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Photonics Technology Letters, IEEE

Issue 4 • Date Feb.15, 2014

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Displaying Results 1 - 25 of 33
  • Front Cover

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

    Page(s): C2
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    Freely Available from IEEE
  • Table of contents

    Page(s): 317 - 318
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  • Decision-Directed Costas Loop Stable Homodyne Detection for 10-Gb/s BPSK Signal Transmission

    Page(s): 319 - 322
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (924 KB) |  | HTML iconHTML  

    This letter demonstrates decision-directed Costas loop stable homodyne detection for 10-Gb/s binary phase shift keying signal fiber-transmission of over 100 km utilizing frequency-stabilized several kilohertz spectral linewidth external cavity laser diodes (E-LDs). We design a phase-locked loop circuit that adopts an injection-current controlled E-LD as its local oscillator; its low phase error allows it to achieve the standard deviation of 1.9°. Owing to this phase-lock performance and the highly coherent light source, the receiver sensitivity approaches within 6 dB of the shot noise limit and the phase-locked loop recovers the optical carrier stably even if the waveform is distorted by the chromatic dispersion of 880 ps/nm after fiber transmission. View full abstract»

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  • 1.8-W Room Temperature Pulsed Operation of Substrate-Emitting Quantum Cascade Lasers

    Page(s): 323 - 325
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (936 KB) |  | HTML iconHTML  

    High-power broad area substrate-emitting distributed feedback (DFB) quantum cascade laser emitting at λ ~ 4.6 μm is reported. Proper second-order DFB grating coupling, low waveguide loss mechanism, and epilayer-down mounting bring about a high vertical radiative optical power. The maximum peak power is as high as 1.82 W at 20 °C and still 1.22 W at 50 °C operated in pulsed mode with a pulsed width of 1 μs and duty cycle of 0.2%. A single-lobed radiation far-field with a divergence angle of 7.9 ° in the ridge-width direction and two-lobed radiation far-field with a divergence angle of 0.61 ° in the cavity-length direction are achieved by depositing the high-reflection coatings on both facets. Robust single-mode emission is continuously tunable by the heat sink temperature up to 115 °C. View full abstract»

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  • Tunable Optoelectronic Oscillator Incorporating a Single Passband Microwave Photonic Filter

    Page(s): 326 - 329
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1881 KB) |  | HTML iconHTML  

    A wideband and continuously tunable optoelectronic oscillator (OEO) incorporating a single passband microwave photonic filter (MPF) is proposed and experimentally demonstrated. The single passband MPF is implemented using a broadband light source, a Mach-Zehnder interferometer (MZI) in which a phase modulator is incorporated in one arm, a dispersion compensating fiber (DCF), and a photodetector (PD). The light wave from the broadband light source is sent to the MZI, and the output signal from the MZI is sent to the DCF and then detected at the PD. The overall operation is equivalent to a single passband MPF with the central frequency of the passband tunable by tuning the length difference between the two arms of the MZI. By incorporating the MPF into an OEO, a microwave signal with a tunable frequency is generated. The proposed OEO is experimentally evaluated. A microwave signal with a tunable frequency from 1 to 12 GHz and a tuning step of 0.5 GHz is generated. The phase noise performance of the generated microwave signal is evaluated. At 6.02 GHz, the phase noise is measured to be -107 dBc/Hz at an offset of 10 kHz. View full abstract»

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  • Electrical Injection Schemes for Nanolasers

    Page(s): 330 - 333
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (800 KB) |  | HTML iconHTML  

    Three electrical injection schemes based on recently demonstrated electrically pumped photonic crystal nanolasers have been numerically investigated: 1) a vertical p-i-n junction through a post structure; 2) a lateral p-i-n junction with a homostructure; and 3) a lateral p-i-n junction with a buried heterostructure. Self-consistent laser-diode simulations reveal that the lateral injection scheme with a buried heterostructure achieves the best lasing characteristics at a low current, whereas the vertical injection scheme performs better at a higher current for the chosen geometries. For this analysis, the properties of different schemes, i.e., electrical resistance, threshold voltage, threshold current, and internal efficiency as energy requirements for optical interconnects are compared and the physics behind the differences is discussed. View full abstract»

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  • Polarization-Dependent Loss Impact on Coherent Optical Systems in Presence of Fiber Nonlinearity

    Page(s): 334 - 337
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (589 KB) |  | HTML iconHTML  

    We investigate the interaction of polarization-dependent loss (PDL) with Kerr nonlinearities by decoupling single- and cross-channel nonlinear distortions in a homogeneous 100-G polarization division multiplexing quadrature phase shift keying (PDM-QPSK) and a hybrid 100-G PDM-QPSK/10-G on/off keying system. Because of the decoupling method, we provide reasons for the interaction, using basic comprehensive examples. Both average Q-factor and its distribution are investigated in both dispersion-managed and dispersion-unmanaged links, showing that realistic PDL values affect outage probabilities notwithstanding a negligible average penalty. View full abstract»

