Showing papers on "Extinction ratio published in 1997"

Al wire-grid polarizer using the s-polarization resonance effect at the 0.8-microm-wavelength band.

Abstract: An aluminum wire-grid polarizer whose period is 0.39 microm has been fabricated on a quartz substrate by electron-beam direct-writing lithography and the lift-off method. By using the s -polarization resonance effect and optimizing structural parameters, characteristics such as a loss of less than 20% and an extinction ratio larger than 1000 have been experimentally obtained at the 0.8- microm -wavelength band. Theoretical analysis is performed and found to be consistent with the experimental results.

Polarisation-insensitive travelling-wave electrode electroabsorption (TW-EA) modulator with bandwidth over 50 GHz and driving voltage less than 2 V

Abstract: The proposed TW-EA modulator has a thin intrinsic layer (a 0.2 /spl mu/m thick strained InGaAlAs (13 nm)/InAlAs (5 nm) MQW) and short interaction length (200 /spl mu/m). The optical 3 dB modulation bandwidth exceeds 50 GHz, and the driving voltages for the 15 dB extinction ratio are 1.7 and 1.9 V for TE and TM modes respectively, at 1.55 /spl mu/m wavelength.

Large-signal analysis of all-optical wavelength conversion using two-mode injection-locking in semiconductor lasers

Abstract: A large-signal analysis is presented for a DC-biased Fabry-Perot laser locked by simultaneous strong optical injection of a CW signal and a modulated signal into different modes. The model is based on the description of injection-locking by Lang (1982) which is shown to hold even under the condition of strong injection and large detuning of the input signals. The following results are obtained: the configuration allows all-optical wavelength conversion in the multigigabit range, and both logically noninverting and inverting conversion is possible. In both operation modes, the conversion mechanism is mainly attributed to dispersive switching which is shown to be very fast above threshold due to injection-locking. Operation up to data rates of 20 Gb/s is possible with reasonable output extinction ratio. The bandwidth is determined by the relaxation oscillation frequency of the laser. It will be extended by decreasing the resonator length, increasing the injected current, and increasing the injected optical power. The output signal is nearly chirp-free. The model is able to explain the main results of previously published experiments.

Directly modulated semiconductor laser having reduced chirp

Abstract: In accordance with the present invention, an in-line fiber Bragg grating is coupled to the output of a directly modulated DFB laser. The grating preferably rejects chirp induced frequencies of light emitted by the DFB laser. Accordingly, light transmitted through the grating is spectrally narrowed and has a higher extinction ratio, thereby decreasing bit error rate probabilities.

Fiber four-wave mixing demultiplexing with inherent parametric amplification

Abstract: We present an all-optical time-division demultiplexer with 22 dB conversion efficiency, using four-wave mixing (FWM) at 1550 nm in a single-mode dispersion-shifted fiber. Error-free demultiplexing of 20 Gb/s data to 10 Gb/s is obtained, with 1.4 dB power penalty at BER=10/sup -9/. We also derive theoretical expressions for the conversion efficiency, the maximum bit rate that is possible to demur and the shape of the switching window. In particular we emphasize the importance of phase-matching in order to achieve a flat switching window. Furthermore the pump must remain undepleted to avoid a detrimental reduction of the extinction ratio due to instantaneous parametric gain saturation.

Long-wavelength resonant vertical-cavity LED/photodetector with a 75-nm tuning range

Abstract: A design for a highly tunable long-wavelength LED/photodetector has been investigated. The device consists of a GaAs-based distributed Bragg reflector (DBR) that is wafer-bonded to InP-based active layers, with a surface-micromachined tunable top DBR mirror to produce the wavelength shift. A 1.5-/spl mu/m device has been fabricated with a continuous tuning range of 75 nm. An extinction ratio of greater than 20 dB existed across the entire tuning range.

Effect of Mach-Zehnder modulator DC extinction ratio on residual chirp-induced dispersion in 10-Gb/s binary and AM-PSK duobinary lightwave systems

Abstract: It is shown through numerical simulation that residual frequency chirping in lithium niobate external modulators, which accompanies devices with a finite-optical extinction ratio, always degrades the performance of lightwave systems that use optical AM-PSK duobinary signaling. This is unlike binary systems which will exhibit either an improvement or degradation, depending on the polarity of residual chirp.

