Electroabsorption waveguide modulators at 1.3 /spl mu/m fabricated on GaAs substrates

An InGaAs-InAlAs multiple-quantum-well (MQW) electroabsorption (EA) waveguide modulator fabricated on a GaAs substrate has been designed and characterized at 1.3-/spl mu/m wavelength for microwave signal transmission on an analog fibre-optic link. The modulator structure with a lattice constant 2.5% larger than that of GaAs is grown upon a 0.7-/spl mu/m-thick three-stage compositionally step-graded In/sub z/Al/sub 1-z/As relaxed buffer. The waveguide modulator exhibits a high-electrooptic slope efficiency of 0.56 V/sup -1/, a 3-dB electrical bandwidth of 20 GHz, and a large optical saturation intensity in excess of 17 mW. These high-speed optoelectronic modulators could potentially be integrated with on-chip GaAs electronic driver circuits.     

Peripheral-coupled-waveguide MQW electroabsorption modulator for near transparency and high spurious free dynamic range RF fiber-optic link

Peripheral coupled waveguide (PCW) design has been deployed in InGaAsP multiple quantum-well (MQW) electroabsorption modulator (EAM) at 1.55-/spl mu/m wavelength. PCW enhances the optical saturation power and reduces the optical insertion loss and the equivalent V/sub /spl pi// simultaneously. A radio-frequency link using a 1.3-mm-long lumped-element PCW EAM has achieved experimentally a link gain of -3 dB, at 500 MHz and at input optical power of 80 mW. The corresponding two-tone multioctave spurious-free dynamic range (SFDR) at the same bias is measured at 118 dB/spl middot/Hz/sup 2/3/. The single-octave SFDR at the third-order null bias is 132 dB/spl middot/Hz/sup 4/5/.     

Low-loss 1.3-μm MQW electroabsorption modulators forhigh-linearity analog optical links

Low-loss InAsP-GaInP multiquantum-well electroabsorption waveguide modulators have been developed for transmitting microwaves as subcarriers over optical fibers. The fiber-to-fiber insertion loss is only 5 dB at 1.32-μm wavelength. The electrooptic slope efficiency of an 185-μm-long 11-GHz bandwidth device is equivalent to a Mach-Zehnder modulator with a V_π of 2.2 V. The linearity performance was characterized for a test link without any form of amplification. A RF-to-RF link efficiency of -25.5 dB, noise figure of 27 dB and suboctave spurious-free dynamic range of 114 dB.Hz^4/5 have been achieved with 16 mW input optical carrier power. The measured 3-dB electrical bandwidth exceeds 20 GHz for a 90-μm-long device     

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

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

15-GHz modulation performance of integrated DFB laser diode EA modulator with identical multiple-quantum-well double-stack active layer

Monolithically integrated InGaAsP 1.55-/spl mu/m ridge waveguide distributed feedback laser diodes with an electroabsorption modulator using an identical active multiquantum-well (MQW) layer structure with two different QW types exhibit low-threshold currents <18 mA. The 3-dBe cutoff frequency of 200-/spl mu/m-long modulators exceeds 15 GHz. 10-Gb/s transmission experiments with a voltage swing of 1.0 V/sub pp/ demonstrate the potential of this novel integration scheme.     

A W-band InAs/AlSb low-noise/low-power amplifier

The first W-band antimonide based compound semiconductor low-noise amplifier has been demonstrated. The compact 1.4-mm/sup 2/ three-stage co-planar waveguide amplifier with 0.1-/spl mu/m InAs/AlSb high electron mobility transistor devices is fabricated on a 100-/spl mu/m GaAs substrate. Minimum noise-figure of 5.4dB with an associated gain of 11.1 dB is demonstrated at a total chip dissipation of 1.8 mW at 94 GHz. Biased for higher gain, 16/spl plusmn/1 dB is measured over a 77-103 GHz frequency band.     

A 1.8-V 10-Gb/s fully integrated CMOS optical receiver analog front-end

A fully integrated 10-Gb/s optical receiver analog front-end (AFE) design that includes a transimpedance amplifier (TIA) and a limiting amplifier (LA) is demonstrated to require less chip area and is suitable for both low-cost and low-voltage applications. The AFE is fabricated using a 0.18-/spl mu/m CMOS technology. The tiny photo current received by the receiver AFE is amplified to a differential voltage swing of 400 mV/sub (pp)/. In order to avoid off-chip noise interference, the TIA and LA are dc-coupled on the chip instead of ac-coupled though a large external capacitor. The receiver front-end provides a conversion gain of up to 87 dB/spl Omega/ and -3dB bandwidth of 7.6 GHz. The measured sensitivity of the optical receiver is -12dBm at a bit-error rate of 10/sup -12/ with a 2/sup 31/-1 pseudorandom test pattern. Three-dimensional symmetric transformers are utilized in the AFE design for bandwidth enhancement. Operating under a 1.8-V supply, the power dissipation is 210 mW, and the chip size is 1028 /spl mu/m/spl times/1796 /spl mu/m.     

