Krishna Myneni

High-precision ranging using a chaotic laser pulse train

We demonstrate the use of a chaotic laser pulse train for high-precision ranging. The pulse train is produced by inducing coherence collapse in an AlGaAs semiconductor laser. Measurements of optical spectra, intensity autocorrelation functions, and ladar ranging are presented.

Electro‐optic properties near the absorption edge of GaAs/AlGaAs multiple‐quantum‐well waveguides

Measurements are reported of the electro‐optic properties of multiple‐quantum‐well p‐i‐n diodes at wavelengths where the waveguide propagation losses are small, 55–110 meV below the exciton resonance. Electroabsorptive and electrorefractive properties were measured as a function of polarization and crystal propagation direction. The electroabsorption and electrorefraction data show that there is a wavelength bandwidth of ∼25 nm where the quadratic electro‐optic coefficient is large (1–7×10−15 cm2/V2) and the magnitude of the electroabsorption is <0.5 dB/mm for applied fields of up to 1×105 V/cm. Compact, high‐dynamic‐range interferometric modulators can be realized in this wavelength band.

Quantum-Noise-Limited Sensitivity-Enhancement of a Passive Optical Cavity by a Fast-Light Medium

We demonstrate for a passive optical cavity containing a dispersive atomic medium, the increase in scale factor near the critical anomalous dispersion is not cancelled by mode broadening or attenuation, resulting in an overall increase in the predicted quantum-noise-limited sensitivity. Enhancements of over two orders of magnitude are measured in the scale factor, which translates to greater than an order-of-magnitude enhancement in the predicted quantum-noise-limited measurement precision, by temperature tuning a low-pressure vapor of non-interacting atoms in a low-finesse cavity close to the critical anomalous dispersion condition. The predicted enhancement in sensitivity is confirmed through Monte-Carlo numerical simulations.

Dispersion enhancement in atom-cavity and coupled cavity systems

We present an entirely linear all-optical method of dispersion enhancement using coupled cavities that leads to a substantial increase in system transmission in comparison with atom-cavity systems. This is achieved by tuning the system to an anomalous dispersion condition by under-coupling at least one of the cavities to the other. The intracavity anomalous dispersion is then associated with a dip in reflection (and in turn with a peak in transmission) rather than with an absorption resonance as in the case of the atomic vapor. We find that in contrast with the atom-cavity system where mode reshaping always contributes to the mode pushing, in coupled cavity systems reshaping of the mode profile can either contribute to or oppose the mode pushing, and even reverse it under appropriate conditions leading to a reduced scale factor in transmission. We demonstrate a method for further optimizing the transmission of both atom-cavity and coupled-cavity systems, but show that this leads to a more rectangular mode profile and a reduction in the scale factor bandwidth. We also derive the cavity scale factor in reflection for both atom-cavity and coupled cavity systems and show that in reflection the reshaping of the mode profile can either contribute to or oppose the mode pushing, but cannot reverse it.

Chaotic scrambling for wireless analog video

We report the implementation of a novel in-band chaotic scrambler for securing wireless analog video. In this demonstration system, an analog video signal is injected into a chaotic oscillator and the output is transmitted through a standard wireless radio link. At the receiver, a descrambler separates the video from the chaotic signal in real time. Experimental results show the scrambled signal effectively hides the original video image, yet the descrambler recovers the original color video with reasonable clarity and detail. Compared to digital encryption, chaotic scrambling offers an efficient, low-cost alternative for masking time-critical analog communications.

Controlling the Sensitivity of an Optical Cavity with Slow and Fast Light

We measure mode pushing in a Fabry-Perot cavity by a dispersive medium and find that the scale factor increases more than the mode width. We discuss the conditions that result in such enhanced cavity sensitivities.

Chaos Synchronization Via The Transmission Of Symbolic Information

We report high‐quality chaotic synchronization of one‐way coupled electronic circuits through a communication channel that transmits only symbolic dynamical information. This is accomplished by converting the synchronization signal into a discrete symbol sequence at the transmitter and then decoding the symbols at the receiver in real time. We find that symbol information is critical in the synchronization process and that an arbitrarily low rms synchronization error can be maintained by only transmitting a single 1‐bit symbol per cycle. This indicates that chaotic synchronization is robust to severe band limiting and/or noise in the coupling channel provided symbol information is preserved. The experimental setup also allows us to explore so‐called achronal synchronization in which the receiver lags or leads the transmitter by fixed time. We discuss fundamental trade‐offs between the accuracy to which the transmitter state can be known, the quality of synchronization, and the delay or anticipation create...

High-precision, accurate optical frequency reference using a Fabry–Perót diode laser

We show that the optical output of a temperature and current-tuned Fabry-Perót diode laser system, with no external optical feedback and in which the frequency is locked to Doppler-free hyperfine resonances of the 87Rb D2 line, can achieve high frequency stability and accuracy. Experimental results are presented for the spectral linewidth, frequency stability, and frequency accuracy of the source. Although our optical source is limited by a short-term spectral linewidth greater than 2 MHz, beat signal measurements from two such sources demonstrate a frequency stability of 1.1 kHz, or minimum Allan deviation of 4×10-12, at an integration time τ=15 s and with a frequency accuracy of 60 kHz at τ=300 s. We demonstrate the use of the optical source for the precision measurement of hyperfine level frequency spacings in the 5P3∕2 excited state of 87Rb and provide an accurate frequency scale for optical spectroscopy.

Fast-light enhancement by polarization mode coupling in a single optical cavity

We present an entirely linear all-optical method of dispersion enhancement that relies on mode coupling between the orthogonal polarization modes of a single optical cavity, eliminating the necessity of using an atomic medium to produce the required anomalous dispersion, which decreases the dependence of the scale factor on temperature and increases signal-to-noise by reducing absorption and nonlinear effects. The use of a single cavity results in common mode rejection of the noise and drift that would be present in a system of two coupled cavities. We show that the scale-factor-to-mode-width ratio is increased above unity for this system and demonstrate tuning of the scale factor by (i) directly varying the mode coupling via rotation of an intracavity half wave plate, and (ii) coherent control of the cavity reflectance which is achieved simply by varying the incident polarization superposition. These tuning methods allow us to achieve unprecedented enhancements in the scale factor and in the scale-factor-to-mode-width ratio by closely approaching the critical anomalous dispersion condition.

Demonstration of shifter-less beam steering in an ultra-wide bandwidth array antenna using synchronized chaos

We demonstrate a new method for electronic beam steering in ultra-wide bandwidth array antennas based on synchronized chaos. Chaotic oscillators generate random-like waveforms that may be well-suited for highly unconventional ultra-wideband radar and spread-spectrum communication applications. The broadband and nonrepeating nature of chaos provides an ideal combination of high range resolution with no range ambiguity. Unlike true random sources, coupled chaotic oscillators can synchronize for coherent power combining. To steer the array, a small detuning is applied to each oscillator to slightly shift its natural frequency. Oscillators that are tuned to run faster will lead those tuned slower, providing a small time shift between the waveforms produced by each oscillator. The approach avoids the need for costly phase shifters or tunable true time delay elements. Our demonstration system consists of a linear array of four directionally coupled radio frequency chaotic oscillators, each of which produces a broadband waveform centered at 137 MHz. Each individual oscillator feeds one of four discone-type antennas spaced a third of a wavelength apart. We present far-field power level measurements characterizing beam formation and steering recorded on an outdoor test range. Our results suggest chaotic arrays could enable a new generation of low-cost, highperformance, ultra-wide bandwidth applications.