Showing papers in "IEEE Photonics Technology Letters in 2007"
TL;DR: In this paper, surface plasmon Bragg gratings formed by a periodic variation of the width of the insulator in a metal-insulator-metal waveguide were numerically analyzed.
Abstract: We propose and numerically analyze surface plasmon Bragg gratings formed by a periodic variation of the width of the insulator in a metal-insulator-metal waveguide. The results indicate that very good filtering characteristics can be achieved in these plasmonic Bragg gratings. To suppress the sidelobes in the transmission spectrum, we further propose S-shaped Bragg cells and find better performance. By introducing a defect into the grating, a defect state with high Q-value is introduced into the bandgap and a Fabry-Peacuterot-like structure is formed
349Â citations
TL;DR: In this article, an optical intradyne receiver experiment with frequency estimation is reported. But this experiment was performed prior to block phase estimation or other phase recovery techniques, for a much higher frequency difference between transmit laser and local oscillator laser.
Abstract: We report on an optical intradyne receiver experiment with frequency estimation. Frequency estimation allows, if performed prior to block phase estimation or other phase recovery techniques, for a much higher frequency difference between transmit laser and local oscillator laser. We demonstrate the feasibility of our approach in a 20-Gb/s quadrature phase-shift keying experiment
289Â citations
TL;DR: In this paper, an eight-fold length reduction of the coupling structure from fiber to photonic wire in SOI, as compared to a linear grating and adiabatic taper, is obtained, without performance penalty.
Abstract: We report experimental results on compact and broadband focusing grating couplers, both in silicon-on-insulator (SOI) and gold on SOI. An eight-fold length reduction of the coupling structure from fiber to photonic wire in SOI, as compared to a linear grating and adiabatic taper, is obtained, without performance penalty. A proof of principle is given for a focusing grating coupler in gold on SOI, with 20% fiber-to-focus efficiency.
289Â citations
TL;DR: In this paper, the authors compare pilot-aided and dataaided phase estimation methods for a CO-OFDM transmission experiment at 8 Gb/s over 1000-km standard single-mode fiber without optical dispersion compensation.
Abstract: Phase estimation is one of the enabling functionalities in coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) receivers. In this letter, we compare pilot-aided and data-aided phase estimation methods for a CO-OFDM transmission experiment at 8 Gb/s over 1000-km standard single-mode fiber without optical dispersion compensation. We also show that as few as five subcarriers are sufficient for pilot-aided phase estimation
231Â citations
TL;DR: The p-i-n photodiode waveguide as discussed by the authors consists of an intrinsic waveguide 500 times250 nm where the optical mode is confined and two thin, 50nm-thick, doped Si wings that extend 5 mum out from either side of the waveguide.
Abstract: Submicrometer silicon photodiode waveguides, fabricated on silicon-on-insulator substrates, have photoresponse from <1270 to 1740 nm (0.8 AW-1 at 1550 nm) and a 3-dB bandwidth of 10 to 20 GHz. The p-i-n photodiode waveguide consists of an intrinsic waveguide 500times250 nm where the optical mode is confined and two thin, 50-nm-thick, doped Si wings that extend 5 mum out from either side of the waveguide. The Si wings, which are doped one p-type and the other n-type, make electric contact to the waveguide with minimal effect on the optical mode. The edges of the wings are metalized to increase electrical conductivity. Ion implantation of Si+ 1times10 13 cm-2 at 190 keV into the waveguide increases the optical absorption from 2-3 dBmiddotcm-1 to 200-100 dBmiddotcm-1 and causes the generation of a photocurrent when the waveguide is illuminated with subbandgap radiation. The diodes are not damaged by annealing to 450 degC for 15 s or 300 degC for 15 min. The photoresponse and thermal stability is believed due to an oxygen stabilized divacancy complex formed during ion implantation
175Â citations
TL;DR: In this paper, an approach to generating and distributing ultrawideband (UWB) pulses based on optical spectral shaping and frequency-to-time conversion using all-fiber components is proposed and demonstrated.
Abstract: An approach to generating and distributing ultrawideband (UWB) pulses based on optical spectral shaping and frequency-to-time conversion using all-fiber components is proposed and demonstrated. In the system, the spectrum of an ultrashort pulse from a mode-locked fiber laser is spectrally shaped by an all-fiber spectrum shaper, to produce a monocycle- or a doublet-shaped power spectrum. Thanks to the frequency-to-time conversion in a dispersive fiber, time-domain optical pulses exhibiting the user-defined shape of the optical power spectrum are obtained. Experiments based on the proposed approach are carried out. UWB monocycle or doublet pulses are generated
175Â citations
TL;DR: In this article, the authors demonstrate simultaneous generation and transmission of a wired-line BB signal and a wireless RF signal on a single wavelength, using one external modulator, and demonstrate that the hybrid signals transmitted over standard single-mode fiber (SSMF) do not suffer from periodic performance fading due to fiber dispersion.
