Asymmetric Fabry-Perot Modulators Research Articles

Large aperture asymmetric Fabry Perot modulator based on asymmetric tandem quantum well for low voltage operation

Large aperture image modulators used as demodulator in receiver path are an important component for the use in three dimensional (3D) image sensing. For practical applications, low voltage operation and high modulation performance are the key requirements for modulators. Here, we propose an asymmetric Fabry-Perot modulator (AFPM) with asymmetric tandem quantum wells (ATQWs) for 3D image sensing. By using ATQWs for the AFPM design, the device operated at -4.25V, and the operating voltage was significantly lower by about 23% compared to -5.5V of a conventional AFPM with 8nm thick multiple QW with a single QW thickness (SQWs), while achieving high reflectivity modulation in excess of 50%. The performance of the fabricated devices is in good agreement with theoretical calculations. The pixelated device shows a high modulation speed of 21.8 MHz over a large aperture and good uniformity. These results show that AFPM with ATQWs is a good candidate as an optical image modulator for 3D image sensing applications.

Design of vertical Ge quantum well asymmetric Fabry-Perot modulator without DBR

We present a vertical Ge quantum well (QW) asymmetric Fabry-Perot modulator design and integration scheme without distributed Bragg reflector (DBR). The field-dependent excitonic absorption and the modulator performance are calculated, showing the wide (20-nm-thick) well design gives a large absorption reduction for the normally-off modulator operation. For a 47 QW modulator, the theoretical contrast ratio exceeds 40 dB at 1 V and increases to 52.3 dB at 4 V bias with a 12.3-dB insertion loss and over-9-nm optical bandwidth (contrast>3dB). This robust DBR-free design can enable high-contrast-ratio Ge QW modulators.

Coverage Range and Cost Comparison of Remote Antenna Unit Designs for In-building Radio over Fiber Technology

Future communication needs to be ubiquitous, broadband, convergent, and seamless. Radio over fiber (RoF) technology is one of the most important enabler in access network for the technologies. Adoption of RoF faces bottleneck in optoelectronics, that they are still expensive, high power consumption, and limited in bandwidth. To solve the problem, transceiver in remote antenna unit (RAU) is developed, i.e. electroabsorption transceiver (EAT) and asymmetric FabryPerot modulator (AFPM). This paper compares their coverage range and cost in providing WCDMA and WLAN services. Needed gain of RF amplifier for supporting picocell is also discussed.

1.55-μm asymmetric Fabry-Perot modulator (AFPM) for high-speed applications

We explored the possibility of using an aysmmetric Fabry–Perot modulator (AFPM) for the application of high-speed external optical modulation at 1.55 μm. Using ten pairs of AlGaInAs–AlInAs as the bottom distributed Bragg mirror (DBR) and semiconductor–air interface as the top mirror, we demonstrated an AFPM with a 3-dB frequency response around 20 GHz and a dc extinction ratio of 4 dB at a reverse bias voltage of 0–5 V (and sharp extinction ratio drop from 0 to 2 V) at operating wavelength 1.55 μm. With a multiple quantum-well intrinsic region of 900 nm, which consists of 50 pairs of InGaAs–InAlAs (8–10 nm), the modulator has the potential for high-frequency applications.

Multiple-quantum-well asymmetric Fabry-Perot modulators for microwave photonic applications

We describe the development of InGaAsP multiquantum-well asymmetric Fabry-Perot modulators (AFPM) for RF-over-fiber applications. Advantages of the AFPM include low drive voltage and loss, high linearity and simple fiber alignment. Experimental results of initial devices, exhibiting 5.5-dB modulation depth and >3-GHz operation, are described. The effect of the optical power on the device performance was assessed, and the modulation bandwidth was found to be unaffected by incident optical powers up to 0 dBm. The linearity of the modulation characteristic was measured by carrying out two-tone intermodulation distortion tests, and a third-order intercept point of 30 dBm was observed.

