Engineering-reflected phase in Fabry–Perot sensors with resonant mirrors

Abstract

Fabry-Perot cavities made with photonic crystal (PC) mirrors and other resonant structures exhibit nontraditional characteristics due to the strong wavelength dependence of their reflected phase. This Letter describes how engineering the phase of PC mirrors enables sensors that are tolerant to variations in laser center frequency and line width. Reflection spectra measurements of Fabry-Perot cavities made with PC mirrors were collected as a function of wavelength and cavity length, providing experimental verification of theory and simulations.

Design and Fabrication of Monolithic Photonic Crystal Fiber Acoustic Sensor

“…The Fabry-Perot reflectivity spectrum here is asymmetric, which is fully discussed in [11]. Furthermore, the reflection spectrum is strongly affected by the phase gradient of the PC mirror [12], [13]. These phase effects are important in the cavity design and affect the location of the maximum slope.…”

Single-Crystal Silicon Photonic-Crystal Fiber-Tip Pressure Sensors

“…Though a PC may have broadband high reflectance, its phase spectrum is not constant [29]. Therefore, the spectral shift due to applied pressure is not constant as spectral features pass through certain wavelengths.…”

“…The cavity length L is difficult to determine without knowing the phase response of the PC, which affects the location of the mirror planes at different wavelengths [29]. In an ideal FP etalon with an air cavity, L is computed by: where λ 1 and λ 2 are reflectance dip or transmission peak locations.…”

Sensors based on silicon photonic crystal mirrors with engineered phase

“…The interesting and ultimately useful (although initially frustrating) thing about PC mirrors is that their optical thickness can take a wide range of values, including negative ones. 3,4 Mirrors with specific curvature of their phase response have long been used for dispersion compensation, particularly in short-pulse lasers. The ability to also engineer the slope of the phase through PC mirrors opens up a large set of novel sensor applications, including ultrasensitive microphones, hydrophones, and pressure sensors, as well as sensors that are robust against laser instability, laser phase noise, and temperature fluctuations.…”