Showing papers on "Extinction ratio published in 2001"

Optical properties of Ag and Au nanowire gratings

Abstract: The optical response of regularly arranged noble metal wires with nanoscopic cross sections (nanowire gratings) strongly depends on the polarization direction of the incident light. We use silver and gold nanowire gratings produced by electron beam lithography to study this effect by optical extinction spectroscopy. For a polarization direction perpendicular to the wire axis, the excitation of a dipolar plasmon mode dominates the extinction spectrum. The spectral position of the plasmon resonance can be tuned by an appropriate choice of nanowire geometry and material. For a polarization direction parallel to the wire axis, the profile of the extinction spectrum varies mainly as a function of the grating constant. In particular, a transmission maximum for small grating constants is found. By combining the surface plasmon excitation and grating effect for orthogonal polarization directions, a spectrally selective polarizer with an extinction ratio of 26 is demonstrated.

Fluorescence suppression in resonance Raman spectroscopy using a high-performance picosecond Kerr gate

Abstract: A high-performance Kerr gate designed for the suppression of fluorescence in both time-resolved and steady-state resonance Raman spectroscopy is described and its performance illustrated. This is an improved version of a system described recently, with superior extinction ratio, higher throughput and wider usable spectral range. Specially designed polarizers are an essential feature of the system. The gate opens for ∼4 ps at 1 kHz repetition rate, throughput in the open state is up to ∼40% (excluding Fresnel losses on optical elements), the extinction ratio in the closed state is 10−5 and the usable spectral range is 300–700 nm with a single set of polarizers. The Kerr gate is driven by ∼500 µJ, 1 kHz, 1 ps laser pulses at 800 nm and we believe that it is currently the most powerful device in operation for the temporal rejection of fluorescence from Raman spectra. It increases the general applicability of Raman spectroscopy as illustrated by picosecond time-resolved resonance Raman spectra of the intramolecular charge transfer state of 4-dimethylaminobenzonitrile and by the ground-state Raman spectrum of unleaded petrol at 400 nm probe wavelength. Copyright © 2001 John Wiley & Sons, Ltd.

Low loss and high extinction ratio strictly nonblocking 16/spl times/16 thermooptic matrix switch on 6-in wafer using silica-based planar lightwave circuit technology

Abstract: We describe a silica-based 16/spl times/16 strictly nonblocking thermooptic matrix switch with a low loss and a high extinction ratio. This matrix switch, which employs a double Mach-Zehnder interferometer (MZI) switching unit and a matrix arrangement to reduce the total waveguide length, is fabricated with 0.75% refractive index difference waveguides on a 6-in silicon wafer using silica-based planar lightwave circuit (PLC) technology. We obtained an average insertion loss of 6.6 dB and an average extinction ratio of 53 dB in the worst polarization case. The operating wavelength bandwidth completely covers the gain band of practical erbium-doped fiber amplifiers (EDFAs). The total power consumption needed for operation is reduced to 17 W by employing a phase-trimming technique which eliminates the phase-error in the interferometer switching unit.

EAM-integrated DFB laser modules with more than 40-GHz bandwidth

Abstract: Electroabsorption modulator (EAM)-distributed feedback (DFB) modules with record-high bandwidth of 41 GHz have been developed. 40-Gb/s nonreturn to zero (NRZ) operation with 12-dB extinction ratio and -1.6-dBm average output power have been successfully achieved by optimizing the EAM length and detuning. A clearly opened eye diagram was maintained even after 80-km nonzero dispersion shifted fiber (NZ-DSF) transmission with dispersion compensation, 40-GHz short pulse trains with 6-ps pulsewidth have been also generated by sinusoidal electrical modulation.

LED driving circuit and optical transmitting module

Abstract: An LED is an element in which when a voltage pulse applied to the intrinsic diode of an electrical equivalent model reaches a peak value, a current suddenly flows to obtain an optical output proportional to the forward current. By utilizing this property, the LED receives a rectangular voltage pulse having a large-current driving ability at a low output impedance, or a voltage pulse having two high levels. The low level of the voltage pulse is set within a voltage range where the extinction ratio of an output signal from the LED can be maintained. Even in an LED having a large internal capacitance, an increase in power consumption can be minimized, the transient response time can be shortened, high-speed modulation can be performed, and output light almost free from pulse waveform distortion can be obtained.

