JP3409606B2 - Semiconductor polarization rotator - Google Patents

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 rotating element used for optical information processing and the like.

[0002]

2. Description of the Related Art Considering the construction of a system utilizing light such as optical communication, optical switching, and optical information processing, optical elements such as an optical fiber, an optical waveguide, an optical switch, an optical receiver, and an optical amplifier are indispensable. . However, these elements need to be used as practical parts by coupling with an optical fiber or by integrating them. In particular, the integration makes it possible to omit the optical axis alignment between the optical fiber and the semiconductor element, which is required with micron accuracy, so that it is robust and the reliability can be expected to increase.

By the way, an ordinary optical fiber does not have a function of maintaining the plane of polarization from the light source, and when it is input to an optical functional element such as a semiconductor optical switch or a semiconductor laser type optical amplifier, it is subject to environmental changes. Accordingly, the polarization state of the signal light may change.

However, in the waveguide structure of the semiconductor device as described above, the waveguide layer or the active layer is generally not isotropic, and the width is several microns, but the thickness is on the order of submicron, and The switching characteristics of the wave layer or the amplification characteristics of the active layer differ depending on the polarization state. Therefore, the output characteristics greatly change depending on the polarization state of the input signal light.

Therefore, as a method of eliminating the polarization dependence,
Polarization diversity example (H. Heidrich, F. Fidorra, M. Ham
acher, K.Kaiser, K.Li, D.Trommer, and G.Unterbosch: ”M
onolithically Integrated Heterodyne Receivers base
d on InP ”, 20th European Conference on Optical Com
munication (ECOC'94), pp.77-80,1994) has been reported. Here, the output of the local light source oscillating with the TE component is TM
A polarization rotation element is integrated in order to have a component.

As a polarization rotator, for example, as shown in FIG. 10, there is known one having a structure in which left and right asymmetric waveguides are alternately arranged with a left and right inverted waveguides with a specific period. Has been.

The polarization rotation element is composed of InGaAs having a band gap wavelength of 1.1 μm on the main surface of the InP substrate 11.
It has a structure in which a P waveguide layer 12, an InP side cladding layer 13, and an InP ridge layer 14 are sequentially stacked. The uppermost InP ridge layer 14 has a ridge structure (protrusion structure) having a predetermined width as can be seen from the name.

The upper surface of the InP ridge layer 14 is a surface having asymmetric heights (height in width) of the left and right surfaces, that is, a high surface 1 and a low surface 2, with the center line therebetween. The high surface 1 and the low surface 2 also appear in a specific cycle along the longitudinal direction of the InP ridge layer 14. In FIG. 11, the high surface 1 appears on the left side and the low surface 2 appears on the right side, and in FIG. 12, the high surface 1 appears on the right side and the low surface 2 appears on the left side.

Generally, since the TE polarized wave component has an electric field in the X direction and the TM polarized wave component has an electric field in the y direction (direction of 90 ° when viewed from the x direction), they are normally orthogonal to each other, and thus the coupled component. Does not have.

Therefore, as shown in FIGS. 11 and 12, by adopting a structure in which the InP ridge layer 14 on the InGaAsP waveguide layer 12 is left-right asymmetrical, the field distribution also becomes asymmetrical, and the connection of the boundaries is made. Under the conditions, the electric field components in the x direction and the y direction are coupled, so that the TE polarized component and the TM polarized component are coupled. This coupling, the component is TE polarization component and T
This causes a transition of the field distribution with the M polarization component, and causes a rotation component with respect to the plane of polarization.

When the structure shown in FIG. 11 and its inverted structure shown in FIG. 12 are used as one block and linearly polarized light is made incident, after passing through this one block, it is converted into linearly polarized light rotated by an angle θ from the incident state. It Therefore, by arranging blocks (for example, n pieces) in multiple stages as shown in FIG. 10, a large rotation angle of nθ can be obtained.

FIG. 13 is a sectional structure according to another reported example of a polarization rotation element. In order to provide coupling between the TE polarization component and the TM polarization component, a part of the waveguide is stepped by etching. The waveguide has a slanted portion. Along with this, the waveguide having the strongest field distribution has an oblique component, so that the coupling efficiency of the TE polarization component and the TM polarization component can be increased.

