Tunable all-optical delays via Brillouin slow light in an optical fiber.
TL;DR: It is demonstrated that stimulated Brillouin scattering can be used to generate all-optical slow-light pulse delays of greater than a pulse length for pulses as short as 16 ns in a single-mode fiber, and strongly suggest that analogous delays can be achieved using stimulated Raman scattering at telecommunication data rates.
Abstract: 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.
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IBM1
TL;DR: In this paper, the trade-offs between resonantly enhanced group delay, device size, insertion loss and operational bandwidth are analyzed for various delay-line designs, and a large fractional group delay exceeding 10 bits is achieved for bit rates as high as 20 Gbps.
Abstract: On-chip optical buffers based on waveguide delay lines might have significant implications for the development of optical interconnects in computer systems. Silicon-on-insulator (SOI) submicrometre photonic wire waveguides are used, because they can provide strong light confinement at the diffraction limit, allowing dramatic scaling of device size. Here we report on-chip optical delay lines based on such waveguides that consist of up to 100 microring resonators cascaded in either coupled-resonator or all-pass filter (APF) configurations. On-chip group delays exceeding 500 ps are demonstrated in a device with a footprint below 0.09 mm2. The trade-offs between resonantly enhanced group delay, device size, insertion loss and operational bandwidth are analysed for various delay-line designs. A large fractional group delay exceeding 10 bits is achieved for bit rates as high as 20 Gbps. Measurements of system-level metrics as bit error rates for different bit rates demonstrate error-free operation up to 5 Gbps.
1,161 citations
TL;DR: It is demonstrated theoretically that an axially varying heterostructure with a metamaterial core of negative refractive index can be used to efficiently and coherently bring light to a complete standstill, and allows for high in-coupling efficiencies and broadband, room-temperature operation.
Abstract: Metamaterials — transparent materials containing tiny metallic inclusions of various shapes and arrangements — cause light to propagate in unusual ways. Now a new, theoretical metamaterial architecture is proposed, with the potential to bring light to a complete standstill. In contrast to previous methods of decelerating and storing light, this scheme simultaneously allows both high in-coupling efficiency and broadband, room-temperature operation. At a critical point a light ray is prevented from propagating; each frequency component (or colour) of the wave stops at a slightly different place, leading to the formation of a 'trapped rainbow'. This work bridges the gap between two important contemporary realms of science, metamaterials and slow light, and may lead to applications in optical data processing and storage or the realization of quantum optical memories. Light usually propagates inside transparent materials in well known ways1. However, recent research2,3,4,5,6 has examined the possibility of modifying the way the light travels by taking a normal transparent dielectric and inserting tiny metallic inclusions of various shapes and arrangements. As light passes through these structures, oscillating electric currents are set up that generate electromagnetic field moments; these can lead to dramatic effects on the light propagation, such as negative refraction. Possible applications include lenses that break traditional diffraction limits3,4 and ‘invisibility cloaks’ (refs 5, 6). Significantly less research has focused on the potential of such structures for slowing, trapping and releasing light signals. Here we demonstrate theoretically that an axially varying heterostructure with a metamaterial core of negative refractive index can be used to efficiently and coherently bring light to a complete standstill. In contrast to previous approaches for decelerating and storing light7,8,9,10,11,12,13, the present scheme simultaneously allows for high in-coupling efficiencies and broadband, room-temperature operation. Surprisingly, our analysis reveals a critical point at which the effective thickness of the waveguide is reduced to zero, preventing the light wave from propagating further. At this point, the light ray is permanently trapped, its trajectory forming a double light-cone that we call an ‘optical clepsydra’. Each frequency component of the wave packet is stopped at a different guide thickness, leading to the spatial separation of its spectrum and the formation of a ‘trapped rainbow’. Our results bridge the gap between two important contemporary realms of science—metamaterials and slow light. Combined investigations may lead to applications in optical data processing and storage or the realization of quantum optical memories.
746 citations
TL;DR: In this article, the authors demonstrate a new resonator with a record Q-factor of 875 million for on-chip devices, which sets a new benchmark for the Q factor on a chip, and also provides full compatibility of this important device class with conventional semiconductor processing.
