Optical Sampling Technique Research Articles

Statistics of a turbulent Raman fiber laser.

We report the experimental study of statistical properties of partially coherent waves emitted by a Raman fiber laser operating in the normal dispersion regime. Using an asynchronous optical sampling technique, we accurately measure the probability density function of the optical power of the Stokes wave that exhibits strong and fast fluctuations. As predicted from numerical simulations presented by Randoux et al. [Opt. Lett.36, 790 (2011)], the statistical distributions of the intracavity Stokes power are found to be very different before and after reflection on the cavity Bragg mirrors. In particular, the Stokes wave incident on fiber Bragg grating mirrors exhibits statistics with tails that are much lower than those defined by the normal law.

Carrier-Envelope Phase Measurement With Linear Optical Sampling

In the few-cycle pulses, the temporal evolution of the electric field sensitively depends on the carrier-envelope phase (CEP). The ability to measure and stabilize the CEP therefore becomes a crucial issue for all applications. However, few studies are focused on the measurement of CEP with coherent linear optical sampling. We propose an efficient method to measure the CEP of the frequency comb pulses by employing a high-resolution linear optical sampling technique. It is shown that constant chirp and pulsewidth of frequency comb pulses have negligible effect on the CEP measurement.

Generation and detection of gigahertz acoustic oscillations in thin membranes

Single crystalline membranes are a perfect model system for the study of coherent acoustic phonon generation and decay in the time domain. Coherent acoustical modes are excited and detected in thin single-crystalline silicon and gallium arsenide membranes with femtosecond pulses in the ultraviolet and infrared wavelength region using the asynchronous optical sampling technique. The measured acoustic spectra are compared with each other and are discussed in terms of different generation and detection mechanisms. A clear dependence of the generated spectra on the absorption length of the pump and probe pulses is observed. It is shown that a short absorption length for the pump pulse leads to the generation of coherent high frequency phonons up to several 100GHz frequencies. Membranes are demonstrated to be useful as broadband acoustic cavities and can help to disentangle details of high frequency phonon dynamics. Two-layer membrane systems offer additional insight into energy transfer in the GHz frequency range and adhesion properties.

Direct intensity sampling of a modelocked terahertz quantum cascade laser

Pulses from an actively modelocked terahertz quantum cascade laser are fully characterized using an optical sampling technique to detect the total instantaneous terahertz intensity. By triggering the quantum cascade laser electronics with a femtosecond laser, we are able to measure both the formation of modelocked pulses and the quasi-steady state. The dependence of the pulse width on the modulation power and drive current are investigated. At low drive currents, we measure transform-limited gaussian-shaped pulses with a FWHM of 19 ps.

Non-degenerated photoluminescence excitation correlation spectroscopy using an optical sampling technique

We have developed a highly time-resolved photoluminescence spectroscopy based on the excitation correlation method. Successive irradiation of a pair of ultrashort light pulses with different wavelength combinations taken from two sub-picosecond lasers has exposed both temporal and energetic correlation in photoluminescence intensity associated with a nonlinear response of a sample. An optical sampling technique has been introduced successfully in order to avoid consideration of the synchronization control of ultrashort light pulses. We have demonstrated the abilities of this technique by applying to the nonlinear photoluminescence dynamics of organic dye molecules in solution.

Effect of hydrogen addition on soot formation in an ethylene/air premixed flame

The effect of hydrogen addition to fuel in soot formation and growth mechanisms is investigated in a rich ethylene/air premixed flame. To this purpose, three-angle scattering and extinction measurements are carried out in flames with different hydrogen contents. By applying the Rayleigh–Debye–Gans theory and the fractal-like description, soot concentration and morphology, with the evaluation of radius of gyration, volume-mean diameter and primary particle diameter are retrieved. To derive fractal parameters such as fractal dimension and fractal prefactor to be used for optical measurements, sampling technique and TEM analysis are performed. In addition, data concerning soot morphology obtained from TEM analysis are compared with the optical results. A good agreement in the value of the primary particle diameter between optical and ex-situ measurements is found. Significant effects of hydrogen addition are detected and presented in this work. In particular, hydrogen addition to fuel is responsible for a reduction in soot concentration, radius of gyration and primary particle diameter.

