JPS58100801A - Production of quartz optical waveguide - Google Patents

Abstract

PURPOSE:To obtain optical waveguides which are homogeneous, and are free from ruggedness and cracks with good controllability of film thickness by using impurity added quartz having a prescribed refractive index difference with respect to a quartz substrate as a target in the stage of sputtering and forming the quartz optical waveguides on the quartz substrate. CONSTITUTION:A doped quartz layer 12 having a desired specific refractive index difference is formed on a quartz substrate 11 by using impurity added quartz having a prescribed refractive index difference with respect to said substrate (for example, quartz doped with 3mol% GeO2) as a target. A Ti layer 13 for mask is vapor-deposited on the layer 12 and a resist layer 14 is coated on the layer 13. Thereafter, patterns of desired waveguides are formed on the resist 14 by a photolithographic method, and with the residual resist 14 as a mask, the layer 13 is etched, then with the layer 13 as a mask, the layer 12 is etched; thereafter the mask 13 is removed. Finally, the waveguide parts 12 are coated with sputtered quartz 15, whereby the quartz optical waveguides having uniform film quality and small transmission losses are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an optical waveguide circuit by controlling the refractive index of quartz glass sputtered onto a substrate.

With the development of optical fiber transmission technology, it is desired that optical waveguide circuits perform functions such as optical branching, optical fiber splitting, and optical demultiplexing that were conventionally performed in space. In particular, optical waveguides using silica glass as a medium are expected to have low loss, are suitable for coupling with optical fibers, and are expected to be mechanically and chemically stable waveguides, so several manufacturing methods have been proposed. ing. Figure 1 is a diagram explaining the method for manufacturing a quartz optical waveguide by chemical vapor deposition (Reference: Mori et al.: Institute of Electronics and Communication Engineers Technical Report 0QIC
8G-1351980). That is, the oxygen whose flow rate is controlled by the mass flow controller MFO1 is
J4. Gaoj4. The vapors POj, , BBrs are introduced into the high-temperature furnace 2, where 810, which becomes the main component of the waveguide, and Gem, , P, O, which become impurities, are introduced into the high-temperature furnace 2.
, B, O, are produced, deposited on a quartz substrate 3, and then transparently vitrified. The impurity distribution in the optical waveguide produced by this method is not uniform, and the surface tends to have unevenness, rounding and light scattering, which causes large losses.

In addition, since it involves a high temperature process reaching 1600"O, cracks are likely to occur due to the difference in thermal expansion coefficient of impurities. Furthermore, it is difficult to use in conjunction with other techniques that require avoiding high temperature processing, such as the production of diffraction gratings. It has some drawbacks.

On the other hand, since around 1970, when optical integrated circuits began to be researched, sputtering has been used as a high-quality thin film manufacturing technique for various materials. For example, the substrate glass is a glass with a high refractive index, and the optical waveguide has excellent uniformity.
It has been obtained that the value is less than 1 an/cIn. However, no optical waveguide has yet been fabricated by sputtering using silica glass, which is expected to have even lower loss than this and is suitable for coupling with optical fibers. The reason is 810. Because it is difficult to control impurities such as gools during tsuttering, there is no established method for creating a minute refractive index difference between the core and cladding, which corresponds to the relative refractive index difference of an optical fiber.

In view of these circumstances, the present invention seeks to provide a method for manufacturing a quartz optical waveguide having a relative refractive index difference comparable to that of an optical core by snotting.

In order to achieve the above object, in a method for producing an optical waveguide in which a quartz glass waveguide is deposited on a quartz substrate by snoku tuttering, impurity-doped quartz having a predetermined refractive index difference with respect to a quartz substrate is chemically deposited. Invention of a method for manufacturing a quartz optical waveguide, characterized in that an optical waveguide having a difference in refractive index is deposited on the quartz substrate by manufacturing it by a vapor deposition method and using the impurity-doped quartz as a target during sputtering. This is the gist of the report.

Next, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that these examples are merely illustrative, and it goes without saying that various changes and improvements may be made without departing from the spirit of the present invention.

FIG. 2 shows a conventional RF sputtering apparatus, in which numeral 5 denotes a sputtering chamber, inside which a substrate 3 and a target 4 are disposed facing each other. 6 is an RF electrode, 7 is a heating coil, 8 is an RF electrode, 0. 9 indicates the pulp, and 10 indicates the exhaust port. If pure quartz is used as the target 4, 810. A thin glass film is deposited. Although the deposition rate varies depending on the type 2 conditions of the sputtering apparatus, it is possible to achieve a deposition rate of about lpm/hour. Figure 3 shows the pressure of mur ions: 3X10 Torr, and the RF output: 200W.
, an example of the deposited film thickness versus sputtering time under the conditions of applied voltage V=1.7 KV.

