增益对一维周期结构慢光传输特性影响

本文以一维周期结构为例,对增益与慢光之间的影响做了更进一步的深入研究. 研究发现,增益对有限长和无限长一维周期结构中的慢光效应具有不同的影响. 对无限长结构,增益的加入会减弱结构的慢光效应. 而对于实际应用中存在的有限长周期结构,增益补偿在一定情况下会增强其慢光效应. 文章的研究对促进周期结构作为慢光器件尤其是作为可调谐慢光器件在高密度光子集成中的广泛应用具有积极意义. 关键词： 增益 慢光效应 一维周期结构 有限长     

Slow-light delay enhancement in small-core pure silica photonic crystal fiber based on Brillouin scattering

We demonstrate that we realize large-delay slow light based on stimulated Brillouin scattering in a short length of our fabricated small-core photonic crystal fiber (PCF). The cavity effect from the partially reflective splices in the end of the PCF enhances slow-light delay significantly. Our experiments show that large slow-light delay can be easily realized in a very short length of the PCF with a moderate pump power. Up to a one-half pulse-width delay is achieved in only 50 m of PCF in a single pump segment.     

Expansion of the relative time delay by switching between slow and fast light using coherent population oscillation with semiconductors

The slow-light effect based on free-carrier population oscillation in semiconductors is analyzed using generalized macroscopic Bloch equations. Using this model, we are able to investigate the relation between the fractional time delay and the intensity of control laser beams for semiconductors. It is found that although increasing the control-beam intensity can enlarge the fractional time delay, the maximum delay that can be achieved is limited and determined by a critical value of the separation between the quasi-Fermi levels of electrons and holes. We also show that there is an intensity threshold for the control beam above which the probe signal becomes gain-assisted fast light rather than slow light. We therefore suggest a method to expand the relative time delay by switching between the fast-light region and the slow-light region through changing the intensity of the control laser beams. PACS 42.25.Bs; 42.70.Nq; 42.79.-e     

Slow light in bacteriorhodopsin solution using coherent population oscillations

Slow light is demonstrated in liquid phase in an aqueous bacteriorhodopsin (bR) solution at room temperature. Group velocity as low as 3 m/s (all the way to c) is achieved by exploiting the photoisomerization property of bR for coherent population oscillations. Slow light in the liquid phase offers several advantages over solids or vapors for a variety of applications: (i) shorter lifetimes of the M state facilitate slow light at higher modulation frequencies, (ii) convection makes it possible to obtain large signal delays even at high input powers, and (iii) solution concentration is another convenient parameter to vary the signal delay over a wide range.     

Nonlinear performance in silicon nitride slow light photonic crystal waveguides with elliptical holes

We propose a slow-light photonic crystal waveguide, which uses a combination of circular and elliptical air holes arranged in a hexagonal lattice with the background material of silicon nitride (refractive index n = 2.06). Large value of normalized delay bandwidth product (NDBP = 0.3708) is obtained. We have analyzed nonlinear performance of the structure. With our proposed geometry strong SPM is observed at moderate peak power levels. Proposed photonic crystal waveguide has slow light applications such as reduction in length and power consumption of all-optical and electro-optic switches at optical frequency.     

Data pulse distortion induced by a slow-light tunable delay line in optical fiber

We experimentally demonstrate an all-optical tunable delay line based on slow light induced by stimulated Brillouin scattering in a highly nonlinear fiber (HNLF) and study the distortion of data pulses with different pulse widths and the induced pattern-dependent distortion on non-return-to-zero data in slow-light systems.     

Light storage via slow-light four-wave mixing

We experimentally demonstrate a light storage via slow-light four-wave mixing in a solid-state medium with a four-level double lambda scheme. Using slow light based on electromagnetically induced transparency, we obtain a slowed four-wave mixing signal pulse together with the slowed probe pulse. During the propagation of light pulses, the storage and retrieval of both the slowed four-wave mixing pulse and the slowed probe pulse are studied by manipulating the intensities of the control fields.     

Slow-light optical bullets in arrays of nonlinear Bragg-grating waveguides

We demonstrate that propagation direction and velocity of optical pulses can be controlled independently in the structures with multiscale modulation of the refractive index in transverse and longitudinal directions. We reveal that, in arrays of waveguides with phase-shifted Bragg gratings, the refraction angle does not depend on the speed of light, allowing for efficient spatial steering of slow light. In this system, both spatial diffraction and temporal dispersion can be designed independently, and we identify the possibility for self-collimation of slow light when spatial diffraction is suppressed for certain propagation directions. We also show that broadening of pulses in space and time can be eliminated in nonlinear media, supporting the formation of slow-light optical bullets that remain localized irrespective of propagation direction.     

