Showing papers on "Extinction ratio published in 2006"

Ultrasmall polarization splitter based on silicon wire waveguides

Abstract: We describe an ultrasmall polarization splitter based on a simple directional coupler consisting of silicon wire waveguides. The size is only 7 x 16 microm(2), and the polarization extinction ratio is about 15 dB for a single coupler. A double-coupler structure improves the extinction ratio to over 20 dB. The excess loss is smaller than 0.5 dB for both types of device. In the device, the shape of the high-speed waveform is retained at any angle of polarization. Our polarization splitter represents a first step towards accomplishing an ultrasmall optical circuit with polarization diversity based on silicon wire waveguides.

All-optical multiple logic gates with XOR, NOR, OR, and NAND functions using parallel SOA-MZI structures: theory and experiment

Abstract: The authors have proposed, simulated, and experimentally demonstrated all-optical multiple logic gates using two parallel semiconductor optical amplifier (SOA)-Mach-Zehnder interferometer (MZI) structures that enable simultaneous operations of various logic functions of XOR, NOR, OR, and NAND. The proposed scheme, which is optimized by adjusting the optical gain and phase differences in SOA-MZI structures with creative and systematic method, has great merits to achieve the reshaped output pulses with high extinction ratio and enable the high-speed operation at over 10 Gb/s through performance enhancement of SOAs. Its validity is confirmed through simulation and experiments at 2.5 and 10 Gb/s, respectively

Chirp-managed directly modulated laser (CML)

Abstract: We demonstrate a new highly dispersion tolerant modulation format using a chirp-managed directly modulated laser (CML) for uncompensated 10-Gb/s transmission over >200 km at 1.55 /spl mu/m. The CML consists of a distributed feedback (DFB) laser followed by an optical filter. We show that the combination of adiabatic chirp from the DFB and filter edge response produces high extinction ratio pulses with nearly uniform phase, abrupt phase shifts at bit transitions, and a correlation between the 1 bits; 1 bits separated by odd number of 0 bits are /spl pi/ out of phase. This results in carrier suppression, 1/2 the bandwidth of standard nonreturn-to-zero, and high tolerance to positive and negative dispersion.

Si Photonic Wire Waveguide Devices

Abstract: Si photonic wire waveguides are attractive for constructing various optical devices that are extremely small because the waveguides can be bent with extremely small curvatures of less than a few micrometers of bending radius. We have fabricated optical directional couplers with the waveguides and demonstrated their fundamental characteristics. Their coupling length was extremely short, several micrometers, because of strong optical coupling between the waveguide cores. We have also demonstrated wavelength-demultiplexing functions for these devices with a long coupled waveguide. Optical outputs from a device with a 100-mum-long coupled waveguide changed reciprocally with a 20-nm wavelength spacing between the parallel and cross ports. We also demonstrated the operation of ultrasmall optical add-drop multiplexers (OADMs) with Bragg grating reflectors made up of the waveguides. The dropping wavelength bandwidth of the OADMs was less than 0.7 nm, and these dropping wavelengths could be precisely designed by adjusting the grating period. Using the Si photonic wire waveguide, we have also demonstrated thermo-optic switches. Metal thin-film heaters were evaporated onto the branch of a Mach-Zehnder interferometer that incorporated the waveguide to achieve switching operations by thermo-optic effects. In these switching operations, we observed more than 30 dB of extinction ratio, less than 90 mW of switching power, and less than 100 mus of switching speed

On-chip microfluidic tuning of an optical microring resonator

Abstract: We describe the design, fabrication, and operation of a tunable optical filter based on a bus waveguide coupled to a microring waveguide resonator located inside a microchannel in a microfluidic chip. Liquid flowing in the microchannel constitutes the upper cladding of the waveguides. The refractive index of the liquid controls the resonance wavelengths and strength of coupling between the bus waveguide and the resonator. The refractive index is varied by on-chip mixing of two source liquids with different refractive indices. We demonstrate adjustment of the resonance by 2nm and tuning the filter to an extinction ratio of 37dB.