A Study of Observing Optical Waveform Applying All Optical Signal Sampling Technique Using a Chirped Periodically Poled Lithium Niobate Wavelength Converter

In order to observing a waveform of a high symbol-rate optical signal, all optical signal sampling technique using a periodically poled LiNbO3 (PPLN) wavelength converter is experimentally investigated. An optical gate is realized by a chirped PPLN having 2.2-nm QPM wavelength range where caused difference frequency generation between a high symbol rate optical signal and short pulses for sampling. An experiment of optical signal sampling is carried out by injecting an optical pulse train with 2.8-ps time width and an 160 Gb/s signal to the PPLN thus basic operation of the proposed scheme is confirmed.

Sampling techniques for single-cell electrophoresis.

Cells are extraordinarily complex, containing thousands of different analytes with concentrations spanning at least nine orders of magnitude. Analyzing single cells instead of tissue homogenates provides unique insights into cell-to-cell heterogeneity and aids in distinguishing normal cells from pathological ones. The high sensitivity and low sample consumption of capillary and on-chip electrophoresis, when integrated with fluorescence, electrochemical, and mass spectrometric detection methods, offer an ideal toolset for examining single cells and even subcellular organelles; however, the isolation and loading of such small samples into these devices is challenging. Recent advances have addressed this issue by interfacing a variety of enhanced mechanical, microfluidic, and optical sampling techniques to capillary and on-chip electrophoresis instruments for single-cell analyses.

SPECTRO-TEMPORAL MISMATCH ANALYSIS OF A TRANSMISSION LINE BASED ON ON-WAFER OPTICAL SAMPLING

We present an optical sampling technique that enables exploration of mismatches of a microstrip transmission line based on reflection analyses of electromagnetic pulses. The external electro-optic sampling scheme with a minute crystal detects high-speed electrical pulses over arbitrary locations of a line with very low-intrusiveness. The temporal pulsed signals measured with an on-wafer optical probing system and the corresponding spectra are obtained to analyze the transfer characteristics of a microstrip transmission line with 20 GHz bandwidth. The spectro-temporal response was cross-checked with commercial instruments. Applications of this optical probing technique to explore mismatches at the terminal port — based on both time and frequency domain reflectometry analyses — are also presented.

Experimental investigation on a software synchronous optical sampling technique based on periodically poled lithium niobate

A software synchronous optical sampling system is constructed based on sum frequency generation (SFG) in periodically poled lithium niobate (PPLN). Five gigahertz of a non-return-to-zero (NRZ) data signal is sampled by sampling pulse with the repetition frequency of 29.31 MHz. The power of the SFG light is set at -23 dBm, and an eye diagram is successfully recovered. A band-pass filter is added before the sampling pulse is subjected to erbium-doped fiber amplifier to reduce gain competition and ensure a high power level of SFG.

Characteristic analysis on temporal evolution of floc size and structure in low-shear flow

A series of flocculation tests were performed to investigate the effect of low-shear rates ( G = 3–16 s −1) on flocculation of kaolin suspension by polyaluminum chloride (PACl), with the goal of understanding floc growth mechanisms. Results were reported in terms of floc average size ( d p ) and boundary fractal dimension ( D pf ), derived from a non-intrusive optical sampling and digital image analysis technique. As expected, the rate of floc aggregation increased with increasing G, resulting in faster changes in aggregate size and structure in the initial stage of flocculation. Nevertheless, steady state was attained faster for D pf than for d p at the same shear rates, possibly due to the self-similarity of fractal aggregates. An interesting finding was that at G = 3 s −1, an obvious plateau was observed for the average-size evolution at steady state; for shear rates of 6 and 7 s −1, the flocs exhibited some decrease after reaching the peak of size, mainly as a result of floc settling at steady state; and for G = 11–16 s −1, a decrease in floc size was possibly attributed to the irreversibility of PACl-floc breakage. The process of floc growth was described using a fractal growth model, which defined flocculation as the result of the combined processes of aggregation and restructuring. The conceptual model could effectively characterize temporal changes in floc size and structure, and found that fragmentation followed by reformation seemed to be more effective in forming larger and more compact aggregates than the restructuring process due to erosion and reformation, which may provide useful insights for the design of flocculation reactors.

