We demonstrate a specially designed vortex sensing diffraction grating that generates multiple vortex patterns in the different diffracted orders. When this grating is illuminated with a separate vortex beam, the sign and order of the topological charge of the incident beam can be easily detected. Experimental results are shown for a variety of vortex beams including fractional values of the topological charge, and where both the diffraction grating and incident vortex illumination beam are generated by two different liquid crystal displays (LCDs). The programmability offered by the LCDs offers extremely convenient flexibility.

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Monolayer transition metal dichalcogenides (TMDs) are promising 2D semiconductors that feature direct bandgaps useful for various quantum and optoelectronic applications. We present on our progress in establishing a cryogenic photoluminescence setup using a cryogenic probe station with bare multi-mode fibers that allows for active-device biasing of novel material platforms. Using this system, we are able to detect the photoluminescence signal from various chemical vapor deposited (CVD) and molecular beam epitaxy (MBE) grown 2D semiconductors on sapphire (0001) substrates in vacuum. We observe a temperature dependent direct bandgap red-shift of around 40nm (from 8K to 450K) for CVD grown monolayer WS2 and CVD grown monolayer WSe2 on sapphire (0001) substrates. We observe a temperature dependent direct bandgap red-shift of around 37nm (from 6K to 450K) for MBE grown monolayer MoSe2 on sapphire (0001) substrates. Interestingly, for monolayer MoS2 on sapphire (0001) substrates, we observe the emergence of a strong photoluminescence signal at cryogenic temperatures below 100K, in addition to the A exciton luminescence signal, which is attributed to bound excitons.

We present a compact optical circular-polarization-splitting common-path interferometer based on a zero-twist liquid-crystal display (LCD). A blazed diffraction grating is encoded onto the LCD. The optical system produces a reference beam that has one sense of circularly polarized light, while the diffracted beam has the opposite sense of circularly polarized light. Using a linear polarizer, these two beams form an interferogram that can be used to analyze optically active media. Experimental results are provided showing the detection of left-handed-rotary and right-handed-rotary media.

Wirelessly transmitting large volumes of information at high data rates underwater is becoming increasingly important for such applications as environmental monitoring and petroleum exploration and maintenance. Underwater free-space optical (FSO) communication addresses the aforementioned need by providing wireless high-data-rate links. Visible light transmission through seawater typically peaks in the blue-green spectrum (475 nm-575 nm), but local clarity conditions, which are dynamic, strongly influence the actual maximum. We describe the development of a new laser-wavelength auto-selection algorithm and system for optimized underwater FSO communication. This system has the potential to improve underwater optical link reliability for high-data-rate communications. First, we describe the laser system and water tube setup for performing optical experiments. Next, we present research on recreating various seawater types (from clear to turbid) in the laboratory using particle suspensions and dye, which will enable wavelength-dependent transmission tests. Finally, we show experimental results from optical water tube tests, and describe the development of the autoselection algorithm.