硅基波导慢光器件及其应用

硅基波导慢光器件是构建全光智能互连和实时高速测控等下一代信息技术的关键器件,在光通信和光信息处理等诸多领域具有显著的技术优势和巨大的应用潜力.随着器件结构的不断创新以及微电子制造技术的不断升级换代,硅基波导慢光器件愈来愈走向实用化.文章介绍了慢光的基本原理,概述了当前国内外硅基波导慢光器件的研究进展,着重分析了基于微环谐振腔的硅基波导慢光器件,并指出了它在具体应用领域中的发展前景.     

Slow-light enhanced optical forces between longitudinally shifted photonic-crystal nanowire waveguides

We reveal that slow-light enhanced optical forces between side-coupled photonic-crystal nanowire waveguides can be flexibly controlled by introducing a relative longitudinal shift. We predict that close to the photonic band edge, where the group velocity is reduced, the transverse force can be tuned from repulsive to attractive, and the force is suppressed for a particular shift value. Additionally the shift leads to symmetry breaking that can facilitate longitudinal forces acting on the waveguides, in contrast to unshifted structures where such forces vanish.     

Enhanced stimulated Raman scattering in slow-light photonic crystal waveguides

We investigate for the first time, to our knowledge, the enhancement of the stimulated Raman scattering in slow-light silicon-on-insulator (SOI) photonic crystal line defect waveguides. By applying the Bloch-Floquet formalism to the guided modes in a planar photonic crystal, we develop a formalism that relates the intensity of the downshifted Stokes signal to the pump intensity and the modal group velocities. The formalism is then applied to two prospective schemes for enhanced stimulated Raman generation in slow-light photonic crystal waveguides. The results demonstrate a maximum factor of 104(66,000) enhancement with respect to SOI channel waveguides.     

Induced transparency in nanoscale plasmonic resonator systems

An optical effect analogous to electromagnetically induced transparency (EIT) is observed in nanoscale plasmonic resonator systems. The system consists of a slot cavity as well as plasmonic bus and resonant waveguides, where the phase-matching condition of the resonant waveguide is tunable for the generation of an obvious EIT-like coupled resonator-induced transparency effect. A dynamic theory is utilized to exactly analyze the influence of physical parameters on transmission characteristics. The transparency effect induced by coupled resonance may have potential applications for nanoscale optical switching, nanolaser, and slow-light devices in highly integrated optical circuits.     

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.     

Effect of multiphoton absorption and free carriers in slow-light photonic crystal waveguides

We examine the effects of multiphoton absorption, free carriers, and disorder-induced linear scattering in slow-light photonic crystal waveguides. We derive an analytic formulation for self-phase modulation including the group velocity scaling of the nonlinear phase shift in materials limited by three-photon absorption as a representative nonlinear process. We investigate the role of free carriers and derive an approximate critical intensity at which these effects begin to strongly modify the optical field. This critical intensity is employed to determine an optimal group index for the self-phase modulation in the slow-light devices. These observations are confirmed with numerical modeling.     

Delay-gain decoupling in Brillouin-assisted slow light

In Brillouin-assisted slow-light the induced delay is always linked to a particular gain; i.e., the delay is directly proportional to the gain expressed in decibels. However, for certain applications this may be restrictive, and techniques to decouple gain and delay are thus of considerable practical interest. We propose a way to effectively decouple these two parameters that, subject to inherent physical constraints, can be used to obtain a delay line capable of providing arbitrary gain (or alternatively an amplifier that can provide arbitrary delay for a fixed gain). The decoupling mechanism relies upon operating the amplifier in the pump-depletion regime. Other advantages of this approach, as well as its limitations in the context of slow-light, are discussed.     

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     

Nonlinear photonics with metallic nanostructures on top of dielectrics and waveguides

We review recent experimental and theoretical studies of the ultrafast and nonlinear optical response of metallic nanostructures on top of dielectric substrates and slab waveguides where plasmon hybridization is a key ingredient. In a first three-pulse all-optical control experiment a hybrid plasmonic mode is turned on or off only a few tens of femtoseconds after its excitation. A second experiment concentrates on the origin of the nonlinear response in a metallo-dielectric photonic crystal structure. We show that the shape of the nonlinear optical spectra provides unambiguous information about the nonlinear optical contribution of the metallic as well as the dielectric part of the structure. Furthermore, we discuss the influence of slow-light on the nonlinear response. All experimental results agree perfectly with numerical scattering matrix calculations as well as simulations based on a classical harmonic oscillator model.     

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.     

Tailoring repulsive optical forces in nanophotonic waveguides

We describe a mechanism and propose design strategies to selectively tailor repulsive-gradient-optical forces between parallel, nanophotonic waveguides via morphology augmented by slow-light band-edge modes. We show that at small separation lengths, the repulsive force can be made nearly 2 orders of magnitude larger than that of standard dielectric waveguides with a square cross section. The increased coupling interactions should enable a wider dynamic range of optomechanical functionality for potential applications in sensing, switching, and nanoelectromechanical systems.     

Transmission of slow light through photonic crystal waveguide bends

The spectral dependence of the bending loss of cascaded 60 degrees bends in photonic crystal (PhC) waveguides is explored in a slab-type silicon-on-insulator system. An ultralow bending loss of (0.05 +/- 0.03) dB/bend is measured at wavelengths corresponding to the nearly dispersionless transmission regime. In contrast, the PhC bend is found to become completely opaque for wavelengths corresponding to the slow-light regime. A general strategy is presented and experimentally verified to optimize the bend design for improved slow-light transmission.     