Spinor slow-light and dirac particles with variable mass

We consider the interaction of two weak probe fields of light with an atomic ensemble coherently driven by two pairs of standing wave laser fields in a tripod-type linkage scheme. The system is shown to exhibit a Dirac-like spectrum for light-matter quasiparticles with multiple dark states, termed spinor slow-light polaritons. They posses an "effective speed of light" given by the group velocity of slow light, and can be made massive by inducing a small two-photon detuning. Control of the two-photon detuning can be used to locally vary the mass including a sign flip. Particularly, this allows the implementation of the random-mass Dirac model for which localized zero-energy (midgap) states exist with unusual long-range correlations.     

Slow-light enhanced correlated photon pair generation in a silicon photonic crystal waveguide

We report the generation of correlated photon pairs in the telecom C-band at room temperature from a dispersion-engineered silicon photonic crystal waveguide. The spontaneous four-wave mixing process producing the photon pairs is enhanced by slow-light propagation enabling an active device length of less than 100?μm. With a coincidence to accidental ratio of 12.8 at a pair generation rate of 0.006 per pulse, this ultracompact photon pair source paves the way toward scalable quantum information processing realized on-chip.     

基于受激布里渊散射的新型多级慢光延时结构的研究

设计了一种基于受激布里渊散射(SBS)的新型多级慢光延时结构.该多级延时结构将两段慢光延时介质用两个环形器相连接,使经过一级延时后剩余的抽运光经过环形器进入到第二段慢光延时介质中作为二级延时的抽运.该结构与传统的多级慢光延时结构相比,不需要为每段延时介质提供独立的抽运系统,结构简单,抽运光利用率高,延时效果显著.实验选...     

Tunable all-optical delays via Brillouin slow light in an optical fiber

We demonstrate a technique for generating tunable all-optical delays in room temperature single-mode optical fibers at telecommunication wavelengths using the stimulated Brillouin scattering process. This technique makes use of the rapid variation of the refractive index that occurs in the vicinity of the Brillouin gain feature. The wavelength at which the induced delay occurs is broadly tunable by controlling the wavelength of the laser pumping the process, and the magnitude of the delay can be tuned continuously by as much as 25 ns by adjusting the intensity of the pump field. The technique can be applied to pulses as short as 15 ns. This scheme represents an important first step towards implementing slow-light techniques for various applications including buffering in telecommunication systems.     

Observation of ultraslow light propagation in a ruby crystal at room temperature

We have observed slow light propagation with a group velocity as low as 57.5+/-0.5 m/s at room temperature in a ruby crystal. A quantum coherence effect, coherent population oscillations, produces a very narrow spectral "hole" in the homogeneously broadened absorption profile of ruby. The resulting rapid spectral variation of the refractive index leads to a large value of the group index. We observe slow light propagation both for Gaussian-shaped light pulses and for amplitude modulated optical beams in a system that is much simpler than those previously used for generating slow light.     

High sensitive and large dynamic range quasi-distributed sensing system based on slow-light π-phase-shifted fiber Bragg gratings

In this paper, we theoretically analyze the slow-light π-phase-shifted fiber Bragg grating (π-FBG) and its applications for single and multipoint/quasi-distributed sensing. Coupled-mode theory (CMT) and transfer matrix method (TMM) are used to establish the numerical modeling of slow-light π-FBG. The impact of slow-light FBG parameters, such as grating length (L), index change (Δn), and loss coefficient (α) on the spectral properties of π-FBG along with strain and thermal sensitivities are presented. Simulation results show that for the optimum grating parameters L = 50 mm, Δn = 1.5×10⁻⁴, and α = 0.10 m^-1, the proposed slow-light π-FBG is characterized with a peak transmissivity of 0.424, the maximum delay of 31.95 ns, strain sensitivity of 8.380 με^-1, and temperature sensitivity of 91.064 °C^-1. The strain and temperature sensitivity of proposed slow-light π-FBG is the highest as compared to the slow-light sensitivity of apodized FBGs reported in the literature. The proposed grating have the overall full-width at half maximum (FWHM) of 0.2245 nm, and the FWHM of the Bragg wavelength peak transmissivity is of 0.0798 pm. The optimized slow-light π-FBG is used for quasi-distributed sensing applications. For the five-stage strain quasi-distributed sensing network, a high strain dynamic range of value 1469 με is obtained for sensors wavelength spacing as small as 2 nm. In the case of temperature of quasi-distributed sensing network, the obtained dynamic range is of 133 °C. For measurement system with a sufficiently wide spectral range, the π-FBGs wavelength grid can be broadened which results in substantial increase of dynamic range of the system.     

