Nonlinear dispersion in a coupled-resonator optical waveguide

The propagation of an optical pulse in a coupled-resonator optical waveguide may be calculated nonperturbatively to all orders of dispersion, in the conventional tight-binding approximation, even though the dispersion relationship is nonlinear. Working in this framework, we discuss limits of the physical parameters and approximations to the exact formulation that highlight the conditions under which pulse distortion can be minimized. The results are fundamental to the design of coupled-resonator optical waveguides and are also relevant to other applications of the tight-binding method.     

Arrayed waveguide Sagnac interferometer

We present a novel device, an arrayed waveguide Sagnac interferometer, that combines the flexibility of arrayed waveguides and the wide application range of fiber or integrated optics Sagnac loops. We form the device by closing an array of wavelength-selective light paths provided by two arrayed waveguides with a single 2 x 2 coupler in a Sagnac configuration. The equations that describe the device's operation in general conditions are derived. A preliminary experimental demonstration is provided of a fiber prototype in passive operation that shows good agreement with the expected theoretical performance. Potential applications of the device in nonlinear operation are outlined and discussed.     

Miniband transmission in a photonic crystal coupled-resonator optical waveguide

We demonstrate in the near infrared the coupled-resonator optical waveguide (CROW) concept that was recently proposed by Yariv et al. [Opt. Lett.24, 711 (1999)]. Two-dimensional photonic crystals have been used to define, in a GaAs-based waveguiding heterostructure, an array of micrometer-sized hexagonal cavities coupled through thin walls. With the photoexcitation of InAs quantum dots as an internal source, the transmission spectra of the coupled resonators show marked minibands and minigaps, in agreement with theoretical predictions.     

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.     

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.     

Novel slow-light waveguide with large bandwidth and ultra low dispersion

To tailor the bandwidth and the group-velocity dispersion, we demonstrate a novel waveguide based on a photonic crystal within a triangular array with crescent-like-shaped air holes. By changing the angle between the waveguide axis and symmetric axis of the air hole from 0 to π/2, we find that the available bandwidth with a nearly constant group index in excess of 22 increases from 7 nm to 13 nm, that the corresponding normalized delay-bandwidth product increases from 0.202 to 0.245, and that the absolute value of the group-velocity dispersion decreases from 13.500 ps²/km to 10 ps²/km. The origin of all the findings is related to the widening of the slow-light region with the increasing of the angle.     

Slow light propagating characteristics through a two-dimensional silicon-based coupled-resonator optical waveguide

The light propagating characteristics of the coupled-resonator optical waveguides (CROWs) are studied by the finite-difference time-domain method. The circular CROWs are constructed by arranging the micro-cavities at a certain distance, which is constructed by removing the air holes along the edge of a circle from a two-dimensional (2D) triangular-lattice photonic crystal (PC). With the increasing of distance between the adjacent cavities, the group velocities of the guiding modes reduce significantly. The circular CROW studied in the paper have much minibands within the band gap, and their respective group velocities can be quite different from each other. This kind of CROW structure can provide different group velocities for the light signals with different frequencies, and avails to the separating and controlling the light signals in the all optic integrated circuits.     

Guided subwavelength slow-light mode supported by a plasmonic waveguide system

We introduce a plasmonic waveguide system, which supports a subwavelength broadband slow-light guided mode with a tunable slowdown factor at a given wavelength. The system consists of a metal-dielectric-metal (MDM) waveguide side-coupled to a periodic array of MDM stub resonators. The slowdown factor at a given wavelength can be tuned by adjusting the geometrical parameters of the system. In addition, there is a trade-off between the slowdown factor and the propagation length of the supported optical mode. Finally, we show that light can be coupled efficiently from a conventional MDM waveguide to the plasmonic waveguide system.     

Ultrawide-bandwidth slow-light system based on THz plasmonic graded metallic grating structures

We explore a novel mechanism for slowing down THz waves based on metallic grating structures with graded depths, whose dispersion curves and cutoff frequencies are different at different locations. Since the group velocity of spoof surface plasmons at the cutoff frequency is extremely low, THz waves are actually stopped at different positions for different frequencies. The separation between stopped waves can be tuned by changing the grade of the grating depths. This structure offers the advantage of reducing the speed of the light over an ultrawide spectral band, and the ability to operate at various temperatures, but demands a stringent requirement for the temperature stability.     

Coriolis force and Sagnac effect

The optical Sagnac effect is considered, when the fictitious gravitational field simulates the reflections from the mirrors. It is shown that no contradiction exists between the conclusions of the laboratory and rotated observers. Because of the acting of a gravity-like Coriolis force, the trajectories of coand anti-rotating photons have different radii in the rotating reference frame, while in the case of equal radii the effective gravitational potentials for the photons have to be different.     

