JPH0371684B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to optical circuit elements. More specifically, the present invention combines an optical waveguide such as a thin film waveguide and an optical fiber with their end faces,
The present invention relates to an optical fiber coupler for coupling light transmitted through an optical fiber into an optical waveguide without coupling loss.

Background of the Technology In the field of optical communications, various optical circuit elements for use there are being researched and developed. In particular, photoconductive path technology is attracting attention in order to miniaturize and mass-produce such devices. One type of optical waveguide device that uses such optical waveguide technology is the optical fiber coupler that will be discussed here. As is well known, an optical fiber coupler is used to couple an optical waveguide (although an optical fiber is also a type of optical waveguide, here we specifically refer to a thin film waveguide) and an optical fiber.

Prior Art and Problems Conventionally, various techniques have been used to couple optical waveguides and optical fibers. The most common method is to connect directly. However, although this method has the advantage of being simple, it has the disadvantage that the coupling loss of light reaches about 20 to 30%. This is because the intensity distribution of the light generated at the end face of the optical fiber, the so-called near-field pattern (hereinafter referred to as NFP), is naturally different from that of the light excited at the end face of the optical waveguide, and therefore, the intensity distribution of the light that is excited at the end face of the optical waveguide is different. This is because an impossible light will come out.

In order to facilitate the incidence of light into the optical waveguide, for example, Roddons is placed between the optical waveguide and the optical fiber.
Attempts have also been made to incorporate optical systems such as Gooded lenses to focus the light output. however,
This method only complicates the system and does not significantly reduce coupling loss. This is because, like the direct connection method explained earlier, no matter how much light is narrowed down, the NFP remains as it is, and cannot become asymmetrical like an optical waveguide. Attempts have also been made to process the end face of the optical fiber into a spherical shape and give that part a lens effect, but this method, like the conventional method described above, does not allow for matching between the NFP of the optical waveguide and that of the optical fiber. Therefore, it is not possible to achieve the expected reduction in coupling loss.

In any case, if the optical coupling loss is large like this, the merit of using an optical waveguide here, that is, the significance of miniaturizing optical circuit elements and making them microscopic, will be negated as a result. becomes.

Object of the invention The object of the invention is to couple an optical waveguide and an optical fiber formed on a substrate,
An object of the present invention is to provide an improved optical fiber coupler in which there is almost no coupling loss of light, or even if there is, it is very small because both NFPs are matched, and the system is not complicated. .

Structure of the Invention As a result of research to achieve the above object, the present inventors processed the tip of an optical fiber and
It has also been found that it is appropriate to make the NFP resemble the NFP of an optical waveguide formed on a substrate. That is, the optical fiber coupler according to the present invention is characterized in that the cladding layer of the optical fiber is obliquely polished to maximize the end face portion thereof.

When obliquely polishing the cladding layer of an optical fiber, it is preferable that the polishing angle is several degrees or less, particularly 5 degrees or less. However, the angle of this polishing can be arbitrarily changed depending on various factors such as the thickness of the cladding layer and the desired NFP. The polishing operation can be carried out according to conventional methods, for example by optical polishing.

Embodiments of the invention The invention will now be described with reference to the accompanying drawings.

Figure 1 shows the optical intensity distribution (NFP) of propagating light in an optical fiber and at its end face. 1 in the diagram
is the core that makes up the center of the optical fiber,
A cladding layer 2 surrounds this. It will be understood from the figure that the NFPx of the optical fiber can be approximated by a symmetric Gaussian distribution.

On the other hand, the NFP of a diffusion type optical waveguide such as a LiNbO ₃ optical waveguide is as shown in FIG. 3 in the figure is a NiNbO ₃ substrate, and Ti
An optical waveguide 4 is embedded. of optical waveguide 4
NFPy is asymmetric, as shown. In particular, from this figure, Δn on the air side of the optical waveguide 4 suddenly becomes O
It can be seen that it converges to . Therefore, when the optical fiber shown in Figure 1 is coupled to this waveguide, the NFP of the two is essentially different, so
A binding loss of approximately 20-20% must be accepted.

Conventionally, in order to increase the incidence efficiency of light into the optical waveguide, a rod 5 (Fig. 3) was interposed between the optical waveguide and the optical fiber, or the tip of the optical fiber was processed to form a tip 6 (Fig. 4). ) is used. However, even with such improvements, no significant improvement can be expected compared to the case of direct contact.

The present invention proposes obliquely polishing the cladding layer 2 of the optical fiber to align the NFP of the optical fiber with the NFP of the optical waveguide, as shown in FIG. S in the figure is a polished surface.

In fact, when the cladding layer 2 of the optical fiber is obliquely polished at a polishing angle θ so that the cutting area of the end face portion thereof is maximized, an NFP as shown in FIG. 6 is obtained. From this figure, in line segment D-D,
The NFPd is symmetrical as in Figure 1 because the cladding layer in that part is not obliquely polished at all, and as the degree of oblique polishing increases, i.e., line segment C-C, line Minute B-B,
It can be seen that as the line segment changes from A to A, the degree of asymmetry gradually increases (c, b, a in the figure).
According to the present invention, after completion of diagonal polishing,
While measuring the NFP, the optical fiber can be cut perpendicular to the optical axis at any location that exhibits an NFP that matches the NFP of the optical waveguide to be coupled.

When the cut optical fiber is coupled to an optical waveguide, it becomes as shown in FIG. In a fiber optic coupler such as that shown, coupling losses can be reduced to nearly zero, or at least very close to zero.

Effects of the Invention According to the present invention, good coupling between an optical waveguide and an optical fiber can be easily achieved without complicating the system. . Furthermore, according to the present invention,
Since the oblique polishing of the optical fiber is suppressed to a few degrees or less, mode conversion loss can be reduced.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing an optical fiber NFP.
Figure 2 is a schematic diagram showing NFP of optical waveguide, Figure 3
4 and 4 are respectively schematic diagrams showing an example of a conventional optical fiber coupler, FIG. 5 is a perspective view showing oblique polishing of an optical fiber according to the present invention, and FIG.
The figure is a schematic diagram showing the NFP of the optical fiber of FIG. 5, and FIG. 7 is a schematic diagram showing an example of the optical fiber coupler of the present invention. In the figure, 1 is the core, 2 is the cladding layer, 3 is the substrate,
And 4 is an optical waveguide.

Claims (1)

[Claims] 1. An optical fiber coupler for coupling an optical waveguide formed on a substrate and an optical fiber, comprising:
An optical fiber coupler characterized in that the cladding layer of the fiber is obliquely polished to maximize the end face portion thereof. 2. The optical fiber coupler according to claim 1, wherein the angle of the diagonal polishing is 5 degrees or less.