Coherent light generators – Particular temperature control – Heat sink
Reexamination Certificate
2002-02-22
2004-10-26
Leung, Quyen (Department: 2828)
Coherent light generators
Particular temperature control
Heat sink
C372S043010
Reexamination Certificate
active
06810049
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor laser device having a greatly stabilized oscillation wavelength to output a high output laser beam and a semiconductor laser module.
BACKGROUND OF THE INVENTION
A demand for increasing the capacity of optical communication networks has been recently heightened because of a proliferation of various multimedia including Internet-delivered multimedia. Responsive to the demand, a WDM (Wavelength Division Multiplexing) communication system has been used. The WDM communication system is a system for performing transmission by using a plurality of wavelengths in a 1,550-nm band. The WDM communication system realizes a remarkable increase of the transmission capacity of a network because optical signals having a plurality of different wavelengths are simultaneously transmitted through one optical fiber and thereby it is unnecessary to construct a new line.
In the case of the light source, or the amplifying light source, of the optical signal, it is desired to accurately control the oscillation wavelength and operate a semiconductor laser element at a high optical output by preventing the thermal saturation of the element. Conventional semiconductor laser devices prevent an oscillation wavelength from becoming unstable, and a semiconductor laser element for outputting a laser beam from being thermally saturated, by setting a thermistor for measuring the temperature of the semiconductor laser element nearby the semiconductor laser element and controlling the temperature of the semiconductor laser element by a temperature controlling element such as a Peltier element.
FIG. 15
is a perspective view of a schematic configuration of a conventional semiconductor laser device. In the case of the semiconductor laser device in
FIG. 15
, a submount
102
formed by AlN having an insulating characteristic and a high heat conductivity is formed on a carrier
101
formed by CuW and a semiconductor laser element
103
for outputting a laser beam L
100
having a predetermined wavelength is formed on the submount
102
. A submount
104
formed by AlN is formed on the carrier
101
and a thermistor
105
for measuring the temperature of a semiconductor laser element is formed on the submount
104
.
The semiconductor laser element
103
and the submount
102
are joined through a metallic thin film
102
a.
The metallic thin film
102
a
is metallized with Ti, Pt, and Au at film thicknesses of 60, 200, and 600 nm in order and the semiconductor laser element
103
and submount
102
are joined to each other by a solder material made of AuSn or the like metallized on the Au film. Moreover, the thermistor
105
and submount
104
are joined each other similarly through the metallic thin film
104
a.
In the case of the semiconductor laser element
103
, the face to be joined with the submount
102
serves as a p-side electrode and the upper face serves as an n-side electrode and an active layer for mainly generating heat is set nearby the submount
102
. A negative electrode is led to the n-side electrode by an Au wire
106
a
and the p-side electrode is led to the positive side carrier
101
through the metallic thin film
102
a
and an Au wire
106
b.
Referring to
FIG. 16
, the submount
102
secures the insulation of the semiconductor laser element
103
and functions as a heat sink of the semiconductor laser element
103
and is joined to a CuW base
106
to be joined to the bottom of the carrier
101
by AuSn solder, and a Peltier module
107
set to the bottom of the base controls the temperature of the semiconductor laser element
103
in accordance with the temperature detected by the thermistor
105
.
Moreover, the thermistor
105
is also insulated from the carrier
101
by the submount
104
similarly to the case of the semiconductor laser element
103
to detect the temperature of the semiconductor laser element
103
through the submount
102
, carrier
101
, and submount
104
respectively having a high heat conductivity.
When performing long distance optical transmission by using the above WDM communication system, it is desireable to increase the output of a laser beam of a signal light source in order to increase the interval between repeaters. Moreover, to improve the amplification capacity of an optical fiber amplifier, it is desirable to increase the output of a semiconductor laser device used for an exciting light source.
To meet the above demands, a conventional embodiment has a semiconductor laser element for oscillating and outputting a laser beam of 250 mW or more as a laser beam for Erbium doped fiber amplifier (EDFA) excitation. However, a conventional semiconductor laser device using the above high output semiconductor laser element has a problem in that the optical output and service life of the semiconductor laser element are deteriorated.
FIG. 16
shows a front view of the above conventional semiconductor laser device including the above described base and Peltier module. The submounts
102
and
104
are separately provided for the semiconductor laser element
103
and the thermistor
105
. The heat generated in the semiconductor laser element
103
is conducted to the thermistor
105
through the metallic thin film
102
a
, submount
102
, metallic thin film
102
b
, carrier
101
, metallic thin film
104
b
, submount
104
, and metallic thin film
104
a
in order as shown by the arrow YA in FIG.
16
. As recognized by the present inventors, because the heat conducting distance is physically increased as described above, detection of the actual temperature of the semiconductor laser element
103
is delayed.
Moreover, because the total of four junction faces corresponding to the metallic thin films
102
a
,
102
b
,
104
b
, and
104
a
are present on the heat conducting path between the semiconductor laser element
103
and the thermistor
105
, heat resistances are generated on these junction faces and thereby, the temperature of the semiconductor laser element
103
is not accurately transferred to the thermistor
105
. That is, the thermistor
105
detects a lower temperature having a large difference from the actual temperature of the semiconductor laser element
103
and therefore, the accuracy of a detected temperature is deteriorated. As a result, the temperature control of the semiconductor laser element
103
performed in accordance with the temperature detected by the thermistor
105
is delayed and because the temperature control at a low accuracy is inevitably performed, the oscillation wavelength of the semiconductor laser element
103
becomes unstable and the optical output and service life of the semiconductor laser element
103
are deteriorated.
Moreover, as shown by the arrow YB in
FIG. 16
, because the total of four junction faces such as two junction faces corresponding to the metallic thin films
102
a
and
102
b
, the junction face between the carrier
101
and the base
106
, and the junction face between the base
106
and the Peltier module
107
are present on the heat conducting path between the semiconductor laser element
103
and the Peltier module
107
, the heating action or cooling action by the Peltier module
107
is deteriorated whenever passing through these junction faces and resultantly, the temperature control of the semiconductor laser element
103
cannot be quickly or accurately performed.
Moreover, when supplying a current of 1 A or more to a semiconductor laser element in order to obtain a high optical output and assuming that the total resistance of an Au thin film in the metallic thin film
102
a
is 0.12&OHgr;, the voltage drop by the Au thin film becomes 0.12 V. Moreover, because the inter-electrode voltage of a semiconductor laser element is approximately 2 V when a current of 1 A is supplied to the semiconductor laser element, the voltage drop of the semiconductor laser element in the resonator length direction becomes un-uniform by 0.12 V. That is, also when considering a current injection path, current injection into a semiconductor laser eleme
Tsukiji Naoki
Wakisaka Tsuyoshi
Yoshida Junji
Leung Quyen
The Furukawa Electric Co. Ltd.
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