JPH05313032A - Manufacture of optical waveguide - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing an optical waveguide, low in loss and useful for a waveguide type optical sensor by evanescent coupling, by ion exchange. CONSTITUTION:A first ion-exchange control mask 4 is formed on a glass base 2 first. This mask is provided with the opening 4A of a waveguide pattern, and the base 2 is submerged in fused salt containing cation capable of raising refractive index to perform first ion exchange. The mask 4 is then removed from the base 2, and a second ion-exchange control mask 5 is formed at a part of a formed optical waveguide 1. A diffraction grating pattern, for instance, is formed in the vicinity of the center of the glass base 2, along the optical waveguide 1, across the length of 5mm. Both faces of the glass base 2 with the second mask 5 formed thereon are independently brought into contact with fused salt containing cation capable of lowering refractive index, and the electric field is applied to the glass base 2 with the mask 5 side as positive potential to perform second ion exchange.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical waveguide by ion exchange, and more particularly to a method for producing a low loss optical waveguide useful for a waveguide type optical sensor by evanescent coupling.

[0002]

2. Description of the Related Art A two-step electric field applied ion exchange method is known as a method for producing an optical waveguide in a glass substrate. In this method, first, the surface of the glass substrate is covered with a film having an ion permeation preventing function, and an opening of a predetermined optical waveguide pattern is provided in this film to form a first ion exchange control mask. Next, this mask-covered glass substrate is immersed in a molten salt containing cations capable of increasing the refractive index of the substrate glass to perform a first-stage ion exchange treatment. After this first stage ion exchange treatment, the mask coating is removed from the substrate.

Next, the surface and the back surface of the substrate covered with the mask are independently brought into contact with a molten salt containing cations capable of decreasing the refractive index, and the surface covered with the mask is applied to the substrate as a positive potential. The waveguide is embedded in the thickness of the substrate by applying the electric field and performing the second stage ion exchange treatment.

According to the above-mentioned two-step electric field application ion exchange method, the coupling loss with a standard single mode optical fiber is 0.2 dB or less per point, and the propagation loss is 0.1 dB / cm.
The following single-mode waveguide with extremely low loss can be produced, and it has been applied to the production of waveguide devices such as branching and merging used for optical fiber communication. FIG. 2 shows a side sectional view of an optical waveguide manufactured by this method. The waveguide 1 has a circular cross section and is uniformly embedded in the glass substrate 2, and the embedded depth is about 15 to 20 μm from the substrate surface.

On the other hand, in a waveguide type optical sensor by evanescent coupling, a lithium niobate crystal substrate is conventionally used as Ti.
A single-mode waveguide manufactured by diffusion and a single-mode waveguide manufactured only by the first-step ion exchange treatment step of the above-described two-step ion exchange method have been used. As an example, FIG. 3 shows a side cross section of an optical waveguide manufactured by the latter method. The waveguide 1 is formed in a semi-circular shape on the surface of the glass substrate 2. When the substance 3 to be measured such as oil adheres to the surface of the waveguide 1, strong evanescent coupling is obtained, and the insertion loss of the waveguide is reduced. Because of the large change, a highly sensitive optical sensor could be manufactured.

[0006]

Since the conventional optical waveguide shown in FIG. 2 has an extremely low loss, no particular problems occur for optical fiber communication, and a good optical device such as a branching junction can be manufactured. Was there. However, when it is used for an optical sensor, since the waveguide is embedded and the evanescent wave does not seep to the substrate surface very much, the insertion loss of the waveguide does not occur even if the substance to be measured adheres to the surface of the waveguide. Was almost unchanged and could not be used as an optical sensor.

The embedding depth is set to several μm by adjusting the conditions of the second-stage ion exchange treatment step of the above-mentioned two-stage ion exchange method.
If it is set to be 10 μm, the evanescent wave will be exuded to the substrate surface so much that it can be used as an optical sensor.
Since the mode field diameter of the waveguide is elliptical, the coupling loss with the single mode fiber is 0.3 to 0.
There was a problem of increasing to 5 dB. Further, the sensitivity of the optical sensor is determined by the buried depth of the waveguide and the refractive index of the substance to be measured, so that there is a problem in that the condition of the second ion exchange treatment step must be adjusted depending on the type of the substance to be measured.