According to Fig. 3, it is clear that sputtering should be performed for 5 to 8 hours in order to fabricate a single mode leading waveguide with a thickness of 5 to 8 μm, which matches the core diameter of the single mode 7 eyeper. Ru. However, it is necessary to control the refractive index of the deposited glass by slightly increasing it relative to the quartz substrate. And the ratio is the relative refractive index difference of ordinary silica optical fiber = 0.2 ~ O,S
% is desirable. The relative refractive index difference △ is 810
．． This can be controlled by doping Goo, P, O, Bo03, etc. into the glass. Conventionally, there has been no example of producing such a quartz waveguide by sputtering, but the present invention is characterized in that the above refractive index difference is obtained by sputtering using quartz doped in advance by chemical vapor deposition as a target. The dope material is generally Goo, and if the required dope lid is expressed in morchi, it will be about 10 times the desired relative refractive index difference expressed in chi (Reference: Kobayashi et al. Report Vol. 26 No. 9 p. 2569
, 197'! ). For example, in order to set Δ to 0.3-, quartz glass may be doped with Gool 3 molten. Such impurity-doped quartz can be easily manufactured by the method shown in FIG. 1 or by chemical vapor deposition or deposition such as the vAD method. When this impurity-doped quartz is used as the target 4 in FIG. 2, 810. and Goo are deposited at a constant rate.

The ratio depends on the sputtering conditions such as voltage, etc. S10. and G
The target impurity-doped cap generally differs from the target because of its different sputtering rate. Figure 4 shows the mr pressure 3 x 10 = T
orr, RF output 200W, 'V: 1.7K
A sub-regular example of the relative refractive index difference between the target and the sputtered film when sputtered under the condition of V is shown. In this way, by experimentally determining the relationship between the relative refractive index difference between the target and the sputter group under the tea juice used, it is possible to fabricate a core portion having a specific relative refractive index difference. The obtained quartz layer is of good quality, almost indistinguishable from the substrate, and has no surface irregularities or cracks. The loss is 1 an/(7) at a wavelength of 0.6328 μm in a slab waveguide.
See below. It is also possible to further reduce the loss by using a buried ridge waveguide. According to this method, the disadvantages of chemical vapor deposition, such as non-uniformity and mechanical instability (surface irregularities and cracks, etc.), are removed by sputtering, and the advantage 1, productivity, can be utilized during target production. .

FIG. 8g5 is a diagram illustrating the process of manufacturing a block-embedded ridge waveguide using the quartz optical waveguide manufacturing method according to this embodiment. (a) First, using the method of this example, Gem,
Quartz containing about 3 mol of 12 is deposited on a quartz substrate 11 to a thickness of 8 μm, Ti 13 for a mask is deposited thereon, and a photoresist is applied. (1,,) Next, the desired waveguide shape (turn only,
A resist 14 is left, and T1 is etched using a plasma etching device using this resist 14 as a mask. (e) Remove all resist and mask T1 as mask 1
In step 3, the deposited GeO3-doped quartz 12 is etched by reactive etching. (d
) After removing the Ti mask 13, pure quartz is deposited by sputtering. Sputtered quartz is shown at 15. As described above, the doped quartz having a relative refractive index difference of about 0.3 degrees is narrowed into the quartz cladding as a ridge waveguide.

As explained above, this embodiment uses sputtering to
Fabricating a quartz waveguide doped with impurities such as Goo, etc.
Therefore, a waveguide with uniform film quality can be produced with good controllability of film thickness. Furthermore, since it does not involve a high-temperature process, it is possible to incorporate processes such as the production of lattices, which has the advantage of wide range of applications.

[Brief explanation of the drawing]

Fig. 1 shows an apparatus for producing a quartz optical waveguide using a conventional chemical vapor deposition method, Fig. 2 shows a sputtering apparatus explaining one embodiment of the apparatus of the present invention, Fig. 3 shows the relationship between sputtering time and sputtered quartz film thickness, and Fig. 4 The figure shows the relationship between the relative refractive index difference of the target and the relative refractive index difference of the sputtered quartz film, and FIGS. 5(&) to (d) show the manufacturing process. l...Mass flow controller, 2...High temperature? ',
3... Substrate, 4... Target, 5... Sputtering container, 6... RF electrode, 7... Heating coil, 8...
・Gas inlet, 9...Pulp, lO...Exhaust port, 1
1...Substrate, I2...Ge01 doped quartz, 13.
...T1 mask, 14...Resist, 15...Sputtered quartz Patent applicant No. 1 Fig./1''2 Fig./l'3 Fig. 0 10 20 30 Spa-Ntachi Nao (Hinata) Fig. 74-Tano "T's ratio 1 'pyr <'mu) T5 figure

Claims (1)

[Claims] In a method for manufacturing an optical waveguide in which a quartz glass waveguide is deposited on a quartz substrate by sputtering, impurity-cooled quartz having a predetermined refractive index difference with respect to the quartz substrate is produced by chemical vapor deposition, and the impurity-doped quartz is A method for manufacturing a quartz optical waveguide, characterized in that an optical waveguide having a refractive index difference is deposited on the quartz substrate by using it as a target during sputtering.