Long-wavelength waveguide multiple-quantum-well (MQW) optical modulator with 30:1 on/off ratio

Large on/off ratio optical modulation of long-wavelength light propagating along the plane of InGaAs/InAlAs multiple-quantum-well (MQW) structures grown by molecular beam epitaxy (MBE) is obtained for the first time. These waveguide MQW optical modulators have a modulation on/off ratio of 30:1 (15 dB) at a driving voltage as low as 9 V, and a capacitance-limited pulse response of 280 ps (FWHM). This measurement is the first step in achieving faster and higher extinction ratio devices.     

Long wavelength waveguide multiple quantum well optical modulators

The first measurements of large anisotropic modulation of long-wavelength light with a large on/off ratio and low driving voltage propagating along the plane of InGaAs/InAlAs multiple quantum well (MQW) structures grown by molecular beam epitaxy (MBE) are reported. Photocurrent response and optical modulation of waveguide pin diodes is measured for incident light polarization parallel and perpendicular to the MQW layers emitting from a color center laser. The incident-light power and wavelength dependence of on/off ratio are also determined.     

High-speed InGaAlAs/InAlAs multiple quantum well optical modulators

High-speed modulation over 22 GHz for waveguided InGaAlAs/InAlAs multiple quantum well (MQW) optical modulators is described. A large on/off ratio of over 25 dB is demonstrated with a low-drive voltage (6 V) operating in the 1.55-μm wavelength region. The design and characteristics of MQW p-i-n modulators are discussed. The causes of large-insertion loss and the required drive voltage bandwidth figure of merit for the MQW modulator are discussed. The frequency response measurements show that the response speed is limited by the RC time constant of the device. This suggests that the speed can be further enhanced by decreasing the size and capacitance of the device     

A low-voltage, high-reflectance-change normally off refractiveGaAs/Al0.2Ga0.8As MQW reflection modulator

We present our optimization of a normally off refractive GaAs/Al _xGa_1-xAs multiple-quantum-well (MQW) reflection modulator with respect to the on/off reflectance change, on/off contrast ratio, and operating voltage. We use optical transfer matrices, theoretically calculated refractive indices, and absorption coefficients to simulate the operation of a normal-incident Fabry-Perot MQW modulator. Our calculations suggest that a normally off refractive GaAs/Al_0.2Ga_0.8As MQW reflection modulator with a reflectance change of 42.9% and an on/off contrast ratio of 1539 for an operating voltage of only 2.44 V can be fabricated by molecular-beam epitaxy (MBE)     

High-speed InGaAlAs/InAlAs multiple quantum well electrooptic phasemodulators with bandwidth in excess of 20 GHz

High-speed phase modulation (in the frequency bandwidth of 20 GHz, the highest yet reported for multiple quantum well (MQW) phase modulators) for waveguided InGaAlAs/InAlAs MQW optical modulators is reported. The modulator successfully operates at a long wavelength of 1-55 μm with a low required voltage for phase shift (Vπ=3.8 V), small intensity modulation depth below 1.5 dB, and without any modulation bandwidth degradation up to 20 GHz under high input optical power of 0 dBm in single-mode fiber     

Tradeoff between phase- and intensity modulation in GaAs/AlGaAsdouble heterostructure and multiple quantum well phase-modulatorwaveguides

The wavelength dependence of phase sensitivity (°/mm V) and intensity modulation of a double-heterostructure (DH) device and a multiquantum-well (MQW) device in the GaAs/AlGaAs material system is studied. The results show the tradeoff between phase modulation and intensity modulation and also show that, for the same intensity modulation, the MQW device produces twice as much phase modulation as the DH device. For example, at an intensity modulation of -1 dB the MQW device has a phase sensitivity of 120°/mm V while the DH device gives a value of ≈60°/mm V     

Polarization dependence of a 1.52 μm InGaAs/InP multiple quantumwell waveguide electroabsorption modulator

