Laser diode module

Details Laser diode module Laser diode module

2001-10-05

2003-06-10

Juba, Jr., John (Department: 2872)

Optical waveguides

With disengagable mechanical connector

Optical fiber to a nonfiber optical device connector

C385S014000, C385S049000, C372S032000, C257S098000

Reexamination Certificate

active

06575641

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a laser diode (LD) module of optical communications system relying upon optical fibers.
This application claims the priority of Japanese Patent Application No. 344843/2000 filed on Nov. 13, 2000 which is incorporated herein by reference.
2. Description of Related Art
FIG. 26
shows an axially-symmetric metal-canned laser diode (LD) module which is one of the most prevalent laser diode modules at present. The predominant LD module has a circular metallic stem
80
having an erect pole
84
on the top, lead pines
90
projecting from the bottom of the stem, an LD chip
85
mounted in a vertical posture on the front wall of the pole
84
, a monitoring photodiode (PD)
86
bonded on the stem beneath the LD
85
, a cylindrical metallic cap
83
covering the LD
85
and the PD
86
, a cylindrical metallic lens holder
81
having a lens
87
and being fitted upon the stem
80
and a conical metallic ferrule holder
82
with a ferrule
89
holding an optical fiber
88
and being soldered on the lens holder
81
. The monitoring photodiode
86
is a “top incidence” type PD which allows light to enter via a top opening around a ring p-electrode.
In the prior art metal-canned LD module, the lens
87
, the LD
85
and the monitoring PD
86
align along an extension of the optical fiber
88
. The metallic lens holder
81
, the metallic stem
80
and the metallic ferrule holder
82
are all rotationally-symmetric around the axial line of the optical fiber
88
. An IC
91
for driving the LD
85
is fitted upon a print circuit board
92
comprising an epoxy board, copper wiring patterns
93
printed on the epoxy board and many bores. The lead pins
90
are inserted in holes and soldered to wiring patterns of the print circuit board. The IC connected wiring patterns are joined to the electrodes of the LD driving IC
91
. The LD driving IC
91
supplies pulse signal currents to the LD
85
.
The metallic stem
80
, the metallic lens holder
81
and the metallic ferrule holder
82
build a metallic package. The path of the light is in parallel to the axial line of the metal package. The monitoring PD
86
, the LD
85
, the lens
87
and the fiber
88
align along the axial line of the package. The metallic package repulses electromagnetic noise. The metal case has also high resistance against water and oxygen. Thus, the metal encapsulated LD module is an excellent device endowed with high reliability and long life time.
The vertically sustained LD
85
emits light in both upward and downward directions. The upward light from the LD
85
transmits signal light which is introduced by the lens
87
into the fiber
88
. The downward light from the LD
85
is power-monitoring light which is sensed by the monitoring PD
86
. The LD power is sent from the monitoring PD
86
to the LD driving IC
91
. The LD driving IC
91
controls the LD via a feedback circuit for maintaining a constant output power in spite of a change of the surrounding temperature or degradation due to aging. The LD driving IC
91
has a function of adjusting the LD power in addition to the role of making signal pulse currents.
The metallic package has a three dimensional structure having the lead pins protruding from the bottom and the fiber at the top. The light progresses in the direction orthogonal to the stem. The signal light from the LD propagates in the space, the lens and the space in series to the fiber. The space propagation disperses the light. The lens is indispensable for converging the dispersed light. The discrete parts should be allocated to the optimum positions which allow the LD to inject the maximum power into the fiber. The optimum positions are determined by measuring the output power at another end of the fiber with displacing the lens holder, the ferrule holder in the x-, y- and z-directions with respect to the stem. The process of allotting the parts to the most suitable spots is called “alignment”.
The print circuit board
92
sustains the LD driving IC
91
. The LD
85
is stored in the metallic case. The LD
85
and the LD driving IC
91
are separated. Drawbacks accompany the prevalent LD module containing the metal cased LD module and the circuit board loaded LD driving IC. The current LD module is bulky, since it contains the print circuit board for maintaining the LD driving IC. The module requires many discrete elements, which raises the parts cost and the assembling cost. The existence of the discrete elements impedes miniaturization of the modules. High cost and big size of the modules inhibit the optical communications networks from prevailing on a large scale. Further development of the optical communications requires miniaturization and cost reduction of the necessary devices.
Planar lightguide circuit (PLC) type optoelectronic modules have been proposed for the sake of propelling miniaturization. Various types of PLC modules have been suggested till now. The proposed PLCs are all still suffering from some difficulties. There are no PLC devices satisfying all the basic requests yet.
{circle around (1)} German Patent DE 43 13 492 C1, “Anordnung zur Ankopplung eines optoelektronischen Empfangselementes an ein optoelektronisches Sendeelement”, proposed an LD module which employs a bottom incidence type PD as a monitoring photodiode (PD). The newly proposed PLC LD module has a silicon substrate with a front V-groove and a rear V-groove dug along the central line of the substrate, an LD chip mounted upon a plateau between the front and the rear V-grooves, a cylindrical lens mounted on the substrate before the front V-groove, an optical fiber directly joined to the lens and a monitoring PD over the rear V-groove on the substrate. On the silicon substrate, the fiber, the cylindrical lens, the front V-groove, the LD, the rear V-groove and the monitoring PD align in series from the front to the back. The LD chip emits signal light in both directions from the front end and the back end. The front light is converged by the lens and is introduced into the fiber. The rear light emanating from the LD is power-monitoring light which is reflected by banks or an end mirror plane of the rear V-groove and is guided into the PD via the bottom. The bottom incidence type PD requires a change of light path. The rear V-groove having the banks and the end mirror respond the request. The beam line of the LD is parallel to the central line of the silicon substrate. Unlike the previous LD module as shown in
FIG. 26
, the PLC type module has two dimensional character, which simplifies the structure of the package. The most significant advantage is to eliminate the time-consuming positive alignment. The position of the fiber is definitely positioned by the V-groove and the positions of the LD and PD are exactly determined by marks attached on the substrate. The simplified structure is favorable for miniaturization. The rear V-groove enables the bottom incidence PD to catch nearly half of the rear light emanating from the LD in the rear direction. The prior art had no LD driving IC on the substrate. Like the previous art of
FIG. 26
, the LD driving IC would be mounted upon another print circuit board and would be joined to the LD by wiring patterns and bonding wires.
{circle around (2)} Y Akahori, T. Ohyama, M. Yanagisawa, Y Yamada, H. Tsunetsugu, Y Akatsu, M. Togashi, S. Mino and Y. Shibata, “A HYBRID HIGH-SPEED SILICA-BASED PLANAR LIGHTWAVE CIRCUIT PLATFORM INTEGRATING A LASER DIODE AND A DRIVER IC”, ECOC 97, Sep. 22-25, 1997, Conference Publication No. 448, IEE, 1997, p 359-362 proposed an improvement of loading LDs and a driving IC on a silicon bench.
FIG. 1
of {circle around (2)} is shown as
FIG. 27
here. An LD
96
is one of an LD array which includes a plurality of LD chips. The LD array is driven by a single driving IC
97
. The transmitting distance is very short of several meters to several tens of meters. The signal repetition rate is 9 Gbps. The LD driving IC
97
is positioned just behind the LD
96
for ensuring the high sign

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