High-speed InGaAsP/InP multiple quantum well, 1.55 mu m singlemode modulator

1.55 mu m single mode ridge waveguide modulators based on electroabsorption in InGaAsP/InP multiple quantum wells (MQW) are reported. A 10 dB extinction ratio was obtained by applying a 2 V drive voltage to a 100 mu m long device with a 3 dB on-state loss. The 3 dB cutoff frequency is 12.5 GHz.<>     

An optimized InGaAsP/InP polarization converter employing asymmetric rib waveguides

In this paper, we report on the design of a compact (/spl ap/ 226 /spl mu/m) on-chip InGaAsP/InP polarization converter based on an asymmetric rib waveguide. Our theoretical analysis demonstrates that the device displays a conversion efficiency of < -25 dB (> 99.68% power conversion between orthogonal polarization) at 1550-nm wavelength with a nearly flat response over the optical C band. Regarding fabrication tolerances, we predict that the most sensitive design parameter is the waveguide width as the conversion efficiency drops to 10 dB for a deviation of /spl plusmn/ 0.1 /spl mu/m from the optimized value.     

Efficient electroabsorption in InGaAsP/InGaAsP MQW optical waveguide

Efficient electroabsorption in an InGaAsP/InGaAsP MQW optical waveguide modulator structure is reported. A 17 dB extinction ratio is obtained by applying a 3.5 V drive voltage to a 78 mu m long waveguide operating at 1.54 mu m under TE-polarisation mode. The on-state attenuation is only 2 dB.<>     

Electroabsorption modulator using intersubband transitions in GaN-AlGaN-AlN step quantum wells

We calculate the high-speed modulation properties of an electroabsorption modulator for /spl lambda/=1.55 /spl mu/m based on Stark shifting an intersubband resonance in GaN-AlGaN-AlN step quantum wells. In a realistic simulation assuming an absorption linewidth /spl Gamma/=100 meV we obtain an RC-limited electrical f/sub 3dB//spl sim/60 GHz at an applied voltage swing V/sub pp/=2.8 V. We also show that a small negative effective chirp parameter suitable for standard single-mode fiber is obtained and that the absorption is virtually unsaturable. The waveguide is proposed to be based on the plasma effect in order to simultaneously achieve a strong confinement of the optical mode, a low series resistance, and lattice-matched cladding and core waveguide layers. Extrapolated results reflecting the decisive dependence of the high-speed performance on the intersubband absorption linewidth /spl Gamma/ are also given. At the assumed linewidth the modulation speed versus signal power ratio is on a par with existing lumped interband modulators based on the quantum confined Stark effect.     

Integrated circuits for a 200 Mbit/s fiber-optic link

A set of three bipolar integrated circuits for a new fiber-optic link is described. The link operates at data rates of 5-200 Mb/s NRZ. The optical transmitter and receiver modules are compact and fit into standard 16-pin dual-in-line sockets. The power consumption of the transmitter module is 530 mW and the receiver module dissipates 310 mW. The optical loss budget is 20 dB, which is sufficient for link lengths of up to 5 or 6 km. The circuits have been designed in a 3-/spl mu/m bipolar process. The chip sizes are 2 mm/spl times/1.75 mm each.     

Lossless InAsP-InGaP modulator at 1.3 /spl mu/m for optical conversion of radio signals up to 40 GHz

We report on an InAsP-InGaP electroabsorption modulator at 1.3 /spl mu/m integrated with a semiconductor amplifier. The fiber-to-fiber insertion gain reaches +10 dB. The 50-/spl mu/m-long modulator section exhibits a bandwidth of 36 GHz and a -17-dB extinction ratio with 3-V drive voltage. The integrated amplifier produced an RF-link efficiency of -26 dB at 20 GHz without any external amplification.     

A novel processing technique to fabricate planar InGaAsP/InP electroabsorption waveguide modulators

A novel processing technique has been developed to fabricate planar electroabsorption waveguide modulators in compound semiconductor heterostructures. The lateral confinement of light is achieved by introducing controllable, reproducible, and stable stresses into semiconductor heterostructures using WNi surface stressor stripes, which also serve as electrodes for the waveguide modulators. Self-aligned helium implantation is employed to achieve electrical isolation using the Stressors as the templates for the ion masks. An increase as large as 33000 times has been obtained in the dc resistance between the neighboring waveguide modulators 25 μm apart. Propagation loss of 1.7 dB/cm is observed in the photoelastic waveguides at a wavelength of 1.53 μm following the He implantation. A post-implant thermal annealing at 310°C for 40 min increases the dc resistance between the neighboring devices to the maximum value, and at the same time reduces the optical loss to its value before ion implantation (less than 1 dB/cm). Using a combination of the photoelastic effect and helium implantation, planar InGaAsP/InP Franz-Keldysh-effect waveguide modulators 430 μm long with a 10 dB extinction ratio at 3 V for the TM mode have been fabricated. Planar electroabsorption quantum-confined Stark effect waveguide modulators have also been demonstrated. This planar device processing technique may prove valuable in future photonic integrated circuit technology.     

