Showing papers on "Extinction ratio published in 2007"

12.5 Gbit/s carrier-injection-based silicon micro-ring silicon modulators

Abstract: We show a scheme for achieving high-speed operation for carrier-injection based silicon electro-optical modulator, which is optimized for small size and high modulation depth. The performance of the device is analyzed theoretically and a 12.5-Gbit/s modulation with high extinction ratio >9dB is demonstrated experimentally using a silicon micro-ring modulator.

All-optical logic based on silicon micro-ring resonators

Abstract: We demonstrate all-optical logic in a micron-size silicon ring resonator based on the free-carrier dispersion effect in silicon. We show AND and NAND operation at 310 Mbit/s with ∼10-dB extinction ratio. The free-carrier-lifetime-limited bit-rate can be significantly improved by active carrier extraction.

High-Speed Control of Lightwave Amplitude, Phase, and Frequency by Use of Electrooptic Effect

Abstract: High-speed control of lightwave using electrooptic (EO) effect is investigated in this paper. Agile optical frequency shift can be achieved by optical single-sideband (SSB) and frequency-shift-keying (FSK) modulators, where high-speed optical phase-shift-keying (PSK) signals can also be generated by using FSK/SSB modulators. We also describe ultrahigh extinction ratio optical intensity modulation (IM) technique for two-tone lightwave signals with high spurious suppression, which is useful for photonic microwave and millimeter-wave generation. In addition, we investigated high-order optical sideband generation techniques: quadruple dual-sideband suppressed carrier (QDSB-SC) modulation and reciprocating optical modulation (ROM). Sub-tetrahertz signals can be obtained from lightwaves with high-order sidebands

Experimental study on the Gaussian-modulated coherent-state quantum key distribution over standard telecommunication fibers

Abstract: In this paper, we present a fully fiber-based one-way quantum-key-distribution (QKD) system implementing the Gaussian-modulated coherent-state (GMCS) protocol. The system employs a double Mach-Zehnder interferometer (MZI) configuration in which the weak quantum signal and the strong local oscillator (LO) go through the same fiber between Alice and Bob, and are separated into two paths inside Bob's terminal. To suppress the LO leakage into the signal path, which is an important contribution to the excess noise, we implemented a scheme combining polarization and frequency multiplexing, achieving an extinction ratio of 70 dB. To further minimize the system excess noise due to phase drift of the double MZI, we propose that, instead of employing phase feedback control, one simply let Alice remap her data by performing a rotation operation. We further present noise analysis both theoretically and experimentally. Our calculation shows that the combined polarization and frequency multiplexing scheme can achieve better stability in practice than the time-multiplexing scheme, because it allows one to use matched fiber lengths for the signal and the LO paths on both sides of the double MZI, greatly reducing the phase instability caused by unmatched fiber lengths. Our experimental noise analysis quantifies the three main contributions to the excess noise, which will be instructive to future studies of the GMCS QKD systems. Finally, we demonstrate, under the ``realistic model'' in which Eve cannot control the system within Bob's terminal, a secure key rate of $0.3\text{bit}∕\text{pulse}$ over a 5km fiber link. This key rate is about two orders of magnitude higher than that of a practical Bennett-Brassard 1984 protocol QKD system.

Compact bandwidth-tunable microring resonators

Abstract: Using interferometric couplers and thermal tuning, we demonstrate a novel design of compact microring resonators on silicon-on-insulator platform with tunable bandwidth from 0.1 to 0.7 nm. The structures present an extinction ratio higher than 23 dB and a footprint of less than 0.001 mm(2), which are suitable for integrated optical signal processing such as reconfigurable filtering and routing.

Design of monolithically integrated GeSi electro-absorption modulators and photodetectors on a SOI platform.

