Signal beam

About: Signal beam is a research topic. Over the lifetime, 1881 publications have been published within this topic receiving 20717 citations.

Positional deviation detecting method

Abstract: A method of detecting a relative positional deviation of a first object having a first grating mark with an optical power and a second object having a second grating mark with an optical power, is disclosed, wherein a projected radiation beam is diffracted by the first and second grating marks in sequence and, on the basis of a position of convergence on a light receiving surface of plural diffraction beams produced by the diffraction through the first and second grating marks and including a signal beam having been diffracted at a predetermined order by each of the first and second grating marks, the relative positional deviation is determined, a detection zone is defined on the light receiving surface, the signal beam is converged upon the detection zone, and a predetermined diffraction beam of the plural diffraction beams which, for a relative positional deviation of the first and second objects, shows displacement different from that of the signal beam is substantially prevented from being converged upon the detection zone.

Optically switched volume holographic elements

Abstract: We optically switched the diffraction efficiency of volume holographic elements recorded in DMP-128 photopolymer by use of a thermal nonlinearity of the liquid crystal 5CB. The liquid crystal was incorporated into the volume grating. The diffraction efficiency of small areas of the grating was switched with a control beam power of several milliwatts. The intensity of a signal beam at a different wavelength and arbitrary power was switched with time constants below 1 ms.

Polarization diversity optical heterodyne receiver with phase adjustment of two i.f. signals for control of a local optical source

Abstract: Two intermediate frequency signals, which are used in a polarization diversity optical heterodyne receiver operable according to demodulation and subsequent combination and have a common intermediate signal frequency variable in an intermediate frequency range, are subjected to delaying (21) relative to each other and then combined (23) into a combined intermediate frequency signal. A frequency discriminator (24) discriminates the intermediate signal frequency of the combined intermediate frequency signal to produce a control signal for use in stabilizing a local optical frequency (14) of a local beam used in combination with a signal beam (11) susceptible to polarization fluctuation. A delay may be given for the delaying to one of the two intermediate frequency signals alone. Alternatively, a delay may be given for the delaying to only one of two local beam components which are coupled to two signal beam components for use in producing the two intermediate frequency signals.

Bistability and symmetry breaking in distributed coupling of counterpropagating beams into nonlinear waveguides

Abstract: By using a modal approach, the distributed coupling of two inhomogeneous, transient waves with opposite angles of incidence into nonlinear waveguides is studied. We show that cross modulation and the coherent interaction via a dynamic grating, nonlinearily induced by the excited counterpropagating leaky waves, provide a longitudinal feedback. This feedback is the necessary prerequisite for bistability to occur. We show that bistability may even appear when one incident beam is weak. Consequently, modulation of the strong signal beam by a weak control pulse can be achieved. Furthermore, we demonstrate that the symmetry of the input signal can be broken beyond a certain intensity and that set-reset flip-flop operation with finite beams is feasible. We demonstrate that the mechanism responsible for this flip-flop operation differs considerably from that acting in the plane-wave case. The optical nonlinearities may be caused by either virtual or real carrier excitation, which models the behavior of semiconductors as well as nonlinear polymers or organic dyes well below or close to a resonance, respectively. For real carrier excitation the interplay of carrier relaxation, diffusion, and the propagation of the excited fields is taken into account.

Four-wave mixing in alexandrite crystals

Abstract: : Degenerate four-wave mixing was observed in alexandrite crystals (BeAl2O4:Cr3+), and the signal beam efficiency and decay rate were measured as functions of pump beam-crossing angle, wave-length, and power. The results are consistent with scattering from excited-state population gratings related to the difference in despersion of the Cr3+ ions in the ground and metastable states. These gratings can be selectively established with Cr3+ ions in the inversion or mirror sites depending on excitattion wavelength. Strong scattering occurs only for pump beams polarized parallel to the b direction of the crystal. Originator- supplied keywords include: Lasers, Alexandrite, Non-Linear Optics.