Nondestructive volumetric optical analysis of corroded copper oxidation using 1700nm swept-source optical coherence microscopy.

This study presents a novel nondestructive analysis method for precise characterization of corroded copper oxidation using optical coherence microscopy (OCM). By exploiting the partial light transmission through metallic oxide layers, we employed a specialized OCM system with a wavelength of 1700nm and enhanced the analysis accuracy compared to conventional optical coherence tomography (OCT). The developed OCM system featured a numerical aperture (NA) of 0.

Analysis of phototoxin taste closely correlates nucleophilicity to type 1 phototoxicity.

Pigments often inflict tissue-damaging and proaging toxicity on light illumination by generating free radicals and reactive oxygen species (ROS). However, the molecular mechanism by which organisms sense phototoxic pigments is unknown. Here, we discover that Transient Receptor Potential Ankyrin 1-A isoform [TRPA1(A)], previously shown to serve as a receptor for free radicals and ROS induced by photochemical reactions, enables to aphotically sense phototoxic pigments for feeding deterrence.

Optically tunable fiber Bragg grating based on a photo-mechanical tuning mechanism.

We present an optically tunable fiber Bragg grating (FBG) based on a photo-mechanical tuning mechanism. Azobenzene containing polymer was utilized as a photo-mechanical tuning agent coated over a bare section of FBG. Controlled by ultraviolet (UV) irradiation, the polymer coating acts as a micro-actuator that deforms the fiber structure.

Nucleophile sensitivity of TRPA1 underlies light-induced feeding deterrence.

Solar irradiation including ultraviolet (UV) light causes tissue damage by generating reactive free radicals that can be electrophilic or nucleophilic due to unpaired electrons. Little is known about how free radicals induced by natural sunlight are rapidly detected and avoided by animals. We discover that Transient Receptor Potential Ankyrin 1 (TRPA1), previously known only as an electrophile receptor, sensitively detects photochemically active sunlight through nucleophile sensitivity.

Femtosecond pulse shaping using wavelength-selective directional couplers: proposal and simulation.

The femtosecond pulse-shaping capabilities of wavelength-selective directional couplers are investigated. Numerical results show that, depending on the coupling length and coupling coefficient, one can achieve very different temporal shapes at the output of the directional couplers. For instance, temporal re-shaping of Gaussian-like pulses into Hermite-Gaussian pulses, parabolic pulses, square temporal waveforms and sequences of equalized multiple pulses with time widths down to the femtosecond range can be achieved using readily feasible fiber/waveguide designs.

A subset of enteroendocrine cells is activated by amino acids in the Drosophila midgut.

The intestine is involved in digestion and absorption, as well as the regulation of metabolism upon sensation of the internal intestinal environment. Enteroendocrine cells are thought to mediate these internal intestinal chemosensory functions. Using the CaLexA (calcium-dependent nuclear import of LexA) method, we examined the enteroendocrine cell populations that are activated when flies are subjected to various dietary conditions such as starvation, sugar, high fat, protein, or pathogen exposure.

TrpA1 Regulates Defecation of Food-Borne Pathogens under the Control of the Duox Pathway.

Pathogen expulsion from the gut is an important defense strategy against infection, but little is known about how interaction between the intestinal microbiome and host immunity modulates defecation. In Drosophila melanogaster, dual oxidase (Duox) kills pathogenic microbes by generating the microbicidal reactive oxygen species (ROS), hypochlorous acid (HOCl) in response to bacterially excreted uracil. The physiological function of enzymatically generated HOCl in the gut is, however, unknown aside from its anti-microbial activity.

The Mosquito Repellent Citronellal Directly Potentiates Drosophila TRPA1, Facilitating Feeding Suppression.

Citronellal, a well-known plant-derived mosquito repellent, was previously reported to repel Drosophila melanogaster via olfactory pathways involving but not directly activating Transient Receptor Potential Ankyrin 1 (TRPA1). Here, we show that citronellal is a direct agonist for Drosophila and human TRPA1s (dTRPA1 and hTRPA1) as well as Anopheles gambiae TRPA1 (agTRPA1). Citronellal-induced activity is isoform-dependent for Drosophila and Anopheles gambiae TRPA1s.

Optical properties of the fiber-optic temperature sensor based on the side-hole fiber filled with indium.

