Showing papers on "Single-mode optical fiber published in 2007"

Photonics : optical electronics in modern communications

Abstract: 1. Electromagnetic Fields and Waves 2. Rays and Optical Beams 3. Dielectric Waveguides and Optical Fibers 4. Optical Resonators 5. Interaction of Radiation and Atomic Systems 6. Theory of Laser Oscillation and Some Specific Laser Systems 7. Chromatic Dispersion and Polarization Mode Dispersion in Fibers 8. Nonlinear Optics 9. Electro-Optics and AO modulators 10. Noise in Optical Detection and Generation 11. Detection of Optical Radiation 12. Periodic Structures 13. Waveguide Coupling 14. Nonlinear Optical Effects in Fibers 15. Semiconductor Lasers 16. Advanced Semiconductor Lasers 17. Optical Amplifiers 18. Classical Treatment of Quantum Optics, Quantum Noise, and Squeezing A. WAVE EQUATION IN CYLINDRICAL COORDINATES AND BESSEL FUNCTIONS B. EXACT SOLUTIONS OF THE STEP-INDEX CIRCULAR WAVEGUIDE C. KRAMERS-KRONIG RELATIONS D. TRANSFORMATION OF A COHERENT ELECTROMAGNETIC FIELD BY A THIN LENS E. FERMI LEVEL AND ITS TEMPERATURE DEPENDENCE F. ELECTRO-OPTIC EFFECT IN CUBIC 43M CRYSTALS G. CONVERSION FOR POWER UNITS AND ATTENUATION UNITS

An Introduction to Fiber Optics

Abstract: 1. Introduction 2. Basic optics 3. The optical fiber 4. Ray analysis of planar optical waveguide 5. Graded index optical fibers 6. Material dispersion 7. Planar waveguides 8. Characteristics of a step-index fiber 9. Graded Index fibers 10. Waveguide dispersion and design considerations 11. Sources for optical fiber communication 12. Detectors for optical fiber and communication 13. Fiber optic communication system design 14. Optical fiber Amplifiers 15. Dispersion compensation and chirping phenomenon 16. Optical solitons 17. Single-mode fiber optic components 18. Single mode optical fiber sensors 19. Measurement methods in optical fiber: I 20. Measurement methods in optical fibers: II 21. Periodic interactions in waveguides 22. Ray equation in Cartesian coordinates 23. Ray paths 24. Leaky modes.

All-fiber Mach-Zehnder type interferometers formed in photonic crystal fiber.

Abstract: We propose simple and compact methods for implementing all-fiber interferometers. The interference between the core and the cladding modes of a photonic crystal fiber (PCF) is utilized. To excite the cladding modes from the fundamental core mode of a PCF, a coupling point or region is formed by using two methods. One is fusion splicing two pieces of a PCF with a small lateral offset, and the other is partially collapsing the air-holes in a single piece of PCF. By making another coupling point at a different location along the fiber, the proposed all-PCF interferometer is implemented. The spectral response of the interferometer is investigated mainly in terms of its wavelength spectrum. The spatial frequency of the spectrum was proportional to the physical length of the interferometer and the difference between the modal group indices of involved waveguide modes. For the splicing type interferometer, only a single spatial frequency component was dominantly observed, while the collapsing type was associated with several components at a time. By analyzing the spatial frequency spectrum of the wavelength spectrum, the modal group index differences of the PCF were obtained from 2.83×10-3 to 4.65 ×10-3 . As potential applications of the all-PCF interferometer, strain sensing is experimentally demonstrated and ultra-high temperature sensing is proposed.

Compact and Highly Efficient Grating Couplers Between Optical Fiber and Nanophotonic Waveguides

Abstract: We present high-efficiency grating couplers for coupling between a single-mode fiber and nanophotonic waveguides, fabricated both in silicon-on-insulator (SOI) and InP membranes using BenzoCycloButene wafer bonding. The coupling efficiency is substantially increased by adding a gold bottom mirror to the structures. The measured coupling efficiency to fiber is 69% for SOI grating couplers and 56% for bonded InP membrane grating couplers

Electronic compensation of chromatic dispersion using a digital coherent receiver.

