Co-propagation Scheme Research Articles

Investigating transfer of coherence, direction of light propagation and Rydberg blockade in a four-level [formula omitted]-type system under linear and nonlinear interaction regimes

This theoretical study reveals that the transfer of coherence (TOC) and the direction of light propagation vector play a crucial role in transitioning from electromagnetically induced transparency (EIT) to electromagnetically induced absorption (EIA) in a four-level closed and open cascade (Ξ)-type light-atom interacting systems (LAIS) under both linear as well as nonlinear interaction regimes. It is found that the amplitudes of the coherence signals are distinctly influenced by the system’s openness driven by the presence of additional dipole allowed levels not connected by the lasers and the type of interaction regimes. The effect of TOC on the EIT to EIA transition is discussed in detail by the velocity-dependent dressed state analysis and velocity mapping of the probe absorption coefficient. The findings also reveal that the efficiency of the counter-propagation scheme of the coupling fields is higher than the co-propagation scheme. Furthermore, we have estimated the Rydberg blockade effect on the probe absorption profiles for some specific velocity groups of atoms, which exhibit probe gain in the medium along with EIT and EIA patterns.

Crosstalk-Aware Counter-Propagating Core Assignment to Reduce Inter-Core Crosstalk and Capacity Wastage in Multi-Core Fiber Optical Networks

Inter-core crosstalk causes serious signal impairment in a multi-core fiber (MCF) optical network. With the extensive usage of data centers, traffic demands become increasingly asymmetric, leading to significant overall capacity wastage if the network is designed with bidirectional links. To alleviate these effects in an MCF optical network, we consider assigning the fiber cores asymmetrically, in a counter-propagating manner. This not only reduces the inter-core crosstalk between counter-propagating fiber cores significantly but also allows the flexibility of assigning different numbers of fiber cores in the opposite directions of a fiber link, thereby avoiding network capacity wastage arising from bidirectional traffic demand asymmetry. To evaluate the benefits of the proposed strategy, we consider the routing, spectrum, and core assignment (RSCA) problem for the MCF optical network. An integer linear programming (ILP) model and an auxiliary graph based heuristic algorithm are developed to optimize network spectrum resource utilization. Simulation studies show the effectiveness of the proposed crosstalk-aware core counter-propagation strategy, which can significantly outperform its counterpart, i.e., the co-propagation scheme, in terms of the total number of MCFs used and average inter-core crosstalk. In addition, the proposed RSCA heuristic algorithm is efficient to perform close to the ILP model, which can minimize the number of MCFs used and crosstalk between neighboring cores.

Resonant nonlinearity enhancement in rubidium vapor with additional optical pumping

We investigate the enhancement of characteristic nonlinear phase shift in warm rubidium vapor for a signal beam using an additional pump laser at different frequency. A numerical model based on density matrix formalism is used. Experimental results of self-rotation and diffraction in a three-wave mixing process as well as beam amplification are shown. For 87Rb transition D2 line with Fg = 1, the nonlinearity to absorption ratio can be enhanced approximately two times with a pump beam tuned at Fg = 2 transition in a co-propagating scheme, which produces strong nonlinear interaction for Fg = 1 line at signal beam powers of ~10 mW.

Single WDM channel efficient wavelength shifting and/or amplification using counterpropagating optical parametric amplifiers

We theoretically and numerically study the difference frequency generation and the signal amplification bandwidth together with the pump wavelength acceptance for counterpropagating optical parametric amplifiers. It is shown that the specific advantage of those amplifiers is that the DFG and amplification bandwidth is much narrower than in a co-propagating scheme, thus making it possible to shift spectrally or to amplify selectively a single channel over the several present in WDM optical fiber communications. Moreover, the pump wavelength acceptance is shown to be as broad as in the co-propagating scheme. The implementation of such counterpropagating optical parametric amplifiers in a quasi-phase-matched LiNbO3 waveguide is discussed.

A novel approach to all-optical wavelength conversion by utilizing a reflective semiconductor optical amplifier in a co-propagation scheme

Nonlinear optical gain modulation in an InGaAsP/InP bulk reflective semiconductor optical amplifier (RSOA) is studied. The differences of the optical properties between RSOAs and conventional SOAs are initially investigated. All-optical wavelength conversion based on nonlinear gain modulation in RSOAs is demonstrated at a bit rate of 2.488Gbit/s. It is shown that a bit-error-rate of <10−9 can be achieved and an extinction ratio of >9dB can be obtained at a bit rate of 2.488Gbit/s with a 231–1 non-return-to-zero (NRZ) pseudorandom bit sequence (PRBS). In comparison with conventional SOAs, wavelength conversion by RSOAs shows much improved performances in high-speed all-optical wavelength conversions.

Experimental and Numerical Small-Signal Analysis of Two Types of Gain-Clamped Semiconductor Optical Amplifiers

The behavior of two types of gain-clamped semiconductor optical amplifiers under small-signal optical modulation is analyzed both numerically and experimentally. The small-signal gain as well as the crosstalk is investigated in two different injecting schemes. Dependence on mean input power and signal frequency is studied. The study reveals a strong dependence of the small-signal gain on the direction of the data signal as compared to the pump signal. The biggest difference between both amplifier types is found in the co-propagation scheme where the RF gain shows a clear resonance in the case the gain clamping is achieved by a longitudinal laser field which results in a decrease of the small-signal gain around the resonance frequency. The behavior of the crosstalk is similar in both cases, however still showing differences due to the origin of the gain clamping, which will be discussed. The experiments confirm the results found in the numerical study in all cases.

Measurement of intrinsic dynamics of SOA using outband optical modulation

A parasitic-free technique using outband optical modulation for measuring a semiconductor optical amplifier&apos;s (SOA&apos;s) dynamic response is proposed. It is demonstrated that a counter-propagating scheme is useful in measuring the carrier lifetimes and the response obtained with a co-propagating scheme includes the transmission function of an SOA.

Electro-optic sampling of single electron beam bunches of ultrashort duration

The effect of ultrafast electron beam bunch dynamics on single shot electro-optic sampling detection schemes is examined. It is shown that ultrashort electron bunch fields of adequate magnitude can dynamically impose additional bandwidth on laser probe pulses. The significance of this effect is evaluated by comparing the dynamics of the laser probe to that of the nonradiative field of a single electron bunch for a given crystal material. Dynamic effects can be distinguished with ultrafast temporal resolution of the transmitted probe spectrum. Furthermore, velocity matching of probe and bunch fields in a co-propagation scheme is less restrictive. Such time resolved spectra then can noninvasively determine single bunch dynamics and represent a new type of electro-optic sampling.

Studies of two-wave mixing of very broad-spectrum laser light in BaTiO_3

We present theoretical and experimental studies of the process of two-wave mixing of broadband radiation in BaTiO3. We show that the energy exchange in such a process can be calculated on the basis of a system of coupled-wave equations in which phase-mismatch diffraction processes are taken into account. Good agreement of the model predictions and measurements performed with a variable-bandwidth Ti:sapphire laser is reported. Reasonable amplification of light with a FWHM spectrum of as much as 10 nm is reported in a standard copropagation scheme; above this value a considerable gain decrease and significant spatial profile changes occur.