Showing papers on "Extinction ratio published in 2003"

A compact two-dimensional grating coupler used as a polarization splitter

Abstract: We demonstrate a novel polarization splitter based on a two-dimensional grating etched in a silicon-on-insulator waveguide. The device couples orthogonal modes from a single-mode optical fiber into identical modes of two planar ridge waveguides. The extinction ratio is better than 18 dB in the wavelength range of 1530-1560 nm and the coupling efficiency is approximately 20%. The device is very compact and couples light only to transverse-electric modes of the planar waveguides. Therefore, it may be used in a polarization diversity configuration to implement a polarization insensitive photonic integrated circuit based on photonic crystal waveguides.

Wavelength channel data rewrite using saturated SOA modulator for WDM networks with centralized light sources

Abstract: This paper describes a method for realizing the efficient utilization of wavelength resources in wavelength-division multiplexing networks with centralized light sources. Using a deeply saturated semiconductor optical amplifier (SOA) modulator located in a remote node (RN), we erase the data on a downstream signal with a low extinction ratio and modulate it with new data to generate an upstream signal. Thus, we use only one wavelength for bidirectional transmission between a center node and an RN, without placing lasers at the RN. In this paper, we analyze the data suppression characteristic of the SOA using a large signal model. We also estimate the bit error rate degradation in the presence of an unsuppressed downstream bit pattern in an upstream signal. We then report experimental results that confirm the basic characteristics of the wavelength channel data rewriter, which we constructed using a linear amplifier and an SOA. Finally, we provide the results of a data transmission experiment that we undertook using the data rewriter.

All-optical regeneration in one- and two-pump parametric amplifiers using highly nonlinear optical fiber

Abstract: We describe the operation of a two-pump parametric optical regenerator. It is shown that higher order parametric coupling provides optical regeneration with a high extinction ratio. Excessive spectral broadening is studied in a two-pump architecture and compared with that of the one-pump parametric regenerator. We show that the spectral widths of the higher order terms can be controlled in amplifiers by using counterphased optical pumps.

Ring-resonator filters in silicon oxynitride technology for dense wavelength-division multiplexing systems.

Abstract: The design and characterization of ring-resonator-based filters with free spectral ranges of 100 and 50 GHz by use of SiO(x)N(y) technology is presented. Fiber-to-fiber insertion losses of 4.4 dB on the drop port and 2.1 dB on the through port have been achieved for a single-ring filter. An interleaver filter for a 25-GHz spaced dense wavelength-division multiplexing system with two cascaded rings is demonstrated. The filter has a 7.4-GHz bandwidth at -1 dB and an extinction ratio of 15 dB and is polarization independent.

Design and fabrication of a significantly shortened multimode interference coupler for polarization splitter application

Abstract: We report that we have successfully designed and fabricated a significantly shortened multimode interference coupler for application in polarization splitter, using a phenomenon that we termed "quasi-state" (QS) imaging effect. First, we identified and analyzed the QS imaging effect, and, based on the QS analysis, designed and fabricated a novel multimode interference (MMI) device with its split length shortened to 1/5 of a normally designed MMI split length. The fabrication is simple and cost effective and the fabricated device shows outstanding characteristics in extinction ratio, signal homogeneity, excess loss, and tolerance in the length of the splitter.

Optical demultiplexer, optical multi-/demultiplexer, and optical device

Abstract: The present invention provides an optical demultiplexer and an optical multi-/demultiplexer at low cost without reducing performance capabilities. The optical demultiplexer includes a multi-mode waveguide having such an optical path length as to cause a difference between first and second wavelengths with respect to a phase difference between zero- and first-order modes to become an integral multiple of π, an input waveguide optically connected to the input side of the multi-mode waveguide such that the optical axis thereof is offset from the center line of the multi-mode waveguide, and two output waveguides optically coupled to the multi-mode waveguide at different positions of the output side of the multi-mode waveguide. The two output waveguides are located in such a manner as to maximize the extinction ratio.

