Detection Of Optical Phase Modulation Research Articles

Utilizing phase memory of a two-level quantum system for adaptive homodyne detection of optical phase modulation

We propose to use phase memory of an ensemble of two-level centers, irradiated by the resonantly tuned detected signal wave, for homodyne interferometric detection of fast optical phase modulation. Collinearly propagating dipole radiation of the excited two-level centers acts as a coherent reference wave (local oscillator) necessary to transform the phase modulation into the amplitude modulation behind the resonant medium. The phase of this radiation follows the average phase of the incident detected wave with the characteristic transverse relaxation time T2 that ensures adaptive properties of this interferometric detection configuration to slowly varying environmental conditions. We present experimental demonstration with the acetylene-filled hollow-core microstructured optical fibers at a wavelength of 1530.37 nm of the acetylene P9 absorption line, which is inside the telecommunications wavelengths range. It is shown that the response is quadratic when the acetylene ∼500 MHz inhomogeneously broadened absorption line is excited in its center, but can be essentially linearized for excitation at one of the line sides.

Adaptive Sagnac interferometer with dynamic population grating in saturable rare-earth-doped fiber

Sagnac fiber interferometer with the dynamic population grating formed in the rare-earth doped fiber is proposed for homodyne adaptive detection of optical phase modulation. The configuration is shown to be a simple all-optical fiber sensor suitable for linear high sensitivity detection of mechanical vibrations, acoustic signals, thermo-optic effect etc. Theoretical consideration shows that the quadratic response of this interferometric configuration associated with the amplitude dynamic grating is observed in the reflected wave mainly, while the recorded phase grating results in the linear energy exchange between the transmitted and reflected from the Sagnac loop light waves. Experiments with the erbium- and ytterbium-doped fiber based adaptive Sagnac configurations (with the operation wavelengths 1485 and 1,064 nm respectively) of the fiber accelerometers confirmed these general conclusions and demonstrated sensitivity of the fiber based interferometric configurations (~3 10⁻⁵ rad/Hz¹/²) governed basically by the noise of the utilized lasers.

Polarization insensitive homodyne detection of optical phase modulation by two-wave mixing in saturable Er-doped fiber

We report linear polarization-insensitive detection of optical phase modulation in an adaptive interferometer based on transient two-wave mixing via dynamic population gratings in saturable Er-doped fiber (EDF). The proposed simple and robust configuration has an all-fiber design based on commercially available elements which makes it promising for applications in optical fiber interferometric sensors and coherent optical communication systems. The experimentally investigated single-mode polarization-maintaining EDF arrangement operated at 1492 nm and demonstrated efficient compensation of the polarization drifts below 100 Hz.

Adaptive polarization-insensitive detection of optical phase modulation with a single detector

A single-detector adaptive configuration for polarization-insensitive homodyne detection of optical phase modulation is proposed. Experiments were performed at a HeNe laser wavelength ( λ=633 nm) and employed GaAs photo-EMF adaptive detectors. It has been shown that residual fluctuations in the output signal are basically due to nonlinearity of the adaptive photodetector response to the intensity of the polarization-modulated signal wave.