JP2827657B2 - Glass waveguide and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass waveguide as an important optical component in an optical communication system such as an optical integrated circuit and a method for manufacturing the same, and more particularly to a glass waveguide with improved isolation and a method for manufacturing the same. .

[0002]

2. Description of the Related Art A glass waveguide is an important optical component for producing a lightweight and compact passive device or module. FIG. 2 shows an example of a transmission / reception module using the glass waveguide 1. As shown, coupler,
A laser diode 3, a lens 4, a photodiode 5, and an optical fiber 6 are mounted on a glass waveguide 1 composed of a multiplexing / demultiplexing circuit or the like. Further, as shown in FIG. 3, the glass waveguide 1 has a core 2 formed in an appropriate pattern on a cladding layer 8 on a quartz glass substrate 7.

In this module, a laser diode 3
The light emitted from is transmitted through the optical fiber 6 after being condensed by the lens 4 and coupled to the core 2 of the glass waveguide 1. On the other hand, light from the optical fiber 6 is transmitted to the photodiode 5 by the glass waveguide 1 and received by the photodiode 5.

[0004]

By the way, in the photodiode 5, a part of the light of the laser diode 3 other than the light received from the optical fiber 6 becomes stray light and is received by the photodiode 5. This stray light is reflected on the photodiode 5
Will result in noise for reception. The stray light other than the received light is generally defined by an isolation A represented by the following equation.

[0005] _{A = -10log 10 (P 2 /} P 1) where, P ₁ is the output of the photodiode 5 when the laser diode 5 is oscillating, the output of the photodiode 5 that is due to stray light, P ₂ Is the laser diode 5
Is the output of the photodiode 5 due to the received light when is not oscillating.

The light emitted from the laser diode 3 and coupled to the glass waveguide 1 propagates not only in the core 2 but also partially in the cladding layer 8, but the light propagating in the cladding layer 8 is quartz glass The light leaks to the substrate 7 and is irregularly reflected in the quartz glass substrate 7, and a part of the light enters the photodiode 5. For this reason, in the conventional glass waveguide 1 shown in FIG. 3, the isolation is greatly reduced due to light leaking from the cladding layer 8 to the substrate 7, and the value of the isolation A is -35 dB or more, although it is desirable. 15--2
Only 0 dB was obtained.

An object of the present invention is to provide a glass waveguide which can solve the above-mentioned drawbacks of the prior art and can greatly improve the isolation, and a method for manufacturing the same.

[0008]

In order to achieve the above object, a glass waveguide according to the present invention comprises a quartz glass or silicon substrate and a quartz glass core covered with a cladding layer. This is one in which a porous glass layer is interposed.

Further, according to the method of manufacturing a glass waveguide of the present invention, a porous glass layer is formed on a substrate made of quartz glass or silicon, and a first cladding layer of quartz glass is formed on the porous glass layer. After forming a quartz glass film on the first cladding layer, an extra portion is removed from the glass film to form a core, and a second cladding of quartz glass is formed so as to cover the core and the first cladding layer. In this case, a layer is formed.

In the present invention, the bulk density of the porous glass layer is preferably 1 to 2 g / cm ^3, and the softening temperature (glass transition temperature) of the porous glass is the core, the first and second claddings. Preferably, it is higher than the softening temperature of the layer. The quartz glass film is preferably formed on the first cladding layer by using electron beam evaporation or ion sputtering.

[0011]

A part of the light propagating in the cladding layer of the glass waveguide tends to leak to the substrate side, but since the porous glass layer exists as a scatterer between the cladding layer and the substrate. Light leaking from the cladding layer to the substrate is scattered by the porous glass layer, and light leaking to the substrate is reduced. In addition, light leaking to the substrate, irregularly reflecting within the substrate, and returning to the cladding layer is also scattered by the porous glass layer,
The penetration of stray light into the cladding layer is suppressed.

The bulk density of the porous glass layer is 1 to 2 g / c
The reason for setting m ³ is as follows. If the bulk density of the porous glass layer is 1 g / cm ³ or less, the porous glass layer shrinks when the clad layer is formed by heat treatment, and the clad layer is not formed uniformly. If the bulk density is 2 g / cm ³ or more, the surface or interface of the porous glass layer will not have irregularities, and the void portion of the porous glass layer will decrease, and the scattering performance of the porous glass layer will decrease. It is.

