Coherent light generators – Particular temperature control – Heat sink
Reexamination Certificate
2000-12-15
2002-11-12
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular temperature control
Heat sink
C372S035000
Reexamination Certificate
active
06480515
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a heat sink for conducting heat from a laser diode and, more particularly, to an optically transparent, heat conductive fluid heat sink for dissipating heat from the light emission side of the laser diode.
Laser diodes emit light from a surface of the structure. In the course of this light emission, the laser diode also generates heat. Without removing the heat from the laser diode structure, the wavelength and the power of the emitted light beam will change and the structure itself may be damaged.
Heat sinks are generally used as a means to cool laser diodes and maintain a constant temperature. A heat sink must instantaneously dissipate the heat that is rapidly produced in the laser diode structure.
A heat sink enhances heat dissipation from a hot surface of the laser diode to a cooler surrounding ambient environment, usually air. The heat sink provides a heat conduction path from the laser diode to the ambient air.
Heat transfer directly across the interface between the surface of the laser diode structure and the coolant ambient air is the least efficient means of dissipating heat and is usually unsuccessful in avoiding heat build-up within the structure of the laser diode. A heat sink lowers the surface/ambient barrier mainly by increasing the surface area that is in direct contact with the coolant ambient atmosphere. This allows more heat to be dissipated and/or lowers the laser diode operating temperature.
The thermal conductivity and cooling surface area of the heat sink must always be weighed against material and manufacturing costs of the heat sink.
Most heat sinks are made from aluminum, because of its low thermal resistance, light weight, and low cost. Copper is also used for heat sinks; although lower in thermal resistance than aluminum, its cost and greater weight make it less desirable for many applications.
Stamped heat sinks are made from a single sheet of aluminum, which is cut and bent to give the desired thermal properties and attached to the laser diode structure.
Bonded-fin heat sinks are made by bonding fins, fabricated from sheet aluminum or through aluminum extrusion, to an aluminum base attached to the laser diode structure. This process increases the surface area over a similar extruded piece, reducing the thermal resistance by ½ to ⅔.
Folded-fin assemblies are bonded-fin assemblies with complex fin shapes. By folding the fins over themselves, these assemblies provide a large surface area in a confined space.
These are all passive heat sinks where the aluminum finned heat sink radiates heat and dissipates the heat through natural convection. Natural convection occurs when there is no externally induced flow and heat transfer relies solely on the free buoyant flow of air surrounding the heat sink.
Forced convection occurs when the flow of air is induced by mechanical means, usually a fan or blower. By adding a fan to a heat sink, it changes from passive cooling, using ambient airflow, to active cooling using its own airflow source. Adding a fan to a typical heat sink almost always improves thermal performance (except in cases with very high local ambient air velocities).
For the most demanding applications, liquid cooling, in place of air cooling, further improves heat sink performance. Liquid cooling can dissipate more heat with considerably less flow volume and maintain better temperature consistency, and do it with less local acoustic noise.
However, all these various heat sinks are positioned on the non-light emitting surface of the laser diode or positioned parallel to the laser cavity of the laser diode.
It is an object of the present invention to provide a heat sink for dissipating heat from the light emission side of the laser diode.
It is a further object of this invention to provide an optically transparent, heat conductive fluid heat sink.
SUMMARY OF THE INVENTION
According to the present invention, a fluid-filled heat sink is positioned on the emission surface of a laser diode. The light beam emitted by the laser diode aperture will propagate though the optically transparent fluid to be transmitted through an output window of the heat sink. Heat generated by the laser diode will be transferred by the thermally conductive fluid to the heat sink housing which will radiate the heat or transfer the heat to a secondary heat sink.
The housing and the interior fluid-filled cavity can be cylindrical in shape which aids in the dissipation of heat and lessens the convection currents from disturbing the light beam in the optical path between the aperture and heat sink output window. The output window can be a lens to focus the light beam if the beam is dispersed by the heat convection currents in the fluid.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4511927 (1985-04-01), Bauer
patent: 5664864 (1997-09-01), Kuth
patent: 5796766 (1998-08-01), Hargis et al.
patent: 6140141 (2000-10-01), Davidson
patent: 6330256 (2001-12-01), Hyren et al.
patent: 6353548 (2002-01-01), Roberts et al.
patent: 6351478 (2002-02-01), Heberle
patent: 2002/0004251 (2002-01-01), Roberts et al.
Jr. Leon Scott
Propp William
Xerox Corporation
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