Showing papers in "IEEE Photonics Technology Letters in 2013"

A Gigabit/s Indoor Wireless Transmission Using MIMO-OFDM Visible-Light Communications

Abstract: This letter reports an experimental demonstration of indoor wireless visible-light communication transmission at 1 Gb/s. The system consists of a four-channel multiple-input multiple-output link that uses white LED sources, each transmitting signals at 250 Mb/s using orthogonal frequency division multiplexing modulation. A nine-channel imaging diversity receiver is used to detect the signals, and an average bit error rate of 10-3 is achieved at the room illumination level of ~1000 lux at 1-m range.

Fiber-Optic Fabry–Pérot Acoustic Sensor With Multilayer Graphene Diaphragm

Abstract: A fiber-optic Fabry-Perot acoustic sensor with a ~100-nm-thick multilayer graphene diaphragm is reported. Acoustic testing demonstrates a pressure-induced deflection of 1100 nm/kPa and a noise equivalent acoustic signal level of ~ 60 μPa/Hz1/2 at the frequency of 10 kHz. The sensor exhibits a flat frequency response from 0.2 to 22 kHz and may be useful for highly sensitive acoustic sensing.

Experimental Investigation of Inter-Modal Four-Wave Mixing in Few-Mode Fibers

Abstract: We experimentally demonstrate nondegenerate four-wave mixing (FWM) between waves belonging to different spatial modes of a 5-km-long few-mode fiber (FMF). Of the three inter-modal FWM (IM-FWM) processes possible, two have been experimentally observed. These IM-FWM processes are found to be phase-matched over very large frequency separations of several Terahertz between the waves. In contrast to FWM in single-mode fibers that require operating near the zero-dispersion wavelength to achieve phase matching, IM-FWM in a FMF can be fully phase matched in the presence of large chromatic dispersion in each spatial mode.

Compensation of a VLC Phosphorescent White LED Nonlinearity by Means of Volterra DFE

Abstract: In this letter, a visible light communication link is analyzed that employs a white phosphorescent light emitting diode (LED) as transmitter and a p-i-n photodiode combined with optical filter as receiver. Four- and eight-level pulse amplitude modulation is used for data transmission. The link is not only limited by a rather small bandwidth of ~20 MHz of the LED, but also its nonlinearity becomes a problem when the modulation index exceeds ~60%. It is shown that a receiver with a decision feedback equalizer (DFE) with nonlinear Volterra feed-forward section up to the second order can efficiently compensate effects of nonlinearity of the transmitting LED and performs up to 5 dB better in terms of optical power than using a standard DFE.

Ultra-High-Contrast and Tunable-Bandwidth Filter Using Cascaded High-Order Silicon Microring Filters

Abstract: High-contrast optical filtering is demonstrated using cascaded silicon microrings. We report an experimental measurement of a record 100 dB pass-band to stop-band contrast, tunable 12–125 GHz passband full-width at half-maximum, band-center insertion loss ripple ${ , and a group delay ripple ${ , using transverse electric polarized light.

Flat-Gain L-Band Raman-EDFA Hybrid Optical Amplifier for Dense Wavelength Division Multiplexed System

Abstract: An efficient gain-flattened L-band optical amplifier is demonstrated using a hybrid configuration with a distributed Raman amplifier (DRA) and an erbium-doped fiber amplifier (EDFA) for 160 × 10-Gb/s dense wavelength division multiplexed system at 25-GHz interval. With an input signal power of 3 mW, a flat gain of >; 10 dB is obtained across the frequency range from 187 to 190.975 THz with a gain variation of ; 8.9 dBm) ever reported for a DRA-EDFA hybrid optical amplifier at reduced channel spacing.

Germanium-on-Silicon Mid-Infrared Arrayed Waveguide Grating Multiplexers

Abstract: In this letter, we describe the use of a germanium-on-silicon waveguide platform to realize an arrayed waveguide grating (AWG) operating in the 5 μm wavelength range, which can be used as a wavelength multiplexer for mid-infrared (midIR) light engines or as the core element of a midIR spectrometer. Ge-on-Si waveguide losses in the range 2.5-3.5 dB/cm for TE polarized light and 3-4 dB/cm for TM polarized light in the 5.15-5.4 μm wavelength range are reported. A 200 GHz channel spacing 5-channel AWG with an insertion loss/crosstalk of 2.5/3.1 dB and 20/16 dB for TE and TM polarization, respectively, is demonstrated.

