Showing papers on "Extinction ratio published in 1996"

All-optical wavelength conversion by semiconductor optical amplifiers

Abstract: Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber.

Polarizing beam splitter based on the anisotropic spectral reflectivity characteristic of form-birefringent multilayer gratings.

Abstract: We introduce a novel polarizing beam splitter that uses the anisotropic spectral reflectivity (ASR) characteristic of a high-spatial-frequency multilayer binary grating. Such ASR effects allow us to design an optical element that is transparent for TM polarization and reflective for TE polarization. For normally incident light our element acts as a polarization-selective mirror. The properties of this polarizing beam splitter are investigated with rigorous coupled-wave analysis. The design results show that an ASR polarizing beam splitter can provide a high polarization extinction ratio for optical waves from a wide range of incident angles and a broad optical spectral bandwidth.

Widely and continuously tunable micromachined resonant cavity detector with wavelength tracking

Abstract: We demonstrate a resonant cavity wavelength tunable detector with a record 30-nm continuous tuning range, 17-dB extinction ratio, and a low 7-V tuning voltage. The detector map be biased to operate in one of two modes. In the first, the detector is tuned to a specific wavelength. In the second, the detector can be tuned to a nominal wavelength and remain locked to the wavelength of the incident light despite wavelength variations. Consequently, this detector is ideal for operation as a cost-effective and robust receiver for WDM communication systems, spectroscopic applications, and wavelength measurement.

Tropospheric aerosol extinction coefficient profiles derived from scanning lidar measurements over Tsukuba, Japan, from 1990 to 1993

Abstract: Mie scattering lidar was used to observe aerosol extinction coefficient profiles in the troposphere over Tsukuba (140 E, 36 N), Japan, for three years from March 1990 to February 1993, and data obtained in fair weather were analyzed. The lidar measurements were made by a vertical scanning mode to generate profiles of extinction coefficients from the lidar level to a 12-km altitude. The extinction coefficients were derived from the lidar signals using a two-component (air molecule and aerosol) lidar equation, in which the ratio of aerosol extinction to backscattering was assumed to be constant. Seasonal average profiles were derived from individual profiles. Three-year average profiles were also calculated and modeled using mathematical expressions. The model profile assumed (1) a constant extinction ratio in the atmospheric boundary layer (ABL), (2) an exponentially decreasing extinction ratio above the ABL, and (3) a constant extinction ratio in the upper troposphere where the extinction ratio can be defined as the ratio of the aerosol extinction coefficient to the air molecule extinction coefficient. The extinction ratios both in the ABL and in the upper troposphere and the scale height that was used to express the exponential decrease were used as three unknown parameters. Seasonal variation of optical thickness that was obtained by integrating extinction coefficients with height was also investigated.

Transmission of directly modulated 2.5-Gb/s signals over 250-km of nondispersion-shifted fiber by using a spectral filtering method

Abstract: We demonstrate 250-km nondispersion-shifted fiber transmission of directly modulated 2.5-Gb/s signals. The chirping-induced power penalty is reduced by using a spectral filter whose transmission peak is tuned to "mark" wavelength of the modulated laser output. A well-known intensity modulation with a sufficiently high extinction ratio is used to suppress the intersymbol interference induced by nonuniform frequency modulation response of semiconductor lasers. The observed results are explained theoretically by using eye closure penalty.

An InGaAs-GaAs vertical-cavity surface-emitting laser grown on GaAs(311)A substrate having low threshold and stable polarization

Abstract: We have fabricated an InGaAs-GaAs vertical-cavity surface-emitting laser (VCSEL) grown on a GaAs(311)A substrate by molecular beam epitaxy (MBE) and demonstrated continuous wave operation at room temperature. A threshold current density of 80 A/cm/sup 2//well and very stable polarization characteristics up to 2.7 times the threshold were achieved. The polarization state with the highest optical intensity was oriented along the [2~33] direction, which is the crystallographic axis exhibiting the maximum gain. An extinction ratio of more than 12.7 dB was obtained between two orthogonal polarization states. The high and anisotropic gain of a (311)A-oriented VCSEL will drastically improve the device performance by optimization and process engineering.

10 Gb/s wavelength conversion with integrated multiquantum-well-based 3-port Mach-Zehnder interferometer

Abstract: All-optical wavelength conversion of 10 Gb/s data with simultaneous regeneration of the extinction ratio is achieved by means of a monolithic 3-port Mach-Zehnder interferometer. The reported devices are based on an all active multiquantum-well waveguide structure with optical amplifiers in the input/output gates. Wavelength conversion is realized by optical cross-phase modulation in a counter propagative operation mode without applying an optical filter. The 3-port Mach-Zehnder interferometer can provide either inversion or noninversion of wavelength converted 10 Gb/s data.

