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Photonics Technology Letters, IEEE

Issue 22 • Date Nov.15, 2012

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  • [Front cover]

    Publication Year: 2012 , Page(s): C1
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    Freely Available from IEEE
  • IEEE Photonics Technology Letters publication information

    Publication Year: 2012 , Page(s): C2
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    Freely Available from IEEE
  • Table of contents

    Publication Year: 2012 , Page(s): 1979 - 1980
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    Freely Available from IEEE
  • Novel Demodulation Method for Fiber-Optic Interferometers Based on \pi/2 Phase Modulation

    Publication Year: 2012 , Page(s): 1981 - 1983
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (769 KB) |  | HTML iconHTML  

    This letter proposes a novel demodulation method for fiber-optic interferometer sensors. A fast square wave is added to the reference arm of the interferometer sensor in the form of phase modulation. Starting from this, we successfully developed a simple demodulation method that can greatly improve the conversion efficiency and overcome the unbalanced influences. Our experiment results show that a very small phase shift of about 6.3 × 10-5 rad can be detected, which proves high signal-to-noise ratio demodulated signal and low distortion in our demodulation method. The linearity between demodulated signal and test signal is shown to be over 99%. View full abstract»

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  • A Bidirectional 60-GHz Wireless-Over-Fiber Transport System With Centralized Local Oscillator Service Delivered to Mobile Terminals and Base Stations

    Publication Year: 2012 , Page(s): 1984 - 1987
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (473 KB) |  | HTML iconHTML  

    We propose a novel 60-GHz wireless-over-fiber (WoF) access system for multigigabit bidirectional data transmission. In conventional microwave wireless system designs, electrical local oscillator (LO) sources are required for frequency conversions in both base station (BS) and mobile terminal (MT), incurring considerable cost for system integration and maintenance at millimeter-wave frequencies. We design a WoF transport system, aiming to centralize system functions in the central office (CO), without requiring electrical LO devices in both BS and MT. In our proposed scheme, LO has been centralized in CO, the LO signal is distributed as a service to carry out frequency up-/down-conversion functions required in BS and MT. Thus, in this simplified system architecture, the overall cost can be reduced and the operation quality of centralized LO service enhanced. The operation principle and feasibility of error-free transmission of multigigabit, bidirectional data streams over both fiber and free space has been demonstrated experimentally. View full abstract»

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  • Teardrop Reflector-Assisted Unidirectional Hybrid Silicon Microring Lasers

    Publication Year: 2012 , Page(s): 1988 - 1990
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (503 KB) |  | HTML iconHTML  

    We study directional bistability in hybrid silicon microring lasers and demonstrate a unidirectional laser. Unidirectional emission is achieved by integrating a passive reflector that feeds laser emission back into the laser cavity to introduce an extra unidirectional gain. We show that the length of the passive reflector is a critical parameter in determining the lasing behavior. View full abstract»

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  • Enhanced Optical Power of InGaN/GaN Light-Emitting Diode by AlGaN Interlayer and Electron Blocking Layer

    Publication Year: 2012 , Page(s): 1991 - 1994
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (657 KB) |  | HTML iconHTML  

    We report on the effect of an AlGaN interlayer with a low Al composition, which is inserted between multiple quantum wells (MQWs) and an AlGaN electron blocking layer (EBL) in light-emitting diodes (LEDs). The band diagram shows that this interlayer reduces the hole barrier height between the last GaN barrier in MQWs and the AlGaN EBL to enhance the hole injection. The optical output power at 20 mA of LEDs with interlayer is increased by 20% more than that of LEDs without an interlayer. This improvement is attributed to the enhanced radiative recombination rate, which is due to a more uniform hole distribution and higher hole concentration in MQWs. View full abstract»

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  • Solution-Processed Photoconductive UV Detectors Based on ZnO Nanosheets

    Publication Year: 2012 , Page(s): 1995 - 1997
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (667 KB) |  | HTML iconHTML  

    A low-cost and complexity-free demonstration of two relatively fast ultraviolet (UV) detectors based on ZnO nanosheets are reported in this letter for the first time. Highly crystalline ZnO nanosheets have been synthesized by a sonochemical method. The proposed UV detectors were fabricated through coating the synthesized materials on Cu electrodes. Experimentally obtained responsivity, detectivity, absorption, and I-V characteristics along with the quantum efficiency are reported. Comparison of the conventional ZnO photo-sensors with nanoparticle-based ones reveals that the proposed nanosheets photosensors have faster response time in the UV region, which might be attributed to low density of defect states (created during synthesis process) on nanosheets surfaces. View full abstract»

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  • Nonlinear Absorption at Optical Telecommunication Wavelengths of InN Films Deposited by RF Sputtering