High-Speed Oxide Confined 850-nm VCSELs Operating Error-Free at 40 Gb/s up to 85 $^{\circ}{\rm C}$

Abstract: We present the temperature dependence of the performance characteristics of our latest generation high-speed oxide confined 850-nm vertical cavity surface-emitting lasers (VCSELs). Using a 7-μm oxide aperture diameter VCSEL, we demonstrate a maximum modulation bandwidth of ~ 27 GHz at room temperature and ~ 21 GHz at 85°C. With a new high-speed optical receiver, these bandwidths enable error-free data transmission (defined as a bit-error-rate <; 10-12) at bit-rates up to 47 Gb/s at room temperature, and up to 40 Gb/s at 85°C.

Porous-Core Photonic Crystal Fiber for Low Loss Terahertz Wave Guiding

Abstract: We report a novel porous-core octagonal photonic crystal fiber (POPCF) for practical low-loss terahertz (THz) wave guiding. The POPCF with a porous core surrounded by an air-hole cladding shows a low material absorption loss of ~0.07 cm-1, or one third of that for the bulk material absorption loss at the operating frequency ~1 THz. In addition, the confinement loss, bending loss, and effective modal area properties of the POPCF are also reported and demonstrated to be relatively low. The proposed POPCF has potential applications for efficient transmission of broadband THz radiation.

Performance Analysis of Hybrid Satellite-Terrestrial FSO Cooperative System

Abstract: In this letter, the transmission of signals in a hybrid satellite-terrestrial free space optical (FSO) cooperative link is considered. In particular, we address the problem of amplify-and-forward (AF) relaying in a hybrid satellite-terrestrial FSO cooperative link, where a masked destination node receives the relayed transmission from an FSO link. The satellite-relay link is assumed to follow the shadowed-Rician fading, and the irradiance of the FSO link between the relay and destination is assumed to follow the gamma-gamma distribution. The approximate average symbol error rate of the considered AF cooperative scheme for M-ary phase shift keying constellation is derived; analytical diversity order of the hybrid cooperative system is also obtained.

Multichannel 120-Gb/s Data Transmission Over 2 $\,\times\,$ 2 MIMO Fiber-Wireless Link at W-Band

Abstract: We experimentally demonstrated a seamlessly integrated fiber-wireless system that delivers multichannel 120-Gb/s data through 80-km fiber and 2-m 2×2 multiple-input multiple-output (MIMO) wireless link at 92-GHz W-band adopting polarization division multiplexing quadrature phase shift keying (PDM-QPSK) modulation. The three-channel 3×40-Gb/s optical PDM-QPSK signals with 12.5-GHz channel spacing are simultaneously upconverted to 92-GHz wireless carrier by optical polarization-diversity heterodyne beating and then transmitted and received by two pairs of transmitter and receiver antennas, which form a full 2×2 MIMO wireless link. At the wireless receiver, a two-stage analog and digital downconversion is performed. Polarization and wireless 2×2 MIMO demultiplexing are realized by constant modulus algorithm based on digital signal processing. The bit-error ratio performance for the 120-Gb/s PDM-QPSK signal is measured after 80-km single-mode fiber-28 and 2-m wireless transmission.

Fast Sensing and Quenching of CMOS SPADs for Minimal Afterpulsing Effects

Abstract: We present a single-photon avalanche diode (SPAD) front-end circuitry, in a cost-effective 0.35 μm CMOS technology, for single-photon detection in the visible wavelength range, aimed at speeding up the sensing of detector ignition and at promptly quenching the avalanche current buildup. The circuit allows the reduction in detrimental effects of afterpulsing through reducing any delays in the electronics intervention on the detector and through a proper time-varying action of the MOS transistors on the different SPAD's operating conditions. The sensing time is reduced down to a few hundreds of picoseconds, with an active quenching transition of about 1 ns for 6 V excess bias, and a final reset in just 3 ns.

