CA1068523A - Optical film type waveguide - Google Patents
Optical film type waveguideInfo
- Publication number
- CA1068523A CA1068523A CA251,610A CA251610A CA1068523A CA 1068523 A CA1068523 A CA 1068523A CA 251610 A CA251610 A CA 251610A CA 1068523 A CA1068523 A CA 1068523A
- Authority
- CA
- Canada
- Prior art keywords
- silicon layer
- polycrystalline silicon
- refractive index
- layer
- light
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/125—Bends, branchings or intersections
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/42—Coupling light guides with opto-electronic elements
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12166—Manufacturing methods
- G02B2006/12195—Tapering
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Optical Integrated Circuits (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An optical waveguide comprising a substrate with a poly-crystalline silicon layer formed on the substrate and having a predetermined pattern and containing one or both of oxygen and nitrogen with the concentration of the atoms selected so that the refractive index in the polycrystalline silicon layer at least near its contact surface is greater than the refractive index of the substrate. In certain of the embodiments the outer surface of the polycrystalline layer is concave or convex.
An optical waveguide comprising a substrate with a poly-crystalline silicon layer formed on the substrate and having a predetermined pattern and containing one or both of oxygen and nitrogen with the concentration of the atoms selected so that the refractive index in the polycrystalline silicon layer at least near its contact surface is greater than the refractive index of the substrate. In certain of the embodiments the outer surface of the polycrystalline layer is concave or convex.
Description
10~85Z3 BACKGROUND OF THE INVENTION ~ `
Field of the Invention :: ' This invention relates in general to optical waveguides and :in more particular to an optical film waveguide suitable as -an optical integrated circuit, a laser light guide or an integrated optical circuit.
Description of the Prior Art Optical fibers have been widely used as optical trans-mission lines and studies have been made to form optical integrated circuits with optical fibers. A clad type and a focusing type are well known for arrangement~of the optical fibers. In the clad type, a core material is clad with a hollow tube formed of material having a lower refractive index than the refractive index of the core material. In the focusing type optical fibers are manu~
factured by a sintering method or a CVD (Chemical Vapor Deposition) method so that the refractive index is distributed in nearly a quadratic curve in the section of optical fibers. Optical integrated circuits have been proposed in which optical wave- `
guides are formed on or in substrates by these above-mentioned met'hods or by an ion implantation method.
Silicon dioxides or various kinds of glass materials are used for optical fibers. The refractive index of SiO2 is about 1.4 and that of the different glass materials is in the range between 1.4 to 1.6. Large variations of the refractive index cannot be obtained although the refractive index can be reduced to a certain extent by the addition of B203 or similar substances into the glass materials. Thus, the conventional optical wave-guide has the disadvantage that loss of optical transmission is very great. Also, high temperatures are required to manufacture these devices and the manufacturing processes are complicated.
Furthermore, the refractive index cannot be accurately controlled.
,-~
;85Z3 SUMMARY OF THE INVENTION
. . . _ So as to overcome the disadvantages of the prior art, the present invention provides a novel waveguide in which poly-crystalline silicon containing oxygen and/or nitrogen is utilized.
In this prior art the grain size of the polycrystalline silicon was in the range from 50 ~ to 1000 ~ but in the present invention there is no upper limit for the concentration of oxygen in the polycrystalline silicon. Oxygen may be contained in the poly-crystalline silicon at the same concentration as in the silicon 10 dioxide. Various shapes of the polycrystalline layer are also -proposed in the invention wherein the edges may be concave or convex, for example.
The present invention provides:
an optical waveguide comprising a substrate and a polycrystalline silicon layer formed on said substrate with a pre-determined pattern, and containing atoms selected from the group consisting of oxygen and nitrogen, the concentration of said atoms in said polycrystalline silicon layer being varied in the direction of thickness of said polycrystalline silicon layer.