Abstract: Hybrid optical access networks, integrating fiber-to-the-home (FTTH) and radio-over-fiber (RoF) systems that share a single distributed infrastructure, are promising for future multiservice access networks. The primary concern is to enable RoF and FTTH systems to transmit both radio-frequency (RF) and baseband (BB) signals on a single wavelength over a single fiber. This study experimentally demonstrates simultaneous generation and transmission of a wired-line BB signal and a wireless RF signal on a single wavelength, using one external modulator. The hybrid signals transmitted over standard single-mode fiber (SSMF) do not suffer from periodic performance fading due to fiber dispersion. Following transmission over 50-km SSMF, the power penalties of both RF and BB signals are less than 0.2 dB
174Â citations
TL;DR: In this paper, a hybrid AlGaInAs-silicon evanescent amplifier incorporating a silicon waveguide with a III-V gain medium is reported, where optical gain is provided by electrical current injection.
Abstract: We report a hybrid AlGaInAs-silicon evanescent amplifier incorporating a silicon waveguide with a III-V gain medium. The optical mode of the hybrid amplifier is mostly confined to the silicon waveguide and evanescently coupled to the AlGaInAs quantum-well (QW) region where optical gain is provided by electrical current injection. These two different material systems are bonded by low-temperature oxygen plasma assisted wafer bonding at 300 degC. The fabricated device shows 13 dB of maximum chip gain with 11 dBm of output saturation power. Evanescent coupling allows a lower active region confinement factor to provide a higher saturation output power than amplifiers with centered QWs, which is important for applications that require linear amplification
165Â citations
TL;DR: In this paper, a dual-loop OEO scheme is reported, which utilizes a polarization-beam splitter and a polarization beam combiner to suppress the sidemodes in each single loop.
Abstract: A dual loop optoelectronic oscillator (OEO) is able to effectively suppress the sidemodes in each single loop. In this paper, a dual-loop OEO scheme is reported. By utilizing a polarization-beam splitter and a polarization-beam combiner, the two loops are directly joined in the optical domain without adding any active electrical device. The laser's phase-to-intensity noise is discussed. We present free-running experimental results, which show a phase noise of -109 dBc/Hz at 10kHz away from the carrier (12 GHz) and a Q value of 1010 with a sidemode suppression ratio of 60 dB, which is improved by 30-50dB in the experimental comparison. Meanwhile, the experimental comparison indicates that no significant noise is introduced by this configuration
158Â citations
TL;DR: In this paper, a highly sensitive liquid-level sensor based on etched fiber Bragg grating (FBG) is proposed and demonstrated, where the transmission dips of FBG spectra are affected by the fraction of the length of the etched FBG that is surrounded by the liquid.
Abstract: A highly sensitive liquid-level sensor based on etched fiber Bragg grating (FBG) is proposed and demonstrated. The transmission dips of FBG spectra are affected by the fraction of the length of the etched FBG that is surrounded by the liquid. The experiments show that for a liquid-level variation of 24 mm, the transmission dip difference changes about 32 dB. Also in the linear region, a high sensitivity of 2.56 dB/mm is achieved.
155Â citations
TL;DR: In this paper, a femtosecond pulse source that uses a mode-locked Tm-Ho oscillator and a self-frequency shift of Raman solitons in TmHo power amplifier is presented.
Abstract: We report a femtosecond pulse source that uses a mode-locked Tm-Ho oscillator and a self-frequency shift of Raman solitons in Tm-Ho power amplifier. The master oscillator mode-locked by an antimonide-based saturable absorber mirror produces 750-fs transform-limited soliton pulses over the tuning range from 1912 to 1972 nm. The soliton self-frequency shift in the amplifier resulted in transform-limited pulses with the wavelength adjusted by varying the amplifier pump power. We obtain ~150-fs soliton pulses at the wavelength of 2150 nm with average power up to 230 mW corresponding to the peak power of 27 kW. The efficiency of Raman conversion ranges from 47% to 62% over the tuning range
TL;DR: In this article, a new class of radio-frequency (RF)-photonic link for the linear transport of analog RF signals is demonstrated and characterized, where simultaneous and separate detection and digitization of optical in-phase and quadrature-phase signals is employed for linear phase demodulation in the digital domain.
