JPS59101605A - Optical waveguide - Google Patents

Abstract

PURPOSE:To obtain an optical waveguide by which the coupling efficiency of an optical fiber and an optical integrated circuit is good and a transmission loss by a bend, etc. of the waveguide is small, by providing a groove whose section is circular on a substrate, and packing this groove with an optical material whose refractive index is higher than that of the substrate. CONSTITUTION:When a tapered mask 3' is formed on a desired substrate 1 and etching is executed by making an argon ion incident vertically from the upper part, the substrate 1 and the mask 3' are etched by non-selectivity of etching. In this case, as for the end part of the mask 3', its dynamical strength is inferior to other part, therefore, it is etched quickly. Usually a substance whose etching rate is sufficiently smaller than the substrate 1 is used for the mask 3', and when etching is executed within the time when an interval L3 of the mask 3' is not varied, it is possible to dig a groove whose depth is D and whose section shape is semi-circular. In this case, thickness L1 of a non-tapered part of the mask 3' is reduced to thickness L1' by etching. In this regard, this semi- circular section structure can be changed by varying a taper angle psi of the mask 3' and a dispersion angle theta of an ion beam.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical waveguide necessary for an optical integrated circuit used in the fields of optical communication and optical information processing. In particular, it adds +y5 to optical waveguides that have good coupling efficiency with optical fibers and transmission efficiency.

[Prior art]

In recent years, the practical application of optical communications has been rapidly progressing, and research and development efforts are being actively carried out to make optical components smaller and more reliable. Optical waveguides are the main components of optical integrated circuits.
It is manufactured using a vapor phase growth method, a liquid phase growth method, a diffusion method, an ion implantation method, a chemical etching method, an ion beam etching method, etc. However, with these methods, it is difficult to control the cross-sectional shape of the optical waveguide. An example of the conventional method is shown in the first example.
This will be explained using figures.

FIG. 1 shows a method of manufacturing an optical waveguide by ion beam etching. As shown in FIG. 1(a), a thin film 2 having a higher refractive index (e.g. 0.5 μm thick GaAs made by MOCVD with high resistance) is deposited on a substrate 1 (e.g. GaAS; refractive index = 3.44). A resist pattern 3 (for example, AZ1350J with a thickness of 1 μm) is formed thereon. When Ar (argon) ions are perpendicularly injected from above and etched for a predetermined period of time, a pattern as shown in FIG. 3(b) is formed. When the resist shown in the f(b) diagram is removed, a desired waveguide 4 is formed on the substrate 1.

In the conventional method, the cross-sectional shape of the etching mask was rectangular or trapezoidal, so the cross-sectional shape of the formed optical waveguide was rectangular. For this reason, it has not been possible to form an optical waveguide having a circular cross-sectional shape with small coupling loss with the optical fiber and low loss due to bending of the guide path.

[Purpose of the invention]

The object of the present invention has been made to solve the above-mentioned problems, and the present invention has an optical fiber and an integrated optical circuit. The purpose is to provide a circular chick and fill the t6 with an optical material having a better refractive index than the substrate.

Since the present invention has the above configuration, the coupling efficiency and transmission efficiency of light with the optical fiber are extremely good.

In the present invention, semicircular wave paths are formed on each of the two substrates in advance, and then they are joined together to form a circular shape easily.

In addition, in the present invention, the term "circular" in cross section does not necessarily mean only a perfect circle, but also includes semicircular quarter circle, crescent shape, oval shape, inverted shape,
Alternatively, it also includes combinations of these and other shapes with gold.

Although the ion beam etching method will be explained here, it is not the essential method. The ion beam etching method is a method in which a chemically inert gas such as Ar is turned into plasma, which is accelerated with a high voltage and made incident on a substrate, thereby physically etching the surface of the substrate. The rate of etching varies depending on the material and, in the case of a single crystal, depending on the orientation of the fine product.

Even if the ion beam that is incident on the substrate surface has sufficient parallelism, it will still fall at a small angle lol! It has l. Therefore, if a taper is added to the cross-sectional shape of the etching mask, some of the inclined ion beams will be incident on the inside of the taper and will etch the substrate. However, since the amount of the ion beam incident on the inside of the taper is smaller than the amount of the ion beam incident on the inside of the taper, the etch weight on the portion shaded by the taper is small. This will be evaluated using FIG. 2 and explained in 111I. 2(a) and 2(b) schematically show some steps of the manufacturing method using the present invention, in which a tapered mask 3' is used instead of the resist 3 in FIG.
The schematic shape of the lifting platform is shown. θ and ψ in FIG. 2(a) are the taper angle of the mask 3' and the dispersion angle of the ion beam, respectively. A tapered mask 3' is formed on a desired substrate 1. Here, the thickness of the tapered part is L2, the thickness of the non-tapered part is Ll,
Let the interval between the masks be L3. When etching is performed by vertically injecting argon ions from above, the substrate 1 and mask 3' are etched due to the non-selectivity of etching.

At this time, the end portions of the mask 3' are etched quickly because their mechanical strength is inferior to other portions.

Generally, if a material with a sufficiently lower etching rate than the substrate 1 is used for the mask 3' and etching is performed within a time period in which the spacing L3 of the mask 3' does not change, the depth D shown in FIG. 2(b) is obtained. You can dig a monument with a semicircular cross section.

