Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
1998-12-31
2001-07-31
Font, Frank G. (Department: 2877)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C356S004050
Reexamination Certificate
active
06267515
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical coupling module suitable for use in terminal stations in optical telecommunications and also to a method of manufacturing the same.
2. Related Art
Recently, a project called “Fiber to the Home” has been in progress, which is extending optical fibers up to individual homes for optical communications with a large traffic capacity.
Under this project, multiplexed light having component beams of wavelength bands of 1.3 &mgr;m and 1.55 &mgr;m, for example, is sent to communication terminals of individual homes.
As optical elements in optical devices at terminal stations to receive multiplexed light such as mentioned above, it has been proposed to use CGH (Computer Generated Hologram) elements as described in the specification of Japanese Patent Application No. 9-147115 (referring to U.S. Ser. No. 09/081,080), for example.
The CGH elements are optical elements manufactured by using a computer program, and therefore those high-precision optical elements can be mounted in compact form on an optical substrate.
If the CGH elements are adopted, it becomes possible to mount optical elements in a compact form on a multi-layer structure of optical substrates. Those optical elements mounted include an optical demultiplexing element to separate the multiplexed light into rays of different wavelengths, or an optical coupling element to separate or couple a ray of one wavelength obtained by demultiplexing.
Therefore, by connecting optical functional elements, that is, a light-emitting element such as a semiconductor laser, and a light-detecting element such as a photodiode, to an optical device formed by a multi-layer structure, it is possible to produce an optical coupling module suitable for optical communication terminal stations capable of bi-directional communications.
For an optical coupling module mentioned above, a semiconductor substrate is generally used. One surface of a semiconductor substrate is polished to a mirror finish by a chemical and mechanical etching to improve the flatness. An optical functional element, such as a semiconductor laser or a photodiode is mounted on the mirror-finished surface of the semiconductor substrate. The optical device is supported on the semiconductor substrate that has the optical functional elements mounted thereon so that the optical functional elements on the semiconductor substrate are optically coupled to the optical device.
When a semiconductor laser is used as an optical functional element, a semiconductor laser of the end face emission type is generally adopted. Therefore, if such an end face emission type optical functional element is mounted on the mirror-finished surface of a semiconductor substrate, light from this optical functional element is emitted in a direction parallel with the mirror-finished surface of the semiconductor substrate, and the optical device, optically coupled to the semiconductor substrate to receive the emitted ray, is supported at the end face of the semiconductor substrate, which has the optical functional element mounted thereon, to form a module of a compact structure.
Because the above-mentioned end face of the semiconductor substrate is a cleavage plane and is not mirror-finished like the surface of the substrate, the flatness of the end face is very bad.
Therefore, when connecting the semiconductor substrate, on which an optical element is mounted, to the above-mentioned optical device supported to the end face of the substrate, the alignment work to align the optical axis of the optical device with the optical functional elements invariably requires three-dimensional adjustment. Therefore, this alignment work is not easy.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an optical coupling module, which is suitable for optical communication terminal stations, facilitates the alignment work and enables reductions in production cost, and to provide a manufacturing method of such a module should be established.
The inventor set eyes on a possibility of better use of the superb flatness of the mirror-finished surface of a semiconductor substrate on which an optical element is mounted, and has made the present invention to solve the above-mentioned problems by utilizing the flat surface to support an optical device optically coupled to the optical functional elements mounted on that surface.
According to the present invention, an optical coupling module comprises a semiconductor substrate having a mirror-finished surface and having mounted on the mirror-finished surface an optical functional element with its optical functional face kept substantially parallel with the mirror-finished surface and with a reverse face, opposite the optical functional face, facing the mirror-finished surface ; and an optical device, which is supported on the mirror-finished surface of the semiconductor substrate in such a way that the optical device is optically coupled to the optical functional elements.
According to the present invention, the optical device optically coupled to the optical functional elements mounted on the semiconductor substrate is supported by the mirror-finished surface of the semiconductor substrate with an excellent flatness obtained by mirror finish. Therefore, in aligning, in other words, positioning the optical device on the semiconductor substrate, the optical device can be placed at a correct position relatively easily by fine adjustment of its position along the (x, y) plane, that is, on the mirror-finished surface.
Thus, it is not necessary to perform three-dimensional adjustment as in alignment in the past. Because the alignment work becomes easy, it can be done by a mechanical process and in an intensive manner.
In order to perform mechanical alignment work, a set of alignment marks to indicate the optimum position for optical coupling may be attached to the mirror-finished surface of the semiconductor substrate and to the end face of the optical device that faces that surface of the semiconductor surface.
The use of the alignment marks showing the optimum position for optical coupling obviates the need of what is called active alignment to adjust the positions of the optical parts according to the actual behavior of light when the optical system including the optical device is in operation. Furthermore, by the use of the alignment marks, the alignment work can be done by what is called passive alignment, which is a mere matching work of the alignment marks in mounting the optical parts. In this way, the alignment work, including the adjustment of the optical axes of the optical device and the optical functional element, becomes all the more easy.
A recess may be formed in the mirror-finished surface so that the optical functional element can be accommodated in the recess. A light-detecting element with a light detection surface of the so-called surface detection type may be used as an optical functional element accommodated in the recess.
The above-mentioned recess for accommodating the optical functional element may be formed by etching the surface of the semiconductor substrate. By chemical etching on the semiconductor substrate, a predetermined recess can be formed relatively easily with high accuracy.
A plurality of light-detecting elements respectively coupled to the optical device may be aligned in the recess.
As an optical functional element optically coupled to the optical device, a light-emitting element of the end face emission type may be used. In addition, a light-detecting element and a light-emitting element respectively coupled optically to the optical device may be arranged in the recess.
To facilitate positioning of the light-detecting element and the light-emitting element in the recess, alignment marks may be attached to the bottom of the recess.
As the alignment marks, the electrodes for optical functional elements formed by photolithography may be used.
To guide a light from an end face emission type light-emitting element, emitted in para
Katsuki Yoichiro
Okuda Keiji
Font Frank G.
Frank Robert J.
OKI Electric Industry Co., Ltd.
Stafira Michael P.
Venable
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