On the other hand, in the optical waveguide of the type shown in FIG. 3, although high sensitivity is obtained, the coupling loss with the single mode fiber is 0.5 to 0.8 dB per point and the propagation loss is 0.2 to. It is as large as 0.3 dB / cm, and the insertion loss increase of the optical waveguide when the substance to be measured adheres to the surface is 5 to 10
There was a very big problem with dB. Therefore, in a system in which optical sensors are connected in series in multiple stages, there is a problem that the transmission margin becomes small and the number of connections is limited.

Further, a material having a refractive index lower than that of the optical waveguide (for example, S
iO ₂ etc.) for several μm to 10 μm can reduce the increase in insertion loss when the substance to be measured is attached, and also increase the sensitivity of the optical sensor and increase the insertion loss of the optical waveguide when the substance to be measured is attached. Although it can be adjusted, there is a problem that the manufacturing process becomes complicated.

[0010]

In order to solve the above-mentioned conventional problems, in the present invention, in the method for producing an optical waveguide by the above-mentioned two-step electric field applied ion exchange method, a substrate surface is formed after the first ion exchange treatment step. A second ion-exchange control mask is formed on a part of the formed optical waveguide and a second ion-exchange treatment is performed, so that the embedded depth of the optical waveguide of the part where the second ion-exchange control mask is formed is smaller than that of the other part. Also, the embedding depth of the optical waveguide is partially changed by making it smaller.

[0011]

By reducing the embedded depth of the optical waveguide only in the portion where the second ion exchange control mask is formed,
Small coupling loss and propagation loss with single mode fiber,
Moreover, the evanescent wave seeps out to the substrate surface, and an optical waveguide usable as an optical sensor can be realized.

Further, by adjusting the embedding depth and the length of the portion having a small embedding depth, the sensitivity of the optical sensor and the substance to be measured can be adhered without changing the conditions of the second ion exchange treatment step. It is possible to realize an optical waveguide in which the increase amount of insertion loss of the optical waveguide can be easily adjusted.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiment shown in FIG. In FIG. 1A, the glass substrate 2 has a first
The ion exchange control mask 4 is formed and the mask is provided with the opening 4A of the waveguide pattern. The glass substrate 2 is a borosilicate optical glass containing Na ions and K ions, and has a refractive index of nd = 1.51.
Is. The first ion exchange control mask 4 was formed by sputtering Ti deposition. The waveguide pattern was linear and was produced by photolithography and etching.

In (b), the glass substrate 2 on which the first ion exchange control mask 4 has been prepared in (a) is immersed in a molten salt containing cations capable of increasing the refractive index of the glass substrate 2. The state after performing the ion exchange process of No. 1 is shown.
In this example, a molten salt containing Tl ions, K ions and the like was used, and the thermal ion exchange was performed at a temperature about 100 ° C. lower than the glass point of the glass substrate 2 for 1 hour.

(C) shows a state after the first ion exchange control mask 4 is removed from the glass substrate 2 after the first ion exchange treatment of (b) by using the same etchant as in (a). The semi-circular optical waveguide 1 is formed on the substrate surface.

(D) shows a state after the second ion exchange control mask 5 is formed on a part of the optical waveguide 1 formed by the first ion exchange treatment of (c). In this example, the second ion exchange control mask 5 is formed by sputtering deposition of Ti similarly to the first mask 4, and a diffraction grating pattern is formed near the center of the glass substrate 2 by photolithography and etching. Fabrication was performed along the waveguide 1 for a length of 5 mm.

The width of the mask portion of the diffraction grating pattern of the second ion exchange control mask 5 was set to 2 μm. The second
0.5mm from both ends of the ion exchange control mask 5
In the region (2), the opening width of the diffraction grating pattern was set so that the opening area of the pattern gradually changed from 90% to 50% of the portion without the second ion exchange control mask 5. Further, in the region other than the above region of the second ion exchange control mask 5, the opening width of the diffraction grating pattern is set to 2 μm, and the opening area of the diffraction grating pattern is 50 μm.
It was made to be constant in%.

In (e), both surfaces of the glass substrate 2 on which the second ion exchange control mask 5 is formed in (d) are independently brought into contact with a molten salt containing a cation capable of decreasing the refractive index, With the side having the first ion exchange control mask 4, that is, the side having the second ion exchange control mask 5 as a positive potential, an electric field was applied to the glass substrate 2 to perform the second ion exchange. The latter state is shown.

In this example, a molten salt containing K ions was used, and an electric field was applied for 1 hour at an electric field strength of 50 V / mm at a temperature about 50 ° C. higher than that of the first ion exchange.

