Coherent light generators – Particular temperature control – Heat sink
Reexamination Certificate
1999-10-29
2001-10-09
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular temperature control
Heat sink
C372S034000
Reexamination Certificate
active
06301279
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor diode lasers. In particular, the present invention relates to semiconductor diode lasers that use a thermal sensor to provide temperature feedback to maximize power-conversion efficiency.
BACKGROUND
Temperature control in a diode laser is important for several reasons. First, temperature control is important because a change in temperature can strongly and adversely effect a laser's power output. For example, a diode laser's power output can be increased by increasing the bias current across the diode laser, but this approach is limited because the increase in current will lead to an increase in the diode laser's temperature. Typically, at least half of the electrical power applied to bias a laser will be lost as heat within the diode. This in turn leads to an increase in the threshold current necessary for sustaining laser oscillation. As a result, the relationship between the bias current and output power becomes nonlinear as the bias current is increased, and ultimately will saturate at a high bias-current level. This is the so-called “rollover” effect; as the bias current is increased, the temperature in the active region increases, and so the power output begins to drop off.
Second, temperature control is important because temperature is related to the output spectrum. Overheating the active region can lead to both a shift of and a broadening of the emitted spectrum. Thus, the ability to control the output spectrum, and consequently, the ability to use the resulting output spectrum, decreases as the active region increases in temperature.
To reduce temperature-related problems in a diode laser, known thermal stabilization systems have been designed to operate with the diode lasers. These thermal stabilization systems include a thermal sensor adjacent to the laser heat sink to provide a feedback signal, and a thermo-electric cooler also adjacent to the laser heat sink where the sensor is fixed. Such thermal stabilization systems are able to support the relatively stable active region temperature under conditions of variable ambient temperature.
Said another way, known thermal stabilization systems have thermal sensors adjacent to the heat sink. These thermal sensors help stabilize the temperature of the heat sink at the spot where the sensor is mounted. In these known thermal stabilization systems, thermal sensors are placed at the heat sink because this is the simplest geometry, and it was generally believed that this was the only possible way to use the thermal sensors. Additionally, those skilled in the known art did not think that the temperature gradient between the thermal sensor and the laser body was substantial enough to degrade performance. For example, it is generally known in the art to use sensors that are not removable. The sensors are fixed in the copper part of the laser fixture adjacent to a laser heat sink. It was generally believed that this was the only possible way to measure the temperature in the laser.
SUMMARY OF THE INVENTION
The present invention is based on a recent discovery by the inventors. Specifically, the inventors recently discovered that the temperature gradient between the sensor and the laser body was so large as to degrade performance unnecessarily. Even worse, the inventors discovered that the temperature gradient between the heat sink and the active region increases non linearly with current. This non-linear increase in the temperature gradient causes feedback control to be suboptimal with regard to stabilizing the temperature in the active region.
To alleviate the problems that the inventors have recognized in the known systems, the present invention introduces systems and methods for improving temperature control in a laser's active region. In one embodiment of the present invention, a semiconductor diode laser with a thermal sensor control comprises a heat sink, a diode-laser structure including an active layer, and a thermal sensor thermally coupled to said diode-laser structure. In this embodiment, the heat sink is separated from the thermal sensor by a first distance, and the heat sink is separated from the active layer by a second distane that is less than the first distance.
REFERENCES:
patent: 5568502 (1996-10-01), Hironaka
patent: 5875204 (1999-02-01), Sato
patent: 6033929 (2000-03-01), Murakami et al.
Connolly John Charles
Garbuzov Dmitri Zalmanovich
Khalfin Viktor Borisovich
Maiorov Mikhail Alexandrovich
Arroyo Teresa M.
Monbleau Davienne
Morris Duane
Plevy Arthur L.
Princeton Lightwave Inc.
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