Further, when the softening temperature of the porous glass layer is higher than the softening temperature of the core or the cladding layer, for example, when the porous glass layer is made of pure SiO ₂ , the porous glass is sintered and vitrified to form the cladding layer or the core. Is formed, the porous glass layer is less likely to be affected by heat.

Further, when a quartz glass film for the core is formed on the first cladding layer by electron beam evaporation or ion sputtering, the porous glass containing a small amount of dopant and having a high softening temperature is made into a transparent glass to form a glass film for the core. Eliminates problems such as deformation of the glass waveguide due to high-temperature heating, which occur when forming the substrate.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the glass waveguide of the present invention.
As shown in the figure, this glass waveguide 10 is formed by forming a porous SiO ₂ glass layer 12 on a quartz glass substrate 11, and then forming a first cladding layer 13 of quartz glass on the porous glass layer 12. , A core 15 and a second cladding layer 16 are sequentially formed.

Next, a method of manufacturing the glass waveguide 10 will be specifically described with reference to FIG. First, a porous glass layer 12 is formed on a quartz glass substrate 11 (FIG. 4).
(A)). This is because the burner (not shown) has the raw material SiC
l ₄ and the fuel, and S
iO ₂ was generated, and the generated SiO ₂ fine particles were deposited on a quartz glass substrate 11 having a diameter of 3 inches and a thickness of 1 mm to a thickness of 50 μm. The bulk density of the deposited porous glass was 0.4 g / cm ³ . Thereafter, the substrate 11 was heated in an electric furnace in a He atmosphere, and the bulk density was 1.
5 g / cm ³ of the porous glass layer 12 was obtained.

Next, a P ₂ O ₅ —B ₂ O ₃ —SiO ₂ -based porous glass film is deposited and formed on the porous glass layer 12 by using a flame hydrolysis reaction, and this is then placed in an electric furnace. To form a first cladding layer 13 having a thickness of 20 μm (FIG. 4B).

Next, a TiO ₂ —SiO ₂ glass film 14 is formed on the first cladding layer 13 by electron beam evaporation.
Was formed (FIG. 4C). This is because while holding the substrate 11 in an electron beam vacuum evaporation apparatus (not shown),
The O ₂ -SiO ₂ glass of the target provided, by heating the tablet by the electron beam, the vapor deposited deposited on the first cladding layer 13, 8 [mu] m thickness of TiO ₂ -Si
An O ₂ -based glass film 14 is formed.

Thereafter, an extra portion was removed from the glass film 14 to form a core 15 (FIG. 4D). To do this, the pattern of the waveguide is transferred by photolithography using a pattern forming apparatus, and then the unnecessary portion of the glass film 14 is removed by reactive ion etching, thereby patterning the waveguide and obtaining the core 15. Was.

Finally, under the same conditions as those for forming the first cladding layer 13, deposition of a porous glass and vitrification are performed to cover the core 15 and the first cladding layer 13.
_Second of P ₂ O ₅ —B ₂ O ₃ —SiO ₂ based glass with a thickness of μm
The clad layer 16 was formed (FIG. 4E).

A glass waveguide device is cut out from the substrate 11 manufactured as described above by dicing, and both end surfaces thereof are polished. Then, a laser diode, a photodiode, an optical fiber, etc. are mounted on the glass waveguide device, and the isolation is measured. Was done. As a result of the measurement, the isolation value was very good at -38 dB. In the glass waveguide element without the porous glass layer 12 in the above embodiment, the isolation was only -18 dB.

In the above embodiment, if the bulk density of the porous glass layer is set to 1 g / cm ³ or less, the porous glass layer contracts during the formation of the clad, and the glass film of the second clad layer is formed uniformly. Was not done. On the other hand, when the bulk density is 2 g / cm ³ or more, the surface of the porous glass layer has no irregularities and the number of pores serving as scatterers in the porous glass layer is reduced, so that the isolation is reduced to −28 dB or less. have done.

In the above embodiment, the case where the substrate is quartz glass has been described. However, using a silicon substrate as the substrate, a porous glass layer is formed in the same manner as described above to produce a glass waveguide device, and the isolation is measured. Was performed, the result was -36d
B and good results were obtained.

