JPS624683B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing 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 important 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. However, in order to realize an optical integrated optical circuit, it is necessary to create an optical waveguide structure that confines light in a quadratic perfect direction within a cross section.

Conventionally, in the manufacture of optical integrated circuits, attempts have been made to form guide paths by sputtering glass, etc., but these have resulted in large transmission losses or are too thin to be suitable for multi-mode transmission.

The present invention was made in view of the above-mentioned drawbacks, and it forms an optical waveguide of the same size as the core part of a low-loss optical fiber by embedding it in a groove of a substrate, thereby reducing the amount of coupling between the optical waveguides. In order to conveniently control the gap and coupling length between the optical waveguides, grooves in a predetermined pattern are formed so as to face the optical waveguides formed in the surface layer from the back side. The present invention provides a method for manufacturing an optical coupling line in which an optical waveguide is formed from the back surface side to contact an optical waveguide on the front surface side through a low refractive index glass film of the optical waveguide formed on the surface.

The present invention uses a substrate made of silicon (Si), quartz glass, crystal (SiC ₂ ), sapphire (Al ₂ O ₃ ), or other materials, and forms grooves in a predetermined pattern on the front and back surfaces of the substrate, and An optical waveguide is formed inside the optical waveguide so that the optical waveguides on the front and back sides are in partial contact with each other through a low refractive index glass film that serves as the cladding of the optical waveguide.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 sequentially shows an example of the manufacturing process of an optical coupling line using a Si substrate according to the method of the present invention.

As shown in Figure 1a, the {100} plane is the surface.
Prepare Si wafer 1. The thickness of the Si substrate is approximately 250μ
It is about m. b is a silicon oxide film formed by thermally oxidizing this Si substrate and patterned using a photoresist. Using a silicon oxide film (SiO ₂ ) 2 as a protective film, the Si substrate 1 is anisotropically formed in a KOH aqueous solution. Etching is performed to form a V-groove or trapezoidal groove with an opening angle of 70.53°. Next, as shown in c, to create an optical waveguide in the groove of the Si substrate,
A glass layer 3a (hereinafter referred to as a cladding layer) which becomes a cladding of the optical waveguide is formed. After forming grooves in the Si substrate 1, a silica glass layer 3a containing SiO ₂ to serve as a cladding layer or a dopant that lowers the refractive index is formed over the entire surface of the substrate by CVD or the like. Note that the thickness of the cladding layer 3a may be any thickness necessary to propagate light. Next, as shown in d, a core layer of the optical waveguide, which has a higher refractive index than the cladding layer 3a, is placed on the upper surface of the cladding layer 3a.
A silica glass layer 4a containing dopants such as P ₂ O ₂ , GeO ₂ and B ₂ O ₃ is deposited by CVD or the like. Glass layer 4 is hereinafter referred to as core glass layer. The deposited thickness of the core glass layer 4 is suitably 60 μm or more in the case of multi-mode use. Next, as shown in e, Si substrate 1
The 7-rad layer 3a and the core glass layer 4a deposited in the grooves are left, and the layers deposited in other parts are removed by etching or the like to flatten the surface. However, depending on the situation, it is acceptable to form irregularities on the surface. Next, as shown in f, a cladding layer 3b is deposited by CVD or the like on the substrate formed in step e, and the core glass layer 4a of the optical waveguide is wrapped around it to form an optical waveguide. Next, as shown in g or j, grooves with a predetermined pattern are formed so as to face the optical waveguide formed on the surface layer from the back surface, and grooves are formed on either the bottom or side surface of the low refractive index glass film 3a of the optical waveguide formed on the surface layer. Expose the glass membrane surface. Next, in the same manner, an optical waveguide is formed on the back surface in contact with the optical waveguide on the front surface via the low refractive index glass film 3a. In h and k, a cladding layer 3d is formed in a groove formed from the back side. i, l deposit a core glass layer 4b on the top surface of the cladding layer 3d;
Cladding layer 3d deposited in the groove of the Si substrate 1
And leave the core glass layer 4b and remove the glass layer deposited on other parts to make the surface flat, and then
A cladding layer 3e is deposited by CVD or the like to form an optical waveguide.

g to i are examples of configuring back-coupled optical coupling lines, and j to l are examples of configuring side-coupled optical coupling lines.

The optical coupling line formed in this way can be arbitrarily controlled by changing the thickness of the cladding layer (3a + 3d) depositing the gap between the two waveguides, and the amount of optical coupling can be changed. can. Furthermore, the loss of the optical waveguide is small and it is extremely effective in practice.