Abstract: We demonstrate and characterize a new class of radio-frequency (RF)-photonic link for the linear transport of analog RF signals. Simultaneous and separate detection and digitization of optical in-phase and quadrature-phase signals is employed for linear phase demodulation in the digital domain. This is shown to allow significantly larger tolerance to imperfect physical implementation of the phase demodulating receiver. Digitizer-limited spur-free dynamic range improvement >12 dBldrHz2/3 is observed in our baseband demonstration. Modulation depths significantly exceeding unity are allowed and demonstrated.
TL;DR: In this article, the authors theoretically analyzed and experimentally demonstrated a novel 4-to 40-GHz frequency quadrupler for radio-over-fiber (ROF) systems.
Abstract: We theoretically analyzed and experimentally demonstrated a novel 4- to 40-GHz frequency quadrupler for radio-over- fiber systems. By using an optical carrier suppression modulation scheme in two cascaded intensity modulators, four-fold microwave or millimeter wave signals are optically generated without the need for an optical and electrical notch filter to remove the residual carrier components. Moreover, the limitation of high drive voltage is greatly reduced through tandem intensity modulation with pi/2 phase shift between two driving signals.
TL;DR: In this paper, the authors proposed a radio-over-fiber (ROF) architecture to reduce the system cost at both central office (CO) and base station (BS).
Abstract: We have proposed a novel radio-over-fiber architecture to reduce the system cost at both central office (CO) and base station (BS). In this architecture, by incorporating the proper dc bias and optical filtering techniques in CO, the optical millimeter- wave (mm-wave) carriers are generated with four times frequency of the local oscillator signal. The BS is simplified by using the separated optical carrier along with downlink mm-wave signals to carry the upstream data. We have experimentally demonstrated optical mm-wave carrier generation up to 64-GHz, and both down- and upstream signal delivery over 20 km fiber with 1-dB power penalty.
TL;DR: In this paper, the experimental demonstration of optical single sideband (SSB) modulation using a directly modulated semiconductor laser under strong optical injection-locking is presented, where the longer wavelength sideband is resonantly amplified by the injection-locked laser cavity mode.
Abstract: We report on the experimental demonstration of optical single sideband (SSB) modulation using a directly modulated semiconductor laser under strong optical injection-locking. Modulation sidebands with 15-dB power ratio between the lower and upper sidebands have been achieved. The longer wavelength sideband is resonantly amplified by the injection-locked laser cavity mode. The radio-frequency performance of the optical SSB after 80-km fiber transmission is significantly improved compared with a typical symmetric sideband modulation of a free-running laser. A 622-Mb/s data transmission on a 20-GHz subcarrier is demonstrated over an 80-km fiber link.
TL;DR: In this paper, the authors reported the first experimental observation in the optical domain of a dramatic width-dependent lateral leakage loss behavior for the TM-like mode of tight vertical confinement ridge waveguides formed in silicon-on-insulator.
Abstract: We report the first experimental observation in the optical domain of a dramatic width-dependent lateral leakage loss behavior for the TM-like mode of tight vertical confinement ridge waveguides formed in silicon-on-insulator. The lateral leakage loss displays a series of sharp cyclic minima at precise waveguide widths, and appears to be inherent to waveguide geometries of central importance to a wide variety of active devices in silicon photonics requiring lateral electrical access. This behavior is not predicted by the often-used effective-index-based methods, but is understood phenomenologically and also compared to prior numerical analysis and predictions of leaky mode behavior. It is shown that TM-like mode operation, critical to the operation of some active component designs, will require precision control of waveguide dimensions to achieve high performance
TL;DR: In this paper, LiNbO3 ridge waveguides were fabricated using a mixture of HF and HNO3 using chromium (Cr) stripes as masks and smooth etched surfaces were obtained by adding some ethanol into the etchant.
Abstract: The fabrication of LiNbO3 ridge waveguides etched by a mixture of HF and HNO3 using chromium (Cr) stripes as masks is reported. Smooth etched surfaces are obtained by adding some ethanol into the etchant. Under-etching is nearly avoided by annealing the sample with the Cr masks before the wet etching process. Low-loss monomode ridge guides with a height of up to 8 mum and a width between 4.5 and 7.0 mum are demonstrated. As an example, the propagation losses in a 6.5-mum-wide and 8-mum-high structure are 0.3 dB/cm for transverse-electric and 0.9 dB/cm for transverse-magnetic polarization, respectively, at 1.55-mum wavelength
TL;DR: In this article, a photonic crystal fiber with circular air holes in the fiber cladding and elliptical air holes inside the fiber core is proposed to achieve both ultrahigh birefringence and ultralow confinement loss.
