Phase Recovery Technique Research Articles

Lensfree sensing on a microfluidic chip using plasmonic nanoapertures

We demonstrate lensfree on-chip sensing within a microfluidic channel using plasmonic nanoapertures that are illuminated by a partially coherent quasimonochromatic source. In this approach, lensfree diffraction patterns of metallic nanoapertures located at the bottom of a microfluidic channel are recorded using an optoelectronic sensor-array. These lensfree diffraction patterns can then be rapidly processed, using phase recovery techniques, to back propagate the optical fields to an arbitrary depth, creating digitally focused complex transmission patterns. Cross correlation of these patterns enables lensfree on-chip sensing of the local refractive index surrounding the near-field of the plasmonic nanoapertures. Based on this principle, we experimentally demonstrate lensfree sensing of refractive index changes as small as ∼2×10(-3). This on-chip sensing approach could be quite useful for development of label-free microarray technologies by multiplexing thousands of plasmonic structures on the same microfluidic chip, which can significantly increase the throughput of sensing.

Electron diffractive imaging of nano-objects using a guided method with a dynamic support

We present a phase recovery technique that utilizes a guiding method with a dynamic support to reconstruct the shape and exit wave of a single MgO nanoparticle in a coherent electron diffraction experiment. The proposed method provides an optimal solution deduced from the electron diffraction pattern alone. The recovered shape has spatial resolution 3.1 nm. The complex exit wave encodes the projected atomic structure of the nanocrystal with resolution about 0.15 nm, and agrees with a multislice simulation. The possibility of imaging nanosized objects at diffraction-limited resolution using a field emission electron microscope is thus demonstrated.

Frequency Estimation in Intradyne Reception

We report on an optical intradyne receiver experiment with frequency estimation. Frequency estimation allows, if performed prior to block phase estimation or other phase recovery techniques, for a much higher frequency difference between transmit laser and local oscillator laser. We demonstrate the feasibility of our approach in a 20-Gb/s quadrature phase-shift keying experiment

Robust time and phase synchronization for continuous phase modulation

A novel joint timing and phase-recovery technique is proposed for continuous phase modulation (CPM) systems based on Kalman filtering and an approximate representation of CPM signals with nonorthogonal exponential expansions (nOEE). Compared with existing techniques, the proposed synchronizer requires a less complex front-end processor, and can achieve reliable acquisition performance with a shorter preamble. The asymptotic stability and convergence of the proposed synchronizer is analyzed, including the effect of statistical channel-modeling errors on the convergence characteristics. The selection of suboptimal nOEEs and the design of triple-initialized Kalman filters are also discussed. Both theoretical and simulation results show that the proposed synchronizer is robust in acquiring and tracking both the time shift and the phase offset on either time-invariant or time-variant channels

Off-resonant defocus-contrast imaging of cold atoms.

We demonstrate the retrieval of column-density images of cold atoms, using a noninterferometric phase-recovery technique based on a single off-resonant and defocused intensity image. The quantitative column density is retrieved via Fourier inversion and remains robust with respect to detuning and defocus. The technique offers excellent prospects for simple, nondestructive imaging of atoms in magnetic and optical traps and condensates.

A class of blind phase recovery techniques for higher order QAM modulations: estimators and bounds

This letter proposes a class of blind feedforward carrier-phase estimators for higher order quadrature amplitude-modulated transmissions. As an extension of the Viterbi and Viterbi (V&V) estimator, a constellation-dependent optimal matched nonlinear estimator is derived such that its asymptotic variance is minimized. The asymptotic variances of the optimal matched and V&V estimators are established in closed-form expressions and compared. Computer simulations are presented to corroborate the theoretical performance analysis.

The potential for transducer characterisation from a single plane scan of intensity values alone

The phase recovery technique has previously been used to determine the vibration properties of an ultrasonic transducer from its radiated pressure intensity field measured over two planes parallel to the transducer's aperture. The results were comparable in quality to those obtained by the Fourier optics back-projection method. This contribution reports on further work carried out on phase recovery and source reconstruction using a single plane of intensity or amplitude data only.

The application of phase recovery techniques to the determination of transducer source distributions

This paper presents the results of further investigations on the applicability of phase recovery techniques to the determination of ultrasonic transducer source distributions, following on from the initial investigations reported by Hurrell [1]. The work described here includes the results of a reconstruction from measurements of the radiated pressure field amplitude from a far from ideal focused transducer, which represents an extremely demanding test of the reconstruction algorithm. These results are compared with those obtained from the well-known back-projection method [2].

A Passive Phase Recovery Technique for Sagnac Interferometers Based on Controlled Loop Birefringence

We analyse the polarization and phase properties of the birefringent Sagnac interferometer in the case of a polarized source. We show that control of loop birefringence allows an arbitrary phase difference to be imposed upon the counter-propagating beams for any source polarization state, with control over the relative states of polarization of the recombining beams. We show how this may be achieved using one half-wave and two quarter-wave plates. We discuss the application of this method in fibre-optic sensors.