JPS6017705A - Manufacture of circular optical waveguide - Google Patents

Abstract

PURPOSE:To improve 0.8dB conventional coupling loss due to a difference of a sectional shape to 0.1dB coupling loss in case of connecting an optical fiber and an optical fiber, in case of coupling an optical waveguide to the optical fiber, by obtaining an optical waveguide in which a sectional shape of a core part is roughly circular. CONSTITUTION:The quantity of a cast solution is adjusted so that the film thickness becomes 100mum. Subsequently, gaseous nitrogen is allowed to flow for 100min by 100ml/min in state that a cast vessel 20 is half closed up tightly, and a sheet-like transparent half solid film 28 is prepared. Next, a photomask plate 22 is placed on the film 28. A mask 23 of the center part of this photomask plate 22 is formed along a core pattern width 200mum of an optical waveguide to be prepared, and a pattern of this mask 23 is prepared so that the light transmitting quantity is small in the center and becomes large toward the circumference. Next, ultraviolet rays 27 are generated from an ultraviolet ray exposing device 26. As an outflow time of the gaseous nitrogen elapses, a shutter 20 is opened in the left and right directions, and fully opened in about 50min.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to a method for manufacturing an optical waveguide, particularly a circular optical waveguide.

(B) Prior art and its problems Conventionally, in order to create a guiding waveguide, a polymer optical waveguide has been obtained by selective photopolymerization. To explain one example, as shown in FIG. 1(a), a mask 2 having a width corresponding to the width of the optical waveguide to be created is placed on a film 1 formed by, for example, casting. Irradiate light 3. The part of the film 1 that is not shielded from light by the mask 2 undergoes photopolymerization due to light irradiation, changes its refractive index, and becomes the cladding part 4.The part of the film 1 that is not shielded from light by the mask 2 undergoes no photopolymerization, so the refraction of the base material remains unchanged. This is the core part 5. In the leading waveguide obtained in this way, the refractive index difference -Δn between the cladding part 4 and the core part 5 is slightly smaller on the back surface than on the front surface, as shown in FIG. 1(b). Therefore, the cross-sectional shape of the optical waveguide is rectangular or trapezoidal.

By the way, in the structure of an optical transmission device, an optical waveguide is often coupled with an optical fiber, but as shown in FIG. 2, the core of the optical fiber 6 has a circular cross section, whereas the optical waveguide Since the core portion 7 has a rectangular cross section, there is a problem in that coupling loss occurs due to the difference in cross section. In order to fundamentally solve this problem and eliminate coupling loss, it is better to make the guide waveguide circular in cross section, but the conventional optical waveguide manufacturing method described above cannot produce an optical waveguide with a circular cross section.

(C) Purpose of the Invention An object of the present invention is to provide a method for manufacturing an optical waveguide that can obtain an optical waveguide whose core portion has a circular cross section.

(d) Structure and effect of the invention In order to achieve the above object, the present invention provides a film-like film of a transparent photopolymerization solution whose refractive index changes when irradiated with ultraviolet light. arranging an ultraviolet light irradiation means capable of irradiating ultraviolet light on the film, and continuously changing the timing of light irradiation of the film-like film by the ultraviolet light irradiation means from the center of the back surface of the film-like film toward the periphery; The depth of the photopolymerized portion inside the film-like film from the surface is formed to vary continuously, so that a circular leading waveguide is obtained in the film-like film.

According to this invention, it is possible to obtain an optical waveguide in which the cross-sectional shape of the core portion is nearly circular, so when coupling to an optical fiber, the coupling loss of 0.8 dB due to the difference in cross-sectional shape of the conventional optical fiber can be reduced. Coupling loss for fiber connections: 0.1
It can be improved up to dB. Therefore, long-distance optical transmission and optical information processing are possible with a small light source using optical fibers and optical waveguides.

Next, the principle of adoption of this invention will be explained in Figures 3 to 5.
This will be explained slightly using figures.

FIG. 3 shows the relationship between the change in refractive index after photopolymerization and the evaporation time of the casting solution.

