Chaoray Hsieh

Compact Fourier-transform volume holographic spectrometer for diffuse source spectroscopy

We present a new idea for diffuse source spectroscopy using a Fourier-transform volume holographic spectrometer formed by a Fourier-transform lens, a volume hologram, and a CCD. We show that this spectrometer can operate well under spatially incoherent light illumination. Furthermore, this spectrometer is less bulky, less sensitive to input alignment, and potentially more appropriate for implementation of highly sensitive spectrometers than conventional spectrometers.

Qualitative demonstration of spectral diversity filtering using spherical beam volume holograms.

We investigate the feasibility of designing spectral diversity filters using spherical beam volume holograms. Our experimental results qualitatively show the separation of the information of different incident wavelength channels using spherical beam volume holograms. The major trade-off in using these holograms is between the degree of spatial spectral diversity and the number of allowed spatial modes (or the divergence angle) of the incident beam.

Multiple order coded aperture spectrometer.

We introduce a multiple order coded aperture (MOCA) spectrometer. The MOCA is a system that uses a multiplex hologram and a coded aperture to increase the spectral range and throughput of the system over conventional spectrometers while maintaining spectral resolution. This results in an order of magnitude reduction in system volume with no loss in resolution.

Dispersion multiplexing with broadband filtering for miniature spectrometers.

We replace the traditional grating used in a dispersive spectrometer with a multiplex holographic grating to increase the spectral range sensed by the instrument. The multiplexed grating allows us to measure three different, overlapping spectral bands on a color digital focal plane. The detectors broadband color filters, along with a computational inversion algorithm, let us disambiguate measurements made from the three bands. The overlapping spectral bands allow us to measure a greater spectral bandwidth than a traditional spectrometer with the same sized detector. Additionally, our spectrometer uses a static coded aperture mask in the place of a slit. The aperture mask allows increased light throughput, offsetting the photon loss at the broadband filters. We present our proof-of-concept dispersion multiplexing spectrometer design with experimental measurements to verify its operation.

Role of recording geometry in the performance of spectral diversity filters with spherical beam volume holograms

We present experimental demonstrations of spectral diversity filters with spherical beam volume holograms for multimodal multiplex spectroscopy. Major properties of filters under diffuse-light illumination are discussed. The comparisons of spectral diversity between the transmission geometry holograms and the reflection geometry holograms are also studied. The results show that there is a trade-off between the degree of the spatial coherence of the source and the spectral diversity of the filter. We also conclude that the reflection geometry holograms have better spectral diversity and less sensitivity to the spatial coherence of the source.

Multifunctional and compact spectrometers based on cylindrical beam volume holograms

We propose a new class of slitless spectrometers using cylindrical beam volume holograms. These holograms disperse an input beam in one direction in an output plane while they do not affect the beam in the perpendicular direction. We show that the spectral mapping of the input beam can be obtained in one direction and the beam can be independently modified in the perpendicular direction. Using this unique property, we demonstrate a spectral wrapping technique to considerably increase the operation spectral range of the slitless spectrometers, without sacrificing their resolution.

Very-high-resolution tandem Fabry-Perot etalon cylindrical beam volume hologram spectrometer for diffuse source spectroscopy

We demonstrate a compact and slitless spectrometer with high resolution formed by cascading a Fabry-Perot etalon (FPE) and a cylindrical beam volume hologram (CBVH). The most significant advantage of this combined spectrometer is that we can independently encode spectral information of a diffuse beam in a 2D plane. Also, we show that in this slitless configuration we can simultaneously benefit from the advantages of both elements: the high resolution of the FPE and the large spectral range of the CBVH. Here, we report on the experimental demonstration of a spectrometer with better than 0.2 nm resolution.

Multiple Order Coded Aperture (MOCA) Spectrometer

We introduce a Multiple Order Coded Aperture (MOCA) spectrometer that uses a cross-dispersive hologram and a coded aperture to achieve improved spectral range over traditional dispersive spectrometers at comparable resolution.

Implementation of spectral diversity filters using spherical beam volume holograms

We present experimental demonstrations of spectral diversity filters using spherical beam volume holograms. Major properties of filters under collimated and diffuse light will be presented. We also show rotation multiplexing can improve the spectral diversity.

Ultra-high resolution and compact volume holographic spectrometers

Compact and efficient spectrometers are of great interest for biological and environmental sensing. In this paper, we describe a new class of spectrometers that work based on diffractive properties of spherical beam volume holograms (SBVHs) and cylindrical beam volume holograms (CBVHs). The hologram in these spectrometers acts as a spectral diversity filter (SDF) that maps different input wavelengths onto different locations in the output plane. The main properties of these holographic SDFs and new techniques for removing the ambiguity between incident wavelength (or the input channel) and incident angle (or the input spatial mode) are discussed. By using CBVHs, we show that the spectral mapping of the input beam can be obtained in one direction and the beam can be independently modified in the perpendicular direction. Using this unique property, we demonstrate a spectral wrapping technique to considerably increase the operation spectral range of spectrometers, without sacrificing their resolution. Finally, it is also shown that by combining CBVHs with a Fabry-Perot interferometer, a true two-dimensional spatial-spectral mapping can be formed, and an ultra-high resolution of 0.2 nm with large spectral bandwidth is demonstrated for this tandem spectrometer.