Other objects, features and advantages of the invention will be readily apparent from the following description of cextain preferred embodiments thereof taken in conjunction with the ac-companying drawings although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the ~ SZ3 disclosure and in which BRIEF DESCRIPIION OF TIlE DRAWINGS
Figure 1 is a perspective view of a partially cutaway optical waveguide;
Figure 2 is a plot of refractive index versus oxygen content and N20/SiH4;
Figure 3 is a graph showing the transmissivity percentage versus wave length;
Figure 4 is a plot of oxygen content and refractive index relative to the height or thickness; :
Figure 5 is a sectional view through an optical waveguide;
Figure 6 is a plot of oxygen content and refractive index -as a function of thickness or height;
Figure 7A is a top plan view of a further embodiment of the invention;
Figure 7B is a sectional view taken on line VIIB-VIIB in Figure 7A;
Figure 8 illustrates a modification of the invention;
Figure 9 illustrates a further modification of the invention;
Figure 10A is a top view of another embodiment of the invention; and Figure 10B iS a sectional view taken on line XB-~3 from Figure 10A.
` 1068SZ3 DESCRIPIION OF THE PREFER~ED EMBODIMENTS
An optical waveguide according to one embodiment of this invention will be described with reference to Figure 1 and to Figure 3.
In Figure 1, a part of an optical waveguide is shown. A
polycrystalline silicon layer 2 is formed on a selected surface of a SiO2 layer 1 which is the uppermost layer in a substrate. The SiO2 layer 1 is formed, for example, by thermal oxidation of a silicon substrate.
In the formation of the polycrystalline silicon layer 2, the silicon substrate including the top layer of SiO2 layer 1 is heated to a tempera-ture range between 600 to 650C in a reaction furnace, while mono silane SiH4, dinitrogen mono oxide N2O and carrier gas are fed into the reaction furnace at predetermined flow rates. SiH4 and N20 thermally decompose on the top SiO2 layer 1 of the heated silicon substrate and a polycrystalline silicon layer 2 is formed on the SiO2 layer 1. The polycrystalline silicon layer 2 may be formed by other CVD methods.
The concentration of oxygen in the polycrystalline silicon layer 2 as well as the refractive index of the polycrystalline silicon layer varies with the gas flow ratio of N2O/SiH4. Figure 2 shows the relationships among the gas flow ratio of N2O/SiH4, the concentration of oxygen (oxygen content), and the refractive index.
In the embodiment shown on Figure 1, the refractive index of the SiO2 layer 1 is about 1. 4, and the gas flow ratio of N2O/SiH4 is selected so that the oxygen content of the polycrystalline silicon layer 2 is 30 wt~, so that the refracti~e index of the polycrystalline silicon layer 2 is about 2.1.- The lower surface of the polycrystalline silicon layer 2 rnakes contact with the upper surface of the SiO2 layer 1 having a refractive index of 1. 4, and the upper surface of the polycrystalline .
.
.
, ~ ~068523 silicon layer 2 makes contact with air having a refractive index of 1.
A light emitting diode or laser (not shown) is coupled to a light inlet (not shown) of the polycrystalline silicon layer 2. Light from the light emitting diode or laser is radiated into the polycrystalline silicon layer
Field of the Invention :: ' This invention relates in general to optical waveguides and :in more particular to an optical film waveguide suitable as -an optical integrated circuit, a laser light guide or an integrated optical circuit.
Description of the Prior Art Optical fibers have been widely used as optical trans-mission lines and studies have been made to form optical integrated circuits with optical fibers. A clad type and a focusing type are well known for arrangement~of the optical fibers. In the clad type, a core material is clad with a hollow tube formed of material having a lower refractive index than the refractive index of the core material. In the focusing type optical fibers are manu~
factured by a sintering method or a CVD (Chemical Vapor Deposition) method so that the refractive index is distributed in nearly a quadratic curve in the section of optical fibers. Optical integrated circuits have been proposed in which optical wave- `
guides are formed on or in substrates by these above-mentioned met'hods or by an ion implantation method.