5-Gb/s XOR optical gate based on cross-polarization modulation in semiconductor optical amplifiers

Abstract: We demonstrate a new design for a XOR optical gate operating in the GHz regime using the cross-polarization modulation effect in a semiconductor optical amplifier. Dynamic and optically controlled polarization rotation in the devices is used to control the output power of the device. Static extinction ratio of the order of 20 dB can be obtained. Bit rate doubling at rate of 1.2 and 2.5 Gb/s have been demonstrated.

Interferometers with coated polarizing beam splitters that are rotated to optimize extinction ratios

Abstract: An interferometer includes a two-frequency laser and a polarizing beam splitter (PBS) that separates a heterodyne beam from the laser into separate beams having different the frequencies and orthogonal polarizations. Optical fibers conduct the separate beams to a beam combiner for interferometer optics. The PBS and/or the beam combiner can use a coating to reflect one linear polarization and transmit an orthogonal linear polarization. To improve extinction ratios in the PBS or the beam combiner, a yaw angle for an input beam is non-zero and corresponds to a peak in the extinction ratio of a reflected beam.

Stacked subwavelength gratings as circular polarization filters

Abstract: We have stacked subwavelength gratings (SWGs) on a single substrate to create a compact, integrated circular polarization filter. The SWGs consist of a wire grid polarizer and a broadband form-birefringent quarter-wave plate (QWP). Rigorous coupled-wave analysis was used to design the QWP for operation over the 3.5–5.0-µm wavelength range. The fabricated silicon broadband QWP exhibited a phase retardance of 82–97° across this wavelength range. Two stacked structures are presented, each with a different wire grid polarizer fabricated on an organic planarization layer (SU-8) that is deposited on a QWP grating. Transmittance measurements of the first structure when illuminated with nominally right- and left-circularly polarized light indicate a circular extinction ratio (CER) limited by the low linear extinction ratio of the polarizer. Use of a wire grid polarizer with a higher extinct ratio led to a stacked SWG structure that demonstrated CERs of 10–45 across the 3.5–5.0-µm wavelength range.

Design considerations in optical add/drop multiplexers based on grating-assisted null couplers

Abstract: The performance of a fully optimized optical add/drop multiplexer (OADM), based on null couplers and tilted Bragg gratings, is studied in detail. It is shown that maximization of the device performance involves three main optimization steps. First, the waveguide asymmetry (V/sub 2//V/sub 1/ ratio) should be optimized in order to minimize the extinction ratio of the unwanted mode at the null coupler waist. Second, the coupler taper shape should he optimized in order to further minimize the aforementioned extinction ratio. Third, the grating tilt angle and relative width can be also optimized to give negligible backreflections at the input port and minimize radiation losses. The results show that the proposed high-performance OADM configuration can meet stringent telecom specifications.

Suppression of level fluctuation without extinction ratio degradation based on output saturation in higher order optical parametric interaction in fiber

Abstract: Optical limiting operation based on output saturation in higher order parametric interaction in dispersion-shifted fiber is reported. The output powers in a parametric amplifier configuration were measured as a function of the signal input power, with the result that new-wavelength light is efficiently generated in addition to the pump, signal, and idler, resulting from a higher order parametric process, and its output power initially increases quadratically and then saturates as the input power increases. By utilizing this output property of the higher order parametric light, suppression of level fluctuation with an improved extinction ratio was demonstrated.

Multiple-chip precise self-aligned assembly for hybrid integrated optical modules using Au-Sn solder bumps

Abstract: We have developed a novel three-dimensional high precision self-aligned assembly using stripe-type Au-Sn solder bumps and a micro-press solder bump formation method. This produces a high bonding precision of 1 /spl mu/m for optical device assembly in both lateral and vertical directions without the need for time-consuming optical axes alignment. Furthermore, we tested a hybrid integrated 4/spl times/4 optical matrix switch, in which multiple SSC-SOAG arrays were simultaneously positioned and optical fibers were passively positioned on a silica based PLC platform using this technology. Four optical chips and seven wiring chips are assembled on a planar lightwave circuit (PLC) platform. The insertion loss for each of these paths at an injection current of 40 mA was within a range of 9/spl plusmn/4 dB. The average extinction ratio was 40 dB. This self-aligned assembly technology was shown to be useful for building hybrid-integrated multichannel optical network components.

