Showing papers on "Single-mode optical fiber published in 1997"

Endlessly single-mode photonic crystal fiber.

Abstract: We made an all-silica optical fiber by embedding a central core in a two-dimensional photonic crystal with a micrometer-spaced hexagonal array of air holes. An effective-index model confirms that such a fiber can be single mode for any wavelength. Its useful single-mode range within the transparency window of silica, although wide, is ultimately bounded by a bend-loss edge at short wavelengths as well as at long wavelengths.

Brillouin gain spectrum characterization in single-mode optical fibers

Abstract: A novel method for Brillouin gain spectrum measurements in optical fibers is presented. It is based on the pump and probe technique with the specificity to use a single laser source together with an external modulator to generate the interacting lightwaves. The high accuracy and inherent stability of the technique makes it suitable for calibration and reference measurements. Different fibers with different refractive index profiles have been tested and characterized. The problem of the evolution of the polarization of the interacting waves is addressed in the article and a polarization insensitive determination of the actual Brillouin gain coefficient is made possible through two successive measurements with different polarizations. The effects of strain and temperature on the Brillouin gain spectrum are also fully characterized.

Overcoming chromatic-dispersion effects in fiber-wireless systems incorporating external modulators

Abstract: We demonstrate two techniques to reduce the effects of fiber chromatic dispersion in fiber-wireless systems incorporating external modulators. We theoretically and experimentally show that the achievable link distance can be increased by varying the chirp parameter of the modulator to give large negative chirp using a dual-electrode Mach-Zehnder modulator (MZM) biased at quadrature. In addition, we show that dispersion can be almost totally overcome by implementing a simple method using the dual-electrode MZM to generate an optical carrier with single sideband (SSB) modulation. We demonstrate the transmission of a 51.8-Mb/s pseudorandom bit sequence (PRBS) at 12 GHz over 80 km of standard single-mode fiber using the SSB generator and measure a bit-error-rate (BER) power penalty due to fiber dispersion of less than 0.5 dB for a BER equal to 10/sup -9/.

Method and apparatus for performing optical measurements using a fiber optic imaging guidewire, catheter or endoscope

Abstract: An imaging system for performing optical coherence tomography includes an optical radiation source; a reference optical reflector; a first optical path leading to the reference optical reflector; and a second optical path coupled to an endoscopic unit. The endoscopic unit preferably includes an elongated housing defining a bore; a rotatable single mode optical fiber having a proximal end and a distal end positioned within and extending the length of the bore of the elongated housing; and an optical system coupled to the distal end of the rotatable single mode optical fiber, positioned to transmit the optical radiation from the single mode optical fiber to the structure and to transmit reflected optical radiation from the structure to the single mode optical fiber. The system further includes a beam divider dividing the optical radiation from the optical radiation source along the first optical path to the reflector and along the second optical path; and a detector positioned to receive reflected optical radiation from the reflector transmitted along the first optical path and reflected optical radiation transmitted from the structure along the second optical path. The detector generates a signal in response to the reflected optical radiation from the reference reflector and the reflected optical radiation from the structure, and a processor generating an image of the structure in response to the signal from the detector. The system provides both rotational and longitudinal scanning of an image.

Noiselike pulses with a broadband spectrum generated from an erbium-doped fiber laser.

Abstract: An erbium-doped fiber laser that produces a train of intense noiselike pulses with a broadband spectrum and a short coherence length is reported. The noiselike behavior was observed in the amplitude as well as in the phase of the pulses. The maximum spectral width obtained was 44 nm. The high intensity and the short coherence length of the light were maintained even after propagation through a long dispersive fiber. A theoretical model indicates that this mode of operation can be explained by the internal birefringence of the laser cavity combined with a nonlinear transmission element and the gain response of the fiber amplifier.

Distributed feedback quantum cascade lasers

Abstract: Pulsed single mode operation of distributed feedback quantum cascade lasers is reported above room temperature at both 5.4 and 8 μm wavelengths. Peak optical powers up to 60 mW at 300 K are obtained with a tuning range of ∼60 nm from 100 to ∼320 K. The linewidth is limited by thermal drift during the pulse with a typical value of 0.3 cm−1 for a 10 ns long pulse at 300 K.

