Metasurfaces are planar structures that locally modify the polarization, phase and amplitude of light in reflection or transmission, thus enabling lithographically patterned flat optical components with functionalities controlled by design. Transmissive metasurfaces are especially important, as most optical systems used in practice operate in transmission. Several types of transmissive metasurface have been realized, but with either low transmission efficiencies or limited control over polarization and phase. Here, we show a metasurface platform based on high-contrast dielectric elliptical nanoposts that provides complete control of polarization and phase with subwavelength spatial resolution and an experimentally measured efficiency ranging from 72% to 97%, depending on the exact design. Such complete control enables the realization of most free-space transmissive optical elements such as lenses, phase plates, wave plates, polarizers, beamsplitters, as well as polarization-switchable phase holograms and arbitrary vector beam generators using the same metamaterial platform.

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Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission

In this article we present a detailed discussion of noise sources in Fourier Domain Optical Coherence Tomography (FDOCT) setups. The performance of FDOCT with charge coupled device (CCD) cameras is compared to current standard time domain OCT systems. We describe how to measure sensitivity in the case of FDOCT and confirm the theoretically obtained values. It is shown that FDOCT systems have a large sensitivity advantage and allow for sensitivities well above 80dB, even in situations with low light levels and high speed detection.

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Performance of fourier domain vs. time domain optical coherence tomography.

Sensitive optical biosensors for unlabeled targets: a review.

Wave propagation and group velocity

We demonstrate high-speed, high-sensitivity, high-resolution optical imaging based on optical frequency-domain interferometry using a rapidly-tuned wavelength-swept laser. We derive and show experimentally that frequency-domain ranging provides a superior signal-to-noise ratio compared with conventional time-domain ranging as used in optical coherence tomography. A high sensitivity of -110 dB was obtained with a 6 mW source at an axial resolution of 13.5 microm and an A-line rate of 15.7 kHz, representing more than an order-of-magnitude improvement compared with previous OCT and interferometric imaging methods.

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High-speed optical frequency-domain imaging

Optical low-coherence reflectometry is used to investigate the internal structure and optical properties of human scalp hair. Regardless of hair color, the refractive index of the cortical region remains within the range of 1.56-1.59. The amplitude of the backscattered infrared light coupled into different-colored hair confirms the relative melanin content. Discontinuities in the refractive index permit identification of distinct structural layers within the hair shaft.

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Characterization of human scalp hairs by optical low-coherence reflectometry.

Optical filtering of amplified spontaneous emission improves measurement dynamic range for frequency response measurements of optoelectronic receivers. For high bandwidth receivers, a novel periodically filtered intensity noise technique is proposed. Response measurements using these techniques on a 1 GHz and 30 GHz receiver are demonstrated. >

High-frequency photodiode characterization using a filtered intensity noise technique

Silicon-germanium (Si-Ge) avalanche photodiodes (APDs) have large gain bandwidth product (GBP) and low excess noise due to the low impact ionization coefficient ratio of silicon. Optical receivers using APDs are able to achieve high-speed and energy efficient optical transceiver systems. We demonstrate a waveguide Si-Ge APD with low breakdown voltage of −10 V, achieving 60 Gb/s PAM4 successfully. A compact APD circuit model was constructed to allow photonic devices and transceiver circuitry co-design. The APD receiver has achieved −16 dBm sensitivity at 50 Gb/s PAM4 with a bit error rate (BER) of 2.4 $\times \,10^{-4}$ . The sensitivity of APD receivers changes with the multiplication gain. In our analysis, compared to a PIN PD receiver the APD receiver operating at optimum gain can obtain $\sim$ 8 dB more sensitivity for NRZ signaling at $ 50 Gb/s and 3–4 dB more sensitivity for PAM4 signaling at 50–100 Gb/s. Also, the APD receiver operating at optimum gain can reduce power consumption by $\sim\!\text{10}\%$ at PAM4 data rates of 50 Gb/s and $\sim\!\text{15}\%$ at 100 Gb/s in a silicon carrier-depletion microring modulator based WDM photonic link.

A Low-Voltage Si-Ge Avalanche Photodiode for High-Speed and Energy Efficient Silicon Photonic Links

Characterization of human scalp hairs by optical low-coherence reflectometry

Backward wave coupling is demonstrated by placing a first-order metal grating in the evanscent field of a single-mode fiber. Guided reflections as high as 38 percent were observed. The device acts as a polarization and frequency filter for both reflected and transmitted light. Polarization extinction ratios greater than 20 and 15 dB were obtained for reflected and transmitted light, respectively.

Wayne V. Sorin

Papers

Characterization of human scalp hairs by optical low-coherence reflectometry.

High-frequency photodiode characterization using a filtered intensity noise technique

A Low-Voltage Si-Ge Avalanche Photodiode for High-Speed and Energy Efficient Silicon Photonic Links

Characterization of human scalp hairs by optical low-coherence reflectometry

A single-mode fiber evanescent grating reflector