Linearized and High Frequency Electrooptic Modulators

Citation

Cummings, Uri Vaughan (2005) Linearized and High Frequency Electrooptic Modulators. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/GTD7-V873. https://resolver.caltech.edu/CaltechETD:etd-05312005-225644

Abstract

An analysis is performed of many standard and linearized electrooptic modulators known in the industry. The transfer functions of these modulators are evaluated under a consistent set of performance figures of merit, which are gain and spur-free dynamic range, using a canonical set of optical link parameters. The tolerance of the needed precision of the parameters of the linearization mechanisms of all of these modulators is compared over the entire interesting range of noise bandwidth.

A computer program was written to analyze the frequency dependence of any modulator transfer function under any set of functional inputs. The program is used to illustrate and compare the frequency dependence of the figures of merit of all of the modulators for which a d-c analysis was performed. Further analysis looks at the effect of greater noise-bandwidth and recovering the frequency-dependent degradation of gain and dynamic range through re-phasing techniques. The gain of directional couplers is analyzed in-depth.

Two novel modulator schemes are produced. The first uses reflective wave techniques to retime the electrical and optical waves half way through the modulator. The second uses fabrication geometry and properties of the linearization technique to make a more robust modulator (applicable to three of the modulators analyzed).

A 94 GHz antenna-coupled directional coupler modulator was initially demonstrated using an old modulator chip from Finbar Sheehy. A peculiar bug with the chip was uncovered. And a new modulator experiment was constructed and many aspects of the experimental apparatus were optimized. Though the revised experiment ultimately did not yield modulation side bands, it did couple a 94 GHz microwave signal into the optical waveguide, and many interesting challenges of high frequency electrooptic modulator fabrication were evaluated and improved upon.

Thesis Files