That is, in this structure, a step is provided on the InP substrate 11 in order to provide the waveguide with an inclined portion, and a bandgap wavelength of 1.1 μm band having a predetermined thickness is sequentially formed on the InP substrate 11. InGaAsP waveguiding layer 1
2, InP side cladding layer 13, InP ridge layer 14
It has a laminated structure.

FIG. 14 is a report example of another polarization rotation element (JJ
GMvan der Tol et.al:A new short and low-loss pas
sive polarization converter on InP, IEEE.Photon.tec
hnol.Lett., vol.7, no.1, pp.32-34 (1995) or ibid, R
ealization of a short integrated optic passive pol
arization converter on InP, IEEE.Photon.technol.Let
It is a sectional view according to t., vol.7, no.8, pp.32-34 (1995).

That is, in this structure, the InP substrate 11
With a bandgap wavelength of 1.1 μm on InGaAs
The P-waveguide layer 12, the InP side cladding layer 13, and the InP ridge layer 14 are sequentially formed to have a predetermined thickness, and the InP ridge layer 14 is partially etched to form a trapezoidal shape having a vertical wall to rotate polarization. I am trying to

[0016]

In the conventional polarization rotation element, since the coupling efficiency of the TE polarization component and the TM polarization component is very small in the structure of FIG. 10, the rotation angle θ of the linearly polarized light is increased.
Becomes smaller and the element length of the polarization rotation element becomes longer.

In the structure shown in FIG. 13 in which the slanted portion is provided in the waveguide, the angle of the slanted portion of the waveguide cannot be formed with good control, so that the manufacturing yield cannot be increased. It was Further, since the waveguide portion having the strongest field distribution is processed, the waveguide loss increases.

Since the polarization rotator shown in FIG. 14 employs wet etching in its manufacture, its controllability is very poor and it cannot be manufactured according to theory.

An object of the present invention is to provide a semiconductor polarization rotator capable of rotating polarized waves with low loss.

Another object of the present invention is the TE polarization component and the TM.
It is an object of the present invention to provide a semiconductor polarization rotator having a short element length and high coupling efficiency of polarization components.

Another object of the present invention is to provide a semiconductor polarization rotator capable of increasing the manufacturing yield.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0023]

The outline of the representative ones of the inventions disclosed in the present application will be briefly described as follows.

[0024] The (1) ridge type linear waveguide a semiconductor polarization rotation element having a semiconductor substrate, in a possible range to the pre-rotation polarized wave with respect Kisho Teijika ray waveguide portion,
A rectangular parallelepiped side wall for polarization rotation made of the same layer structure as the linear waveguide has one surface facing the side surface of the linear waveguide.
As described above, one row is provided asymmetrically with respect to the linear waveguide along both sides of the linear waveguide, and both polarization rotation side walls per unit distance in the direction along the linear waveguide have the same period. They are arranged with the existence probabilities specified by the functions based on mutually different phases.

As a concrete configuration, the polarization rotation side walls on both sides of the linear waveguide are opposed to each other and are arranged at equal pitches, and the length of each polarization rotation side wall along the linear waveguide is set. Is a length defined by a function that satisfies the existence probability, and the phase of the period of the function is such that there is a half-cycle difference between the polarization rotation side wall rows on both sides of the linear waveguide. ing. Further, linear sidewalls that linearly extend along both sides of the linear waveguide are provided on the semiconductor substrate,
Straight line sidewall and the polarization rotation for the side wall which is integrally formed, its
From one side edge of the linear sidewall as one side of the faces to a side surface of the linear waveguides projecting toward the straight waveguide
It has a comb shape .

(2) In the specific construction of the above-mentioned means (1), the lengths of the polarization rotating side walls on both sides of the linear waveguide along the linear waveguide are constant, and the polarization on both sides of the linear waveguide is constant. The pitch of the wave rotation side wall row has a length defined by a function satisfying the existence probability, and the phase of the cycle of the function is a half cycle difference between the polarization rotation side wall rows on both sides of the linear waveguide. It is configured to have.

(3) In the configurations of the means (1) and the means (2), the semiconductor polarization rotator includes a semiconductor substrate, a waveguide layer provided on the semiconductor substrate, and a waveguide layer on the semiconductor substrate. A spacer layer provided, an etching stop layer provided on the entire area of the spacer layer, and the linear waveguide and the side wall for polarization rotation or the linear waveguide and the side wall for polarization rotation provided on the etching stop layer. It is composed of a clad layer forming a side wall and a cap layer provided on the clad layer.