Long-Period Fiber Grating Cascaded to an S Fiber Taper for Simultaneous Measurement of Temperature and Refractive Index

Abstract: A novel, low-cost, and simple dual-parameter measurement scheme based on a cascaded optical fiber device composed of a long-period fiber grating (LPFG) and an S fiber taper Mach-Zehnder interferometer (SFT-MZI) is proposed and demonstrated. The crosstalk problem is solved as different resonance peaks of the LPFG and the MZI possess different refractive index (RI) and temperature sensitivities. Experimental results show distinctive spectral sensitivities of -52.57 nm/refractive index unit (RIU) and 45.87 pm/°C by the LPFG, and 311.48 nm/RIU (in the RI range of 1.33-1.37) and 12.87 pm/°C by the SFT-MZI. The simultaneous measurement of external RI and the temperature is experimentally demonstrated by the sensor. The RI and temperature calculated by the sensor matrix agree well with the actual RI and temperature in the experiment.

Low Power Mach–Zehnder Modulator in Silicon-Organic Hybrid Technology

Abstract: We report on a silicon-organic hybrid modulator based on a Mach-Zehnder interferometer (MZI) operating at 10 Gbit/s with an energy consumption of 320 fJ/bit. The device consists of a striploaded slot waveguide covered with an electro-optic polymer cladding. The MZI modulator is poled to be driven in push-pull operation by a single coplanar RF line. Our nonlinear coefficient r33 = 15 pm/V in combination with an 80 nm narrow slot enables RF peak-to-peak drive voltages as low as 800 mVpp to suffice for an extinction ration of 4.4 dB for a 1.5 mm long modulator.

Ultra-Compact and Low-Loss Polarization Rotator Based on Asymmetric Hybrid Plasmonic Waveguide

Abstract: We propose a novel hybrid plasmonic polarization rotator based on mode interference. Operating at the telecommunication wavelength of 1.55 μm, the rotation length is very short (3.2 μm), while the polarization conversion efficiency is as high as 99.5%. The total device insertion loss is only 1.38 dB, much smaller than the common level of plasmonic devices. It also has potential to realize integrated waveplates for various polarization states.

Ultra-Broadband Tapered Mode-Selective Couplers for Few-Mode Optical Fiber Networks

Abstract: Tapered mode-selective couplers are shown to allow for ultra-broadband mode-division multiplexing of few-mode optical fiber. Using appropriate three-core configurations, modes of arbitrary spatial-orientation can be demultiplexed. The successful fabrication of these wavelength-insensitive couplers would represent the realization of compact low-loss mode-multiplexers for use in high-bandwidth few-mode fiber networks.

Highly Sensitive Temperature Measurements With Liquid-Core Microbubble Resonators

Abstract: The thermal shifting of whispering gallery modes (WGMs) in a microbubble resonator is investigated. The thermal shift rate is determined for different modes when the core of the microbubble is filled with air, water and ethanol. Sensitivities as high as 100 GHz/K (0.2 nm/K at wavelength of 775 nm) are observed when the microbubble core is filled with ethanol. This is the largest thermal shift rate reported for a WGM resonator. We also show that thermal behavior of the WGMs in a thin-shelled, air-filled microbubble is different from a solid microsphere. The measured shifts are compared against finite element model simulations. Q-factors for the higher order modes are typically 105, equivalent to a measurement resolution of 8.5 mK.

Stokes Space-Based Optical Modulation Format Recognition for Digital Coherent Receivers

Abstract: We present a technique for modulation format recognition for heterogeneous reconfigurable optical networks. The method is based on Stokes space signal representation and uses a variational Bayesian expectation maximization machine learning algorithm. Differentiation between diverse common coherent modulation formats is successfully demonstrated numerically and experimentally. The proposed method does not require training or a constellation diagram to operate, is insensitive to polarization mixing or frequency offset and can be implemented in any receiver capable of measuring Stokes parameters.

A Multiport Microsecond Optical Circuit Switch for Data Center Networking

Abstract: We experimentally evaluate the network-level switching time of a functional 23-host prototype hybrid optical circuit-switched/electrical packet-switched network for datacenters called Mordia (Microsecond Optical Research Datacenter Interconnect Architecture). This hybrid network uses a standard electrical packet switch and an optical circuit-switched architecture based on a wavelength-selective switch that has a measured mean port-to-port network reconfiguration time of 11.5 $\mu{\rm s}$ including the signal acquisition by the network interface card. Using multiple parallel rings, we show that this architecture can scale to support the large bisection bandwidth required for future datacenters.