Silver nanowire array infrared polarizers

Abstract: A silver nanowire array micropolarizer within an anodic alumina membrane (AAM) was fabricated by anodization of pure Al foil and electrodeposition of Ag, respectively. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy investigations reveal that the nanowires are essentially single crystals, and have an average diameter of 90 nm. Spectrophotometer measurements show that the silver nanowire arrays embedded in the AAM can only transmit vertically polarized light to the wires. An extinction ratio of 25–26 dB and average insertion loss of 0.77 dB in the wavelength range 1–2.2 μm were obtained, respectively. Therefore the Ag nanowire/AAM can be used as a wire-grid type polarizer.

Ultracompact high-efficiency polarizing beam splitter with a hybrid photonic crystal and conventional waveguide structure

Abstract: We propose an ultracompact high-efficiency polarizing beam splitter that operates over a wide wavelength range and is based on a hybrid photonic crystal and a conventional waveguide structure. Within a small area (15μm ×and 10μm), this polarizing beam splitter separates TM- and TE-polarized modes into orthogonal output waveguides. Results of simulations with the two-dimensional finite-difference time-domain method show that 99.3% of TM-polarized light is deflected by the photonic crystal structure (with a 28.0-dB extinction ratio), whereas 99.0% of TE-polarized light propagates through the structure (with a 32.2-dB extinction ratio). Wave vector diagrams are employed to explain the operation of a polarizing beam splitter. Tolerance analysis reveals a large tolerance to fabrication errors.

Flexible low-voltage electro-optic polymer modulators

Abstract: A high-performance electro-optic (EO) polymer modulator on a flexible substrate was fabricated using a polymer substrate layer lift-off method. The SU-8 polymer has widely different adhesion properties on Si and gold substrates that makes selective lift-off possible. The flexible EO polymer modulators on a 100-μm polymer substrate layer have a Vπ of 2.6 V and extinction ratio better than 20 dB at 1550 nm. The bending loss of the flexible waveguide was unchanged at bending radii as small as 1.5 mm, and no effect on Vπ was observed for a 5 mm bending radius.

STOLAS: switching technologies for optically labeled signals

Abstract: GMPLS-based labeled optical burst switching (LOBS) networks are being considered as the next-generation optical Internet. GMPLS includes wavelength switching next to label and fiber (space) switching. We present a new concept of optically labeling bursts of packets suitable for LOBS networks supported by GMPLS. It is based on angle modulation, which enables control information to modulate the phase or frequency of the optical carrier, while payload data are transmitted via intensity modulation (IM). In particular, the optical label is orthogonally modulated, with respect to the payload, using either frequency shift keying or differential phase shift keying. We present a performance analysis of the modulation schemes by means of simulations where the influence of the payload IM extinction ratio and laser linewidth are investigated. In addition, the transmission performance of an IM/FSK combined modulated signal is experimentally validated at 10 Gb/s, demonstrating at the same time an FSK label swapping operation. Finally, a suitable optical label-controlled switch design is proposed that takes advantage of these novel labeling techniques, and efficiently combines widely tunable, fast switching lasers and SOA-MZI wavelength converters with an arrayed waveguide grating router.

Magneto-optical imaging setup for single vortex observation

Abstract: A recently developed high-resolution magneto-optical imaging (MOI) setup is reviewed. It is the first MOI system capable of resolving the individual vortices in a type-II superconductor. We give a detailed description of the whole setup, and discuss its measured properties in terms of magnetic sensitivity and signal-noise characteristics. A simple model for the image intensity distribution due to a vortex lattice is developed, and for the intensity profile across a single vortex, we find good agreement between model calculations and experimental data. The minimum vortex spacing resolved experimentally is 1.3 μm. Our analysis shows that increased resolution can most easily be achieved by increasing the light input intensity, but maximum resolution is ultimately limited by the effective extinction ratio through the optical system and mechanical vibrations in the setup.