According to the above-mentioned means (1), since the side wall for polarization rotation is arranged close to the ridge type straight waveguide, in the straight waveguide portion facing the side wall for polarization rotation, Since the waveguide field distribution is pulled obliquely upward on the side wall for polarization rotation, the coupling effect of TE polarization and TM polarization can be increased and the polarization can be rotated.

The introduction of the periodic structure asymmetry for rotating the polarization is defined by the functions of the two polarization rotation side walls per unit distance in the direction along the straight waveguide in the same period and different phases. It is obtained by arranging with a certain existence probability, and by providing a half-cycle difference between the side walls for polarization rotation on both sides.

The function representing the period can be arbitrarily set by changing the length and spacing (pitch) of the polarization rotation side wall. Therefore, by giving an optimum periodic function to the waveguide structure, the polarization rotation can be performed more effectively.

Further, the semiconductor polarization rotating element of the present invention positionally separates a single ridge type linear waveguide for guiding light and a side wall for polarization rotation which gives structural asymmetry. As a result, it is possible to prevent an increase in propagation loss of the waveguide because it is unlikely to be affected by processing accuracy and damage during manufacturing.

Further, since the ridge type linear waveguide, the side wall for polarization rotation and the linear side wall have the same layer structure, they can be formed with high accuracy and reproducibility by the photolithography technology and the photoetching technology established together. The manufacturing yield can be improved.

(2) According to the above-mentioned means (2), the introduction of the periodic structural asymmetry for rotating the polarized wave is achieved by the length of each polarization rotation side wall on both sides of the linear waveguide along the linear waveguide. And the pitch of the side walls for polarization rotation on both sides of the linear waveguide is set to a length defined by a function that satisfies the existence probability, and a difference of half period between the side walls for polarization rotation on both sides. It is obtained by having.

The function representing the period can be arbitrarily set by changing the length and spacing (pitch) of the polarization rotation side wall. Therefore, by giving an optimum periodic function to the waveguide structure, the polarization rotation can be performed more effectively.

According to the above-mentioned means (3), in addition to the effect of the above-mentioned means (1), the height and width of the polarization rotation side wall can be formed with high accuracy.

That is, since the etching stop layer is provided on the waveguide layer via the spacer layer and the cap layer is provided on the cladding layer, the etching can be performed by wet etching. As a result, the width of the polarization rotation side wall during etching can be suppressed by the cap layer, and the etching depth can be made constant by the etching stop layer, so that the cross-section size of the polarization rotation side wall is highly accurate. Can be formed.

In addition, since the etching surface of wet etching is smoother than dry etching, the surface of the remaining etching stop layer is also smoothed and the surface of the etching stop layer is scattered to the semiconductor substrate due to light scattering. It is possible to reduce the amount of light escaped and reduce the loss.

[0038]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

In all the drawings for explaining the embodiments, parts having the same functions are designated by the same reference numerals, and the repeated description thereof will be omitted.

(Embodiment 1) FIGS. 1 to 3 are views relating to a semiconductor polarization rotator according to Embodiment 1 of the present invention.
2 is a plan view of the semiconductor polarization rotator, FIG. 2 is a partial enlarged cross-sectional view taken along the line AA of FIG. 1, and FIG. 3 is a partial enlarged cross-sectional view showing a manufacturing state of the semiconductor polarization rotator. .

As shown in FIG. 1, the semiconductor polarization rotator of the first embodiment has a ridge-type linear waveguide 40 along the center line on the upper surface of an elongated rectangular semiconductor substrate 30. In addition, the ridge-type side wall 41 for polarization rotation is the linear waveguide 4 described above.
One line is provided asymmetrically with respect to the straight waveguide 40 along both sides of 0. The polarization rotation side wall 41
Has a rectangular shape, and one side (one surface) faces the side surface of the linear waveguide 40.

Further, the polarization rotation side wall 41 is connected to and supported by a ridge-type straight side wall 42 provided along both side edges of the semiconductor substrate 30.

As will be described later, the polarization rotation side wall 41 and the straight side wall 42 are formed by an etching technique and have an integrated structure. Therefore, the polarization rotation side wall 4
1 has a shape protruding from one side edge of the linear side wall 42 toward the linear waveguide 40 at a constant interval, and has a shape like a comb. Then, the tip end surface faces the side surface of the linear waveguide 40.

