JP2002022980A - Optical waveguide element and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problems when an optical waveguide element is manufac tured by utilizing a photoinduced refractive index change by irradiation with a laser beam, that, if a plane such as a glass substrate or the like is perpendicu larly irradiated with the laser beam and the laser beam is focused to its inside, a condense spot is made elliptic and the section of the waveguide is made elliptic, and such section of the waveguide can be the cause for the significant loss in the propagation of the light and is also undesirable in coupling to an optical fiber. SOLUTION: A layer for forming the core of the glass optical waveguide is formed as a silicate glass layer containing Al2O3. The content of the Al2O3 is specified to be from 3 to 35 mol%. A layer which forms a clad is formed as a silicate glass layer containing B2O3 and the content of the B2O3 is specified to be from 3 to 35 mol%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element for guiding light in a medium, and more particularly to an element for guiding light in a medium, wherein the waveguide is formed in a thin film formed on a substrate. The present invention relates to an optical waveguide manufactured by continuously forming a refractive index change region inside a thin film.

[0002]

2. Description of the Related Art Optical waveguides used in optical communication and the like are roughly divided into those using plastic, those using glass, those using semiconductor materials, and those using ferroelectric materials such as lithium niobate. Can be classified. Above all, optical waveguides using glass are weather resistant,
It is excellent in transparency, and is mainly used in the field of optical communication. Such an optical waveguide can be used not only for splitting or combining light but also as a switch element, a filter, or the like.

An optical waveguide must have a structure in which a region having a high refractive index is formed in a medium and light is selectively propagated. The ion exchange method and the flame hydrolysis method are known as typical methods for producing such a region having a high refractive index through which light selectively propagates using glass.

Regarding the ion exchange method, for example, BJ
Luh et al., Journal of Lightwave Technology, 16 volumes, 4
No., (1998), p. 583, a molten salt containing Ag ⁺ , Tl ⁺ , K ⁺ or Li ⁺ ions is brought into contact with a glass substrate surface layer through a slit-shaped opening of a metal film or the like to form a glass substrate. By exchanging the Na ⁺ ions therein, a refractive index change region is formed on the surface layer of the glass substrate to form an optical waveguide.

In order to embed the optical waveguide in the glass, the glass substrate on which the optical waveguide is formed is heated to diffuse the ion-exchanged Ag ⁺ , Tl ⁺ , K ⁺ or Li ⁺ ions into the glass, or Ag ⁺ in the glass surface was immersed in molten salt containing again Na ⁺ ions, Tl ^+, re exchange K ⁺ or Li ⁺ ions and Na ⁺ ions. There is also a method of applying an electric field during ion exchange. Na ⁺ ion is A
The outermost high refractive index region formed by g ⁺ , Tl ⁺ , K ⁺ or Li ⁺ ions is moved below the surface. As a result, the waveguide is embedded under the glass surface, and low propagation loss is ensured. The core of the optical waveguide manufactured by this method has a diameter of 10 μm.
One having a semicircular or nearly circular cross section before and after can be created.

In the flame hydrolysis method, two glass fine particle layers for lower cladding and a core are deposited on the surface of a silicon substrate by flame hydrolysis of silicon tetrachloride and germanium tetrachloride, and the fine particle layer is made transparent by high-temperature heating. Modifies into a glass layer. Next, a core having an optical circuit pattern is formed by photolithography and reactive etching.
An example of device fabrication using this method is reported in a paper by T. Mizuochi et al. (Ibid., Vol. 16, No. 2, (1998), p. 265). Although a quartz optical waveguide can be manufactured by this method, the manufacturing procedure is considerably complicated. Further, since the deposited thin film is basically used as the waveguide, the cross-sectional shape of the waveguide tends to be flat, and the coupling characteristics with the optical fiber are not so good.

The above method uses a photolithography technique using a photomask on which a waveguide pattern is formed. A method of directly writing with a laser to form a region having a high refractive index is disclosed in Japanese Unexamined Patent Publication (Kokai) No. H11-260,197. 9-3112
No. 37 is disclosed. This is a method of forming an optical waveguide by irradiating a laser having a high peak output value into the inside of glass. In this method, a laser beam having a peak power intensity of 10 ⁵ W / cm ² or more is focused inside the glass to cause a structural change that causes a change in the refractive index inside the glass material. The optical waveguide is formed by relatively moving the optical waveguide. Since this method does not use a mask or the like, the process is simple and can be said to be a method that can easily cope with design changes and the like.

