Conventional Phase Conjugation Research Articles

Noise suppression using quasi-phase conjugation in digital holographic microscopy

Various approaches for generating phase-conjugate signal have been recently proposed that exploit the advantage of noise suppression in digital holographic microscopy (DHM). This study presents a reproducible method for generating a time-independent quasi-phase conjugated signal, which is simple, compact, and cost-effective in a linear medium. Used in conjunction with adaptive optics or conventional phase conjugation technique, our method suppresses the influence of diffraction and has less constraint on wavelength and polarization state. Such a configuration generates quasi-phase conjugated signal in real time and supports multi-wavelength input simultaneously. The optical system produces images of high magnification and high resolution of 228.1 line pairs per mm (i.e. 2.19μm) and has low spatial standard deviation of 0.2 nm. In addition, scattering noise of 15 degrees diffusing angle from object is suppressed effectively.

Self-focusing in the ocean using out-of-band phase conjugation

Phase conjugation methods have been used in underwater acoustics because of their remarkable spatial self-focusing performance in inhomogeneous, dynamically changing environments. However, phase conjugation devices have stringent constraints such as acoustic transmitters and receivers working simultaneously in the same frequency band, which complicates the implementation of these devices and prevents their wide deployment in the ocean. Here, we introduce the out-of-band phase conjugation (OBPC) for ocean acoustics through which phase conjugation waves are generated at integer multiples of the incident wave frequency. The different bands translate into remarkably simple implementations while maintaining excellent spatial focusing in challenging shallow ocean environments. Furthermore, the resolution of OBPC is significantly higher than that of conventional phase conjugation. An interesting phenomenon typical to out-of-band phase conjugation is the generation of phantom paths along which some of the energy in the phase conjugated wave is focused.

On representing and correcting wavefront errors in high-contrast imaging systems

Conventional adaptive-optics systems correct the wavefront by adjusting a deformable mirror (DM) based on measurements of the phase aberration taken in a pupil plane. The ability of this technique, known as phase conjugation, to correct aberrations is normally limited by the maximum spatial frequency of the DM. In this paper we show that conventional phase conjugation is not able to achieve the dark nulls needed for high-contrast imaging. Linear combinations of high frequencies in the aberration at the pupil plane "fold" and appear as low-frequency aberrations at the image plane. After describing the frequency-folding phenomenon, we present an alternative optimized solution for the shape of the deformable mirror based on the Fourier decomposition of the effective phase and amplitude aberrations.

Photorefractive Multi-Beam Induced Phase Conjugation

We demonstrate the simultaneous phase conjugation of multiple beams incident on the a face of a photorefractive barium titanate crystal. The input beam power, angle and position were set so that no phase conjugation occurs unless a switchable incoherent inducing beam is present on the — c face of the crystal. The use of the inducing technique with two mutually pumped phase conjugations for four input beams, or one self-pumped and one mutually pumped phase conjugation for three input beams can be performed in a crystal. Unlike the setup of conventional phase conjugation, which requires more precise arrangements, the novel setup of the multi-beam induced phase conjugation is relatively relaxed. The mechanism responsible for our discovery is qualitatively explained, and possible applications are mentioned.

NONRECIPROCAL OPTICAL SYSTEMS WITH PHASE-CONJUGATING MIRRORS — A NEW CLASS OF OPTICAL IMAGING SYSTEM

A method for removing some of the restrictions imposed in conventional phase conjugation imaging applications is proposed. It provides the possibility of transformation of both the image scale and its distance from the imaging lens system. Theoretical treatments and numerical results for the paraxial as well as the nonparaxial cases are presented, along with experimental demonstrations of the feasibility of this method.