A ridge-waveguide In_0.53Ga_0.47As/InP multiple-quantum-well (MQW) electroabsorption modulator operating at a wavelength of 1.52 μm is demonstrated. The modulator exhibits large polarization-dependent electroabsorption behavior which favors the modulation of the TM mode. At a reverse bias of 10 V, the modulator has a 24.5-dB extinction ratio for the TM mode, whereas that for the TE mode is only 11.1 dB. Polarization-dependent saturation of absorption has been observed in this device for incident optical power levels of less than 1 mW     

100 ps waveguide multiple quantum well (MQW) optical modulator with 10:1 on/off ratio

By incorporating two quantum wells into a capillary waveguide, we have made the first MQW optical modulator with an on/off ratio of at least 10:1. Furthermore, this device was used to generate an optical pulse less than 100 ps long, the fastest to date with an MQW device.     

High-frequency InGaAs/InP multiple-quantum-well buried-mesa electroabsorption optical modulator

We describe the structure and performance characteristics of an InGaAs/InP multiple-quantum-well (MQW) electro-absorption buried-mesa optical modulator. The device is fabricated with two metal-organic chemical-vapour-deposition (MOCVD) growth steps, wherein small-area circular (40?m diameter) PIN diodes are buried with Fe-doped semiinsulating (SI) InP regrowth. The modulator has a relatively low insertion loss (4.5 dB) with 25% modulation depth and very high modulation bandwith (5.3 GHz) operating at 1.62?m wavelength.     

Optically bistable operation in InGaAs/lnAIAs MOW laser diodes using resonant tunnelling effect

A new type of optically bistable operation using a resonant tunnelling effect has been achieved for InGaAs/lnAIAs MQW laser diodes for the first time. A clear optical bistability with a large on/off ratio was observed in the light output/voltage characteristics. Optical memory operation was also obtained with this MQW laser diode.     

Amplitude and phase modulation in a 4 μm-thick GaAs/AlGaAsmultiple quantum well modulator

The experimental results of a 4 μm-thick GaAs/AlGaAs MQW modulator show an ~10:1 on/off ratio with an applied voltage of 20 V (Δα~6×10³/cm at E~50 kV/cm) and ~0.4 πrad of phase shift with an applied voltage of 10 V (Δn~0.04 at E~25 kV/cm). Such high electro-optical modulations have previously been reported only in MQW optical waveguide modulators     

全固源分子束外延InAsP/InGaAsP多量子阱1.55μm激光器

利用新型全固源分子束外延技术 ,对 1 .5 5 μm波段的 In As P/ In Ga As P应变多量子阱结构的生长进行了研究。实验表明 ,较低的生长温度或较大的 / 束流比有利于提高应变多量子阱材料的结构质量 ,而生长温度对材料的光学特性有较大的影响。在此基础上生长了分别限制多量子阱激光器结构 ,制作的氧化物条形宽接触激光器实现了室温脉冲工作 ,激射波长为 1 5 63 nm,阈值电流密度为 1 .4k A/ cm2 。这是国际上首次基于全固源分子束外延的 1 .5 5 μm波段 In As P/ In Ga As P多量子阱激光器的报道     

Reduction of linewidth enhancement factor in InGaAsP-InPmodulation-doped strained multiple-quantum-well lasers

The linewidth enhancement factor α in InGaAsP-InP modulation-doped strained multiple-quantum-well (MQW) lasers has been evaluated theoretically and experimentally. A reduction of the α-parameter due to modulation doping is demonstrated. A small α-parameter of less than 1 is obtained not at wavelength for the gain peak but within certain range of wavelength where the gain is positive. The smaller α-parameter in modulation-doped strained MQW lasers should result in performance improvements that are advantageous for optical communication system applications     

80 Gbit/s wavelength conversion using MQW electroabsorption modulator in delayed-interferometric configuration

Absorption recovery time and cross-phase modulation characteristics of an MQW electroabsorption modulator (EAM) were experimentally analysed. 80 Gbit/s error-free operation of a wavelength converter using the MQW EAM in a delayed-interferometer configuration was demonstrated for the first time.     