[0008]

However, when a laser beam is irradiated perpendicularly to a plane such as a glass substrate to focus on the inside, there is a problem that the condensed spot becomes elliptical.
Regarding this point, the Science and Technology Promotion Foundation Creative Science and Technology Promotion Project Hirao Induction Project Interim Report (No. 2 (July 1997
Mon.), p. 36). When the substrate is moved in a direction perpendicular to the beam while keeping such a spot shape, the waveguide section becomes elliptical. Such a waveguide section causes a significant loss in light propagation, and is not preferable for coupling with an optical fiber. The present invention has been made to solve such a problem, and an object of the present invention is to provide an optical waveguide having a small propagation loss and a small coupling loss with an optical fiber by laser drawing.

[0009]

Means for Solving the Problems The present inventors have found that the degree to which the light-induced refractive index change due to the laser beam occurs differs depending on the difference in the glass components. Thereby, the above problem can be solved. That is, the glass containing Al ₂ O ₃ easily causes a change in the refractive index induced by light, and the glass containing B ₂ O ₃ hardly exhibits the effect. Al ₂ O ₃ a layer containing a formed on a glass substrate containing B ₂ O _3, by using a glass layer containing B ₂ O ₃ as a protective layer, certain desired only photoinduced refractive index change in thickness I wake up.

[0010] For this, the layer forming the core of the glass optical waveguide and silicate glass layer containing Al ₂ O _3, Al ₂
The content of O ₃ is from 3 mol% to 35 mol%. Further, a layer of the cladding as a silicate glass layer containing B ₂ O _3, to content of B ₂ O ₃ and 3 mol% or more than 35 mol%. Focusing laser light on glass having such a composition causes a structural change inside the glass material, inducing a refractive index, and moving the focus point relative to the glass material. Thereby, an optical waveguide is formed by generating a refractive index change region.

[0011]

Embodiments of the present invention will be described below. The optical waveguide of the present invention focuses a laser beam having an energy amount sufficient to cause a photoinduced refractive index change on a glass material, causes a structural change inside the glass material, changes the refractive index, and collects the light. It is produced by moving a light spot relatively to a glass material. As a material composition, glass containing B ₂ O ₃ is used as a substrate or an underlayer,
The glass layer containing l ₂ O ₃ arranged thereon. The surface of the glass layer may be further covered with a glass layer containing B ₂ O ₃ in order to prevent ablation by laser and to protect a portion to be an optical waveguide layer. This configuration is shown in FIG.

The inventors have found that the degree of change in the photo-induced refractive index caused by laser light differs depending on the difference in glass components. It is the gist of the present invention to solve the above problem by combining materials having different glass components.

In the thin film and the substrate having the above-described structures, by appropriately setting the laser energy, Al ₂
The layer containing O ₃ causes a laser-induced refractive index change, and B ₂ O ₃
Can be prevented from causing a change in the refractive index. Therefore, an optical waveguide controlled to a desired thickness and width can be manufactured two-dimensionally.

Various methods for forming a thin film can be used to produce the above-mentioned thin film layer. However, the thickness of the optical waveguide is required to be about 10 μm in consideration of compatibility with the optical fiber. A high-speed plasma CVD method or the like is preferable. Further, the above-described flame hydrolysis method, a general sputtering method, a vapor deposition method, or the like is also possible.

As the laser beam, the light-induced refractive index change
10 seconds at the focal point to ^FiveW / cm^TwoMore than
It is desirable to have a peak power density. Peak power
Density is output energy per pulse (J) / pulse
The peak output (W) expressed by the ratio of the width (seconds) is the irradiation unit surface
It is a value expressed as a product. 10 peak power intensity^FiveW
/ Cm^TwoIf it is less than the specified value, the photo-induced refractive index change does not occur,
No waveguide is formed. The higher the peak power intensity, the lighter
The induced refractive index change is promoted, and the optical waveguide is easily formed.
You. However, laser light with an excessively large amount of energy
It is difficult to obtain practically. Therefore, narrow the pulse width
Pulse laser with high peak output
The use of is preferred.

