Showing papers on "Single-mode optical fiber published in 2006"

Recent Advances of VCSEL Photonics

Abstract: A vertical-cavity surface emitting laser (VCSEL) was invented 30 years ago. A lot of unique features can be expected, such as low-power consumption, wafer-level testing, small packaging capability, and so on. The market of VCSELs has been growing up rapidly in recent years, and they are now key devices in local area networks using multimode optical fibers. Also, long wavelength VCSELs are currently attracting much interest for use in single-mode fiber metropolitan area and wide area network applications. In addition, a VCSEL-based disruptive technology enables various consumer applications such as a laser mouse and laser printers. In this paper, the recent advance of VCSEL photonics will be reviewed, which include the wavelength extension of single-mode VCSELs and their wavelength integration/control. Also, this paper explores the potential and challenges for new functions of VCSELs toward optical signal processing

Low-loss subwavelength plastic fiber for terahertz waveguiding.

Abstract: We report a simple subwavelength-diameter plastic wire, similar to an optical fiber, for guiding a terahertz wave with a low attenuation constant. With a large wavelength-to-fiber-core ratio, the fractional power delivered inside the lossy core is reduced, thus lowering the effective fiber attenuation constant. In our experiment we adopt a polyethylene fiber with a 200 µm diameter for guiding terahertz waves in the frequency range near 0.3 THz in which the attenuation constant is reduced to of the order of or less than 0.01 cm−1. Direct free-space coupling efficiency as high as 20% can be achieved by use of an off-axis parabolic mirror. Furthermore, all the plastic wires are readily available, with no need for complex or expensive fabrication.

Arbitrary-bandwidth Brillouin slow light in optical fibers

Abstract: Brillouin slow light in optical fibers is a promising technique for the development of all-optical buffers to be used in optical routers. The main drawback of this technique up to now has been its narrow bandwidth, normally restricted to 35 MHz in conventional single-mode optical fibers. In this paper we demonstrate experimentally that Brillouin slow light with an arbitrary large bandwidth can be readily obtained in conventional optical fibers using a simple and inexpensive pump spectral broadening technique. In our experiments, we show the delaying of 2.7 ns pulses over slightly more than one pulse length with only some residual broadening (<25%) of the pulse width. We see no limit to extend this technique to the delaying of GHz-bandwidth signals.

All-fiber multimode-interference-based refractometer sensor: proposal and design

Abstract: A novel all-fiber refractometer sensor is proposed, which is based on multimode interference in the multimode fiber core section sandwiched between two single-mode fibers. A wide-angle beam propagation method in the cylindrical coordinate is employed as the modeling tool for simulation and design of the proposed refractometer sensor. The design for a refractometer is presented that shows that the refractometer would have an estimated resolution of 5.4 x 10(-5) for refractive indices from 1.33 to 1.45 and of 3.3 x 10(-5) for refractive indices from 1.38 to 1.45 through the choice of an appropriate length of the multimode fiber core section.

Light propagation with ultralarge modal areas in optical fibers.

Abstract: We demonstrate robust single-transverse-mode light propagation in higher-order modes of a fiber, with effective area Aeff ranging from 2100 to 3200 μm2. These modes are accessed using long-period fiber gratings that enable higher-order-mode excitation over a bandwidth of 94 mm with greater than 99% of the light in the desired mode. The fiber is designed such that the effective index separation between modes is always large, hence minimizing in-fiber mode mixing and enabling light propagation over lengths as large as 12 m, with bends down to 4.5 cm radii. The modal stability increases with mode order, suggesting that Aeff of this platform is substantially scalable.

Photonic generation of microwave signal using a dual-wavelength single-longitudinal-mode fiber ring laser

Abstract: A novel approach for the generation of high-frequency microwave signals using a dual-wavelength single-longitudinal-mode fiber ring laser is proposed and demonstrated. In the proposed configuration, a dual-wavelength fiber Bragg grating (FBG) with two ultranarrow transmission bands in combination with a regular FBG is used to ensure single-longitudinal-mode operation of the fiber ring laser. A semiconductor optical amplifier is employed as the gain medium in the ring cavity. Since the two lasing wavelengths share the same gain cavity, the relative phase fluctuations between the two wavelengths are low and can be used to generate a low-phase-noise microwave signal without need of a microwave reference source. Three dual-wavelength ultranarrow transmission-band FBGs with wavelength spacing of 0.148, 0.33, and 0.053 nm are respectively incorporated into the laser. Microwave signals at 18.68, 40.95, and 6.95 GHz are obtained by beating the dual wavelengths at a photodetector. The spectral width of the generated microwave signals as small as 80 kHz with a frequency stability better than 1 MHz in the free-running mode at room temperature is obtained.