Regenerative properties of a pump-modulated four-wave mixing scheme in dispersion-shifted fibers

Abstract: A new scheme for all-optical signal reshaping is proposed. It is shown that proper adjustment of the operating conditions of a wavelength converter based on four-wave mixing (FWM) in dispersion-shifted fiber (DSF) results in significant extinction ratio enhancement and noise suppression of the converted signal. The key issue in the proposed idea is the application of the modulation bitstream on the input pump wave. Detailed numerical simulation shows that it is possible to achieve a wavelength-converted output with extinction ratio of 20 dB when the extinction ratio of the input signal is 10.5 dB, while at the same time, the improvement in the Q-factor is almost 6 (from 6.5 at the input, it becomes more than 12 at the output). The theoretical predictions have been experimentally confirmed by measuring the transfer function of the FWM in a 17-km-long DSF under different operating conditions. The obtained results are in a very good agreement with those predicted theoretically.

High external feedback resistance of laterally loss-coupled distributed feedback quantum dot semiconductor lasers

Abstract: External optical feedback effects on quantum dot (QD) laterally loss-coupled (LLC) distributed feedback (DFB) lasers are reported for the first time in this letter. The critical external feedback ratio that causes coherence collapse of the QD DFB is measured to be -14 dB. No spectral broadening at this feedback level is observed within the 0.06-nm resolution of the optical spectrum analyzer (OSA). Self-homodyne measurements also confirm that the rebroadened linewidth of the QD DFB under -14-dB feedback is still much smaller than the feedback-free linewidth. Under 2.5-Gb/s modulation, eye-diagram measurements show that the signal-to-noise ratio starts to degrade at a feedback ratio of -30 dB in the QD LLC-DFB, about 20 dB higher than a typical quantum-well DFB at the same output power and extinction ratio.

Silica-based waveguide-type 16 x 16 optical switch module incorporating driving circuits

Abstract: We developed a 16/spl times/16 optical matrix switch module in which we incorporated a silica-based thermooptic switch chip and driving circuits. The module exhibited excellent levels of performance, namely a low insertion loss and a high extinction ratio. This is the largest scale waveguide-type matrix switch module yet reported. Driving circuits with a serial-to-parallel control signal conversion function enabled us to realize a new module structure that is both simple and flexible for use with larger scale switches.

Ultrafast all optical switching by use of pulse trapping across zero-dispersion wavelength

Abstract: Ultrafast all optical switching by use of pulse trapping across zero dispersion wavelength in optical fiber is demonstrated both experimentally and numerically for the first time. Only an arbitrary single pulse among four pulses with temporal separation of about 1.5 ps is successfully picked off with almost perfect extinction ratio. The spectrogram of the optical switching is directly observed using the X-FROG technique. The characteristics of all optical switching are analyzed numerically by the use of strict coupled nonlinear Schrodinger equations and the numerical results are in agreement with the experimental ones. It is interesting to note that although the other pulses are also overlapped with the soliton pulse, they are not trapped.

Analog characterization of low-voltage MQW traveling-wave electroabsorption modulators

Abstract: In this paper, high-speed traveling-wave electroabsorption modulators (TW-EAMs) with strain-compensated InGaAsP multiple quantum wells as the absorption region for analog optical links have been developed. A record-high slope efficiency of 4/V, which is equivalent to a Mach-Zehnder modulator with a V/sub /spl pi// of 0.37 V and a high extinction ratio of > 30 dB/V have been measured. A detailed study of the nonlinearity and the spurious-free dynamic range (SFDR) is presented. By optimizing the bias voltage and the input optical power, the SFDR can be improved by 10-30 dB. After minimizing the third-order distortion, an SFDR as high as 128 dB-Hz/sup 4/5/ is achieved at 10 GHz. A simple link measurement was made using this EAM and an erbium-doped fiber amplifier and a 50-/spl Omega/ terminated photodetector. At 10 GHz, a link gain of 1 dB is achieved at a detected photocurrent of 7.6 mA with higher gains at lower frequencies. The dependence of link gains on bias voltage, input optical, and radio frequency powers are investigated in detail.