As shown in FIG. 2, the polarization rotation side wall 41 has the same layer structure as the linear waveguide 40 and has a predetermined height. The height of the polarization rotation side wall 41 is the same as that of the linear waveguide 40, and is, for example, about 1.4 μm.

The polarization rotation side wall 41 is formed by the linear waveguide 4
They are opposed to each other with 0 in between, and are arranged at equal pitches (d ₁ ). For example, d ₁ is 10 μm.

The length L ₁ of the polarization rotation side wall 41 along the lengthwise direction of the linear waveguide 40 is, for example, 0.5.
It is changed from μm to 9.5 μm. The function expressing this change was L ₁ = 4.5 sin (aZ) +5. The period aZ = 100 μm. The phase of the period has a difference of a half period between the polarization rotating side wall rows on both sides of the linear waveguide 40.

The linear waveguide 40 and the polarization rotation side wall 41.
The distance c between and is a narrow distance that can rotate the polarized wave. The distance c is, for example, 1.5 μm. In order to rotate the polarized wave, the shorter the distance c is, the better. However, when the linear waveguide 40 and the polarized wave rotation side wall 41 are formed by etching, the reproduction of the formation of the groove (trench) interval between them is reproduced. It is decided by nature.

Further, the polarization rotation is performed by the polarization rotation side wall 41.
Does not occur when the distance from the linear waveguide 40 is about 5 μm. Therefore, in the first embodiment, the distance between the straight waveguide 40 and the straight sidewall 42 is selected to be 5 μm.

The introduction of the periodic structural asymmetry for rotating the polarized wave is a function of the side walls 41 for rotating both polarizations per unit distance in the direction along the straight waveguide 40, which are functions of different phases in the same period. It is obtained by arranging with a specified existence probability and by providing a half-cycle difference between the polarization rotation side wall rows on both sides.

FIG. 5 shows the length ratio of the polarization rotation side wall 41 close to the linear waveguide 40 per unit length with respect to the light propagation direction Z (see FIG. 1). The propagating light senses the presence of side walls for polarization rotation (that is, the left side wall and the right side wall) on both sides macroscopically in the form represented by the function [L1 = 4.5 sin (aZ) +5]. here,
Since the phase of the existence probability of the left and right polarization rotation side walls is shifted by 180 degrees, a macroscopic asymmetry of the waveguide structure is realized, and the TE polarization component and the TM polarization component are coupled (T
The electric field components in the x direction and the y direction cause coupling under the connection conditions at the boundary between the E polarization component and the TM polarization component). This coupling component causes a transition of the field distribution between the TE polarization component and the TM polarization component, and causes a rotation component with respect to the plane of polarization.

The function representing the period can be arbitrarily set by changing the length and spacing (pitch) of the polarization rotation side wall. Therefore, by giving an optimum periodic function to the waveguide structure, the polarization rotation can be performed more effectively.

The semiconductor polarization rotator of the first embodiment has a sectional structure as shown in FIG. That is, the semiconductor polarization rotator is formed on the upper surface of the InP substrate 30 with a band gap wavelength of 1.3 μm and an I of 0.3 μm.
nGaAsP waveguide layer 31, In having a thickness of 1.5 μm
It has a structure in which the P clad layer 32 is sequentially laminated.

Further, the InP clad layer 32 is etched into a predetermined shape, and as described above, the linear waveguide 40 and the polarization rotation side wall 41 and the linear waveguide 40 having the height of 1.4 μm and the width of 2 μm are formed. The side wall 42 is formed.

Such a semiconductor polarization rotator is manufactured by the following method.

As shown in FIG. 3, first, an InP substrate 30 having a crystal surface of (001) is prepared, and then the I
On the nP substrate 30, an InGaAsP waveguide layer 31 having a band gap wavelength of 1.3 μm and a thickness of 0.3 μm, and an InP clad layer 32 having a thickness of 1.5 μm are formed by MOCVD.
Form by the method.

Next, by the plasma CVD method, the above I
A SiO ₂ film 35 is deposited on the entire surface of the nP clad layer 32.