High Resolution Distributed Strain or Temperature Measurements in Single-and Multi-mode Fiber Using Swept-Wavelength Interferometry

Abstract: We describe use of swept-wavelength interferometry for distributed fiber-optic strain and temperature sensing in single mode and gradient index multimode fiber. The method is used to measure strain in a four-strand multimode cable under twist.

Ultrafast all-optical differentiators

Abstract: We report the experimental realization of an ultrafast all-optical temporal differentiator. Differentiation is obtained via all-fiber filtering based on a simple diffraction grating-assisted mode coupler (uniform long-period fiber grating) that performs full energy conversion at the optical carrier frequency. Due to its high bandwidth, this device allows processing of arbitrary optical signals with sub-picosecond temporal features (down to 180-fs with the specific realizations reported here). Functionality of this device was tested by differentiating a 700-fs Gaussian optical pulse generated from a fiber laser (@ 1535nm). The derivative of this pulse is an odd-symmetry Hermite-Gaussian waveform, consisting of two linked 500-fs-long, π-phase-shifted temporal lobes. This waveform is noteworthy for its application in advanced ultrahigh-speed optical communication systems.

Ultralong Raman Fiber Lasers as Virtually Lossless Optical Media

Abstract: By transforming the optical fiber span into an ultralong cavity laser, we experimentally demonstrate quasilossless transmission over long (up to 75 km) distances and virtually zero signal power variation over shorter (up to 20 km) spans, opening the way for the practical implementation of integrable nonlinear systems in optical fiber. As a by-product of our technique, the longest ever laser (to the best of our knowledge) has been implemented, with a cavity length of 75 km. A simple theory of the lossless fiber span, in excellent agreement with the observed results, is presented.

Coherently coupled high-power fiber arrays

Abstract: A four-element fiber array has demonstrated 470 watts of coherently phased, linearly polarized light energy in a single far-field spot. Each element consists of a single-mode fiber-amplifier chain. Phase control of each element is achieved with a Lithium-Niobate phase modulator. A master laser provides a linearly polarized, narrow linewidth signal that is split into five channels. Four channels are individually amplified using polarization maintaining fiber power amplifiers. The fifth channel is used as a reference arm. It is frequency shifted and then combined interferometrically with a portion of each channel's signal. Detectors sense the heterodyne modulation signal, and an electronics circuit measures the relative phase for each channel. Compensating adjustments are then made to each channel's phase modulator. This effort represents the results of a multi-year effort to achieve high power from a single element fiber amplifier and to understand the important issues involved in coherently combining many individual elements to obtain sufficient optical power for directed energy weapons. Northrop Grumman Corporation and the High Energy Laser Joint Technology Office jointly sponsored this work.

Towards CARS Endoscopy

Abstract: We provide a proof-of-principle demonstration of CARS endoscopy. The design utilizes a single mode optical fiber with a focusing unit attached to the distal end. Picosecond pump and Stokes pulse trains in the near infrared are delivered through the fiber with nearly unaltered spectral and temporal characteristics at intensities needed for endoscopy. CARS endoscopic images are recorded by collecting the epi-CARS signal generated at the sample and raster scanning the sample with respect to the fiber. This CARS endoscope prototype represents an important step towards in situ chemically selective imaging for biomedical applications.

Versatile chromatic dispersion measurement of a single mode fiber using spectral white light interferometry

Abstract: We present a versatile and accurate chromatic dispersion measurement method for single mode optical fibers over a wide spectral range (200 nm) using a spectral domain white light interferometer. This technique is based on spectral interferometry with a Mach-Zehnder interferometer setup and a broad band light source. It takes less than a second to obtain a spectral interferogram for a few tens of centimeter length fiber sample. We have demonstrated that the relative group velocity, the chromatic dispersion and the dispersion slope of a sample fiber can be obtained very accurately regardless of the zero-dispersion wavelength (ZDW) of a sample after frequency dependent optical phase was directly retrieved from a spectral interferogram. The measured results with our proposed method were compared with those obtained with a conventional time-domain dispersion measurement method. A good agreement between those results indicates that our proposed method can measure the chromatic dispersion of a short length optical fiber with very high accuracy.

