Phase Shift Cancellation Research Articles

Nonlinear Phase-Shift Cancellation by Taking the Geometric Mean of WDM-Signal Phase-Conjugate Pair

Nonlinear Phase-Shift Cancellation by Taking the Geometric Mean of WDM-Signal Phase-Conjugate Pair

Optical diversity transmission using WDM signal and phase-conjugate lights through multi-core fiber.

This paper proposes a maximum-ratio combining (MRC) scheme for a WDM signal and phase-conjugate pair (PCP) diversity transmission to cancel nonlinear phase-shift. A transfer function approximation for nonlinear phase-shift cancellation is formulated. It shows, with the help of a numerical calculation, that span-by-span chromatic dispersion compensation is more effective than the lumped equivalent at the receiver. This is confirmed in a 2-core diversity 5 channel WDM transmission experiment over 3-spans of 60km MCF with 25 Gbit/s-QPSK PCP. The peak Q-value was enhanced by 3.6dB through MRC, resulting in superior bitrate-distance product and optical power density limit, compared to twice the single core transmission.

Wave-function analysis of dynamic cancellation of ac Stark shifts in optical lattice clocks by use of pulsed Raman and electromagnetically-induced-transparency techniques

We study analytically the dynamic cancellation of ac Stark shift in the recently proposed pulsed electromagnetically-induced-transparency (EIT-)Raman optical lattice clock based on the wave-function formalism. An explicit expression for the time evolution operator corresponding to the effective two-level interaction Hamiltonian has been obtained in order to explain the atomic phase shift cancellation due to the ac Stark shift induced by the time-separated laser pulses. We present how to determine an optimum value of the common detuning of the driving fields at which the atomic phase shift cancels completely with the parameters for the practical realization of the EIT-Raman optical lattice clock with alkaline-earth-metal atoms.

Characterization of SiOxNy anti-reflective coatings using SIMS and RBS/HFS

Silicon oxynitride films formed using low-temperature plasma-enhanced chemical vapor deposition (PECVD) are being investigated as anti-reflective coatings (ARC) for deep- ultraviolet (DUV) photolithography. SiOxNy films reduce undesirable substrate reflections by phase-shift cancellation that is dependent on the film refractive index, extinction coefficient, and film thickness. The accurate characterization of these films is necessary in order to maintain quality control over the process. The challenge presented to the process engineers and metrologists is to use a standardized protocol for a high degree of accuracy and reproducibility in composition while achieving optimal depth resolution. A protocol based on combining the strengths of multiple techniques was investigated. Specifically, the quantitative nature of Rutherford backscattering spectrometry (RBS) and hydrogen forward scattering (HFS) was desired while the depth resolution and detection limits of low energy, quadrupole secondary ion mass spectroscopy (SIMS) was necessary. Several SiOxNy films, 10–30 nm thick, were deposited on p-type 〈100〉 Si and analyzed using RBS, HFS, and SIMS. The average composition of the films from RBS and HFS were used to normalize the depth profiles of the SIMS analysis for a comprehensive analysis of the H, N, O and Si concentrations. This multiple technique approach overcomes the weaknesses of each technique and provides a higher level of quantification and reproducibility than either technique alone.

Formal theory of equivalent potentials in solids: II. Scattering theory approach for muffin-tin potentials

Different equivalent potentials variously proposed for muffin-tin ionic potentials in solids are described in a unified manner as obeying a conservation condition for the scattering amplitudes. This condition is the basis of a reformulation of the problem in which a projector operator method is used to generate different families of equivalent potentials. When the projectors are constructed with bound and scattering states, one obtains the orthogonalized plane wave pseudopotentials. When these are in and out projectors in real space, with respect to the muffintin spheres, one obtains the augmented plane wave effective potentials. It is shown that the plane wave representation of the generator of this family yields the Slater effective potential. A special choice consisting of eliminating the potential inside, while leaving the right surface value to ensure matching, yields the Ziman pseudopotential, whose precise relationship with Slater's is thus established. A quantitative theory of phase shift cancellation is proposed and applied to perform a phase shift analysis of the orthogonalized plane wave pseudopotentials. It is shown that the number of multiples of π deducted from the trace of the phase shift operator is equal to the number of pseudo-bound energy levels (of the pseudo-Hamiltonian) which lie above the energy level under study.