Interferometer, adjusting method therefor, stage apparatus having the interferometer, and exposure apparatus having the stage apparatus

Abstract: This invention relates an interferometer having a structure for suppressing measurement errors arising from leakage light by minimizing nonlinear errors due to the leakage light in a polarization beam splitter for splitting incident light into a first polarized light component and a second polarized light component, and apparatuses to which the interferometer is applied. The interferometer includes an adjustment mechanism for adjusting the angle of light incidence on the beam splitting surface of the polarization beam splitter such that the extinction ratio of the polarization beam splitter is minimized by using the dependence of the polarization beam splitter on the incident angle.

Dispersion-penalty-free transmission over 130-km standard fiber using a 1.55-μm, 10-Gb/s integrated EA/DFB laser with low-extinction ratio and negative chirp

Abstract: Transmission performance of a 10-Gb/s integrated electroabsorption modulator/DFB laser has been evaluated in terms of the eye margin degradation and the receiver sensitivity penalty caused by the chromatic dispersion in the standard (non-DSF) fiber. Combination of low extinction ratio (/spl epsi/=5 dB) and negative chirp (/spl Delta/v=-0.01 nm) operation allows 10-Gb/s transmission over 130-km standard fiber without any dispersion penalty in receiver sensitivity (for 10/sup -9/ BER) and with a 7% eye margin for 10/sup -15/ BER.

Optical path length trimming technique using thin film heaters for silica-based waveguides on Si

Abstract: The authors propose a practical optical path length trimming technique and demonstrate this using thin film heaters for silica based planar lightwave circuits (PLCs). Irreversible refractive index changes up to 1.5/spl times/10/sup -4/ can be obtained to trim the PLC response by simply controlling the heating power and time. This technique is applied successfully to thermo-optic switches to maximise their extinction ratios.

Semiconductor optical modulation device

Abstract: The invention provides a semiconductor optical modulation device which has low power dissipation, high extinction ratio and high speed response features. An n-type InP clad layer, an n - -type InAlAs-InAlGaAs composition inclination multiple layer, a p-type InP clad layer and a p + -type InGaAs contact layer are layered on an n-type InP substrate. The layers are etched up to an intermediate location of the n-type clad layer to form a rib waveguide, and a positive electrode is formed on an upper portion of the rib waveguide. Further, a negative electrode is formed on the substrate.

Crosstalk analysis and system design of time-division multiplexing of polarization-insensitive fiber optic Michelson interferometric sensors

Abstract: The time-division multiplexing of polarization-insensitive fiber optic Michelson interferometric sensors (TDM-PIFOMI) with compensating interferometer is presented. The lead crosstalk in a general time-division multiplexing of the fiber optic interferometric sensors is described and demonstrated. The sensor crosstalk of TDM-PIFOMI for optical gate with finite extinction ratio is analyzed and using a laser source with adequate coherence length to reduce sensor crosstalk is suggested. The delay fiber crosstalk and noise of TDM-PIFOMI by Rayleigh backscattering is analyzed and demonstrated. We also suggest some methods that could possibly reduce the effect of the Rayleigh backscattered light. Finally, the advanced system design of TDM-PIFOMI is described.

40 Gbit/s all-optical wavelength conversion by semiconductor optical amplifiers

Abstract: The authors present 40 Gbit/s all-optical wavelength conversion experiments using crossgain modulation in bulk type semiconductor optical amplifiers specially designed for high speed operation. Polarisation-independent conversion is demonstrated with 9 dB extinction ratio and 30 dB (BW = 1 nm) signal-to-ASE ratio for the converted signal.

Phase-engineered III-V MQW Mach-Zehnder modulators

Abstract: We have optimized the negative frequency chirp while maintaining a high extinction ratio in an InP-InGaAsP multiple-quantum-well (MQW) Mach-Zehnder modulator. Our procedure is to elongate one modulator arm such that a /spl pi/ phase shift is produced at zero bias relative to the opposing arm. The resulting de extinction ratio is improved to /spl ap/16 dB from 10 dB relative to a symmetric design. The frequency chirp of the modulator at the rising edge is about -3 GHz enabling excellent transmission performance over a 95 km of conventional fiber.

