier to manufacture.

Therefore, it is easy to monolithically integrate the semiconductor laser and the semiconductor optical modulator of the present invention, and the extinction ratio, which is an important element for a modulator, can be made sufficiently large.
It can be applied to high-performance optical fiber communications, and its effects are extremely large.

[Brief explanation of the drawing]

Figure 1 shows a conventional directional coupling type optical modulator, Figure 2 shows a conventional Matsuhatsu Ender interferometer type optical modulator, and Figure 3 ((L)
and (b) is for explaining the basic operation of the present invention,
Figures 4 (CL) and (b) are diagrams showing an embodiment of a semiconductor optical modulation element that changes and modulates the optical waveguide function by current injection.
) and FIGS. 5(α) and (b) are diagrams showing an embodiment of the present invention of a semiconductor optical modulator with improved modulation factor and extinction ratio as shown in FIG. 3, and FIGS. FIG. 7 is a diagram illustrating another embodiment in which the waveguide function is changed and modulated (by light irradiation). 1.2... Optical waveguide, 3, 4... Electrode, 5... Modulation signal, 6... N-type 1nP substrate, 7... InGc
LASP optical waveguide layer, 8-P type I'rLP layer, 9---
n-type 1nGCLA8F cap layer, 10, 10',
10', 11... Electrode, 12... Zinc diffusion region, 13... Modulation current, 14... Modulation light, 15...
・Multilayer quantum well structure, 16...n type 1. nP layer, 17
-1nGaASP layer. Patent Applicant International Telegraph and Telephone Corporation Patent Attorney Megumi Yamamoto - No. 1 Figure 112 Figure 111i3 Figure (a) (b) Figure 4 (a) (b) Figure 5 (a) (b)

Claims (3)

[Claims] (1) By forming an optical waveguide region on a semiconductor substrate and controlling the waveguide function of the optical waveguide region using modulation energy injected from the outside, the input light introduced into the optical waveguide region is modulated. What is claimed is: 1. A semiconductor optical modulation element characterized by outputting a signal. (2) The semiconductor optical modulator according to claim 1, wherein the modulation energy is a modulation current injected into or near an optical waveguide region. (3) The semiconductor optical modulator according to claim 1, wherein the modulated energy is modulated light that is irradiated onto or near an optical waveguide region.