A slow-light laser radar system with two-dimensional scanning

We propose a multi-aperture slow-light laser radar with two-dimensional scanning. We demonstrate experimentally that we can use two independent slow-light mechanisms, namely dispersive delay and stimulated Brillouin scattering, to dynamically compensate the group delay mismatch among different apertures, while we use optical phase locking to control the relative phases of the optical signals emitted from different apertures, as the system steers the beam in two dimensions.     

Numerical study of converting beat-note signals of dual-frequency lasers to optical frequency combs by optical injection locking of semiconductor lasers

The optical injection locking of semiconductor lasers to dual-frequency lasers is studied by numerical simulations. The beat-note signals can be effectively transformed to optical frequency combs due to the effective four wave-mixing in the active semiconductor gain medium. The low-noise Gaussian-like pulse can be obtained by locking the relaxation oscillation and compensating the gain asymmetry. The simulations suggest that pulse trains of width below 30 ps and repetition rate in GHz frequency can be generated simply by the optical injection locking of semiconductor lasers. Since the optical injection locking can broaden the spectrum and amplify the optical power simultaneously, it can be a good initial stage for generating optical frequency combs from dual-frequency lasers by multi-stage of spectral broadening in nonlinear waveguides.     

Experimental constraints of using slow-light in sodium vapor for light-drag enhanced relative rotation sensing

We report on experimental observation of electromagnetically induced transparency and slow-light (v_g ≈ c/607) in atomic sodium vapor, as a potential medium for a recently proposed experiment on slow-light enhanced relative rotation sensing [Shahriar et al. Phys. Rev. Lett. (submitted for publication), http://arxiv.org/abs/quant-ph/0505192.]. We have performed an interferometric measurement of the index variation associated with a two-photon resonance to estimate the dispersion characteristics of the medium that are relevant to the slow-light based rotation sensing scheme. We also show that the presence of counter-propagating pump beams in an optical Sagnac loop produces a backward optical phase conjugation beam that can generate spurious signals, which may complicate the measurement of small rotations in the slow-light enhanced gyroscope. We identify techniques for overcoming this constraint. Conclusions reached from the results presented here will pave the way for designing and carrying out an experiment that will demonstrate the slow-light induced enhancement of rotation sensing.     

Time delay enhancement in stimulated-Brillouin-scattering-based slow-light systems

We show a simple method of time delay enhancement in slow-light systems based on the effect of stimulated Brillouin scattering. The method is based on the reduction of the absolute Brillouin gain by a loss produced by an additional pump laser. With this method we achieved pulse delays of nearly 100 ns in a standard single-mode fiber. In the presented approach the delay or acceleration of optical signals is decoupled from their amplification or attenuation, which allows the adaptation of the pulse amplitudes to the given application.     

Adiabatic transfer of surface plasmons in non-Hermitian graphene waveguides

We investigate the energy transfer of surface plasmon polaritons (SPPs) based on adiabatic passage in a non-Hermitian waveguide composed of three coupled graphene sheets. The SPPs can completely transfer between two outer waveguides via the adiabatic dark mode as the waveguides are lossless and the coupling length is long enough. However, the loss of graphene can lead to breakdown of adiabatic transfer schemes. By utilizing the coupled mode theory, we propose three approaches to cancel the nonadiabatic coupling by adding certain gain or loss in respect waveguides. Moreover, the coupling length of waveguide is remarkably decreased. The study may find interesting application in optical switches on a deep-subwavelength scale.     

掺铒聚合物狭缝波导放大器的增益特性研究

设计了一种高浓度稀土铒掺杂聚合物填充硅狭缝结构的平面光波导放大器（工作波长1 550 nm,泵浦波长1 480 nm）,能够在低泵浦下获得高增益,可以应用于硅基光互联的损耗补偿。通过扫描电镜照片观察发现,合成的铒掺杂聚合物材料具有良好的纳米狭缝填充能力。考虑铒离子的合作上转换和激发态吸收,利用铒离子四能级跃迁模型,建立原子速率方程和光功率传输方程,数值仿真分析了聚合物光学性质、狭缝波导结构参数及信号光泵浦光功率等放大器增益特性的影响因素。这种具有纳米截面尺寸的光波导放大器,获得4.5 dB的信号光相对增益仅需要1.5 mW的泵浦光,展现了良好的集成光学应用前景。为了进一步提高增益,引入了多层狭缝结构,四层狭缝波导的重叠积分因子比一层狭缝的高42%。     

Dynamic control of the terahertz rainbow trapping effect based on a silicon-filled graded grating

We theoretically propose a scheme to realize the dynamic control of the properties of the terahertz(THz) rainbow trapping effect(RTE) based on a silicon-filled graded grating(SFGG) in a relatively broad band via optical pumping.Through the theoretical analysis and finite-element method simulations, it is conceptually demonstrated that the band of the RTE can be dynamically tuned in a range of ~0.06 THz. Furthermore, the SFGG can also be optically switched between a device for the RTE and a waveguide for releasing the trapped waves. The results obtained here may imply applications for the tunable THz plasmonic devices, such as on-chip optical buffers, broad band slow-light systems, and integrated optical filters.     

Coupled-resonator optical waveguides: Q-factor and disorder influence

Coupled resonator optical waveguides (CROW) can significantly reduce light propagation pulse velocity due to pronounced dispersion properties. A number of interesting applications have been proposed to benefit from such slow-light propagation. Unfortunately, the inevitable presence of disorder, imperfections, and a finite Q value may heavily affect the otherwise attractive properties of CROWs. We show how finite a Q factor limits the maximum attainable group delay time; the group index is limited by Q, but equally important the feasible device length is itself also limited by damping resulting from a finite Q. Adding the additional effects of disorder to this picture, limitations become even more severe due to destructive interference phenomena, eventually in the form of Anderson localization. Simple analytical considerations demonstrate that the maximum attainable delay time in CROWs is limited by the intrinsic photon lifetime of a single resonator.