Self-referencing a continuous-wave laser with electro-optic modulation

We phase-coherently measure the frequency of continuous-wave (CW) laser light by use of optical-phase modulation and f-2f nonlinear interferometry. Periodic electro-optic modulation (EOM) transforms the CW laser into a continuous train of picosecond optical pulses. Subsequent nonlinear-fiber broadening of this EOM frequency comb produces a supercontinuum with 160 THz of bandwidth. A critical intermediate step is optical filtering of the EOM comb to reduce electronic-noise-induced decoherence of the supercontinuum. Applying f-2f self-referencing with the supercontinuum yields the carrier-envelope offset frequency of the EOM comb, which is precisely the difference of the CW laser frequency and an exact integer multiple of the EOM pulse repetition rate. Here we demonstrate absolute optical frequency metrology and synthesis applications of the self-referenced CW laser with <5E-14 fractional accuracy and stability.Comment: 8 pages, 4 figure

Trellis phase codes for power-bandwith efficient satellite communications

Support work on improved power and spectrum utilization on digital satellite channels was performed. Specific attention is given to the class of signalling schemes known as continuous phase modulation (CPM). The specific work described in this report addresses: analytical bounds on error probability for multi-h phase codes, power and bandwidth characterization of 4-ary multi-h codes, and initial results of channel simulation to assess the impact of band limiting filters and nonlinear amplifiers on CPM performance

Direct GMSK modulation at microwave frequencies

Congestion in the radio spectrum is forcing emerging high rate wireless communication systems into upper microwave and millimeterwave frequency bands, where transceiver hardware architectures are less mature. One way to realize a simple and elegant hardware solution for a microwave transmitter is to exploit the advantages of directly modulating the phase of the carrier signal. A modulation method requiring continuous phase control of the carrier signal over the full 360 degree range is Gaussian Minimum Shift Keying (GMSK). Unfortunately, it is very difficult to design a microwave circuit to provide linear phase control of a carrier signal over the full 360 degree range using traditional methods. A novel method of obtaining continuous, linear phase modulation of a microwave carrier signal over the full 360 degree range is proposed. This method is based on controlling a phase shifter, at a subharmonic of the desired output carrier frequency, and then using a frequency multiplier to obtain the desired output frequency. The phase shifter is designed to be highly linear over a fraction of the full 360 range. The frequency multiplier is a nonlinear circuit that shifts the frequency by *'N'. The subtle part of this nonlinear operation is that the multiplier also multiplies the instantaneous phase of the phase shifter output signal by *'N', thus expanding the linear phase shift range to the required 360 degrees. Using this nonlinear frequency multiplication principle, the modulator can readily be extended into the millimeterwave region. A prototype circuit is designed and performance results are presented for this method of carrier phase modulation at 18 GHz. The prototype circuit is realized with very simple hardware, containing only a single microwave active device. An extension to the modulator involving phase locking or injection locking of a power oscillator is also suggested for obtaining higher power modulated output signals. In addition to direct continuous phase modulation, the proposed method is also suitable for a wide variety of transceiver applications, including phase synchronization of antenna and oscillator arrays, phased array antenna beam steering, indirect frequency modulation, and ultra-small carrier frequency translation

Instabilities, solitons and rogue waves in PT-coupled nonlinear waveguides

We considered the modulational instability of continuous-wave backgrounds, and the related generation and evolution of deterministic rogue waves in the recently introduced parity–time (PT )-symmetric system of linearly coupled nonlinear Schr¨ odinger equations, which describes a Kerr-nonlinear optical coupler with mutually balanced gain and loss in its cores. Besides the linear coupling, the overlapping cores are coupled through the cross-phase-modulation term too. While the rogue waves, built according to the pattern of the Peregrine soliton, are (quite naturally) unstable, we demonstrate that the focusing cross-phase-modulation interaction results in their partial stabilization. For PT -symmetric and antisymmetric bright solitons, the stability region is found too, in an exact analytical form, and verified by means of direct simulations.Fundação para a Ciência e a Tecnologia (FCT)Binational (US–Israel) Science Foundation

Sensitivity to measurement perturbation of single atom dynamics in cavity QED

We consider continuous observation of the nonlinear dynamics of single atom trapped in an optical cavity by a standing wave with intensity modulation. The motion of the atom changes the phase of the field which is then monitored by homodyne detection of the output field. We show that the conditional Hilbert space dynamics of this system, subject to measurement induced perturbations, depends strongly on whether the corresponding classical dynamics is regular or chaotic. If the classical dynamics is chaotic the distribution of conditional Hilbert space vectors corresponding to different observation records tends to be orthogonal. This is a characteristic feature of hypersensitivity to perturbation for quantum chaotic systems.Comment: 11 pages, 6 figure

Method for real-time measurement of the nonlinear refractive index

In this work, we propose a novel method for continuous real-time measurement of the dynamics of the nonlinear refractive index n2. This is particularly important for characterizing phenomena or materials (such as biological tissues, gases and other compounds) whose nonlinear behavior or structure varies rapidly with time. The proposed method ingeniously employs two powerful tools: the spectral broadening induced by self-phase modulation and the real-time spectral analysis using the dispersive Fourier transformation. The feasibility of the technique is experimentally demonstrated, achieving high-speed measurements at rates of several MHz