Abstract: We present a design of monolithically integrated GeSi electroabsorption modulators and photodetectors for electronic-photonic integrated circuits on a silicon-on-insulator (SOI) platform. The GeSi electroabsorption modulator is based on the Franz-Keldysh effect, and the GeSi composition is chosen for optimal performance around 1550 nm. The designed modulator device is butt-coupled to Si(core)/SiO(2)(cladding) high index contrast waveguides, and has a predicted 3 dB bandwidth of >50 GHz and an extinction ratio of 10 dB. The same device structure can also be used for a waveguide-coupled photodetector with a predicted responsivity of > 1 A/W and a 3 dB bandwidth of > 35 GHz. Use of the same GeSi composition and device structure allows efficient monolithic process integration of the modulators and the photodetectors on an SOI platform.

Polarization beam splitter using a binary blazed grating coupler.

Abstract: A novel polarization beam splitter using a two-layer grating coupler is proposed and demonstrated. It can directly couple the normally incident light from fiber into two separate waveguides according to their polarization states while splitting them. It realizes high coupling efficiency and a good extinction ratio by using binary blazed grating couplers. The coupling length is less than 14 microm. The extinction ratio is better than 20 dB for both polarizations over a 40 nm wavelength range, and the coupling efficiencies for the two layers are 58% and 50%.

High Extinction Ratio Mach–Zehnder Modulator Applied to a Highly Stable Optical Signal Generator

Abstract: Research into optical modulators has made remarkable progress in recent years This paper discusses the possibility of applying the high extinction ratio optical modulator to a high-stability and high-frequency (over 100 GHz) optical reference signal generator High-frequency reference signals are generated by a highly stable optical two-tone generator, which is used for high-rate communication and astronomical application One method to generate two optical signals is producing them from a pair of laser sources using an optical phase-locked loop for feed back control; however, the optical phase-locked loop has a stability problem in its operation A good alternative method to the optical phase-locked scheme is the LiNbO3 Mach-Zehnder (MZ) optical intensity modulator, which is capable of generating two highly stable optical signals (upper sideband and lower sideband components) by applying a sinusoidal microwave signal to an input laser signal The two optical signals require phase stability better than 10-13 in the Allan standard deviation, vibration robustness, and polarization maintaining capability The signal coherence loss estimated from the phase stability of the two optical signals generated by the MZ modulator shows that the optical MZ modulator has the ability to generate highly stable optical signals

High bandwidth SOI photonic wire ring resonators using MMI couplers.

Abstract: A ring resonator in SOI photonic wire waveguides is demonstrated using a compact MMI coupler with 3μm × 9 μm footprint as the coupling element. We achieved high bandwidth of 0.25 nm, and a quality factor Q of ∼ 6000 for rings with a radius of 50 μm. Unlike directional coupler based rings, these resonators have a wavelength independent Q and extinction ratio over more than 30 nm wavelength range, and there is no loss penalty for increasing the bandwidth. Compared to their directional coupler based counterparts, these resonators also have less demanding fabrication requirements and are compatible with high speed signal processing and optical delay lines.

Silicon microring carrier-injection-based modulators/switches with tunable extinction ratios and OR-logic switching by using waveguide cross-coupling.

Abstract: We demonstrate silicon microring carrier-injection-based modulators/switches with waveguide cross-coupling. We tune the modulator extinction ratio by forward-biasing either the microring or cross-coupled waveguide p-i-n diode, while modulating the other. We also demonstrate OR-logic switching functionality by simultaneously applying two different electrical data streams across the microring and cross-coupled waveguide diodes. For both the modulator and the switch, we observe NRZ pattern-dependent optical waveform distortions.

Terahertz wave switch based on silicon photonic crystals.

Abstract: A compact and integrated terahertz (THz) wave photonic crystal switch is proposed in silicon. The switch operates based on a dynamic shift of the photonic bandgap by using an external applied electric field. The plane wave expansion method and the finite-difference time-domain method are used to verify and analyze the characteristics of the proposed THz wave switch. Numerical simulation results show that the THz wave switch has a high extinction ratio of 29.9 dB.