Silicon dioxides or various kinds of glass materials are used for optical fibers. The refractive index of SiO2 is about 1.4 and that of the different glass materials is in the range between 1.4 to 1.6. Large variations of the refractive index cannot be obtained although the refractive index can be reduced to a certain extent by the addition of B203 or similar substances into the glass materials. Thus, the conventional optical wave-guide has the disadvantage that loss of optical transmission is very great. Also, high temperatures are required to manufacture these devices and the manufacturing processes are complicated.
Furthermore, the refractive index cannot be accurately controlled.
,-~
;85Z3 SUMMARY OF THE INVENTION
. . . _ So as to overcome the disadvantages of the prior art, the present invention provides a novel waveguide in which poly-crystalline silicon containing oxygen and/or nitrogen is utilized.
In this prior art the grain size of the polycrystalline silicon was in the range from 50 ~ to 1000 ~ but in the present invention there is no upper limit for the concentration of oxygen in the polycrystalline silicon. Oxygen may be contained in the poly-crystalline silicon at the same concentration as in the silicon 10 dioxide. Various shapes of the polycrystalline layer are also -proposed in the invention wherein the edges may be concave or convex, for example.
The present invention provides:
an optical waveguide comprising a substrate and a polycrystalline silicon layer formed on said substrate with a pre-determined pattern, and containing atoms selected from the group consisting of oxygen and nitrogen, the concentration of said atoms in said polycrystalline silicon layer being varied in the direction of thickness of said polycrystalline silicon layer.
Other objects, features and advantages of the invention will be readily apparent from the following description of cextain preferred embodiments thereof taken in conjunction with the ac-companying drawings although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the ~ SZ3 disclosure and in which BRIEF DESCRIPIION OF TIlE DRAWINGS
Figure 1 is a perspective view of a partially cutaway optical waveguide;
Figure 2 is a plot of refractive index versus oxygen content and N20/SiH4;
Figure 3 is a graph showing the transmissivity percentage versus wave length;
Figure 4 is a plot of oxygen content and refractive index relative to the height or thickness; :
Figure 5 is a sectional view through an optical waveguide;
Figure 6 is a plot of oxygen content and refractive index -as a function of thickness or height;
Figure 7A is a top plan view of a further embodiment of the invention;
Figure 7B is a sectional view taken on line VIIB-VIIB in Figure 7A;
Figure 8 illustrates a modification of the invention;
Figure 9 illustrates a further modification of the invention;
Figure 10A is a top view of another embodiment of the invention; and Figure 10B iS a sectional view taken on line XB-~3 from Figure 10A.
` 1068SZ3 DESCRIPIION OF THE PREFER~ED EMBODIMENTS
An optical waveguide according to one embodiment of this invention will be described with reference to Figure 1 and to Figure 3.
In Figure 1, a part of an optical waveguide is shown. A
polycrystalline silicon layer 2 is formed on a selected surface of a SiO2 layer 1 which is the uppermost layer in a substrate. The SiO2 layer 1 is formed, for example, by thermal oxidation of a silicon substrate.
In the formation of the polycrystalline silicon layer 2, the silicon substrate including the top layer of SiO2 layer 1 is heated to a tempera-ture range between 600 to 650C in a reaction furnace, while mono silane SiH4, dinitrogen mono oxide N2O and carrier gas are fed into the reaction furnace at predetermined flow rates. SiH4 and N20 thermally decompose on the top SiO2 layer 1 of the heated silicon substrate and a polycrystalline silicon layer 2 is formed on the SiO2 layer 1. The polycrystalline silicon layer 2 may be formed by other CVD methods.
The concentration of oxygen in the polycrystalline silicon layer 2 as well as the refractive index of the polycrystalline silicon layer varies with the gas flow ratio of N2O/SiH4. Figure 2 shows the relationships among the gas flow ratio of N2O/SiH4, the concentration of oxygen (oxygen content), and the refractive index.
In the embodiment shown on Figure 1, the refractive index of the SiO2 layer 1 is about 1. 4, and the gas flow ratio of N2O/SiH4 is selected so that the oxygen content of the polycrystalline silicon layer 2 is 30 wt~, so that the refracti~e index of the polycrystalline silicon layer 2 is about 2.1.- The lower surface of the polycrystalline silicon layer 2 rnakes contact with the upper surface of the SiO2 layer 1 having a refractive index of 1. 4, and the upper surface of the polycrystalline .