Next, after forming a photoresist film 36 on the SiO ₂ film 35, the photoresist film 36 is patterned by a conventional photolithography technique, and the patterned photoresist film 36 is patterned by a photoetching technique. The SiO ₂ film 35 is patterned using the as a mask for etching. SiO ₂ film 35 remaining on the InP clad layer 32
Are portions of the straight waveguide 40, the polarization rotation side wall 41, and the straight side wall 42 of FIG.

Next, the InP clad layer 32 is etched by dry etching using CH ₄ / H ₂ . Since the InP clad layer 32 has a thickness of 1.5 μm, trench etching is performed so that a thickness of about 0.1 μm remains. This is due to the etching
This is for safety (margin) in manufacturing because the nGaAsP waveguide layer 31 is not etched.

The characteristics of the element of the first embodiment will be described.

The semiconductor polarization rotator has a structure in which side walls 41 for polarization rotation are arranged asymmetrically on both sides of the linear waveguide 40. As shown in FIG. 4, as a result of arranging the polarization rotation side wall 41 close to the linear waveguide 40, the field distribution 45 of the waveguide is pulled up in the direction of the polarization rotation side wall 41, that is, diagonally upward. The wave rotation effect occurs.

FIG. 6 is a graph showing the correlation between the propagation distance Z of light and the relative optical output of each polarization of light in the semiconductor polarization rotator of the first embodiment. Incident light is TE polarized. As the Z value increases, the TE polarization decreases,
The polarization increases. TM polarization becomes maximum when Z = 450 μm.

FIG. 7 is a graph showing the correlation between the propagation distance Z of light and the insertion loss of the element in the semiconductor polarization rotating element of the first embodiment. The loss of the reference (ridge-type linear waveguide having no side wall for polarization rotation) was 6 dB. The breakdown of the loss is 5 dB as the coupling loss with the fiber, and the remaining 1 dB as the propagation loss in the waveguide.

Although the loss tends to increase a little as the light propagates, the loss increase amount is about 0.4 dB even at Z = 450 μm where complete polarization rotation from TE polarized light to TM polarized light can be obtained. , The propagation loss is 8.9 dB / c
m, which is a sufficiently low value for practical use.

(Second Embodiment) FIG. 8 shows a second embodiment of the present invention.
FIG. 3 is a plan view of the semiconductor polarization rotation element that is

The polarization rotation side walls on both sides of the linear waveguide are arranged on the basis of the existence probabilities defined by the functions of different phases in the same period, but in the second embodiment, the polarization rotation side walls are arranged. The length L ₂ along the straight waveguide 40 of 41 is a fixed length (for example, 10 μm), and the polarization rotation side wall 41 is provided.
The pitch (d ₂ ) is changed. The d ₂ is changed from 0.5 μm to 9.5 μm.
The function expressing this change is d ₂ = 4.5 sin (aZ) +5
And The period aZ = 100 μm. The phase of the period has a difference of a half period between the polarization rotating side wall rows on both sides of the linear waveguide 40. The distance between the linear waveguide 40 and the polarization rotation side wall 41 is about 1.5 μm.

The second embodiment also has the characteristics shown in the graphs of FIGS. 6 and 7.

Therefore, effective polarization rotation can be achieved.

(Third Embodiment) FIG. 9 shows a third embodiment of the present invention.
FIG. 3 is a plan view of the semiconductor polarization rotation element that is

As shown in FIG. 9, the semiconductor polarization rotator according to the third embodiment has a thickness of 0.
InG with a bandgap wavelength of 1.3 μm and a band of 3 μm
aAsP waveguide layer 31, InP spacer layer 46, InGaAsP etching stop layer 47 having a band gap wavelength of 1.3 μm and a thickness of 0.01 μm, and a thickness of 1.
The InP clad layer 32 and the InGaAs cap layer 49 having a thickness of 5 μm are sequentially laminated.

Further, the InP clad layer 32 and I
The nGaAs cap layer 49 is patterned in the same manner as in the case of the first embodiment to form the linear waveguide 40, the polarization rotation side wall 41, and the linear side wall 42.

The extending direction of the ridge type linear waveguide 40 is the (011) direction.

Such a semiconductor polarization rotator is manufactured by the following method.

First, the crystal plane of the surface becomes (001) I
After preparing the nP substrate 30, an InGaAsP waveguide layer 31 having a band gap wavelength of 1.3 μm and a thickness of 0.3 μm, an InP spacer layer 46, and
Bandgap wavelength 1.3μ with thickness of 0.01μm
m-band InGaAsP etching stop layer 47, InP clad layer 32 having a thickness of 1.5 μm, InGaA
The s cap layer 49 is formed by the MOCVD method.