Abstract: Ultrahigh-Q optical resonators are being studied across a wide range of fields, including quantum information, nonlinear optics, cavity optomechanics and telecommunications. Here, we demonstrate a new resonator with a record Q-factor of 875 million for on-chip devices. The fabrication of our device avoids the requirement for a specialized processing step, which in microtoroid resonators8 has made it difficult to control their size and achieve millimetre- and centimetre-scale diameters. Attaining these sizes is important in applications such as microcombs and potentially also in rotation sensing. As an application of size control, stimulated Brillouin lasers incorporating our device are demonstrated. The resonators not only set a new benchmark for the Q-factor on a chip, but also provide, for the first time, full compatibility of this important device class with conventional semiconductor processing. This feature will greatly expand the range of possible ‘system on a chip’ functions enabled by ultrahigh-Q devices.
632 citations
TL;DR: In this paper, a detailed overview of stimulated Brillouin scattering (SBS) in single-mode optical fibers is presented, with a particular emphasis on analytical analysis of the backreflected power and SBS threshold in optical fibers with various index profiles.
Abstract: We present a detailed overview of stimulated Brillouin scattering (SBS) in
single-mode optical fibers. The review is divided into two parts. In the first part,
we discuss the fundamentals of SBS. A particular emphasis is given to analytical
calculation of the backreflected power and SBS threshold (SBST) in optical fibers
with various index profiles. For this, we consider acousto-optic interaction in the
guiding geometry and derive the modal overlap integral, which describes the
dependence of the Brillouin gain on the refractive index profile of the optical
fiber. We analyze Stokes backreflected power initiated by thermal phonons, compare
values of the SBST calculated from different approximations, and discuss the SBST
dependence on the fiber length. We also review an analytical approach to calculate
the gain of Brillouin fiber amplifiers (BFAs) in the regime of pump depletion. In the
high-gain regime, fiber loss is a nonnegligible effect and needs to be accounted for
along with the pump depletion. We provide an accurate analytic expression for the BFA
gain and show results of experimental validation. Finally, we review methods to
suppress SBS including index-controlled acoustic guiding or segmented fiber links.
The second part of the review deals with recent advances in fiber-optic applications
where SBS is a relevant effect. In particular, we discuss the impact of SBS on the
radio-over-fiber technology, enhancement of the SBS efficiency in Raman-pumped
fibers, slow light due to SBS and SBS-based optical delay lines, Brillouin
fiber-optic sensors, and SBS mitigation in high-power fiber lasers, as well as SBS in
multimode and microstructured fibers. A detailed derivation of evolutional equations
in the guided wave geometry as well as key physical relations are given in
appendices.
576 citations
TL;DR: In this article, the authors present the state-of-the-art research in this fascinating field and possible outcomes in the near future, as well as a review of the current state of the art in this field.
Abstract: The ubiquitous role of optical fibres in modern photonic systems has stimulated research to realize slow and fast light devices directly in this close-to-perfect transmission line. Recent progress in developing optically controlled delays in optical fibres, operating under normal environmental conditions and at telecommunication wavelengths, has paved the way towards real applications for slow and fast light. This review presents the state-of-the-art research in this fascinating field and possible outcomes in the near future.
380 citations
References
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01 Jan 1989TL;DR: The field of nonlinear fiber optics has advanced enough that a whole book was devoted to it as discussed by the authors, which has been translated into Chinese, Japanese, and Russian languages, attesting to the worldwide activity in the field.
Abstract: Nonlinear fiber optics concerns with the nonlinear optical phenomena occurring inside optical fibers. Although the field ofnonlinear optics traces its beginning to 1961, when a ruby laser was first used to generate the second-harmonic radiation inside a crystal [1], the use ofoptical fibers as a nonlinear medium became feasible only after 1970 when fiber losses were reduced to below 20 dB/km [2]. Stimulated Raman and Brillouin scatterings in single-mode fibers were studied as early as 1972 [3] and were soon followed by the study of other nonlinear effects such as self- and crossphase modulation and four-wave mixing [4]. By 1989, the field ofnonlinear fiber optics has advanced enough that a whole book was devoted to it [5]. This book or its second edition has been translated into Chinese, Japanese, and Russian languages, attesting to the worldwide activity in the field of nonlinear fiber optics.
