JPH11211925A - Optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute passive alignment with a laser chip by constituting an under clad which reduces not only a refractive index but also thickness rather than an over clad. SOLUTION: As an under clad 2, an SiO2 thin film is formed on the surface of a silicon substrate 1, for example, by thermal diffusion. The refractive index of the SiO2 thin film is about 1.46, for example, and since the difference of the refractive index from a core 3 is remarkable, it sufficiently plays the role of barrier. The core 3 is formed by applying polymer materials onto the surface of the under clad 2 with a spinner, and the core is worked into square cross section by performing photolithography or etching working. The refractive index of the polymer core 3 is about 1.54, for example, and this refractive index can be exactly controlled and regulated by adding a fluorine or benzene ring. An over clad 4 is similarly formed by applying polymer materials onto the surface of the under clad 2 and core 3 by the spinner as well. The refractive index of the over clad 4 is about 1.535 as Δ=0.3% from the core.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide, and more particularly to an optical waveguide in which a polymer optical waveguide and a semiconductor laser are integrated on the surface of a silicon substrate, in which the deviation of the optical axis in the height direction is reduced.

[0002]

2. Description of the Related Art A conventional example will be described with reference to FIG. FIG.
Is a polymer optical waveguide. In this polymer optical waveguide, it is necessary to form an under clad 2 having a thickness of about 20 μm on the surface of the silicon substrate 1, but it is difficult to control the thickness of the under clad 2 in submicron units. there were. Reference numeral 3 denotes a core for guiding light.
Reference numeral 4 denotes an over clad having a slightly lower refractive index than the core 3 and having a thickness sufficient to confine light. In general,
The refractive index of the core 3 is configured to be high, the refractive index of the over cladding 4 is slightly lower than the refractive index of the core 3, and the refractive index of the under cladding 2 is further lower than the refractive index of the over cladding 4.

[0003]

When the under clad 2 is formed by, for example, spin coating, the under clad 2 is formed as follows.
In the case of coating with a thickness of μm, it is extremely difficult to control the film thickness on a submicron basis with respect to the uniformity within a wafer surface and the uniformity between wafers. On the other hand, when the laser chip 5 is flip-chip bonded to the silicon substrate 1 and the height control is to be performed for the passive alignment with respect to the waveguide, it is essential to ensure the submicron height accuracy for the single mode waveguide. That is. From the above, it can be said that passive alignment between the waveguide and the laser chip 5 is extremely difficult. The present invention provides an optical waveguide that solves the above-mentioned problem.

[0004]

A core having a high refractive index, an over cladding having a refractive index slightly lower than the core and having a thickness sufficient to confine light, and a substrate.
An optical waveguide constituted by the under clad 2 formed on the surface and having a lower refractive index and a smaller thickness than the over clad 4 was formed.

[0005] Claim 2: In the optical waveguide according to claim 1, the core 3 constitutes an optical waveguide made of a polymer material. Claim 3: In the optical waveguide according to any one of claims 1 and 2, the over cladding 4 constitutes an optical waveguide made of a polymer. Claim 4: In the optical waveguide according to any one of claims 1 to 3, the under clad 2 is formed by forming the substrate 1 from silicon and forming the under clad 2 on the surface thereof.
An optical waveguide composed of an iO ₂ thin film was formed.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
This will be described with reference to FIG. FIG. 1 is a sectional view of an optical waveguide according to the present invention.
FIG. FIG. 1 shows a method of manufacturing an optical waveguide according to the present invention.
This will be described with reference to FIG. (Step 1) First, as the under cladding 2, silicon
SiO on the surface of substrate 1 by thermal diffusion _TwoForm a thin film.

[0007] The thermal diffusion technique of this SiO ₂ thin film is a skillful technique, and is not applicable to the formation of a film having a thickness of about 1 to 2 µm.
Thickness control with an accuracy of about 0.1 μm can be easily achieved. The refractive index of the SiO ₂ thin film is about n = 1.46. Since the refractive index difference between the SiO ₂ thin film and the core 3 is large, it plays a sufficient role as a barrier.

(Step 2) A core material 3 is formed by applying a polymer material, for example, polyimide to the surface of the under clad 2 made of a SiO ₂ thin film by using a spinner. Next, the core 3 is processed into a square cross section of about 7 × 7 μm by performing photolithography and etching.

The core 3 having such a shape and size becomes a single-mode optical waveguide for the optical wavelength bands of 1.3 μm and 1.55 μm, and has a high coupling efficiency with the optical fiber. The refractive index of the polymer core 3 is about n = 1.54, and the refractive index can be accurately controlled and adjusted by adding a fluorine or benzene ring. (Step 3) Similarly, the over cladding 4 is formed by spinning a polymer material, for example, polyimide on the surfaces of the under cladding 2 and the core 3. In this case, it is not necessary to pay particular attention to the thickness control.

The refractive index of the over cladding 4 is set to Δ = 0.3% with respect to the core, and n is set to 1.535. By the above-described method of manufacturing an optical waveguide, it is possible to easily achieve a film thickness control with an accuracy of about ± 0.1 μm in forming a film thickness of about 1 to 2 μm, and therefore, from the silicon substrate 1 surface to the center of the core 3. The height of the single mode optical waveguide can be configured to be much more precisely controlled as compared with the conventional example.

FIG. 2 is a perspective view showing an embodiment of the optical waveguide of the present invention applied to a laser chip 5. As shown in FIG. In FIG. 2, reference numeral 51 denotes a bonding pad.
The core 3 of the optical waveguide and the laser chip 5 correspond appropriately. FIG. 2 shows an application example in which the optical waveguide is applied to the laser chip 5, and this is generally set and coupled appropriately even when applied to an optical fiber.

[0012]

Be as evident from the foregoing description, according to the present invention, by forming the undercladding by SiO ₂ thin film of 1 to 2 [mu] m, the film thickness controllability of the under-cladding was remarkably improved ± 0 A tolerance of about 1 μm can be ensured, and passive alignment with the laser chip 5 can be performed.

Since the SiO ₂ thin film is used as an insulating film of the electrode of the laser chip 5 to which the optical waveguide of the present invention is applied, it is always necessary. One step is omitted, which leads to cost reduction and yield improvement. Further, in the case of forming a SiO ₂ thin film having a thickness of about 1 to 2 μm, it is possible to easily control the film thickness with an accuracy of about ± 0.1 μm. Can be configured as a single mode optical waveguide with much more precise control as compared with the conventional example.

[Brief description of the drawings]

FIG. 1 illustrates an embodiment.

FIG. 2 is a perspective view showing an application example of the embodiment of the present invention.

FIG. 3 illustrates a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Under clad 3 Core 4 Over clad 5 Laser chip 51 Bonding pad

Claims (4)

[Claims] 1. A core having a high refractive index, an overcladding having a refractive index slightly lower than that of the core and having a thickness sufficient to confine light, and a refractive index higher than that of the overcladding formed on the substrate surface. An optical waveguide comprising an under cladding having a low thickness and a small thickness. 2. The optical waveguide according to claim 1, wherein the core is made of a polymer material. 3. The optical waveguide according to claim 1, wherein the over cladding is made of a polymer. 4. The optical waveguide according to claim 1, wherein the undercladding is formed of a silicon substrate, and the undercladding is formed of a SiO ₂ thin film formed on the surface thereof. Optical waveguide.