Long wavelength vertical-cavity semiconductor optical amplifiers

Abstract: This paper overviews the properties and possible applications of long wavelength vertical-cavity semiconductor optical amplifiers (VCSOAs). A VCSOA operating in the 1.3-/spl mu/m wavelength region is presented. The device was fabricated using wafer bonding; it was optically pumped and operated in reflection mode. The reflectivity of the VCSOA top mirror was varied in the characterization of the device. Results are presented for 13 and 12 top mirror periods. By reducing the top mirror reflectivity, the amplifier gain, optical bandwidth, and saturation output power were simultaneously improved. For the case of 12 top mirror periods, rye demonstrate 13-dB fiber-to-fiber gain, 0.6 nm (100 GHz) optical bandwidth, a saturation output power of -3.5 dBm and a noise figure of 8.3 dB. The switching properties of the VCSOA are also briefly investigated. By modulating the pump laser, we have obtained a 46-dB extinction ratio in the output power, with the maximum output power corresponding to 7-dB fiber-to-fiber gain. All results are for continuous wave operation at room temperature.

Integrated surface-emitting laser and modulator device

Abstract: An integrated surface emitting laser and modulator device is disclosed that includes a detector for monitoring the optical power output of the laser and another detector for monitoring an extinction ratio of the modulator. A cleave physically and electrically separates the laser from the modulator device. The device has a collimating lens disposed on a top surface.

Integrated polarisation beam splitter using waveguide birefringence dependence on waveguide core width

Abstract: A novel integrated polarisation beam splitter on a silica-based planar lightwave circuit that utilises the waveguide birefringence dependence on waveguide core width is proposed. It was successfully confirmed that the fabricated splitter has a polarisation extinction ratio of >21 dB over a wide wavelength range of 1530 to 1620 nm.

2.3 picoseconds optical gate monolithically integrating photodiode and electroabsorption modulator

Abstract: A novel ultra-high-speed optical gate monolithically integrating a uni-travelling-carrier photodiode and a travelling-wave electroabsorption modulator (TW-EAM) is presented. By using the nonlinear extinction characteristics of the EAM, the minimum gate opening time of 2.3 picoseconds with an extinction ratio of 14 dB is achieved.

High-speed all-optical AND gate using nonlinear transmission of electroabsorption modulator

Abstract: We investigated an all-optical logic AND operation at 10 Gb/s using nonlinear transmission of electroabsorption modulator pumped with two counterpropagating data streams. The transmitted pump itself was used as the output of the optical gate to obtain high extinction ratio, and high-output peak powers. The gate has been tested using 2/sup 31/-1 long pseudorandom bit sequence. The logical output of the gate has an extinction ratio of more than 10 dB with good eye opening. Our measurements of the gate transmission window show that all-optical logic operation up to 100 Gb/s is feasible.

Novel cell-AGC technique for burst-mode CMOS preamplifier with wide dynamic range and high sensitivity for ATM-PON system

Abstract: We propose a novel cell-AGC technique for an ATM-cell based burst optical receiver on a 156 Mbps subscriber system. The cell-AGC controls transimpedance gain according to the burst cell power and enables reception of burst signals with low extinction ratio. In addition, to realize high sensitivity, we developed an amplifier that is stable under changes in ambient conditions and deviations of transistor characteristics on IC. By adopting these techniques in a CMOS preamplifier-IC, the detectable power difference between burst cells was enlarged to more than 30 dB, and the minimum sensitivity was improved to less than -39.3 dBm. These performances show our new IC fully satisfy high sensitivity specification of an ATM-PON system, and incorporating this IC in the system makes it more flexible and economical.