Five-Port Optical Router Based on Microring Switches for Photonic Networks-on-Chip

Abstract: We demonstrate a five-port optical router that is suitable for large-scale photonic networks-on-chip. The optical router is designed to passively route the optical signal travelling in one direction and actively route the optical signal making a turn. In the case that an XY dimension-order routing is used, the passive routing feature guarantees that the maximum power consumption to route the data through the network is a constant that is independent of the network size. The fabricated device has an efficient footprint of ~ 460 × 1000 μm2. The routing functionality of the device is verified by using a 12.5-Gbit/s optical signal. The capability of multiwavlength routing for the optical router is also explored and discussed.

Integrated Ultra-Low-Loss 4-Bit Tunable Delay for Broadband Phased Array Antenna Applications

Abstract: We demonstrate the design, fabrication, and characterization of a 4-bit tunable delay in an ultra-low-loss ${\rm Si}_{3}{\rm N}_{4}$ planar platform. Temporal delays up to 12.35 ns with resolution of 0.85 ns are measured, for a total of 2.407 meters of propagation length. The TE waveguide propagation loss is measured to be $(1.01\pm 0.06)~{\rm dB}/{\rm m}$ at a wavelength of 1550 nm with the lowest loss of $(0.57\pm 0.08)~{\rm dB}/{\rm m}$ at 1591 nm.

Blind Equalization of Receiver In-Phase/Quadrature Skew in the Presence of Nyquist Filtering

Abstract: In-phase and quadrature skew inside a coherent receiver, caused by misalignments, can severely limit performance. Future 400G systems employing higher order modulation formats and Nyquist filtering are especially sensitive to this. A blind adaptive equalizer is proposed to track and compensate the skew while also performing matched filtering. Performance is investigated in simulation for 56 GBd polarization division multiplexed 16-quadrature amplitude modulation (PDM-16QAM) and experimentally for 6 GBd PDM quadrature phase shift keying (PDM-QPSK) and PDM-16QAM, where compensation for delays up to half a symbol period are demonstrated without penalty. At 30% delay skew, the maximum skew recommended by Optical Internetwork Forum (OIF) for PDM-QPSK, a gain of 1.6 dB for PDM-QPSK, and a gain of more than 5 dB for PDM-16QAM is observed compared with using a conventional equalizer.

Spatial Compounding Algorithm for Speckle Reduction of Dynamic Focus OCT Images

Abstract: Optical coherence tomography is capable of imaging the microstructures within tissues. To preserve the transverse resolution at all imaging depths, we implement a dynamic focusing scheme. To improve the quality of images further, a simple speckle reduction scheme is employed which uses the vibration introduced by the translation stage used for axial scanning. A spatial compounding technique is developed based on co-registration followed by an averaging algorithm. We conclude that the degree of speckle reduction achieved is worth the expense of more complicated processing required.

High-Sensitivity Displacement Sensor Based on a Bent Fiber Mach–Zehnder Interferometer

Abstract: A simple, low-cost, and high-sensitivity optical fiber displacement sensor is presented and fabricated by concatenating two core-offset joints (COJs) with a separation length of 13 mm using a commercial fusion splicer. The two COJs construct an in-line Mach-Zehnder interferometer (MZI). When the MZI is bent to have a bending radius of ~ 17 mm, the interference pattern of the MZI depends strongly on the bending radius. According to this character, we scheme the bent MZI as a displacement sensor in two ways providing two different bending types of the bent MZI. The displacement sensitivities obtained are up to 0.835 and 0.227 nm/μm in the large displacement variation ranges of 350 and 1000 μm, respectively.

On-Chip Photonic-Assisted Instantaneous Microwave Frequency Measurement System

Abstract: A novel instantaneous frequency measurement system based on a programmable photonic chip frequency discriminator is experimentally demonstrated. The microwave signal whose frequency is to be measured is used to modulate the phase of an optical carrier. An optical ring resonator (ORR) in an add-drop configuration is used as a phase-to-intensity modulation converter. By simultaneously using the through and drop outputs of the ORR, an amplitude comparison function (ACF) can be established. Using this ACF, frequency estimation with a standard deviation of 93.6 MHz in the frequency range of 0.5-4 GHz can be achieved. The ACF is fully programmable by tuning the ORR resonance. This is the first demonstration of an instantaneous frequency measurement system using a compact programmable photonic chip.