.
.
, ~ ~068523 silicon layer 2 makes contact with air having a refractive index of 1.
A light emitting diode or laser (not shown) is coupled to a light inlet (not shown) of the polycrystalline silicon layer 2. Light from the light emitting diode or laser is radiated into the polycrystalline silicon layer
2 through the light inlet. The light is totally reflected by the contact surfaces between the polycrystalline silicon layer 2 and the SiO2 layer 1, and between the polycrystalline silicon layer 2 and air because the refractive index of the polycrystalline layer 2 is greater than the refractive indexes of the SiO2 layer l and air. The light is totally reflected and transmitted to a light outlet (not shown) of the polycrystalline silicon layer 2. Thus, an optical waveguide is formed. ~ photo-coupler may be formed by coupling a photo-diode to the light outlet of the polycrystalline silicon layer 2.
When the polycrystalline silicon layer 2 is formed on a layer of material other than SiO2, the oxygen content of the polycrystalline silicon layer 2 is controlled so that the refractive index of the poly-crystall~ne silicon layer 2 at least near the contact surface with the layer of the other material is larger than the refractive index of the layer o~ the other material. With such control, the above-described total reflection can be obtained.
As shown in Figure 3, the light transmissivity of the poly-crystalline silicon layer 2 varies with the oxygen content of the poly-crystalline silicon layer 2. As apparent from Figure 2 and Figure 3, light of shorter wave length cannot always be used for the whole range of refractive indexes from l. 4 to 4. lIowever, even light of shorter wave leng~h can be used for the range of refractive indexes from 1.4 to 2. 2. Moreover, the polycrystalline silicon layer has the advantage that ~Ot;85Z3 it can be formed at relatively low temperat-lres, according to the CVD
method.
According to this invention, as shown on Figure 4, the refractive index can be varied in the thickness direction of the poly-crystalline silicon layer 2. In such a case, the gas flow ratio of N20/SiH4 is varied during the formation of the polycrystalline silicon layer 2 to obtain the gradient oxygen content, and thus, the gradient refractive index. In Figure 4, the solid curve shows the variation of the oxygen content, the chain line "n" the variation of the refractive index, and x represents the height or thickness from the contact sur-face between the polycrystalline silicon layer 2 and the SiO2 layer 1.
Figure 5 is a sectional view of a part of an optical wave-guide according to a further embodiment of this invention. In this embodiment, a polycrystalline silicon layer 4 having a gradient oxygen content, and a gradient refractive index n, as shown in Figure 6, is formed on a silicon substrate 3. The refractive index of the silicon substrate 3 is relatively as large as layer 4. However, the refractive index of the polycrystalline silicon layer 4 as a light propagating body decreases from its center axis towards both its contact surfaces.
Accordingly, the light advancing in that body will be confined within the central portion of the light propagating body.
Since the oxygen content varies in the thickness direction of the polycrystalline silicon layer 4 in such a manner as shown in Figure 6, the property of the central portion of the polycrystalline silicon layer 4 is nearer to that of a pure polycrystalline silicon layer, while the property of the upper and lower portions of the polycrystalline silicon layer 4 is nearer to that of a SiO2 layer. Accordingly, when ;8SZ3 the polycrystalline silicon layer 4 is etched to form a predetermined pattern of the polycrystalline silicon by a mixed etching solution of HF
and NH4 which is an etchant for SiO2 in a conventional photo-process, the side surfaces of the pattern become convex, since the etching rate for SiO2 is higher than that for pure polycrystalline silicon.
Figure 7A and Figure 7B show an optical directional coupler according to a further embodiment of this invention. Polycrystalline silicon layers 4a and 4b formed as patterns are formed by the etching operation of the polycrystalline silicon layer 4 shown in Figure 5. For the above-described reason, the side surfaces of the polycrystalline silicon layers 4a and 4b are convex, and they function as convex lenses.