As shown in the figure, the shorter the evaporation time and the smaller the amount of solvent and monomer evaporated, that is, the greater the amount of monomer contained, the greater the change Δn in the refractive index after photopolymerization, and conversely, the longer the evaporation time, the greater the change in refractive index. Δn becomes smaller. That is, for the evaporation time TI<T2<T3, the refractive index change is Δn1>Δn
There is a relationship of 2>Δn3.

Furthermore, the refractive index distribution inside the film also changes depending on the evaporation time.

FIG. 4 shows the refractive index distribution inside the film as a function of evaporation time. When photopolymerized with a short evaporation time,
Although the difference in refractive index at the surface increases, the ultraviolet light does not reach the surface until the scattering due to phase separation between the base material and the monomer becomes large and deep, so the refractive index change occurs only near the surface [Figure 4 (b)]
See T1].

Conversely, if the evaporation time is increased, the change in the refractive index on the surface is small, but since the amount of monomer contained is small, phase separation between the base material and the monomer does not occur significantly, and light attenuation is also small, so the change on the back surface is the same as on the front surface. A slight change in refractive index occurs, resulting in a substantially flat refractive index difference distribution [see T3 in FIG. 4(b)].

From the above, if we change the evaporation time, that is, the timing of photopolymerization by irradiating ultraviolet light, we can obtain the result shown in Fig. 4(a).
As shown in FIG. 4, the boundary position between the core portion 8 and the cladding portion 9 in the depth direction (see TI, T2, and T3 in FIG. 4(a)) can be changed, thereby controlling the cross-sectional shape of the core portion. It turns out that you can do it.

Figure 5 shows the axis center 1 of the film IO forming the optical waveguide.
1 shows the refractive index difference distribution in the axial direction and the depth direction when the photopolymerization timing is continuously changed in the width direction, that is, toward the peripheral portion 12. These refractive index difference distributions in the width direction and depth direction are shown in the axial direction of the optical waveguide, and the photopolymerization is performed at point a at the timing of TI, at point A at the timing of T2, and at point C at the timing of T3. It is something that (TI<T2<73); In the figure, the photopolymerized portion 13 of the film 10 has a lower refractive index than the non-polymerized portion 14, and forms the cladding portion 4.

Therefore, when the core and the cladding boundary are viewed in the cross-sectional direction, a clear boundary line cannot be obtained, but if a certain threshold value (Δns) is set for the refractive index difference, a virtual boundary line such as 15 can be drawn. can. If the photopolymerization timing is controlled so that the curve 15 has a semicircular shape, an optical waveguide having a semicircular cross section can be obtained.

(e) Description of Examples The present invention will be explained in more detail below with reference to Examples.

FIG. 6 is a sectional view showing one embodiment of the present invention. In the figure, 20 is a cast container, and 21 is a cast container 2.
22 is a photomask plate having a mask 23; 24 is a shutter 2;
This is a light shutter plate with 5. The shutter 25 can be moved from the center to the left and right within the optical shutter plate 24 in an analog manner. 26 is an ultraviolet exposure device that generates parallel ultraviolet rays 27.

When manufacturing a circular optical waveguide, a casting solution is first put into the casting container 20. The casting container 20 is pre-cleaned, for example with methylene chloride CH2Cl12, before being filled with the casting solution. For the casting solution, for example, bisphenol Z-based polycarbonate PC is used as the base material.
270g, methyl acrylate MA42mA as monomer
, methylene chloride CH2Cj as solvent! z 1000g
, benzoin ethyl ether BZEE2 as photosensitizer
．． 1g.

A blend of 0.7 g of hydroquinone HQo is used as an inhibiting material.

The amount of casting solution is adjusted so that the film thickness is 100 μm. Further, the liquid level is leveled by adjusting the spirit level 21.

Next, the cast container 20 is semi-closed, and nitrogen gas is flowed at 100 m 1 /min for 100 minutes to evaporate a portion of the solvent and monomer, thereby creating a sheet-like transparent semi-solid film 28 .

Subsequently, the photomask plate 22 is placed on the film 28. The mask 23 in the center of this photomask plate 22 is
It is formed along the core pattern width of 200 μm of the optical waveguide to be created, and the pattern of this mask 23 is created such that the amount of light transmitted is small at the center and large at the periphery.