    Publication Year: 2012 , Page(s): 1998 - 2000
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (395 KB) |  | HTML iconHTML  

    We report on the nonlinear optical absorption of InN films deposited on GaN templates by radio-frequency (RF) sputtering. The layers are characterized through the pump-probe technique at 1.55 μm, by obtaining a nonlinear absorption coefficient of 167±30 cm/GW with a nonlinear response recovery time of 380 fs. This nonlinear behavior is attributed to a two-photon absorption process followed by a free carrier absorption by the photogenerated carriers. These results render InN films deposited by RF sputtering particularly suitable for ultrafast all-optical devices based on low-cost technology. View full abstract»

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  • Photonic Generation of Precisely \pi Phase-Shifted Binary Phase-Coded Microwave Signal

    Publication Year: 2012 , Page(s): 2001 - 2004
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1542 KB) |  | HTML iconHTML  

    A novel photonic approach to generating a precisely π phase-shifted binary phase-coded microwave signal is proposed and experimentally demonstrated. A phase modulator is employed to generate two ±1st-order sidebands and an optical carrier. Due to the inherent ±π/2 phase shifts of the two ±1st-order sidebands, a binary phase-coded microwave signal with a precise phase shift of π is generated through beating one sideband with the optical carrier at a time, which is realized by joint use of a polarization-maintaining fiber Bragg grating and a polarization modulator to select one of the two sidebands and the optical carrier. The generation of a binary phase-coded microwave signal with a precise π phase shift and with a tunable frequency from 18 to 22 GHz is experimentally demonstrated. View full abstract»

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  • Time Division Multiplexing Optical Time Domain Reflectometry Based on Dual Frequency Probe

    Publication Year: 2012 , Page(s): 2005 - 2008
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (421 KB) |  | HTML iconHTML  

    A new frequency coding method is proposed and experimentally demonstrated that employs a phase modulator driven by sequential radio frequency and a synchronously controlled acoustooptic modulator to generate time division multiplexing probe pulses for coherent optical time domain reflectometry (C-OTDR). Each probe pulse contains two probe frequencies that are symmetrical regarding the frequency of local oscillator (LO). Heterodyne between the backscattered Rayleigh light of the dual frequency probe pulse and LO generates the same intermediate frequency. Experimental results show that the new C-OTDR, using ten frequency-coded probe pulses, brings an 8.0-dB dynamic range enhancement, compared with conventional C-OTDR. View full abstract»

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  • Experimental Investigations of 3-D-/4-D-CAP Modulation With Directly Modulated VCSELs

    Publication Year: 2012 , Page(s): 2009 - 2012
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4065 KB) |  | HTML iconHTML  

    In this letter, we present experimental investigations of multidimensional multilevel carrierless amplitude phase (CAP) modulation with directly modulated vertical cavity surface-emitting lasers. The signals are transmitted over 20 km of standard single-mode fiber (SSMF). For multilevel 3-D-CAP, bit rates of 468.75 and 937.5 Mb/s are achieved at two levels/dimension and four levels/dimension, respectively. For 4-D-CAP, bit rates of 416.67 and 833.3 Mb/s are achieved at two levels/dimension and four levels/dimension, respectively. For all signals, a bit-error rate below the forward error correction limit of 2.8 × 10-3 for error-free reception is achieved after 20 km of SSMF transmission. Spectral efficiencies of 2.68 and 2.08 b/s/Hz are reported for 3-D-CAP and 4-D-CAP, respectively. We believe that multidimensional modulation formats represent an attractive solution for providing more flexibility for optical fiber systems. View full abstract»

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  • Light-Extraction Enhancement by Cavity Array-Textured N-Polar GaN Surfaces Ablated Using a KrF Laser

    Publication Year: 2012 , Page(s): 2013 - 2015
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1671 KB) |  | HTML iconHTML  

    The creation of KOH-etched pyramidal patterns on the N-GaN surface is considered to be the most effective texturing method for improving the light-extraction efficiency of GaN LEDs. Using KrF-laser ablation, concave downward cavities are formed on the N-GaN surface. This letter demonstrates that KrF-laser-ablated cavities enhance the light-extraction efficiency of the KOH-etched pyramidal N-GaN surface by 25%. With further etching by KOH, the curved-surface sidewall of laser-ablated cavities do not form pyramids; instead, relatively large inclined facet sidewalls are formed in the laser-ablated cavities. We believe that these inclined facet sidewalls in laser-ablated cavities further enhance the light-extraction efficiency of KOH-etched pyramidal N-GaN surfaces. View full abstract»

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  • Analytical Fiber-Optic Channel Model in the Presence of Cross-Phase Modulation