Effect of the finite extinction ratio of an electro-optic modulator on the performance of distributed probe-pump Brillouin sensor systems.

Abstract: The effect of the finite extinction ratio of an electro-optic modulator (EOM) on the Brillouin frequency measurement of a distributed Brillouin-based fiber optic sensor is studied. An EOM with a finite extinction ratio limits the application of Brillouin optical time domain analysis in a distributed Brillouin-based fiber optic sensor. This results in confusion in specifying the location of the strained region and in error in detecting the Brillouin frequency and hence in strain and temperature measurement.

Integrated optics polarization beam splitter using form birefringence

Abstract: A method for separating the orthogonal polarization components of an incident optical signal into two spatially separated output ports is described. The method comprises a Mach-Zehnder interferometer where one of the two branches has a section of waveguide that exhibits form-birefringence. This integrated optic Polarization Beam Splitter (PBS) is broadband, has high extinction ratio, and has characteristics that are tunable.

Wavelength- and time-selective all-optical channel dropping in periodically poled Ti:LiNbO 3 channel waveguides

Abstract: Wavelength- and time-selective channel dropping by sum frequency generation of a 10-GHz channel out of a 4 /spl times/ 10 GHz optical time-division-multiplexed signal has been demonstrated using two fully packaged Ti : PPLN wavelength converters. Less than -15 dB of channel dropping extinction ratio is observed with average (peak) coupled pump power of 100 mW (2 W).

All-optical subcarrier labeling based on the carrier suppression of the payload

Abstract: We report on a new approach to all-optical subcarrier labeling based on sideband generation through carrier-suppression of the payload. The experimental transmission over 50-km standard fiber of a 10-Gb/s payload data multiplexed with a synchronized 1.25-Gb/s subcarrier label is carried out with less than 1-dB receiver power penalty, clearly demonstrating the feasibility of this sideband optical labeling scheme. The requirements to the modulation index and dc bias along with the limitation of the input extinction ratio are discussed.

Polarization splitter/combiner in high index contrast Bragg reflector waveguides

Abstract: Novel designs of polarization devices based on Bragg reflector waveguides in a high index contrast silicon-on-insulator (SOI) platform have been proposed. Brewster angle condition is incorporated in the periodic structures. Numerical simulations with a 3D semivectorial beam propagation method demonstrate the device performance as TE mode polarizer with high TE to TM extinction ratio and TE/TM mode polarization splitter and combiner with high polarization splitting efficiency.

Lossless electroabsorption modulator monolithically integrated with a semiconductor optical amplifier and a passive waveguide

Abstract: We have developed a monolithic integrated device consisting of an electroabsorption modulator and a semiconductor optical amplifier (SOA) connected by a deep-ridge passive waveguide by means of butt-joint selective area growth. Lossless operation with a high extinction ratio of 32 dB and clear eye opening at 10 Gb/s are successfully achieved. We confirm that the optical injection should be from the SOA side of the device to obtain a wide error-free range of incident optical power from -20 to +10 dBm. Our device could lead to richly functional photonic integrated circuits comprising arrayed waveguide gratings (AWGs) for advanced wavelength-division-multiplexing networks, since the passive waveguide has the same structure as AWGs.

Wireless optical communications via diversity reception and optical preamplification

Abstract: Atmospheric optical communication systems that use optical preamplifiers and diversity reception to combat the effects of atmospheric turbulence are addressed. The effects of atmospheric turbulence, background light, source extinction ratio, amplified spontaneous emission, and receiver thermal noise are considered in a context of a semiclassical photon-counting approach. The particular diversity techniques that are investigated include aperture averaging, linear combining, and adaptive optics. Numerical results, obtained using a conditional Gaussian approximation, quantify the link margin improvement due to optical preamplification and diversity reception.