Semiconductor optical amplifier

Abstract: A semiconductor optical amplifier which has a good extinction ratio and a simple structure includes an optical waveguide having at least a curved portion. The optical waveguide has light input and output ends offset from each other to keep optical fibers out of alignment with each other at respective opposite ends of the optical waveguide.

Silicon-on-insulator asymmetric optical switch based on total internal reflection

Abstract: Based on the large cross-section single-mode rib waveguide condition, total internal reflection (TIR) and the plasma dispersion effect, a silicon-on-insulator (SOI) asymmetric optical waveguide switch with transverse injection structure has been proposed and fabricated, in which the SOI technique utilizes silicon and silicon dioxide thermal bonding and back-polishing. The device performance is measured at a wavelength of 1.3 /spl mu/m. It shows that the extinction ratio and insertion loss are less than -18.1 and 6.3 dB, respectively, at an injection current of 60 mA. Response time is 110 ns.

An aluminum-wire grid polarizer fabricated on a gallium–arsenide photodiode

Abstract: An aluminum-wire grid polarizer fabricated directly on a gallium–arsenide photodiode is used to realize a polarization-selective photodetector. Since all of the light transmitted through the wire grid, including higher-order diffraction components, can be detected at the photodiode and since a resonance of incident electromagnetic waves is utilized, the required grid period can be significantly larger. With a grid period of 600 nm and normal incident light at 715 nm, an extinction ratio of 16 can be obtained both for light detected at the photodiode and light reflected from the surface. If light detected at the photodiode is to be optimized, a higher extinction ratio of 30 and a loss of 30% have been experimentally obtained as well. These experimental results are in good agreement with our theoretical simulation.

Amplitude Sensitive Optical Heterodyne and Phase Lock in Technique on Small Optical Rotation Angle Detection of Chiral Liquid

Abstract: A novel method in which an optical polarized heterodyne polarimeter and lock-in technique are used to measure low concentration glucose solution based on the detection of an amplitude sensitive heterodyning signal is proposed. The linearity and the sensitivity of the measurements are enhanced in comparison with those of conventional methods in which a Pockels cell, Faraday rotator, and rotating linear polarizer are used to modulate the incident light source. A pseudo heterodyning carrier and delayed optical heterodyning technique is also discussed in comparison with the proposed amplitude sensitive optical heterodyne method. During the detection of glucose solution, the measurable rotation angle reaches 10-4 deg and a sensitivity of a concentration to 10 mg/d l in 1 cm optical path length is obtained. Further improvements such as using a better intensity stabilized laser and a high extinction ratio Glan-Thompson polarizer will allow the detection sensitivity of the measuring optical rotation angle to reach 10-5 deg.

All-fiber-optic nonreciprocal modulator

Abstract: A new all-fiber-optic nonreciprocal device using two acousto-optic frequency shifters is proposed and demonstrated. When the device was operated as an optical isolator, an extinction ratio of 22 dB was obtained. The device's unique modulation capability is also described.

ARROW-B type polarization splitter with asymmetric Y-branch fabricated by a self-alignment process

Abstract: We have proposed and demonstrated a polarization splitter based on an ARROW-B type waveguide. This device has an asymmetric Y-branch configuration, connecting a waveguide with a large modal birefringence to a low-birefringent waveguide which is channeled by a stripe lateral confinement structure. The device can achieve a high extinction ratio without precise mask alignment, since these two waveguides are connected by a self-alignment process. In addition, a low insertion loss is achieved because of adiabatic Y-branching. We designed this device at the wavelength of 1.55 /spl mu/m and fabricated it using RF sputtering. As a result, high extinction ratios of -19.4 dB for TE mode and -19.0 dB for TM mode were achieved.