Accordingly, the polycrystalline silicon layer 4a can be optically and partially coupled with the polycrystalline silicon layer 4b in such a manner when a radius of the convex surface and the distance between the polycrystalline silicon layers 4a and 4b are suitably selected.
When the polycrystall~ne silicon layer 4 of Figure 5 is etched to form a predetermined pattern of the polycrystalline silicon by another mixed etching solution of HF, HNO3 and CH3COOH, which is an etchant for silicon the side surfaces of the pattern become concave, since the etching rate for SiO2 is lower than that for pure polycrystalline silicon.
Figure 8 shows an optical waveguide according to a further embodiment of this invention, in which a concave side surface is formed in the polycrystalline silicon layer 4 by the above-described method.
A semiconductor laser chip 5 is arranged adjacent to the polycrystalline silicon layer 4. The optical waveguide comprising the substrate 3 and the polycrystalline silicon layer 4 formed on the substrate 3, and the -10~85Z3 semiconductor laser chip 5 are combined with a heat sink 6. Light from the laser chip 5 can be positively transmitted through the poly-crystalline silicon layer 4. Generally, light is radiated in a wide angle from the semiconductor laser chip 5. A large quantity of light is re-flected by the surface of the light inlet of a conventional waveguide when the light is transmitted into the waveguide and it is clifficult to guide all the light into the light inlet in the conventional optical waveguide.
However, since the light inlet is concave in the waveguide of Figure 8, the light from the laser chip 5 will be effectively incident on the light inlet of the waveguide without total reflection at the surface of the light inlet.
In the conventional optical waveguide, it is undesirable to attach the semiconductor laser chip on the central portion of the heat sink having a large area, since the light from the semiconductor laser chip is reflected by the surface of the heat sink. However, according to the embodiment of Figure 8, the semiconductor laser chip 5 can be attached on the central portion of the heat sink without the possibility that the light will be reflec~ed by the surface of the heat sink.
Accordingly, the optical waveguide according to this invention has very desirable heat dissipation characteristics.
Figure 9 shows an optical waveguide according to a further embodiment of this invention. In this embodiment, the light inlet portion of the polycrystalline silicon layer 4 is shaped to be triangular or fan shaped in form. By such an arrangement, the transmission efficiency of the light can be improved. The inlet surface may be flat.
Figure lOA and Figure lOB show an optical waveguide according to a still further embodiment of this invention. In this lO~i~SZ3 embodiment, an opening is made in the silicon substrate 3 and the polycrystalline silicon layer 4 is formed on the silicon substrate 3 by the conventional etching method. At the opening, the semiconductor laser chip 5 is fixed onto the silicon substrate 3. The depth of the opening is nearly equal to the level of the light-emitting portion of the semiconductor laser chip 5. The light inlet portion of the polycrystalline silicon layer 4 surrounds the semiconductor laser chip 5. The heat from the laser chip S is transmitted through the silicon substrate 3 to the heat sink 6. By such an arrangement, the transmission efficiency of the light can be further improved more than in the embodiment of Figure 9. The thermal conductivity of the silicon substrate 3 is higher than that of the material (III-V groups chemical compound) of the laser chip 5, and the area of the silicon substrate is relatively large. Thus, this embodiment has very advantageous heat dissipation characteristics.
Although the use of a polycrystalline silicon layer containing oxygen has been described in the above embodiments, a polycrystalline silicon layer containing nitrogen may be also used. The refractive index of the polycrystalline silicon layer can be varied by changing the nitrogen content. At a nitrogen content of zero, the refractive inde~ is 4. It can be varied from 4 to 2.0 by increasing the nitrogen content.
Accordingly, a polycrystalline silicon layer containing nitrogen can be used for all of the above embodiments, instead of a polycrystalline silicon layer containing oxygen. Moreover, a polycrystalline silicon layer containing a mixture of both oxygen and nitrogen may be used for the above embodiments.
