Relative Optical Phase Research Articles

ON/OFF phase shift keying for chaos-encrypted communication using external-cavity semiconductor lasers

Synchronization phenomena of two chaotically emitting semiconductor lasers subject to delayed optical feedback are investigated. The lasers are unidirectionally coupled via their optical fields. Our experimental and numerical studies demonstrate that the relative optical feedback phase is of decisive importance: a characteristic synchronization scenario evolves under variation of the relative optical-feedback phase mediating cyclically between chaos synchronization in conjunction with coherent fields, and uncorrelated states in conjunction with incoherent fields. As a key result, we propose, and numerically demonstrate, a novel ON/OFF phase shift keying method opening up new perspectives for applications in communication systems using chaotic carriers.

Conditional-Phase Switch at the Single-Photon Level

We present an experimental realization of a two-photon conditional phase switch, related to the " c-phis;" gate of quantum computation. This gate relies on quantum interference between photon pairs and generates entanglement between two optical modes through the process of spontaneous parametric down-conversion (SPDC). The interference effect serves to enhance the effective nonlinearity by many orders of magnitude, so it is significant at the quantum (single-photon) level. By adjusting the relative optical phase between the classical pump for SPDC and the pair of input modes, one can impress a large phase shift on one beam which depends on the presence or absence of a single photon in a control mode.

Measurement of the relative optical phase between amorphous and crystalline regions of the phase-change media of optical recording

We describe a method of measuring the relative optical phase on reflection between amorphous and crystalline regions of the phase-change media of optical data storage. With a red He-Ne laser (wavelength, 632.8 nm) the relative phases on two quadrilayer optical disk stacks were measured and found to be ~40 degrees . The results are in good agreement with the calculated values based on the known layer thicknesses and refractive indices of the stacks. For calibration purposes the height of a known step on an otherwise flat silicon substrate was measured with the same apparatus. The proposed method is fairly simple to set up, can measure both front-surface and through-substrate types of optical disk, and can be used with any laser that has long coherence length.

Polarization-locked temporal vector solitons in a fiber laser: experiment

We experimentally observe polarization-locked vector solitons in a passively mode-locked fiber laser. The vector soliton pulse is composed of components along both principal polarization axes of the linearly birefringent laser cavity. For certain values of birefringence and pulse energy these components propagate with a constant relative optical phase of ±π/2, and hence the pulse has a fixed elliptical polarization state. The linear birefringence of the cavity is canceled by the nonlinear birefringence created by the unequal amplitudes of the two polarization components. This dynamic equalization of the phase velocities of the components results in the stable propagation of an elliptically polarized vector soliton pulse. Under different conditions we also observe the nonlinear instability of the fast principal axis as an intracavity pulse linearly polarized along the slow axis of the cavity. We present the experimental characterization of both the polarization-locked vector soliton and the fast axis instability and discuss the nonlinear mechanism creating both phenomena.

Femtosecond Material Response Probed by Phase-Stabilized Optical Heterodyne Detected Impulsive Stimulated Raman Scattering

Femtosecond material response of several liquid samples were measured with use of a newly developed “phase-stabilized” optical heterodyne detected impulsive stimulated Raman scattering (ISRS) spectrometer. In this apparatus, the ISRS signal generated with ordinary transient grating geometry is mixed with femtosecond optical pulses (local oscillator, LO) in an interferometer, and the interfered intensity is detected. The subwavelength-accuracy adjustment/stabilization is achieved for the optical path length in the interferometer so that the relative optical phase between the ISRS signal and LO can be controlled. The ISRS signals linearized to each tensor element of the third-order response function were obtained, and discussed.

Phase-stabilized optical heterodyne detection of impulsive stimulated Raman scattering

An optical heterodyne detection of impulsive stimulated Raman scattering (ISRS) has been carried out for liquid samples using a 50 fs mode-locked Ti:sapphire laser as a light source. In this measurement, the optical path length in the interferometer was actively adjusted while monitoring the interference of a reference laser so that the relative optical phase between the ISRS signal and the local oscillator was stabilized. This method enabled us to obtain the ISRS signals which are linearized to the third-order material response function. The changes in the ISRS signal with the change of the heterodying phase and the polarization condition are discussed.

Routes to control of intense-field atomic polarizability.

When atoms or molecules interact with intense bichromatic laser light, the relative optical phase between the two colors influences the formation of an electron wave packet in the continuum, further motion of the wave packet, and the phase accumulated by the wave packet on its trajectory. We show how the control over the wave packet motion can be used to generate single subfemtosecond pulses in the extreme ultraviolet spectral region. We also demonstrate control over the phase of the atomic polarizability.

On the preparation and measurement of superpositions of chiral amplitudes

We examine the preparation and detection of superpositions of chiral amplitudes of a handed molecule, showing that specific sequences of phase-controlled ultrashort light pulses enable the preparation and measurement of chiral coherences. It is found that certain choices of relative optical phase between the pulses of the preparation sequence set up left–right superpositions that would be inaccessible by tunneling dynamics alone.

Many-port homodyne detection of an optical phase.

We present a quantum analysis of the measurement of a relative optical phase using a many-port method that can be implemented using arrays of photodetectors in the limit of a large number of detector elements. Its application to coherent states and states not describable by the semiclassical theory shows that the many-port method has in principle several advantages compared to an eight-port method previously studied. In some cases, especially for very weak fields, the many-port method provides a more faithful characterization (i.e., a smoother distribution) of the distribution of the relative phase than does the eight-port method. The definition used here for the relative phase between two fields is an operational one, not corresponding to any presently known Hermitian phase operator. We discuss the conditions under which our phase definition corresponds to the best estimate in the maximum-likelihood sense. We find that if the many-port data set is analyzed in a way that retains the contributions from zero photon counts, the many-port phase distribution takes on a character that resembles other phase distributions, such as the Pegg-Barnett or Wigner phase distributions, that show very small modulation depth in the case of weak fields.

Phase-sensitive 3.39 μm Doppler interferometer

The phase-sensitive 3.39 μm Doppler interferometer is designed to make relative optical phase measurements by permitting measurements of optical phase independent of the source amplitude fluctuations. This interferometer utilizes a Doppler shifting technique to produce relative optical path length information from the optical component under test. This information is in the form of phase differences between two audio frequencies. These phase differences are sensed and displayed by a high-resolution zero crossing electronic phase meter. The phase angle displayed is directly correlated with the optical phase difference between the sample and the reference beam. Normal laboratory environment accuracy of the instrument is λ/16 at 3.39 μm.