Digital Optical Spectrum Analyzer

GMU ECE 2012 Senior Design Project of the Year

Team Spectrum Jacob Dilles, PM Jason Hartman Mary Hatfield Kevin Nicotera Elton Williams Dr. Qiliang Li, ECE Dept. Supervisor Dr. Mingzhen Tian, Physics Dept. Supervisor

Executive Summary

An Optical Spectrum Analyzer (OSA) is a scientific instrument used to measure fine structure in the spectral characteristics of a continuous wave (CW) laser.

High resolution OSAs use a tunable optical band-pass filter called a Scanning Fabry-Pérot Interferometer (SFPI). This device consists of two mirrors arranged to form an optically resonant confocal cavity. The transmission frequency of the SFPI depends on the spacing between the mirrors, which is changed by applying voltage to a piezoelectric transducer mounted between them. The control unit sweeps the resonant wavelength of this cavity at a fixed rate – analogous to tuning a radio receiver across the dial – and the transmitted intensity within the cavity is plotted against time to form a picture of the optical frequency spectrum.

Commercial SFPI controllers widely used in physics research are analog systems and have many limitations accordingly. They are expensive, requiring a dedicated oscilloscope for output display and data capture. Being analog in nature, they are not suited to collect quantitative data, or provide context for displayed data. They are not user friendly; controls directly adjust parameters of an analog ramp generator making them difficult to operate. Existing units require complex setup procedures and constant adjustments to maintain a steady picture. Finally, they are limited in resolution by the finesse of the FP cavity.

Team Spectrum has developed the Digital Optical Spectrum Analyzer (DOSA), a low-cost stand-alone digital SFPI control system. The DOSA is compatible with existing SFPI hardware, offered as a drop-in replacement for analog controllers currently in use. This digital controller does not require an oscilloscope for data acquisition, providing equivalent functionality with drastically reduced system cost. The DOSA is intuitive to operate, with a fully integrated user-friendly graphical interface. Our software offers an enhanced automated setup process and drastically simplifies measurement operation.

On 14 December 2012 Team Spectrum received the prestigious GMU ECE Outstanding Senior Design Project Award for this work. The DOSA prototype is currently being used for quantum physics doctoral research, under the supervision of Dr. Ming Tian of the George Mason University Physics department, in an effort to quantify the quality of a NIR external cavity diode laser.

Click on the Project Poster (above) to see an enlarged JPEG

Other Links

• Official GMU ECE awards page, which hosts a summery of the project and award.
• Google+ Team Spectrum Build Log photo gallery.
• Video recording of the 30 Nov 2012 final presentation (ppt is below) on the department playlist, which includes:
  • group 1 - caribou cam
  • group 2 - arm charge
  • group 3 - led light
  • group 4 - digital optical spectrum analyzer (that's us)
  • group 5 - gps boat