In the formation of the polycrystalline silicon layer containing nitrogen, the above described CVD method can be used, and N~13 is fed into the reaction furnace, instead of N20. The refractive index can be controlled by varying the flow rate of NH3.
The polycrystalline silicon layer has a good passivation effect on a semiconductor device. Also, very little stress due to thermal expansion of the polycrystalline silicon layer is imposed on the substra~e. Accordingly, the polycrystalline silicon layer formed on a normal integrated circuit can be used both as a passivation layer and as an optical waveguide.
When the polycrystalline silicon layer is formed on the silicon substrate in the above embodiments, the oxygen content of the polycrystalline silicon layer varies in the thickness direction as shown by "x" in ~igure 6. However, when the upper surface of the poly-crystalline silicon layer contacts air, the refractive index near the upper surface is not reduced so much as shown in Figure 6. When a layer of material having a lower refractive index is formed on the polycrystalline silicon layer, the thickness of the polycrystalline silicon layer can be reduced.
Although the invention has been described with respect to preferred embodiments, it is not to be so limited, as changes and modifications may be made which are within the full intended scope as defined by the appended claims.
: ~ . . . . .
When the polycrystalline silicon layer 2 is formed on a layer of material other than SiO2, the oxygen content of the polycrystalline silicon layer 2 is controlled so that the refractive index of the poly-crystall~ne silicon layer 2 at least near the contact surface with the layer of the other material is larger than the refractive index of the layer o~ the other material. With such control, the above-described total reflection can be obtained.
As shown in Figure 3, the light transmissivity of the poly-crystalline silicon layer 2 varies with the oxygen content of the poly-crystalline silicon layer 2. As apparent from Figure 2 and Figure 3, light of shorter wave length cannot always be used for the whole range of refractive indexes from l. 4 to 4. lIowever, even light of shorter wave leng~h can be used for the range of refractive indexes from 1.4 to 2. 2. Moreover, the polycrystalline silicon layer has the advantage that ~Ot;85Z3 it can be formed at relatively low temperat-lres, according to the CVD
method.
According to this invention, as shown on Figure 4, the refractive index can be varied in the thickness direction of the poly-crystalline silicon layer 2. In such a case, the gas flow ratio of N20/SiH4 is varied during the formation of the polycrystalline silicon layer 2 to obtain the gradient oxygen content, and thus, the gradient refractive index. In Figure 4, the solid curve shows the variation of the oxygen content, the chain line "n" the variation of the refractive index, and x represents the height or thickness from the contact sur-face between the polycrystalline silicon layer 2 and the SiO2 layer 1.
Figure 5 is a sectional view of a part of an optical wave-guide according to a further embodiment of this invention. In this embodiment, a polycrystalline silicon layer 4 having a gradient oxygen content, and a gradient refractive index n, as shown in Figure 6, is formed on a silicon substrate 3. The refractive index of the silicon substrate 3 is relatively as large as layer 4. However, the refractive index of the polycrystalline silicon layer 4 as a light propagating body decreases from its center axis towards both its contact surfaces.
Accordingly, the light advancing in that body will be confined within the central portion of the light propagating body.
Since the oxygen content varies in the thickness direction of the polycrystalline silicon layer 4 in such a manner as shown in Figure 6, the property of the central portion of the polycrystalline silicon layer 4 is nearer to that of a pure polycrystalline silicon layer, while the property of the upper and lower portions of the polycrystalline silicon layer 4 is nearer to that of a SiO2 layer. Accordingly, when ;8SZ3 the polycrystalline silicon layer 4 is etched to form a predetermined pattern of the polycrystalline silicon by a mixed etching solution of HF
and NH4 which is an etchant for SiO2 in a conventional photo-process, the side surfaces of the pattern become convex, since the etching rate for SiO2 is higher than that for pure polycrystalline silicon.
Figure 7A and Figure 7B show an optical directional coupler according to a further embodiment of this invention. Polycrystalline silicon layers 4a and 4b formed as patterns are formed by the etching operation of the polycrystalline silicon layer 4 shown in Figure 5. For the above-described reason, the side surfaces of the polycrystalline silicon layers 4a and 4b are convex, and they function as convex lenses.