FDTD microcavity simulations: design and experimental realization of waveguide-coupled single-mode ring and whispering-gallery-mode disk resonators

Abstract: We investigate the properties of high-Q, wide free-spectral-range semiconductor microcavity ring and disk resonators coupled to submicron-width waveguides. Key optical design parameters are characterized using finite-difference time-domain (FDTD) solutions of the full-wave Maxwell's equations. We report coupling efficiencies and resonant frequencies that include the effects of waveguide dispersion and bending and scattering losses. For diameters of 5 /spl mu/m, the microcavity resonators can have Q's in the several thousands and a free spectral range of 6 THz (50 nm) in the 1.55 /spl mu/m, wavelength range. Studies of the transmittance characteristics illustrate the transition from single-mode resonances to whispering-gallery-mode resonances as the waveguide width of the microring is increased to form a solid microdisk. We present nanofabrication results and experimentally measured transmission resonances of AlGaAs/GaAs microcavity resonators designed in part with this method.

Photonic crystals and microdisk cavities based on GaInAsP-InP system

Abstract: This paper presents a preliminary guide to realize microcavity semiconductor lasers exhibiting spontaneous emission control effects. It includes: 1) theoretical consideration on the effects; 2) processing techniques for semiconductor microcavities; and 3) some demonstrations of photonic crystal and microdisk cavity. It was shown that, even with a spectral broadening of electron transition, thresholdless lasing operation and alternation of spontaneous emission rate are expected in a cavity satisfying the single mode condition that only one mode is allowed in the transition spectrum. An ideal three-dimensional (3-D) photonic crystal has the potentiality for realizing this condition. In two-dimensional (2-D) crystals and microdisk cavities, thresholdless operation is also expected, but the alternation of spontaneous emission rate may be negligible due to the insufficient optical confinement. In the experiment, some processing techniques for GaInAsP-InP system were investigated and methane-based reactive ion beam etching was selected because of the smooth sidewalls and adaptability to arbitrary structures. A GaInAsP-InP 2-D photonic crystal constructed by submicron columns was fabricated using this method. Owing to the slow surface recombination of this material, a polarized photoluminescence and peculiar transmission spectra were observed at room temperature (RT), which can be explained by a photonic band calculation. However, some technical improvement is necessary for clear demonstration of photonic bandgap, which is minimally required for device applications. In contrast to this, a GaInAsP-InP microdisk cavity of 2 /spl mu/m in diameter, which corresponds to the cavity volume 2.5 times the single-mode condition, has achieved RT lasing with threshold current as low as 0.2 mA. Further reduction of diameter and realization of continuous-wave (CW) operation will provide a significant regime for the observation of spontaneous emission control effects.

Single-mode amplifiers and compressors based on multi-mode fibers

Abstract: To amplify and compress optical pulses in a multi-mode (MM) optical fiber, a single-mode is launched into the MM fiber by matching the modal profile of the fundamental mode of the MM fiber with a diffraction-limited optical mode at the launch end. The fundamental mode is preserved in the MM fiber by minimizing mode-coupling by using relatively short lengths of step-index MM fibers with a few hundred modes and by minimizing fiber perturbations. Doping is confined to the center of the fiber core to preferentially amplify the fundamental mode, to reduce amplified spontaneous emission and to allow gain-guiding of the fundamental mode. Gain-guiding allows for the design of systems with length-dependent and power-dependent diameters of the fundamental mode. To allow pumping with high-power laser diodes, a double-clad amplifier structure is employed. For applications in nonlinear pulse-compression, self phase modulation and dispersion in the optical fibers can be exploited. High-power optical pulses may be linearly compressed using bulk optics dispersive delay lines or by chirped fiber Bragg gratings written directly into the SM or MM optical fiber. High-power cw lasers operating in a single near-diffraction-limited mode may be constructed from MM fibers by incorporating effective mode-filters into the laser cavity. Regenerative fiber amplifiers may be constructed from MM fibers by careful control of the recirculating mode. Higher-power Q-switched fiber lasers may be constructed by exploiting the large energy stored in MM fiber amplifiers.

Volterra series transfer function of single-mode fibers

Abstract: A nonrecursive Volterra series transfer function (VSTF) approach for solving the nonlinear Schrodinger (NLS) wave equation for a single-mode optical fiber is presented. The derivation of the VSTF is based on expressing the NLS equation In the frequency domain and retaining the most significant terms (Volterra kernels) in the resulting transfer function. Due to its nonrecursive property and closed-form analytic solution, this method can excel as a tool for designing optimal optical communication systems and lumped optical equalizers to compensate for effects such as linear dispersion, fiber nonlinearities and amplified spontaneous emission (ASE) noise from optical amplifiers. We demonstrate that a third-order approximation to the VSTF model compares favorably with the split-step Fourier (recursive) method in accuracy for power levels used in current optical communication systems. For higher power levels, there is a potential for improving the accuracy by including higher-order Volterra kernels at the cost of increased computations. Single-pulse propagation and the interaction between two pulses propagating at two different frequencies are also analyzed with the Volterra method to verify the ability to accurately model nonlinear effects. The analysis can be easily extended to include inter-channel interference in multi-user systems like wavelength-division multiple-access (WDM), time-division multiplexed (TDM), or code-division multiplexed (CDM) systems.