All-optical switch utilizing intersubband transition in GaN quantum wells

Abstract: Intersubband transition (ISBT) in GaN quantum wells (QWs) was investigated from the viewpoint of application to ultrafast all-optical switches. The effect of crystalline quality on the absorption saturation characteristics was examined and reduction of edge dislocations was found to be a crucial factor in decreasing operation energy. Then, the switching performance was investigated for devices with improved crystalline quality. Modulation of signal pulses with a pulse interval of less than 1 ps was confirmed. Another device displayed gate-switch operation with an extinction ratio of greater than 10 dB. Comparison of the absorption recovery process in both devices suggested that the process is strongly affected by the QW structure

Asymmetric Fano resonance and bistability for high extinction ratio, large modulation depth, and low power switching.

Abstract: We propose a two-ring resonator configuration that can provide optical switching with high extinction ratio (ER), large modulation depth (MD) and low switching threshold, and compare it with two other conventional one-ring configurations. The achievable input threshold is n2IIN ~10-5, while maintaining a large ER (> 10dB) and MD (~ 1) over a 10-GHz (0.1 nm) optical bandwidth. This performance can also be achieved by the ring-enhanced Mach-Zehnder interferometer, and is one to two orders of magnitude better than the simple bus-coupled one-ring structures, because of the use of asymmetric Fano resonance as opposed to the usual symmetric resonance of a single ring. The sharpness and the asymmetricity of the Fano resonance are linked to the low switching threshold and the high extinction ratio, respectively, and also accounts for the different dependence on ring dimensions between the one- and two-ring structures.

1 × 2 optical switch devices based on semiconductor-to-metallic phase transition characteristics of VO2smart coatings

Abstract: We have successfully fabricated two types of 1 × 2 optical switch devices, namely, all-optical switch (VO2/quartz) and electro-optical switch (VO2/TiO2/ITO/glass) based on the semiconductor-to-metallic phase transition characteristic of vanadium dioxide (VO2) smart coatings. The VO2 active layer, the TiO2 buffer layer and the ITO transparent conductive electrode used in these devices were achieved by reactive pulsed laser deposition. The optical switching of the fabricated devices was investigated at λ = 1.55 µm. The semiconductor (on) to metallic (off) phase transition was controlled by photo-excitation of VO2 in the case of the all-optical switch and by an external electric field applied between the ITO and the VO2 layer in the case of the electro-optical switch. The extinction ratio (on/off) is found to be much higher for the all-optical switch than for the electro-optical switch. For the all-optical switch, extinction ratios of about 22 and 12 dB are obtained in the transmission and reflection modes, respectively. In the case of the electro-optical switch, the extinction ratio is about 12 dB in the transmission mode and 5 dB in the reflection mode. Finally, to explain our optical switching results, we propose a simple model based on the energy band diagram of VO2 in which the charge density increases under an external excitation (either photo-excitation or an electrical field), and then induces the semiconductor-to-metallic phase transition in the VO2 active layer.

Adiabatic and Multimode Interference Couplers on Silicon-on-Insulator

Abstract: Adiabatic and multimode interference (MMI) 3-dB couplers based on silicon-on-insulator rib waveguides were fabricated and measured. For testing purposes, pairs of identical couplers were cascaded to form Mach-Zehnder interferometers. The adiabatic couplers showed excess on-chip loss of ~0.5 dB, extinction ratio (ER) of 15-20 dB, and a wide spectral range. The MMI couplers processed on the same wafer showed similar loss per coupler, higher ER, and limited spectral characteristics

Highly efficient temporal cleaner for femtosecond pulses based on cross-polarized wave generation in a dual crystal scheme

Abstract: We present an experimental demonstration of a renewed set up, with respect to the one described in [A. Jullien et al, Opt. Lett. 30, 920 (2005)], that enables more reliable and robust performances in the increase of the contrast ratio (CR) of energetic femtosecond pulses. The new approach is based on the use of two successive crystals situated at optimum position that generate cross polarized waves whose individual effect interferes constructively. This arrangement overcomes the limitation of the single crystal schemes for temporal cleaning – the early saturation of the transmission efficiency, previously observed when either using a relatively thick crystal or increasing intensities up to its damage threshold. A theoretical model that predicts the output CR is developed for the first time. It shows that the CR depends on the initial CR and the extinction ratio of the polarizers used. The measured temporal CR 10-10 is in accordance with theoretical predictions.