15,770 citations
TL;DR: In this paper, an experimental demonstration of electromagnetically induced transparency in an ultracold gas of sodium atoms, in which the optical pulses propagate at twenty million times slower than the speed of light in a vacuum, is presented.
Abstract: Techniques that use quantum interference effects are being actively investigated to manipulate the optical properties of quantum systems1. One such example is electromagnetically induced transparency, a quantum effect that permits the propagation of light pulses through an otherwise opaque medium2,3,4,5. Here we report an experimental demonstration of electromagnetically induced transparency in an ultracold gas of sodium atoms, in which the optical pulses propagate at twenty million times slower than the speed of light in a vacuum. The gas is cooled to nanokelvin temperatures by laser and evaporative cooling6,7,8,9,10. The quantum interference controlling the optical properties of the medium is set up by a ‘coupling’ laser beam propagating at a right angle to the pulsed ‘probe’ beam. At nanokelvin temperatures, the variation of refractive index with probe frequency can be made very steep. In conjunction with the high atomic density, this results in the exceptionally low light speeds observed. By cooling the cloud below the transition temperature for Bose–Einstein condensation11,12,13 (causing a macroscopic population of alkali atoms in the quantum ground state of the confining potential), we observe even lower pulse propagation velocities (17?m?s−1) owing to the increased atom density. We report an inferred nonlinear refractive index of 0.18?cm2?W−1 and find that the system shows exceptionally large optical nonlinearities, which are of potential fundamental and technological interest for quantum optics.
3,438 citations
TL;DR: In this paper, small group velocities of order 90 m/s and large group delays of greater than 0.26 ms were observed in an optically dense hot rubidium gas ( $\ensuremath{\approx}360\mathrm{K}$).
Abstract: We report the observation of small group velocities of order 90 m/s and large group delays of greater than 0.26 ms, in an optically dense hot rubidium gas ( $\ensuremath{\approx}360\mathrm{K}$). Media of this kind yield strong nonlinear interactions between very weak optical fields and very sharp spectral features. The result is in agreement with previous studies on nonlinear spectroscopy of dense coherent media.
1,042 citations
"Tunable all-optical delays via Bril..." refers background in this paper
...For a sufficiently rapid change in the refractive index, the second term on the right-hand side of Eq. (1) can dominate, resulting in values of the group index that exceed 106 [2, 3 ]....
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TL;DR: In this paper, it is shown that the group velocity gives the velocity with which a pulse of light propagates through a material system, depending on the value of group velocity vg in comparison to the velocity of light in vacuum.
Abstract: Recent research has established that it is possible to exercise extraordinary control of the velocity of propagation of light pulses through a material system. Both extremely slow propagation (much slower than the velocity of light in vacuum) and fast propagation (exceeding the velocity of light in vacuum) have been observed. This article summarizes this recent research, placing special emphasis on the description of the underlying physical processes leading to the modification of the velocity of light. To understand these new results, it is crucial to recall the distinction between the phase velocity and the group velocity of a light field. These concepts will be defined more precisely below; for the present we note that the group velocity gives the velocity with which a pulse of light propagates through a material system. One thus speaks of “fast” or “slow” light depending on the value of the group velocity vg in comparison to the velocity of light c in vacuum.
269 citations
"Tunable all-optical delays via Bril..." refers background in this paper
...The concept of slow light makes use of rapid spectral changes in the refractive index [ 1 ] as the group index ng is given by ng = n+ω dn dω . (1)...
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TL;DR: This novel technique is shown to provide high-resolution characterization of SBS even under saturation operation in a simple and stable setup in which the spectrum is translated from the optical to the electrical domain, sweeping the frequency of an electrical signal generator.
Abstract: We introduce an enhanced method for the characterization of stimulated Brillouin scattering (SBS) spectra in single-mode fiber that is based on optical single-sideband modulation. This novel technique is shown to provide high-resolution characterization of SBS even under saturation operation in a simple and stable setup in which the spectrum is translated from the optical to the electrical domain, sweeping the frequency of an electrical signal generator. Experimental results are used to demonstrate the performance of the system in measuring the detailed structure of acoustic modes in three types of single-mode fiber.
99 citations
"Tunable all-optical delays via Bril..." refers result in this paper
...This value is appreciably larger than those determined from previous measurements [6] in various optical fibers....
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