Design of InGaAsP multiple quantum-well Fabry-Perot modulators for soliton control

The use of synchronous optical modulators is effective in reducing the pulse timing jitter in long-distance soliton transmission. The inherently polarization-insensitive characteristics of the Fabry-Perot multiple quantum-well (MQW) electroabsorption modulator make it a potentially suitable device for this application. We investigate the intensity and phase modulation characteristics of symmetric and asymmetric Fabry-Perot modulators, and show that, by positioning the resonant wavelength <30 nm away from the exciton absorption peak to obtain negative chirp operation, both configurations can be used to successfully reduce timing jitter in a 20 Gb/s soliton system.

1.5 μm asymmetric Fabry–Perot modulators with two distinct modulation and chirp characteristics

This letter discusses the design and the realization of asymmetric Fabry–Perot modulators with InP/InGaAsP distributed Bragg reflectors and 80 AlInGaAs quantum wells. We demonstrate two types of modulators utilizing two different top reflectors: an InP to air interface and a Si/SiO2/Si coating. The first modulator showed a monotonic reduction in the reflectivity as the bias voltage increased, and achieved a 2.2 dB insertion loss and a 15 dB contrast ratio at the resonant wavelength. The second modulator showed an initial reduction and then an increase in the reflectivity as the bias changed from 0 to −10 V. The chirp calculation based on the measured data reveals that the second modulator exhibits two distinct positive and negative chirp characteristics.

Thermally-actuated reflection mode asymmetric Fabry–Perot modulator utilizing a thin transparent elastomeric film

This letter describes a thermally-actuated reflection mode asymmetric Fabry–Perot modulator that consists of a thin transparent elastomeric film bounded by partially and highly reflecting metallic mirrors. The thickness of the transparent layer determines the intensity of light reflected from the modulator; changes in its thickness modulate the reflectivity. Electrical current flowing through the highly reflecting mirror provides a source of heat for controlling, by thermal expansion, the thickness of the elastomeric film. Modulators with this design show contrast ratios &amp;gt;15 dB and insertion losses &amp;lt;0.3 dB.

High-performance two-wavelength asymmetric Fabry-Perot modulator with a decoupled cavity design

We have demonstrated a high-performance two-wavelength asymmetric Fabry-Perot modulator (AFPM) by using a novel decoupled cavity design. In this new design, the middle mirror supplies a back-mirror reflectivity for the short-wavelength modulator and, at the same time, a front-mirror reflectivity for the long-wavelength modulator. The front mirror is designed to be transparent at the long wavelength and reflective at the short wavelength to eliminate the interference between the two modulators. With this decoupled cavity design, we greatly simplified the matching requirement for the two cavities and obtain much more flexibility in the device design. Experimentally, we have demonstrated a two-wavelength modulator operated at 860 and 890 nm with operating voltages of 3.4 and 6.2 V and reflectivity changes of 62% and 44%, respectively.

Radiation hardness of electro-optic asymmetric Fabry-Perot modulators

Analog optical links for LHC experiments are being developed, using electro-optical modulators as front-end transmitters. In the inner trackers, these devices will be subject to a harsh radiation environment, combining ionizing radiation and hadrons, up to 10 Mrads and 10 14 (neutron-equivalent)/cm 2, over the experiment lifetime. The radiation hardness of the Asymmetric Fabry-Perot Modulator (AFPM) has been tested, with both kinds of radiations, up to LHC total doses and fluences. Results confirm a radiation hardness which qualifies the AFPM for application in the detector front ends.

Time stability of asymmetric Fabry-Perot modulator-based analog lightwave links

Lightwave links for analog signal transfer are being developed and evaluated for application in high-density interconnects. The reflective links are based on compact electrooptic intensity modulators connected by ribbons of single-mode fibers to remotely located transceivers (lasers and photoreceivers) and read-out electronics. For long term characterization, four asymmetric Fabry-Perot modulator (AFPM) prototypes have been continuously operated and monitored during a period of eight months. The collected data allow evaluation of the system time stability and simulation of the possible recalibration procedures. The recalibration requirements to achieve the desirable accuracy and reliability are inferred statistically.