Polarization beam splitter based on a photonic crystal heterostructure

Abstract: The design and characterization of a photonic crystal (PC) polarization beam splitter (PBS) that operates with an extinction ratio of greater than 15 dB for both polarizations are presented. The PBS is fabricated on a silicon-on-insulator (SOI) wafer where the input and output ports consist of 5 μm wide ridge waveguides. A large spectral shift is observed in the dispersion plots of the lowest-order even (TE-like) and odd (TM-like) modes due to the SOI confinement. Because of this shift, the TE-like mode is close to a directional gap at the top of the band, and the TM-like mode is in a low-frequency regime where the dispersion surface is almost isotropic. We show that the TE-like mode has very high reflection at the interface between the two PCs, whereas the TM-like mode exhibits a very high transmission.

Fast and stable wavelength-selective switch using double-series coupled dielectric microring resonator

Abstract: We demonstrated a hitless wavelength-channel-selective switch (hitless tunable add-drop filter) using thermooptic effect of double series coupled dielectric microring resonator. Using a dielectric material as the core, the response time was reduced to 105 (rise time) and 15 mus (fall time), which are 15-fold and 100-fold faster than that of polymer material, and the reproducibility by the heat cycle test was also improved to less than 0.01 nm. The tuning range of wavelength-selective switch was expanded to 13.3 nm using the Vernier effect, and a large extinction ratio of more than 20 dB was realized

Very-low-driving-voltage electroabsorption modulators operating at 40 Gb/s

Abstract: This paper has demonstrated a 40-Gb/s low-driving-voltage electroabsorption modulator (EAM) having InGaAlAs/InAlAs multiquantum-well active core. A narrow core buried with polyimide provides a strong optical and electrical confinement, resulting in a maintained large extinction ratio (ER) and an increased 3-dB down frequency. The fabricated EAM shows a 3-dB down frequency as large as 46 GHz, even for the active-core length as long as 200 /spl mu/m. The EAM operates at 40 Gb/s with an RF ER of 10.5 dB at a driving voltage as low as 0.79 V.

All-optical AND gate with improved extinction ratio using signal induced nonlinearities in a bulk semiconductor optical amplifier

Abstract: An all-optical AND gate based on optically induced nonlinear polarization rotation of a probe light in a bulk semiconductor optical amplifier is realized at a bit rate of 2.5Gbit/s. By operating the AND gate in an up and inverted wavelength conversion scheme, the extinction ratio is improved by 8dB compared with previously published work.

Dual-Wavelength InAlGaAs–InP Laterally Coupled Distributed Feedback Laser

Abstract: The design and operation of a novel dual-wavelength laterally coupled (LC) distributed feedback (DFB) semiconductor laser are reported. The laser has two different grating periods, one on each sidewall. Stable dual-mode emission, with low threshold currents and good extinction ratio approaching 30 dB, has been demonstrated. Generation of millimeter-wave signals by photomixing has been performed, and the linewidths of each of the individual modes and of the beat mode have been measured as a function of the injection current. It is observed that while the linewidth of the separate modes has a modest dependence on the injection level, the linewidth of the beat mode experiences a strong decrease as the injected current increases

All-optical AND and NAND gates based on cascaded second-order nonlinear processes in a Ti-diffused periodically poled LiNbO(3) waveguide.

Abstract: All-optical AND and NAND gates have been demonstrated in a Ti-diffused periodically poled LiNbO3 channel waveguide which has two second-harmonic phase-matching peaks by cascaded sum-frequency-generation/difference-frequency-generation (cSFG/DFG) and sum-frequency-generation (SFG) processes. The conversion efficiency of signal to idler (AND gate signal) was approximately 0 dB in cSFG/DFG process. In the second SFG process, more than 15 dB extinction ratio between signal and dropped signal (NAND gate signal) has been observed.

Low-loss Si wire waveguides and their application to thermooptic switches

Abstract: We demonstrate low-loss Si wire waveguides with good thermal stability and thermooptic (TO) switches made from them. The propagation losses of the fabricated waveguides were around 2 dB/cm and the coupling losses to an external fiber were 0.4 dB. These values were achieved by improving the fabrication process and introducing spot-size converters made from inorganic materials. Using these waveguides, we made two types of TO switches, a 1×1 switch with a multimode interference (MMI) branch and a 2×2 switch with a 3-dB directional coupler. Both switches exhibited a high extinction ratio of more than 30 dB at a low electric power of 30 mW and a switching time shorter than 200 µs.