All-optical wavelength conversion of NRZ and RZ signals using a nonlinear optical loop mirror

Abstract: Wavelength conversion using a nonlinear optical loop mirror (NOLM) is investigated. Our interest is in considering nonreturn-to-zero (NRZ) and return-to-zero (RZ) signals with a high-duty ratio resulting in a nonlinear phase shift of the counterpropagating wave that is not negligible and reduces the extinction ratio considerably compared to signals with a low-duty ratio. It is shown how the NOLM can be used for high-duty signals anyhow by configuring/adjusting the NOLM, particularly the polarization controller inserted in the loop. This paper gives a mathematical description of the NOLM utilizing the Jones calculus and considers different ways of adjusting the polarization controller. The nonlinear phase shifts are calculated and a reasonable confinement for the walk-off is given. Furthermore, the probability density function of the extinction ratio depending on the duty ratio of the control signal and the configuration of the NOLM for either parallel or orthogonal polarizations of the counterpropagating signal waves is derived and evaluated for some exemplary parameters.

Tunable Mach-Zehnder polarization splitter using height-tapered Y-branches

Abstract: A tunable TE/TM polarization splitter, based on a Mach-Zehnder interferometer with an electrooptic switch, is demonstrated in GaAs-AlGaAs. Symmetric and asymmetric Y-branches employing height-tapered waveguides are used to achieve power splitting and mode sorting, respectively, in the interferometer. The device has an extinction ratio of /spl sim/20 dB and an excess loss less than 1.5 dB for both TE and TM polarized light. The device can be reconfigured by tuning the switching voltage for operation at both 1.3- and 1.55-pm wavelengths.

Extinction ratio of cross-gain modulated multistage wavelength converters: model and experiments

Abstract: Extinction ratio conservation, wide dynamic range, and large operating wavelength window are important features for all-optical wavelength converters. Practical converters may probably be multistage devices and have to be precisely modeled. We present an experimental analysis and phenomenological modeling of single- and multistage wavelength converters using cross-gain modulation in polarization insensitive multiquantum-well optical amplifiers. One of the studied double-stage converters is able to produce a large extinction ratio improvement with a regeneration factor higher than 1.5 for any conversion in the 1.53-1.56-/spl mu/m window. The phenomenological model yields a very good agreement with the experimental results.

Method and apparatus for driving laser diode in which deterioration of extinction ratio is prevented

Abstract: In the apparatus for driving a laser diode, a light receiving element detects a light output level of the laser diode to produce an electric signal. That is, the light receiving element detects a first electric signal when the laser diode is driven based upon an ON signal, and a second electric signal when the laser diode is driven based upon an OFF signal. A control circuit outputs a control signal in response to the signal. A driving circuit drives the laser diode in response to the control signal such that a difference between the first electric signal and the second electric signal is maintained at a constant value.

Broad-band tunable electroabsorption modulated laser for WDM application

Abstract: Design and fabrication of the first 1.55-/spl mu/m wavelength tunable electroabsorption modulated laser integrated with a bent waveguide distributed-feedback (DFB) laser is reported. A low-threshold high-efficiency and stable single-longitudinal-mode operation is obtained when the electrodes of the bent DFB waveguide were uniformly pumped. In a normal configuration where the modulator part is used as an intensity modulator (i.e., AR coating on the modulator side and HR coating on the DFB side), stable single longitudinal mode output power close to 40 mW in free space is obtained with a 0-V bias to the modulator and an extinction ratio of up to 15 dB at 2.5 V. This single mode stability is due to the continuously distributed phase shift implemented in the structure thus reducing the photon pile-up inside the laser cavity as compared to an abruptly quarter-wave phase shifted DFB laser. With a nonuniform injection in the multiple electrodes, it was possible to select one particular single longitudinal mode out of the three neighboring modes inside the broad reflection band of the reflector. A wavelength tuning range of about 3.5 nm was obtained while maintaining an optical output power of more than 2 dBm from each mode. The device has a very low chirp (0.01-nm peak-to-peak) when modulated with a 2.5 Gb/s pseudorandom binary sequence (PRES) data stream and an error-free transmission over 200 km of non-DSF fiber has been demonstrated for all four wavelength channels separated by 100-GHz spacing. Also, when the modulator part of the structure is used as a phase tuning element (i.e., antireflective (AR) coating on the DFB side and HR coating on the modulator side), we have successfully demonstrated high-speed optical packet switching with a fast and wide tunable wavelength range. The optical packets can be modulated at 2.5 Gb/s and may be switched among four wavelength channels in less than one bit period.

