Optical module

Details Optical module Optical module

2001-03-21

2003-12-02

Glick, Edward J. (Department: 2882)

Optical waveguides

With disengagable mechanical connector

Optical fiber to a nonfiber optical device connector

C385S080000, C385S089000, C385S092000

Reexamination Certificate

active

06655856

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical module used for optical communications, for example, an optical module such as an optical transmitter, an optical receiver, an optical demultiplexer, or an optical multiplexer. In particular, it relates to the improvement of a package structure and a portion where optical fibers are fixed.
2. Description of the Related Art
In a prior-art optical module, optical coupling between an optical fiber and an optical device such as a photo diode (PD) and a laser diode (LD) was often achieved via a free space by using a lens. Such a lens is used for focusing light. When the light exits once in the free space, it is effective to provide the lens. Also, since the coupling is made via a free space, problems such as the difference in thermal expansion coefficient between the optical fiber and element, stress, and distortion do not occur. A prior-art example will be described with reference to the optical transmitter and the receiver.
FIG. 1
is a longitudinal section showing an example of the transmitter which is most commonly adopted for practical use. An outer fence comprises a metallic circular stem
1
, a cylindrical metallic lens holder
2
, and a metallic conic ferrule holder
3
. The housing has a shape with an axial-symmetric three-dimensional expanse. A pole
4
is provided on the upper surface of the stem
1
and on the side thereof, an LD
5
is fixed. The LD has its end faces directed in the vertical direction so that light is emitted in the axial direction. An upper surface-illuminated type monitor PD
6
is fixed on the central part of the stem
1
. A cylindrical cap
7
is attached so that the LD
5
and the PD
6
are surrounded. Furthermore, a lens holder
2
is fixed so that the cap is surrounded. A lens
8
is positioned directly above the LD
5
.
A tubular ferrule
9
grasps the tip end of an optical fiber
10
. The ferrule
9
is inserted in a hole on the top portion of the ferrule holder
3
. The axis of the optical fiber
10
exists on the center line of a metallic package (the stem
1
, lens holder
2
, and ferrule holder
3
). That is, the center of the stem
1
, the PD
6
, the LD
5
, the lens
8
, and the optical fiber
10
are lined on the center line. The lens holder
2
and the ferrule holder
3
each having a three-dimensional structure are aligned with respect to the x-y surface and the ferrule
9
is aligned in the z direction, and they are then fixed. Herein, lead pins
11
are terminal ends to connect to an external electric circuit.
This is an example of an LD module, however, a PD module having a similar three-dimensional structure is also used. Herein, illustration thereof is omitted. In either three-dimensional structure, a beam of light is perpendicular to the stem surface and the optical fiber protrudes from the top portion of the package. The ray of light exits from the optical fiber to the free space and enters the optical element, or it exits from the optical element and enters the optical fiber via the free space.
The module having such a three-dimensional structure covered by the metal package is advantageous in that it can shut out external noise, has a long life without being affected by moisture and oxygen in the open air, and also has high reliability.
The present structures of the LD module shown in FIG.
1
and the PD module are excellent. However, there is a considerable number of components, alignment thereof takes much time and labor, and the production cost is high. In addition, they have the drawback of having a large shape. The shape and structure without change has limited cost reduction.
Therefore, in order to achieve further reduction in cost and size, active research and development has been devoted to modules of a surface-mount type, etc. A structure of a module wherein an optical fiber is fixed parallel to a bench surface so that a beam of light is parallel with a substrate surface (package surface) is generally referred to as the surface-mount type. In the surface-mount type, various types are included. In some of the types, a free space (air, vacuum) is provided between an optical fiber and an optical device, and in other types, the space between an optical fiber and an optical device is covered by a resin. The present invention relates to a module wherein the section between the optical fiber and devices is covered by a resin. The object of the present invention is to provide a module that the section between the optical fiber and devices is covered by a resin. Now, a prior art wherein such a section is covered by a resin will be described.
For example, a structure as in
FIG. 2
has been studied. A horizontal Si substrate
12
is mounted on a horizontal package terrace
13
. A Planar Lightwave Circuit (PLC) layer
14
is formed on the Si substrate
12
. This comprises an SiO
2
layer formed thereon by oxidizing the Si substrate or an SiO
2
layer by sputtering. In fact, by doping Ge, etc. on a part of the SiO
2
layer, a part with a high refractive index is linearly formed and it serves as a light guide (waveguide). On the Si substrate
12
, an LD
15
is fixed on an extension of the waveguide (axis). And immediately behind thereof, a PD
16
for monitoring is mounted. This serves to monitor LD power and to maintain the LD power stably.
A fixing portion
17
is provided at the front end of the waveguide, and in a hole
18
thereof, the tip end of an optical fiber
19
is inserted and fixed. The optical fiber
19
, the waveguide, the LD
15
, and the PD
16
are lined up straight on the substrate surface. Light which is emitted from the LD propagates in parallel with the surface of the substrate. Therefore, the structure is referred to as the surface-mount type. A transparent silicone resin
21
covers the terminal end
20
of the waveguide, the LD
15
, and the PD
16
. The light which is emitted forward from the LD
15
propagates through the transparent resin
21
and enters the waveguide terminal end
20
. The light which is emitted rearward from LD
15
propagates through the transparent resin
21
and enters the PD
16
. The light from the LD propagates only through the resin without going out to the free space. Naturally, the resin must be transparent since the light passes therethrough.
However, since the transparent resin
21
lacks moisture resistance and stress resistance, the outside thereof is covered by a black epoxy resin
22
. Since the epoxy resin becomes a hard and solid coating when being hardened, the epoxy resin is excellent in airtightness, mechanical strength, and moisture resistance, etc. Thus, by double-sealing the PD and LD by means of two types of resins with different properties, necessary characteristics such as moisture resistance, stress resistance, and strength are realized, while allowing light to pass therethrough.
The prior-art example of
FIG. 2
has been suggested, for example, in {circle around (1)} “Highly reliable resin-sealed LD-PD module” by Fumio Ichikawa, Mitsuo Fukuda, Yasufumi Yamada, Kuniharu Kato, Koji Sato, and Hiroshi Toba, in the General Convention of the Electronic Society of 1998, C-3-161, p.327.
A silicone resin which is transparent and flexible is used for portions through which light needs to pass such as the PD, LD, and the end of the waveguide. The outside thereof is covered by a strong epoxy resin, whereby environment resistance is enhanced. There are a fewer number of components. Because of the sealing means of the resins, the module is lower in price than a metal package. Because of the surface-mount type, the time and labor for alignment is unnecessary. Since the structure does not have a three-dimensional structure but has a two dimensional structure, a smaller size can be achieved.
While such an element as described above has been newly suggested, it has not yet reached the stage for practical use. If a simple module structure becomes possible, a small and low-price optical module can be provided, so that optical communication may spread widely to ordinary homes.

Affiliated with

Also associated with

Rating

Optical module does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical module, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical module will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3110027