| Customized multilayered stacks of dielectric materials may be configured for use as compact, resonant, transmissive optical phase modulators for broadband optical signals. The design, analysis, fabrication, and experimental characterization of a customized multilayered dielectric stack intended for use as a transmissive phase modulator are presented. The stack is designed to exhibit a spectral bandpass region of high transmittance in the near infrared, bounded by regions of high reflectance. Within the transmission bandpass, the phase component of the complex transmission coefficient varies such that a near-linear phase change is exhibited. The transmission bandpass region has a wavelength bandwidth of 21 nm, equivalent to a frequency bandwidth of 6.3 THz, and an edge-to-edge transmitted relative phase change of greater than 4π radians. The slope of the stack's phase function with respect to wavelength corresponds to a group index of 6.64, a value higher than that available from bulk dielectric materials per unit thickness. Collectively, these traits provide a favorable region within which phase modulation of ultrashort optical pulses may be implemented through the modulation of the stack's effective refractive index or propagation path length. This combination of a region of high transmission over a broad bandwidth with adjustable phase change of greater than 4π has not been previously identified as a methodology for transmissive phase modulation.; The use of a bandpass configuration as a candidate for phase modulation implementation is a departure from the use of traditional periodic structures, such as the Distributed Bragg Reflector (DBR). The narrowband transmission characteristics of a standard Distributed Bragg Reflector and other related configurations are contrasted with the broadband transmission of the optimized bandpass modulator. Techniques for implementing rapid phase modulation while maintaining high average signal transmission levels over a broad bandwidth are explored. The fabricated sample is experimentally characterized using a Mach-Zehnder interferometer and imaging spectrometer to measure spectral transmittance, transmitted relative phase and transmitted relative phase modulation in response to a variable angle-of-incidence. The computationally predicted values for transmittance, transmitted relative phase, and transmitted relative phase modulation are compared to the measured experimental data. Suggested directions for further research are provided. |
