Optical communication device

Details Optical communication device Optical communication device

2001-06-21

2004-05-11

Palmer, Phan T. H. (Department: 2874)

Optical waveguides

With disengagable mechanical connector

Optical fiber to a nonfiber optical device connector

C385S049000, C385S088000, C385S092000

Reexamination Certificate

active

06733190

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical communication device, for example, an optical transmitting device (LED module or LD module), an optical receiving device (PD device), an optical transmitting/receiving device (LD/PD module or LED/PD module), a WDM filter and other optical devices. The aim of the present invention is to reduce the temperature dependence of the optical properties of the optical communication devices.
This application claims the priority of Japanese Patent Application No. 2000-238002 filed on Aug. 7, 2000 which is incorporated herein by reference.
2. Description of Related Art
An example of the most prevalent PD modules is shown in FIG.
1
. The PD module has intrinsically a three-dimensional structure stored in a metallic package. The metallic package has a metallic disc stem
2
having pins
1
below the bottom. A photodiode (PD) chip
4
is mounted via a submount
3
upon the stem
2
. A cylindrical cap
6
having a lens
5
is fixed upon the stem
2
above the PD
4
. A cylindrical sleeve
7
having an opening above the cap
6
is welded upon the stem
2
at a bottom end. A ferrule
8
is inserted into the axial opening of the sleeve
7
. The ferrule
8
seizes an end of an optical fiber
9
. The bottom ends of the ferrule
8
and the fiber
9
are slantingly polished.
An elastic bend-limiter
10
is attached to the top of the sleeve
7
. The optical fiber
9
carries optical signal light from another unit or a station. The signal light emitted from the optical fiber
9
propagates in the space, passes the lens
5
and enters the PD chip
4
at right angles. The sleeve
7
is aligned by giving light to the fiber
9
, moving the sleeve
7
in two-dimensional directions (x and y directions), measuring the light power by the PD
4
and searching the spot which brings the maximum power to the PD
4
, and fixed to the most suitable spot. The positive two-dimensional or one-dimensional alignment is indispensable for such a three-dimensional type module for optimizing the spots of the parts. The ferrule
8
is also aligned in the z-direction by supplying test light to the fiber
9
, moving the ferrule
8
in the axial direction (z-direction) and seeking the spot for giving the maximum power to the PD, and fixed at the most suitable spot. The cap
6
, the sleeve
7
and the ferrule
8
require the alignment. The PD module shown in
FIG. 1
is now the most prevalent module which excels in sensitivity, reliability and life time. A similar metallic packaged LD module is also prevalent in the present optical communication networks. The pervasive modules, however, have weak points of the indispensable alignment, the large size and the high cost. A further progress of the optical communication requires a still more reduction of the sizes and costs of LD modules and PD modules. Recent researches are ardently directed to the planar lightguide circuit (PLC) type optical devices.
{circle around (1)} T. Nishikawa, Y. Inaba, G. Tohmon, T. Uno, Y. Matsui, “Surface Mounting LD Module on a Silicon Substrate”, PROCEEDINGS OF THE 1997 IEICE GENERAL CONFERENCE, C-
3-63
, p248 (1997),
{circle around (2)} Jun-ichi Sasaki, Masataka Itoh, Hiroyuki Yamazaki, Masayuki Yamaguchi, “Si bench for highly efficient optical coupling using passively-aligned spot-size converter integrated laser diode”, PROCEEDINGS OF THE 1997 IEICE GENERAL CONFERENCE, C-3-65, p250 (1997),
{circle around (3)} A. Hirai, R. Kaku, T. Maezawa, K. Takayama, T. Harada, “Silicon V-Groove Substrate for Optical Modules”, PROCEEDINGS OF THE 1997 IEICE GENERAL CONFERENCE, C-3-66, p251 (1997).
These reports propose some kinds of PLC type LD modules and PD modules. These proposed improvements have not been manufactured yet on the practical scale.
An example of the simplest PLC type PD modules is shown in
FIG. 2
(plan view) and
FIG. 3
(sectional view). The PD module
11
has a silicon bench
12
with an upper step
13
and a lower step
14
. The upper step
13
supports an optical fiber
19
and the lower step
14
sustains a PD (photodiode)
15
. The PD
15
is a waveguide type PD having a horizontal waveguide with a horizontal sensing region
22
. The Si bench
12
has V-grooves
16
and
17
formed in the axial direction by anisotropic etching.
The fiber
19
is partially held by a ferrule
18
. The ferrule
18
and the fiber
19
are fixed upon the V-grooves
16
and
17
. Another end of the ferrule can be attached to or detached from another optical device. The end
20
of the optical fiber is vertical to the light axis. Light
21
emanating from the end
20
of the optical fiber
19
enters the front end
23
of the PD
15
, propagates in the waveguide sensing region
22
and induces photocurrent in the PD
15
. The photocurrent is the receiving signal. In the module, the LD is mounted on the same substrate as the PD. The core of the fiber
19
and the sensing region
22
of the PD
15
lie horizontally on a straight line. The PD module
11
is built without alignment. Exclusion of the alignment reduces the cost of manufacturing the PD module
11
. Elimination of the lens decreases the part cost. Thus, the module would be a small sized inexpensive PD module. A similar PLC type LD module can be obtained in a similar manner by replacing the PD by an LD in FIG.
2
and FIG.
3
.
The prior art of the figures places the optical parts (the PD
15
, the ferrule
18
and the fiber
19
) on the Si bench
12
horizontally. The fiber
19
is directly coupled to the PD
15
without lens, which reduces the number of parts and the size of the module.
The example makes use of the optical fiber
19
as a medium for introducing the signal light to the module. The optical fiber can be replaced by a light waveguide. The waveguide (front end incidence) type PD can be also replaced by a top-incidence type PD or a bottom-incidence type PD. The situation is similar to the LD module which emits signal light toward the fiber.
The prior art of PLC type modules make V-grooves by anisotropic etching on the single-crystal silicon bench and prints positioning marks on the silicon bench for determining the position of a PD chip or an LD chip. The V-grooves and the positioning marks enable the manufacturers to mount the PD, the LD and the fiber at the desired positions with accuracy. The mounting of the parts at the spots in accordance with the guidance of the marks or the V-grooves is called “passive alignment” in contrast to the active alignment of the prior art of FIG.
1
. The passive alignment enables the PLC type module of FIG.
2
and
FIG. 3
to reduce the cost of assembly, the cost of parts and the cost of packaging.
The prior art of FIG.
2
and
FIG. 3
has an apparent drawback of the big refractive index difference among the fiber, the PD and the air gap. The large refractive index difference would induce strong reflection at the boundaries of the air and the PD or the fiber. The reflection would arise the difficult problem of the returning light to the LD as well as the energy loss by the reflection. The reflection loss increases in proportion to the square of the refractive index difference. The LD returning light induces instability of the LD oscillation.
An ordinary remedy for reducing the reflection is to fill the air gap between a fiber end
26
and the PD (or LD) with a transparent resin
24
, as shown in
FIG. 4
or FIG.
5
. The transparent resin
24
prevents the signal light from reflecting at the fiber end
26
. Silicone-type resins or acrylate-type resins having a refractive index nearly equal to the fiber refractive index (n=1.4~1.5) are often chosen as the transparent resin. The reflection is reduced nearly to zero at the fiber end since the transparent resin has a refractive index akin to the fiber. Someone have proposed such contrivances of filling the resin for reducing the reflection at the fiber end.
{circle around (4)} Japanese Patent Laying Open No. 7-181343, (181343/'95) “Optical waveguide part and manufacture of the same”, suggested a PD module hav

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