A highly sensitive temperature sensor was made by use of a side-hole glass fiber filled with indium metal, and its optical properties were investigated. The temperature sensitivity of the fiber-optic temperature sensor was dλ/dT=-7.38 nm/K.

25-terahertz-bandwidth all-optical temporal differentiator.

An all-optical temporal differentiator with a record operation bandwidth of ~25 THz (~200 nm, at least one order of magnitude larger than any previously reported temporal differentiation technology) is experimentally demonstrated based on a simple and compact all-fiber wavelength-selective directional coupler. The fabricated directional coupler can be used to process optical signals with time features as short as a few tens of femtosecond. A Gaussian-like optical pulse with a time-width of 250-fs is experimentally differentiated with a processing error of 2.

Wavelength-selective directional couplers as ultrafast optical differentiators.

Wavelength-selective directional couplers with dissimilar waveguides are designed for ultrafast optical differentiation within the femtosecond regime (corresponding to processing bandwidths > 10 THz). The theoretically proposed coupler-based differentiators can be produced by wavelength matching of the propagation constants of two different waveguides in the coupler at the center wavelength. A single directional coupler can be designed to achieve either a 2nd-order differentiator or a 1st-order differentiator by properly fixing the product of coupling coefficient and coupling length of the coupler.

Real-time complex temporal response measurements of ultrahigh-speed optical modulators.

We demonstrate a technique for direct, real-time characterization of the complex (amplitude and phase) temporal response of ultrahigh-speed (GHz-bandwidth) optical modulators. The demonstrated technique is based on pulse interferometry combined with time-frequency mapping processes using fiber linear dispersion. A new mechanism is incorporated to overcome the temporal resolution (bandwidth) limitation of the detectable modulation response in our previously reported setup.

Photonic temporal integrator for all-optical computing.

We report the first experimental realization of an all-optical temporal integrator. The integrator is implemented using an all-fiber active (gain-assisted) filter based on superimposed fiber Bragg gratings made in an Er-Yb co-doped optical fiber that behaves like an 'optical capacitor'. Functionality of this device was tested by integrating different optical pulses, with time duration down to 60 ps, and by integration of two consecutive pulses that had different relative phases, separated by up to 1 ns.

All-optical temporal integration of ultrafast pulse waveforms.

An ultrafast all-optical temporal integrator is experimentally demonstrated. The demonstrated integrator is based on a very simple and practical solution only requiring the use of a widely available all-fiber passive component, namely a reflection uniform fiber Bragg grating (FBG). This design allows overcoming the severe speed (bandwidth) limitations of the previously demonstrated photonic integrator designs.

Simple and highly sensitive optical pulse-characterization method based on electro-optic spectral signal differentiation.

A very simple self-referenced, linear pulse-characterization technique based on spectral phase reconstruction by frequency-domain signal differentiation is introduced. This technique can be implemented using electro-optic intensity modulation of the pulse under test with a synchronized RF sinusoid. The pulse spectral phase profile can be accurately and unambiguously reconstructed from only two measured energy spectra, i.

Stabilization of a fiber-optic two-arm interferometer for ultra-short pulse signal processing applications.

We experimentally demonstrate a stable ultrafast first-order temporal differentiator using a fiber-optic Michelson interferometer incorporating a simple feedback stabilization control, which is based on dithering a single wavelength cw reference. Feedback control signals are acquired by a phase-lock-loop and used for automatically adjusting and maintaining the resonance wavelength of the differentiator at the pulse center wavelength without dithering or disturbing the interferometer arms. Picosecond odd-symmetry Hermite-Gaussian waveforms using the implemented first-order differentiator have been stably generated.

Frequency-domain modal delay measurement for higher-order mode fiber based on stretched pulse interference.

We propose and demonstrate a novel modal delay measurement technique for a higher-order mode fiber (HOF) based on optical frequency-domain reflectometry (OFDR) using an extremely simple, entirely passive, and ultrafast wavelength sweeping mechanism, namely, dispersion-induced optical pulse stretching. We obtained a high temporal resolution of approximately 1.12 ps, which was sufficient for discerning the four excited modes in an HOF with a length of only approximately 5 m.

Direct time-response measurement of high-speed optical modulators based on stretched-pulse interferometry.

