JPS6237362B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a connection between an optical fiber and an optical thin film line (hereinafter referred to as a thin film line).

Conventionally, various methods have been proposed for introducing light into thin film lines. FIG. 1 shows a thin film line 12 provided on the surface of a substrate 11 using a prism coupler.
A prism 13 is placed on the upper surface of the light beam with a gap of about a fraction of the wavelength of light therebetween. (Generally, the gap may be a transparent layer with a refractive index smaller than that of the thin film lines 12 and 13.) The light is focused into a beam of an appropriate spot size, and the thin film line 12 is removed from the bottom surface of the introducing prism 13 as shown by the arrow. incident at an angle that causes total internal reflection. In the state of total reflection, the electromagnetic field of light decreases exponentially below the bottom of the prism 13, but the thin film line 1
2 is close to the bottom surface, the light passes through the thin film line 12. If the incident angle is selected so that the propagation constant in the Z direction (as shown) in the prism is equal to the propagation constant of one propagation mode traveling in the thin film line, light energy is efficiently coupled into the thin film line. Second
The figure shows a method using a phase grating. A dielectric phase grating 23 is formed on the upper surface of a thin film line 22 provided on a substrate 21 . The light beam (arrow) obliquely incident on the phase grating 23 has a spatial phase variation in the Z direction. Since the light beam is given a different phase delay depending on the passing location while diagonally passing through the phase grating 23, when it reaches the upper surface of the thin film line 22, there are many waves having distinct spatial phase fluctuations in the Z direction. The waves become superimposed. By appropriately selecting the angle of incidence, if the phase variation of one of these waves is matched with the phase variation of the propagation mode of the thin film line, the wave of that propagation mode is selectively excited into the thin film line.

All of the conventional coupling methods described above have the following drawbacks.

b. A coupler (for example, a prism or a phase grating) is required on the thin film line.

(b) In order to efficiently couple the incident beam to the fine thin film line, it is necessary to focus the incident beam appropriately.
When using a short focal length lens such as a conventional microscope objective lens, the lens must be brought very close together, but this approach is very difficult due to the lens support frame.

Next, as a method of simply introducing light directly from an optical fiber to a thin film line without using an optical coupler, as shown in FIG. It is conceivable to condense light in the thickness direction of the thin film line 32 by utilizing reflection at 35 and refraction (immediate lens action) between the fiber crat 33 and air.
In this case, the fiber core 34 is
Since the diameter of the fiber core is quite large, the light emitted from each point of the fiber core, for example, 1, 2, and 3, is focused at different positions such as 1', 2', and 3'. Therefore, the coupling efficiency is low.

In order to eliminate the above-mentioned drawbacks, the present invention has been devised so that the tip of the optical fiber has a special shape, and the light emitted from the multimode optical fiber is condensed to increase the coupling efficiency, and the light is directly input to the thin film line. This is what was done.

In order to achieve this object, the present invention provides an optical fiber and a thin film line perpendicular to the optical fiber, the tip of the core glass of the optical fiber is deformed into an elongated shape, and the tip of the optical fiber is parallel to the elongated shape. It has a slope that crosses the core glass diagonally, and on the side of the optical fiber glass opposite to the slope, the long direction of the thin film line is perpendicular to the above-mentioned elongated shape, and it is further reflected by the slope. The thin film line is arranged so that the emitted light is incident on the thin film line.

The present invention will be explained in detail below with reference to the drawings.

In the present invention, as shown in FIG. 4, if the shape of the core glass at the tip of the optical fiber is approximately a long and narrow straight line as shown at 44, and the tip of the optical fiber is made oblique as shown at 45, the light emitted from the core glass 44 will be The points corresponding to points 1, 2, and 3 in FIG. 3 are approximately equidistant when viewed from the surface that acts as a lens due to the difference in refractive index with the outside of the optical fiber 43, that is, air, so the shift in the light convergence point is greatly reduced. At this focal point, Figure 4b
As shown in FIG.
The thin film line 4 is perpendicular to the long axis 42a of the
By placing the second end face, high coupling efficiency can be achieved. FIG. 5 shows one embodiment of processing an optical fiber to achieve the objectives of the present invention. First, as shown in Figures a and b, an optical fiber 69 is sandwiched between glass rods 66 and 67 having the same outer diameter and the same quality, and is pulled while being heated by arc discharge or flame. Then, as shown in Figure c, the clads 66, 67 and the clad 69 are integrated, and the outer periphery near the center, that is, near the D-D line, becomes circular. The core glass therefore has an elongated shape as shown at 64. The core glass is polished along line D-D parallel to the long axis of the longest core glass and diagonally across it as shown in Figure e. This allows the optical fiber to be shaped to suit the purpose of the present invention. The initial objective can be achieved by setting the end face of the thin film line 62 as the focal point as shown in figures f and g. In addition, as another optical fiber processing method, as shown in FIG.
7 may be placed. Then, the end face processed in the same manner as in FIG. 5 described above will have an elongated core glass shape as shown in FIG. 6d, but this is due to the shape above the center of the optical fiber glass. Also, by changing the outer diameter of the glass rods that are bundled together, the outer diameter that acts as a lens can also be controlled. Such a modification can be made into an optimal configuration depending on the parameters of the optical fiber, and this method can also be applied to a single molded fiber.

As described above, according to the present invention, when an optical fiber and a thin film line are coupled, it is possible to easily couple them with high efficiency without providing a coupler on the thin film line or using short focal length lenses. Therefore, it is very effective.

[Brief explanation of the drawing]

FIGS. 1 and 2 are side views showing a conventional method of coupling light to a thin film line. Figure 3 shows a conventional method of coupling light to a thin film line, where a is a plan view and b is an A-A
A cross-sectional view along the line. FIG. 4 shows a coupling structure from an optical fiber to a thin film line according to the present invention; a is a plan view, and b is a sectional view taken along the line B-B. FIG. 5 is a process diagram for producing the optical fiber used in the present invention, in which a is a side view of the optical fiber sandwiched between glass rods of the same diameter and the same quality, and b is a front view of a. c is a side view of the optical fiber, etc. in a, heated and stretched, and d is c.
A cross-sectional view taken along line C-C. e is a side view of the optical fiber in c polished obliquely along the C-C line, f and g are layout views in which the optical fiber in e and the thin film line are combined, and f is a plan view thereof. g is a sectional view taken along line D-D of f. FIG. 6 is another example of the optical fiber used in the present invention, and a is a side view of the optical fiber before processing with a glass rod of the same quality and diameter placed underneath it. b is a front view of a.
c is a side view after processing. d is a front view of c.

Claims (1)

[Claims] 1 The core at the tip of the optical fiber is deformed into an elongated shape, and the tip of the optical fiber has a slope that is parallel to the long axis of the aforementioned core and crosses the core diagonally, and the tip of the optical fiber on the opposite side of the slope A light characterized in that the optical thin film line is arranged on the cladding side in a direction in which the long axis of the optical thin film line is perpendicular to the long axis of the core, and the light reflected on the slope is incident on the optical thin film line. Fiber coupling device.