Miniature, feedback-stabilized sources of broad-band light are under development for use in the illumination and calibration of imaging spectrometers and other optoelectronic scientific instruments. These sources would be designed and fabricated by use of techniques developed for semiconductor integrated circuits and extended to microelectromechanical systems (MEMS). In the original intended application, a device of this type would supplant the onboard calibrator (OBC) in NASA's airborne visible/infrared imaging spectrometer (AVIRIS).
Conventional OBCs contain off-the-shelf light bulbs and discrete electronic and optical components. In contrast, the developmental light sources have the potential to be smaller, less massive, and less power-hungry by several orders of magnitude (see table). The developmental light sources would be microfabricated out of silicon in predominantly planar geometries like those of typical integrated circuits; consequently, it would be relatively easy to integrate the light sources with silicon-based electronic drive circuitry and with optical fibers. In comparison with conventional OBCs, the developmental light sources would be relatively insensitive to fluctuations in temperature. Moreover, because they would be less massive, they would operate with shorter stabilization times.
A device of the type under development would be a fully integrated, monolithic optoelectronic system that would include a micromachined incandescent lamp, a fiber-optic output coupler, and an infrared photodetector and associated electronic circuitry for negative-feedback stabilization of the current supplied to (and thus the brightness and temperature of) the lamp. Micromachined incandescent lamps like those that would be incorporated into these devices were described in "Micromachined Broad Band Light Sources" (NPO-20655),NASA Tech Briefs, Vol. 25, No. 4 (April 2001), page 44. A prototype that included only a lamp has been demonstrated (see figure). Integration of a lamp with a photodetector and feedback circuitry is a goal of proposed development efforts for the near future.
Key Parameters of current and developmental OBCs for the AVIRIS are compared. The values for the developmental OBC are estimates based partly on the anticipated integration of all optical and electronic components.
This work was done by Thomas George, Eric Jones, Michael Eastwood, Margaret Tuma, and Richard Hansler of Caltech forNASA's Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
Intellectual Property group
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109
Refer to NPO-20935.