Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
2002-01-02
2003-12-23
Davie, James (Department: 2828)
Coherent light generators
Particular beam control device
Optical output stabilization
Reexamination Certificate
active
06667997
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical module used in a transmitter for transmitting optical signals, such as a semiconductor laser module or the like, and a method of making the same. The present invention particularly relates to an optical module suitable for use in a light-signal transmission in a wavelength division multiplexing (WDM) communication system and a method of making the same.
2. Discussion of the Background
Generally, the field of dense WDM requires optical transmitters to produce light-signals at stable wavelengths for a long time. To accomplish this, it has been developed an optical module that includes a wavelength monitor located in the package thereof. One of the prior art optical modules including the wavelength monitor is disclosed, for example, in Japanese Patent Laid-Open Application No. Hei 12-56185.
Referring first to
FIG. 20
, there is shown an optical module constructed according to the prior art and having a wavelength monitor. The optical module includes a laser diode
50
for outputting a laser beam with a predetermined wavelength; an optical fiber
51
optically coupled with the laser diode
50
and adapted to externally deliver the laser beam outputted from the laser diode
50
at its front end face (right side as viewed in FIG.
20
); an optical filter
52
having its cutoff wavelength substantially equal to the lasing wavelength of the laser diode
50
; a beam splitter
53
including a half mirror for dividing a monitoring laser beam outputted from the laser diode
50
at its back end face (left side as viewed in
FIG. 20
) into two laser beam components; a first photodiode for receiving one of the two laser beam components divided by the beam splitter
53
after it has passed through the optical filter; a second photodiode
55
for receiving the other laser beam component from the beam splitter
53
; a Peltier module
56
for regulating the temperature in the laser diode
50
; and a control unit
57
for controlling the Peltier module
50
to control the wavelength in the laser diode
50
, based on PD currents outputted from the first and second photodiodes
54
,
55
.
Between the laser diode
50
and the optical fiber
51
is disposed a condensing lens
58
for coupling the laser beam from the front end face of the laser diode
50
with the optical fiber
51
. Between the laser diode
50
and the beam splitter
53
is also disposed a collimating lens
59
for collimating the laser beam outputted from the back end face of the laser diode
50
.
The laser diode
50
, condensing lens
58
and collimating lens
59
are fixedly mounted on an LD carrier
60
. The first and second photodiodes
54
,
55
are fixedly mounted on first and second PD carriers
61
,
62
, respectively.
The beam splitter
53
, optical filter
52
and first and second PD carriers
62
are fixedly mounted on a metallic base plate
63
that is fixedly mounted on the surface of the LD carrier
60
. The LD carrier
60
is fixedly mounted on the Peltier module
56
.
The laser diode
50
, beam splitter
53
, optical filter
52
, condensing lens
58
, collimating lens
59
, LD carrier
60
, first PD carrier
61
, second PD carrier
62
, metallic base plate
63
and Peltier module
56
are housed within a package
64
. The tip end of the optical fiber
51
is held by a ferrule
65
that is fixedly mounted on the side of the package
64
through a sleeve
66
.
The laser beam outputted from the front end face of the laser diode
50
is condensed by the condensing lens
58
and then enters the optical fiber
51
held by the ferrule
65
before it is externally delivered therefrom.
On the other hand, the laser beam outputted from the back end face of the laser diode
50
is collimated by the collimating lens
59
and then enters the beam splitter
53
wherein the laser beam is divided into two laser beam components, directed to a Z-axis direction (or direction of transmission) and an X-axis direction, (or direction of reflection) perpendicular to the Z-axis direction. The laser beam component directed to the Z-axis direction is subjected to wavelength filtering by the optical filter
52
, and is then received by the first photodiode
54
while the laser beam component directed to the X-axis direction is received by the second photodiode
55
. PD currents outputted from the first and second photodiodes
54
,
55
enter the control unit
57
that, based on the received PD currents, controls the temperature in the Peltier module
56
to control the wavelength in the laser diode
50
.
In the conventional optical module that contains the wavelength monitor, the first and second photodiodes
54
,
55
are for respectively receiving the divided laser beam components and cannot be arranged in the same plane since the laser beam is divided by the half-mirror type beam splitter
53
into such two laser beam components directed to the Z-axis direction and X-axis direction perpendicular to the Z-axis direction. Thus, the prior art device, as recognized by the present inventor, must use two separate PD carriers
61
and
62
for fixedly supporting the first and second photodiodes
54
,
55
. As a result, the number of parts increases to raise the manufacturing cost.
The half-mirror type beam splitter
53
has a wavelength dependency since the laser beam is divided into two laser beam components, one reflected by the mirror and one transmitted the mirror. The dense WDM particularly requires high-precision wavelength control of laser beam. As recognized by the present inventors, the wavelength dependency on the laser beam components divided by the half mirror may lead to error in the wavelength control.
Each of the two PD carriers
61
and
62
must independently be subjected to optical aligning. As a result, the number of manufacturing steps increases to prolong the manufacturing time.
Moreover, the wavelength characteristic of the optical filter
52
is variable depending on the angle of incident light. Notwithstanding, the prior art device fixedly mounts the optical filter
52
on the metallic base plate
63
and incorporates the metallic base plate
63
into the optical module before the wavelength monitor unit is completed in assembly. In such a procedure, the set angle of incident light relative to the optical filter
52
can not be changed after the wavelength monitor unit has been incorporated into the optical module. This is disadvantageous in that any desired wavelength characteristic of the optical filter
52
cannot be provided due to failures in the position and angle of the wavelength monitor unit in the optical filter or depending on the position and angle of the wavelength monitor unit when it has been incorporated into the optical filter. This reduces yields for optical module.
In addition, the conventional optical module is not readily scalable. The lack of scalability is due to an increase in the parts needed to ensure a reproducible and obstruction-free optical paths from the laser diode to the respective photodiodes.
SUMMARY OF THE INVENTION
One aspect of the present invention is to address the above-identified and other deficiencies and limitations associated with conventional optical module devices and optical transmission methods.
In contrast to the prior art, the present invention provides an optical module that can be produced with reduced manufacturing cost and time and that can be reduced in size with its improved wavelength stability for the laser beam, and a method of making such an optical module.
The present invention also provides an optical module that can be adjusted relating to its angle of incident light relative to the optical filter to provide a predetermined wavelength characteristic for improving yields, after assembled, and a method of making such an optical module.
The present invention provides an optical module that includes
a light-emitting device for outputting a laser beam;
an optical fiber for receiving and externally delivering the laser beam outputted from the light-emitting device at one
Nasu Hideyuki
Nomura Takehiko
Davie James
The Furukawa Electric Co. Ltd.
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