Holographic Fabry-Perot spectrometer.
We propose a spectrum analyzer based on the properties of a hologram recorded with the field transmitted by a Fabry-Perot etalon. The spectral response of this holographic Fabry-Perot spectrometer (HFPS) is analytically investigated in the paraxial approximation and compared with a conventional Fabry-Perot etalon of similar characteristics. We demonstrate that the resolving power is twice increased and the free spectral range (FSR) is reduced to one-half. The proposed spectrometer could improve the operational performance of the etalon because it can exhibit high efficiency and it would be insensible to environmental conditions such as temperature and vibrations. Our analysis also extends to another variant of the HFPS based on holographic multiplexing of the transmitted field of a Fabry-Perot etalon. This device increases the FSR, keeping the same HFPS performance.
High resolution coherent spectral analysis method based on Brillouin scattering in an optical fiber.
High-resolution optical spectral analysis method is of significant importance for those who want to explore the physical world from the frequency domain. Aiming at the resolution degradation of classical coherent optical spectrum analysis (COSA) caused by the mirror phenomenon, this paper modifies the COSA system by introducing two homologous Brillouin scattering beams to serve as the pre-filter and local oscillator (LO), respectively. The central frequencies of the pre-filtered signal and the LO are locked by the Brillouin frequency shifts of those two Brillouin scattering beams. By means of this modification, the pre-filtered signal is located at either the upper-frequency-shifted side or the lower-frequency-shifted sides of the LO but could not exist on both sides of the LO. The proposed method could cancel the mirror phenomenon and thus improve the systematic resolution to 1.3 MHz in theory and 2 MHz in practice.
New photopolymer used as a holographic recording material.
The composition and the holographic behavior of a new photopolymer with high diffraction efficiencies (30% at 514 and 60% at 633 nm) are described.