Coherent light generators – Particular temperature control
Patent
1995-06-22
1997-10-21
Scott, Jr., Leon
Coherent light generators
Particular temperature control
372 36, H01S 304
Patent
active
056804105
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to an operational temperature stabilizing respectively wavelength stabilizing semi-conductor laser diode having an integrated temperature control element.
2. State of the Art
Conventional semiconductor laser diodes have been known since as early as 1962 when two research groups demonstrated GaAs laser diodes independently of one another yet practically at the same time. However, it took a long time to turn the first laser diodes, still requiring nitrogen cooling, into devices capable of solving the simple-looking task of emitting a continuous laser beam at room temperature.
The rate of development of the diode laser sped up tremendously during the last 15 years, and laser diodes became one of the fastest developing laser technologies. On the one hand, this technology was stimulated by the spread of "fiber-optic communication" which required semiconductor light sources, and, on the other hand, the need for compact, inexpensive light sources in numerous data-processing applications. As a result, the quality of the offered laser diodes increased greatly, but also the demand therefor.
The wavelength (peak wavelength) emitted by a laser diode also depends very heavily on the operational temperature in addition to the operational current. (Unless specifically defined in a different manner hereinafter, the term "temperature" shall mean the operational temperature of the laser diode respectively of the laser chip.) Typical values of the temperature drift are about 0.25 nm/.degree.C. in the case of GaAlAs laser diodes and about 0.5 nm/.degree.C. in the case of InGaAsP laser diodes.
The matter becomes more complicated due to the fact that many diode lasers are able to oscillate simultaneously in many different modes, each with a different wavelength. If the temperature changes, the laser, e.g., can jump from a longitudinal mode into another mode ("mode-hopping") and thereby abruptly alter its (peak) wavelength. This can occur if the pulse length changes during pulsed operation or if the operational current and starting power alter during the duration of operation.
An increase in the operational current can shift continuous wave laser diodes from a multi-mode state to a state which is strongly dominated by a single mode. The entire problem can become very complicated due to the fact that the emitted wavelength can gradually change and then jump abruptly to another value. This behavior can cause frequency instabilities and/or temperature changes as well as an increase in noise at the mode-hopping points.
In the case of applications that require wavelength stability, active temperature control that maintains the laser diodes at a fixed temperature can therefore contribute to minimizing many of the aforementioned problems.
DESCRIPTION OF THE INVENTION
The object of the present invention is, for wavelength stabilization and/or power stabilization, to build a laser diode the operational temperature of which is maintained at a fixed value that the user can set by means of active temperature control.
As the advantage of the compact construction of conventional laser diodes should be retained in any event, the present invention has, i.a., the object to make smaller respectively miniaturize and integrate all the components required for temperature control next to the laser chip in a usual-sized housing.
According to the state of the art, achieving temperature stabilization of laser diodes is usually attempted by means of suited cooling. Examples deserving mention herein are for instance large surfaces (if need be assisted by fans),
The present invention is based on it being strikingly understood that a suited temperature control of the laser diode or better said of the laser chip can also be attained by using thermistors. In particular, this occurs by employing posistors ("PTC resistors" or "PTCs" short) utilized as heat and/or control elements.
When using PTCs as heating elements, the temperature of the laser chip is "heated" to a value above the ambient temper
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patent: 4338577 (1982-07-01), Sato et al.
patent: 5042042 (1991-08-01), Hori et al.
patent: 5499258 (1996-03-01), Kawano et al.
Wittke et al "Stabilization of CW Injection Lasers"; RCA Technical Notes, TN No.: 1005, 3 sheets, Apr. 9, 1975.
Kim Yoon-Ok
Pries Ralph
Yoon Dae-Hin
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