Igor Khrushchev

Nanofabricated media with negative permeability at visible frequencies

A great deal of attention has recently been focused on a new class of smart materials—so-called left-handed media—that exhibit highly unusual electromagnetic properties and promise new device applications. Left-handed materials require negative permeability µ, an extreme condition that has so far been achieved only for frequencies in the microwave to terahertz range. Extension of the approach described in ref. 7 to achieve the necessary high-frequency magnetic response in visible optics presents a formidable challenge, as no material—natural or artificial—is known to exhibit any magnetism at these frequencies. Here we report a nanofabricated medium consisting of electromagnetically coupled pairs of gold dots with geometry carefully designed at a 10-nm level. The medium exhibits a strong magnetic response at visible-light frequencies, including a band with negative µ. The magnetism arises owing to the excitation of an antisymmetric plasmon resonance. The high-frequency permeability qualitatively reveals itself via optical impedance matching. Our results demonstrate the feasibility of engineering magnetism at visible frequencies and pave the way towards magnetic and left-handed components for visible optics.

Depressed cladding, buried waveguide laser formed in a YAG:Nd 3+ crystal by femtosecond laser writing

Depressed cladding waveguides have been formed in laser crystals by a tightly focused beam of a femtosecond laser. A laser based on a depressed cladding waveguide in a neodymium-doped YAG crystal has been demonstrated for what is believed to be the first time.

Direct inscription of Bragg gratings in coated fibers by an infrared femtosecond laser

Inscription of fiber Bragg gratings through the coating of a nonphotosensitized standard telecommunication fiber is demonstrated for what is believed to be the first time. Highly reflective gratings were produced by direct point-by-point writing with an infrared femtosecond laser. The length of the gratings presented ranged from 5 to 26 mm. The technique does not require a special coating, as standard coatings are transparent to infrared radiation. Inscription through the coating improves the mechanical strength of the processed segment of fiber.

Distributed Bragg reflector fiber laser fabricated by femtosecond laser inscription.

A femtosecond laser inscription technique is proposed for the fabrication of a fiber grating laser directly into a nonphotosensitive gain fiber. A distributed Bragg reflector fiber grating laser is realized in a conventional, untreated Er:Yb-codoped fiber as an illustration. Robust, single-mode, single-polarization laser operation at temperatures in excess of 600 degrees C is further achieved without compromising performance. A nonlinear, thermally induced wavelength shift is also observed at elevated temperatures.

Photoinduced Modifications in Fiber Gratings Inscribed Directly by Infrared Femtosecond Irradiation

The structure of fiber Bragg gratings inscribed point-by-point by an infrared femtosecond laser is studied by quantitative phase microscopy. Results show that these gratings present a central region with a depressed refractive index surrounded by an outer corona with increased refractive index. The refractive index profile suggests the presence of microvoids embedded in a region of the core

Multiwavelength pulse source for OTDM/WDM applications based on arrayed waveguide grating

A 13-wavelength channel 10-GHz pulse source is demonstrated using a novel scheme incorporating a dispersion-imbalanced fiber loop mirror and an arrayed waveguide grating. The output high-quality pulses are 5 ps wide with the pedestal suppression in excess of 25 dB.

Bending characteristics of fiber long-period gratings with cladding index modified by femtosecond laser

A femtosecond laser has been used to asymmetrically modify the cladding of fiber containing long-period gratings. Following modification, devices in single-mode fiber are shown to be capable of sensing the magnitude and direction of bending in one plane by producing blue and red wavelength shifts depending upon the orientation of the bend. The resulting curvature sensitivities were -1.62 and +3.82 nmmiddotm. Devices have also been produced using an elliptical core fiber to study the effects of the cladding modification on the two polarization eigenstates. A cladding modification applied on the fast axis of the fiber is shown to affect the light in the fast axis much more significantly than the light in the orthogonal state; this behavior may ultimately lead to a sensor capable of detecting the direction of bending in two dimensions for applications in shape sensing

Tunable dispersion compensator based on distributed Gires-Tournois etalons

We report a novel tunable dispersion compensator (TDC) based on all-fiber distributed Gires-Tournois etalons (DGTE), which is formed by overlapped chirped fiber gratings. Two DGTEs of opposite dispersion slope work together to generate a tunable periodical dispersion profile. The demonstrated TDCs have the advantages of multichannel operation, extremely low group-delay ripple, low loss, and low cost.

10-gb/s transmission over 100 mm of standard fiber using 2R regeneration in an optical loop mirror

The transmission of a 10-Gb/s data stream was demonstrated experimentally over a practically unlimited distance in a standard single-mode fiber system using nonlinear optical loop mirrors as simple in-line 2R regenerators. Error-free propagation over 100 000 km has been achieved with terrestrial amplifier spacing.

Experimental observation of autosoliton propagation in a dispersion-managed system guided by nonlinear optical loop mirrors

Observation of autosoliton propagation in a dispersion-managed optical transmission system controlled by in-line nonlinear fiber loop switches is reported for what is believed to be the first time. The system is based on a strong dispersion map with large amplifier spacing. Operation at transmission rates of 10 and 40 Gbits/s is demonstrated.