Third-harmonic generation in slow-light chalcogenide glass photonic crystal waveguides

We demonstrate third-harmonic generation (THG) in a dispersion-engineered slow-light photonic crystal waveguide fabricated in AMTIR-1 chalcogenide glass. Owing to the relatively low loss and low dispersion in the slow-light (c/30) regime, combined with the high nonlinear figure of merit of the material (～2), we obtain a relatively large conversion efficiency (1.4×10(-8)/W(2)), which is 30× higher than in comparable silicon waveguides, and observe a uniform visible light pattern along the waveguide. These results widen the number of applications underpinned by THG in slow-light platforms, such as the direct observation of the spatial evolution of the propagating mode.     

Numerical study on SBS slow light systems using a super-Gaussian filtered incoherent pump

We numerically investigate the performance improvement and its limitations using super-Gaussian filtered incoherent pumping in Stimulated Brillouin Scattering (SBS) slow light systems, especially for 2.5-Gb/s return-to-zero (RZ) OOK data streams. As compared to regular Gaussian filtering schemes, super-Gaussian filters can reduce the signal broadening without sacrificing the generated delay. On the other hand, although the figure-of-merits (FOM) in terms of the normalized delay and signal Q-factor products can be improved as well, additional sub-pulses may appear and subsequently the curve of FOM versus slow-light bandwidth exhibits a fluctuated behavior.     

Bragg reflection waveguide: Anti-mirror reflection and light slowdown

The effect of the light group velocity reduction in dielectric Bragg reflection waveguide structures (SiO₂/TiO₂) in the vicinity of the cutoff frequency is studied experimentally. The effect of anti-mirror reflection specific to Bragg reflection waveguides is described and employed to detect slow light. Experiments were performed using Ti:sapphire laser pulses ∼100 fs in length. The group index n _g ∼ 30 with a fractional pulse delay (normalized to the pulse width) of ∼10 is demonstrated. The problems and prospects of the implementation of slow-light devices based on Bragg reflection waveguide structures are discussed.     

Slow-light spatial solitons

We numerically and experimentally report the observation of slow-light spatial solitons in a Kerr medium owing to light amplification by stimulated Raman scattering. This was achieved in a CS2 nonlinear planar waveguide that possesses both a strong self-focusing nonlinearity to generate the spatial Raman soliton and a Raman susceptibility sharp enough to induce the slow-light process simultaneously. We show that the Raman Stokes component is optically delayed by more than 120 ps for a 140 ps Raman pulse duration and only 3 cm of propagation length, while propagating as a spatial soliton beam.     

Low power penalty tunable slow light using vertical-cavity surface-emitting laser amplifier

A tunable slow light of 2.5-Gb/s pseudo-random binary sequence signal using a 1550-nm vertical-cavity surface-emitting laser (VCSEL) is experimentally demonstrated. The influences of the bias current and the gain saturation on the slow light are investigated. With bias current increasing, tunable optical group delay up to 98 ps is obtained at room temperature. Demonstration of the time delay between 16 and 24 ps by signal intensity change is reported. Under an appropriate bias current, by tuning the input signal to track the peak gain wavelength of the VCSEL, slow light of a power penalty as low as 1 dB is achieved. With such a low power penalty, the VCSEL has a great potential application as a compact optical buffer.     

High-sensitive refractive index sensing and excellent slow light based on tunable triple plasmon-induced transparency in monolayer graphene based metamaterial

A patterned monolayer graphene metamaterial structure consisting of six graphene blocks and two graphene strips is proposed to generate triple plasmon-induced transparency(PIT).TriplePIT can be effectively modulated by Fermi levels of graphene.The theoretically calculated results by coupled mode theory show a high matching degree with the numerically simulated results by finite-difference time-domain.Intriguingly,the high-sensitive refractive index sensing and excellent slow-light performance ca...