In addition, as the low refractive index glass forming the cladding layer of the optical waveguide, for example, SiO ₂ glass deposited by CVD method, SiO ₂ −B ₂ O ₃ glass, SiO ₂ glass doped with fluorine, etc. are used. Good too. As the high refractive index glass forming the core of the optical waveguide, for example, P ₂ O ₅ deposited by CVD method, etc.
Low-loss glasses such as doped silica glass doped with GeO ₂ , B ₂ O ₃ , etc., phosphate glass, etc. can be used, but are not limited to these. The core glass layer may be formed by precipitating the powder on the substrate and drying, firing, and melting the powder. Further, a low loss dielectric material such as ZnCl ₂ may be used. When glass is used as the substrate for forming the optical waveguide, the optical waveguide may be formed using high-frequency sputtering, which does not cause a significant rise in substrate temperature.

FIG. 2 is a schematic diagram showing an embodiment of coupling an optical solid-state circuit manufactured by the method of the present invention and an optical fiber. Figure 2a shows an example of optical multiplexing, in which the wavelengths λ emitted from optical fibers 5, 6, and 7 are respectively
The light waves of ₁ , λ ₂ , and λ ₃ are coupled to the optical waveguide, , and propagated through the optical waveguide, , and are coupled at coupling parts A, B, and C between the optical waveguide and the optical waveguide formed on the back side. occurs, and the light waves of wavelengths λ ₁ , λ ₂ , and λ ₃ are combined in the optical waveguide and coupled to the fiber 8 . Conversely, when performing optical branching, the wavelengths λ ₁ , λ ₂ , λ emitted from the fiber 8
The light waves of _{λ 3} and λ ₄ are coupled to the optical waveguide formed on the back surface and propagate through the optical waveguide, and coupling occurs at coupling portions C, B, and A between the optical waveguide and the optical waveguide formed on the front surface. A light wave with wavelength λ ₃ is C
It is coupled to an optical waveguide at a portion thereof and is emitted to a fiber 7. The light wave of wavelength λ ₂ is coupled to the optical waveguide at part B and is emitted to the fiber 6 . A light wave of wavelength λ ₁ is coupled to the optical waveguide at part A and output to fiber 5 . The light wave with wavelength λ ₄ propagates through the optical waveguide as it is and is emitted to fiber 9 . Second
Figure b is another example of photosynthesis, where the optical fiber 1
The light waves of wavelengths λ ₂ and λ ₁ emitted from the wavelengths 0 and 11 are coupled to the optical waveguides, respectively. The light wave of wavelength λ ₁ propagating through the optical waveguide formed on the back side is connected to the optical waveguide formed on the front side.
Coupling occurs at A′, and wavelengths λ ₁ , λ
_{The two} light waves are combined and emitted to the fiber 12.

Note that the wavelength λ ₁ that is not coupled at the coupling part A′
The light waves propagate through the optical waveguide as they are and are emitted to the fiber 13, which can be used as a monitor or the like.

The wavelength selection and the adjustment of the coupling amount are performed by controlling the coupling length and gap of the coupling portion between the optical waveguide formed on the front side and the optical waveguide formed on the back side.

As is clear from the above explanation, the optical circuit of the present invention is composed of optical waveguides deposited by CVD method etc., has low light attenuation, can form multiple optical waveguides at the same time, and has the ability to branch and couple light. It has the advantage that two optical solid-state circuits can be formed simultaneously.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the process of manufacturing an optical circuit according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of coupling an optical solid-state circuit manufactured in the embodiment with an optical fiber. 1: Si substrate, 2: Protective plate, 3a to 3e: Clad layer, 4a, 4b: Core layer, 5 to 13: Optical fiber, ~: Optical waveguide, A: Optical waveguide and coupling part, B: Optical waveguide and C: A coupling portion between an optical waveguide and A′: A coupling portion between an optical waveguide and an optical waveguide.

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 depositing a glass film with a lower refractive index than the glass deposited in the groove on the surface to form an optical waveguide, the optical waveguide formed on the surface layer is faced from the back side. Form grooves in a predetermined pattern so as to expose at least a part of the low refractive index glass film surface of the optical waveguide formed on the surface layer, and contact the optical waveguide on the surface side through the low refractive index glass layer. A method for manufacturing an optical coupling line, characterized in that an optical waveguide is formed on the back side.