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  • Signal-to-Noise Ratio Improvement in BOTDA Using Balanced Detection

    Page(s): 338 - 341
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1338 KB) |  | HTML iconHTML  

    Brillouin optical time domain analysis (BOTDA) relies typically on the interaction among two counter-propagating waves: 1) a pulsed pump wave and 2) a modulated probe wave. The modulated probe wave has typically two sidebands, located at ±νB with respect to the pump frequency. Conventional systems detect the time-resolved gain/loss by detecting only the upper/lower wavelength sideband. In this letter, we show that BOTDA can strongly benefit from the use of balanced detection among the two sidebands. In particular, the detected signal can be doubled while the noise only grows by a factor of (2)1/2, leading to a (2)1/2 signal-to noise ratio (SNR) increase. Moreover, any common-mode noise in the probe signal path (e.g., master laser noise, modulator drifts, and so forth) is eliminated, rendering the system more robust. We validate the principle by experimental results that highlight the benefits of the technique in terms of the SNR. View full abstract»

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  • Performance Characteristics of UV-C AlGaN-Based Lasers Grown on Sapphire and Bulk AlN Substrates

    Page(s): 342 - 345
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (587 KB) |  | HTML iconHTML  

    The performance characteristics of optically pumped laser heterostructures emitting in the UV-C spectral range between 272 and 279 nm are investigated. The laser heterostructures were grown by metal-organic vapor phase epitaxy on (0001) planar AlN/sapphire, epitaxially laterally overgrown (ELO) AlN/sapphire, and bulk AlN substrates with threading dislocation densities ranging from 2×1010 to 104 cm-2. We found that the defect density strongly affects the laser performance. The lowest pulse threshold energy density of 50 mJ/cm2 under resonant optical pumping condition was obtained for an AlGaN multiple quantum well laser grown pseudomorphically on low defect density bulk AlN substrate. Lasing was also observed for AlGaN MQW heterostructures grown on ELO AlN/sapphire templates. The laser emission in all lasers was TE polarized. However, no lasing was observed for heterostructures grown on high defect density AlN/sapphire. View full abstract»

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  • All-Polarization-Maintaining Femtosecond Fiber Lasers Using Graphene Oxide Saturable Absorber

    Page(s): 346 - 348
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (443 KB) |  | HTML iconHTML  

    We demonstrate the mode-locking operation in an all-polarization-maintaining (all-PM) erbium-doped fiber laser by exploiting graphene oxide saturable absorber for the first time. The self-started, environmentally stable laser directly generates linearly polarized soliton pulses of 502 fs duration at a repetition rate of 48.2 MHz with an extinction ratio of 21.3 dB. The optical spectrum centered at 1555.92 nm has 3-dB bandwidth of 6 nm. This unique combination of the all-PM configuration and the novel graphene oxide saturable absorber offers an ideal approach to fabricate a compact single-polarization femtosecond source with high environmental stability. View full abstract»

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  • Monolithic InP Receiver Chip With a Variable Optical Attenuator for Colorless WDM Detection

    Page(s): 349 - 351
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (423 KB) |  | HTML iconHTML  

    We demonstrate a monolithically integrated quadrature coherent receiver photonic integrated circuit (PIC) on an InP substrate. The PIC comprises a 90° optical hybrid, a variable optical attenuator (VOA), and four RF photodetectors. With a dynamic range of 25 dB, the VOA enables the usage of the receiver PIC for colorless WDM detection. View full abstract»

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  • Optical SEFDM System; Bandwidth Saving Using Non-Orthogonal Sub-Carriers

    Page(s): 352 - 355
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (798 KB) |  | HTML iconHTML  

    We propose and demonstrate a new optical spectrally efficient frequency division multiplexing (O-SEFDM) system, where non-orthogonal and overlapping sub-carriers are employed to provide higher spectral efficiency relative to optical-orthogonal frequency division multiplexing (O-OFDM). The O-SEFDM technique can increase spectral efficiency in both the electrical and optical domains. It is experimentally shown that for bandwidth saving up to 25%, we can achieve the same performance as O-OFDM. This is the first experimental verification of 25% optical faster than the Nyquist rate. Furthermore, for approximately the same spectral efficiency, 4QAM O-SEFDM outperforms standard 8QAM by 1.6 dB. It is experimentally shown that a lower-order modulation format can achieve a better performance by replacing a higher one. View full abstract»

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  • Entanglement-Preserving Photonic Switching: Full Cross-Bar Operation With Quantum Data Streams

    Page(s): 356 - 359
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (630 KB) |  | HTML iconHTML  

