Frequency-modulated continuous-wave lidar using I / Q modulator for simplified heterodyne detection

This is the published version. © Copyright 2012 Optical Society of AmericaA frequency-modulated continuous-wave (FMCW) lidar is demonstrated with heterodyne detection. The lidar transmitter utilizes an electro-optic / modulator for the first time to generate carrier-suppressed and frequency-shifted FM modulation. This eliminates the need for an acousto-optic frequency shifter commonly used in heterodyne lidar transmitters. It also allows the use of a much wider modulation bandwidth to improve the range resolution. The capability of complex optical field modulation of the / modulator provides an additional degree of freedom compared with an intensity modulator, which will benefit future lidar applications

Complex-optical-field lidar system for range and vector velocity measurement

A grant from the One-University Open Access Fund at the University of Kansas was used to defray the author’s publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.A coherent lidar system based on the measurement of complex optical field is demonstrated for the first time. An electro-optic in-phase/quadrature (I/Q) modulator is used in the lidar transmitter to realize carrier-suppressed complex optical field modulation in which the positive and the negative optical sidebands can carry independent modulation waveforms. A fiber-optic 90° hybrid is used in the lidar receiver for coherent heterodyne detection and to recover the complex optical field. By loading a constant modulation frequency on the lower optical sideband and a wideband linear frequency chirp on the upper sideband, vector velocity and target distance can be measured independently. The wide modulation bandwidth of this lidar system also enabled unprecedented range resolution and the capability of measuring high velocity unambiguously

Digital Phase Noise Compensation for DSCM-Based Superchannel Transmission System With Quantum Dot Passive Mode-Locked Laser

We propose a simplified digital phase noise compensation technique for a Nyquist pulse-shaped digital subcarrier multiplexed (DSCM) coherent optical transmission system, employing an optical frequency comb based on Quantum dot passive mode-locked laser (QD-PMLL). Our results show that the impact of dominant common mode phase noise can be efficiently compensated at the receiver by digitally mixing the data sideband with the complex conjugate of the residual carrier component. This digital mixing technique resulted in better bit error rate performance compared to the conventional mth power Viterbi-Viterbi algorithm for QPSK and blind phase noise compensation for 16-quadratic-amplitude modulation formats, especially in the presence of large phase noise. To this end, exploiting the mutual coherence between the mode-locked comb lines of QD-PMLL, we numerically demonstrate its potential applicability as a transmission source for coherent optical superchannel transmission

Fiber Laser Based Two-Photon FRET Measurement of Calmodulin and mCherry-E0GFP Proteins

This is the peer reviewed version of the following article: Adany, P., Johnson, C. K. and Hui, R. (2012), Fiber laser based two-photon fret measurement of calmodulin and mcherry-E0GFP proteins. Microsc. Res. Tech., 75: 837–843. doi:10.1002/jemt.22002, which has been published in final form at http://doi.org/10.1002/jemt.22002. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.The speed and accuracy of Förster Resonance Energy Transfer (FRET) measurements can be improved by rapidly alternating excitation wavelengths between the donor and acceptor fluorophore. We demonstrate FRET efficiency measurements based on a fiber laser and photonic crystal fiber as the source for two-photon excitation (TPE). This system offers the potential for rapid wavelength switching with the benefits of axial optical sectioning and improved penetration depth provided by TPE. Correction of FRET signals for cross excitation and cross emission was achieved by switching the excitation wavelength with an electrically controlled modulator. Measurement speed was primarily limited by integration times required to measure fluorescence. Using this system, we measured the FRET efficiency of calmodulin labeled with Alexa Fluor 488 and Texas Red dyes. In addition, we measured two-photon induced FRET in an E0GFP-mCherry protein construct. Results from one-photon and two-photon excitation are compared to validate the rapid wavelength switched two-photon measurements

40-Gbps vestigial sideband half-cycle Nyquist subcarrier modulation transmission experiment and its comparison with orthogonal frequency division multiplexing

This is the published version. Copyright 2014 Society of Photo-optical Instrumentation EngineersWe experimentally demonstrate the superior performance of a 40-Gbps 16-QAM half-cycle Nyquist subcarrier modulation (SCM) transmission over a 100-km uncompensated standard single-mode fiber using dual-drive Mach-Zehnder modulator-based vestigial sideband intensity modulation and direct detection. The impact of modulator chirp on the system performance is experimentally evaluated. This Nyquist-SCM technique is compared with optical orthogonal frequency division multiplexing in both back-to-back and 100-km transmission experiments, and the results show that the Nyquist system has a better performance

Iterative intersymbol interference cancellation in vestigial sideband Nyquist–subcarrier modulation system

This is the published version. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)The intersymbol interference caused by dispersion, chirp, and a vestigial sideband filter in intensity modulation and a direct detection single carrier system is analyzed theoretically and numerically. An iterative nonlinear intersymbol interference cancellation technique is proposed and experimentally demonstrated in a 40- Gbps 16-QAM Mach-Zehnder modulator-based vestigial sideband intensity modulation and direct detection halfcycle Nyquist–subcarrier modulation system over a 100-km uncompensated standard single-mode fiber transmission for the first time. The experimental results show that 2.2-dB receiver sensitivity improvement is obtained at the forward error correction limit by using the iterative technique

Digital Compensation of Relative Phase Noise for DSCM Based Coherent Transmission System Using Forward Pumped Distributed Raman Amplification

We experimentally demonstrate pilot aided compensation of relative phase noise (RPN) in a distributed Raman amplified coherent fiber optic system with forward pumping. This technique effectively eliminates the error floor that arises when conventional phase noise compensation algorithms track RPN, especially in the context of higher order modulation formats and low baud rate signals. Extrapolating the experimental results, we also demonstrate through measurement and simulation, the effectiveness of pilot aided RPN compensation in a 25 Gbaud, 16-QAM modulated digital-subcarrier system with 2.5 Gbaud and 5 Gbaud subcarriers.This work was supported in part by US National Science Foundation under Grant 1409853

Tunable millimeter-wave generation with subharmonic injection locking in two-section strongly gain-coupled DFB lasers

©2000 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Using two-section dual-mode strongly gain-coupled (SGC) distributed feedback (DFB) lasers, tunable millimeter-wave (mm-wave) generation from 18 to 40 GHz can be achieved under CW bias conditions, Due to its high speed and excellent dynamic single-mode yield in SGC DFB lasers, each section can be individually modulated to beyond 10 GHz. Using subharmonic injection locking, the linewidth of the generated mm-wave can be significantly reduced and is found to be less than 30 Hz which is limited by the stability of the microwave source and the resolution of the spectrum analyzer. This device provides a useful source to high-bit-rate optical systems and/or high-frequency wireless communications

Fiber chromatic dispersion and polarization-mode dispersion monitoring using coherent detection

©2005 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.We propose and experimentally demonstrate a nondestructive method to monitor chromatic dispersion (CD) and polarization-mode dispersion (PMD) in traffic-carrying wavelength-division-multiplexing optical systems. Coherent heterodyne detection is used to down convert the spectrum of digitally modulated signal from optical domain into radio-frequency (RF) domain. By analyzing group delay difference and polarization walkoff between different frequency components through proper RF signal processing, both CD and PMD can be precisely determined. Good agreement between experimental results and theoretical values has been obtained