    Publication Year: 2012 , Page(s): 2016 - 2019
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    A simple but accurate analytical model for the fiber-optic channel affected by cross-phase modulation (XPM) is proposed and validated through numerical simulations. The model describes XPM as a time-varying and frequency-selective complex fading, whose impact and statistical properties can be analytically investigated. As an example, the proposed model is applied to derive an analytic lower bound to the channel capacity and to investigate the coherence properties of the channel. View full abstract»

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  • Enlarged Photodetection Using {\rm SiO}_{x} Nanowire Arrays

    Publication Year: 2012 , Page(s): 2020 - 2023
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1359 KB) |  | HTML iconHTML  

    We have synthesized perpendicular SiOx nanowire (NW) arrays on Si substrates and investigated them using scanning electron microscopy. Transmission electron microscopy and energy-dispersive spectroscopy have been used to investigate the single NW structure. A near-infrared emission at 700 nm is observed. In/SiOx NW and In/SiOx thin film (TF) contacts exhibit Schottky behavior. The SiOx NW-based devices show six-fold improvements in photodetection efficiency in white-light illumination, compared to SiOx TF-based devices under reverse bias condition. View full abstract»

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  • Bidirectional Hybrid OFDM-WDM-PON System for 40-Gb/s Downlink and 10-Gb/s Uplink Transmission Using RSOA Remodulation

    Publication Year: 2012 , Page(s): 2024 - 2026
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (387 KB) |  | HTML iconHTML  

    We experimentally demonstrate a bidirectional hybrid orthogonal frequency-division-multiplexing wavelength-division-multiplexing passive optical network (OFDM-WDM-PON) system. The proposed scheme uses OFDM signals occupying different portions of the available signal spectrum for uplink and downlink signal transmissions to reduce the effects of Rayleigh backscattering, chromatic dispersion, and power fading. A 40-Gb/s downlink signal transmission based on a single sideband modulated OFDM signal, and a 10-Gb/s uplink signal transmission using remodulation of a reflective semiconductor-optical-amplifier are realized. View full abstract»

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  • Large Port Count Wavelength Routing Optical Switch Consisting of Cascaded Small-Size Cyclic Arrayed Waveguide Gratings

    Publication Year: 2012 , Page(s): 2027 - 2030
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4885 KB) |  | HTML iconHTML  

    We propose a highly scalable switch architecture suitable for client-side cross-connect switches in reconfigurable optical add/drop multiplexers and optical switching in data centers. It consists of cascaded cyclic arrayed waveguide gratings (AWGs). We develop a 270 × 270 prototype switch consisting of an assembly of arrayed small switches and couplers and AWGs that are fabricated on planar lightwave circuit chips. Transmission experiments verify its technical feasibility. View full abstract»

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  • CMOS Compatible Silicon-on-Insulator Polarization Rotator Based on Symmetry Breaking of the Waveguide Cross Section

    Publication Year: 2012 , Page(s): 2031 - 2034
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (411 KB) |  | HTML iconHTML  

    A polarization rotator in silicon-on-insulator technology based on breaking the symmetry of the waveguide cross section is reported. The 25- μm-long device is designed to be integrated with standard grating couplers without the need for extra fabrication steps. Hence, fabrication is carried out by a 2-etch-step complementary metal-oxide-semiconductor compatible process using 193-nm deep ultraviolet lithography. A polarization conversion efficiency of more than -0.85 & dB with insertion losses ranging from -1 to -2.5 & dB over a wavelength range of 30 nm is demonstrated. View full abstract»

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  • Performance Improvement of OOK Free-Space Optical Communication Systems by Coherent Detection and Dynamic Decision Threshold in Atmospheric Turbulence Conditions

    Publication Year: 2012 , Page(s): 2035 - 2037
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB) |  | HTML iconHTML  

    In this letter, we analyze the performance improvement of on-off-keying free-space optical communication systems in atmospheric turbulence conditions due to coherent detection and the dynamic decision threshold (DDT) scheme. Our analytical results show that the DDT scheme provides a 5.7-dB power reduction for achieving a bit error rate of 10-3 compared with the conventional fixed decision threshold scheme. In addition, the improvement achieved by the DDT scheme is related to the strength of amplitude and phase fluctuations, not to the power of the local oscillator. View full abstract»

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  • Lateral Stress Detection Using a Tapered Fiber Mach–Zehnder Interferometer

    Publication Year: 2012 , Page(s): 2038 - 2041
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (901 KB) |  | HTML iconHTML  