광-전자파 기반 20 GHz급 펄스 샘플링 오실로스코프

본 논문에서는 전자 소자 기반의 상용 오실로스코프에 의한 기존의 펄스 신호 측정 방법의 주파수 한계를 극복하기 위하여 전기광학 기반의 측정 방법을 기술하였다. 펄스폭 0.1 ps의 펨토초 레이저와 광다이오드를 사용하여 20 GHz 주파수 범위에 대응되는 전자기 펄스를 발생시키고, 마이크로스트립 선로를 통해 전송되는 전자기 펄스를 검출하기 위하여 전기광학 샘플링 기법을 이용하였다. 마이크로스트립 선로 위의 매우 근접한 거리에서 광학 결정 프로브를 이용하여 비접촉식으로 펄스 신호를 검출하고, 선로의 출력단 펄스 신호를 기존의 오실로스코프로 측정하여 두 측정 결과를 서로 비교하였다. This paper presents an optical sampling technique which can be used to overcome the limited bandwidth of a commercial electronic sampling oscilloscope for pulsed signal measurement. Employing an ultrafast laser with 0.1 ps pulse duration, 20 GHz electromagnetic pulses were generated through a fast photodiode. These pulses were transmitted through a microstrip line and sampled with an optically triggered electro-optic system. Two sampled 20 GHz pulses - measured independently over the transmission line with a non-contacting electro-optic method and conventional electronic one through a coaxial cable - were compared.

Experimental validation of a chromatic dispersion monitoring technique using optical asynchronous sampling and double sideband filtering

In this paper we propose and experimentally demonstrate a novel technique that uses optical asynchronous sampling and double sideband filtering. The purpose is to demonstrate a technique with proper acquisition time, that dismisses a fast photodetector using optical domain sampling techniques. It also does not need an high power regime to work, as those techniques employing nonlinear effects. The technique relates chromatic dispersion with the Peak-to-Average Power Ratio (PAPR), which makes this technique power independent, suitable for reconfigurable networks where packets travel through disctint paths, thus leading to different power levels.

A Study of Observing Optical Waveform Applying All Optical Signal Sampling Technique Using a High Nonlinear Fiber

All optical signal sampling technique using a high nonlinear fiber is experimentally investigated in order to observing a waveform of a high symbol-rate optical signal. Optical sampling pulses having time width of 2.8 ps are generated from an output of a semiconductor mode lock laser module by reducing the pulses using optical gates. Envelope of the optical signal is sliced to the slow rate signal by the sampling pulses through the effect of four wave mixing caused in the high nonlinear fiber. Applying this manner, simple and less alignment system is realized. In order to confirm the basic operation of the scheme, signal conversion efficiencies to idler light are evaluated by using two types of fiber. Moreover, optical signal sampling experiments are carried out by using a 160 Gb/s On-Off-Keying signal.

Direct Measurement of Vector Polarization-Mode Dispersion From Repeated Random Data by Use of Linear Optical Sampling

Polarization-dependent optical sampling techniques measure the complex electric field, allowing one to monitor the degrading effects of a communication channel. Here we show the ability to extract the polarization-mode dispersion of the transmission channel from a remote measurement of transmitted repeated 10-Gb/s differential phase-shift keying modulated data. This approach is independent of modulation format and data rate. We demonstrate results both with and without referencing to the laser phase. We achieve a differential group delay resolution of 0.2 ps for an unreferenced measurement.