    As the field of quantum communications matures and adopts larger network topologies, it will require switches capable of multiplexing and demultiplexing entangled photons between network nodes. Such switches will need to operate at high speeds, with low loss, and minimal signal-band noise, while also retaining the quantum state of the routed photons. We present an all-optical, fiber-based, dual-in, dual-out switch that has a switching window of 45 ps and an insertion loss of <;3.0 dB. In addition, the switch introduces minimal degradation to the quantum state of the routed entangled photons. As a test of the switch's utility, we demultiplex a single quantum channel from a 6.5-GHz dual-channel quantum data stream. The recovered quantum state exhibits a fidelity of 96.2%±1.2% with the prepared state. View full abstract»

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  • Pulse-Width Tuning in a Passively Mode-Locked Fiber Laser With Graphene Saturable Absorber

    Page(s): 360 - 363
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (389 KB) |  | HTML iconHTML  

    An absorption-adjustable graphene saturable absorber is used in a simple fiber laser system for an active control of the pulse-width of optical pulses. Such a saturable absorber is created by tightly attaching the graphene film onto the upper surface of the microfiber, thus an enhanced evanescence-field interaction between the propagating light along the microfiber length and graphene can be achieved. By tuning the polarization state of the light beam launched into the saturable absorber from TE to TM mode, the pulse-width of the pulses is varied between ~ 9.24 and ~ 2.32 ps. View full abstract»

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  • 80-km Coherent DWDM-PON on 20-GHz Grid With Injected Gain Switched Comb Source

    Page(s): 364 - 367
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (394 KB) |  | HTML iconHTML  

    We have proposed and experimentally demonstrated a 6 × 40-Gb/s long reach dense wavelength division multiplexed passive optical network downlink system operating over 80 km of standard single mode fiber. The six optical channels with 20 GHz spacing are generated by an externally injected gain switched optical comb source. Each comb line is imposed with a 6-GBd polarization division multiplexed quadrature amplitude modulation, which included a 20% overhead for forward error correction. A worst case channel sensitivity of -35.6 dBm (54 photons/bit) at a bit error rate of 1.5×10-2 was achieved, yielding a system loss budget of 40 dB. View full abstract»

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  • A Single-Input Multiple-Output Optical System for Mobile Communication: Modeling and Validation

    Page(s): 368 - 371
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (426 KB) |  | HTML iconHTML  

    A single-input multiple-output optical communication system based on an LED transmitter and a receiving pixel grid of a camera is considered. The LED image received at a reference distance is modeled using a Gaussian mixture and the pixel values at any other desired distance are estimated using the reference image. Both optimal and suboptimal pixel combining techniques are analyzed. The experimental validation includes placement of the camera on a motorized translation stage to analyze the effects of random locations of the LED image on the pixel grid. Results show excellent agreement between proposed model and the experiment. When random image locations over the pixel grid due to mobility are considered, a receiver that uses only the best pixel is found to lose more than 50% of the received power over a maximal ratio combiner at a distance of 2 m. View full abstract»

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  • Variational Approximations for {\rm LP}_{l1} Modes of Graded-Index Few-Mode Fibers

    Page(s): 372 - 375
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (483 KB) |  | HTML iconHTML  

    Two parameter variational fields for the LPl1 modes of a graded index few-mode fiber have been proposed. Using these, the propagation constant, the normalized group delay and the normalized dispersion parameter have been calculated for few representative modes. The accuracies of the results have been calculated by comparison with the exact results obtained from the numerical solution of the scalar wave equation. As expected, the two parameter fields give better accuracies than the single-parameter fields available in the literature. Furthermore, it is observed that the accuracy decreases for higher order LPl1 modes. Thus, these fields may be used in few-mode fiber-based photonic devices, which utilize lower order LPl1 modes. View full abstract»

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  • Orthogonal Basis Expansion-Based Phase Noise Suppression for PDM CO-OFDM System

    Page(s): 376 - 379
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (535 KB) |  | HTML iconHTML  

    In this letter, we develop an orthogonal basis expansion (OBE)-based phase noise suppression method for polarization-division-multiplexed (PDM) coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. Compared with the conventional phase noise suppression approach, the OBE method not only significantly promotes the system tolerance of laser phase noise, but also improves the system robustness against nonlinear phase noise. The theoretical analysis is validated by numerical simulations of PDM CO-OFDM systems with 16-quadrature-amplitude-modulation format. View full abstract»

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  • Highly Nonlinear Dispersion-Flattened Slotted Spiral Photonic Crystal Fibers

    Page(s): 380 - 383
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (884 KB) |  | HTML iconHTML  

