Showing papers on "Photonic-crystal fiber published in 2010"

High-power ZBLAN glass fiber lasers: Review and prospect

Abstract: ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), considered as the most stable heavy metal fluoride glass and the excellent host for rare-earth ions, has been extensively used for efficient and compact ultraviolet, visible, and infrared fiber lasers due to its low intrinsic loss, wide transparency window, and small phonon energy. In this paper, the historical progress and the properties of fluoride glasses and the fabrication of ZBLAN fibers are briefly described. Advances of infrared, upconversion, and supercontinuum ZBLAN fiber lasers are addressed in detail. Finally, constraints on the power scaling of ZBLAN fiber lasers are analyzed and discussed. ZBLAN fiber lasers are showing promise of generating high-power emissions covering from ultraviolet to mid-infrared considering the recent advances in newly designed optical fibers, beam-shaped high-power pump diodes, beam combining techniques, and heat-dissipating technology.

Pulse preserving flat-top supercontinuum generation in all-normal dispersion photonic crystal fibers

Abstract: Supercontinuum (SC) generation in all-normal dispersion photonic crystal fiber under high energy femtosecond pumping is numerically investigated. It is shown that coherent octave spanning SC spectra with flatness of better than ±1 dB can be achieved over the entire bandwidth. A single pulse is maintained in the time domain, which may be externally compressed to the sub-10 fs regime even by simple linear chirp elimination. The single optical cycle limit is approached for full phase compensation, leading to peak power spectral densities of multiple kilowatts/nanometer. The generated SC is therefore ideal for applications which require high broadband spectral power densities as well as a defined pulse profile in the time domain. The properties of the generated SC are shown to be independent of the input pulse duration.

Optical deposition of graphene and carbon nanotubes in a fiber ferrule for passive mode-locked lasing

Abstract: Mode-locked fiber lasers are currently undergoing a significant evolution towards higher pulse energies and shorter pulse durations. A key enabler in this progress has been the discovery of novel saturable absorbers (SA) such as carbon nanotubes (CNT) and graphene. The exceptional properties of CNTs as SA have been extensively studied in recent years. Graphene, a one atom thick planar sheet of carbon atoms arranged into a hexagonal lattice, has been recently proposed as an alternative to CNTs in several photonics applications. Here, we propose a method for the integration of graphene into a fiber ferrule using an optical deposition technique, which has been also employed for the deposition of CNT directly on the core of a fiber edge and in tapered fibers. We investigate and compare the optical properties of CNT-SA and graphene-SA fabricated by this optical deposition technique. Soliton-like, mode-locked lasing is confirmed using an erbium doped optical fiber in an all-fiber ring cavity laser configuration.

Review of long period fiber gratings written by CO2 laser

Abstract: This paper presents a systematic review of long period fiber gratings (LPFGs) written by the CO2 laser irradiation technique. First, various fabrication techniques based on CO2 laser irradiations are demonstrated to write LPFGs in different types of optical fibers such as conventional glass fibers, solid-core photonic crystal fibers, and air-core photonic bandgap fibers. Second, possible mechanisms, e.g., residual stress relaxation, glass structure changes, and physical deformation, of refractive index modulations in the CO2-laser-induced LPFGs are analyzed. Third, asymmetrical mode coupling, resulting from single-side laser irradiation, is discussed to understand unique optical properties of the CO2-laser-induced LPFGs. Fourthly, several pretreament and post-treatment techniques are proposed to enhance the efficiency of grating fabrications. Fifthly, sensing applications of the CO2-laser-induced LPFGs are investigated to develop various LPFG-based temperature, strain, bend, torsion, pressure, and biochemical sensors. Finally, communication applications of the CO2-laser-induced LPFGs are investigated to develop various LPFG-based band-rejection filters, gain equalizers, polarizers, and couplers.

Femtosecond laser fabricated fiber Bragg grating in microfiber for refractive index sensing.