(F) shows a state after the second ion exchange control mask 5 is removed from the glass substrate 2 after the second ion exchange in (e) using the same etchant as in (a). Shows. In this example, the embedded depth of the optical waveguide is about 1 at the portion without the second ion exchange control mask 5.
5 μm, about 7 μm at the center of the second ion exchange mask 5
It was m.

The optical waveguides produced in the above-described examples were single mode at a wavelength of 1.3 μm, and the excess loss of the waveguide having a length of 35 mm was low at about 1.0 dB. The breakdown of the loss is that the coupling loss with the single mode fiber is 0.15 dB per point, and the propagation loss is 0.06 dB /
cm, the radiation loss in the region where the burying depth was changed was 0.25 dB per location. Further, as a result of coating the waveguide with oil having a refractive index nd = 1.52, the insertion loss of the optical waveguide increased by about 1.0 dB.

In this embodiment, the opening area of the central portion of the second ion exchange control mask 5 is 50% of the area without the second ion exchange control mask 5, but the opening area is 30%.
In the range of from 80% to 80%, the embedded depth of the waveguide is almost proportional to the opening area, so that the required sensitivity can be obtained according to the transmission margin and noise of the optical sensor system and the refractive index of the substance to be measured. The opening area may be determined.

Although the length of the second ion exchange control mask 5 is set to 5 mm, the sensitivity of the sensor and the insertion loss increase amount of the optical waveguide when the substance to be measured adheres are determined by the second ion exchange control. Since it is almost proportional to the length of the mask 5, if the length of the second ion exchange control mask 5 is determined according to the transmission margin and noise of the optical sensor system and the refractive index of the substance to be measured as in the case of the opening area. Good.

That is, the second ion exchange control mask 5
By adjusting the opening area and length of the central part of the, it is possible to easily realize a low loss waveguide type optical sensor according to various optical sensor systems and substances to be measured without changing the waveguide manufacturing process. .

In this embodiment, the radiation loss in the region where the embedded depth of the optical waveguide changes is 0.
Although it was 25 dB, it can be reduced by increasing the length of the region in which the opening area of the second ion exchange control mask 5 is changed to make the change of the embedding depth more gradual.

Although the present invention has been described based on one embodiment, various manufacturing methods other than the embodiment can be adopted. For example, in the present embodiment, the Ti film is used as the second ion exchange control mask 5, but if it is a substance such as SiO ₂ having a smaller refractive index than the optical waveguide 1 and having an ion permeation preventing function, the second film is used. After performing the ion exchange treatment of No. 2, it can be used without removing the second ion exchange control mask 5.

[0027]

According to the present invention, it is possible to reduce the loss of a waveguide type optical sensor by evanescent coupling, and the sensor sensitivity and the substance to be measured adhere depending on the optical sensor system and the refractive index of the substance to be measured. In this case, it is possible to manufacture an optical waveguide in which the amount of increase in insertion loss can be easily adjusted.

[Brief description of drawings]

1A to 1F are cross-sectional views showing an embodiment of the present invention step by step.

FIG. 2 is a cross-sectional view and a side cross-sectional view showing an optical waveguide manufactured by a conventional two-step electric field application ion exchange method.

FIG. 3 is a cross-sectional view and a side cross-sectional view showing an optical waveguide manufactured by a conventional one-step thermionic exchange treatment.

[Explanation of symbols]

 1 Optical Waveguide 2 Glass Substrate 3 Target Substance 4 First Ion Exchange Control Mask 4A Pattern Aperture 5 Second Ion Exchange Control Mask

Claims (1)

[Claims] 1. A surface of a glass substrate is coated with a film having an ion permeation preventing function, and a predetermined optical waveguide pattern opening is provided in the film to form a first ion exchange control mask. A first ion exchange treatment in which the mask is removed from the substrate to form an optical waveguide on the substrate surface after the substrate glass is immersed in a molten salt containing cations capable of increasing the refractive index to perform the ion exchange treatment. The step and the mask-coated surface and the back surface of the substrate are independently brought into contact with a molten salt containing cations capable of decreasing the refractive index, and the mask-coated surface is applied to the substrate as a positive potential. A second ion exchange treatment step of embedding the waveguide in the substrate thickness by applying an electric field to perform ion exchange, and a method of producing an optical waveguide by a two-step electric field application ion exchange method In the method, a second ion exchange control mask is formed on a part of the optical waveguide formed after the completion of the first ion exchange step, and the second ion exchange is performed, so that the embedded depth of the optical waveguide is partially changed. A method of manufacturing an optical waveguide, which is characterized in that the optical waveguide is changed.