Stable single-mode operation of a narrow-linewidth, linearly polarized, erbium-fiber ring laser using a saturable absorber

Abstract: This paper describes the design and operation of a stable narrow-linewidth linearly polarized fiber ring laser using a polarization-maintaining (PM) erbium-doped fiber as a saturable absorber. The effect of the PM fiber on suppressing mode hopping is experimentally demonstrated and optimum conditions for single-mode operation are identified. Laser output power is /spl sim/ 4.7 mW at 1535 nm for a pump power of 94 mW, the polarization extinction ratio is 24.8 dB, the SNR is larger than 45 dB, the relative intensity noise is below -104 dB/Hz at frequencies above 150 kHz, and the linewidth is less than 1.5 kHz. Potential applications of the fiber laser for interferometric or spectroscopic fiber sensors are briefly discussed.

Single-mode low-loss chalcogenide glass waveguides for the mid-infrared.

Abstract: We demonstrate the design, fabrication, and characterization of single-mode low-loss waveguides for mid-infrared (MIR) wavelengths. Planar waveguide structures were fabricated from multilayer thin films of arsenic-based chalcogenide glasses followed by the creation of channel waveguides by using the photodarkening effect. Propagation losses as low as 0.5 dB/cm were measured for a quantum cascade laser end-fire coupled into the waveguides. This is a first step toward the design and fabrication of integrated optical components for MIR applications.

Wavelength-division-multiplexed Millimeter-waveband radio-on-fiber system using a supercontinuum light source

Abstract: We propose to use a supercontinuum (SC) for a low-phase-noise multiwavelength light source in wavelength-division-multiplexing (WDM) millimeter-waveband (mm-waveband) radio-on-fiber (RoF) systems. We demonstrate the generation of low-phase-noise 60-GHz-band RoF signal. We also demonstrate the generation of two-channel WDM 60-GHz-band RoF signals and the transmission of the signals over a 25-km standard single-mode fiber (SMF) using photonic upconversion. The single multiwavelength light source can be shared with a number of users and simplifies the system configuration, which would allow the realization of high-reliability as well as low-cost RoF systems. Finally, the RoF network capacity with a single SC light source is estimated to be over 10 000 channels when the spectrum of the SC light source is fully utilized.

30-gb/s signal transmission over 40-km directly modulated DFB-laser-based single-mode-fiber links without optical amplification and dispersion compensation

Abstract: Based on a recently proposed novel optical-signal-modulation technique of adaptively modulated optical orthogonal frequency-division multiplexing (AMOOFDM), numerical simulations of the transmission performance of AMOOFDM signals are undertaken in directly modulated DFB laser (DML)-based single-mode-fiber (SMF) links without optical amplification and dispersion compensation. It is shown that a 30-Gb/s transmission over a 40-km SMF with a loss margin of greater than 4.5 dB is feasible in the aforementioned simple configuration using intensity modulation and direct detection (IMDD). In addition, the DFB-laser frequency chirp and the transmission-link loss are identified to be the key factors limiting the maximum achievable transmission performance of the technique. The first factor is dominant for transmission distances of 80 km. It is also observed that fibers of different types demonstrate similar transmission performances, on which fiber nonlinear effects are negligible.

Beam quality factor of higher order modes in a step-index fiber

Abstract: The beam quality factor (or M2-parameter) for linearly polarized (LP)-modes of a step-index fiber is calculated in a closed form, as a function of the fiber V-number. It is shown that M2 sharply peaks for all fiber modes when they are close to cutoff. Particularly simple expressions are derived in the limit Vrarrinfin. Two practically important coherent superpositions of modes are considered for which the degree of degradation of the beam quality due to the higher order mode content is calculated. The reported results can be useful for designing large-core high-power fiber lasers, amplifiers, and fiber-based beam delivery systems, when preservation of the spatial beam quality is important

