JP2783871B2 - Waveguide optical device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical element for electrically controlling the phase, intensity, path and the like of light traveling in a waveguide.

(Prior Art) For example, in optical communication, an element that can electrically control the phase, intensity, propagation path, and the like of an optical signal propagating in a waveguide is required. As such an element, one using a change in light due to the acousto-optic effect of the waveguide, one using a change in light due to the electro-optic effect of the waveguide, one using a directional coupler, and, for example, Literature (IEICE Technical Report MW86−
22 (1986)), there is a waveguide type optical element made of a semiconductor material, which changes the refractive index of a waveguide by carrier injection.

A waveguide-type optical element that changes the refractive index of a waveguide by carrier injection (hereinafter referred to as this type of optical element when referred to as a waveguide-type optical element) is smaller in size than other elements. It is advantageous in that it can be easily formed, has excellent separation ability, and is easily integrated.

Hereinafter, the configuration of the conventional total reflection type waveguide optical device disclosed in the above document will be briefly described with reference to FIGS. 4 (A) and 4 (B), and particularly to FIG. 4 (B). Here, FIG. 4 (A) is a plan view schematically showing a conventional waveguide type optical device, and FIG. 4 (B) shows this waveguide type optical device in FIG. 4 (A). FIG. 2 is a cross-sectional view taken along the line II of FIG.

In FIG. 4 (B), reference numeral 11 denotes an n-type InP substrate. On the n-type InP substrate 11, i-type InGaAsP
An optical waveguide layer 13, an n-type InP cladding layer 15, and an n-type InGaAsP cap layer 17 are provided. A zinc diffusion layer 11a for current confinement is formed in a predetermined region (a region other than a current path) of the n-type InP substrate 11, and an n-type InP cladding layer 15 and an n-type InGaAsP cap layer 17 are respectively provided. A zinc diffusion layer 16 for current confinement is formed in a predetermined region (a region serving as a current path). Further, an SiO ₂ film 19 is formed on a region of the n-type InGaAsP cap layer 17 other than the region where the zinc diffusion layer 16 is formed. Furthermore, n-type InGaAs
A p-side electrode 21 is connected to a region of the P cap layer 17 which has become P-type due to zinc diffusion, and an n-type electrode 23 is formed on the back surface of the n-type InP substrate 11.

In this conventional waveguide type optical device, an i-type InGaAsP optical waveguide layer 1 is used.
3, the region corresponding to the lower side of the zinc diffusion layer 16 becomes the variable refractive index region 13a. Then, by applying a predetermined voltage between the p-side electrode 21 and the n-side electrode 23, carriers are injected into the optical waveguide layer 13, so that the refractive index of the refractive index variable region 13a changes, and the waveguide type optical element Is turned on.

(Problems to be Solved by the Invention) However, in the above-described waveguide type optical element, even if it is attempted to extract carriers from the optical waveguide layer in order to turn it off, holes and electrons as carriers are simultaneously extracted. Is structurally difficult. For this reason, carriers have to be erased by recombination of electrons and holes, so that the operating speed of the waveguide type optical element is limited by the carrier lifetime and cannot be performed at high speed. .

The present invention has been made in view of such a point,
Accordingly, it is an object of the present invention to provide a waveguide type optical device capable of improving the operation speed.

(Means for Solving the Problems) In order to achieve this object, according to the present invention, there is provided a waveguide-type optical element including at least an optical waveguide layer on a semiconductor substrate, wherein light traveling through the optical waveguide layer is provided. In a waveguide type optical element in which control is performed by changing the refractive index of the optical waveguide layer caused by carriers injected into the optical waveguide layer, the semiconductor substrate is an n ⁺ type semiconductor substrate, and the n ⁺ type semiconductor substrate is In order from the substrate side, an n-type semiconductor layer in which the carrier concentration decreases as going upward from the substrate side, a refractive index of the n-type semiconductor layer and a refractive index of a semiconductor layer formed on the optical waveguide layer. comprising an optical waveguide layer constituted by the i-type semiconductor layer having a high refractive index, at least the conduction band than the optical waveguide layer is energetically higher semiconductor layer, and n ⁺ -type semiconductor layer also, and the n ⁺ An electrode provided on the type semiconductor layer, And an electrode provided on the back surface of the substrate.

(Operation) According to the configuration of the waveguide type optical element of the present invention, the following operation can be obtained.

... Since the semiconductor substrate is an n ⁺ type semiconductor substrate, majority carriers become electrons.

... Since an n-type semiconductor layer whose carrier concentration decreases from the substrate side toward the top is provided on the semiconductor substrate, when a voltage is applied to the waveguide type optical element so that the n ⁺ substrate side has a negative potential, Electrons are smoothly injected into the optical waveguide layer. Further, since a semiconductor layer having a conduction band higher in energy than the optical waveguide layer is provided on the opposite side of the optical waveguide layer from the substrate side, electrons injected into the optical waveguide layer are effectively stored in the optical waveguide layer. . As a result, the refractive index of the optical waveguide layer changes efficiently, and the waveguide type optical element can be turned on.