Abstract: Digital signal processing (DSP) combined with a phase and polarization diverse coherent receiver is a promising technology for future optical networks. Not only can the DSP be used to remove the need for dynamic polarization control, but also it may be utilized to compensate for nonlinear and linear transmission impairments. In this paper we present results of a 42.8Gbit/s nonlinear transmission experiment, using polarization multiplexed QPSK data at 10.7GBaud, with 4 bits per symbol. The digital coherent receiver allows 107,424 ps/nm of chromatic dispersion to be compensated digitally after transmission over 6400km of standard single mode fiber.

Coherent transfer of an optical carrier over 251 km.

Abstract: We transfer an optical frequency over 251 km of optical fiber with a residual instability of 6x10(-19) at 100 s This instability and the associated timing jitter are limited fundamentally by the noise on the optical fiber and the link length We give a simple expression for calculating the achievable instability and jitter over a fiber link Transfer of optical stability over this long distance requires a highly coherent optical source, provided here by a cw fiber laser locked to a high finesse optical cavity A sufficient optical carrier signal is delivered to the remote fiber end by incorporating two-way, in-line erbium-doped fiber amplifiers to balance the 62 dB link loss

Enhanced Kerr nonlinearity in sub-wavelength diameter As2Se3 chalcogenide fiber tapers

Abstract: We experimentally demonstrate enhanced Kerr nonlinear effects in highly nonlinear As2Se3 chalcogenide fiber tapered down to subwavelength waist diameter of 1.2 µm. Based on self phase modulation measurements, we infer an enhanced nonlinearity of 68 W-1m-1. This is 62,000 times larger than in standard silica singlemode fiber, owing to the 500 times larger n2 and almost 125 times smaller effective mode area. We also consider the potential to exploit the modified dispersion in these tapers for ultra-low threshold supercontinuum generation.

Directly Modulated Self-Seeding Reflective Semiconductor Optical Amplifiers as Colorless Transmitters in Wavelength Division Multiplexed Passive Optical Networks

Abstract: The deployment rate of wavelength division multiplexed passive optical networks (WDM-PONs) is expected to accelerate with the availability of cost-efficient wavelength-specific transmitters. Fueled by this promise, we propose and experimentally demonstrate a novel scheme that facilitates the use of reflective semiconductor optical amplifiers (RSOAs) as colorless upstream transmitters. Central to the scheme is the use of a passive reflective path that is placed at the remote node (RN) to reflect a spectral slice of the broadband amplified spontaneous emission (ASE) light emitted from each RSOA. The reflected spectral slice, termed as a seeding light, establishes a self-seeding of the RSOA with measurements indicating the self-seeded output to be incoherent with a low relative intensity noise. The subsequent direct modulation of the self-seeding RSOA with nonreturn-to-zero data at 1.25 Gb/s for upstream transmission exhibits good transmission and crosstalk performance after traversing 21 km of single-mode fiber. Our proposed scheme eliminates the need for centralized broadband sources, external modulators, and active temperature control within the RN and between the RN and the optical network unit. Aside from the feasibility study of self-seeding RSOAs, we investigate the upstream performance dependence on the characteristics of the seeding light. Our investigations reveal that there exists a noise floor limit of the bit error rate (BER) of the self-seeded upstream signal. The noise floor is shown to vary with an initial optical seeding power that affects the level of ASE noise suppression of the self-seeded upstream signal. None the less, the RSOA self-seeds at a user-defined wavelength with a sufficient suppression of ASE noise to achieve a BER=10-9 with only -30.5 dBm of initial optical seeding power. Our characterization of the frequency response of the RSOA reveals a high-pass filter response that suppresses the modulation on the reflected seeding light, and thus stabilizing the self-seeded output. Collectively, these features highlight the potential of using the self-seeding RSOAs to realize a cost-efficient WDM-PON solution in the near future

Ultrafast-laser inscription of a three dimensional fan-out device for multicore fiber coupling applications.