Silicon Microtoroidal Resonators With Integrated MEMS Tunable Coupler

Abstract: A single crystalline silicon microtoroidal resonator with integrated MEMS-actuated tunable optical coupler is demonstrated for the first time. It is fabricated by combining hydrogen annealing and wafer bonding processes. The device operates in all three coupling regimes: under-, critical, and over-coupling. We have also developed a comprehensive model based on time-domain coupling theory. The experimental and theoretical results agree very well. The quality factor (Q) is extracted by fitting the experimental curve with the model. The unloaded Q is as high as 110 000, and the loaded Q is continuously tunable from 110 000 to 5400. The extinction ratio of the transmittance is 22.4 dB. This device can be used as a building block of resonator-based reconfigurable photonic integrated circuits

40-Gb/s Direct Modulation With High Extinction Ratio Operation of 1.3- $\mu$ m InGaAlAs Multiquantum Well Ridge Waveguide Distributed Feedback Lasers

Abstract: Direct modulation at 40 Gb/s of a 1.3-mum InGaAlAs distributed feedback ridge waveguide laser is experimentally demonstrated. By combination of the high differential gain of an InGaAlAs multiquantum well active layer, a short cavity length of 100 mum, and a low-resistance notch-free grating, it achieves high bandwidth of 29 GHz and high-extinction ratio of 5 dB at 40-Gb/s modulation. Moreover, the laser operates at a record maximum ambient temperature of 60degC under 40-Gb/s directly modulation. It also achieves 40-Gb/s modulated transmission over 2 km with a low power penalty of 0.25 dB at 25degC .

Manufacture of 3-D Microfiber Coil Resonators

Abstract: Three-dimensional microflber coil resonators are experimentally demonstrated in air. Two-turn, three-turn, and four- turn microcoil resonators are fabricated by wrapping a microflber on a low refractive index rod. The extinction ratio and free spectrum range are ~10 dB and ~1 nm, respectively. The spectrum optimization by the tuning of the pigtails is investigated.

All-optic scheme for automatic polarization division demultiplexing.

Abstract: We describe a cost effective scheme to automatically separate two polarization channels in a polarization division multiplexing (PDM) system, without having to modify the existing transmitter or receiver electronics or software. We experimentally validate the concept by achieving an extinction ratio of more than 28-dB between two demultiplexed channels. Finally, we successfully demonstrate the PDM scheme in a 1.12-Tb/s (14x2x40-Gb/s) system over 62-km of transmission fiber.

Simultaneous demonstration on all-optical digital encoder and comparator at 40 Gb/s with semiconductor optical amplifiers.

Abstract: We proposed and experimental demonstrated all-optical two line-four line encoder and two bit-wise comparator of RZ data streams at 40Gb/s based on cross gain modulation (XGM) and four wave mixing (FWM) in three parallel SOAs. Five logic functions for digital encoder and comparator between two signals A and B: AB, AB, AB, AB and AOmicronB, were achieved simultaneously. The first three optical logics are realized based on XGM in SOAs, the fourth is realized with FWM, and the fifth is the mixing result of the first and the fourth. A detuning filter is employed to improve the output performance. The output extinction ratio (ER) for the XGM operation is above 10dB, and the ER for FWM operation is around 8 dB. Wide and clear eye patterns for the five logic outputs can be observed.

Proposal for an Ultracompact Polarization-Beam Splitter Based on a Photonic-Crystal-Assisted Multimode Interference Coupler

Abstract: An ultracompact polarization-beam splitter (PBS) combining a multimode interference (MMI) coupler and some photonic crystal (PC) structures is presented. The MMI coupler is designed to collect polarized powers reflected by or transmitted through an internal PC structure. The simulation result shows that the designed PBS is very short (about 50 mum), and has a low insertion loss, a high extinction ratio, and a broad bandwidth

Broadband nanowire-grid polarizers in ultraviolet-visible-near-infrared regions

Abstract: Broadband nanowire-grid polarizers were designed and numerically simulated using the finite difference time domain (FDTD) method. Using a broadband stimulation source, optical properties of the polarizers were analyzed in the ultraviolet (UV)-visible-near infrared (NIR) regions. Specifically, the extinction ratios and optical transmittances of transverse magnetic (TM) and transverse electric (TE) modes were characterized for different metal materials and geometrical parameters including wire-grid periods, metal-wire fill ratios, and spacing between wire-grid layers. Based on the simulation results, an extra broadband polarizer with an average extinction ratio higher than 70 dB and transmission efficiency over 64% in the range of 0.3 to 5 µm was proposed.