... Since the optical waveguide layer is composed of an i-type semiconductor layer, light absorption by free carriers does not occur in this layer. Therefore, the extent to which the optical signal is absorbed by the optical waveguide layer can be reduced. Further, since the refractive index of the optical waveguide layer is higher than the refractive indexes of the layers above and below the optical waveguide layer, the optical signal is efficiently confined in the optical waveguide layer.

... When a voltage is applied to the waveguide type optical element so that the n ⁺ substrate side has a positive potential, electrons can be extracted from the optical waveguide layer. However, since a semiconductor layer having a higher conduction band than the optical waveguide layer in terms of energy is provided on the optical waveguide layer, it is possible to prevent electrons from flowing into the optical waveguide layer from the semiconductor layer above the semiconductor layer. Yes (block action). As a result, the waveguide type optical element can be quickly turned off.

... The n ⁺ type semiconductor layer provided on the uppermost layer improves ohmic properties with an electrode formed thereon, and gives a stronger electric field to the optical waveguide layer.

(Example) Hereinafter, an example of a waveguide type optical element of the present invention will be described with reference to the drawings.

It should be noted that the drawings used in the following description are only schematically shown to the extent that the present invention can be understood. Therefore, it should be understood that the dimensions, shapes, and arrangement relationships of the components in the drawings are merely examples, and the present invention is not limited only to these.

FIG. 1 is a view for explaining an embodiment in which the present invention is applied to a total reflection type (crossed type) waveguide type optical element as shown in FIG. FIG. 3 is a cross-sectional view showing a crossing portion of an element cut in a direction orthogonal to a waveguide.

The waveguide type optical element of this embodiment is an n ⁺ type semiconductor substrate.
An n ⁺ -type InP substrate 31 is used.

On the n ⁺ -type InP substrate 31, there is provided an n-type InGaAsP cladding layer 33 as an n-type semiconductor layer in which the carrier concentration decreases as going upward from the substrate 31 side. The formation of the n-type InGaAsP cladding layer 33 in which the carrier concentration decreases as going upward from the substrate 31 side can be performed by decreasing the impurity concentration as the semiconductor layer grows.

Further, an optical waveguide layer 3 is formed on the n-type InGaAsP cladding layer 33.
5, an i-type semiconductor layer having a refractive index higher than the refractive index of the n-type InGaAsP cladding layer 33 and the refractive index of the semiconductor layer 37 (described later) formed on the optical waveguide layer 35;
An optical waveguide layer 35 composed of a type InGaAsP layer is provided.

Further, on the i-type InGaAsP optical waveguide layer 35, an optical waveguide layer 3
An n-type InGaAsP block layer 37 is provided as a semiconductor layer whose conduction band is higher in energy than the semiconductor layer whose conduction band is higher in energy than that of the semiconductor layer formed on this semiconductor layer. . The height of the conduction band is controlled by
This can be achieved by changing the composition ratio. Further, the n-type InGaAsP block layer 37 of this embodiment has a structure having a protrusion 37a partially protruding in a ridge shape and a structure having a recess 37b in the protrusion 37a. According to the ridge-shaped protrusion 37a, light can be efficiently confined in the optical waveguide layer 35.

Further, the concave portion 37b of the n-type InGaAsP block layer 37 has n ⁺
It is provided with a n ⁺ -type InP layer 39 serving as a type semiconductor layer, the n ⁺
On top -type InP layer 39 is the first electrode 41, also, n ⁺ -type InP substrate 31
The second electrode 43 is provided on the back surface of the first electrode.

FIG. 2 (A) is an energy band diagram of the waveguide type optical device having the above-described configuration in a state where no voltage is applied between the first and second electrodes 41 and 43. Show. In FIG. 2 (A), 51 indicates a Fermi level, 53 indicates a conduction band, and 55 indicates a valence band.

The bandwidth of the i-type InGaAsP optical waveguide layer 35 is the
nGaAsP cladding layer 33, n-type InGaAsP block layer 37 and n ⁺
N-type layer 39 is smaller than the bandwidth of each
The height of the conduction band of the InGaAsP block layer 37 is higher than that of each of the i-type InGaAsP optical waveguide layer 35 and the n ⁺ -type InP layer 39. Electrons are n-type n-type InGaAsP cladding layers 33
⁺ Stopped near the InP substrate 31 side (the area indicated by 57 in FIG. 2 (A)).