[0024]

As apparent from the above description, the following effects can be obtained according to the present invention.

(1) According to the glass waveguide of the first aspect, since the porous glass layer serving as a scatterer is formed between the substrate and the cladding layer (first cladding layer), the cladding layer is formed. Light leaking from the substrate to the substrate is scattered by the porous glass layer, and light leaking to the substrate is greatly reduced. Further, even if there is light that leaks to the substrate and diffuses into the substrate and tries to return to the cladding layer again, the light is scattered by the porous glass layer, so that the penetration of stray light into the cladding layer is favorably suppressed. Therefore, the isolation of the glass waveguide can be greatly improved.

(2) According to the method of manufacturing a glass waveguide according to the second aspect, the core, the first and second cladding layers of the silica-based glass are usually made of a porous glass by utilizing a flame hydrolysis reaction. The film is formed by depositing a film and heating it to form a transparent glass. By the existing equipment and technology used to form these, a porous glass provided as a scatterer can also be formed, and easily and reliably. The glass waveguide of the present invention can be manufactured.

(3) According to the glass waveguide or the method of manufacturing the same according to the third or fourth aspect, if the bulk density of the porous glass layer is 1 g / cm ³ or more, the first cladding layer and the like are subjected to heat treatment. When forming, it is possible to prevent the porous glass layer from shrinking and giving deformation and distortion to the clad layer and the like. Further, when the bulk density of the porous glass layer is 2 g / cm ³ or less, many irregularities and pores on the surface of the porous glass layer can be retained, and a porous glass layer having high scattering performance can be obtained.

(4) According to the method for manufacturing a glass waveguide according to the fifth aspect, if the softening temperature of the porous glass layer is higher than the softening temperature of the core or the first and second cladding layers, When the glass is sintered and vitrified to form a clad layer or a core, the porous glass layer is less likely to be affected by heat, and a desired porous glass layer can be reliably formed.

(5) According to the method of manufacturing a glass waveguide according to the sixth aspect, if a quartz glass film is formed on the first cladding layer by using electron beam evaporation or ion sputtering, the amount of dopant is reduced. It is possible to avoid problems such as deformation of the glass waveguide due to high temperature when forming a glass film for the core by turning a porous glass with a high softening temperature into a transparent glass, and to accurately form a glass waveguide having a core with a high softening temperature. Can be manufactured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a glass waveguide according to the present invention.

FIG. 2 is a schematic configuration diagram showing a conventional optical transceiver module using a glass waveguide.

FIG. 3 is a cross-sectional view of the glass waveguide of FIG. 2;

FIG. 4 is a process chart showing one embodiment of a method for manufacturing the glass waveguide of FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 glass waveguide 2 core 3 laser diode 4 lens 5 photodiode 6 optical fiber 7 quartz glass substrate 8 cladding layer 10 glass waveguide 11 substrate 12 porous glass layer 13 first cladding layer 14 glass film 15 core 16 second cladding layer

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B ^6/ 12-6/138

Claims (6)

(57) [Claims] (1) A quartz glass or silicon substrate and a quartz glass core coated with a cladding layer,
A glass waveguide having a porous glass layer interposed therebetween. 2. The porous glass layer has a bulk density of 1 to 2 g.
The glass waveguide according to claim 1, wherein the ratio is / cm ³ . 3. A porous glass layer is formed on a substrate made of quartz glass or silicon, a first cladding layer of quartz glass is formed on the porous glass layer, and quartz glass is formed on the first cladding layer. After forming the film, an extra portion is removed from the glass film to form a core, and a second cladding layer of quartz glass is formed so as to cover the core and the first cladding layer. To manufacture a glass waveguide. 4. The porous glass layer has a bulk density of 1 to 2 g.
4. The method for producing a glass waveguide according to claim ³ , wherein / cm ³ is set. 5. The softening temperature of the porous glass layer is equal to the first softening temperature.
The method for manufacturing a glass waveguide according to claim 3, wherein the softening temperature is higher than the softening temperatures of the cladding layer, the core, and the second cladding layer. 6. A glass waveguide according to claim 3, wherein said quartz glass film is formed on said first clad layer by electron beam evaporation or ion sputtering. Manufacturing method.