All-optical demultiplexing of 160–10Gbit∕s signals with Mach-Zehnder interferometric switch utilizing intersubband transition in InGaAs∕AlAs∕AlAsSb quantum well

Abstract: We have developed a Mach-Zehnder interferometric all-optical switch employing intersubband transition in an InGaAs∕AlAs∕AlAsSb-coupled double quantum well waveguide. The recently discovered cross-phase modulation phenomenon was utilized as the switching mechanism; the nonlinear index of refraction for transverse electric polarized light is induced by intersubband optical excitation using transverse magnetic pump light. We demonstrate the demultiplexing operation of 160Gbit∕s data signals to 10Gbit∕s using this switch. At the input control pulse energy of 8pJ, the demultiplexed signals showed an extinction ratio better than 10dB, and an error-free demultiplexing was achieved.

Optimization of optical ring resonator devices for sensing applications

Abstract: The Q-factor of an optical resonance device determines the width of its transmission resonances. For this reason, in sensing applications of optical resonators, it is commonly assumed that the Q-factor fully determines resonator sensitivity. Practically, the latter is not exactly correct. In this Letter, the parameters responsible for the sensitivity of resonance devices (i.e., the steepness and the sharpness of the transmission resonance) are analyzed. It is shown that, for given intrinsic losses of a single ring resonator sensor, the slope of the resonance is largest if its extinction ratio is 9.5 dB, while the resonance is sharpest if its extinction ratio is 6 dB. For a sensor consisting of several identical ring resonators coupled to a bus waveguide, the largest slope and sharpness parameters correspond to the extinction ratios of ∼9 dB and ∼4.5 dB, respectively. The determined optimum parameters can be achieved by tuning the coupling between the resonator rings and the waveguide.

Effect of Host Polymer on Microfiber Resonator

Abstract: We observe that changing the surrounding material from air to a low refractive index polymer can considerably alter the transmission spectrum of a microfiber knot around a given wavelength. We report on a silica microfiber knot resonator about 180 m in diameter. Using a supercontinuum source, we study its transmission when air and when a low index polymer are used as cladding. The resonator shows similar extinction ratio and Q-factor for both cladding materials. However, embedding the resonator in the polymer down-shifts the optimal operating wavelength by about 20%.

PINIP based high-speed high-extinction ratio micron-size silicon electrooptic modulator.

Abstract: We propose an electro-optic device in silicon based on a p-i-n-i-p device structure for charge transport. The proposed device exhibits carrier injection time of 10 ps and extraction time of 15 ps enabling 100 GHz operation. When integrated into a resonator the micron-size device operates at 40 Gbit/s with 12 dB extinction ratio and 2.25 fJ/bit/micron-length power dissipation. The proposed device is limited in speed only by the photon lifetime of the resonator.

A High-Performance Ultracompact Optical Interleaver Based on Double-Ring Assisted Mach–Zehnder Interferometer

Abstract: We present an ultracompact and high-performance optical interleaver based on a microring assisted Mach-Zehnder interferometer using an ultrahigh-index-contrast waveguide (17% Delta). The device, a 100/200-GHz interleaver at 1.55-mum region, exhibits flat and nearly square passband and better than -30-dB stopband extinction ratio. Fiber-to-fiber loss is -2.2 dB. Passband bandwidth is 90 and 121 GHz at -1 and -20 dB, respectively. The dimension of this interleaver chip is 12times1 mm. Design optimization is also discussed for further performance improvement.

Remodulation schemes with reflective SOA for colorless DWDM PON

Abstract: Feature Issue on Passive Optical Network Architectures and TechnologiesThis article presents remodulation schemes with reflective semiconductor optical amplifiers (RSOAs), which have recently been developed for application to the wavelength-division-multiplexed passive optical network (WDM-PON). The remodulation schemes have a common feature that the optical signal modulated with downstream data is reused to carry the upstream data through the RSOA in the subscriber-side equipment by a series of processes such as being flattened out, reflected at the rear facet of the RSOA, and then remodulated with upstream data. The major advantage of remodulation schemes is the possibility of realizing the simplest WDM-PON optical link structure, which is directly reflected in cost-effectiveness of the network both in equipment and maintenance. Three schemes are presented; the simplest one is to use the RSOA gain saturation, the second uses the effect of frequency detuning on the extinction ratio of optical signal, and the third uses RSOA gain control by dynamically varying the current injection. Feasibilities of those schemes are discussed in the view of commercial application to WDM-PON.