Photonics and lasers : an introduction

Abstract: Preface. PART I: PROPAGATION OF LIGHT. 1. Overview. 1-1 Photonics Defined. 1-2 Fiber Optic Communications. 1-3 Overview of Topics. 2. Review of Optics. 2-1 The Nature of Light. 2-2 Light at a Boundary. 2-3 Light Passing through. 2-4 Imaging Optics. 3. Planar Waveguides. 3-1 Waveguide Modes. 3-2 Mode Chart. 3-3 Dispersion. 4. Cylindrical Waveguides. 4-1 Acceptance Angle and Numerical Aperture. 4-2 Cylindrical Waveguide. 5. Losses in Optical Fibers. 5-1 Absorption Loss. 5-2 Scattering. 5-3 Bending Losses. 6. Dispersion in Optical Fibers. 6-1 Graded Index Fiber. 6-2 Intramodal Dispersion. 7. Fiber Connections and Diagnostics. 7-1 Fiber Connections. 7-2 Losses in Fiber Connections. 7-3 Fiber Loss Diagnostics. 8. Photonic Crystal Optics. 8-1 1-D Photonic Crystals. 8-2 2-D Photonic Crystals. 8-3 3-D Photonic Crystals. 9. Nonlinear Optics. 9-1 Fundamental Mechanisms. 9-2 Frequency Conversion. 9-3 Nonlinear Refractive Index. 9-4 Electro-optic Effects. PART II: GENERATION AND DETECTTION OF LIGHT. 10. Review of Semiconductor Physics. 10-1 Uniform Semiconductors. 10-2 Layered Semiconductors. 11. Light Sources. 11-1 The LED. 11-2 The Laser Diode. 12. Light Source to Waveguide Coupling Efficiency. 12-1 Point Source. 12-2 Lambertian Source. 12-3 Laser Source. 13. Optical Detectors. 13-1 Thermal Detectors. 13-2 Photon Detectors. 13-3 Noise in Photon Detectors. Part 2 Generation and Detection of Light. 14. Photodiode Detectors . 14-1 Biasing the Photodiode. 14-2 Output Saturation. 14-3 Response Time. 14-4 Types of Photodiodes. 14-5 Signal-to-Noise Ratio. 14-6 Detector Circuits. PART 3: LASER LIGHT. 15. Lasers and Coherent Light. 15-1 Overview of Laser. 15-2 Optical Coherence. 16. Optical Resonators. 16-1 Mode Frequencies. 16-2 Mode Width. 16-3 Fabry-Perot Interferometer. 17. Gaussian Beam Optics. 17-1 Gaussian Beams in Free. 17-2 Gaussian Beams in a Laser. 17-3 Gaussian Beams Passing. 18. Stimulated Emission and Optical Gain. 18-1 Transition Rates. 18-2 Optical Gain. 19. Optical Amplifiers. 19-1 Gain Coefficient. 19-2 Total Gain of Amplifier. 20. Laser Oscillation. 20-1 Threshold Condition. 20-2 Above Lasing Threshold. 21. CW Laser Characteristics. 21-1 Mode Spectrum of Laser. 21-2 Controlling the Laser. 22. Pulsed Lasers. 22-1 Uncontrolled Pulsing. 22-2 Pulsed Pump. 22-3 Theory of Q-Switching. 22-4 Methods of Q-Switching. 22-5 Theory of Mode Locking. 22-6 Methods of Mode Locking. 23 Survey of Laser Types. PART 4: LIGHT-BASED COMMUNICATIONS. 23-1 Optically Pumped Lasers. 23-2 Electrically Pumped Lasers. 24 Optical Communications. 24-1 Fiber Optic CommunicationsSystems. 24-2 Signal Multiplexing. 24-3 Power Budget in Fiber Optic. 24-4 Optical Amplifiers. 24-5 Free-Space Optics. Bibliography. Appendix A: Solid Angle and the Brightness Theorem. Appendix B: Fourier Synthesis and the Uncertainty Relation. List of Symbols. Index.

Microchannels in conventional single-mode fibers.

Abstract: Microchannels are fabricated into conventional single-mode fibers by femtosecond laser processing and chemical etching. Fabrication limitations imposed by the fiber geometry are highlighted and resolved through a simple technique without compromising fabrication flexibility. A microfluidic fiber device consisting of a 4 μm wide microchannel that intersects the fiber core for refractive index sensing is further demonstrated. © 2006 Optical Society of America.

Suppression of stimulated Raman scattering in a high power Yb-doped fiber amplifier using a W-type core with fundamental mode cut-off.

Abstract: We demonstrate the suppression of stimulated Raman scattering in a high power, single-mode Yb-doped fiber amplifier using a W-type core structure. Raman-scattered light is not guided by the core. The amplifier consists of a master oscillator power amplifier (MOPA) system, seeded with 103 ps pulses at 32 MHz repetition rate in the final amplification stage. An average output power of 53 W, which corresponds to 13 kW of peak power, was achieved in the 23 m long W-type double-clad fiber without any significant loss of power due to transfer from the signal wavelength at 1060 nm to the Raman Stokes wavelength at 1114 nm and amplified spontaneous emission from Yb-ions at longer wavelengths (~1070 nm). The power conversion efficiency at 1060 nm was 80% with respect to the absorbed pump power.

