Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
2001-12-12
2003-10-28
Davie, James (Department: 2828)
Coherent light generators
Particular beam control device
Optical output stabilization
C372S032000, C372S036000
Reexamination Certificate
active
06639923
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device for optical communication, and more particularly to a semiconductor laser device in which a laser beam is radiated from a semiconductor laser placed in a hermetically-sealed package and is transmitted to an optical fiber through a window of the package.
2. Description of Related Art
In optical communication using an optical fiber, a semiconductor laser device is used. In this semiconductor laser device, a semiconductor laser (hereinafter, called a laser diode) is placed in a hermetically-sealed package, and a laser beam radiated from the semiconductor laser is transmitted to an optical fiber through a window of the package.
FIG. 16
is a view showing the configuration of a conventional semiconductor laser device. In
FIG. 16
,
101
indicates a laser diode configured to radiate a forward laser beam for optical communication and radiating a backward laser beam.
102
indicates a lens, arranged in front of the laser diode
101
, for collimating the forward laser beam radiated from the laser diode
101
.
103
indicates a package window through which the forward laser beam collimated in the lens
102
is output. The forward laser beam radiated from the laser diode
101
is transmitted through the package window
103
and is coupled to an optical fiber
105
through an optical interface unit
104
.
106
indicates a photo diode, arranged in the rear of the laser diode
101
, for receiving the backward laser beam radiated from the laser diode
101
and monitoring a light intensity of the backward laser beam to adjust a light intensity or wavelength of the forward laser beam according to the monitored light intensity of the backward laser beam.
107
indicates an LD carrier on which the laser diode
101
is mounted.
108
indicates a PD carrier on which the photo diode
106
is fixed.
109
indicates a base carrier on which the LD carrier
107
and the PD carrier
108
are mounted.
110
indicates a hermetically-sealed package in which the members of the conventional semiconductor laser device are arranged. The package window
103
is placed in a frontal side area of the hermetically-sealed package
110
.
In the conventional semiconductor laser device having the above configuration, a control operation is performed to maintain intensity of the forward laser beam of the laser diode
101
to a constant value. In detail, because the intensity of the forward laser beam radiated from the laser diode
101
linearly changes with the intensity of the backward laser beam radiated from the laser diode
101
, the backward laser beam radiated from the laser diode
101
is received in the photo diode
106
, and a driving current supplied to the laser diode
101
is controlled so as to maintain a monitoring current generated in the photo diode
106
. Therefore, the intensity of the forward laser beam of the laser diode
101
can be maintained to a constant value.
Also, a part of the forward laser beam radiated from the laser diode
101
is not transmitted through the package window
103
but is reflected on the package window
103
as a reflected laser beam. Therefore, in cases where the reflected laser beam is incident on the photo diode
106
, the monitoring current generated in the photo diode
106
changes due to the reflected laser beam. In this case, even though the intensity of the backward laser beam received in the photo diode
106
is constant, the monitoring current is increased. Therefore, a problem has arisen that it is difficult to accurately control the driving current supplied to the laser diode
101
. Also, in cases where the reflected laser beam is incident on a forward laser beam emitting point of the laser diode
101
, laser beam radiation characteristics of the laser diode
101
are changed. Therefore, it is further difficult to accurately control the driving current supplied to the laser diode
101
.
To prevent the reflected laser beam from being incident on the photo diode
106
, a conventional semiconductor laser device has been disclosed in Published Unexamined Japanese Patent Application No. H7-162080 (1995). In this conventional semiconductor laser device, a light shielding member is soldered to an upper surface of the laser diode
101
.
However, in cases where a manufacturing method of the direct soldering of the light shielding member to the upper surface of the laser diode
101
is adopted, a problem has arisen that the size and weight of the light shielding member is limited.
Also, it is required that a bonding wire is connected with the upper surface of the laser diode
101
to feed a driving current to the laser diode
101
. However, in cases where the size of the light shielding member is enlarged, no bonding wire can be connected with the upper surface of the laser diode
101
. Therefore, a conductive light shielding member is soldered to the upper surface of the laser diode
101
to supply a driving current to the laser diode
101
through the conductive light shielding member.
However, in the conventional semiconductor laser device for the optical communication, there is a case where the driving current is modulated to change the value of the driving current and is supplied to the laser diode
101
through a binding wire. Therefore, in cases where a modulated driving current is supplied to the laser diode
101
through the conductive light shielding member, an electric resistance of the conductive light shielding member for the modulated driving current is increased, and a problem has arisen that modulation characteristics of the modulated driving current are changed by the increased electric resistance of the conductive light shielding member.
Also, another conventional semiconductor laser device has been disclosed in the application. In this conventional semiconductor laser device, a lateral width of a light shielding member is shorter than that of the laser diode
101
so as to expose an upper surface of the laser diode
101
on a side of the light shielding member, and a bonding wire is directly attached to the upper surface of the laser diode
101
to supply a driving current to the laser diode
101
. However, because the lateral width of the light shielding member is short, there is a probability that a part of the reflected laser beam passes through an area near to a side surface of the light shielding member so as to be incident on the photo diode
106
.
SUMMARY OF THE INVENTION
An object of the present invention is to provide, with due consideration to the drawbacks of the conventional semiconductor laser device, a semiconductor laser device in which a reflected laser beam is reliably prevented from being received in a photo diode on condition that the supply of a driving current to a laser diode is not disturbed.
The object is achieved by the provision of a wavelength monitoring device of a first inventive idea. That is, the wavelength monitoring device comprises a semiconductor laser configured to radiate a forward laser beam and a backward laser beam, a photo detector configured to receive the backward laser beam radiated from the semiconductor laser, a lens configured to converge the forward laser beam radiated from the semiconductor laser, a window which transmits a most portion of the forward laser beam converged by the lens and on which the remaining portion of the forward laser beam is reflected as a reflected laser beam, a lens fixing member to which the lens is fixed, and a light shielding member, supported by the lens fixing member, for shielding the photo detector from the reflected laser beam.
In the above configuration, the light shielding member shields the photo detector from the reflected laser beam. Accordingly, the light shielding member can reliably prevent the reflected laser beam from being received in the photo detector without giving an adverse influence of the light shielding member on a driving current supplied to the semiconductor laser through a bonding wire.
The object is also achieved by the provision of a
Adachi Akihiro
Hirano Yoshihito
Imaki Masao
Masuda Kenji
Nishimura Yasunori
Burns Doane , Swecker, Mathis LLP
Davie James
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