Abstract: A fan-out device has been fabricated using ultrafast-laser waveguide-inscription that enables each core of a multicore optical fiber (MCF) to be addressed by a single mode fiber held in a fiber V-groove array (FVA). By utilizing the unique three-dimensional fabrication capability of this technique we demonstrate coupling between an FVA consisting of a one-dimensional array of fibers and an MCF consisting of a two-dimensional array of cores. When coupled to all cores of the MCF simultaneously, the average insertion loss per core was 5.0 dB in the 1.55 mum spectral region. Furthermore, the fan-out exhibited low cross-talk and low polarization dependent loss.

Graded-index fiber lens proposed for ultrasmall probes used in biomedical imaging

Abstract: The quality and parameters of probing optical beams are extremely important in biomedical imaging systems both for image quality and light coupling efficiency considerations. For example, the shape, size, focal position, and focal range of such beams could have a great impact on the lateral resolution, penetration depth, and signal-to-noise ratio of the image in optical coherence tomography. We present a beam profile characterization of different variations of graded-index (GRIN) fiber lenses, which were recently proposed for biomedical imaging probes. Those GRIN lens modules are made of a single mode fiber and a GRIN fiber lens with or without a fiber spacer between them. We discuss theoretical analysis methods, fabrication techniques, and measured performance compared with theory.

Numerical modeling of transverse mode competition in strongly pumped multimode fiber lasers and amplifiers

Abstract: A model based on propagation-rate equations with consideration of transverse gain distribution is built up to describe the transverse mode competition in strongly pumped multimode fiber lasers and amplifiers. An approximate practical numerical algorithm by multilayer method is presented. Based on the model and the numerical algorithm, the behaviors of multitransverse mode competition are demonstrated and individual transverse modes power distributions of output are simulated numerically for both fiber lasers and amplifiers under various conditions.

502 Watt, single transverse mode, narrow linewidth, bidirectionally pumped Yb-doped fiber amplifier

Abstract: High power operation of narrow linewidth optical fiber amplifiers is usually limited by the onset of stimulated Brillouin scattering. In this paper, we present results demonstrating over 500 Watts of power in a single mode beam from a fiber designed to suppress stimulated Brillouin scattering through a reduction in the overlap of the optical and acoustic fields. Simulations demonstrate the potential for this fiber to achieve greater than 1000 Watts of output power.

Mode coupling and cavity–quantum-dot interactions in a fiber-coupled microdisk cavity

Abstract: A quantum master equation model for the interaction between a two-level system and whispering-gallery modes (WGMs) of a microdisk cavity is presented, with specific attention paid to current experiments involving a semiconductor quantum dot (QD) embedded in a fiber-coupled AlxGa1−xAs microdisk cavity. In standard single mode cavity QED, three important rates characterize the system: the QD-cavity coupling rate g, the cavity decay rate kappa, and the QD dephasing rate gamma[perpendicular]. A more accurate model of the microdisk cavity includes two additional features. The first is a second cavity mode that can couple to the QD, which for an ideal microdisk corresponds to a traveling wave WGM propagating counter to the first WGM. The second feature is a coupling between these two traveling wave WGMs, at a rate beta, due to backscattering caused by surface roughness that is present in fabricated devices. We consider the transmitted and reflected signals from the cavity for different parameter regimes of {g,beta,kappa,gamma[perpendicular]}. A result of this analysis is that even in the presence of negligible roughness-induced backscattering, a strongly coupled QD mediates coupling between the traveling wave WGMs, resulting in an enhanced effective coherent coupling rate g=sqrt(2)g0 corresponding to that of a standing wave WGM with an electric field maximum at the position of the QD. In addition, analysis of the second-order correlation function of the reflected signal from the cavity indicates that regions of strong photon antibunching or bunching may be present depending upon the strength of coupling of the QD to each of the cavity modes. Such intensity correlation information will likely be valuable in interpreting experimental measurements of a strongly coupled QD to a bimodal WGM cavity.

Fusion splicing small-core photonic crystal fibers and single-mode fibers by repeated arc discharges.