Accordingly, the polycrystalline silicon layer 4a can be optically and partially coupled with the polycrystalline silicon layer 4b in such a manner when a radius of the convex surface and the distance between the polycrystalline silicon layers 4a and 4b are suitably selected.
When the polycrystall~ne silicon layer 4 of Figure 5 is etched to form a predetermined pattern of the polycrystalline silicon by another mixed etching solution of HF, HNO3 and CH3COOH, which is an etchant for silicon the side surfaces of the pattern become concave, since the etching rate for SiO2 is lower than that for pure polycrystalline silicon.
Figure 8 shows an optical waveguide according to a further embodiment of this invention, in which a concave side surface is formed in the polycrystalline silicon layer 4 by the above-described method.
A semiconductor laser chip 5 is arranged adjacent to the polycrystalline silicon layer 4. The optical waveguide comprising the substrate 3 and the polycrystalline silicon layer 4 formed on the substrate 3, and the -10~85Z3 semiconductor laser chip 5 are combined with a heat sink 6. Light from the laser chip 5 can be positively transmitted through the poly-crystalline silicon layer 4. Generally, light is radiated in a wide angle from the semiconductor laser chip 5. A large quantity of light is re-flected by the surface of the light inlet of a conventional waveguide when the light is transmitted into the waveguide and it is clifficult to guide all the light into the light inlet in the conventional optical waveguide.
However, since the light inlet is concave in the waveguide of Figure 8, the light from the laser chip 5 will be effectively incident on the light inlet of the waveguide without total reflection at the surface of the light inlet.
In the conventional optical waveguide, it is undesirable to attach the semiconductor laser chip on the central portion of the heat sink having a large area, since the light from the semiconductor laser chip is reflected by the surface of the heat sink. However, according to the embodiment of Figure 8, the semiconductor laser chip 5 can be attached on the central portion of the heat sink without the possibility that the light will be reflec~ed by the surface of the heat sink.
Accordingly, the optical waveguide according to this invention has very desirable heat dissipation characteristics.
Figure 9 shows an optical waveguide according to a further embodiment of this invention. In this embodiment, the light inlet portion of the polycrystalline silicon layer 4 is shaped to be triangular or fan shaped in form. By such an arrangement, the transmission efficiency of the light can be improved. The inlet surface may be flat.
Figure lOA and Figure lOB show an optical waveguide according to a still further embodiment of this invention. In this lO~i~SZ3 embodiment, an opening is made in the silicon substrate 3 and the polycrystalline silicon layer 4 is formed on the silicon substrate 3 by the conventional etching method. At the opening, the semiconductor laser chip 5 is fixed onto the silicon substrate 3. The depth of the opening is nearly equal to the level of the light-emitting portion of the semiconductor laser chip 5. The light inlet portion of the polycrystalline silicon layer 4 surrounds the semiconductor laser chip 5. The heat from the laser chip S is transmitted through the silicon substrate 3 to the heat sink 6. By such an arrangement, the transmission efficiency of the light can be further improved more than in the embodiment of Figure 9. The thermal conductivity of the silicon substrate 3 is higher than that of the material (III-V groups chemical compound) of the laser chip 5, and the area of the silicon substrate is relatively large. Thus, this embodiment has very advantageous heat dissipation characteristics.
Although the use of a polycrystalline silicon layer containing oxygen has been described in the above embodiments, a polycrystalline silicon layer containing nitrogen may be also used. The refractive index of the polycrystalline silicon layer can be varied by changing the nitrogen content. At a nitrogen content of zero, the refractive inde~ is 4. It can be varied from 4 to 2.0 by increasing the nitrogen content.
Accordingly, a polycrystalline silicon layer containing nitrogen can be used for all of the above embodiments, instead of a polycrystalline silicon layer containing oxygen. Moreover, a polycrystalline silicon layer containing a mixture of both oxygen and nitrogen may be used for the above embodiments.