All-Optical Format Conversion From NRZ to BPSK Using a Single Saturated SOA

Abstract: All-optical format conversion from nonreturn-to-zero (NRZ) to binary phase-shift keying format is experimentally demonstrated at 8 Gb/s using a single semiconductor optical amplifier (SOA). The conversion is based on the gain and phase modulations of the SOA on an input NRZ signal of finite extinction ratio

High speed (>11 GHz) modulation of BCB-passivated 1.55 [micro sign]m InGaAlAs-InP VCSELs

Abstract: MBE-grown InGaAlAs-InP vertical cavity surface emitting lasers with buried tunnel junction for 1.55 µm wavelength, passivated with benzocyclobutene (BCB) and coplanar contacts, are presented. The devices show superior modulation bandwidths up to 11.6 GHz. Wide open eye diagrams with 6 dB extinction ratio enable error-free data transmission at 10 Gbit/s in back-to-back configuration and over different fibres.

Power and polarization beam-splitters, mirrors, and integrated interferometers based on air-hole photonic crystals and lateral large index-contrast waveguides

Abstract: Air hole 2D photonic crystals (PhC) and air slots have been used in association with semiconductor ridge waveguides to produce highly compact beam-splitters (less than 10 µm×10 µm) for power or polarization separators and mirrors. An efficiency of 99% (in both 2D and 3D formulations) has been obtained for the power beam-splitter using finitedifference time-domain (FDTD) simulations-and around 95% has been measured experimentally for structures realized in silicon-on-insulator (SOI) waveguides. In the polarization splitter, an extinction ratio as large as 11 dB was also reached experimentally. Examples of combinations of these elements in the form of interferometers are also presented.

Polarization-dependent transmission through subwavelength anisotropic aperture arrays.

Abstract: The use of polarized light as an approach to further control the extraordinary transmission (EOT) through nanostructured metallic films has recently gained attention. In this work, it is shown that aperture shape and orientation not only determine the intensity of the polarized light emitted, corroborating the previous work of others, but also can be used to spectrally tune the relative peak intensity of surface plasmon polaritons modes. The high extinction ratio of high aspect ratio apertures lends itself to the creation of micron-sized structures that emit at different wavelengths depending upon the orientation of linearly polarized incident light. This has many potential applications including the prospect of color shifting pixels for high definition television (HDTV) and thin film electroluminescent (TFEL) devices as well as novel polarization mode dispersion control components.

Magneto-Optic-Based Fiber Switch for Optical Communications

Abstract: In this paper, the use of the Faraday effect in a optical on-off switch is investigated for application in wide spread usage in fiber networks. This is the first reported magneto-optic switch for optical fiber networks. Light does not exit from the fiber except when propagating into the MO rotator, thus this is an all fiber switch. The extinction ratio was stabilized and faster switching was observed when the domain walls are pinned and only rotation occurred. Integrated magnetooptics is the final frontier for the improvement of the device characteristics as well as the commercialization of such a magneto-optic switch. Finally the issues of implementation and operation of the integrated magneto-optical switch and the techniques of growing high quality garnet thin films for this purpose are demonstrated.

Optimizing imaging polarimeters constructed with imperfect optics

Abstract: Imaging polarimeters are often designed and optimized by assuming that the polarization properties of the optics are nearly ideal. For example, we often assume that the linear polarizers have infinite extinction ratios. It is also usually assumed that the retarding elements have retardances that do not vary either spatially or with the angle of incidence. We consider the case where the polarization optics used to develop an imaging polarimeter are imperfect. Specifically, we examine the expected performance of a system as the extinction ratio of the diattenuators degrades, as the retardance varies spatially, and as the retardance varies with incidence angle. It is found that the penalty in the signal-to-noise ratio for using diattenuators with low extinction ratios is not severe, as an extinction ratio of 5 causes only a 2.0 dB increase in the noise in the reconstructed Stokes parameter images compared with an ideal diattenuator. Likewise, we find that a system can be optimized in the presence of spatially varying retardance, but that angular positioning error is far more important in rotating retarder imaging polarimeters.

