JPS624682B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of an optical solid-state circuit used for optical communications and the like.

Recent optical fibers have low loss and can be used for transmission over a wide range of wavelengths. Therefore, optical wavelength division multiplexing transmission in which lights of different wavelengths are transmitted through the same fiber becomes possible. In optical multiplexing transmission, which transmits multiple optical signals with different wavelengths through optical fibers, the optical signals are split into two or more optical fibers at key points in the transmission system depending on the purpose, or vice versa. It is an essential problem to combine the lights from the above optical fibers into one fiber.

In addition, optical couplers that split and combine light of the same wavelength are not only used for monitoring purposes, but are also essential devices for two-way communication using light sources of the same wavelength.
Additionally, a multi-branch coupler is a very effective optical device for transmitting signals from one location to multiple locations. Therefore, it is expected that optical integrated circuits with such functions will have the same potential for development as semiconductor ICs.

Conventionally, in the manufacture of optical integrated circuits, attempts have been made to form waveguides by glass sputtering, etc., but these have resulted in large transmission losses or are too thin to be suitable for multi-mode transmission. In addition, light coupling is achieved by bringing two optical waveguides close to each other on the order of several thousand Å to several μm, so that the light propagating in one optical waveguide gradually moves into the other optical waveguide as it progresses. This is done by There is no known conventional coupling line with a filter.

The present invention has been made in view of the above-mentioned points, and provides an optical coupling circuit with a filter in which a dielectric multilayer film filter is arranged between two waveguides.

The present invention uses silicon (Si), quartz glass (SiO ₂ ),
A groove pattern is formed on the surface of a substrate made of quartz, sapphire (Al ₂ O ₃ ), or other material, and a glass layer that will become the cladding of the optical waveguide is deposited by CVD or the like, and the refractive index is higher than that of the glass layer. After depositing a glass layer, which will become the core of a large optical waveguide, by CVD, etc., the glass layer deposited in areas other than the part that will become the optical waveguide is removed by etching or surface polishing, and the substrate surface is made flat. Then, a glass layer serving as a cladding layer is deposited thereon to form an optical waveguide that confines light. An optical waveguide is formed on the back side in the same way as on the front side, but after forming a groove on the back side, a dielectric multilayer film filter is formed in the groove. Thereafter, an optical waveguide similar to that on the front side is formed on the back side so that the two optical waveguides are in contact with each other via the filter.

An embodiment of the optical solid-state circuit of the present invention will be described below.
A detailed explanation will be given using drawings.

FIG. 1 is a cross-sectional structural diagram of an embodiment of an optical coupling circuit with a filter according to the present invention. (a) is an example of a back-to-back type, and (b) is an example of a side-to-side type. 1 is a Si substrate whose surface is a {100} plane, which has been anisotropically etched to form grooves in a predetermined pattern. 3a is on the front side, 3b
is a core glass with a high refractive index that serves as a light waveguide formed on the back side. 2a to 2d are optical waveguides 3
It is a glass with a low refractive index that functions to confine light by wrapping it around a and 3b, and is hereinafter referred to as clath glass. 4 is a dielectric multilayer filter having wavelength selectivity.

When manufacturing such optical solid-state circuits, Si is used as a substrate, and when groove patterns are formed, a caustic alkali, such as a KOH aqueous solution, or an amine-based aqueous solution, such as a hydrazine (NH ₂ NH ₂ ) aqueous solution, is used as an etching solution. , grooves are formed on the Si surface using the dependence of etching rate on surface orientation.
When the above etching solution is used, the etching rate of Si generally exhibits anisotropy, and the etching rate of the {111} plane is lower than that of other planes. for example,
SiO ₂ of an appropriate shape for a Si substrate with {100} plane as the surface
When an etching protection film such as Si ₃ N ₄ is formed and anisotropic etching is performed, a V-groove with an opening angle of 70.53° is formed. The embodiment shown in the figure utilizes this groove as a place for forming an optical waveguide.
Further, as described above, a dielectric multilayer film filter is formed in the groove formed on the back side.

FIG. 2a is a schematic diagram showing an embodiment of the present invention in which the optical solid-state circuit and optical fiber are coupled to perform optical demultiplexing. I~ is an optical waveguide. A to C are dielectric multilayer films formed between the optical waveguides on the front side and the back side. 5 to 9 are fibers. Wavelengths λ ₁ , λ ₂ , λ ₃ , λ emitted from the fiber 8
The light wave _{No. 4} is coupled to an optical waveguide formed on the back side of the substrate. A light wave with a wavelength λ ₁ propagating through the optical waveguide has a wavelength λ ₁ formed between the optical waveguide formed on the back side and the optical waveguide formed on the front side.
The light passes through the dielectric multilayer film A that reflects light of other wavelengths, is coupled to the optical waveguide, and is emitted to the fiber 5. Similarly, a light wave with a wavelength λ ₂ propagating through an optical waveguide has a wavelength λ 2 formed between the optical waveguides.
The light of No. ₂ passes through the dielectric multilayer film B5 that reflects light of other wavelengths, is coupled to the optical waveguide, and is emitted to the fiber 6. Similarly, a light wave with a wavelength λ ₃ propagating through an optical waveguide passes through a dielectric multilayer film C formed between the optical waveguides, which transmits light with a wavelength λ ₃ and reflects light with other wavelengths, and is coupled to the optical waveguide. is,
The light is emitted to the fiber 7. The light wave of wavelength λ ₄ propagating through the optical waveguide is reflected by the dielectric multilayer films A, B, and C, and is thus emitted to the fiber 9.

