SignificanceStimulated emission depletion (STED) is a powerful super-resolution microscopy technique that can be used for imaging live cells. However, the high STED laser powers can cause significant photobleaching and sample damage in sensitive biological samples. The dynamic intensity minimum (DyMIN) technique turns on the STED laser only in regions of the sample where there is fluorescence signal, thus saving significant sample photobleaching. The reduction in photobleaching allows higher resolution images to be obtained and longer time-lapse imaging of live samples. A stand-alone module to perform DyMIN is not available commercially.AimIn this work, we developed an open-source design to implement three-step DyMIN on a STED microscope and demonstrated reduced photobleaching for timelapse imaging of beads, cells, and tissue.ApproachThe DyMIN system uses a fast multiplexer circuit and inexpensive field-programmable gate array controlled by Labview software that operates as a stand-alone module for a STED microscope. All software and circuit diagrams are freely available.ResultsWe compared time-lapse images of bead samples using our custom DyMIN system to conventional STED and recorded a ∼46% higher signal when using DyMIN after a 50-image sequence. We further demonstrated the DyMIN system for time-lapse STED imaging of live cells and brain tissue slices.ConclusionsOur open-source DyMIN system is an inexpensive add-on to a conventional STED microscope that can reduce photobleaching. The system can significantly improve signal to noise for dynamic time-lapse STED imaging of live samples.
Nonlinear chalcogenide microresonators and microspheres are an ideal platform to explore nonlinear optical effects in a compact footprint. Chalcogenide glasses are particularly attractive, with high nonlinearities and long wavelength transparency. Applications including, cascaded Brillouin generation, photosensitive control, sensing and frequency comb generation.
Chalcogenides are a material platform for infrared nonlinear optics with high transmission and nonlinearity, but are susceptible to changes in bond structure during fabrication. These changes affect both the linear and nonlinear optical properties of the chalcogenide. We analyze the structure and optical properties of thermally evaporated and annealed Ge28Sb12Se60 to determine why these changes occur and how they can be rectified. We observe that thermally evaporated Ge28Sb12Se60 has an increased selenium content, increased bandgap, increased concentration of heteropolar bonds, and lower third order nonlinearity. We further observe that annealing above the glass transition temperature reduced the concentration of heteropolar bonds and increased the third order nonlinearity by a factor of four.
Chalcogenide glass (ChG) which contain one or more chalcogen elements is one of the most interesting material for infrared (IR) photonics owing to its unique optical properties, such as high refractive index, strong optical nonlinearity, and wide infrared transparency.
In this paper, we experimentally demonstrate high-quality ChG micro-disk resonators on oxidized silicon wafers fabricated by the standard UV photolithography and lift-off. Quality factor of micro-disk resonators are often limited by optical scattering loss induced by lithographically defined edge roughness. Thermal reflow of chalcogenide itself may significantly reduce edge roughness, but thermal shrinkage and deformation of the material during the reflow make it hard to precisely control the overall size and shape of the fabricated device. Instead, we reduce the sidewall roughness using thermal reflow of photoresist and modified bi-layer lift-off process. Typically, the thermal reflow of resist destroys the undercut or vertical sidewall profile of developed resist layer, making it extremely difficult or impossible to subsequently use lift-off or etching for patterning. We address this issue by first wet etching the silica substrate to undercut the reflowed photoresist, creating an overhang required for lift-off. ChG film is then deposited to produce a micro-disk resonator with much improved edge roughness. To finally create a micro-disk resonator on a silica pillar, we adopt vapor etching of the silica substrate. With optimized conditions of reflow and undercut, we obtained high quality ChG disk-resonators with extremely smooth edge profile, operating in the infrared region. Complete characterization results will be presented at the conference. The new method is compatible with traditional CMOS process and thus expected to have great potentials for fabricating high quality photonic integrated devices.
Supercontinuum based sources and measurement techniques are developed, enabling optical ultra-broadband studies of nano-scale photonic crystal devices and integrated photonic circuits over 1.2 - 2.0 micron wavelength range. Experiments involving 1-D periodic photonic crystal microcavity waveguides and 3-D periodic photonic crystals with embedded point defects are described. Experimental findings are compared with rigorous electromagnetic simulations.
In this paper, we describe the design theory for the supercontinuum spectrum generation in an optical fiber. To generate a wideband supercontinuum spectrum, the balance between fiber nonlinearity and the amount of group velocity dispersion is important. Secondly, the experimental results of supercontinuum generation are shown. A few kinds of optical fibers such as a highly nonlinear dispersion-shifted fiber and a highly nonlinear bismuth-oxide fiber are tested. Finally several applications of supercontinuum light are described. We demonstrate multi-wavelength light source, wavelength conversion, multiplexing format conversion, and optical characterization using a supercontinuum light source.
Bismuth oxide-based erbium-doped fiber amplifiers (Bi-EDFAs) are attractive because of their broad gain bandwidth and high gain per unit length. In this paper, several applications of broadband bismuth oxide-based erbium-doped fiber lasers (Bi-EDFLs) are reviewed including a wideband tunable single frequency Bi-EDFL, a femtosecond passively mode-locked Bi-EDFL, and applications to broadband spectrum generation.
A Bismuth Oxide-based Erbium-doped fiber (Bi-EDF) is a promising optical amplifier because it exhibits broad gain bandwidth and high gain in a very short device length. In this paper, broadband Bismuth Oxide-based Erbium-doped fiber lasers (Bi-EDFLs) are reviewed including a wavelength tunable L-band passively mode-locked Bi-EDFL and a C- and L-band continuously tunable single frequency Bi-EDFL.
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