Abstract: Fiber Bragg grating (FBG) is fabricated in the microfiber by the use of femtosecond laser pulse irradiation. Such a grating can be directly exposed to the surrounding medium without etching or thinning treatment of the fiber, thus possessing high refractive index (RI) sensitivity while maintaining superior reliability. The grating in the microfiber may have a number of propagation modes in its transmission spectrum, depending on the fiber diameter, and the higher order of mode has larger RI sensitivity. The RI sensitivity also depends on the fiber diameter and a smaller diameter corresponds to a large sensitivity. The maximum sensitivity obtained is approximately 231.4 nm per refractive index unit at the refractive index value of approximately 1.44 when the fiber diameter is approximately 2 microm. The FBG fabricated in the microfiber has high potential in various types of optical fiber sensor applications.

Quantum frequency translation of single-photon states in a photonic crystal fiber.

Abstract: We experimentally demonstrate frequency translation of a nonclassical optical field via four-wave mixing (Bragg-scattering process) in a photonic crystal fiber (PCF). The high nonlinearity and the ability to control dispersion in PCF enable efficient translation between nearby photon channels within the visible to-near-infrared spectral range, useful in quantum networks. Heralded single photons at 683 nm were translated to 659 nm with an efficiency of 28.6±2.2 percent. Second-order correlation measurements on the 683- and 659-nm fields yielded g(683)(2) (0)=0.21±0.02 and g(659)(2) (0)=0.19±0.05, respectively, showing the nonclassical nature of both fields.

Photonic lanterns: a study of light propagation in multimode to single-mode converters

Abstract: The “photonic lantern,” an optical fibre device that has emerged from the field of astrophotonics, allows for a single-mode photonic function to take place within a multimode fibre. We study and evaluate the modal behaviour of photonic lanterns as well as the conditions for achieving low-loss between a multimode fibre and a “near-diffraction limited” single-mode system. We also present an intuitive analogy of the modal electromagnetic propagation behaviour along the photonic lantern transition in terms of the Kronig-Penney model in Quantum Mechanics.

Fiber in-line Mach-Zehnder interferometer fabricated by femtosecond laser micromachining for refractive index measurement with high sensitivity

Abstract: We report a compact fiber in-line Mach-Zehnder interferometer for refractive index sensing with high sensitivity and precise sensing location. One arm of the interferometer contains a microcavity formed by removing part of the fiber core near the core and cladding interface by femtosecond laser micromachining, and the other arm remains in line with the remaining part of the fiber core. Such a fiber in-line Mach-Zehnder interferometer exhibits an extremely high refractive-index-sensitivity of −9370 nm/RIU (refractive index unit) within the refractive index range between 1.31 and 1.335.

A selectively coated photonic crystal fiber based surface plasmon resonance sensor

Abstract: We propose a novel design for a photonic crystal fiber based surface plasmonic resonance sensor. The sensor consists of selectively metal-coated air holes containing analyte channels, which enhance the phase matching between the plasmonic mode and the core-guided mode. Good refractive index sensitivity as high as 5500 nm/RIU (refractive index unit) can be achieved in the proposed structure. Compared with the entirely coated structure, the selectively coated sensor design demonstrates narrower resonance spectral width. Moreover, the greater resonance depth can improve the sensing performance in terms of signal to noise ratio (SNR). The improvements in spectral width and SNR can both contribute to a better detection limit for this refractive index sensor.

Design of optomechanical cavities and waveguides on a simultaneous bandgap phononic-photonic crystal slab

