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Journal of the Physical Society of Japan

Total Reflection Enhancement in an Incoherent-Gain Prism Coupler towards Optical Switches and Photonic Transistors

Jian Qi Shen

Published Mar 25, 2014• 2 citations
Publisher

Abstract

An incoherent-gain prism coupler that can lead to enhanced total reflection is suggested by taking full advantage of pumped electric-dipole allowed transition that leads to gain-assisted negative permittivity. The tunable reflection spectrum of the prism coupler is quite sensitive to frequency detuning (e.g., 107 times that in conventional metal-substrate prism couplers) since the incoherent-gain optical response presented here results from atomic dipole-allowed transition. The present gain-assisted prism coupler, which can exhibit an unusual effect of dispersion-sensitive tunable reflection enhancement, has potential applications in design of new quantum optical and photonic devices, e.g., frequency-sensitive optical switches and photonic transistors.

DOI
10.7566/jpsj.83.044401

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An incoherent-gain prism coupler that can lead to enhanced total reflection is suggested by taking full advantage of pumped electric-dipole allowed transition that leads to gain-assisted negative permittivity. The tunable reflection spectrum of the prism coupler is quite sensitive to frequency detuning (e.g., 107 times that in conventional metal-substrate prism couplers) since the incoherent-gain optical response presented here results from atomic dipole-allowed transition. The present gain-assisted prism coupler, which can exhibit an unusual effect of dispersion-sensitive tunable reflection enhancement, has potential applications in design of new quantum optical and photonic devices, e.g., frequency-sensitive optical switches and photonic transistors.
An experimentally feasible configuration of a prism coupler with an electromagnetically-induced-transparency (EIT) medium layer, e.g., a semiconductor-quantum-dot (SQD) medium, deposited upon its prism base is suggested for generating tunable surface-plasmon-polariton resonance. Such surface-plasmon-polariton resonance and optical excitation of a surface plasmon wave can be manipulated by switchable quantum interference among SQD multilevel transitions driven by two external control fields. When an incident probe field is coupled into a surface plasmon wave excitation mode, the surface-plasmon-polariton (SPP) resonance at the interface between the SQD medium layer and the substrate will arise, and the quantum-coherently controllable reflection spectrum of the probe field on the prism base can be achieved. In this process, destructive and constructive quantum interference (determined by the intensity ratio of the two external control fields) in the SQD multilevel system plays a key role for achieving the tunable reflection spectrum. The EIT-based surface-plasmon-polariton resonance presented here will have three characteristics (some of them would be attractive): (i) switchable quantum interference exhibited by surface plasmon wave excitation, (ii) quantum-coherently controllable surface plasmon polaritons by external optical fields, (iii) surface wave sensitive to dispersion of the SQD quantum coherent medium. Such an effect of controllable optical response based on the quantum-interference switchable surface-plasmon-polariton resonance in the EIT-prism coupler may find some potential applications in design of new photonic and quantum optical devices.
A three-dimensionally isotropic negative permeability of a neutral alkali-metal atomic medium, in which a fine-structure magnetic dipole-allowed transition in terahertz band is pumped for population transfer (and hence incoherent gain for negative permeability can be realized), is suggested based on quantum optical approach. The effects relevant to photonic resonance and quantum coherence are involved in the present quantum optical scheme of pumped magnetic-dipole allowed transition. The incoherent-gain assisted atomic medium (with fine-structure transition involved) may have some attractive features, e.g., three-dimensionally isotropic and homogeneous negative permeability for high-gain wave amplification at terahertz frequencies. Such a gain-assisted negative-permeability medium can be a candidate of magnetically resonant materials for artificial composite metamaterials, e.g., it may serve as a substrate of lossy negative-index materials for loss compensation or as a supporting medium for high-gain amplification of a TE-mode surface plasmon-like wave.
We study both the steady and the dynamic optical response of cold atoms trapped in an optical lattice and driven to the three-level $\mathrm{\ensuremath{\Lambda}}$ configuration. These atoms are found to exhibit gain without population inversion when an incoherent pump is applied to activate spontaneously generated coherence. Gain-assisted double photonic band gaps characterized by reflectivities over 100% then grow up near the probe resonance due to the periodic distribution of the atomic density. These band gaps along with the neighboring allowed bands of transmissivities over 100% can be tuned by modulating the control field in amplitude, frequency, and, especially, phase. Consequently it is viable to realize a reflector, an amplifier, or a splitter when a weak incident light pulse is totally reflected in the photonic band gaps, totally transmitted in the allowed bands, or equally reflected and transmitted in the intersecting regions. Our results have potential applications in all-optical networks with respect to fabricating dynamically switchable devices for manipulating photon flows at low-light levels.
Abstract—A scheme of double-negative left-handed atomic vapor medium based on dressed-state assisted simultaneous electric and magnetic resonances is suggested. In this mechanism, simultaneous electric- and magnetic-dipole allowed transitions of atoms are driven by an optical wave by taking full advantage of both mixed-parity dressed-state assisted resonance and incoherent population pumping in a quantum-coherent atomic medium (e.g., alkali-metal atomic vapor). Since the simultaneously negative permittivity and permeability can be achieved in a same frequency band, such an atomic vapor will exhibit an incoherent-gain double-negative refractive index that is three-dimensionally isotropic and homogeneous. The imaginary part of the negative refractive index of the present atomic vapor would be drastically suppressed or would become negative because of loss compensation through incoherent population transfer. The quantum-coherent left-handed atomic vapor presented here will have four characteristics: i) three-dimensionally isotropic and homogeneous negative refractive index, ii) double-negative atomic medium at visible (and infrared) wavelengths, iii) tunable negative refractive index based on dressed-state quantum coherence, and iv) high gain due to incoherent pumping action.
Graphene-assisted resonant transmission and enhanced Goos-Hänchen shift are investigated in a two-prism frustrated-total-internal-reflection configuration. Due to the excitation of surface plasmons induced by graphene in low terahertz frequency range, there exist the resonant transmission and anomalous Goos-Hänchen shifts in such optical tunneling configuration. As compared to the case of quantum well, graphene sheet with unique optical properties can enhance the resonant transmission with relatively low loss, and modulate the large negative and positive Goos-Hänchen shifts by adjusting chemical potential or electron relaxation time. These intriguing phenomena may lead to some potential applications in graphene-based electro-optic devices.
A new scheme for overcoming losses with incoherent optical gain in a quantum-coherent left-handed atomic vapor is suggested. In order to obtain low-loss, lossless or active left-handed media (LHM), a pump fleld, which aims at realizing population inversion of atomic levels, is introduced into a four-level atomic system. Both analytical and numerical results are given to illustrate that such an atomic vapor can exhibit intriguing electric and magnetic responses required for achieving simultaneously negative permittivity and permeability (and hence a gain-assisted quantum-coherent negative refractive index would emerge). The quantum-coherent left-handed atomic vapor presented here could have four fascinating characteristics: i) three-dimensionally isotropic negative refractive index, ii) double- negative atomic medium at visible and infrared wavelengths, iii) high-gain optical ampliflcation, and iv) tunable negative refractive index based on quantum coherent control. Such a three-dimensionally isotropic gain medium with negative refractive index at visible and infrared frequencies would have a potential application in design of new quantum optical and photonic devices, including superlenses for perfect imaging and subwavelength focusing.