Abstract: A photonic crystal fiber (PCF) with circular air holes in the fiber cladding and elliptical air holes in the fiber core is proposed. According to calculation, both ultrahigh birefringence (larger than 0.01) and ultralow confinement loss (less than 0.001dB/km) can be achieved simultaneously over a large wavelength range for a PCF with only four rings of circular air holes in the fiber cladding. The confinement loss in this PCF can be effectively reduced while the birefringence almost remains the same. The proposed design of the PCF is a solution to the tradeoff between the birefringence and the confinement loss for the originally reported highly birefringent elliptical-hole PCF. Moreover, an approach to modify the effective index of fiber core is also suggested in this letter
TL;DR: In this paper, a radio-over-fiber configuration using an optical phase modulator along with optical filtering to generate an optical millimeter wave for carrying downstream data and centralized lightwave for carrying upstream data was designed.
Abstract: We have designed a novel radio-over-fiber configuration using an optical phase modulator along with optical filtering to generate an optical millimeter-wave for carrying downstream data and centralized lightwave for carrying upstream data. Since the remaining optical carrier with high power has been reused, the optical power is effectively utilized; therefore, the system cost can be reduced. We have calculated the power margin, and found that the margin is large even if no boosted erbium-doped fiber amplifier is used in the system. The eye diagrams and bit-error-rate performance at the receivers have been evaluated
TL;DR: In this article, it was shown that for multicarrier systems such as coherent optical orthogonal frequency division multiplexed systems (CO-OFDM), not only does PMD not cause any impairment, but it also provides a benefit of polarization diversity against polarization-dependent-loss-induced fading and consequently improves the system margin.
Abstract: Although polarization-mode dispersion (PMD) greatly impairs conventional high-speed single-carrier systems, it is shown that for multicarrier systems such as coherent optical orthogonal frequency-division-multiplexed systems (CO-OFDM), not only does PMD not cause any impairment, but it also provides a benefit of polarization diversity against polarization-dependent-loss-induced fading and consequently improves the system margin. The PMD benefit to fiber nonlinearity reduction in CO-OFDM systems is also predicted
TL;DR: In this paper, the authors derived closed-form expressions for the nonlinearity in the optical I/Q modulator, represented by two-tone intermodulation products as a function of the bias point and modulation index.
Abstract: In this letter, we conduct analysis on the optimum design for RF-to-optical up-converter in coherent optical OFDM systems using an optical I/Q modulator. We first derive closed-form expressions for the nonlinearity in the optical I/Q modulator, represented by two-tone intermodulation products as a function of the bias point and modulation index. Additionally, we perform a numerical simulation to identify Q-penalty and the excess modulation insertion loss under various transmitter conditions. We find that in contrast to the direct-detected system, the optimal modulator bias point for the coherent system is pi, where the Q-penalty and excess loss are minimized
TL;DR: In this paper, a ring resonator-based 1-times-8 optical beam forming network (OBFN) was proposed for phased array antenna systems, where a binary tree topology is used for the network such that a different number of ORRs is cascaded for delay generation at each output.
Abstract: Optical ring resonators (ORRs) are good candidates to provide continuously tunable delay in optical beam forming networks (OBFNs) for phased array antenna systems. Delay and splitting/combining elements can be integrated on a single optical chip to form an OBFN. A state-of-the-art ring resonator-based 1times 8 OBFN chip has been fabricated in complementary metal-oxide-semiconductor-compatible waveguide technology. A binary tree topology is used for the network such that a different number of ORRs is cascaded for delay generation at each output. In this letter, the principle of operation is explained and demonstrated by presenting some measurement results on the 1times 8 OBFN chip.
TL;DR: In this paper, a coupled optoelectronic oscillator employing nonpolarization-maintaining components and an erbium-doped fiber amplifier that generates 9.4 GHz microwave signals with -150dBc/Hz phase noise at 10- to 100-kHz offset, and 2-fs jitter (integrated in 100-Hz to 100kHz range) optical pulses was reported.
Abstract: Ultralow jitter optical pulse sources are much needed in optical communications, optical sampling, and metrology applications. We report a coupled optoelectronic oscillator employing nonpolarization-maintaining components and an erbium-doped fiber amplifier that generates 9.4-GHz microwave signals with -150-dBc/Hz phase noise at 10- to 100-kHz offset, and 2-fs jitter (integrated in 100-Hz to 100-kHz range) optical pulses. To our knowledge, this is the lowest phase noise and time jitter reported in the same frequency range for such mode-locked laser-based systems
TL;DR: A low-temperature bonding of vertical-cavity surface-emitting laser (VCSEL) chips on Si substrates was achieved by using plasma activation of Au films as mentioned in this paper.