Abstract: In this paper we study and design quasi-2D optomechanical crystals, waveguides, and resonant cavities formed from patterned slabs. Two-dimensional periodicity allows for in-plane pseudo-bandgaps in frequency where resonant optical and mechanical excitations localized to the slab are forbidden. By tailoring the unit cell geometry, we show that it is possible to have a slab crystal with simultaneous optical and mechanical pseudo-bandgaps, and for which optical waveguiding is not compromised. We then use these crystals to design optomechanical cavities in which strongly interacting, co-localized photonic-phononic resonances occur. A resonant cavity structure formed by perturbing a “linear defect” waveguide of optical and acoustic waves in a silicon optomechanical crystal slab is shown to support an optical resonance at wavelength λ0 ≈ 1.5 µm and a mechanical resonance of frequency ωm/2π ≈ 9.5 GHz. These resonances, due to the simultaneous pseudo-bandgap of the waveguide structure, are simulated to have optical and mechanical radiation-limited Q-factors greater than 107. The optomechanical coupling of the optical and acoustic resonances in this cavity due to radiation pressure is also studied, with a quantum conversion rate, corresponding to the scattering rate of a single cavity photon via a single cavity phonon, calculated to be g/2π = 292 kHz.

Recent progress and novel applications of photonic crystal fibers

Abstract: Photonic crystal fibers present a wavelength-scale periodic microstructure running along their length. Their core and two-dimensional photonic crystal might be based on varied geometries and materials, enabling light guidance due to different propagation mechanisms in an extremely large wavelength range, extending to the terahertz regions. As a result, these fibers have revolutionized the optical fiber technology by means of creating new degrees of freedom in the fiber design, fabrication and applicability. This report aims to provide a detailed statement on the recent progress and novel potential applications of photonic crystal fibers.

Miniature all-silica optical fiber pressure sensor with an ultrathin uniform diaphragm

Abstract: This paper presents an all-silica miniature optical fiber pressure/acoustic sensor based on the Fabry-Perot (FP) interferometric principle. The endface of the etched optical fiber tip and silica thin diaphragm on it form the FP structure. The uniform and thin silica diaphragm was fabricated by etching away the silicon substrate from a commercial silicon wafer that has a thermal oxide layer. The thin film was directly thermally bonded to the endface of the optical fiber thus creating the Fabry-Perot cavity. Thin films with a thickness from 1microm to 3microm have been bonded successfully. The sensor shows good linearity and hysteresis during measurement. A sensor with 0.75 microm-thick diaphragm thinned by post silica etching was demonstrated to have a sensitivity of 11 nm/kPa. The new sensor has great potential to be used as a non-intrusive pressure sensor in a variety of sensing applications.

Maximizing the bandwidth of supercontinuum generation in As_2Se_3 chalcogenide fibers

Abstract: We describe in detail a procedure for maximizing the bandwidth of supercontinuum generation in As2Se3 chalcogenide fibers and the physics behind this procedure. First, we determine the key parameters that govern the design. Second, we find the conditions for the fiber to be endlessly single-mode; the fiber should be endlessly single-mode to maintain high nonlinearity and low coupling loss. We find that supercontinuum generation in As2Se3 fibers proceeds in two stages — an initial stage that is dominated by four-wave mixing and a later stage that is dominated by the Raman-induced soliton self-frequency shift. Third, we determine the conditions to maximize the Stokes wavelength that is generated by four-wave mixing in the initial stage. Finally, we put all these pieces together to maximize the bandwidth. We show that it is possible to generate an optical bandwidth of more than 4 μm with an input pump wavelength of 2.5 μm using an As2Se3 fiber with an air-hole-diameter-to-pitch ratio of 0.4 and a pitch of 3 μm. Obtaining this bandwidth requires a careful choice of the fiber’s waveguide parameters and the pulse’s peak power and duration, which determine respectively the fiber’s dispersion and nonlinearity.

Long distance transmission in few-mode fibers

Abstract: Using multimode fibers for long-haul transmission is proposed and demonstrated experimentally. In particular few-mode fibers (FMFs) are demonstrated as a good compromise since they are sufficiently resistant to mode coupling compared to standard multimode fibers but they still can have large core diameters compared to single-mode fibers. As a result these fibers can have significantly less nonlinearity and at the same time they can have the same performance as single-mode fibers in terms of dispersion and loss. In the absence of mode coupling it is possible to use these fibers in the single-mode operation where all the data is carried in only one of the spatial modes throughout the fiber. It is shown experimentally that the single-mode operation is achieved simply by splicing single-mode fibers to both ends of a 35-km-long dual-mode fiber at 1310 nm. After 35 km of transmission, no modal dispersion or excess loss was observed. Finally the same fiber is placed in a recirculating loop and 3 WDM channels each carrying 6 Gb/s BPSK data were transmitted through 1050 km of the few-mode fiber without modal dispersion.

