Very low voltage, normally-off asymmetric Fabry-Perot reflection modulator

Using the electro-absorptive properties of approximately=150 AA quantum wells in an asymmetric Fabry-Perot modulator (AFPM), a normally-off reflection modulator with very low drive voltage was demonstrated. With this device contrasts of more than 6 Db at normal incidence in reflection have been achieved, with a voltage swing of only 3.5 V and >     

A GaAs/AlGaAs asymmetric Fabry-Perot reflection modulator with veryhigh contrast ratio

Performance results for a normally on, electroabsorptive, surface-normal Fabry-Perot reflection modulator are presented. The device employs a cavity with a 100 Å GaAs/100 Å Al_0.3 Ga_0.7As multiple quantum well and top and bottom quarter-wave mirrors with 4 and 19.5 periods, respectively. Very low values of off-state reflectance were measured, giving a maximum contrast ratio >1000 (30 dB) and a maximum reflectance difference of 64.3%. The contrast ratio is, to the authors' knowledge, the largest reported to date     

Zero chirp asymmetric Fabry-Perot electroabsorption modulator using coupled quantum wells

A zero-chirp asymmetric Fabry-Perot reflection InGaAs QW modulator is created by placing coupled quantum wells in the intrinsic region of a reverse-biased p-i-n diode asymmetric Fabry-Perot cavity. Unlike single quantum wells which necessarily produce chirping during the switching cycle, these coupled quantum wells provide large absorption changes with zero refractive index changes over the entire voltage swing; the resultant cavity structure shows reflectivity changes with zero experimental phase change over the same voltage range. The tradeoff in reflectivity change required in order to obtain zero chirp is described. This tradeoff is a result of the different switching mechanisms used in coupled quantum wells versus single quantum wells.     

High tolerances for a low-voltage, high-contrast, low-insertion-loss asymmetric Fabry-Perot modulator

The authors report on the reduction of the operating voltage of a GaAs/AlGaAs multiple-quantum-well asymmetric Fabry-Perot modulator to approximately 4.2 V for a high-contrast ( approximately 15 dB), low-insertion-loss ( approximately 3 dB) device. This improvement on modulator performance makes the device suitable for a practical system and has been accomplished by an increase of the front reflectivity to approximately 43%. The authors discuss general design issues and show that the higher finesse cavity does not have to lead to low fabrication and environmental tolerances. On the contrary, this device's tolerance to fabrication and environmental factors is expected to have been improved.<>     

The applications of an interdiffused quantum well in a normally onelectroabsorptive Fabry-Perot reflection modulator

A Fabry-Perot reflection-type modulator which uses interdiffused AlGaAs-GaAs quantum wells as the active cavity material has been studied and optimized theoretically. An asymmetric Bragg reflector structure (modeled by transfer matrices), with a doped depletion layer in the heterostructure, has been considered. This is the first study to model such a material system in this type of modulator, and the results show improvement in modulation property over its as-grown rectangular quantum-well modulator. In particular, the change of reflectance in the diffused quantum-well modulator is almost 0.6 to 0.7, which is higher than that of the typically available values (~0.5 to 0.6), while the OFF-state on-resonance reflectance is almost close to zero. The operation voltage is also reduced by more than half as the interdiffusion becomes extensive. The finesse of the more extensively diffused quantum well also increases. Both of these features contribute to an improvement of the change of reflectance in the modulator. The operation wavelengths can be adjusted over a range of 100 nm. However, the absorption coefficient change of the diffused quantum well increases only when there is a small amount of interdiffusion     

High-contrast reflection modulation at normal incidence in asymmetric multiple quantum well Fabry-Perot structure

The authors have modelled the properties of a multiple quantum well pin diode optical modulator with the natural semiconductor reflectivity (R approximately=0.3) at its front surface and a high reflector (R approximately=0.95), such as an integrated semiconductor quarter-wave stack, at the back. By using resonant electroabsorption, rather than electrorefraction, the calculations show that it is possible to achieve contrast ratios of over 200, with less than 3 dB insertion loss.<>     

InGaAs-InP superlattice electroabsorption waveguide modulator

An electroabsorption waveguide modulator with an extinction ratio for TE-polarized light at 1550 nm of more than 20 dB for a voltage swing of less than 3 V, and low insertion losses has been realized, which exploits the Wannier-Stark effect in an InGaAs-InP short period superlattice, grown by chemical beam epitaxy. Even for a fixed voltage swing of 2.6 V, a good transmission contrast has been obtained in a wide wavelength range     

Millimeter-wave asymmetric Fabry-Perot modulators

We have designed, fabricated, and characterized GaAs-AlGaAs (λ=864 nm) asymmetric Fabry-Perot modulators with ≈37 GHz modulation frequency response, comparable to the fastest waveguide modulators. The modulation response saturates at high optical powers due to saturation of the excitonic absorption and heating effects, but the frequency response is independent of the incident optical intensity, since it depends only on the RC time constant, and not on the carrier transit time. The device design takes advantage of the fact that the quantum-confined Stark effect is more pronounced at some distance from the absorption edge to achieve a modulator with ⩾20 dB contrast and ≈3 dB insertion loss for ±2 V operating voltage, but only 21 fF capacitance. The DC bias used to move the operating point off the absorption edge has the additional benefits of improving the linearity and chirp of the device, as well as the saturation intensity. Here we present measurements of the modulation and photocurrent responses of the modulators, calculate the RC and transit times for the device, analyze the saturation mechanisms, and discuss the linearity and chirp of the device from the perspective of a high-speed digital optical communications system     

Low-voltage fourth-order CMOS sigma-delta modulator implementation

A low-voltage, high-speed, fourth-order sigma-delta modulator implementation is presented. The low-voltage and high-speed operation are obtained by using a novel combination of architectural features, proper circuit structure selections, specific clocking strategies, and efficient circuit optimisation algorithms. Measurement results from fabricated CMOS chip prototypes show a good match with simulations     

Low-voltage modulator and self-biased self-electro-optic-effect device

We have demonstrated a quantum-well waveguide modulator with large (7:1) on/off ratio at low bias voltage (less than 1V) compatible with high-speed electronics. The unique structure of this device permits bistable and other self-electro-optic-effect operations without an external power supply.     