At this time, the thickness Ll of the non-tapered part of the mask 3' in FIG. 2(a) is changed by etching so that the thickness shown in FIG.
I'm hungry for l/. Note that this semicircular cross-sectional shape can be increased by changing the taper angle ψ of the mask 3' and the dispersion angle θ of the ion beam.

The present invention uses a tapered etching mask 3',
Then, a groove having a semicircular cross section is formed on the substrate 1 by ion beam etching, and an optical material having a higher refractive index than the substrate 1 is deposited or epitaxially grown in this groove to form a buried optical waveguide. Alternatively, after the surface of this optical waveguide is flattened, two optical waveguides are pasted together from both sides to form an optical waveguide with a circular cross section.

[Embodiments of the invention] Example 1 Embodiments of the present invention will be described in detail below using a scale.

FIG. 3 shows a cross-sectional view of an optical waveguide according to the present invention. A tapered resist pattern (mask 3' in FIG. 2(a)) is formed on an n-type GaAs substrate l that will become a photonic integrated bath substrate.The thickness L2 of the resist at the tapered part is 2.0 μm.
, Lt'z0.50 μm, taper angle ψ 70 degrees,
Pattern spacing Ls'k1. As Oμmn, 0215
Ar ion total acceleration voltage 500■ with angular dispersion of degrees
A tile with a semicircular newspaper shape and a depth of 1.0 μm was dug in Base 1 with a length of 1.0 cm using a direct shot with a curved finger for 22 minutes at a low current and a degree of 0.4 mA/Crn2.

After that, the mist was removed, and high resistance GaAS2 having a refractive index higher than that of the substrate 1 was coated with 0.5% by MOCVD. It was applied to a thickness of um. When a He-Ne laser beam with a wavelength of 1.15 μm was passed through this, the light was transmitted through the high resistance GaAs 2 g using the same principle as a normal lip type optical waveguide, and the conduction loss was 0.
It was very good at 2 dB/crn.

Example Missing = An optical waveguide shown in FIG. 3 was prepared in the same manner as in Example 1, and the narrow surface of the high-resistance GaAs film 2 was etched, leaving only the central semicircular portion to form an optical waveguide. This has a wavelength of 1.1
When a 5 μm He-['J e laser beam was passed through it, the transmission loss was as good as 0.3 dB/crn. Further, a Gao-s A 142A S film was epitaxially grown to a thickness of 0.5 μm from above. Wavelength 1.
When the 15 μm l(e-N e laser beam was crushed), the transmission loss was improved by 0.1 dB/z.

Example 3 In the optical waveguide shown in FIG. 3, which was prepared in the same manner as in Example 1, the surface of the high-resistance QaAS film 20 was etched so that only a large semicircular portion remained. Two of the same materials were glued together to produce an optical waveguide 4 having a circular cross section as shown in FIG. When a He-Ne laser beam with a wavelength of 1.15 μm was passed through this, the transmission loss was very good at 0.02 dB/z. In addition, when bonding with the optical fiber was performed, the coupling loss was as small as 0.1d13; The coupler will be explained using FIG. 5.

As shown in FIG. 5(a), a resist bag 3 is created on the GaASM board 1. Pattern dimension Ll +
L2 +L4, Ls are each Lt = 0-50
μm+ L2"'2-07"m+L4"'
2.01' m+L 5-1.01' m.

Taber angle ψ of resist 3 and dispersion angle θ of ion beam
are set to 70 degrees and 15 degrees, respectively, and the acceleration voltage is 50 degrees.
0V, 'a current density 1j [22 minutes 1a at 0.4 mA/cm2
Perform etching and make a 1/4 circular groove x, 0 μm.
I dug a length of 1.0□□□. Then remove resist 3,
(b) As shown in the figure, GaAs has a higher refractive index than the substrate 1.
Epitaxially grow the film 2 to a thickness of 0.5 μm,
The substrate 1 and the quarter-circular epitaxial film 2 were flattened by etching so that they were on the same plane, forming two parallel four-wave paths. A He-Ne laser beam with a wavelength of 1.15 μm on one of these two parallel optical waveguides? When the light was incident, the power ratio at the output yIM was 1.=1, indicating that it was a good directional coupler.

Also, by gluing two of these directional couplers together, (C)V
Two parallel lights 4 with a semicircular cross-sectional shape as shown in
Wave path 4 was created. On one side of this optical waveguide, a wavelength of 1.15
When pm He-Nev laser light was input, the power ratio at the output was 1:1, making it a very good directional coupler. ,,.

Examples 1 to 4 of the above 6C were conducted using dry etching using argon ions, but similar results were obtained in experiments using reactive ion beam etching and wet etching.

〔Effect of the invention〕

As shown in the above embodiments, according to the present invention, the coupling loss between the optical waveguide on the substrate and the optical fiber can be made smaller than that of an optical waveguide with a rectangular cross-section, and the transmission loss due to bending etc. can also be reduced. can.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a conventional rectangular waveguide, and FIG. 2 is a cross-sectional view showing part of the manufacturing process used in the present invention.
2...High refractive index group, 3...Resist, 3' Fig. 1 (0-) (c) TZ Fig. (b) Ryo, Fig. 3 σ Fig. (θ-) (b) <C)

Claims (1)

[Claims] In an optical waveguide having at least two or more tapered resist patterns formed on a substrate and a groove formed on the substrate by dry etching or wet etching, the groove has a circular cross section and t. An optical waveguide characterized by being filled with an optical material having a higher refractive index than the plate.