Ultrafast nonlinear optofluidics in selectively liquid-filled photonic crystal fibers.

Abstract: Selective filling of photonic crystal fibers with different media enables a plethora of possibilities in linear and nonlinear optics. Using two-photon direct-laser writing we demonstrate full flexibility of individual closing of holes and subsequent filling of photonic crystal fibers with highly nonlinear liquids. We experimentally demonstrate solitonic supercontinuum generation over 600 nm bandwidth using a compact femtosecond oscillator as pump source. Encapsulating our fibers at the ends we realize a compact ultrafast nonlinear optofluidic device. Our work is fundamentally important to the field of nonlinear optics as it provides a new platform for investigations of spatio-temporal nonlinear effects and underpins new applications in sensing and communications. Selective filling of different linear and nonlinear liquids, metals, gases, gain media, and liquid crystals into photonic crystal fibers will be the basis of new reconfigurable and versatile optical fiber devices with unprecedented performance. Control over both temporal and spatial dispersion as well as linear and nonlinear coupling will lead to the generation of spatial-temporal solitons, so-called optical bullets.

Cross-talk free and ultra-compact fiber optic sensor for simultaneous measurement of temperature and refractive index.

Abstract: We propose and demonstrate a cross-talk free simultaneous measurement system for temperature and external refractive index (ERI) implemented by dual-cavity Fabry-Perot (FP) fiber interferometer. The sensing probe consists of two cascaded FP cavities formed with a short piece of multimode fiber (MMF) and a micro-air-gap made of hollow core fiber (HOF). The fabricated sensor head was ultra-compact; the total length of the sensing part was less than 600 mum. Since the reflection spectrum of the composite FP structures is given by the superposition of each cavity spectrum, the spectrum measured in the wavelength domain was analyzed in the Fourier or spatial frequency domain. The experimental results showed that temperature could be determined independently from the spatial frequency shift without being affected by the ERI, while the ERI could be also measured solely by monitoring the intensity variation in the spatial frequency spectrum. The ERI and the temperature sensitivities were approximately 16 dB/RIU for the 1.33-1.45 index range, and 8.9 nm/ degrees C at low temperature and 14.6 nm/ degrees C at high temperature, respectively. In addition, it is also demonstrated that the proposed dual-cavity FP sensor has potential for compensating any power fluctuation that might happen in the input light source.

Miniaturized fiber taper reflective interferometer for high temperature measurement.

Abstract: We present an ultra-small all-silica high temperature sensor based on a reflective Fabry-Perot modal interferometer (FPMI). Our FPMI is made of a micro-cavity (~4.4 μm) directly fabricated into a fiber taper probe less than 10 μm in diameter. Its sensing head is a miniaturized single mode-multimode fiber configuration without splicing. The sensing mechanism of FPMI is the interference among reflected fundamental mode and excited high-order modes at the end-faces. Its temperature sensitivity is ~20 pm/°C near the wavelength of 1550 nm. This kind of sensor can work in harsh environments with ultra-large temperature gradient, but takes up little space because of its unique geometry and small size.

Supercontinuum generation in a high index doped silica glass spiral waveguide.

Abstract: We demonstrate supercontinuum (SC) generation at both 1550 nm and 1288 nm in a compact (< 5mm2) 45 cm spiral waveguide composed of CMOS-compatible doped high-index glass. While both wavelengths have weak dispersion and are near zero dispersion points, they present different symmetries. At 1550nm, the normal dispersion regime takes place at longer wavelengths, whereas at 1290nm it is at shorter wavelengths, and we observe features in the SC spectra that clearly reflect this. In particular, the spectrum at 1550 nm is more than 300 nm wide (limited by detection) and is well reproduced by simulations based on the measured dispersion. This work represents a practical on-chip broadband wavelength source with potential use in many important applications.