Abstract: A low-temperature bonding of vertical-cavity surface-emitting laser (VCSEL) chips on Si substrates was achieved by using plasma activation of Au films. After the surfaces of Au films were cleaned using an Ar radio frequency plasma, bonding was carried out by contact in ambient air with applied static pressure. The experimental results showed that surface morphological change (the reduction of asperity width) as well as removal of adsorbed organic contaminants by plasma treatment significantly improved the quality of joints. At a bonding temperature of 100degC, the die-shear strength exceeded the failure criteria of MIL-STD-883.
TL;DR: In this article, a symmetric pump phase-sensitive amplification (SP-PSA) was used for phase regeneration of a phase-noise degraded nonreturn-to-zero differential phase-shift keying signal, significantly improving signal quality.
Abstract: Symmetric-pump phase-sensitive amplification (SP-PSA) is investigated experimentally. Symmetric pump waves are derived using carrier-suppressed return-to-zero modulation. The SP-PSA is used for phase regeneration of a phase-noise degraded nonreturn-to-zero differential phase-shift keying signal, significantly improving signal quality
TL;DR: In this article, the impact of pump phase modulation (PM) on the bandwidth of single-pumped fiber-optic parametric amplifiers was analyzed and the measured values and the calculations showed that the impact on bandwidth by pump PM is small compared to the impact from the dispersion curvature.
Abstract: We analyze the impact of pump phase modulation (PM) on the bandwidth of single-pumped fiber-optic parametric amplifiers. The measured values and the calculations show that the impact on bandwidth by pump PM is small compared to the impact from the dispersion curvature. A bandwidth of 100 nm with a gain of 11.5plusmn2 dB is achieved. This is also used to build a widely tunable fiber ring laser
TL;DR: Digital infinite impulse response (IIR) filtering is proposed as a means for compensating chromatic dispersion in homodyne-detected optical transmission systems with subsequent digital signal processing.
Abstract: Digital infinite impulse response (IIR) filtering is proposed as a means for compensating chromatic dispersion in homodyne-detected optical transmission systems with subsequent digital signal processing. Compared to finite impulse response (FIR) filtering, IIR filtering achieves dispersion compensation (DC) using a significantly smaller number of taps. DC of 80 and 160 km in a 10-Gb/s binary phase-shift-keying is experimentally compared for the two filtering schemes. IIR filtering can achieve performance similar to the FIR filtering scheme.
TL;DR: In this article, the authors describe a simple method to measure the optical signal-to-noise ratio (OSNR) of on-off-keying (OOK) and differential phase-shift keying (DPSK) signals using an optical delay interferometer (ODI) having a sinusoidal and tunable passband.
Abstract: We describe a simple method to measure the optical signal-to-noise ratio (OSNR) of on-off-keying (OOK) and differential phase-shift-keying (DPSK) signals by using an optical delay interferometer (ODI) having a sinusoidal and tunable passband. This OSNR monitoring method is independent of chromatic dispersion, polarization-mode dispersion, and noise polarization. We show experimentally that accurate OSNR measurements are made for a 10-Gb/s OOK signal by using a 1-bit ODI and a 40-Gb/s DPSK signal by using a partial-bit ODI with the OSNR ranging from 5 to 25 dB.
TL;DR: In this article, the authors reported the highest speed distributed sensing of dynamic strain based on stimulated Brillouin scattering in optical fibers, achieving a sampling rate of 1 kHz, more than an order of magnitude higher than the former best result.
Abstract: We report the highest speed distributed sensing of dynamic strain based on stimulated Brillouin scattering in optical fibers. A sampling rate of 1 kHz, more than an order of magnitude higher than the former best result, is achieved by applying a simplified Brillouin optical correlation domain analysis with optimized time gates and an unbalanced Mach-Zehnder delay line. In experiments, we present the measurement of various dynamic strains at the maximum frequency of 200 Hz with 10-cm spatial resolution and 20-m measurement range.
TL;DR: In this article, a high-resolution strain and temperature sensor by using a polarimetric distributed Bragg reflector fiber laser is presented, where the mean wavelength and polarization beat frequency of the laser output are utilized to determine the strain and temperatures of the sensor.
Abstract: We present a high-resolution strain and temperature sensor by using a polarimetric distributed Bragg reflector fiber laser. The mean wavelength and polarization beat frequency of the laser output are utilized to determine the strain and temperature of the sensor. Experimental results show that the sensor has a capability of sensing strain and temperature simultaneously, with root mean square deviations of 9.3 mu epsiv and 0.05degC, respectively.