Conversely, when performing optical multiplexing, as shown in Figure 2b,
By inputting a light wave with a wavelength λ ₁ into the fiber 5, a light wave with a wavelength λ ₂ into the fiber 6, a light wave with a wavelength λ ₃ into the fiber 7, and a light wave with a wavelength λ ₄ into the fiber 9, an optical waveguide is formed. Coupling is performed between the fiber 8 and the wavelength λ.
₁ to _λ4 light waves are emitted.

Note that the wavelength λ that is not coupled to the optical waveguide by the dielectric multilayer films A, B, and C formed between the optical waveguides is
₁ , λ ₂ , and λ ₃ are transmitted through the respective optical waveguides,
, respectively through optical fibers 5', 6',
7', so it can be used as a monitor.

FIG. 3 is a schematic diagram showing another embodiment in which the optical solid-state circuit and optical fiber of the present invention are coupled to perform optical demultiplexing.

Light waves of wavelengths λ ₁ and λ ₂ emitted from the fiber 10 are coupled to an optical waveguide formed on the back side of the substrate. The light wave with a wavelength λ ₁ propagating through the optical waveguide has a wavelength λ ₁ formed between the optical waveguide formed on the front side of the substrate and the optical waveguide formed on the back side.
The light passes through the dielectric multilayer film A that transmits light of other wavelengths and reflects light of other wavelengths, is coupled to an optical waveguide, and is emitted to the fiber 11. In addition, as the low refractive index glass that forms the cladding of the optical waveguide, for example, CVD
SiO ₂ glass deposited by methods such as SiO ₂ −B ₂ O ₃
Glass: Glass such as SiO ₂ doped with fluorine may be used.

As the high refractive index glass forming the core of the optical waveguide, for example, glass deposited by CVD method etc.
Low-loss glass such as doped silica glass doped with P ₂ O ₅ , GeO ₂ , B ₂ O ₃ or the like or phosphate glass can be used, but is not limited to this. The dispersed glass fine powder is precipitated on the substrate forming the optical waveguide,
This may be dried, fired, and melted to form a glass layer. As the dielectric multilayer film, a film in which thin films of SiO ₂ and TiO ₂ are deposited alternately is used, but the dielectric film is not limited to this, and the dielectric film may be made of materials such as MgF ₂ and ZnS.

When glass is used as the substrate for forming the optical waveguide, high-frequency sputtering may be used to form the optical waveguide, which does not cause a significant rise in substrate temperature.

As is clear from the above description, the optical coupling circuit with a filter according to the present invention can accurately control the coupling length and gap between two waveguides, and by controlling this, Not only can the amount of propagating light transferred into the other waveguide be changed, but there is also a dielectric multilayer filter between the gaps that has wavelength selectivity, so that it is possible to change the amount of light that propagates into the other waveguide. Light waves can be separated. Furthermore, compared to an optical demultiplexer using lenses, mirrors, etc., a much smaller solid-state circuit can be constructed. Further, by using the filter-equipped coupling circuit according to the present invention in combination with a solid-state optical circuit that performs optical multiplexing, branching, etc., there is an advantage that a compact solid-state optical circuit having various functions can be formed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional structural diagram of an optical coupling circuit with a filter according to the present invention, and FIGS. 2 and 3 are examples of coupling between an optical solid-state circuit and an optical fiber. 1: Silicon substrate, 2a to 2d: Low refractive index clad glass, 3a, 3b: High refractive index core glass serving as a light waveguide, 4: Dielectric multilayer film, ~
: Optical waveguide, A to C: Dielectric multilayer film each having different wavelength selectivity, 5 to 11: Fiber.

Claims (1)

[Claims] 1 Form grooves in a predetermined pattern on the substrate surface, cover the grooves with a glass film, deposit a glass layer with a higher refractive index than the glass film on top of the grooves to fill the grooves, and then remove excess from the substrate surface. After removing the glass layer and making the surface flat, and forming an optical waveguide by depositing a glass film with a lower refractive index than the glass deposited in the groove on the surface, the light beam formed on the surface layer is A predetermined pattern of grooves is formed to face the waveguide, and either one of the glass film surfaces of the low refractive index glass film coated on the groove bottom and groove side surfaces of the substrate of the optical waveguide formed in the surface layer is exposed. , a dielectric multilayer film was formed on the exposed low refractive index glass film surface, and then an optical waveguide was formed on the back side in contact with the optical waveguide on the front side through the dielectric multilayer film. Features an optical coupling circuit with a filter.