The high angular and spectral selectivity of volume holograms have been used in fields like astronomy, spectroscopy, microscopy, and optical communications to perform spatial filtering and wavefront selection. In particular, imaging systems that utilize volume holograms to perform range-based wavefront selection have allowed for the potential to have full 24-hour observational custody of artificial satellites by enabling daytime observations. We previously introduced the Advanced Volume Holographic Filter (AVHF) which demonstrated a significant system bandwidth improvement while maintaining high angular selectivity. Presented here is a theoretical basis for maximizing the bandwidth of the AVHF systems. We experimentally demonstrate an improvement of 40.7-41.4x compared to the un-optimized AVHF systems.
Phase unwrapping algorithms have widely been studied and implemented with efforts aimed at unwrapping wrapped phase signals. However, the presence of noise and unreliable fringe quality poses a major obstacle for the retrieval of reliable phase signals. While many techniques have been implemented to deal with the aforementioned issues, most algorithms are application dependent or difficult to implement. Here we present a simple yet effective global phase unwrapping algorithm, that does not resort to Least-Squares Minimization, making use of Fast-Fourier Transform (FFT) based spectral differentiation, Signal Dependent Rank Ordered Mean (SD-ROM) filtering, and Fuzzy Logic Edge Detection (FLED). The proposed algorithm was tested using simulated, noisy, wrapped phaseograms and has shown to improve image and fringe quality, as well as overall retrieved phase reliability.
We are describing the capability to measure the phase of the return signal in a tabletop radar range. The radar rage has a scale factor of 100,000 which allows to use near IR wavelength instead of radio frequency. Accurate scale models are manufactured using multiphoton 3D printer with nanometric resolution. We demonstrated that using phase shifting interferometry, this radar range can retrieve the phase of the radar cross section of complex objects similar to SAR or ISAR radar systems.
We present a new type of filter that improves the SNR of systems where polychromatic signal and noise are located at different distances within the same line of sight. The filter is based on holographic technology that allows for the discrimination of wavefronts by range. In using a combination of two holographic elements, a pre-disperser and a thick volume hologram, we were able to significantly increase the spectral bandwidth of the filter, from 9nm without the pre-disperser to 70nm with both holographic elements. Laboratory proof of concept demonstrated that such a filter is capable of an SNR improvement of 15 dB for a monochromatic source, and up to 7.6 dB for a polychromatic source. This filter can find applications in astronomic observation, satellite or space debris tracking, and free-space optical communication.
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