Auto-cladded large-core optical fibers

Abstract: Embodiments of auto-cladded optical fibers are described. The fibers may have a refractive index profile having a small relative refractive index change. For example, the fiber may include an auto-cladded structure having, e.g., a trough or gradient in the refractive index profile. A beam of light propagating in the fiber may be guided, at least in part, with the auto-cladded structure. In some embodiments, the optical fiber may be all glass. In some embodiments, the optical fiber may include a large-core or an ultra large-core.

Microstructured chalcogenide optical fibers from As(2)S(3) glass: towards new IR broadband sources.

Abstract: The aim of this paper is to present an overview of the recent achievements of our group in the fabrication and optical characterizations of As2S3 microstructured optical fibers (MOFs). Firstly, we study the synthesis of high purity arsenic sulfide glasses. Then we describe the use of a versatile process using mechanical drilling for the preparation of preforms and then the drawing of MOFs including suspended core fibers. Low losses MOFs are obtained by this way, with background level of losses reaching less than 0.5 dB/m. Optical characterizations of these fibers are then reported, especially dispersion measurements. The feasibility of all-optical regeneration based on a Mamyshev regenerator is investigated, and the generation of a broadband spectrum between 1 µm and 2.6 µm by femto second pumping around 1.5 µm is presented.

Strong infrared spectral broadening in low-loss As-S chalcogenide suspended core microstructured optical fibers

Abstract: We report the fabrication and characterization of the first guiding chalcogenide As2S3 microstructured optical fibers (MOFs) with a suspended core. At 1.55 µm, the measured losses are approximately 0.7 dB/m or 0.35 dB/m according to the MOF core size. The fibers have been designed to present a zero dispersion wavelength (ZDW) around 2 µm. By pumping the fibers at 1.55 µm, strong spectral broadenings are obtained in both 1.8 and 45-m-long fibers by using a picosecond fiber laser.

Single-polarization high power fiber lasers and amplifiers

Abstract: A novel polarization maintaining optical fiber, which can be used as a high-power polarization maintaining fiber laser or amplifier, is described. Insensitivity of the polarization state to external fiber bending and temperature changes is accomplished by minimizing polarization mode-coupling via reducing stresses inside the fiber core via increasing the fiber diameter. Alternatively, polarization mode-coupling can be minimized by an optimization of the fiber coating to minimize stresses at the interface between the fiber and the coating. As a result insensitivity to polarization mode-coupling is obtained at greatly reduced values of birefringence compared to small-diameter fibers. The fiber is of significant use in any application where polarization stability is important, and will be useful in telecommunications applications in particular for reducing polarization mode dispersion. An implementation in a parabolic pulse-producing fiber laser is also described as one specific high power example.

Casting method for producing low-loss chalcogenide microstructured optical fibers

Abstract: We report significant advances in the fabrication of low loss chalcogenide microstructured optical fiber (MOF). This new method, consisting in molding the glass in a silica cast made of capillaries and capillary guides, allows the development of various designs of fibers, such as suspended core, large core or small core MOFs. After removing the cast in a hydrofluoric acid bath, the preform is drawn and the design is controlled using a system applying differential pressure in the holes. Fiber losses, which are the lowest recorded so far for selenium based MOFs, are equal to the material losses, meaning that the process has no effect on the glass quality.

Some features of the photonic crystal fiber temperature sensor with liquid ethanol filling

Abstract: We introduce a novel photonic crystal fiber (PCF) temperature sensor that is based on intensity modulation and liquid ethanol filling of air holes with index-guiding PCF. The mode field, the effective refractive index and the confinement loss of PCF were all found to become highly temperature-dependent when the thermo-optic coefficient of the liquid ethanol used is higher than that of silicon dioxide and this temperature dependence is an increasing function of the d/Λ ratio and the input wavelength. All the experiments and simulations are discussed in this paper and the temperature sensitivity of transmission power was experimentally determined to be 0.315 dB/°C for a 10-cm long PCF.

