Transmission Group Delay Research Articles

Group delay time of fermions in graphene through tilted potential barrier

The group delay time of Dirac fermions subjected to a tilting barrier potential along the $ x $-axis is investigated in graphene. We start by finding the eigenspinor solution of the Dirac equation and then relating it to incident, reflected, and transmitted beam waves. This relationship allows us to compute the group delay time in transmission and reflection by obtaining the corresponding phase shifts. We discovered that the barrier width, incident energy, and incident angle can all be used to modify the group delay time, and that the particles travel through the barrier at the Fermi velocity $ v_F $. Our findings also show that the transmission group delay might be controlled, and that gate voltage control could be useful in graphene-based tilting barriers.

Phase control of the transmission in cavity magnomechanical system with magnon driving

We investigate the coherent control of the transmission spectrum in a cavity magnetomechanical system consisting of microwave photon, magnon, and phonon modes, where the microwave cavity is driven by a strong pump field and a weak probe field, and the magnon is driven by a weak microwave source. Different from a single transparency window in the absence of the phonon–magnon interaction, two transparency windows and three absorption dips can be observed in the presence of the phonon–magnon interaction, which originates from the joint interaction of phonon–magnon and photon–magnon. In addition, two absorption dips located at both sides of the central absorption dip can be modulated asymmetrically into amplification and absorption by varying the magnetic field amplitude of the magnon driving field. Interestingly enough, the relative phase of applied fields could have profound effects on both the transmission spectrum and the group delay of the output field by choosing the appropriate magnetic field amplitude of the magnon driving field. The transmission group delay can be switched between positive to negative and vice versa by adjusting the relative phase between the applied fields. The present results illustrate the potential to utilize the relative phase for controlling the microwave signal in the cavity magnomechanical system, as well as guidance in the design of information transduction and quantum sensing.

Multi-channel optomechanically induced amplification in a parity-time-symmetric Laguerre-Gaussian rovibrational-cavity system

This paper studies the response of a parity-time-symmetric Laguerre-Gaussian-cavity optomechanical system to a weak probe field, where an active cavity is coupled to a Laguerre-Gaussian rovibrational-cavity system. It is shown that three-amplification-peak profile emerges for the probe transmission. The transmission rate can be adjusted by controlling the coupling coefficient, the pump amplitude and the topological charge. Besides, we find that the light transmission group delay can be altered between positive and negative value by adjusting the coupling coefficient and the topological charge. This study can be applied to light propagation manipulation and quantum precision measurement.

Tunable slow and fast light in an atom-assisted optomechanical system

We theoretically investigate the slow and fast light effects of a probe laser in an optomechanical double-ended cavity filled with a bunch of identical two-level cold 87Rb atoms. It is shown that the presence of atoms can transfer the optomechanically induced transparency (OMIT) window into the steeper Fano shapes and the broader normal-mode splitting shapes. We find that the transmission group delay related to the Fano resonance is much greater than that of the OMIT and normal-mode splitting at the resonances, meanwhile, with the growing of the atomic number, the slow light becomes increasingly significant. The value of reflection group delay related to the OMIT and normal-mode splitting is positive, while the value related to the Fano resonance is significantly negative. This indicates that the reflection parts of output field contain both slow light and fast light. Therefore, via changing the atomic number and detuning, we can realize not only the manipulation of the magnitudes of the group delay and advance, but also a tunable switch from slow light to fast light.