Asymmetric Fabry-Perot modulator with a waveguide geometry

Modulation characteristics of a dual waveguide structure consisting of a polymer ridge waveguide coupled to a semiconductor resonator containing quantum wells are described. The intensity of light transiting the polymer waveguide is modulated when the absorption of the quantum wells is varied by the Stark effect. Intensity modulation occurs since increased absorption broadens the resonance. A 2V change in bias results in a contrast ratio of 20 over a few Angstrom wavelength-range.

Waveguide version of an asymmetric Fabry–Perot modulator

We show that the high contrast property of vertical cavity asymmetric Fabry–Perot modulators can also be obtained in a waveguide geometry. Increasing the absorption in one arm of a waveguide directional coupler causes the transmission through the other arm to decrease, go to zero, and then increase again. Thus, by adjusting the coupling length and the absorption, an infinite contrast ratio can theoretically be obtained with a low insertion loss. The waveguide geometry is not only more convenient than normal incidence for fiber-based devices, but also provides a larger optical bandwidth. We present the design equations and provide a first order model of device operation.

Evaluation of the tolerance of asymmetric Fabry-Perot modulators with respect to realistic operating conditions

This paper is concerned with asymmetric Fabry-Perot modulators (AFPM's) that use the electroabsorptive effect in GaAs-AlGaAs multiple quantum wells (MQW) to yield optical modulation. Although these devices may attain excellent peak-performance characteristics, their resonant nature makes them susceptible to variations in manufacture and to the operational conditions and this will ultimately limit their actual practical implementation. We examine in detail the tolerance of an AFPM to concurrent fluctuations of the main parameters that affect the performance, and evaluate the limitations of the current state-of-the-art. Thus we develop a procedure by which the overall tolerance of resonant structures may be realistically calculated, and identify a parameter of merit that enables an optimization in that respect. A number of ways to minimize the effect on the final performance are also addressed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design trade-offs and evaluation of the performance: attainable by GaAs-Al/sub 0.3/Ga/sub 0.7/As asymmetric Fabry-Perot modulators

We use a semi-empirical theoretical model to evaluate the performance ultimately attainable by normally-on asymmetric Fabry-Perot modulators (AFPMs) that incorporate GaAs-Al/sub 0.3/Ga/sub 0.7/As multiple quantum wells (MQW). Various optimization criteria are employed and the calculations address issues that involve both the micro-resonator design and the quantum-well region. Thus we evaluate the minimum required barrier width in order to compare between different well widths, and examine the final AFPM performance in many respects, considering not only the modulation itself but also the tolerances and the speed of the device. Finally, we proceed to the design of example devices where some characteristics have been specifically optimized.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application of anodic oxidation for postgrowth tailoring of InGaAsP/InP asymmetric Fabry-Perot modulator reflection spectra

Reflection spectrum tuning of InGaAsP/InP asymmetric Fabry-Perot modulators (AFPMs) using anodic oxidation followed by anodic oxide removal is reported for the first time. 30 – 40 nm tuning of the reflection spectra of double and single Bragg stack mirror AFPM structures with better than λ/100 accuracy has been achieved.

Millimeter-wave asymmetric Fabry-Perot modulators

We have designed, fabricated, and characterized GaAs-AlGaAs (/spl lambda/=864 nm) asymmetric Fabry-Perot modulators with /spl ap/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 /spl ges/20 dB contrast and /spl ap/3 dB insertion loss for /spl plusmn/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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electro-optic modulation using asymmetric Fabry–Perot laser diode amplifiers

We report the use of laser diode amplifiers, whose facets have unequal mirror reflectivities, as asymmetric Fabry–Perot modulators. Due to the presence of optical gain in these devices we observe modulation of reflected light with both large absolute modulation depth and high contrast ratio.

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/cm/sup 2/). 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. >

Optical neural network with quantum well devices

An optical implementation of a second-order, translation-invariant neural network algorithm is described. The active devices are two arrays of integrated asymmetric Fabry-Perot modulators. The device and the array characteristics are given. The arrays are used, with passive optics, to provide optical input, matrix multiplication, and weighted interconnects in a cascaded optical system. The detailed parameters of the system are discussed, and the operation is assessed in terms of noise tolerance. Translation invariance is confirmed. Finally, the relative merits of the devices and algorithm are considered.