Highly birefringent microstructured fibers with enhanced sensitivity to hydrostatic pressure.

Abstract: We designed, manufactured and characterized two birefringent microstructured fibers that feature a 5-fold increase in polarimetric sensitivity to hydrostatic pressure compared to the earlier reported values for microstructured fibers. We demonstrate a good agreement between the finite element simulations and the experimental values for the polarimetric sensitivity to pressure and to temperature. The sensitivity to hydrostatic pressure has a negative sign and exceeds −43 rad/MPa × m at 1.55 μm for both fibers. In combination with the very low sensitivity to temperature, this makes our fibers the candidates of choice for the development of microstructured fiber based hydrostatic pressure measurement systems.

Femtosecond laser-assisted selective infiltration of microstructured optical fibers.

Abstract: A new method of selectively infiltrating microstructured optical fibers with the assistance of femtosecond laser micromachining is presented. With this technique, any type of air-holes in the cross-section of the microstructured optical fibers can be selectively infiltrated with liquids, which opens up a highly efficient, precise, flexible and reliable way of selective infiltrating and has high potential in the fabrication of novel hybrid-structured optical fibers and the devices based on them.

Broadband true time delay for microwave signal processing, using slow light based on stimulated Brillouin scattering in optical fibers.

Abstract: We experimentally demonstrate a novel technique to process broadband microwave signals, using all-optically tunable true time delay in optical fibers. The configuration to achieve true time delay basically consists of two main stages: photonic RF phase shifter and slow light, based on stimulated Brillouin scattering in fibers. Dispersion properties of fibers are controlled, separately at optical carrier frequency and in the vicinity of microwave signal bandwidth. This way time delay induced within the signal bandwidth can be manipulated to correctly act as true time delay with a proper phase compensation introduced to the optical carrier. We completely analyzed the generated true time delay as a promising solution to feed phased array antenna for radar systems and to develop dynamically reconfigurable microwave photonic filters.

Fiber delivered probe for efficient CARS imaging of tissues

Abstract: We demonstrate a fiber-based probe for maximum collection of the coherent anti-Stokes Raman scattering (CARS) signal in biological tissues. We discuss the design challenges including capturing the back-scattered forward generated CARS signal in the sample and the effects of fiber nonlinearities on the propagating pulses. Three different single mode fibers (fused silica fiber, photonic crystal fiber and double-clad photonic crystal fiber) were tested for the probe design. We investigated self-phase modulation, stimulated Raman scattering (SRS) and four-wave-mixing (FWM) generation in the fiber: nonlinear processes expected to occur in a two-beam excitation based probe. While SPM and SRS induced spectral broadening was negligible, a strong non phase-matched FWM contribution was found to be present in all the tested fibers for excitation conditions relevant to CARS microscopy of tissues. To spectrally suppress this strong contribution, the probe design incorporates separate fibers for excitation light delivery and for signal detection, in combination with dichroic optics. CARS images of the samples were recorded by collecting the back-scattered forward generated CARS signal in the sample through a multi-mode fiber. Different biological tissues were imaged ex vivo in order to assess the performance of our fiber-delivered probe for CARS imaging, a tool which we consider an important advance towards label-free, in vivo probing of superficial tissues.

Temperature-Insensitive Torsion Sensor With Enhanced Sensitivity by Use of a Highly Birefringent Photonic Crystal Fiber

Abstract: We report on enhanced torsion sensitivity by using a highly birefringent photonic crystal fiber (HB-PCF)-based Sagnac interferometer. In order to increase the torsion sensitivity, we introduced an anisotropic microstructure into the cross section of an HB-PCF by enlarging the size of air holes of one row. This can result in a high birefringence of the order of 10-3 and low sensitivities to bending and temperature. The torsion sensitivity was measured to be high with ~0.06 nm/°.