Extremely low-voltage Fabry-Perot reflection modulators

A normally-on-electroabsorptive surface-normal Fabry-Perot reflection modulator with a reflection change of 47% for an operating voltage swing of only 2 V, i.e. 23%/V, is discussed. The structure has an active region of twenty-four 100-Å-GaAs/100-Å-Al_0.2 Ga_0.8As multiple quantum wells, sandwiched between two quarter-wavelength grating mirrors with the bottom one more reflective. The wavelength range over which more than half of the maximum reflection change is observed is as wide as ~7 nm for 2 V     

Fabrication and characterisation of a 4×4 array ofpolymer-based asymmetric Fabry-Perot reflection modulators

The fabrication and optical characterisation of a 4×4 array of asymmetric Fabry-Perot (AFP) electro-optic modulators is reported. The electro-optic material used, a cross-linked polymer based on an azo-benzene derivative, offers the potential for high time-bandwidth modulation. The uniformity of the spatial light modulator is evaluated, and a contrast ratio exceeding 4:1 can be obtained simultaneously at each of the 16 pixel positions     

Low-voltage high-speed travelling wave InGaAsP-InP phase modulator

A high-speed low-drive-voltage travelling wave electrodes InGaAsP-InP phase modulator operated at 1.55 /spl mu/m is demonstrated. The modulator is fabricated using a multiple quantum-well optical waveguide with an on chip integrated termination resistor. A small signal bandwidth of 35 GHz and a V/spl pi/ of 1.8 V has been demonstrated.     

Bulk Fabry-Perot intensity modulator for LIDAR systems

This letter reports on a built Fabry-Perot modulator operating at high optical intensities in the blue-green optical region. The design, fabrication, and characterization of a prototype modulator using LiNbO/sub 3/ as the host material with mirrors deposited directly on the end facets of the crystal are described. A measured modulation depth of 23.9% was achieved.     

Fabry-Perot bistable cavity optimization on reflection

An analysis of bistable Fabry-Perot action in reflection is presented. Optimum values for the cavity reflective coatings and cavity length are determined. Reasons are given why reflection-mode operation rather than transmission-mode operation should be preferred for device applications. Two prototype devices, an all-optical SR (Set-Reset) flip-flop and an all-optical clock, are described.     

Electroabsorptive Fabry-Perot reflection modulators with asymmetricmirrors

A normally-on electroabsorptive surface-normal Fabry-Perot reflection modulator is reported with an on/off ratio of 22, insertion loss of 3.7 dB, and bandwidth of 3.4 nm for an operating voltage swing of 11 V. The asymmetric Fabry-Perot structure is made with asymmetric mirrors using a quarter-wavelength grating of 15 1/2-periods on the bottom and an air-semiconductor interface on the top. The active region is 1.4 μm thick and composed of 100Å GaAs/100 A Al_0.2Ga_0.8As multiple quantum wells. The structure provides both high-efficiency and bandwidth for surface-normal modulators     

Surface-normal electroabsorption reflection modulators usingasymmetric Fabry-Perot structures

The authors discuss a family of surface-normal electrooptic reflection modulators using asymmetric Fabry-Perot (ASFP) structures with GaAs-AlGaAs multiple quantum wells (MQWs) as the active medium. When an optimized top mirror reflectivity (~75%) is used, a voltage swing as low as 2 V is enough to change the device reflectivity by more than 40% with a contrast ratio of 50. A comparison with various Fabry-Perot structures shows that the ASFP is the best structure in terms of its operating voltage requirement and optical bandwidth. A sensitivity analysis shows that tolerances of 2 nm in operating wavelength, 0.5 V in operating voltage, 0.3% in layer thickness control or 10°C in temperature variation can be expected from ASFPs with a finesse ~10     

Low-drive-power asymmetric Mach-Zehnder modulator with band-limitedoperation

A novel 2×2 asymmetric Mach-Zehnder interferometric modulator is fabricated on Ti:LiNbO₃ waveguide and tested at microwave frequency. Band-limited operation was realized by using a traveling-wave periodic polarity reversed structure with the asymmetric strip line as the modulator electrode instead of the conventional coplanar waveguide. For a modulator with a three-section polarity reversed electrode, a 3-dB bandwidth of 7 GHz was obtained experimentally from 9 to 16 GHz centered at 12 GHz     

High power performance of asymmetric Fabry-Perot MQW modulators

We have demonstrated experimentally that a normally-on surface normal asymmetric Fabry-Perot modulator can still operate at high optical powers (equivalent to intensities of >20 kW/cm²). We have identified two distinct operating regimes: one thermally assisted regime where the maximum reflection change increases at high powers and peak values of 75% are achieved, and one nonthermal regime where reflection changes approaching 55% are achieved albeit at higher applied voltages     

低压压电陶瓷相移器及其在电子散斑干涉计量中的应用

介绍了一种新型低压压电陶瓷相移器及其驱动电路的原理、结构和标定方法，并简述了它在电子散斑干涉计量（ＥＳＰＩ）中的应用。