Elizabeth T. Kunkee

Electrorefractive Coupled Quantum Well Modulators: Model and Experimental Results

Theoretical modeling of InP coupled-quantum-well electroabsorptive and electrorefractive modulators is presented. Key mathematical transformations are developed that allow efficient computation of electrorefraction for a complex multiparameter coupled quantum well structure. The model is realized in the Mathematica platform and is used to simulate the impact of well and barrier composition and thickness on Mach-Zehnder modulator performance. The advantage of using coupling between quantum wells is quantified and in addition, it is shown that linewidth broadening is a key input to the model and has a critical impact on modulator performance. The model is compared to experimental data from phase modulators and Mach-Zehnder intensity modulators.

Simultaneous optical amplification and splitting for lower-noise and higher-gain microwave signal distribution

Semiconductor optical amplifiers are investigated for use in large optical signal distributions systems requiring high dynamic range. The impact of amplifier length on the gain and noise figure of the microwave signal is illustrated experimentally. The performance of a device which simultaneously splits and amplifies the optical signal using the principle of multimode interference will be discussed, and it will be shown that this device has potentially higher performance that the previous generation Y-branch/amplifier combination.

Semiconductor optical modulators for high-performance analog rf photonic links and signal processing

Semiconductor based optical modulators offer flexibility in providing engineerable optical transfer characteristics that can target specific applications. Use of quantum well active regions provides the capability of efficient and linearized transfer characteristics that can benefit analog RF systems in terms of link gain, noise figure and spur free dynamic range. We present experimental results demonstrating the potential for improvements in modulator linearity and efficiency using quantum well based Mach-Zehnder modulators.

Analog Signal Splitting and Amplification for Optically-Controlled Phased-Array Antennas

In this work, multimode interference in a semiconductor optical amplifier is used to simultaneously split (× 10) and amplify a RF signal on an optical carrier.

Semiconductor electrorefractive modulators

Experimental and analytical results for semiconductor electro-refractive modulators will be presented. Modulation structures investigated include quantum wells, coupled quantum wells and quantum dots.

Quantum dots: a new approach to low V π optical modulators

Preliminary analysis has shown that quantum dots enable tens of millivolt-range operation of phase-shifters in a semiconductor Mach-Zehnder interferometer modulator. Our methodology based upon the quantum dot experimental work of Hse et al, makes use of his measured exciton line shapes to estimate refractive index changes in a PIN structure in which the intrinsic laser is loaded with self-organizing quantum dots and their associated wetting layers. We consider both forward and reversed bias cases; in the former, the interferometer phase shift sections become DFB lasers, and in the latter, the phase shift is caused by the quantum-confined Stark effect (QCSE). With the latter, we found a trade-off between low operating voltage and modulating bandwidth. For a phase shifter insertion loss of 5 dB, a 250-micron long phase section will yield a pi/2 control voltage of 50 mV at a bandwidth of around 18 GHz. Ifi 90 mV control voltage swing can be tolerated, the modulator bandwidth increases to 30 GHz. If a resonant tunneling diode (RTD) is made part of the assembly, the local E-field is enhanced by a factor of 5 to 10, thereby reducing the drive requirements even further. Similar, though narrower bandwidth results were noted for the DFB laser phase modulator concept.

High power, high-frequency waveguide photodetectors

Optical RF analog applications are generating great interest for a number of reasons including the flexibility of fiber optic systems and the enormous RF signal processing capability offered by photonics. A limitation to the insertion of RF photonics has been the availability of high performance photonic components that can deliver on the advantages offered by photonic systems. In this paper we will discuss test results of InGaAsP-InP based waveguide photodetectors targeting optical RF analog applications.

Mach-Zehnder quantum well modulators for aerospace applications

We provide experimental benchmark data and identify aerospace applications for which quantum well Mach-Zehnder modulators are well suited. An InP MZM gives a V-pi of 2.0, insertion loss of 11 dB, and bandwidth of 8 GHz.

Photonically enabled RF spectrum analyzer demonstration

A RF spectrum analyzer with high performance and unique capabilities that traditional all-electronic spectrum analyzers do not exhibit is demonstrated. The system is based on photonic signal processing techniques that have enabled us to demonstrate the spectral analysis of a 1.5 GHz bandwidth with a 1.4 ms update time and a resolution bandwidth of 31 kHz. We observed a 100% probability of intercept for all signals, including short pulses, during the measurement window. The spectrum analyzer operated over the 0.5 to 2.0 GHz range and exhibited a spur-free dynamic range of 42 dB. The potential applications of such a system are extensive and include: detection and location of transient electromagnetic signals, spectrum monitoring for adaptive communications such as spectrum-sensing cognitive radio, and battlefield spectrum management.

Modeling and Test of Traveling-Wave Electrode Mzch-Zehnder InP/InGaAsP Quantum Well Modulators

We present a theoretical model and experimental validation for electrode design of semiconductor traveling wave modulators. An InP Mach-Zehnder interferometer gives a Vpi of 1.7 V, optical insertion loss of 11 dB, and bandwidth of 8 GHz.