Mach Zehnder

We show that the phase sensitivity $\Delta \theta$ of a Mach-Zehnder interferometer fed by a coherent state in one input port and squeezed-vacuum in the other one is i) independent from the true value of the phase shift and ii) can reach the Heisenberg limit $\Delta \theta \sim 1/N_T$, where $N_T$ is the average number of particles of the input states. We also show that the Cramer-Rao lower bound, $\Delta \theta \propto 1/ \sqrt{|\alpha|^2 e^{2r} + \sinh^2r}$, can be saturated for arbitrary values of the squeezing parameter $r$ and the amplitude of the coherent mode $|\alpha|$ by a Bayesian phase inference protocol.

A digitally operated optical quadrature-amplitude modulation (QAM) modulator based on a single multielectrode Mach-Zehnder modulator is presented. Generation and performance of 64QAM are studied in detail. Simulation results show that a single modulator with 13 electrodes, each of which is driven by either one of the voltages 0 or 1.68 vπ, provides close-to-ideal 64QAM constellation despite the inherent nonlinearity of the modulator. Moreover, employing a sufficient number of electrodes, close to ideal error performance can be obtained for any constellation order, or shape. Simulations results are demonstrated for several different square constellations: 16QAM and 256QAM, and nonsquare constellations: 32QAM and 128QAM. A brief discussion on the utilization of the proposed scheme as a predistorter is also given.

We describe an important second-order effect in the counter-phase optical interference cancellation system [also referred to as the opto-cancellation system (OCS)]. The uniformity of signal cancellation provided by the OCS, across a nonzero instantaneous bandwidth, is limited due to Vπ mismatches in the electro-optic modulators comprising the system. The effect of these mismatches on the cancellation is examined quantitatively.

Astronomical spectroscopy at submillimeter wavelengths holds much promise for fields as diverse as the study of planetary atmospheres, molecular clouds and extragalactic sources. Fourier transform spectrometers (FTS) represent an important class of spectrometers well suited to ...