Digital optical switch based on oversized polymer rib waveguides

Abstract: The authors report a novel digital optical switch that is based on polymer rib waveguides with large cross-sections. The switches use the highly thermal stable polymer Cyclotene 3022™ (benzocyclobutene) and show insertion losses of 20 dB.

Poling-induced waveguide polarizers in electrooptic polymers

Abstract: In order to demonstrate polymeric waveguide polarizers, photobleached polymer waveguides supporting both TE and TM modes are integrated with poling induced polymer waveguides that support either TE or TM modes. Fabrication parameters like UV exposures and poling voltages are controlled to reduce excess losses due to the mode profile mismatch between the connected waveguides. A TM-pass polarizer is realized by poling the polymer in the vertical direction. For TE-pass polarizer the polymer is poled horizontally by using four poling electrodes which enhance the uniformity of the poling field direction. The measured excess loss is less than 0.5 dB, and polarization extinction ratios for TM-pass and TE-pass polarizers are 20.7 dB and 17.1 dB, respectively.

Polarisation insensitive semiconductor optical amplifier with integrated electroabsorption modulators

Abstract: The authors demonstrate a 1.55 /spl mu/m wavelength multiquantum well semiconductor optical amplifier, integrated with bulk layer electroabsorption modulators and passive waveguide beam expanders at the input and output ports. The device has a fibre to fibre gain of 9 dB, an extinction ratio of 15 dB per modulator, a spectral range >35 nm, and polarisation sensitivity <1 dB.

Low drive voltage (1.5 Vp.p.) and high power DFB-LD/modulator integrated light sources using bandgap energy controlled selective MOVPE

Abstract: The authors have reduced modulator drive voltage in DFB-LD/modulator integrated light sources (DFB/MODs) taking fabrication tolerance into account. By enhancing the quantum confined Stark effect through well width increase and optimising the doping profile, DFB/MODS with >13 dB extinction ratio at 1.5 V and >4 mW (+6 dBm) output power at 100 mA were achieved while maintaining a reasonably large fabrication tolerance.

All-optical wavelength conversion by semiconductor optical amplifiers : Special issue on multiwavelength optical technology and networks

Abstract: Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber.

Polarizing beam splitters constructed of form-birefringent multilayer gratings

Abstract: We introduce a novel polarizing beam splitter that uses the anisotropic spectral reflectivity (ASR) characteristics of a high spatial frequency multilayer binary grating. By combining the form birefringence effect of a high spatial frequency grating with the resonant reflectivity of a periodic multilayer structure, the ASR characteristics for the two orthogonal linear polarizations are obtained. Such ASR effects allow us to design an optical element that is transparent for TM polarization but reflective for TE polarization. The properties of the polarizing beam splitter are investigated using rigorous coupled-wave analysis. The design results show that an ASR polarization beam splitter can provide a high polarization extinction ratio for optical waves from a wide range of incident angles and a broad optical spectral bandwidth. Such ASR polarizing beam splitters are uniquely suitable for image processing and optical interconnection applications.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Total internal reflection optical switch with injection region isolated by oxygen ion implantation

Abstract: The characteristics of InGaAsP/InP total internal reflection optical switches were improved by adopting Oxygen ion implantation in forming electrical isolation, which can confine injected carriers successfully and obtain good perpendicular reflective ‘wall” whose transparency is controlled by injected carriers Operating at 13-μm wavelength, the extinction ratio at the reflected port of the optical switch is 185 dB at a low injection current of 26 mA and the off-state crosstalk is –188 dB

Proposal and analysis of an ultrashort directional-coupler polarization splitter with an NLC coupling layer

Abstract: We propose a novel, high-performance directional-coupler polarization splitter using a nematic liquid crystal (NLC) as the coupling layer. The beam propagation method is used to investigate the propagation characteristics of the device under various conditions. Results of numerical calculations relevant to the design conditions are presented. Because of the large birefringence of NLC, a very short device length of 140 /spl mu/m is achievable at a high extinction ratio of 28 dB.

Multifunctional characteristics of 1.5-μm two-section amplifier-modulator-detector SOA

Abstract: The multifunctional characterization of a two-section amplifier-modulator-detector semiconductor optical amplifier (AMD-SOA) is presented. Detectivity is analyzed in terms of bandwidth and responsivity while modulation properties are characterized by temporal response and extinction ratio. Receiver sensitivities of -26 dBm at 155 Mb/s and -19.5 dBm at 622 Mb/s and error-free signal modulation/transmission with simultaneous 10 dB amplification at 622 Mb/s with a 2/sup 23/-1 PRBS signal are reported. This device could find application as transparent add-drop node in photonic packet-switched optical ring networks.