40 Gb/s all-optical NRZ to RZ format conversion using single SOA assisted by optical bandpass filter

Abstract: We propose a novel all-optical format conversion from nonreturn-to-zero (NRZ) to return-to-zero (RZ) based on single semiconductor optical amplifier (SOA) and a detuning optical bandpass filter (OBF). By adopting the ultrafast SOA model associated with intraband mechanism, the 40Gb/s NRZ-to-RZ format conversion is successfully demonstrated with numerical simulation. We investigate the influence of the filter detuning, extinction ratio, conversion efficiency, output pulsewidth, and filter bandwidth. These simulation results confirm the feasibility of our scheme. The proposed scheme is robust and potential for applications in future optical networks.

All‐optical logic or gate using two cascaded semiconductor optical amplifiers

Abstract: A novel all-optical logic OR gate based on cross-gain modulation (XGM) using a two-cascaded semiconductor optical amplifiers (SOAs) in a counterpropagating topology is presented. The attractive issue of the proposed method is that the logic OR gate can be obtained at a probe wavelength by taking advantage of the positive gain variation of one of the two used SOAs in the counterpropagating configuration. This reported feasibility study shows the all-optical logic OR gate can be easily achieved with an extinction ratio higher than 7 dB.© 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1568–1570, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22560

Narrowband, polarization insensitive all-fiber acousto-optic tunable bandpass filter.

Abstract: We demonstrate an all-fiber acousto-optic tunable bandpass filter exhibiting narrow optical bandwidth and negligible polarization dependence by employing a novel ultraviolet (UV)-induced core-mode blocker written in a high numerical aperture (NA) fiber. It was demonstrated that the device had the measured 3-dB optical bandwidth of 0.65 nm, the polarization-dependent center-wavelength splitting of 0.05 nm and the extinction ratio of -22dB at the wavelength around 1550 nm. The details of the transmission characteristics and the loss mechanism of the core-mode blocking element inscribed in the high NA fiber are discussed.

Passive broadband silicon-on-insulator polarization splitter.

Abstract: We present the implementation of a novel wavelength independent polarization splitter on a silicon-on-insulator platform. The waveguide splitter is based on a zero-order arrayed waveguide grating (AWG) configuration. The splitting function is realized by employing cladding stress-induced birefringence. The device demonstrated a TE to TM splitting ratio better than -15 dB over a 20 nm tuning range centered around lambda=1550 nm and better than -10 dB over our entire accessible wavelength range from lambda=1465 nm to 1580 nm. The highest splitting extinction ratio achieved was -20 dB. To our knowledge, this is the first reported passive broadband polarization splitter based on AWG.

High-Temperature Dynamics, High-Speed Modulation, and Transmission Experiments Using 1.3- $\mu\hbox{m}$ InGaAs Single-Mode VCSELs

Abstract: High-temperature dynamics, including small and large signal modulation response, of 1.28-μm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) with highly strained InGaAs quantum wells have been investigated. The VCSELs are oxide-confined with a relatively large oxide aperture for high output power and have a surface relief for fundamental mode operation. An inverted surface relief is used to improve manufacturability and to suppress oxide modes that otherwise appear in VCSELs with a large detuning between the cavity resonance and the gain peak. The size dependence of the modulation bandwidth and bandwidth limitations are investigated. A VCSEL with an optimum combination of oxide aperture and surface relief diameters produces clear open eyes with an extinction ratio of > 6 dB at OC-48 and 10-GbE bit rates from 25 °C to 85 °C under constant drive conditions. The same VCSEL is also shown to be capable of error-free transmission (BER < 10-9) over 9 km of standard single-mode fiber under the same conditions.