Photonic crystal fibers guide light by corralling it within a periodic array of microscopic air holes that run along the entire fiber length Largely through their ability to overcome the limitations of conventional fiber optics—for example, by permitting low-loss guidance of light in a hollow core—these fibers are proving to have a multitude of important technological and scientific applications spanning many disciplines The result has been a renaissance of interest in optical fibers and their uses

https://science.sciencemag.org/content/sci/299/5605/358.full.pdf

Photonic crystal fibers

A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation in photonic crystal fiber

Extremely narrow optical resonances in cold atoms or single trapped ions can be measured with high resolution. A laser locked to such a narrow optical resonance could serve as a highly stable oscillator for an all-optical atomic clock. However, until recently there was no reliable clockwork mechanism that could count optical frequencies of hundreds of terahertz. Techniques using femtosecond-laser frequency combs, developed within the past few years, have solved this problem. The ability to count optical oscillations of more than 1015 cycles per second facilitates high-precision optical spectroscopy, and has led to the construction of an all-optical atomic clock that is expected eventually to outperform today's state-of-the-art caesium clocks.

Optical frequency metrology

We stabilized the carrier-envelope phase of the pulses emitted by a femtosecond mode-locked laser by using the powerful tools of frequency-domain laser stabilization. We confirmed control of the pulse-to-pulse carrier-envelope phase using temporal cross correlation. This phase stabilization locks the absolute frequencies emitted by the laser, which we used to perform absolute optical frequency measurements that were directly referenced to a stable microwave clock.

/pdf/carrier-envelope-phase-control-of-femtosecond-mode-locked-4lkf4vexna.pdf

Carrier-envelope phase control of femtosecond mode-locked lasers and direct optical frequency synthesis

Recent observations show that the probability of encountering an extremely large rogue wave in the open ocean is much larger than expected from ordinary wave-amplitude statistics. Although considerable effort has been directed towards understanding the physics behind these mysterious and potentially destructive events, the complete picture remains uncertain. Furthermore, rogue waves have not yet been observed in other physical systems. Here, we introduce the concept of optical rogue waves, a counterpart of the infamous rare water waves. Using a new real-time detection technique, we study a system that exposes extremely steep, large waves as rare outcomes from an almost identically prepared initial population of waves. Specifically, we report the observation of rogue waves in an optical system, based on a microstructured optical fibre, near the threshold of soliton-fission supercontinuum generation--a noise-sensitive nonlinear process in which extremely broadband radiation is generated from a narrowband input. We model the generation of these rogue waves using the generalized nonlinear Schrodinger equation and demonstrate that they arise infrequently from initially smooth pulses owing to power transfer seeded by a small noise perturbation.

Optical rogue waves

Nonlinear Interactions in Air-Silica Microstructure Optical Fibers

PROBLEM TO BE SOLVED: To provide a device which exhibits a relatively large nonlinear interaction at visible and near IR (vis-nir) wavelengths. SOLUTION: A suitably designed optical waveguide exhibits an abnormal (positive) dispersion over the continuous body of the vis-nir wavelength and the fiber 10 in one embodiment exhibits zero dispersion at a visible wavelength (for example, about 760 nm). These characteristics are achieved by mutually matching a core region 12 and the refractive index difference between the core region 12 and a clad 14 (making the core region 12 relatively small and making the refractive index difference relatively large). In a more preferable embodiment, the zero dispersion point occurs at the vis-nir wavelength. For example, the optical waveguide is fine structure fiber 10 having the silica core 12 enclosed by the relative thin inner clad 14 having a plurality of capillary holes 14 and 1 enabling the refractive index waveguide in the core 12. The patterns of the cross sections of the holes are for example, hexagonal or triangular. COPYRIGHT: (C)2007,JPO&INPIT

Fine structure optical fiber

The present invention uses wavelength conversion to increase the bandwidth of optical communication systems. In an exemplary embodiment, a combination of wavelength conversion and amplification with a discrete optical amplifier (OA) to allow communications systems to operate in wavelength bands λ′ outside the gain bandwidth of the OA. A transmitter launches signal channels (λ1′, λ2′, . . . , λ′N) that are outside the gain bandwidth λ. A wavelength conversion device upstream of the amplifier maps channels λ′1, λ′2, . . . λ′N to corresponding wavelengths λ1, λ2, . . . λN within λ. The OA directly amplifies the converted signals and a second wavelength conversion device downstream of the amplifier maps the amplified signals back to the original channels λ′1, λ′2, . . . λ′N. This increases the capacity of the optical communication systems by facilitating the use of both signals that lie within the OA gain bandwidth λ and signals that can be converted to wavelengths within λ. Associated wavelength converters, transmitters and receivers are also described. This approach applies not only to the use of EDFAs, but also to gain-flattening elements, dispersion-compensating fibers, variable attenuators, and any intermediate components having bandwidths smaller than the transmission fiber.

Optical fiber communication system employing wavelength converter for broadband transmission

A fiber optic system comprises an optical transmitter, an optical receiver, and an optical fiber transmission path that optically couples the transmitter and the receiver to one another. The transmission path includes a first section that has negative dispersion at an operating wavelength λ0 greater than about 1300 nm and a second section that includes a MOF. The MOF has relatively large anomalous dispersion at λ0 and is sufficiently long to compensate the accumulated negative dispersion in the first section. In one embodiment the MOF comprises a core, a lower index cladding that includes one or more layers of air holes surrounding the core, characterized in that the diameter of the core is less than about 8 μm and the difference in effective refractive index between the core and cladding is greater than about 0.1 (10%). Preferably, the cladding contains no more than 2 layers of air holes and the distance between the II nearest edges of adjacent air holes is less than about 1 μm.

Microstructure optical fibers for dispersion management in optical communication systems

Summary form only given.We have developed a technique for measuring the continuum generated using microstructure optical fiber and have shown that the continuum has well-behaved spectral phase in a /spl sim/25-nm-bandwidth region near 850 nm. Our technique is based on the Temporal Analysis by Dispersing a Pair Of Light E-fields (TADPOLE) and FROG techniques. Our laser is capable of 20-fs pulses with /spl sim/100-nm bandwidths, so about a dozen straightforward measurements could yield the spectral phase for the entire continuum, whether uncompressed or compressed to a single cycle, without the need for extremely thin crystals.

Jinendra Kumar Ranka

Papers

Nonlinear Interactions in Air-Silica Microstructure Optical Fibers

Fine structure optical fiber

Optical fiber communication system employing wavelength converter for broadband transmission

Microstructure optical fibers for dispersion management in optical communication systems

Measuring the intensity and phase of ultrabroadband continuum