Patent Application
20050265664
1. Field of Invention
The invention relates to an optical coupling structure and, in particular, to a coupling structure between a fiber and an optical waveguide.
2. Related Art
Optical waveguides have many advantages such as highly stable, easy for mass production, easy to be integrated, highly sensitive, and unperturbed by electromagnetic waves. Therefore, they can be used in various kinds of environments. Planar lightwave circuits (PLC's) utilize semiconductor processes to make all kings of optical waveguide channels on a plane in order to provide functions of beam splitting, beam merging, and optical switches. Separated devices are integrated in this way on a complete platform to reduce whole module sizes, system complexity, and signal loss, and increase the reliability and yield of the devices.
The PLC uses a silicon chip as the substrate and has three layers of materials with different indices of refraction deposited thereon. The upper and lower layers are cladding layers. The middle layer is the waveguiding layer with a higher index of refraction. How to align and couple an optical waveguide to a fiber on the waveguide chip to transmit optical signals to other optical device and to reduce losses caused by the coupling is an important subject in the field of waveguide chip designs. The coupling between fibers and optical waveguides has been improved continuously. In the beginning, the fiber-waveguide coupling is between a single-channel waveguide and a single fiber. This is easier to be implemented. However, current optical waveguides have evolved toward high-density waveguide arrays. For example, the beam splitter in the optical waveguide is used to split the beam in a fiber to multiple fibers according to predetermined proportions of optical energy. It is also called a coupler. The one-to-many structure of the beam splitter has an input optical waveguide split into several receiving optical waveguides. Therefore, the single-channel waveguide to single fiber method is infeasible.
The coupling method currently used between the PLC and the fiber is to prepare a V-shape groove on an optical waveguide chip by etching. The V-shape groove fixes the fiber so that its kernel lies along a line in order to ensure the matching with the optical waveguide array. However, when a beam enters from the fiber surface to the receiving optical waveguide and from the optical waveguide to the fiber surface, the incident light is perpendicular to the cutting surfaces of them. This generates noisy reflective light from the cutting surfaces that enters the receiving optical waveguide, resulting in non-synchronous resonance. Therefore, optical loss occurs at the alignment coupling between the optical waveguide and the fiber. This affects the optical flux into and out of optical waveguides.
In view of the foregoing, an objective of the invention is to provide a coupling structure between a fiber and an optical waveguide. By preparing an optical waveguide on a substrate and using an aligning groove, a good alignment can be achieved when the fiber is disposed in the groove to align with the optical waveguide, effectively reducing the coupling loss. The interface between the fiber and the optical waveguide has a non-perpendicular angle with the progressing direction of the light. This can avoid the reflection that occurs when the interface is perpendicular to the incident light and the noisy reflection at the cutting surfaces. This can effectively reduce or suppress noises during the transmission process.
The disclosed coupling structure couples the transmitting beam between a fiber and an optical waveguide. It is featured in that the substrate contains an optical waveguide region and a plurality of aligning grooves for containing the fibers. The optical waveguide region is provided with optical circuits and input/output (I/O) surfaces of the optical circuits. The I/O surfaces face the aligning grooves. The optical circuits aim at the positions for coupling with the optical fibers. The terminals of the optical circuits touch the I/O surfaces. A non-perpendicular angle is formed between the I/O surfaces and the progressing direction of the incident light.
Moreover, the cutting surfaces of the aligning grooves and the fibers can have a non-perpendicular angle with the progressing direction of the incident light and be parallel to the I/O surfaces in the optical waveguide region. The angle between the I/O surfaces and the progressing direction of the incident light has two preferred ranges. The angle is between 70 and 90 degrees if it is positive, whereas it is between −90 and −70 degrees if it is negative.
The invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein:
The invention uses a beam splitter made of the optical waveguide as an embodiment. The optical path constructed from the beam splitters and the fibers along with its coupling structure is made on a substrate. It can be used in a fiber communication and other optical systems.
As shown in
The I/O surfaces of the optical waveguide are not perpendicular to the progressing direction of the incident light but may have an arbitrary slant angle. Noisy reflections can thus be greatly reduced.
The input surface and the receiving surface may also have non-perpendicular angle with respect to the progressing direction of the incident light. Here the input surface and the receiving surface are parallel to the I/O surfaces. With reference to
The cutting surfaces of the second aligning groove 231 and the output fiber touch the receiving surface 232. The optical waveguide region 220 is a one-to-many beam splitter. The several optical circuits 223 installed in the optical waveguide region 220 can split the incident light received by the optical input region 210 into several output beams to the optical output region 230. The optical waveguide region 220 has a first I/O surface 221 and a second I/O surface 222. Both ends of each optical circuit 223 touch the first I/O surface 221 and the second I/O surface 222. The first I/O surface 221 and the second I/O surface 222 have an angle about 82 degrees with respect to the progressing direction of the incident light. The input surface 212 of the optical input region 210 is parallel to the first I/O surface 221. The receiving surface 232 of the optical output region 230 is parallel to the second I/O surface 222. Each of the optical circuits 223 is aligned to couple to the corresponding fiber.
The input surface, the receiving surface, and the I/O surfaces of the disclosed coupling structure between a fiber and an optical waveguide can be formed using the semiconductor photolithography process with appropriate masks, followed by etching, or any other machining or body machining method. There are two preferred ranges of the angle between the I/O surfaces and the progressing direction of the incident light. The angle is between 70 and 90 degrees if it is positive, whereas it is between −90 and −70 degrees when it is negative. In the current embodiment, the angle is 82 degrees. Of course, it can be −82 degrees.
Certain variations would be apparent to those skilled in the art, which variations are considered within the spirit and scope of the claimed invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 93115644 | Jun 2004 | TW | national |