A simple technique for the direct measurement of the complex temporal response of a high-speed electro-optic (EO) modulator is proposed. This technique recovers the amplitude and phase temporal profiles of an instantaneous modulation over the duration of a chirped pulse (obtained by linear dispersion) using Fourier-transform interferometry, and it exploits the time-to-frequency mapping induced by the pulse dispersion process. The method can be implemented by using either time- or frequency-domain interferometric detection, allowing the characterization of modulation bandwidths in the tens-of-gigahertz range.

Fast and accurate group delay ripple measurement technique for ultralong chirped fiber Bragg gratings.

A simple and very precise group delay ripple (GDR) measurement technique for linearly chirped fiber Bragg gratings (CFBGs) is proposed. It is based on real-time optical Fourier transformation of an ultrashort pulse directly induced by the CFBG dispersion. We have experimentally demonstrated highly accurate characterization of the GDR profile of a commercial 10-m-long CFBG with a dispersion of +2000 ps/nm, having achieved a remarkably small standard deviation in our measurements of about 4 ps over a bandwidth of 28 nm.

Transform-limited picosecond pulse shaping based on temporal coherence synthesization.

A simple and efficient optical pulse re-shaper based on the concept of temporal coherence synthesization is proposed and analyzed in detail. Specifically, we demonstrate that an arbitrary chirp-free (transform-limited) optical pulse waveform can be synthesized from a given transform-limited Gaussian-like input optical pulse by coherently superposing a set of properly delayed replicas of this input pulse, e.g.

Optical frequency domain reflectometry based on real-time Fourier transformation.

We propose and demonstrate an ultrahigh-speed optical frequency domain reflectometry (OFDR) system based on optical frequency-to-time conversion by pulse time stretching with a linearly chirped fiber Bragg grating (LCFG). This method will be referred to as OFDR based on real-time Fourier transformation (OFDR-RTFT). In this approach, the frequency domain interference pattern, from which the desired axial depth profile is reconstructed, can be captured directly in the time-domain over the duration of a single stretched pulse, which translates into unprecedented axial line acquisition rates (as high as the input pulse repetition rate).

Analysis of nonlinear frequency sweep in high-speed tunable laser sources using a self-homodyne measurement and Hilbert transformation.

We have proposed and demonstrated a novel measurement technique for characterizing nonlinear frequency sweep in high-speed tunable laser sources by using a simple self-homodyne setup and Hilbert transformation. Measurement results, such as the variation in frequency scanning rate during a frequency sweeping process, are presented for a temperature-tuned distributed feedback laser diode and external cavity tunable laser. The time-varying optical phase of the incident light of a laser is calculated from the integration of the instantaneous optical frequency, and the tuning rate is obtained from its derivative.

Frequency-domain intermodal interferometer for the bandwidth measurement of a multimode fiber.

A new bandwidth measurement technique for a multimode optical fiber (MMF) using a frequency-domain intermodal interferometer is proposed. We have demonstrated that the relative modal delay (RMD) of a MMF can be obtained easily and accurately based on an optical frequency-domain reflectometry (OFDR) technique by using an intermodal interference signal among the excited modes of a MMF. As an example, a photonic crystal fiber with a few modes is prepared and its RMD is measured by using our proposed measurement technique.

Fourier-domain low-coherence interferometry for differential mode delay analysis of an optical fiber.

We propose a novel mode analysis and differential mode delay measurement method for an optical fiber using Fourier-domain low-coherence interferometry. A spectral interferometer based on a Mach-Zehnder interferometer setup was used with a broadband source and an optical spectrum analyzer to detect relative temporal delays between the guided modes of a few-mode optical fiber by analyzing spectral interference signals. We have shown that experimental results of the proposed method agree well with those results obtained by using a conventional time-domain measurement method.

Suppression of nonlinear frequency sweep in an optical frequency-domain reflectometer by use of Hilbert transformation.

A compensation technique for reducing the effect of nonlinear optical frequency swept in an optical frequency-domain reflectometer (OFDR) is proposed. The instantaneous sweep optical frequency of an OFDR laser source is directly obtained by analysis of the interference signal from an auxiliary interferometer with a Hilbert transformation. Beating OFDR data from a main interferometer are regenerated with respect to the measured instantaneous optical frequency.