Ultrashort optical pulse monitoring using asynchronous optical sampling technique in highly nonlinear fiber

An asynchronous optical sampling scheme based on four-wave mixing (FWM) in highly nonlinear fiber (HNLF) is experimentally demonstrated. Based on this scheme, 10-GHz input pulse train with 1.8-ps pulse width is successfully sampled in 100-m HNLF. A single pulse at 10 GHz with 2.3-ps pulse width is rebuilt by using a 50-MHz frequency tunable free-running fiber laser as the sampling pulse source (SPS). 40-GHz pulse train is used as the input signal. The rebuilt waveforms, together with the low-jitter eye diagram, are also presented.

Dual-Channel Linear Optical Sampling for Simultaneously Monitoring Ultrafast Intensity and Phase Modulation

This paper proposes a novel optical sampling technique for monitoring ultrafast signal waveforms. The dual-channel sampling system, which employs two parallel interferometers offset by a slight relative delay, enables us to observe not only intensity but also phase (frequency) modulation without any restriction as regards signal coherence. The proposed method, based on linear interaction with local short-pulses, also allows the measurement of ultrafast signals without any electrical bandwidth limitation. The performance advantages of the proposed method are clarified through experiments, in which we successfully observe the intensity and frequency modulation of 10-Gbit/s gain-switched laser diode pulses and 160-Gbit/s optical time-division multiplexing signals, whose coherence time is much shorter than the sampling period.

Nearly Shot-Noise-Limited Performance of Dual-Channel Linear Optical Sampling for Ultrafast DPSK Signals

This paper describes a newly developed dual-channel linear optical sampling technique for observing ultrafast optical differential phase-shift keying (DPSK) signals. As the proposed measurement scheme offsets two parallel interferometers by a relative delay corresponding to 1-symbol length of the DPSK signal, the measured phase distribution reflects the signal quality which is determined by the phase difference between adjacent symbols. This technique, based on interferometric optical gating by local short-pulses, also offers ultrafast measurement at symbol rates of greater than 100 Gsymbol/s. Moreover, its detection sensitivity can reach the shot noise limit. The waveform degradation caused by the coherence of the light source and the pattern effect of the phase modulator is successfully observed in continuous waves and 10-Gsymbol/s nonreturn-to-zero DPSK signals, and the constellation measurement is demonstrated for a 160-Gsymbol/s return-to-zero DPSK signal. Measurement system noise is also discussed for characterizing the detection sensitivity, and the nearly shot-noise-limited performance is experimentally verified.

Gigahertz optical spin transceiver

We present a time-resolved optical technique to measure electron spin dynamics with GHz dynamical bandwidth, transform-limited spectral selectivity, and phase-sensitive (lock-in) detection. Use of a continuous-wave (CW) laser and fast optical bridge enables greatly improved signal-to-noise characteristics compared to traditional optical sampling (pump-probe) techniques. We demonstrate the technique with a measurement of GHz-spin precession in n-GaAs. This approach may be applicable to other physical systems where stroboscopic techniques cannot be used because of either noise or spectral limitations.

Combining acoustics and video to image fish in the acoustic dead zone

A stationary acoustical‐optical platform (AOP) has been developed to detect groundfish presence and to estimate biomass. The AOP is a new approach to fisheries science because sampling from a platform on the ocean floor overcomes limitations of traditional surface acoustic surveys, where echoes from groundfish near the seafloor are obscured by stronger reflections from the ocean bottom. The AOP capitalizes on the complementary strengths of acoustical and optical sampling techniques by using acoustics for fish enumeration and optics for species identification and measurements of fish length. Each AOP is equipped with four video cameras, two 200‐kHz sonar transducers, and a suite of environmental sensors. One sonar face is mounted in the horizontal direction to image the area directly above the seafloor, whereas the second transducer is oriented vertically to sample the water column above the platform. Acoustic backscatter, target species, size, and observation angle were quantified when fish were simultaneously detected by the sonar and optical sensors. Calculations of target strengths were then related to fish size and orientation, for incorporation into biomass estimates. The AOP is designed to be used in an observation system with multiple platforms elements, so fish populations can be monitored over large spatial scales. [Work supported by NOAA.]