    We propose a new type of highly nonlinear spiral photonic crystal fiber (PCF) with flat and low dispersion over a wide wavelength range. The new PCF structure adopts an elliptical slot core. The simulation results show that the nonlinear coefficients in our proposed PCF are (quasi-TE mode) and 226 W-1 m-1 (quasi-TM mode) at the wavelength of 1.55 μm and the nonlinear coefficient increases with the wavelength increasing. It is also demonstrated that ultraflattened dispersion of 0.91 ps/(nm·km) (quasi-TE mode) and 1.33 ps/(nm·km) (quasi-TM mode) can be achieved over a 150-nm wavelength range, and two near-zero dispersion slopes of -1.25×10-3 ps/(nm2·km) (quasi-TE mode) and -4.82×10-3 ps/(nm2·km) (quasi-TM mode) at 1.55 μm can also be obtained. Owing to its high nonlinear coefficient and flattened dispersion, the proposed slotted spiral PCF will have great potential for all-optical signal processing applications. View full abstract»

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  • Optically Pumped Edge-Emitting GaAs-Based Laser With Direct Orange Emission

    Page(s): 384 - 386
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (540 KB) |  | HTML iconHTML  

    Room temperature lasing operation at 599 nm for a AlGaInP/AlInP/GaAs edge-emitting laser structure is reported. The structure was grown on GaAs substrate and pumped optically with a 532 nm Q-switched laser. The lasing threshold for a 2 mm long and 25 μm wide ridge waveguide structure was 30 mW of average pump power. The orange output beam had an optical spectral width of 1.7 nm. View full abstract»

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  • Distributed Temperature Sensing in Polymer Optical Fiber by BOFDA

    Page(s): 387 - 390
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    Distributed temperature measurements in a perfluorinated graded-index polymer optical fiber (POF) with 50- μm core diameter are reported for the first time, to the best of our knowledge. Brillouin optical frequency-domain analysis is shown to be able to resolve spatially the temperature-dependent Brillouin frequency shift profile along a 20-m POF fiber sample, at a nominal spatial resolution of 4 m. The results indicate that POFs are potentially useful for distributed temperature measurements based on stimulated Brillouin scattering. View full abstract»

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  • THz Difference-Frequency Generation in MOVPE-Grown Quantum Cascade Lasers

    Page(s): 391 - 394
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (562 KB) |  | HTML iconHTML  

    We report mass-producible room-temperature electrically-pumped THz sources based on intra-cavity difference-frequency generation in mid-infrared InGaAs/AlInAs/InP quantum cascade lasers. Devices are grown by a commercial foundry using metal organic vapor phase epitaxy. A dual-stack active region possessing giant optical nonlinearity for 3.5 THz generation and a non-collinear Cherenkov waveguide THz outcoupling scheme is employed. Fabry-Pérot devices provided broad emission in the 3-4 THz range with a peak power of 5 μW. Single color THz sources were processed using surface distributed feedback gratings to produce narrowband emission at 3.5 THz with nearly 40 μW of peak power and a mid-infrared-to-THz conversion efficiency of 0.36 mW/W2. To better understand the dynamics of the DFG process, time gated spectral measurements of the mid-infrared pumps were performed and simultaneous lasing over the duration of the applied bias pulse was observed, thereby resulting in efficient difference frequency generation. View full abstract»

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  • High Beam Quality of In-Phase Coherent Coupling 2-D VCSEL Arrays Based on Proton-Implantation

    Page(s): 395 - 397
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    Two-dimensional coherently coupled arrays of vertical cavity surface emitting lasers were fabricated using proton implantation. A 2 × 2 array with the far field beamwidth of 3.6° ( 1.18×diffraction limited), the output power of 0.45 mW, and the spectral line width of 0.2 nm was achieved for continuous wave operation at room temperature. It showed an excellent beam quality due to the in-phase coupling among the elements in the array. The array performance dependence on injection current level and thermal effects was discussed. The processing for the arrays is considerably simple and can be used as an alternative to other array implementations. View full abstract»

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  • Reduced Complexity MLSD Receivers for Nonlinear Optical Channels

    Page(s): 398 - 401
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    We present a novel maximum likelihood sequence detection (MLSD) receiver structure for nonlinear channels. This scheme is derived by treating the NLC as a multiple input/multiple output system. Then, orthogonal signal components are computed using a special form of space-time whitened matched filter (ST-WMF) obtained by a modified Gram-Schmidt orthogonalization of the Volterra kernels of the NLC. The MLSD receiver consists of the ST-WMF followed by a Viterbi detector (VD) with multidimensional branch metrics. The space orthogonalization and noise whitening achieved by the ST-WMF provide an efficient way to reduce the receiver complexity in the presence of highly dispersive NLC. Complexity reduction is crucial in practical applications such as intensity modulation/direct detection (IM/DD) optical channels. As an example, the number of states of the VD in ST-WMF-MLSD required on a 10 Gb/s, 700 km, IM/DD fiber-optic link is reduced eight times compared with an oversampled MLSD. 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