Abstract: We demonstrate a novel method for low-loss splicing small-core photonic crystal fibers (PCFs) and single-mode fibers (SMFs) by repeated arc discharges using a conventional fusion splicer. An optimum mode field match at the interface of PCF-SMF and an adiabatic mode field variation in the longitudinal direction of the small-core PCF can be achieved by repeated arc discharges applied over the splicing joint to gradually collapse the air holes of the small-core PCF. This method is simple and offers a practical solution for light coupling between small-core PCFs and SMFs.

Efficient operation of diode-pumped single-frequency thulium-doped fiber lasers near 2 μm

Abstract: Efficient operation of diode-pumped single-frequency fiber lasers at wavelengths from 1740 to 2017 nm has been demonstrated by using a very short piece of newly developed single-mode active fiber, i.e., heavily thulium-doped germanate glass fiber. At 1893 nm, the single-frequency fiber laser has a pump threshold of 30 mW, a slope efficiency of 35%, and maximum output power of 50 mW with respect to the launched power of single-mode pump diodes at 805 nm. To the best of our knowledge, this is the highest lasing efficiency achieved in single-frequency fiber lasers operating near 2 μm. Frequency noise of the single-frequency fiber laser at 1893nm has been characterized and compared with that of single-frequency fiber lasers at 1 and 1.55 μm.

Gain-guided, index-antiguided fiber lasers

Abstract: Optical fibers with large diameter cores having a negative index step from cladding to core combined with an adequately large gain coefficient in the core provide near-optimal mode properties for fiber lasers delivering robust single transverse mode operation with very large mode areas. Basic properties and simple design formulas for such fibers are presented.

Compact, single-frequency all-fiber Q-switched laser at 1 μm

Abstract: We demonstrate a unique, all-fiber, actively Q-switched laser operating in the 1 microm region. The laser is compact, single mode, single frequency, highly polarized, and exhibits high peak power. The laser cavity is constructed without external coupling, utilizing fiber Bragg gratings that permit feedback at only a single polarization. By using a piezoelectric to press the fiber and modulate the fiber birefringence, the cavity is switched between high and low loss states, permitting Q-switching. We demonstrate this Q-switching at repetition rates up to 700 KHz.

Infrared single mode chalcogenide glass fiber for space.

Abstract: An important measuring technique under study for the DARWIN planet finding mission, is nulling interferometry, enabling the detection of the weak infrared emission lines of an orbiting planet. This technique requires a perfect wavefront of the light beams to be combined in the interferometer. By using a single mode waveguide before detection, wavefront errors are filtered and a virtually perfect plane wavefront is obtained. In this paper the results on the development and the optical characterisation of suitable infrared transmitting chalcogenide glasses and mid-IR guiding optical fibers are reported. Two different preform techniques for manufacturing core-cladding chalcogenide fibers are described. Two types of step index fibers, prepared with Te 2As3Se5 chalcogenide glasses, offer single mode guidance at 10.6 μm. © 2007 Optical Society of America.

Single-Mode Waveguides With SU-8 Polymer Core and Cladding for MOEMS Applications

Abstract: Fabrication and optical characterization of single-mode polymeric embedded waveguides are performed. A specific material combination (SU-8 2005 as core and the modified SU-8 mr-L 6050XP as cladding) is chosen in order to obtain a small refractive index difference for single-mode propagation combined with the conventional fabrication method UV lithography to facilitate the integration of different types of optical detection methods on lab-on-a-chip systems. We analyze the behavior of the refractive index and carefully observe how the value of the refractive index can be tailored during processing. We show that we can fabricate waveguides with an index difference in the order of 10-3 , where both the core material and the cladding material are based on SU-8. The refractive index measurements are performed on thin polymeric films, while further optical characterizations are performed on waveguides with a height of 4.5 mum. We study the mode profiles of these waveguides and confirm that only the fundamental mode is excited. We also study the absorption spectra of the material in the wavelength range 800-1600 nm combined with cut-back measurements. We find that the waveguides have a propagation loss of 0.2-3 dB/cm in this wavelength range

Swept-wavelength interferometric interrogation of fiber Rayleigh scatter for distributed sensing applications

