JPH1090541A - Trench type semiconductor polarized wave rotating element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor polarized wave rotating element with which a desired rotating angle is obtainable at a short element length and which is high in yield. SOLUTION: The semiconductor polarized wave rotating element which is provided with a rectangular parallelepiped-shaped ridge waveguide extending in an optical waveguide direction on an optical waveguide consisting of a flat planer optical waveguide layer 22 and clad layers 21, 22 holding the optical waveguide layer 22 therein and is formed with grooves 31 alternated with forming positions to the right and left at every specific period of the optical waveguide direction around the ridge waveguide, by which the element is constituted. As a result, the addition of periodic perturbations to the direction orthogonal with the optical waveguide is made possible and asymmetricalness arises in the field distribution of the waveguide and therefore, the coupling efficiency between a TE polarized wave and a TM polarized wave is increased. The efficient rotation of the polarized waves at the short element length is thus made possible, the structure is simplified and the yield of the manufacture is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to optical communication, optical switching,
The present invention relates to a semiconductor polarization rotator used for optical information processing and the like.

[0002]

2. Description of the Related Art Optical devices such as an optical fiber, an optical waveguide, an optical switch, an optical receiver, and an optical amplifier are indispensable for constructing a system using light such as optical communication, optical switching, and optical information processing.

Further, these elements need to be made into practical parts by coupling with an optical fiber or by integrating them. In particular, since the integration can eliminate the optical axis alignment between the optical fiber and the semiconductor element, which is required with a precision of μm, it is robust and reliability can be expected to increase.

By the way, in a normal optical fiber,
It does not have the function of maintaining the plane of polarization from the light source, and when input to an optical functional element performed with a semiconductor optical switch or semiconductor laser type optical amplifier, the polarization state of the signal light changes according to environmental changes. May fluctuate.

However, the waveguide structure of a semiconductor device as described above generally has a waveguide layer or an active layer that is not isotropic and has a width of several microns but a thickness of a submicron order. Since the switching characteristics of the waveguide layer or the amplification characteristics of the active layer differ depending on the polarization state, the output characteristics vary greatly depending on the polarization state of the input signal light.

Therefore, as a method of eliminating the polarization dependence, an example of polarization diversity (references: H.Heidrich, F.Fi
dorra, M. Hamacher, K. Kaiser, K, Li, D. Trommer, and
G. Unterborsch: "Monolithically Integrated Heterody
ne Receivers based on InP ", 20th European Conferenc
e on Optical Communication (ECOC'94), pp77-80, 1994)
Have been reported.

In this example, a polarization rotation element is integrated in order to provide a TM component to the output of a local light source oscillating by a TE component.

[0008] As shown in FIG.
It has a waveguide that is asymmetrical about the z-axis in the xz plane. That is, an InP ridge layer 14 having a step-like shape in the x-axis direction is formed on a flat plate having the InGaAsP waveguide layer 12 interposed between the InP substrate 11 and the InP side cladding layer 13. Further, this InP ridge layer 14
With a specific period, the left and right sides are reversed, and the shape is alternately arranged in the z-axis direction.

FIG. 3 is a sectional view taken along the line AA in FIG. Note that the cross section in the direction of the arrow BB has a structure which is reversed left and right (with respect to the y axis) with respect to FIG.

Generally, the TE polarization component has an electric field in the x direction, and the TM polarization component has an electric field in the y direction (a direction at 90 ° when viewed from the x direction). And has no binding component.

Therefore, by adopting the structure having the left-right asymmetry shown in FIG. 3, the field distribution also has asymmetry,
Since the electric field components in the x direction and the y direction are coupled under the connection condition at the boundary (near the stepped step portion), coupling of the TE polarization component and the TM polarization component occurs.

The coupling component causes a transition of the field distribution between the TE polarization component and the TM polarization component, and generates a rotation component with respect to the polarization plane.

When the structure shown in FIG. 3 and the structure obtained by inverting the structure are arranged to form one block, and linearly polarized light is incident,
After passing through this one block, the light is converted into linearly polarized light rotated by an angle θ from the incident state.

Thus, a large rotation angle of nθ can be obtained by arranging blocks (for example, n blocks) in multiple stages as shown in FIG.

[0015]

However, in the structure shown in FIG. 2, since the coupling efficiency between the TE polarization component and the TM polarization component is very small, the rotation angle θ also becomes small, and it is difficult to obtain a desired rotation angle. Increases the element length.

It should be noted that FIG. 3 and its inverted structure need to be considered as one block because, similarly to the unevenness of the diffraction grating, the phase of the TE polarization component and the TM polarization component is periodically inverted (sign). Inversion).

FIG. 4 is a report example of another sectional structure. In the figure, 11 is an InP substrate, 12 is an InGaAsP waveguide layer,
13 is an InP side cladding layer, and 14 is an InP ridge layer. In this configuration, a step is provided in a part of the waveguide layer 12 by etching to provide a coupling between the TE polarization component and the TM polarization component, and the waveguide has an oblique portion. . Along with this, since the waveguide portion having the strongest field distribution has an oblique component, the coupling efficiency between the TE polarization component and the TM polarization component can be increased.