Optical elements for use in spectroscopic ellipsometer and polarimeter systems

Abstract: Disclosed are optical elements for use in ellipsometer/polarimeter systems which do not introduce significant deviation and/or displacement into the propagation direction of a beam of electromagnetic radiation caused to interact therewith, even when said optical elements are caused to continuously rotate. Specifically disclosed is a Polarizer system with a high extinction ratio which can be used at infrared wavelengths, as well as a number of retarder systems with retardation vs. wavelength dispersion characteristics which are within a range of acceptability. In addition, certain disclosed optical elements demonstrate limited immunity to beam alignment changes.

Automated fusion-splicing of polarization maintaining fibers

Abstract: An advanced splicing technique for polarization maintaining (PM) fibers has been derived based on the polarization observation by lens-effect-tracing (POL) method. With this technique, azimuthal alignment on common types of PM fibers can be automatically performed in a passive way by an automated fusion splicer. Because the method permits an accurate estimation of the splice's extinction ratio before and after actual splicing, the quality of the splice call be estimated without having to make an active measurement. The experiment results illustrated in the paper show a mean extinction ratio 32.2 with 2.73 dB standard deviation and mean difference between measured and estimated extinction ratio 0.18 dB, respectively, for six different types of PM fibers.

1.3 μm strain-compensated InAsP/InGaP electroabsorption modulator structure grown by atmospheric pressure metal–organic vapor epitaxy

Abstract: High quality 15-period strain-compensated InAsP/InGaP electroabsorption (EA) modulator structures have been grown by atmospheric pressure metal–organic vapor epitaxy. The incorporation of large compressive strain (∼1.7%) in the InAsP wells and tensile strain (∼−1.8%) in the InGaP barriers necessitated the growth of a few InP monolayers between the wells and barriers. The high structural quality of such samples has been demonstrated by (cross-sectional transmission electron microscopy analysis to be free of misfit dislocations and thickness undulations. The detection of a sharp and abrupt room-temperature exciton peak both in the photoconductivity and photoluminescence measurements further confirmed their excellent optical quality. 100 μm cavity length EA modulators fabricated in these structures exhibited excellent performances namely, an extinction ratio higher than 20 dB for 2.5 V drive voltage, a 3 dB bandwidth over 20 GHz, and low coupling losses to fiber (less than 2.5 dB per facet).

Bandpass traveling-wave Mach-Zehnder modulator in LiNbO 3 with domain reversal

Abstract: A bandpass traveling-wave Mach-Zehnder modulator is demonstrated in a Z-cut LiNbO/sub 3/ substrate where quasi-phase-matching is achieved by using a crystal domain reversal and a simple uniform coplanar waveguide electrode structure. The domain reversal was created, by using electric-field poling, to implement the three-section alternating electrooptic interaction. At the operating wavelength /spl lambda/=1.32 /spl mu/m, the modulator has a 15 GHz-broad bandpass response centered at 25-GHz 3.6-dB fiber-to-fiber insertion loss, 12 V on-off voltage at the center frequency, and -33-dB extinction ratio.

Interferometric noise in lightwave systems with optical preamplifiers

Abstract: Penalties from multi-path interference in transmission systems employing optical preamplifiers have been investigated experimentally as well as theoretically. Calculations of the fraction of errors originating from the four possible combinations of received and interfering bit are carried out to identify the dominant cause of the power penalties. With perfect extinction ratio, the penalties from phase noise induced intensity noise (PIIN) are significant only at moderate levels of relative crosstalk (-30 dB to -18 dB), whereas the error floors (infinite penalty) are caused by beat noise originating from crosstalk and amplified spontaneous emission and a reduction in extinction ratio. Nonperfect extinction ratios increases the sensitivity to PIIN.

Analysis and experiment of thin metal-clad fiber polarizer with index overlay

Abstract: Fiber polarizers, based on side-polished single-mode fibers covered with a deposited thin metal film and index overlay, were investigated by us. By modeling their interaction region as a layered planar structure and using the quasi-ray-optic method, we theoretically examined the resonant absorption of light in this structure. In such an approach, the characteristics of fiber polarizers can be found without solving the refractive index of any surface plasmon mode. Fiber polarizers with different liquid overlays were presented by us and polarization extinction ratio about 60 dB was achieved. Our theoretical analyzes agreed with experimental results. The advantages of our approach are discussed.