In the formation of the polycrystalline silicon layer containing nitrogen, the above described CVD method can be used, and N~13 is fed into the reaction furnace, instead of N20. The refractive index can be controlled by varying the flow rate of NH3.
The polycrystalline silicon layer has a good passivation effect on a semiconductor device. Also, very little stress due to thermal expansion of the polycrystalline silicon layer is imposed on the substra~e. Accordingly, the polycrystalline silicon layer formed on a normal integrated circuit can be used both as a passivation layer and as an optical waveguide.
When the polycrystalline silicon layer is formed on the silicon substrate in the above embodiments, the oxygen content of the polycrystalline silicon layer varies in the thickness direction as shown by "x" in ~igure 6. However, when the upper surface of the poly-crystalline silicon layer contacts air, the refractive index near the upper surface is not reduced so much as shown in Figure 6. When a layer of material having a lower refractive index is formed on the polycrystalline silicon layer, the thickness of the polycrystalline silicon layer can be reduced.
Although the invention has been described with respect to preferred embodiments, it is not to be so limited, as changes and modifications may be made which are within the full intended scope as defined by the appended claims.
: ~ . . . . .
Claims (4)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An optical waveguide comprising a substrate and a polycrystalline silicon layer formed on said substrate with a predetermined pattern, and containing atoms selected from the group consisting of oxygen and nitrogen, the concentration of said atoms in said polycrystalline silicon layer being varied in the direction of thickness of said polycrystalline silicon layer.
2. An optical waveguide according to Claim 1, in which a side surface of said polycrystalline silicon layer is convex.
3. An optical waveguide according to Claim 1, in which a side surface of said polycrystalline silicon layer is concave.
4. An optical waveguide according to Claim 1, wherein said polycrystalline silicon layer contains varying concentrations of said atoms whereby the concentration of said atoms in said silicon layer increases from the center axis towards the periphery thereof.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5361575A JPS51129248A (en) | 1975-05-02 | 1975-05-02 | Optical waveguide |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1068523A true CA1068523A (en) | 1979-12-25 |
Family
ID=12947796
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA251,610A Expired CA1068523A (en) | 1975-05-02 | 1976-04-30 | Optical film type waveguide |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS51129248A (en) |
| CA (1) | CA1068523A (en) |
| DE (1) | DE2619269A1 (en) |
| GB (1) | GB1532469A (en) |
| NL (1) | NL7604644A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57198410A (en) * | 1981-06-01 | 1982-12-06 | Nippon Sheet Glass Co Ltd | Optical plane circuit equipped with optical coupler |
| JPS59143109A (en) * | 1983-02-04 | 1984-08-16 | Sumitomo Electric Ind Ltd | Optical integrated circuit |
| DE3438949C2 (en) * | 1983-10-25 | 1994-03-10 | Canon Kk | Printing device |
| JPS6111708A (en) * | 1984-06-28 | 1986-01-20 | Nippon Telegr & Teleph Corp <Ntt> | Channel optical waveguide with end face lens and its production |
| CN108957901A (en) * | 2018-08-08 | 2018-12-07 | 中国科学院福建物质结构研究所 | Polarized crystal waveguide device and its preparation method and application |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2205728C3 (en) * | 1972-02-08 | 1979-01-04 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Optical component consisting of a multilayer semiconductor body |
-
1975
- 1975-05-02 JP JP5361575A patent/JPS51129248A/en active Pending
-
1976
- 1976-04-26 GB GB1688276A patent/GB1532469A/en not_active Expired
- 1976-04-29 NL NL7604644A patent/NL7604644A/en not_active Application Discontinuation
- 1976-04-30 CA CA251,610A patent/CA1068523A/en not_active Expired
- 1976-04-30 DE DE19762619269 patent/DE2619269A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| NL7604644A (en) | 1976-11-04 |
| JPS51129248A (en) | 1976-11-10 |
| GB1532469A (en) | 1978-11-15 |
| DE2619269A1 (en) | 1976-11-11 |
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