However, since this oblique angle cannot be manufactured with high accuracy, there has been a problem that the manufacturing yield cannot be increased.

An object of the present invention is to provide a high-yield semiconductor polarization rotator capable of obtaining a desired rotation angle with a short element length in view of the above problems.

[0020]

According to the present invention, in order to achieve the above object, at least one ridge formed on a semiconductor substrate and at least one optical waveguide layer located in or below the ridge are provided. The present invention proposes a trench-type semiconductor polarization rotator having a trench, the formation position of which is switched to the left and right around the ridge at every specific period in the longitudinal direction of the ridge.

According to the trench type semiconductor polarization rotating element, a trench is dug near the left and right of the ridge in parallel with the waveguide, and the trench has a specific period length.
Periodic perturbation can be added in the direction orthogonal to the optical waveguide, and asymmetry occurs in the field distribution of the waveguide, so that the coupling effect between TE polarization and TM polarization increases, and the short element length Thus, the polarization can be efficiently rotated.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a semiconductor polarization rotating element according to a first embodiment of the present invention, and FIG. 5 is a sectional view taken along line AA in FIG. This cross-sectional view is in the xy plane as in FIG. In the figure, 21 is In
A P substrate (semiconductor substrate) 22 has a band gap wavelength of 1.
3 μm band InGaAsP waveguide layer (0.3 μm thickness), 2
Reference numeral 3 denotes an InP side cladding layer (0.2 μm thick).

Reference numeral 30 denotes a ridge waveguide, which is provided on the InP side cladding layer 23, has a rectangular parallelepiped shape extending in the optical waveguide direction, and has an InP cladding layer 24 (1.5 μm
Thickness), and the width of the InP cladding layer is 2 μm.
It is.

Reference numeral 31 denotes a trench having a depth of 1.
It is dug vertically over a width of 2.0 μm, and is provided periodically in the z-axis direction at intervals of 100 μm on both the left and right sides separated from the ridge waveguide 30 by 0.5 μm. Are shifted by a half cycle.

By forming an element in which the grooves 31 are arranged on both sides of the ridge waveguide 30 in this manner, an element length of 800
A polarization rotation of 80 degrees was realized at μm.

As described above, according to the semiconductor polarization rotator of the first embodiment, the ridge waveguide 30 is formed on the ordinary optical waveguide, and the grooves 31 are periodically formed on both left and right sides of the ridge waveguide 30. The coupling effect between TE polarization and TM polarization is increased based on the asymmetry obtained by alternately providing the polarization, and the polarization can be efficiently rotated with a short element length. Furthermore, since the structure is simple, a semiconductor polarization rotator with a high yield can be obtained.

Next, a second embodiment of the present invention will be described. FIG. 6 is a sectional view showing a semiconductor polarization rotator according to a second embodiment of the present invention. This cross-sectional view is similar to FIG.
It is in the xy plane. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals. Further, the difference between the first embodiment and the second embodiment is that the InGaAsP waveguide layer 22 in the first embodiment is removed, and the InGaAsP waveguide layer is provided in the ridge waveguide 30. .

That is, reference numeral 21 denotes an InP substrate on which the ridge waveguide 30 is formed. Reference numeral 25 denotes an InGaAsP waveguide layer having a bandgap wavelength of 1.3 μm (0.
24 and 26 are InP side cladding layers (0.2 μm and 24 μm, respectively) provided so as to sandwich the waveguide layer 25.
1.0 μm thick), and the ridge waveguide 3
0, and the ridge width is 2 μm.

The groove 31 has a depth of about 1.0 μm and a width of 2.
It is dug vertically over 0 μm. Such a groove 31
Are periodically provided in the z-axis direction at intervals of 200 μm on both the left and right sides at a distance of 0.5 μm from the ridge waveguide 30, and the left and right sides have a structure in which the dug region is shifted by a half period.

By providing such a ridge waveguide 30 and forming the groove 31, a polarization rotation of 80 degrees was realized with an element length of 1600 μm.

Next, a third embodiment of the present invention will be described. FIG. 7 is a sectional view showing a semiconductor polarization rotator according to a third embodiment of the present invention. This cross-sectional view is similar to FIG.
It is in the xy plane. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals. Further, the difference between the first embodiment and the third embodiment is that in the third embodiment, a waveguide layer is formed in the ridge waveguide 30 in addition to the configuration of the first embodiment. It is in.

That is, 21 is an InP substrate, and 22 is an InGaAsP waveguide layer (0.
3 μm), 23 is an InP side cladding layer (0.1 μm).
m, and 24 and 26 are InP cladding layers (each of 0.
25 is a InGaAsP waveguide layer (0.3 μm) having a band gap wavelength of 1.3 μm.
Thickness), and the ridge width is 2 μm.