The laser beam is focused by a focusing device such as a lens. At this time, the focal point is adjusted so as to be located inside the glass material. By moving the converging point relatively inside the glass material, a continuous refractive index change region serving as an optical waveguide is formed inside the glass material. More specifically, the glass material is continuously moved with respect to the laser light focal point, so that the focal point is relatively moved.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

[0018]

EXAMPLE A laminated structure 10 as shown in FIG. 1 was manufactured by using a plasma CVD method. As a basic membrane configuration,
Glass substrate 20 / buffer layer 22 containing B ₂ O ₃ / Al ₂
The intermediate layer 24 containing O ₃ / the protective layer 26 containing B ₂ O ₃ are formed. As raw materials, TEOS (tetraethoxysilane), B (OC ₂ H ₅ ) ₃ (triethoxyboron, TE
B), Al (CH ₃ ) ₃ (trimethylaluminum, TM
A) was used. A quartz glass was used for the substrate 20, and a film was formed thereon.

Basically, this raw material may be used, but Ge (OCH ₃ ) and HF are mixed for adjusting the refractive index. Ge
(OCH ₃ ) is oxidized to GeO ₂ and has a function of increasing the refractive index. Further, HF is decomposed and taken into glass as F ions, thereby reducing the refractive index. This was adjusted so that the refractive index of the layer containing Al ₂ O ₃ was increased. In forming each layer, oxygen was mixed, and the flow rate ratio between the raw material and oxygen was set to raw material: oxygen = 7: 233, and sufficient oxidation was advanced.

FIG. 2 is a schematic view of the plasma CVD apparatus 30. Opposite plate electrodes 34 and 36 are provided in the reaction chamber 32, and the glass substrate 20 is placed on one of the electrodes 34. The reaction chamber 32 is evacuated with a vacuum pump and once evacuated,
The source gas 4 is supplied through a gas inlet 38 provided in the other electrode 36.
6 is introduced. Heater 40 provided in both electrodes 34 and 36
The electrode is heated by heating, and the substrate 20 is heated. The substrate temperature was 400 ° C. Next, both electrodes 3
A high frequency power is supplied between 4, 36. RF (high frequency) power for generating the plasma 44 was 250 W.

The buffer layer 22 is made of S containing 5 mol% of B ₂ O _3.
iO ₂ / GeO ₂ was adjusted so that the refractive index became 1.46. The film thickness was about 10 μm. The intermediate layer 24 has Al
5 mol% of ₂ O ₃ was contained, and B ₂ O ₃ was not mixed. The refractive index of the intermediate layer 24 was adjusted to 1.49, and the film thickness was 10 μm.
Laminated. The last protective layer 26 was laminated with the same composition as that of the buffer layer 22 to a thickness of about 25 μm. The refractive index of the protective layer 26 is also 1.
46.

If the content of Al ₂ O ₃ exceeds 35 mol%, the thermal expansion coefficient cannot be matched with the clad material, which causes a problem in reliability. Therefore, it is preferable that the content is 35 mol% or less. When the content of B ₂ O ₃ is increased, a problem occurs in the weather resistance. Also in this case, it is desirable that the upper limit is 35 mol%. On the other hand, when the content of Al ₂ O ₃ and B ₂ O ₃ is less than 3 mol%, the effect on the photo-induced refractive index change by laser irradiation is not sufficiently exhibited.

Even in this state, a waveguide structure was formed. When light having a wavelength of 1.3 μm was introduced, light guided to the intermediate layer 24 was observed. However, although the refractive indices are different in the laminating direction of the films and the light has a confinement effect, the film surface direction is uniform and there is no light confinement effect.

The sample thus obtained was irradiated with a laser. As shown in FIG.
Was condensed by a lens 52 and irradiated. Pulse laser beam 5
A pulse width of 15 oscillated from a Ti: Al ₂ O ₃ laser (not shown) excited by an argon laser is set to 0.
0 femtoseconds, repetition frequency 200 kHz, wavelength 80
Laser light of 0 nm and an average output of 600 mW was used.
A laser beam whose intensity has been adjusted to 400 mW by passing through an ND filter (not shown) is applied to an NA (numerical aperture).
The light was condensed by a 0.3 × 10 × objective lens 52 and irradiated so as to form a converging point 54 inside the substrate 20 having the laminated structure.