Then, the above-mentioned I is formed by the plasma CVD method.
A SiO ₂ film is deposited on the entire surface of the nP clad layer 32.

Next, as in the case of the first embodiment,
After forming a photoresist film on the SiO ₂ film, with patterning the photoresist film by photolithography conventional, the SiO ₂ film photoresist film said patterned by photoetching technique as an etching mask Pattern. The SiO ₂ film is etched with C ₂ F ₂ / SF ₂ .

Next, the uppermost InGaAs cap layer 49 was etched by RIBE using Cl ₂ gas, and then the InP clad layer 32 (1.5 μm thick) was wet-etched using a mixed solution of hydrochloric acid and phosphoric acid. Etching is performed to a depth of 1.5 μm to form a ridge type linear waveguide 40, a polarization rotation side wall 41, and a linear side wall 42, respectively, as in the case of the first embodiment.

The semiconductor polarization rotator of the third embodiment has the same effects as the semiconductor polarization rotator of the first embodiment and the following effects.

(1) In on the InGaAsP waveguide layer 31
The InGaAsP etching stop layer 47 is provided via the P spacer layer 46, and the InP clad layer 32 is formed.
Since the InGaAs cap layer 49 is provided on the
nGaAs cap layer 49 and InP clad layer 32
Can be performed by wet etching. As a result, the width of the polarization rotation side wall during etching can be suppressed by the InGaAs cap layer 49, and the etching depth can be made constant by the InGaAsP etching stop layer 47. The dimensions can be formed with high precision.

(2) Since the etching surface of wet etching is smoother than dry etching, the surface of the remaining InGaAsP etching stop layer 47 is also smoothed and is caused by light scattering on the surface of etching stop layer 47. The amount of light that escapes to the semiconductor substrate is reduced and the loss can be reduced.

[0080]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) In the semiconductor polarization rotator of the present invention, since the waveguide field distribution can be raised obliquely upward due to the presence of the adjacent polarization rotation side wall, the TE polarization and the TM polarization can be obtained.
The coupling effect with polarized waves can be increased.

(2) According to the present invention, regarding the introduction of the periodic structural asymmetry for rotating the polarization, the lengths of the polarization rotation side walls on both sides of the linear waveguide in the waveguide direction are as follows.
It can be realized by changing in the same cycle and different phase, or by changing the interval (pitch) of each of the two polarization rotation side wall rows with respect to the waveguide direction in the same cycle and different phase. As a result, low loss and 450
Polarization rotation can be realized in a short section of μm, and the element length can be shortened. Further, there is an advantage that the function representing this period can be arbitrarily set by changing the length and the interval of the polarization rotation side wall. Therefore, by giving an optimum periodic function to the waveguide structure, the polarization rotation can be performed more effectively.

(3) The semiconductor polarization rotator of the present invention can be manufactured by the conventional technology for manufacturing a semiconductor polarization rotator having a ridge-type linear waveguide simply by changing the etching pattern in manufacturing the semiconductor polarization rotator. The manufacturing yield can be improved.

(4) The semiconductor polarization rotator having the etching stop layer and the cap layer can be manufactured by controlling the height of the ridge by the action of the etching stop layer, and at the same time, the width of the straight waveguide is etched by the cap layer. Since it is possible to prevent thinning, it is possible to form a ridge type linear waveguide and a polarization rotation side wall with high precision. Since the semiconductor polarization rotating element according to the present invention largely depends on the ridge shape (particularly the depth), this structure and manufacturing method are important.

(5) In the semiconductor polarization rotator of the present invention, since the waveguide of light is a ridge type straight waveguide, an increase in loss can be almost ignored. Therefore, according to the present invention, it is possible to rotate a polarized wave with low loss and to realize a semiconductor polarization rotating element having a high yield.

[Brief description of drawings]

FIG. 1 is a plan view of a semiconductor polarization rotation element that is Embodiment 1 of the present invention.

FIG. 2 is a partial enlarged cross-sectional view taken along the line AA of FIG.

FIG. 3 is a partial enlarged cross-sectional view showing a manufacturing state of the semiconductor polarization rotation element according to the first embodiment.