Theory of nonlinear Sagnac effect

A nonlinear wave interaction is considered as a technique to increase the rotation sensitivity of the ring laser. The gyroscopic scale factor K is calculated in an active laser gyro with a dispersive medium. K is in reverse proportion to the group index n* = n + vdn/dv of the medium. In a monolithically-integrated GaAs ring laser, the value K ∼5000 is obtainable (radius ∼1 cm) in a linear case. In the presence of a strong wave, the dynamic nonlinear anomalous dispersion can provide an increase of K by 10–100 times in the vicinity of critical points where n* passes zero. An expression of K is derived for the nonlinear Sagnac effect. The nonlinear dispersion is discussed in terms of “slow/fast” light.     

New waveguide modes in anisotropic structures

The existence of new hybrid waveguide modes of properly tailored integrated optical waveguides consisting of ultrathin films clad by positive birefringent media is pointed out.     

String corrections to the Sagnac effect

In an effort to investigate string effects in physical observations, we have analyzed the rotating Kerr–Sen metric in a Sagnac type experiment and have deduced exact expressions for the delay. For an Earth bound configuration, it turns out that a correction to the basic Sagnac delay by an order of ∼10⁻¹⁴ s leads to a terrestrial dilatonic charge of amount ∼10²⁴ esu, a value nearly 200 times larger than the electronic charge of the Earth's magnetosphere.     

Sagnac effect in the colliding-pulse-mode-locked dye ring laser

A colliding-pulse-mode-locked dye ring laser was mounted on a rotary stage and the beat frequency of the two output pulse trains was measured as a function of the rotation rate. The measurements are in good agreement with the Sagnac theory.     

Notes on the Sagnac effect in general relativity

The Sagnac effect can be described as the difference in travel time between two photons traveling along the same path in opposite directions. In this paper we explore the consequences of this characterisation in the context of General Relativity. We derive a general expression for this time difference in an arbitrary space-time for arbitrary paths. In general, this formula is not very useful since it involves solving a differential equation along the path. However, we also present special cases where a closed form expression for the time difference can be given. The main part of the paper deals with the discussion of the effect in a small neighbourhood of an arbitrarily moving observer in their arbitrarily rotating reference frame. We also discuss the special case of stationary space-times and point out the relationship between the Sagnac effect and Fizeau’s “aether-drag” experiment.     

Time biasing due to the slow-light effect in distributed fiber-optic Brillouin sensors

The influence of the slow-light effect on the performance of distributed Brillouin sensors is studied. We show that, while in most situations it can be neglected, it may greatly affect the results obtained for certain experimental configurations. More specifically, for one of the experimental arrangements described in the literature (a strong continuous-wave pump and a weak pulsed probe) we show that this effect induces a large time biasing of the traces that depends not only on the fiber length but also on the frequency separation between pump and probe. This biasing reduces the available resolution in this experimental arrangement.     

Nonreciprocal coupling effects in gyrotropic waveguide structures

Nonreciprocal couplers in gyrotropic materials offer a new possibility for the realization of integrated optical isolators and circulators. This paper presents a theoretical analysis of such devices. We apply the finite-difference method and coupled mode as well as normal mode theory to neighbouring gyrotropic rib waveguides. Conclusions for the design of nonreciprocal devices are drawn.     

Gravitational radiation antennas using the Sagnac effect

A new class of gravitational antennas that utilize the general relativistic Sagnac effect is proposed. These antennas may be more efficient than the Weber bar by a factor of (c/v_s)⁴ 10¹⁹, wherev _sis the velocity of sound in the bar. A specific case of such an antenna consisting of a superfluid helium Josephson interferometer is considered. A general relativistic theory of the interaction of the superfluid with the gravitational field is given. Using this theory, the phase shift due to a gravitational plane wave on one such antenna is obtained. More generally, the proposed interferometer involves the interplay of general relativity and quantum theory and may afford the possibility of testing general relativity in the laboratory at the quantum mechanical level. The possibility of detecting gravitons, assuming nearly unit coupling efficiency for the antenna, is explored.This essay received the second award from the Gravity Research Foundation for the year 1981-Ed.Research was supported by NSF grant No. PHY 79-13146.Research was supported by NSF grant No. ECS-8009834.     

Control of four-wave mixing phase-matching condition using the Brillouin slow-light effect in fibers

All-optical control of the phase-matching condition in four-wave mixing (FWM) processes is demonstrated using the Brillouin slow-light effect in optical fibers. A counterpropagating stimulated Brillouin scattering (SBS) pump has been used to control the phase velocity of the FWM pump in a wavelength conversion scheme. Both experimental results and theoretical simulations show an SBS-controlled 20 dB difference on the wavelength conversion efficiency.     

Waveguide modes in coupled-resonator optical waveguides

Coupling between cavities within coupled-resonator optical waveguides (CROWs) affects transmission properties. Our results show that, in addition to the number of the waveguide modes, the group velocity of electromagnetic waves transmitted in the CROWs can be controlled by changing the stiffness of coupling between cavities. This is significant for the applications.