The groove 31 has a depth of about 1.0 μm and a width of 2.0 μm.
It is dug vertically over μm. Such a groove 31 is periodically provided in the z-axis direction at intervals of 90 μm on both the left and right sides separated from the ridge waveguide 30 by 0.5 μm, and the dug region on the left and right is shifted by a half period. I have.

By providing such a ridge waveguide 30 and forming the groove 31, an element length of 810 μm and
Twice polarization rotation was realized.

Next, a fourth embodiment of the present invention will be described. FIG. 8 is a sectional view showing a semiconductor polarization rotator according to a fourth embodiment of the present invention. This cross-sectional view is similar to FIG.
It is in the xy plane. In the figure, the same components as those of the third embodiment are denoted by the same reference numerals. The difference between the third embodiment and the fourth embodiment is that, in the fourth embodiment, the upper surface of the ridge waveguide 30 and the lower surface of the InP substrate 21 are added to the structure of the third embodiment. An electrode is formed so that the refractive index of the waveguide layer can be changed.

That is, 21 is an InP substrate, and 22 is an InGaAsP waveguide layer (0.
3 μm), 23 is an InP side cladding layer (0.1 μm).
m, and 24 and 26 are InP cladding layers (each of 0.
25 is a InGaAsP waveguide layer (0.3 μm) having a band gap wavelength of 1.3 μm.
Thickness), and the ridge width is 2 μm.

Further, an n-electrode 32 made of, for example, AuGeNi is formed on the lower surface of the InP substrate 21, and a p-electrode 33 made of, for example, AuZnNi is formed on the upper surface of the ridge waveguide 30.

The groove 31 has a depth of about 1.0 μm.
It is dug vertically over a width of 2.0 μm. Such a groove 31 is periodically provided in the z-axis direction at intervals of 90 μm on both the left and right sides separated from the ridge waveguide 30 by 0.5 μm, and the dug region on the left and right is shifted by a half period. I have.

According to the above-described structure, the refractive index of the waveguide layer can be changed by applying a voltage between the electrodes 32 and 33 to cause a current to flow. Becomes possible. Thus, with the element length set to 810 μm, a current of 40 mA was passed between the electrodes 32 and 33, and a polarization rotation of 86 degrees was realized.

In the first to fourth embodiments described above, the material for forming the waveguide layer on the InP substrate 21 is In.
Although the GaAsP material system has been described, a similar effect can be obtained by using another material system, and an arbitrary operating wavelength can be set by selecting a material system.

It is also possible to use a thin layer of InP or InGaAsP as an etching stop layer for convenience of fabrication.

Further, the position of the waveguide layer can be arranged at any position (for example, the top, center, bottom, etc.) in the ridge waveguide 30. It is also possible to have a waveguide layer.

In the case where a plurality of waveguide layers are provided in the ridge waveguide 30, the composition of each waveguide layer may be different, or all the waveguide layers may have the same composition.

Further, in the fourth embodiment, the electrodes 32,
Although the example in which 33 is provided has been described, it is needless to say that the same effect as in the fourth embodiment can be obtained even if an electrode is added to the configuration of another embodiment as in the fourth embodiment.

[0045]

As described above, according to the present invention, a ridge is formed on a normal optical waveguide, and the formation position is switched to the left and right with the ridge as a center at every specific period in the longitudinal direction of the ridge. By forming the trench, it becomes possible to add a periodic perturbation in a direction orthogonal to the optical waveguide, and asymmetry occurs in the field distribution of the waveguide, so that the coupling effect between the TE polarization and the TM polarization. Increases,
Polarization can be efficiently rotated with a short element length. Furthermore, since the structure is simple, it can be manufactured with high yield.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a semiconductor polarization rotator according to a first embodiment of the present invention.

FIG. 2 is an external perspective view showing a conventional semiconductor polarization rotating element.

FIG. 3 is a sectional view taken along line AA in FIG. 2;

FIG. 4 is a cross-sectional view showing another conventional semiconductor polarization rotating element.

FIG. 5 is a sectional view showing a semiconductor polarization rotator according to the first embodiment of the present invention;

FIG. 6 is a sectional view showing a semiconductor polarization rotating element according to a second embodiment of the present invention.

FIG. 7 is a sectional view showing a semiconductor polarization rotator according to a third embodiment of the present invention;

FIG. 8 is a sectional view showing a semiconductor polarization rotating element according to a third embodiment of the present invention.

[Explanation of symbols]

21: InP substrate (semiconductor substrate), 22: InGaAs
P waveguide layer, 23... InP side cladding layer, 24, 26
... InP cladding layer, 25 ... InGaAsP waveguide layer, 3
0: Ridge waveguide, 31: Groove (trench), 32, 33
…electrode.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Louis Wayne Nippon Telegraph and Telephone Corporation 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo

Claims (1)

[Claims] 1. A ridge formed on a semiconductor substrate and at least one optical waveguide layer located in or below the ridge, wherein the ridge is provided at a specific period in the longitudinal direction of the ridge. A trench type semiconductor polarization rotator comprising a trench whose formation position is switched right and left around the center.