Next, ultraviolet light 27 is generated from ultraviolet exposure device 26 . However, initially, the shutter 25 is in a fully closed state, and as the outflow time of the nitrogen gas, that is, the evaporation time, passes, the shutter 20 gradually opens to the periphery in both left and right directions. Approximately 5
The opening/closing speed of the shutter 25 is adjusted so that it is fully open in 0 minutes.

When the shutter 25 is first opened, the elapsed evaporation time is short and the amount of monomer contained is large, so a relatively large change in refractive index occurs due to photopolymerization with a small amount of light, but the change is large only in the surface layer. The cladding portion is formed only in a portion shallower than the surface.

Eventually, as the shutter 25 is opened one after another as the evaporation time elapses, the cladding portion is gradually formed deeper. The interface 29 between the core and the cladding is formed in a semicircular shape as shown in the figure. In this process, the mask 23 is configured so that the amount of light transmitted increases from the center to the periphery, and the photopolymerization rate is approximately proportional to the amount of light irradiation, so the photopolymerization rate decreases at the periphery. becomes large, and the refractive index change also becomes large, which helps the interface 29 between the core and the cladding to become semicircular.

After the completion of the exposure in step 2, the cast container 20 is left at room temperature for 30 minutes or more as a post-treatment, and then the cast container 20 is transferred to a vacuum dryer (not shown) and dried at 90° C. for about 10 hours.

Next, as shown in FIG. 7, the surface is coated 193 with a low refractive index coating agent to a thickness of 10 μm.
0 and has a semicircular core portion 31.
The two pieces are stacked one on top of the other so as to form a circular shape, and bonded together using, for example, hot pressing.

This allows easy coupling with a large-diameter optical fiber having a core diameter of 200 μm with low loss.

In addition, in the above example, the case where the film was created by the casting method was explained, but other methods,
For example, the membrane may be created using centrifugal force using a spinner or the like.

In addition, in the above example, a case was explained in which a mask plate and a shack were used to control the photopolymerization conditions, but instead of this, the scanning timing of the laser beam may be controlled to selectively irradiate the light. You can do it like this.

In addition, in the above embodiment, an optical waveguide with a semicircular cross section is first created, and two semicircular optical waveguides are bonded together to create an optical waveguide with a circular cross section. Alternatively, a circular optical waveguide may be integrally formed by simultaneously exposing both sides of the back surface.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining a conventional optical waveguide manufacturing method, and FIG. 1(a) is a cross-sectional view of the conventional optical waveguide, and FIG.
b) is a diagram showing the refractive index difference distribution in the depth direction of the optical waveguide;
Figure 2 is a perspective view showing the coupling of a conventional optical waveguide and optical fiber, Figure 3 is a diagram showing the change in refractive index with respect to the evaporation time of the cast solution, and Figure 4 is a diagram showing the refractive index difference distribution with respect to the evaporation time of the cast solution. FIG. 4(a) is a diagram showing changes in the boundary between the core and cladding with respect to evaporation time;
Figure (b) is a diagram showing the refractive index difference distribution in the depth direction depending on the evaporation time, Figure 5 is a diagram showing the refractive index difference distribution in the width direction and depth direction with respect to the photopolymerization timing, and Figure 6 is a diagram showing the refractive index difference distribution in the width direction and depth direction with respect to the photopolymerization timing. FIG. 7 is a cross-sectional view of a circular optical waveguide manufactured by the same example. 20: Cast container, 23: Mask, 25: Shock, 26: Ultraviolet exposure device, 27: Ultraviolet light, 28: Film membrane (Figure 1 (a) (1)) Figure 2 Figure 3 1 1 1

Claims (1)

[Claims] (1) An ultraviolet light irradiation means capable of selectively irradiating ultraviolet light to any location is arranged on the surface of a film-like film of a transparent photopolymerization solution whose refractive index changes when irradiated with ultraviolet light. The timing of light irradiation on the film-like film by the ultraviolet light irradiation means is continuously changed from the center of the surface of the film-like film toward the periphery, and the depth from the surface of the photopolymerized portion inside the film-like film is A method for producing a circular optical waveguide, wherein the optical waveguide is formed so that the optical waveguide changes continuously to obtain a circular optical waveguide in the film-like film.