Duncan MacFarlane

Physical phaseplate for the generation of a millimeter-wave hermite-Gaussian beam

This paper demonstrates the design, fabrication and characterization of a physical phaseplate, which transforms plane waves to Hermite-Gaussian mode beams. The phaseplate is designed for a HG11 mode, working at E-band from 71 to 76 GHz. Simulations were run in ANSYS HFSS, a full-wave electromagnetic simulator, and compared to measured results for phaseplates fabricated with laminate substrates and polymer sheets. The simulations and measurements are in good agreement and demonstrate the designed Hermite-Gaussian beam.

Square dielectric THz waveguides.

A holey cladding dielectric waveguide with square cross section is designed, simulated, fabricated and characterized. The TOPAS waveguide is designed to be single mode across the broad frequency range of 180 GHz to 360 GHz as shown by finite-difference time domain simulation and to robustly support simultaneous TE and TM mode propagation. The square fiber geometry is realized by pulling through a heat distribution made square by appropriate furnace design. The transmitted mode profile is imaged using a vector network analyzer with a pinhole at the receiver module. Good agreement between the measured mode distribution and the calculated mode distribution is demonstrated.

Experimental demonstration of a dual-channel E-band communication link using commercial impulse radios with orbital angular momentum multiplexing

In this paper, we use commercial impulse radios and spiral phase plates to generate two different orbital angular momentum (OAM) beams from 71 GHz to 76 GHz. In addition, we have experimentally demonstrated that those two different OAM beams can be multiplexed and demultiplexed over the same frequency radio channel at 2 meters range. At the same time, those two channels can work independently with channel crosstalk less than −15 dB and bit-error-rate (BER) less than 9.65 × 10−10.

Stability of Ince–Gaussian beams in elliptical core few-mode fibers

A comparative stability analysis of Ince-Gaussian and Hermite-Gaussian modes in elliptical core few-mode fibers is provided to inform the design of spatial division multiplexing systems. The correlation method is used to construct crosstalk matrices that characterize the spatial modes of the fiber. Up to six low-order modes are shown to exhibit about -20u2009u2009dB crosstalk. The crosstalk performance of each mode set is found to be similar. However, a direct comparison between modes of equal Gouy phase shift, a parameter that ensures identical beam quality, and phase at the detector, demonstrates better relative power transmission for Ince-Gaussian beams. This result is consistent with the natural modes supported by a 100xa0m elliptical core fiber for which a mode ellipticity of ϵ=2 was found to be optimal. The relative power difference is expected to be magnified over longer fiber lengths in favor of Ince-Gaussian modes.

Z-transform techniques in the design of Mach-Zehnder modulators

The slew rate of a Mach-Zehnder Modulator (MZM) may be improved by adding appropriate feedback to the classic single stage finite impulse response (FIR) configuration.

Design, fabrication, and demonstration of a dielectric vortex waveguide in the sub-terahertz region

A sub-terahertz vortex dielectric waveguide was designed and fabricated in the cyclic olefin copolymer (TOPAS) compound. The annular index profile was engineered using a holey cladding to support operation from approximately 200-300xa0GHz. The vortex waveguide was tested at 280xa0GHz using an OAM-endowed Laguerre-Gaussian mode generated by a stepped spiral phase plate.

Orbital angular momentum multiplexing using low-cost VCSELs for datacenter applications

Development of 4×28 Gb/s free space data communications link based on OAM multiplexing using 850nm VCSELs is presented. Passive optical mode sorters are used for MUX (transmit) and DeMUX (receive).