80-MHz bandpass /spl Delta//spl Sigma/ modulators for multimode digital IF receivers

Three fully differential bandpass (BP) /spl Delta//spl Sigma/ modulators are presented. Two double-delay resonators are implemented using only one operational amplifier. The prototype circuits operate at a sampling frequency of 80 MHz. The BP /spl Delta//spl Sigma/ modulators can be used in an intermediate-frequency (IF) receiver to combine frequency downconversion with analog-to-digital conversion by directly sampling an input signal from an IF of 60 MHz to a digital IF of 20 MHz. The measured peak signal-to-noise-plus-distortion ratios are 78 dB for 270 kHz (GSM), 75 dB for 1.25 MHz (IS-95), 69 dB for 1.762 MHz (DECT), and 48 dB for 3.84 MHz (WCDMA/CDMA2000) bandwidths. The circuits are implemented with a 0.35-/spl mu/m CMOS technology and consume 24-38 mW from a 3.0-V supply, depending on the architecture.     

A 10-Gb/s receiver with series equalizer and on-chip ISI monitor in 0.11-/spl mu/m CMOS

A 10-Gb/s receiver is presented that consists of an equalizer, an intersymbol interference (ISI) monitor, and a clock and data recovery (CDR) unit. The equalizer uses the Cherry-Hooper topology to achieve high-bandwidth with small area and low power consumption, without using on-chip inductors. The ISI monitor measures the channel response including the wire and the equalizer on the fly by calculating the correlation between the error in the input signal and the past decision data. A switched capacitor correlator enables a compact and low power implementation of the ISI monitor. The receiver test chip was fabricated by using a standard 0.11-/spl mu/m CMOS technology. The receiver active area is 0.8 mm/sup 2/ and it consumes 133 mW with a 1.2-V power supply. The equalizer compensates for high-frequency losses ranging from 0 dB to 20 dB with a bit error rate of less than 10/sup -12/. The areas and power consumptions are 47 /spl mu/m /spl times/ 85 /spl mu/m and 13.2 mW for the equalizer, and 145 /spl mu/m /spl times/ 80 /spl mu/m and 10 mW for the ISI monitor.     

Investigation of optical feedback in high-speed electroabsorption modulated lasers with a window region

The optimum waveguide design for optical feedback reduction in a 10-Gb/s electroabsorption modulated laser has been discussed. A device with a 30-/spl mu/m-long window region exhibited as much as 10-15-dB reduction, which is verified by experimental results and the beam propagation calculation. Using a tilted waveguide with the window region, the feedback factor is reduced to as low as -40 dB. Besides low optical feedback, the tilted-and-straight modulator has a sufficient dc extinction ratio and a far-field profile allowing larger than 60% fiber-coupling efficiency.     

A low-voltage folded-switching mixer in 0.18-/spl mu/m CMOS

Scaling of CMOS technologies has a great impact on analog design. The most severe consequence is the reduction of the voltage supply. In this paper, a low voltage, low power, AC-coupled folded-switching mixer with current-reuse is presented. The main advantages of the introduced mixer topology are: high voltage gain, moderate noise figure, moderate linearity, and operation at low supply voltages. Insight into the mixer operation is given by analyzing voltage gain, noise figure (NF), linearity (IIP3), and DC stability. The mixer is designed and implemented in 0.18-/spl mu/m CMOS technology with metal-insulator-metal (MIM) capacitors as an option. The active chip area is 160 /spl mu/m/spl times/200 /spl mu/m. At 2.4 GHz a single side band (SSB) noise figure of 13.9 dB, a voltage gain of 11.9 dB and an IIP3 of -3 dBm are measured at a supply voltage of 1 V and with a power consumption of only 3.2 mW. At a supply voltage of 1.8 V, an SSB noise figure of 12.9 dB, a voltage gain of 16 dB and an IIP3 of 1 dBm are measured at a power consumption of 8.1 mW.     

40 Gbit/s electroabsorption modulators with impedance-controlled electrodes

A novel travelling-wave electroabsorption optical modulator, electrically matched for 50 /spl Omega/ loads of driving circuit drivers, was developed. The scattering parameter of electric reflection (S/sub 11/) from this modulator is less than -20 dB at 20 GHz. It can thus enable a 40 Gbit/s, 2 km SMF transmission with a 0.3 dB penalty at a 1.3 /spl mu/m wavelength.     

10-Gb/s limiting amplifier and laser/modulator driver in 0.18-/spl mu/m CMOS technology

A limiting amplifier incorporates active feedback, inductive peaking, and negative Miller capacitance to achieve a voltage gain of 50 dB, a bandwidth of 9.4 GHz, and a sensitivity of 4.6 mV/sub pp/ for a bit-error rate of 10/sup -12/ while consuming 150 mW. A driver employs T-coil peaking and negative impedance conversion to achieve operation at 10 Gb/s while delivering a current of 100 mA to 25-/spl Omega/ lasers or a voltage swing of 2 V/sub pp/ to 50-/spl Omega/ modulators with a power dissipation of 675 mW. Fabricated in 0.18-/spl mu/m CMOS technology, both prototypes operate with a 1.8-V supply.