Coherent light generators – Particular temperature control
Patent
1994-08-08
1995-08-01
Scott, Jr., Leon
Coherent light generators
Particular temperature control
372 32, 372 46, H01S 304
Patent
active
054385792
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a wavelength stabilizing apparatus for stabilizing the wavelength of laser light exiting, for example, from a semiconductor laser.
BACKGROUND ART
It has been conventionally known that the oscillation wavelength of a semiconductor laser (hereinafter referred to merely as an LD) greatly varies due to a slight temperature variation and injection current variation.
It has been proposed that, by making injection current control and temperature control while regulating a wavelength reference with the use of the Fabry-Perot resonator having a periodic transmission spectral characteristic, the oscillation wavelength of LD is locked to a predetermined mode of the Fabry-Perot resonator so that the oscillation wavelength is stabilized.
At that time, in view of the necessity to oscillate LD near the predetermined mode of the Fabry-Perot resonator it is necessary to stabilize the temperature of LD as the pre-process of the wavelength stabilization. Further it is necessary to stabilize the temperature of the Fabry-Perot so as to obtain the characteristic of a stabilized transmission spectral characteristic.
In order to stabilize the temperature of an LD 4 provided in an LD resonator 2, an LD temperature sensor 6 is provided near LD 4, as shown in FIG. 15, so as to detect the temperature of LD 4. Based on a temperature detection signal output from the LD temperature sensor 6, a temperature controller 8 controls a drive current in a Peltier element 10 so that the temperature of LD 4 is maintained at a predetermined temperature. It is to be noted that a fin member 12 for heat dissipation is provided at a Peltier element 10.
As shown in FIG. 16 in the neighborhood of a solid type etalon 16 provided in an etalon holder 14, an etalon temperature sensor 18 for detecting the temperature of the etalon 16 is provided so as to stabilize the temperature of the Fabry-Perot resonator. A temperature detection signal is output from the etalon temperature sensor 18 and, based on the temperature detection signal, a temperature controller 22 controls a drive current in a Peltier element 24 so that the temperature of the etalon 16 is maintained at a predetermined level. It is also to be noted that the Peltier element 24 is equipped with a fin element 26 for heat dissipation.
The following two conditions are required to achieve the wavelength stabilization of LD.
(1) LD is oscillated in the neighborhood of a predetermined mode of the Fabry-Perot resonator.
(2) A Fabry-Perot resonator is achieved which has a stabilized reference without being susceptible to an influence from an ambient temperature variation.
The conventional method poses the problem that, if the ambient temperature varies even in the case where the temperature of LD is stabilized, it is difficult to oscillate LD near the Fabry-Perot resonator (the problem encountered due to the ambient temperature variation). Further, there is also the problem that the LD's wavelength, though slightly with the passage of time, drifts even if the injection current and temperature are constant (the problem encountered with the passage of time).
Explanation will be given below about the following two problems.
<The Problem Encountered From the Ambient Temperature Variation>
As shown in FIGS. 15 and 16, the LD temperature sensor 6 and etalon temperature sensor 18 do not have their measuring points aligned with the mounting positions of LD 4 and etalon 16, problems as set out below arise in the case where ambient temperature in LD 4 and etalon 16 varies in the LD holder 2 and etalon holder 14, respectively.
The problem under consideration will be explained below with reference to FIG. 17. In FIG. 17, the abscissa denotes a thermal resistive value with the position of the LD temperature sensor 6 (etalon temperature sensor 18) set as a reference and the ordinate, the temperature involved.
As shown in FIG. 17, the temperature (T.sub.A) of the LD temperature sensor 6 (etalon temperature sensor 18) is stabilized to the set reference level (T.s
REFERENCES:
patent: 4689659 (1987-08-01), Watanabe
patent: 4710631 (1987-12-01), Aotsuka et al.
patent: 4792957 (1988-12-01), Kollanyi
patent: 4821273 (1989-04-01), Hori
patent: 5018154 (1991-05-01), Ohashi
patent: 5265110 (1993-11-01), Naya
Eda Yukio
Fujimoto Hirohisa
Hiroshi Yukawa
Hisata Nahoko
Jr. Leon Scott
Olympus Optical Co,. Ltd.
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