System for tuning an integrated optical switch element

Abstract: A system for tuning an integrated optical switch element (100) utilizes a reflected portion (212) from a light signal (204) that is propagated into a first input port (106) defined on one side of an interaction region (110) of the optical switch element. The reflection occurs beyond an opposite side of the interaction region from the side on which the light signal is introduced. The reflected portion (212) is detected at a second input port (108) of the optical switch element (100) on the same side of the interaction region (110) as the side on which the light signals are introduced. The reflected portion (212) is used to tune the optical switch element (100) to a desired switch state by minimizing the reflection detected at the second input port (108). By minimizing the reflected portion (212) detected at the second input port (108) for a desired switch state, the strength of the optical signal (204) through the wave guide channels (206, 208) intended to be used to propagate the light signal in the desired switch state is maximized. As a result, the switching extinction ratio for the optical switch element (100) in the desired switch state is optimized. The system can be used to selectively tune a single optical switch element, or can be used to selectively tune multiple integrated optical switch elements that form an optical switch matrix on a common substrate, for example.

Iterative method to determine an averaged backscatter-to-extinction ratio in cirrus clouds.

Abstract: An iterative method to determine an average backscatter-to-extinction ratio and extinction coefficient simultaneously in cirrus clouds is proposed. The method is based on Klett's inversion, which is constrained by the total optical depth. A signal-to-noise ratio greater than 3 at the cloud top is required for an error in the backscatter-to-extinction ratio lower than 20% to result. The method has been tested with simulated lidar signals. An application to an experimental lidar signal is discussed.

Demonstration of an all-optical data format transparent WDM-to-TDM network node with extinction ratio enhancement for reconfigurable WDM networks

Abstract: We demonstrate a nearly penalty free, all-optical and robust WDM-to-TDM network node that converts two input WDM channels into one high-speed TDM signal. Our node incorporates the very useful functions of: 1) WDM input data-format transparency; 2) time multiplexing; 3) wavelength shifting; and 4) extinction ratio enhancement of the output TDM signal. We demonstrate the principle of this network node by converting two 1-Gb/s NRZ WDM channels at 1552 and 1548 nm into a 2-Gb/s NRZ TDM signal at 1558-nm, while incurring only a 0.2 dB power penalty.

Semiconductor modulator with a shift

Abstract: A MQW semiconductor Mach Zehnder phase modulator is formed by two Y-junctions (12, 32), each having a single waveguide (14) optically coupled with two branch waveguides (18, 20). The branch waveguides of the two Y-juntions are optically coupled in Mach-Zehnder configuration that, under zero bias conditions, has one interferometric arm longer than the other to provide a .pi. phase shift. The additional length is preferably accommodated in the branches of the Y-junctions. The phase shift, in combination with voltage dependent absorption properties and non-linear phase variations of the MQW guided regions in the Mach-Zehnder modulator results in a negative chirp and high extinction ratio for an equal, push-pull device configuration.

All-optical format conversion from NRZ to RZ signals using a walk-off balanced nonlinear fibre loop mirror

Abstract: The authors have successfully demonstrated a novel scheme for signal conversion from the non-return-to-zero to return-to-zero formats by using a walk-off balanced nonlinear fibre loop mirror with duty ratio controllability and with no extinction ratio degradation. This scheme may be very useful in all-optical communication systems as an interfacing device for low speed local networks with high speed optical trunk lines.

Silica-based low loss and high extinction ratio 8/spl times/8 thermo-optic matrix switch with path-independent loss arrangement using double Mach-Zehnder interferometer switching units

Abstract: We describe a low loss and high-extinction ratio 8/spl times/8 thermo-optic matrix switch with a reduced 8 stage configuration composed of silica-based planar lightwave circuits. The average insertion loss and the extinction ratio were 5.1 dB and 60.3 dB, respectively.

Ultrashort low-loss optical multiquantum-well GaAs/GaAlAs vertical directional coupler switch

Abstract: An optical GaAs/GaAlAs multiquantum-well vertical directional coupler switch with a device length of 85 /spl mu/m is presented. At a wavelength of 854 nm the voltage necessary for switching was 5 V, associated with a transmission loss of only 2 dB in the switched state and an extinction ratio of greater than 10 dB. The device parameters were chosen so as to enable monolithic integration.