Abstract: We review recent advancements in making high resolution distributed strain and temperature measurements using swept-wavelength interferometry to observe the spectral characteristics of Rayleigh scatter in optical fibers. Current methods available for distributed strain or temperature sensing in optical fiber include techniques based on Raman, Brillouin, and Rayleigh scattering. These techniques typically employ optical time domain reflectometry and are thus limited in spatial resolution to 0.1 to 1 m. Fiber Bragg gratings can yield higher spatial resolution but are difficult to multiplex in large numbers for applications requiring wide scale coverage. Swept-wavelength interferometry allows the Rayleigh scatter amplitude and phase to be sampled with very high spatial resolution (10s of microns). The Rayleigh scatter complex amplitude can be Fourier Transformed to obtain the Rayleigh scatter optical spectrum and shifts in the spectral pattern can related to changes in strain or temperature. This technique results in distributed strain measurements with 1 μe resolution or temperature measurements with 0.1 C resolution. These measurements can be made with sub-cm spatial resolution over a 100 m measurement range or with sub-10 cm resolution over a 1 Km range. A principle advantage of this technique is that it does not require specialty fiber. Thus, measurements can be made in pre-installed single mode or multimode fibers, including those used for telecommunication networks. Applications range from fault monitoring in short range communications networks, structural health monitoring, shape sensing, pipeline and electrical transmission line monitoring, to perimeter security. Several examples are discussed in detail.

High-accuracy fiber-optic shape sensing

Abstract: We describe the results of a study of the performance characteristics of a monolithic fiber-optic shape sensor array. Distributed strain measurements in a multi-core optical fiber interrogated with the optical frequency domain reflectometry technique are used to deduce the shape of the optical fiber; referencing to a coordinate system yields position information. Two sensing techniques are discussed herein: the first employing fiber Bragg gratings and the second employing the intrinsic Rayleigh backscatter of the optical fiber. We have measured shape and position under a variety of circumstances and report the accuracy and precision of these measurements. A discussion of error sources is included.

High-conversion-efficiency widely-tunable all-fiber optical parametric oscillator.

Abstract: A high-conversion-efficiency widely-tunable all-fiber optical parametric oscillator is described. It is based on modulation instability in the normal dispersion regime near the fiber’s zero-dispersion wavelength. A 40 m long dispersion-shifted fiber is used in a synchronously pumped ring cavity. We demonstrate continuous sideband tuning from 1300 to 1500 nm and 1600 to 1860 nm by tuning the pump wavelength between 1532 and 1556 nm. Internal conversion efficiencies of up to 40% are achieved.

Mode scalability in bent optical fibers

Abstract: This paper introduces a simple, analytical method for generalizing the behavior of bent, weakly-guided fibers and waveguides. It begins with a comprehensive study of the modes of the bent step-index fiber, which is later extended to encompass a wide range of more complicated waveguide geometries. The analysis is based on the introduction of a scaling parameter, analogous to the V-number for straight step-index fibers, for the bend radius. When this parameter remains constant, waveguides of different bend radii, numerical apertures and wavelengths will all propagate identical mode field distributions, except scaled in size. This allows the behavior of individual waveguides to be broadly extended, and is especially useful for generalizing the results of numerical simulations. The technique is applied to the bent step-index fiber in this paper to arrive at simple analytical formulae for the propagation constant and mode area, which are valid well beyond the transition to whispering-gallery modes. Animations illustrating mode deformation with respect to bending and curves describing polarization decoupling are also presented, which encompass the entire family of weakly-guided, step-index fibers.

Optical Absorption in Commercial Single Mode Optical Fibers in a High Energy Physics Radiation Field

Abstract: This paper reports on the radiation induced attenuation of light at 1310 nm and 1550 nm in 12 commercially available single mode (SM) optical fibres. The fibres samples are exposed to gamma rays from a 60Co source and to a high energy physics radiation field. The attenuation is studied as a function of total dose, dose rate, light power and temperature. Radiation resistant fibres from one manufacturer show an extraordinary low attenuation for light at 1310 nm that does not exceed 5 dB/km even after a total dose of 1 MGy. Some 3000 km of this type of fibre have been produced by the manufacturer and quality assurance measurements of the production batches are presently ongoing.