Fiber Optic Current Sensor Based on Special Spun Highly Birefringent Fiber

Abstract: A fiber optic current sensor based on a polarization-rotated reflected interferometer has been constructed. A special spun highly birefringent fiber is designed and achieved for the sensor by heating and spinning commercial linearly birefringent fiber. In contrast with conventional fibers, the fiber integrates a function of a quarter wave plate. Particularly, fabricating and working principle of the current sensor head using the fiber are expounded. The sensor achieves an accuracy with 0.5% and good linearity shown in temperature dependence (a temperature drift of 0.008%/ °C) over a temperature range 40 °C -70 °C. Further, under simple temperature compensation, the sensor accuracy is within ±0.1% over in a wide range of current and temperature ranges.

On the Field Enhancement and Performance of an Ultra-Stable SPR Biosensor Based on Graphene

Abstract: The effect of graphene on the electric field enhancement and performance of SPR-based sensor has been proposed and compared with Ag-Au bimetallic configuration. We found that a monolayer of graphene on Ag not only addresses the oxidation problem of Ag, but it also shows field enhancement as compared with the widely reported Ag-Au bimetallic combination. Detailed calculations and simulations show that the proposed graphene-based sensor has higher sensitivity and narrower full-width at half-maximum than bimetallic. In addition, the better biomolecules adhesion due to graphene because of π-stacking interaction may open a new window for ultra-stable high performance biosensors for real time bimolecular interactions.

A Novel BLU-Free Full-Color LED Projector Using LED on Silicon Micro-Displays

Abstract: In this letter, we have described the design and fabrication of a novel backlight-unit (BLU)-free full-color light emitting diode (LED) based projector. The prototype used three active matrix addressable light emitting diode on silicon (LEDoS) micro-displays with peak emission wavelengths of 630, 535, and 445 nm. The LEDoS micro-displays were realized by integrating monolithic micro-LED arrays and silicon-based integrated circuits using a flip-chip bonding technique. Since the LEDoS micro-displays are self-emitting, conventional BLUs used in liquid crystal displays were not needed. Using a trichroic prism to combine the light from the three LEDoS chips, we have produced the world's first three-LEDoS projector. This BLU-free three-LEDoS projector consists of much fewer optical components and has significantly higher light utilization efficiency compared with conventional projectors.

Widely Tunable Single Longitudinal Mode Fiber Laser With Cascaded Fiber-Ring Secondary Cavity

Abstract: A widely tunable single longitudinal mode (SLM) fiber laser with cascaded Type I and Type II fiber ring secondary cavities, which uses a tunable fiber Bragg grating (FBG) as the mode-restricting and wavelength-tuning element, is proposed and demonstrated. Since the cascaded fiber rings can effectively expand the pass-band spacing to make the mode selection with the FBG easier, the stability of SLM oscillation can be improved by suitably optimizing the coupling ratio of optical couplers in Type II fiber ring to ensure that at least one and only one longitudinal mode dominates in the selected pass-band. When the fiber ring lengths are designed to make their expanded pass-band spacing be a value from 0.5 to 1 times of the 3-dB bandwidth of the FBG, the mode competitions between both neighboring pass-bands and main cavity modes, may be effectively eliminated, making the laser maintain mode-hop-free SLM oscillations while it is widely tuned.

Symmetric 40-Gb/s TWDM-PON With 39-dB Power Budget

Abstract: Time- and wavelength-division multiplexed passive optical network (TWDM-PON) has been selected by full service access networks as a primary solution for next generation PON stage 2 in April 2012. In this letter, we propose and demonstrate a symmetric 40-Gb/s TWDM-PON with 39-dB power budget. A reflective semiconductor optical amplifier is used in optical network unit as a pre-amplifier to enhance the sensitivity of downstream signals. For the upstream direction, a thermally-tuned directly modulated laser with 10-Gb/s modulation rate is used as upstream colorless source, and a chirp management filter is employed in optical line terminal to mitigate chromatic dispersion therefore enabling fiber transmission. Symmetric 40-Gb/s TWDM-PON is experimentally demonstrated with a power budget of 39 dB, which could support 25-km fiber transmission and 1:1000 splitting ratio.