FIG. 4 shows a semiconductor polarization rotator according to the first embodiment,
It is a schematic diagram which shows the state where the field distribution of light was pulled up diagonally upward by the side wall for polarization rotation.

FIG. 5 is a graph showing a correlation between a sidewall existence probability per unit distance and a distance with respect to a light propagation direction.

FIG. 6 is a graph showing a correlation between relative light output and light propagation distance.

FIG. 7 is a graph showing a correlation between optical loss and light propagation distance.

FIG. 8 is a plan view of a semiconductor polarization rotation element that is Embodiment 2 of the present invention.

FIG. 9 is a partially enlarged cross-sectional view of a semiconductor polarization rotation element that is Embodiment 3 of the present invention.

FIG. 10 is a perspective view showing a conventional semiconductor polarization rotator.

11 is a schematic cross-sectional view taken along the line AA of FIG.

12 is a schematic cross-sectional view taken along the line BB of FIG.

FIG. 13 is a schematic sectional view showing an outline of another conventional semiconductor polarization rotator.

FIG. 14 is a schematic sectional view showing the outline of another conventional semiconductor polarization rotator.

[Explanation of symbols]

1 ... High surface, 2 ... Low surface, 11 ... InP substrate, 12 ... I
nGaAsP waveguide layer, 13 ... InP side cladding layer,
14 ... InP ridge layer, 30 ... InP substrate, 31 ... In
GaAsP waveguide layer, 32 ... InP clad layer, 35 ... S
iO ₂ film, 36 ... Photoresist film, 40 ... Straight waveguide, 41 ... Polarization rotating side wall, 42 ... Straight side wall, 45 ... Field distribution, 46 ... InP spacer layer, 47 ... InGaAsP
Etching stop layer, 49 ... InGaAs cap layer.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-63-147114 (JP, A) JP-A-4-241304 (JP, A) JP-A-5-82908 (JP, A) JP-A-5- 341231 (JP, A) JP-A 7-168045 (JP, A) JP-A 8-271842 (JP, A) JP-A 7-221387 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/126

Claims (5)

(57) [Claims] 1. A semiconductor polarization rotation element having a straight waveguide of the ridge type semiconductor substrate, before Kisho Teijika ray possible distance to rotate the polarization relative to waveguide section, said
A rectangular parallelepiped side wall for polarization rotation composed of the same layer structure as the linear waveguide faces one side of the side wall of the linear waveguide.
As described above, one row is provided asymmetrically with respect to the linear waveguide along both sides of the linear waveguide, and both polarization rotation side walls per unit distance in the direction along the linear waveguide are mutually in the same cycle. A semiconductor polarization rotator characterized by being arranged with a probability of existence that is defined by a function of different phases. 2. The polarization-rotating side walls on both sides of the linear waveguide face each other and are arranged at equal pitches, and the length of each of the polarization-rotating sidewalls along the linear waveguide is equal to the existence probability. The length is defined by a satisfying function, and the phase of the period of the function has a difference of a half period between the side walls for polarization rotation on both sides of the linear waveguide. 1
The semiconductor polarization rotator according to. 3. The length of each polarization rotating side wall on both sides of the linear waveguide along the linear waveguide is constant, and the pitch of the polarization rotating side wall rows on both sides of the linear waveguide is equal to the existence probability. The length is defined by a satisfying function, and the phase of the period of the function has a difference of a half period between the side walls for polarization rotation on both sides of the linear waveguide. 1. The semiconductor polarization rotation element according to 1. Wherein said straight side wall that linearly extends along both sides of the straight waveguide on the semiconductor substrate is provided, the
Straight side walls and the polarization rotation for the side wall which is integrally formed, the
A comb protruding from one side edge of the straight side wall toward the straight waveguide so that one surface faces a side surface of the straight waveguide.
The semiconductor polarization rotator according to any one of claims 1 to 3, wherein the semiconductor polarization rotator has a mold shape . 5. A semiconductor substrate, a waveguide layer provided on the semiconductor substrate, a spacer layer provided on the waveguide layer, an etching stop layer provided on the entire region of the spacer layer, and the etching stop layer. A cladding layer provided on the linear waveguide and the polarization rotation side wall or forming the linear waveguide, the polarization rotation side wall and the straight side wall, and a cap layer provided on the cladding layer. The semiconductor polarization rotator according to any one of claims 1 to 4.