A voltage is applied between the first and second electrodes 41 and 43 of the waveguide type optical device having the above-described configuration so that the first electrode 41 is positive and the second electrode 43 is negative. Then, n
The electrons stopped near the n ⁺ InP substrate 31 in the type InGaAsP cladding layer 33 approach and are injected into the i-type InGaAsP optical waveguide layer 35. These electrons are accumulated in the i-type InGaAsP optical waveguide layer 35 by the action of the InGaAsP block layer 37. Then, due to the plasma effect of the electrons, the refractive index of the i-type InGaAsP optical waveguide layer 35 changes, and as a result, the optical signal propagating through the i-type InGaAsP optical waveguide layer 35 is controlled.

FIG. 3 shows a state in which a voltage is applied with the first electrode 41 being positive and the second electrode 43 being negative, and electrons are present on the lower part of the protruding portion 37a of the optical waveguide layer 35 of the embodiment of the waveguide type optical device. It is the figure which showed the collected state typically. FIG. 2 (B) is an energy band diagram of the waveguide type optical element according to the embodiment in a state where a voltage is applied with the first electrode 41 being plus and the second electrode 43 being minus.

On the other hand, when a voltage is applied between the first and second electrodes 41 and 43 with the first electrode 41 being negative and the second electrode 43 being positive, electrons accumulated in the i-type InGaAsP optical waveguide layer 35 are obtained. Is drawn out to the substrate 31 side. At this time, the n ⁺ type InP layer 41
The flow of electrons from the side into the optical waveguide layer 35 is prevented by the action of the n-type InGaAsP block layer 37. Therefore, the waveguide type optical element is turned off. FIG. 2C shows the first electrode 41.
FIG. 9 is an energy band diagram of the waveguide type optical element of the embodiment in a state where a voltage is applied with the minus sign and the second electrode 43 plus.

The above is the description of the embodiments of the waveguide type optical element of the present invention. However, the present invention is not limited to the above-described embodiment, and various modifications as described below can be added.

In the above-described embodiment, the substrate is an n ⁺ -type InP substrate 31, and an n-type InGaAsP cladding layer 33, an i-type InGaAsP optical waveguide layer 35, an n-type InGaAsP block layer 37 and an n ⁺ -type InP layer 39 are provided on the substrate 31. In this order. However, the constituent materials of the waveguide type optical element are not limited to these. For example, the substrate is an n ⁺ -type GaAs substrate, and on this substrate, an n-type GaAlAs cladding layer, an i-type GaAs optical waveguide layer, an n-type GaAlAs block layer 37 and
The same effect as that of the embodiment can be expected also in the case where the n ⁺ type GaAs layer is provided in this order.

The above embodiment is an example in which the present invention is applied to a total reflection type waveguide optical device. However, the present invention can also be applied to a directional coupler type optical element.

(Effects of the Invention) As is clear from the above description, according to the waveguide type optical element of the present invention, although the carrier is an electron, the electron is transmitted to the optical waveguide layer despite its simple structure. Injection and extraction of electrons from the optical waveguide layer can be easily performed. Therefore, high-speed operation is possible as compared with a conventional waveguide type optical element in which holes and electrons are used as carriers and carriers are eliminated by recombination of electrons and holes.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of a waveguide type optical element according to an embodiment, FIGS. 2 (A) to 2 (C) are energy band diagrams for explaining the embodiment, and FIG. FIGS. 4 (A) and 4 (B) are diagrams for explanation of the prior art. 31... N ⁺ type semiconductor substrate, 33... N in which the carrier concentration decreases as going upward
Type semiconductor layer (cladding layer) 35 i-type optical waveguide layer 37 Semiconductor layer (block layer) having a conduction band higher in energy than at least the optical waveguide layer 37a Projecting portion 37b Concave portion 39 n ⁺ semiconductor layer 41 first electrode 43 second electrode 51 Fermi level 53 conduction band 55 valence band 57 region where electrons are stopped.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/00-1/025 G02F 1/29-1/313 G02F 1/35-3/02 G02B 6 / 12-6/14

Claims (1)

(57) [Claims] 1. A waveguide type optical device comprising at least an optical waveguide layer on a semiconductor substrate, wherein control of light traveling through the optical waveguide layer is performed by:
In a waveguide type optical element performed by changing the refractive index of the optical waveguide layer caused by carriers injected into the optical waveguide layer, a semiconductor substrate is an n ⁺ type semiconductor substrate, and the substrate side is provided on the n ⁺ type semiconductor substrate. An n-type semiconductor layer in which the carrier concentration decreases upward from the substrate side, and a refractive index of the n-type semiconductor layer and a refractive index higher than the refractive index of the semiconductor layer formed on the optical waveguide layer. an optical waveguide layer constituted by the i-type semiconductor layer having a refractive index, at least energetically higher conduction band than the optical waveguide layer semiconductor layer, comprising the n ⁺ -type semiconductor layer, the n ⁺ -type semiconductor layer And a back surface of the substrate, respectively, provided with electrodes.