As shown in FIG.
The refractive index changing region 58 is generated while moving in a direction perpendicular to the beam at a speed of m / s. Finally, the refractive index was changed over the entire length of the intermediate layer 24, and the optical waveguide 60 was manufactured. However, since the refractive index changing region 58 is formed only in the area irradiated with the condensed laser light in the plane, as shown in FIG. The cross section can be shaped like a square.

The produced optical waveguide was evaluated by the following method. A light emitting diode (L) having a center wavelength at 1.3 μm
The light of ED) is guided to the end face of the optical waveguide produced by the single mode optical fiber for 1.3 μm, and the center is adjusted so that the intensity of the light emitted from the other end of the optical waveguide becomes maximum. The emitted light was observed at the end face using an infrared CCD camera. When the laser irradiation operation was not performed, it was observed that the light that had spread in the lateral direction was confined only to the laser irradiation portion. From this, it was found that only the intermediate layer had a slightly higher refractive index than the upper, lower, left and right regions. That is, the refractive index of the Al ₂ O ₃ layer was further increased, but the refractive index of the layer containing B ₂ O ₃ was not changed.

Further, the loss of the obtained waveguide was estimated at a wavelength of 1.3 μm as in the evaluation of the waveguide mode. The light from the LED that passed through the optical fiber was coupled close to the incident end of the optical waveguide, coupled again to the optical fiber at the exit end, and finally the output from the optical waveguide was measured by an optical spectrum analyzer. The space between the optical fiber and the optical waveguide was fixed with an ultraviolet curable resin having a refractive index of about 1.48. The propagation loss of the optical waveguide measured by the cutting method is
It was sufficiently small at 0.1 dB / cm. On the other hand, the coupling loss with the optical fiber was estimated to be 0.5 dB. This coupling loss is described in Journal of Lightwave Technology, Vol. 17, No. 5, (199
9) 0.8 dB of the silica-based optical waveguide shown on page 771
Less than.

[0028]

According to the present invention, there is provided an optical waveguide manufacturing method for drawing an optical waveguide by moving a material vertically with respect to laser light by utilizing the effect of changing the refractive index of a material by laser light irradiation. The cross section of the waveguide can be made to be rectangular or nearly circular, and the waveguide characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a laminated structure for producing an optical waveguide according to the present invention.

FIG. 2 is a schematic view of a film forming apparatus used for manufacturing a laminated structure.

FIG. 3 is a schematic view of manufacturing an optical waveguide by laser writing according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Laminated structure 20 Glass substrate 22 Buffer layer 24 Intermediate layer 26 Protective layer 30 Plasma CVD device 32 Reaction chamber 34, 36 Electrode 38 Source gas inlet 40 Heater 42 High frequency power supply 44 Plasma 46 Source gas 50 Laser beam 52 Lens 54 Focus point 58 Refractive index change region 60 Optical waveguide

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G02B 6/13 G02B 6/12 MF term (reference) 2H047 PA11 PA22 QA04 QA07 TA31 4G059 AA20 AB05 AC30 4G062 AA06 BB01 BB02 BB05 BB06 CC10 DA05 DA06 DA07 DA08 DB03 DB04 DB05 DC03 DC04 DC05 DD01 DE01 DF01 EA01 EA10 EB01 EC01 ED01 EE01 EF01 EG01 FA01 FA10 FB01 FC01 FD01 FE01 FF01 FG01 FH01 FJ01 FK01 FL01 GA01 GA10 GB01 GG01 GM01 GG01 GM01

Claims (5)

[Claims] 1. A light guide comprising: a core made of a glass material whose refractive index changes due to a structural change caused by light irradiation; and a clad made of a glass material whose refractive index does not substantially change by said light irradiation. Wave element. 2. The method according to claim 1, wherein the layer forming the core is silicate glass containing Al ₂ O ₃ and the layer forming the cladding is silicate glass containing B ₂ O ₃ . Optical waveguide device. 3. A method according to claim 1, wherein the content of Al ₂ O ₃ is 3 mol% or more.
The optical waveguide device according to claim 2, wherein the content is at most mol%. 4. The optical waveguide device according to claim 2, wherein the content of B ₂ O ₃ is 3 mol% or more and 35 mol% or less. 5. A laser beam condensed to cause a structural change inside the glass material to change the refractive index, and the converging point is moved relative to the glass material to change the refractive index. 5. The method for manufacturing an optical waveguide device according to claim 1, wherein a region is formed.