This is the first installment of the patent. The numbers refer to the figures adjoining the patent. I will call this 1 of 15.
Detailed Description of the Invention
FIG.1 is a block-diagram of a laser modulation system 10 generally in accordance with an embodiment of the invention. Included within the modulation system 10 is a transmitting laser 12, a first laser stabilization feedback section(circuit) 13, a second laser stabilization feedback section (circuit) 14 and a laser modulation section 16.
The transmitting laser 12 may be any distributed feedback(DFB) laser (13,000 Angstrom units wavelength) compatible with an appropriate temperature control. The junction current of the laser 12 is provided by a current controlled source (not shown) supplying a rated current with no more that 0.1% ripple.
Temperature control of the laser 12 is accomplished using an active heat control device 18 and balancing heat source 20. The active heat control device 18 can be a temperature control device located within a mounting surface (e.g. a heat sink) of the. laser 12. The device 18 may be implemented using a thermocouple sensor and controller coupled to any thermally active temperature control device (e.g., a Peltier effect thermoelectric heater/cooler). The operating temperature of the heat control 18 of the laser 12 may be held to an appropriate set point temperature (e.g. 32' F.) with an appropriate limitation on temperature variation (e.g., no more than 0.1 F).
The balancing heat source 20 is directed to stabilization of cavity dimensions by temperature control and may be implemented using an appropriately sized nichrome wire wrapped around the outside of the cavity of the laser 12 and surrounded by a thermally conductive, electrically non-conductive material (e.g., soreison, etc). The heat source 20 may be used to provide an appropriately stable cavity temperature (e.g., 32.l F +- .001 F) to restrict cavity mode hopping of an output of the DFB laser 12.
The paradigm laser 40 may be a low power diode laser operating with a junction current fixed to within 0.1% and operating at 13,000 Angstrom units wavelength. The paradigm laser 40 may be calibrated using an appropriate instrument standard (e.g., a Zeiss DK-2 Spectrophotometer using a quartz-iodine lamp that is NBS traceable) to a known energy level in each wavelength. The paradigm laser 40 may also be stabilized using a temperature controlled heat sink and an active temperature controller similar to that used by the transmitting laser 12.
The fundamental problem associated with the stability of the transmitting laser 12 and paradigm laser has been determined to be control of the resonant modes operating within the cavity. Control of the resonant modes, in turn, is highly dependent upon the dimension of the laser cavity. The temperature of the cavity has been determined to be a significant factor in the cavity dimension and laser stability. Further, where attempts are made to control the cavity temperature, the cavity temperature often overshoots a set point due to the thermal lag (and thermal mass) associated with each laser 12, 40. The solution to the problem in fact has been found to lie in control of the cavity temperature by modelling the laser cavity as a transient thermodynamic system. Using embedded thermistors and a summing operation amplifier, it has been found that the active temperature controller 18 can be adapted to follow the transient temperature using techniques previously described by the inventor.(for example, Palmer, J.R., Transient Heat Transfer in Flat Plates, Vol. II Constant Temperature, Pro Sc Publications, San Diego, CA (1995)).
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