Optical Properties of Single Layer Non-Absorptive Broadband CLC Polarizers

Abstract: We report for the first time the results of theoretical study on the optical properties of single layer non-absorptive broadband cholesteric liquid crystals (BBCLC) polarizers. The objective of this study is to understand the effect of material parameters and sample configuration on the performake of BBCLC films and therefore provide guidance for the fabrication of high quality single layer broadband polarizers. The study is based on Berreman's 4×4 matrix formalism. Nonlinear pitch distribution across the cell thickness is used in the simulation. Pitch gradient smaller than 20nm/μm is found necessary for high extinction ratio for chosen material system. The extinction ratio decreases significantly when the incident angle (internal angle) is greater than 20° and an extinction revere region is found in the case of large angle of incidence. The theoretical results are compared with the experimental results of Reveo's broadband polarizers and show reasonably good agreement.

Electro-absorption type semiconductor optical modulator having a quantum well structure

Abstract: Disclosed is an electro-absorption type semiconductor optical modulator utilizing the Quantum Confinement Stark Effect, in which a quantum well structure introduced in its optical absorption layer is arranged to have a potential structure such that one of the electron affinity and the energy of the top of the valence band increases in the laminating direction, while the other decreases, thereby canceling the built-in field. It is intended to lower the drive voltage and to enhance an on/off ratio (extinction ratio). Thus, the absorption peak becomes narrow at a no bias state to attain a low drive voltage and an enhanced extinction ratio.

Optical-loop buffer that enhances the extinction ratio of the buffered signal

Abstract: An all-optical-loop buffer (100) that restores the extinction ratio of the buffered signal such as an ATM cell. The buffer takes advantage of the cross-gain compression and wavelength shifting effected by semiconductor optical amplifiers (SOAs 118, 132). A received signal (λ 1 ) is coupled (104) to the buffer loop (101), amplified (110), and combined (114) with a low-energy unmodulated second signal (116) at a different wavelength (λ 2 ). The combined signal is amplified by an SOA (118) to modulate the second signal with an inverse of the modulation of the first signal. The received signal is extracted (128) from the SOA's output and attenuated (126). The modulated second signal is extracted (124) from the SOA's output, amplified (122), and combined (130) with the extracted received signal. The combined signal is amplified by another SOA (132) to modulate the received signal with an inverse of the modulation of the second signal, thereby enhancing the extinction ratio of the received signal. The enhanced signal is then extracted (134) from the combined signal to substantially reproduce the signal as originally received. This signal may again be sent through the buffer loop, and the process may be repeated for as often as the signal needs to be buffered.

Polarization-selective mode coupling in two-mode Hi-Bi fibers

Abstract: We propose and demonstrate a mode coupler which converts either of the LP/sub 01/ polarization states in a two-mode high-birefringence (Hi-Bi) fiber to the LP/sub 11/ mode with the same polarization. We use coupled-mode theory to develop design rules based on the polarization splitting of the beat length between the two lower-order modes. The device can be operated either as a narrow-band device in a region with large intermodal group delay difference or as a broadband device in a region with zero group delay difference. We use this novel device as a key component in a two-mode Hi-Bi fiber polarizer. In this configuration either of the polarization eigenstates can be selected and transmitted with an adjustable extinction ratio which can be as large as 30 dB. The coupling loss in the transmitted state of polarization can be less than 0.2 dB. In the broadband polarizer we demonstrate -20 dB extinction over 42 nm with a potential for considerable improvement. We also propose and experimentally investigate an increased differential group delay obtained by propagating one polarization state in the LP/sub 11/ mode instead of in the LP/sub 01/ mode. The largest differential group delay measured in this configuration is 14.5 ps/m which is seven times larger than the differential group delay between the polarization modes. We discuss several possible uses in fiber sensors and measure the transmission of a proposed two-coupler configuration.

Shaping the digital optical switch using evolution strategies and BPM

Abstract: An evolution strategy is utilized to optimize the shape of an adiabatic Y-switch. Compared to a linear structure, the digital extinction ratio is increased from 21 to 43 dB.