High-speed mid-IR modulator using Stark shift in step quantum wells

Abstract: We show in calculations that there is a capability for high speeds with a low applied voltage in modulators based on intersubband transitions in step quantum wells (QWs). A waveguide based on surface plasmons is assumed to achieve the necessary tight confinement of the optical field. In a structure with 8 GaInAs-AlGaInAs-AlInAs step QWs, we obtain a device capacitance of 14 fF corresponding to a RC limitation of electrical f/sub 3 dB/=190 GHz. The extinction ratio of 6.6-/spl mu/m light is 10 dB at an applied voltage of 0.9 V and T=300 K. By simple reasoning, we find that the device capacitance is approximately proportional to the absorption linewidth cubed when the linewidth is considered in the device design. Thus, the linewidth is very decisive for the modulation speed. We propose to place the dopants asymmetrically in the barriers in order to reduce broadening caused by doping induced potential fluctuations. In addition, the doping levels in the outermost barriers of the multi-QW structure are proposed to be reduced and asymmetrical, in order to achieve a uniform electric field over the step QWs, which is shown to increase the achievable f/sub 3 dB/ very markedly.

Widely tunable external cavity diode laser using a MEMS electrostatic rotary actuator

Abstract: The deep reactive ion etching (DRIE) MEMS actuators have enabled a small form factor, low cost tunable laser source ideal for many DWDM applications. External cavity diode lasers using rotary electrostatic MEMS actuators achieve 10-dBm outputs over the C band with 40-nm continuous tuning and 15-ms locking to 50-GHz ITU channels. The performance of the MEM-ECDL meets telecommunications requirements for optical power, side mode suppression, polarization extinction ratio, relative intensity noise, and linewidth. The required wavelength accuracy of 2.5 GHz has been demonstrated using simple closed loop control of the MEMS actuator voltage. The laser can be packaged in a compact 14-pin butterfly package.

Multilevel optical signals optimized for systems having signal-dependent and signal-independent noises, finite transmitter extinction ratio and intersymbol interference

Abstract: Methods and apparatus are described to transmit and receive information encoded in multilevel optical signals that take on at least three intensity levels. Intensity levels of a transmitted multilevel optical signal are optimized to minimize a transmitted optical power required to achieve a specified decision error probability, taking account of an arbitrary admixture of impairments, including signal-dependent noise, signal-independent noise, a finite transmitter extinction ratio, and intersymbol interference. The optimizations described are implemented using analytical or numerical techniques, depending on the admixture of impairments, and can be used to achieve equal or unequal decision error probabilities at a set of decision thresholds.

Transmission performance of 10-Gb/s optical duobinary transmission systems considering adjustable chirp of nonideal LiNbO/sub 3/ Mach-Zehnder modulators due to applied voltage ratio and filter bandwidth

Abstract: We investigate interplay between the residual and applied chirp of optical duobinary modulated signals in order to improve transmission performance. To find the best performance for 10-Gb/s optical duobinary transmission systems, we consider the residual chirp accompanying from the finite extinction ratio, the applied chirp adjusted by the applied voltage ratio (the chirp parameter) between two electrodes of LiNbO/sub 3/ modulators, and the bandwidth of electrical low-pass filters used in duobinary transmitters. The simulation results suggest that nearly zero chirp during the mark ('1') period and large peak chirp at the middle of the space ('0') provide the best transmission performance. This zero chirp around marks and high peak chirp at the middle of each space can be controlled by the applied voltage ratio between two electrodes of modulator and the filter bandwidth, respectively.

Add-drop multiplexer with UV-written Bragg gratings and directional coupler in SiO/sub 2/-Si integrated waveguides

Abstract: The needs of wavelength multiplexers is growing and therefore optical add-drop multiplexers (OADMs) become key components for the advanced high bit rate telecommunication networks. Currently, one of the solutions to make OADMs use fiber Bragg gratings and circulators. In order to take advantage of integrated optics and to avoid the use of expensive circulators, we perform this kind of OADM in ridge silica waveguide on silicon. This technology makes possible short based directional coupler (DC) device. In previous work, we firstly realized an OADM which involves a symmetrical directional coupler combined with two Bragg gratings inside the coupling zone. The results meet difficult tradeoff between a high extinction ratio and a narrow spectral width of the rejection band. This paper reports some fabrication improvements for DC-OADM that lead to more efficient components, progress results from a lot of works concerning both the photo-writing process of Bragg gratings and the lowering of the waveguide internal stresses. Thus, we show that apodization of gratings and low birefringence in the waveguides enables us to achieve DC-OADM with an extinction ratio of 30 dB and a spectral bandwidth less than 1.5 nm.

