Performance of serial time-encoded amplified microscope

Serial time-encoded amplified microscopy (STEAM) is an entirely new imaging modality that enables ultrafast continuous real-time imaging with high sensitivity. By means of optical image amplification, STEAM overcomes the fundamental tradeoff between sensitivity and speed that affects virtually all optical imaging systems. Unlike the conventional microscope systems, the performance of STEAM depends not only on the lenses, but also on the properties of other components that are unique to STEAM, namely the spatial disperser, the group velocity dispersion element, and the back-end electronic digitizer. In this paper, we present an analysis that shows how these considerations affect the spatial resolution, and how they create a trade-off between the number of pixels and the frame rate of the STEAM imager. We also quantify how STEAM's optical image amplification feature improves the imaging sensitivity. These analyses not only provide valuable insight into the operation of STEAM technology but also serve as a blue print for implementation and optimization of this new imaging technology.

Simultaneous mechanical-scan-free confocal microscopy and laser microsurgery

We demonstrate an endoscope-compatible single-fiber-based device that performs simultaneous confocal microscopy and high-precision laser microsurgery. The method is based on mapping of two-dimensional sample coordinates onto the optical spectrum and allows us to perform two-dimensional imaging and microsurgery without any mechanical movement of the probe or the sample. The technology holds promise for creating highly miniaturized endoscopes for applications such as brain tumor, pediatric, and endovascular surgeries where high-precision, small, and flexible probes are required.

Serial time-encoded amplified imaging for real-time observation of fast dynamic phenomena

Ultrafast real-time optical imaging is an indispensable tool for studying dynamical events such as shock waves, chemical dynamics in living cells, neural activity, laser surgery and microfluidics. However, conventional CCDs (charge-coupled devices) and their complementary metal-oxide-semiconductor (CMOS) counterparts are incapable of capturing fast dynamical processes with high sensitivity and resolution. This is due in part to a technological limitation-it takes time to read out the data from sensor arrays. Also, there is the fundamental compromise between sensitivity and frame rate; at high frame rates, fewer photons are collected during each frame-a problem that affects nearly all optical imaging systems. Here we report an imaging method that overcomes these limitations and offers frame rates that are at least 1,000 times faster than those of conventional CCDs. Our technique maps a two-dimensional (2D) image into a serial time-domain data stream and simultaneously amplifies the image in the optical domain. We capture an entire 2D image using a single-pixel photodetector and achieve a net image amplification of 25 dB (a factor of 316). This overcomes the compromise between sensitivity and frame rate without resorting to cooling and high-intensity illumination. As a proof of concept, we perform continuous real-time imaging at a frame speed of 163 ns (a frame rate of 6.1 MHz) and a shutter speed of 440 ps. We also demonstrate real-time imaging of microfluidic flow and phase-explosion effects that occur during laser ablation.

Electrical control of parametric processes in silicon waveguides

We demonstrate electrical tuning of phase mismatch in silicon wavelength converters. Active control of birefringence induced by a thin-film piezoelectric transducer integrated on top of the waveguides is used for dispersion engineering. The technology provides a solution for compensating the phase mismatch caused by fabrication errors in integrated waveguides. It also offers a mean to dynamically control the relative dispersion between interacting waves and hence, to introduce electronic control of optical parametric processes.

Energy harvesting in silicon wavelength converters

Nonlinear loss is the central problem in silicon devices that operate using nonlinear optical effects. Wavelength converters are one example of such devices, wherein high optical intensities required for nonlinear interactions cause two-photon absorption and severe free-carrier absorption. In this paper, we report the first demonstration of nonlinear photovoltaic effect in silicon wavelength converters. This useful phenomenon allows us to eliminate the nonlinear loss caused by free-carrier absorption, while harvesting the optical power that is normally consumed by two-photon absorption.

Surface modes in two-dimensional photonic crystal slabs with a flat dielectric margin

We report numerical simulations of surface modes in two-dimensional high-index-contrast photonic crystal slabs with a flat dielectric margin of width on the order of the photonic crystal periodicity. Our calculations using plane wave expansion method reveal multiple surface guided modes within the photonic band gap, with some high-order modes exhibit relatively flat dispersion curves. We calculate the finite-length surface waveguide modes transmission and field patterns using two dimensional finite-difference time-domain method. We verify the surface mode dispersion curves by using spatial Fourier transform of the mode field patterns. Our study on surface modes under small ambient refractive index changes (5 x 10(-3)) shows that lower order modes exhibit larger wavelength shifts on the order of 1 nm. We also design a 4-port 3-channel bidirectional coupler using a conventional dielectric waveguide side coupled to the multimode surface waveguide.