    In this letter, a novel approach to measure local lateral stress using a tapered fiber Mach-Zehnder interferometer (TFMZI) is proposed and demonstrated. The transmission spectra of the TFMZI are measured under different transverse pressures and loading positions. The responses of the TFMZI are analyzed in a spatial frequency domain by fast Fourier transform of the corresponding transmission spectra. The proposed approach allows an effective detection of lateral stress-induced fiber deformation at different positions along a TFMZI. View full abstract»

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  • Performance Evaluation of CDMA-DMT for 1-mm SI-POF Short-Range Transmission Links

    Publication Year: 2012 , Page(s): 2042 - 2045
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (332 KB) |  | HTML iconHTML  

    In this letter, the code division multiple access discrete multitone (CDMA-DMT) modulation scheme is experimentally investigated for transmission over an intensity modulation direct-detection link of 100 m of 1-mm polymethyl methacrylate step-index plastic optical fibers. CDMA-DMT is a multicarrier modulation scheme combining the merits of both CDMA and DMT and in which CDMA is utilized to perform a spreading operation of the data symbols in the frequency domain using orthogonal spreading codes. It is experimentally shown that CDMA-DMT performs better than conventional DMT in terms of achieved bit-error rate, for transmission rates in the range of 1 Gbps and over the same experimental configuration. View full abstract»

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  • Performance Improvement of 40-Gb/s Electroabsorption Modulator Integrated Laser Module With Two Open-Circuit Stubs

    Publication Year: 2012 , Page(s): 2046 - 2048
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (565 KB) |  | HTML iconHTML  

    In this letter, we propose and demonstrate a compact, low-cost, and easy to manufacture microstrip line with two open-circuit stubs to alleviate impedance mismatching of a packaged 40-Gb/s electroabsorption modulator integrated laser (EML) module. For comparison, two 1550-nm EML modules are fabricated, the only difference being that one of them is made with open-circuit stubs, while the other is not. It is revealed that the open-circuit stubs technique expands the 3-dB modulation bandwidth from 25.2 to 33.6 GHz, and the suppression of the input return loss below -10 dB in the range of the higher frequency of the sub-assembly with chip is also successfully demonstrated. Further evidence showing the advantage of the EML module with open-circuit stubs over the one without open-circuit stubs include the effective reduction in the RMS jitter of the eye diagram from 1.4 to 1.2 ps, as well as the improvement of the sensitivity, which changes from -8.3 to -9.5 dBm measured with the same receiver. View full abstract»

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  • Variation of Relative Intensity Noise With Optical Power in InGaAsP Semiconductor Optical Amplifier

    Publication Year: 2012 , Page(s): 2049 - 2051
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1018 KB) |  | HTML iconHTML  

    Relative intensity noise (RIN) is an index to evaluate the amount of noise compared to the optical intensity, which is widely believed to be increased by optical amplification. A previous paper, however, pointed out that theoretically the RIN of the output light of a semiconductor optical amplifier can be reduced from that of the input light, and that the RIN level is determined by the output optical power almost independently from the RIN level of the input light. Detailed experimental data to support these postulations are given in this letter. View full abstract»

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  • Effect of Paired Apertures in a Periodic Hole Array on Higher Order Plasmon Modes

    Publication Year: 2012 , Page(s): 2052 - 2055
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (964 KB) |  | HTML iconHTML  

    We demonstrate that the transmission of higher-order surface plasmon modes in the mid-infrared range can be enhanced through rectangular hole array on the basis of paired apertures. Experiments prove that enhanced high-order transmission can be generated by either identical shapes or combinations of different hole shapes in pairs. The structure factor is adopted to explain the observed intensity of enhanced transmission. Numerical simulations of the enhanced second-order mode verify a significant field enhancement in a unit cell of pairs. It is clarified that the separation between the paired apertures and the paired resonance is the key to determine certain higher-order plasmon modes to be enhanced. View full abstract»

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  • Honeycomb Photonic Crystal Waveguides in a Suspended Silicon Slab

    Publication Year: 2012 , Page(s): 2056 - 2059
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (737 KB) |  | HTML iconHTML  

    We report experimental evidence of light guiding at telecommunication wavelengths along line-defect honeycomb-lattice photonic crystal waveguides created in suspended silicon slabs. Numerical results show that the guided bands correspond to modes below the cladding light line so they are inherently lossless, although the measurements show quite high losses owing to fabrication imperfections. Honeycomb photonic crystals are a suitable platform for confining light and sound in nanoscale waveguides. View full abstract»

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Aims & Scope

This letters journal addresses all aspects of the IEEE Photonics Society Constitutional Field of Interest with emphasis on photonic/lightwave components and applications, laser physics and systems and laser/electro-optics technology.

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Meet Our Editors

Editor-in-Chief
Dr. Seb J. Savory
University College London