InGaAlAs Multiple-Quantum-Well Optical Phase Modulators Based on Carrier Depletion

We fabricated carrier-depletion-type optical phase modulators which contain an InGaAlAs multiple-quantum well (MQW) in a p-n junction, and investigated their phase modulation characteristics at the wavelengths of 1.55-1.62 mum under reverse biased conditions. Fabricated devices showed large modulation efficiencies up to 89deg/mm/V and smaller wavelength-dependence than that of conventional MQW phase modulators. Carrier-depletion-type optical phase modulators are attractive for optical integrated devices such as optical matrix switches for future wavelength-division-multiplexing photonic networks.     

Optimizing the bias and modulation voltages of MQW Mach-Zehndermodulators for 10 Gb/s transmission on nondispersion shifted fiber

The chirp and optical extinction ratio of a multiple quantum-well (MQW) Mach-Zehnder modulator depend on the device design and on the voltage waveforms applied to the arm electrodes. For 10 Gb/s transmission over nondispersion shifted fiber, joint optimization of the bias and modulation voltages is considered for a conventional modulator and a π-phase-shift modulator. Measured attenuation and phase constants for an optical signal propagating in the modulator waveguide are used to accurately model the Mach-Zehnder modulators. The influence of asymmetric Y-branch waveguides in the modulators is examined taking into consideration group velocity dispersion and self-phase modulation arising from the Kerr nonlinearity. When the modulators are operated with maximum optical extinction ratio, the dispersion limited transmission distance depends on the device design (phase-shift and Y-branch splitting ratio) and modulation format (dual drive or single drive). Optimization of the bias and modulation voltages reduces this dependence significantly, while also increasing the dispersion limited transmission distance     

InGaAs/InGaAsP MQW optical amplifier integrated withgrating-assisted vertical-coupler noise filter

A photonic integrated circuit with an InGaAs/InGaAsP multiple-quantum-well (MQW) traveling-wave optical amplifier and a grating-assisted vertical-coupler filter as a noise filter have been demonstrated. A fiber-to-amplifier/filter gain of ~0.5 dB and a 3-dB filter bandwidth (FWHM) of ~70 Å at 1.56 μm filter center wavelength have been achieved. This photonic circuit is potentially suitable as a building-block for preamplifier lightwave receivers or high-gain, high-power optical amplifiers which are essential for optical communication systems and lightwave networks     

Substantial reduction of dynamic wavelength chirp of 2 Gbit/s pseudorandom optical signal using three-contact InGaAsP/InP multi-quantum-well distributed-feedback laser

Linewidths as low as 0.08 nm (-20 dB) have been achieved for a three-contact multi-quantum-well (MQW) distributed-feedback (DFB) laser subject to NRZ pseudorandom modulation at 2 Gbit/s. These linewidths are substantially narrower than those observed using equivalent single-contact devices, the improved spectral performance being achieved by using the central device region to control the wavelength of the light generated.<>     

Wide-wavelength polarization-independent optical modulator based on tensile-strained quantum well with mass-dependent width

We have fabricated a multiple-quantum-well (MQW) waveguide optical modulator incorporating tensile strain and quantum well with mass-dependent width (QWMDW) for the first time. The structure was built on a strain relief InAlGaAs buffer layer grown on a GaAs substrate. Polarization-independent modulation with more than -10 dB extinction (at 8 V reverse voltage) was achieved over a very wide operating range, from 858 to 886 nm wavelength.     

Modulation of visible light by AlAs-AlGaAs multiple-quantum-wellp-i-n structures

We report measurements on the modulation of visible light by a multiple-quantum-well (MQW) modulator designed for normal incidence. The MQW structure is composed of AlAs-Al_xGa_1-xAs with an Al concentration x=0.41. The structure exhibits an exciton absorption peak at 608 nm in the visible part of the spectrum. The phase and amplitude modulation properties of this structure mere studied using a Michelson interferometer that employed a novel double lock-in detection technique. Phase and amplitude modulation were studied as a function of the wavelength to determine their maxima. In our structure, phase modulation up to 200 and amplitude modulation up to 8% were observed. These values are comparable to what is typically achieved by using waveguide geometry