Signal Propagation Over Polarization-Maintaining Fibers: Problem and Solutions

Abstract: Polarization-maintaining (PM) fibers are able to preserve the state of polarization (SOP) of a signal in the fiber reference frame. The SOP follows one of the axes of the fiber defined by the mechanical constraint that has been inserted during manufacturing. This ability is characterized by the polarization extinction ratio, which should be as high as possible. It is known to be very high (often above 50 dB) for the fiber itself. However, the somewhat low polarization extinction ratios (often between 20 and 30 dB) of connections (connectors, splices, ...) induce strong distortions of the signal. The authors first explain why for one PM patch cord, i.e., a fiber and its connectors, with numerical and analytical models. They then extend these models to a patch-cord concatenation. Finally, they show and compare analytically and numerically different solutions to this problem: fiber length reduction, polarizer insertion, high-performing connectors, and axis alternation. The latest solution consisting in alternating the slow and the fast axes from one fiber to the next one is particularly efficient. They have implemented these solutions for the purpose of the source of the "Laser MegaJoule", and it exhibits far better performance

A high port-count wavelength-selective switch using a large scan-angle, high fill-factor, two-axis MEMS scanner array

Abstract: We present a high-port-count (scalable to 1 times 32) wavelength-selective switch (WSS) using a large scan-angle, high fill-factor, two-axis analog micromirror array in conjunction with a densely packed two-dimensional array of fiber collimators. A partially populated (1 times 9) WSS exhibits a fiber-to-fiber insertion loss of 5.57 plusmn 1.4 dB and an extinction ratio of 51 plusmn 11 dB. The channel spacing is 100 GHz

10 Gbit/s all-optical non-return to zero-return-to-zero data format conversion based on a backward dark-optical-comb injected semiconductor optical amplifier.

Abstract: By using a semiconductor optical amplifier backward injected by a dark-optical-comb pulse train at 10GHz, we demonstrate a 10Gbit/s all-optical nonreturn-to-zero (NRZ) to return-to-zero (RZ) format conversion of an incoming optical pseudorandom binary sequence (PRBS) data strieam. Both the polarity and the wavelength of data are conserved during format conversion. Without any preamplification, the extinction ratio of degraded optical NRZ PRBS data is greatly improved from 7.13 to 13.6dB after NRZ-to-RZ conversion. An ultralow bit-error rate of 10−12 at a data rate as high as 10Gbits/s is obtained with a received optical power of −18.3dBm. The converted RZ PRBS data exhibit a negative power penalty of >3.7dB compared with the NRZ PRBS data at a bit-error rate of 10−12.

All-Optical Clock Recovery From NRZ-DPSK Signal

Abstract: All-optical clock recovery (CR) from 20-Gb/s nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) signal is demonstrated, with an all-fiber delay interferometer (DI) and a mode-locked semiconductor optical amplifier (SOA) fiber laser. The tunable DI serves as an all-optical DPSK demodulator and the phase-modulated NRZ-DPSK signal is converted into the intensity-modulated pseudoreturn-to-zero (PRZ) signal, with the enhancement of the clock component. Followed SOA fiber-laser is used to achieve CR from the PRZ signal. Fixed bit pattern and 231-1 pseudorandom binary sequence NRZ-DPSK signals are used to test the performance of the proposed system. It is shown that the recovered clock signal with the extinction ratio over 10 dB and the root-mean-square timing jitter of 800 fs can be achieved

Waveband converters based on four-wave mixing in SOAs

Abstract: Four wave mixing (FWM) is distinguished from other wavelength conversion techniques by its ability to simultaneously convert a number of input wavelength channels. In this case, optical signal-to-noise ratio (OSNR) is insufficient to describe the performance of the device as many effects are involved. A multiwavelength FWM model is used here to simulate a waveband converter (WBC). The numerical model predicts the waveform of the FWM product. Based on that output, the Q factor of the signal and the power penalty induced to the signal can be calculated to evaluate the performance of such a device. Meanwhile, an analytical model is used for the calculation of the signal power levels and the standard deviation of the fluctuation; hence, it describes the constituent effects-namely, the extinction ratio (ER) degradation, the OSNR degradation, the gain modulation (GM) related crosstalk, and interference. The model's validity is tested against the numerical results. To the best of the authors' knowledge, this is the first time that a numerical model and an analytical model are used to systematically investigate a WBC and to identify the specific effects and derive the design rules. These rules are tested in the experiment. Finally, a tunable WBC (TWBC) based on the dual-pump configuration is described and implemented experimentally