Demonstration of a Long-Reach DWDM-PON for Consolidation of Metro and Access Networks

Abstract: We demonstrate a bidirectional long-reach 64-channel dense wavelength division multiplexing passive optical network (DWDM-PON) based on wavelength-locked Fabry-Peacuterot laser diodes (F-P LDs) with 50-GHz channel spacing. The mode control of the F-P LDs enhances the output power and decreases the required injection power. Packet-loss-free transmission in both 64 upstream and 64 downstream channels is obtained, guaranteeing more than 100 Mb/s per channel through 70 km of single mode fiber without the need for an optical amplifier. The demonstrated DWDM-PON can consolidate a metro network into an access network by bypassing the central offices within its reach. The capacity of the long-reach DWDM-PON is also discussed

Single-Frequency operation of External-Cavity VCSELs: Non-linear multimode temporal dynamics and quantum limit.

Abstract: We present an experimental and theoretical investigation of the non-linear multimode dynamics of external–cavity VCSELs emitting at 1 and 2.3 μm. We account for the stable single–frequency and linearly polarized emission by these laser sources, even in the presence of quantum noise and non-linear mode interactions originating from Four–Wave–Mixing via population pulsations in the quantum-wells. This fact is a consequence of the mode antiphase dynamics. Thanks to the high-Q external cavity configuration, the laser dynamics fall into the oscillation-relaxation-free class-A regime. The characteristic time to achieve single mode emission is ~1 ms for a 15 mm long cavity with an antireflection coated structure and no spectral filter, as for an “ideal” homogeneous gain laser. The side mode suppression ratio is as high as 40 dB, close to the quantum limit. The laser linewidth is at the quantum limit, and is ~1 Hz at 1mW output. An experimental value <20 kHz has been established. Under standard conditions, without spectral filtering, the optimum cavity length for highly coherent single mode operation is expected in the range 5 to 30 mm. Finally, for cavity lengths typically shorter than 5 mm, we rather have an “ideal” homogeneous gain class-B laser, exhibiting oscillation-relaxation of the intensity in the 0.1 GHz range. These properties contrast with the intrinsic strongly non-linear dynamics of conventional semiconductor lasers.

Design of single-moded holey fibers with large-mode-area and low bending losses: the significance of the ring-core region.

Abstract: One of the major trends in optical fiber science is to be able to obtain fibers with large-mode-area (LMA), optimized for various applications such as high power delivery, fiber amplifiers, and fiber lasers. In order to ensure the high beam quality and the ultimate controllability of the damage threshold in the fiber’s material, it is required to have a LMA property and of course to operate in a single mode fashion. While the conventional fibers have some difficulties in providing simultaneously LMA, single mode operation, as well as low macro-bending loss characteristics, all-silica holey fibers are highly attractive candidates for realizing LMA single-mode fibers with low bending losses. In this paper, we present a novel type of effectively single-mode holey fibers with effective mode area of about 1400 μm2, small allowable bending radius as small as 5 cm, good beam quality factor of 1.15, and high confinement losses exceeding 1 dB/m for the higher-order mode at 1.064-μm wavelength.

A silicon-based spot-size converter between single-mode fibers and Si-wire waveguides using cascaded tapers

Abstract: Theoretical and experimental performances of a robust Si-based spot-size converter (SSC) for efficient coupling between a single-mode fiber and a photonic Si-wire waveguide are reported. The SSC is comprised of cascaded horizontal linear and vertical nonlinear up tapers measured 2.0mm and 86μm in length, respectively, in a silicon-on-insulator substrate. The fine modal field of a Si-wire waveguide, 0.54×0.38μm2 in diameters, was expanded to diameters of 5.1×9.2μm2 with measured net transmission loss of 0.5dB at the wavelength of 1.55μm by the miniature SSC.

Very large-core, single-mode, gain-guided, index-antiguided fiber lasers.

Abstract: Lowest-order, single-mode laser oscillation is reported in gain-guided index-antiguided fiber lasers having core diameters from 100 to 400 μm. A model is presented explaining how to select resonator mirrors to assure single-mode operation.