Stored Energy, Transmission Group Delay and Mode Field Distortion in Optical Fibers

The relationship between transmission group delay and stored energy in optical fibers is discussed. We show by numerical computations that the group delay of an optical pulse of finite bandwidth transmitted through a piece of a low loss optical fiber of unit length is proportional to the energy stored by the standing wave electromagnetic field. The stored energy-group delay ratio typically approaches unity as the confinement loss converges to zero. In case of a dispersion tailored Bragg fiber, we found that the stored energy-group delay ratio decreased while the confinement loss increased compared to those of the standard quarterwave Bragg fiber configuration. Furthermore, a rapid variation in the group delay versus wavelength function due to mode-crossing events (in hollow core photonic bandgap fibers for instance) or resonances originating from slightly coupled cavities, surface or leaking modes in index guiding, photonic bandgap, or photonic crystal fibers always results in a rapid change in the mode-field distribution, which seriously affects splicing losses and focusability of the transmitted laser beam. All of these factors must be taken into consideration during the design of dispersion tailored fibers for different applications.

Tunable optical properties in engineered one-dimensional coupled resonator optical waveguides

In this paper, the optical properties in finite size tilted and engineered one dimensional coupled resonator optical waveguide have been investigated. The large dependence of the optical transmittance, dispersion parameter and its higher order slope such as transmittance group delay, third order dispersion and intrinsic waveguide induced loss on the oblique incidence and fraction factor, as the ratio of the optical thicknesses of two adjacent layers, have been studied. Our results showed that as a consequence of changing the fraction factor, at normal incidence, photonic band gap zone, flat portion of third order dispersion curve and maximum magnitude of the transmission group delay can be tuned in long range of wavelength (red shift) slightly. Despite of slight tuning the optical properties in one dimensional coupled resonator optical waveguide by changing the fraction factor, incidence angle has a significant large magnitude of tunability in the overall region of operational wavelength. This fact yields us by changing the incidence from 30 to 60, the operational wavelength can be tuned between two main optical communication windows, while by changing the fraction factor, dispersion and its higher order can be fine tuned in each of optical communication windows which are very useful in wavelength division multiplexing systems and planar lightwave circuits.

Adjustable dispersion compensating in one dimensional coupled resonator planar optical waveguides

In this paper, the optical properties in finite size one dimensional coupled resonator optical waveguide are investigated. The large dependence of the group velocity, dispersion parameter and its higher order slope such as transmission group delay, third order dispersion and intrinsic waveguide induced loss have been studied. By engineering the optical contrast ratio of the medium by using some accessible and compatible materials, according to the equivalent layers theory, the above mentioned parameters can either be adjusted or enhanced dramatically, according to the configuration of the optical networks and users’ requirements. Also, by setting proper choice of the optical contrast ratio, super flattening of the transmittance group delay, third order dispersion spectrum and reduced intrinsic waveguide induced loss can be realized. Our results show the potential applications of the device for preventing the satellite pulse creating and transmitting pulse information distortion in multichannel lightwave systems.

Resonance-enhanced group delay times in an asymmetric single quantum barrier

It is shown that transmission and reflection group delay times in an asymmetric single quantum barrier are greatly enhanced by the transmission resonance when the energy of incident particles is larger than the height of the barrier. The resonant transmission group delay is of the order of the quasibound state lifetime in the barrier region. The reflection group delay can be either positive or negative, depending on the relative height of the potential energies on the two sides of the barrier. Its magnitude is much larger than the quasibound state lifetime. These predictions have been observed in microwave experiments.

The reflection and transmission group delay times in an asymmetric single quantum barrier

The reflection and transmission group delay times are systematically investigated in an asymmetric single quantum barrier. It is reported that the reflection times in both evanescent and propagating cases can be either negative or positive, depending on the relative height of the potential energies on the two sides of the barrier. In the evanescent case where the energy of incident particles is less than the height of the barrier, the reflection and transmission times in the opaque limit are both independent of the barrier’s thickness, showing superluminality. On the other hand, in the propagating case where the energy of incident particles is larger than the height of the barrier, the reflection and transmission times as the periodical function of the barrier’s thickness can be greatly enhanced by the transmission resonance. It is also shown that the transmission time and the reflection times for the two propagation directions in the same asymmetric configuration satisfy the reciprocal relation, as consequence of time reversal invariance in quantum mechanics. These phenomena may lead to novel applications in electronic devices.