Recent advances in large-scale silica-based thermo-optic switches

Abstract: This paper describes recent progress on large-scale integrated thermo-optic switches including N X N switches (up to 16 X 16), 1 X N switches (up to 1 X 128), N-arrayed 2 X 2 switches (up to 16-arrayed for optical add/drop multiplexers, which all employ silica-on-silicon planar lightwave circuit technology. These switches exhibit low insertion loss, low polarization loss and high switch extinction ratio. I also describe a trial with the goal of reducing drive power consumption, and report the reliability of the thermo-optic switch modules.

2 x 2 optical waveguide switch with bow-tie electrode based on carrier-injection total internal reflection in SiGe alloy

Abstract: Based on the total internal reflection and the plasma dispersion effect of SiGe alloy, a 2/spl times/2 intersectional rib optical waveguide switch with bow-tie electrode has been proposed and fabricated for the wavelength of 1.3-/spl mu/m operation. The thickness of the SiGe layer is 2.6 /spl mu/m and the width is 9 /spl mu/m. The branch angle of the switch is 2/spl deg/ and the bow-tie angle is 1.5/spl deg/. The on-state crosstalk is -19.6 dB, the off-state extinction ratio is 38.5 dB and the off-state insertion loss is less than 1.70 dB. The switching time is about 180 ns.

Laser diode driving method and circuit which provides an automatic power control capable of shortening the start-up period

Abstract: A technique for driving a laser diode on the basis of automatic power control (APC) is disclosed. The technique uses, for the bottom level feedback control, a constant reference voltage instead of a variable intermediate signal generated in the peak level feed back control. The constant reference voltage may be either a reference voltage for the peak level control or a separately generated voltage. A technique for setting the extinction ratio to 1/n is also disclosed.

Thin flexible polariser of Ag-nanoparticle-dispersed fluorinated polyimide

Abstract: A thin (14.8 /spl mu/m thick) flexible polariser that can be used at wavelengths between 600 and 900 nm was prepared using silver-nanoparticle-dispersed fluorinated polyimide film. The extinction ratio of the polariser was >25 dB, and the optical loss for the transmitting polarisation including surface reflection was <1.3 dB at 850 nm. The optical and mechanical properties were retained after annealing at 150/spl deg/C for 1 h.

100/spl deg/C, 10 Gb/s directly modulated InGaAsP DFB lasers for uncooled Ethernet applications

Abstract: Combining an optimised active region based on InGaAsP strained MQW (multi quantum well) and a low parasitic lateral confinement region, we fabricated 10 Gb directly modulated uncooled DFB lasers which represent, we believe, the state of art. Our DFB lasers work up to 100/spl deg/C (substrate base temperature) with eye diagram perfectly open (showing an extinction ratio > 5 dB) and with bit error rate over 10 km without an error floor. Up to 90/spl deg/C our DFBs show threshold current as low as 29 mA. optical power as high as 13 mW and meet perfectly a 10 Gb scaled Ethernet mask with extinction ratio > 6 dB.

Novel optical waveguide switch using cascaded mach-zehnder interferometers

Abstract: An optical signal switch has improved port isolation and extinction ratio by utilizing cascaded or tandem Mach-Zehnder Interferometer (MZI) with thermo-optical or electro-optical refractive index-modulating electrodes on the MZI arms.

Extinction ratio improvement and wavelength conversion based on four-wave mixing in a semiconductor optical amplifier

Abstract: We have demonstrated an extinction ratio improvement of more than 3 dB at 2.5 Gb/s with a method based on four-wave mixing in a semiconductor optical amplifier. A wavelength conversion and a data format conversion from nonreturn-to-zero (NRZ) to return-to-zero (RZ) have been simultaneously achieved.

A holey fibre Raman amplifier and all-optical modulator

Abstract: We demonstrate the use of a short length of highly nonlinear holey fibre (HF) to obtain strong L-band Raman amplification. Using a 75 m long HF fibre with an effective area of 2.85 /spl mu/m/sup 2/ we obtain internal gains of over 42 dB and a noise figure of /spl sim/6 dB. In addition using the same fibre we obtain an 11 dB extinction ratio in Raman induced all-optical modulation experiments.