Helen Kung - Ph.D. Oral Examination

[Helen L. Kung]

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                University Ph.D. Oral Examination

              Miniature optical wavelength sensors

                               Helen L. Kung

            Department of Electrical Engineering
                           Stanford University

                           CIS-X auditorium

                 Thursday, October 24th, 2002
                        9:00 AM-10:00 AM
             (Refreshments served at 8:45 AM)
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Recent semiconductor processing technology has been applied to the 
miniaturization of optical wavelength sensors.   Compact spectral sensors 
could enable new applications such as wavelength monitors integrated with 
diode-lasers, portable chemical and biological detection, and mobile 
hyperspectral imaging arrays.   We have investigated existing designs and 
developed novel architectures for wavelength sensing.  Many traditional 
wavelength sensors such as grating spectrometers, Michelson interferometers 
and Fabry-Perot tunable filters have been miniaturized using conventional 
technology, but these systems have design trade-offs among resolution, 
operating range, throughput, multiplexing, and complexity.  We have 
developed a new wavelength sensing architecture that balances these 
parameters for applications involving imaging arrays of spectrometers.

In this talk we present two different wavelength sensors based on sampling 
standing waves.  Both sensors measure the wavelength-dependent period of 
optical standing waves formed by the interference of a forward and 
reflected wave from
  a mirror.  The first device is a wavelength monitor, which measures the 
wavelength and power of a monochromatic source. The device is a GaAs NIPIN 
structure with two single quantum wells to sample the standing wave. The 
second device is a spectrometer that can also act as a selective spectral 
coherence sensor.  The spectrometer contains two components; a large 
displacement piston-motion MEMS mirror and a thin GaAs photodiode flip-chip 
bonded to a quartz substrate.  The spectrometer was demonstrated to have a 
resolution of 100 cm-1 (7.5 nm @ 866 nm) over an operating range of 633 
nm  866 nm. The performance of this spectrometer is similar to that of a 
Michelson in resolution, operating range, throughput and multiplexing but 
with the added advantages of fewer components and one-dimensional, 
arrayable architecture.
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