Photon pair generation using four-wave mixing in a microstructured fibre: theory versus experiment

Abstract: We develop a theoretical analysis of four-wave mixing used to generate photon pairs useful for quantum information processing. The analysis applies to a single mode microstructured fibre pumped by an ultra-short coherent pulse in the normal dispersion region. Given the values of the optical propagation constant inside the fibre, we can estimate the created number of photon pairs per pulse, their central wavelength and their respective bandwidth. We use the experimental results from a picosecond source of correlated photon pairs using a micro-structured fibre to validate the model. The fibre is pumped in the normal dispersion regime at 708 nm and phase matching is satisfied for widely spaced parametric wavelengths of 586 and 894 nm. We measure the number of photons per pulse using a loss-independent coincidence scheme and compare the results with the theoretical expectation. We show a good agreement between the theoretical expectations and the experimental results for various fibre lengths and pump powers.

Chromatic dispersion profile optimization of dual-concentric-core photonic crystal fibers for broadband dispersion compensation

Abstract: Chromatic dispersion profile of dual-concentric-core photonic crystal fibers is optimized for broadband dispersion compensation of single mode fibers (SMFs) by using genetic algorithm incorporated with full-vector finite-element method. From the numerical results presented here, it is found that by increasing the distance between central core and outer ring core, larger negative dispersion coefficient and better dispersion slope compensation are possible. There is a tradeoff between the magnitude of negative dispersion coefficient and dispersion slope compensation due to the concave dispersion profile of dual-concentric-core photonic crystal fibers. In spite of the tradeoff, dual-concentric-core photonic crystal fibers having larger negative dispersion coefficient as well as compensating for dispersion slope of SMFs in the entire C band with large effective area can be designed.

Propagation loss in single-mode ultrasmall square silicon-on-insulator optical waveguides

Abstract: Silicon-on-insulator (SOI) optical waveguides insure high electromagnetic field confinement but suffer both from sidewall roughness responsible of scattering effects and from leakage toward the silicon substrate. These two mechanisms are the main sources of loss in such optical waveguides. Considering the case of single-mode ultrasmall square SOI waveguides, propagation loss is calculated at telecommunication wavelengths taking into account these two loss contributions. Leakage toward the substrate and scattering effects strongly depend on the waveguide size as well as on the operating wavelength.

Optical fiber long-period grating with solgel coating for gas sensor

Abstract: The novel long-period fiber grating (LPFG) film sensor is composed of the long-period grating coated with solgel-derived sensitive films. The characteristics of the transmissivity of the LPFG film sensor are studied. By analyzing the relation among the sensitivity S-n, the thin film optical parameters, and the fiber grating parameters, the optimal design parameters of the LPFG film sensor are obtained. Data simulation shows that the resolution of the refractive index of this LPFG film sensor is predicted to be 10(-8). Experimentally, a LPFG film sensor for detection Of C2H5OH was fabricated, and a preliminary gas-sensing test was performed. (c) 2006 Optical Society of America.

Hollow-core microstructured polymer optical fiber.

Abstract: We have fabricated microstructured polymer optical fibers that guide light in a hollow core using the photonic bandgap mechanism. The hollow core allows the use of polymer fibers to be extended to wavelength ranges where material absorption typically prohibits their use, with attenuation lower than the material loss observed in the infrared. The fabrication method is similar to other microstructured polymer optical fibers, which has favorable implications for the feasibility of manufacturing such bandgap fibers.

Design of single-polarization single-mode photonic crystal fiber at 1.30 and 1.55 /spl mu/m

Abstract: Single-polarization single-mode (SPSM) operation of a highly birefringent (HB) photonic crystal fiber (PCF) is investigated in detail by using a full-vector finite-element method (FEM) with anisotropic perfectly matched layers (PMLs). The cutoff wavelengths of the two linearly polarized principal states can be designed by varying the structure parameters of the PCF. The confinement loss and splice loss to standard single-mode fiber for particular SPSM PCFs are calculated and optimized at both 1.30 and 1.55 /spl mu/m.

Chiral fiber gratings

Abstract: Examples of adiabatic modification of optical fiber parameters while maintaining single-mode propagation are discussed in the paper. It is found that adiabatic variation of polarization of fiber mode enables efficient coupling of a PM fiber supporting linearly polarized modes and a chiral fiber supporting circularly or elliptically polarized modes.