Drive circuit and drive method of semiconductor laser module provided with electro-absorption type optical modulator

Abstract: The present invention aims at providing a drive circuit and a drive method for a semiconductor laser module including an electro-absorption type optical modulator, capable of obtaining a stable optical output without controlling a module temperature to be constant. To this end, the drive circuit of the present invention detects a temperature in the semiconductor laser module comprising a semiconductor laser and an EA modulator, and based on the detected temperature, controls a drive current supplied to the semiconductor laser and a bias voltage and a modulated electric signal applied to the EA modulator, so that average power, an extinction ratio and an optical cross point of an optical signal output from the semiconductor laser module are held to be constant.

Demonstration of an all-optical switch by use of a multiwavelength mutual injection-locked laser diode.

Abstract: Error-free all-optical packet switching is demonstrated by use of a multiwavelength mutual injection-locked Fabry-Perot laser diode. A 10-Gbit/s data signal is switched on and off with an extinction ratio of 16.9 dB when an optical control signal is turned off and on with a power difference of only 3 dB.

Small-chirp 40-Gbps electroabsorption modulator with novel tensile-strained asymmetric quantum-well absorption layer

Abstract: A small-chirp 40-Gbps electroabsorption modulator (EAM) with a novel tensile-strained asymmetric quantum-well (QW) absorption layer has been demonstrated for the first time. The strain and the band line-up of the asymmetric QW structure were designed in order to obtain a small-chirp operation, a clear eye opening, and a high extinction ratio simultaneously. The chirp measured as /spl alpha/-parameter was reduced without any penalty of extinction ratio and eye opening. The measured /spl alpha/-parameter was smaller than 1.5 at any bias voltage from 0 to -2 V. The measured 3-dB bandwidth of a 75-/spl mu/m-long EAM exceeded 50 GHz at -1 V bias voltage. Under a 40-Gbps modulation, a clear eye opening was obtained, and the eye diagram showed no violation of the standard STM256/OC768 mask. The measured dynamic extinction ratio was over 11 dB.

Laser light generator control circuit and laser light generator control method

Abstract: The laser light generator control circuit comprises a load section, a control section, a bias current circuit section, and a modulation current circuit section. The load section generates a monitor voltage V 1 that corresponds to the optical current corresponding to the amount of light received by a monitor light receiving element for receiving light from the laser light generator. The control section selects a combination (Db, Dm) in accordance with the result of comparing a value corresponding to the monitor voltage V 1 , and a reference value, from a group of combinations (Db, Dm) n that comprises a plurality of combinations (Db, Dm) of a value Db that corresponds to the bias current and a value Dm that corresponds to the modulation current, these combinations being specified so that the light emission power and the extinction ratio are constant, and generates a first control signal V 2 and a second control signal V 3 on the basis of the selected combination (Db, Dm).

Transmission performance of 10-Gb/s 1550-nm transmitters using semiconductor optical amplifiers as booster amplifiers

Abstract: We have demonstrated the transmission performance of 10-Gb/s transmitters based on LiNbO/sub 3/ modulator using semiconductor optical amplifiers (SOAs) as booster amplifiers. Utilizing the negative chirp converted in SOAs and self-phase modulation induced by high optical power, we can successfully transmit 10-Gb/s optical signals over 80 km through the standard single-mode fiber with the transmitter using SOAs as booster amplifiers. SOAs can be used for booster amplifiers with a careful adjustment of the operating conditions. In order to further understand an SOA's characteristics as a booster amplifier, we model SOAs and other subsystems to verify the experimental results. Based on the good agreement between the experimental and simulation results, we can find the appropriate parameters of input signals for SOAs, such as extinction ratio, rising/falling time, and chirp parameter to maximize output dynamic range and available maximum output power (P/sub o,max/).

A novel structural VO2 micro-optical switch

Abstract: In this letter, a novel optical switch based on vanadium dioxide (VO2) thin film on substrates of silicon (100) has been fabricated. The vanadium dioxide thin films were deposited by reactive ion beam sputtering followed by a post-annealing. The testing result shows the insertion loss of the optical switches is about 1–2 dB, and the extinction ratio is up to 26 dB. The speed of the switches is as fast as 60 ns.