Experimental study of integrated-optics microcavity resonators: Toward an all-optical switching device

Abstract: An integrated all-optical switch based on a high-Q nonlinear cylindrical microcavity resonator is proposed. The switch consists of single mode planar waveguides that allow coupling light in and out to a microresonator, exhibiting whispering gallery modes. Due to the high Q factor and the small dimensions, fast switching at low power is feasible for devices based on presently available nonlinear polymers as the active material. In this approach, the transmission of an integrated optical waveguide close to a microcavity has been measured and related to the resonances of the cylindrical microcavity.

Lasing characteristics of GaInAsP-InP strained quantum-well microdisk injection lasers with diameter of 2-10 /spl mu/m

Abstract: We have obtained pulsed lasing operation in 2-5-/spl mu/m diameter microdisk injection lasers using GaInAsP-InP compressively-strained multiple-quantum-well (MQW) wafers around room temperature. The effective cavity volume of the 2-/spl mu/m-diameter device is the smallest among those for any type of electrically-pumped lasers. The threshold current of this device was as low as 0.2 mA. Cavity modes in emission spectra observed under CW conditions coincide well with theoretically predicted whispering gallery modes. Further reduction of diameter to less than 1.5 /spl mu/m will realize the condition for spontaneous emission almost coupling into a single mode, which results in thresholdless lasing operation.

Large effective area single mode optical waveguide

Abstract: A single mode optical waveguide fiber having a core refractive index profile of at least four segments (26, 28, 30, 36, 38, 40, 42) is disclosed. The main features of the core design are at least two non-adjacent core profile segments (26, 30, 36, 40) have positive Δ %; are, at least two non-adjacent segments (28, 32, 38, 42) have negative Δ %. The novel waveguide core design provides a single mode waveguide which is suitable for high rate, long regenerator spacing systems which incorporate optical amplifiers. The waveguide core structure also lends itself to the manufacture of dispersion managed waveguide fiber.

Single-mode optical fibre surface plasma wave chemical sensor

Abstract: We describe a new design of optical fibre surface plasma wave chemical sensor. The basic sensor consists of a tapered single-mode optical fibre with a thin layer of silver evaporated onto the tapered section. The gradually changing diameter of the fibre along the taper and the variation in silver depth around the taper result in a distributed coupling between the guided mode of the fibre and the surface plasma wave. As a result, the coupling to the surface plasma wave occurs over an enlarged spectral range. The device shows good sensitivity to refractive index with refractive index changes of 5 × 10 −4 being detectable. The device is compact, simple to make, and has applications as a biochemical or immunosensor.

Dispersion compensating single mode waveguide

Abstract: A dispersion compensating single mode optical waveguide fiber designed to change the wavelength window of operation of a link from 1310 nm to 1550 nm. The dispersion compensating waveguide fiber is characterized by a core glass region refractive index profile comprised of at least three segments. The segment on the waveguide center has a positive relative refractive index. At least one segment, spaced apart from, the waveguide centerline has a negative relative refractive.

Polarization Evolution and Polarization Instability of Solitons in a Birefringent Optical Fiber

Abstract: Ultrashort optical solitons with different states of polarization are used to map the polarization evolution in a fixed section of a weakly birefringent fiber. Soliton polarization evolution was compared to linear propagation. A significant change in the polarization behavior between the solitons and linear regime is observed. Although solitons contain a continuum of instantaneous intensities, they transform their polarization as a unit, demonstrating the particlelike nature of solitons.

Stretched-pulse optical fiber communications

Abstract: We compare numerically long-distance propagation of two types of nonlinear pulses: a stretched pulse in a fiber with alternating normal and anomalous dispersion and a soliton in a fiber with uniformly anomalous dispersion. Numerical evaluation of timing jitter and Q factor reveals that stretched pulses can be propagated over longer distances than solitons with the same (averaged) fiber dispersion in the presence of weak fixed-frequency filtering. We also examine pulse-to-pulse interactions between stretched pulses and the influence of fluctuations of the fiber dispersion.

Tapered rib fiber coupler for semiconductor optical devices

Abstract: A monolithic tapered rib waveguide for transformation of the spot size of light between a semiconductor optical device and an optical fiber or from the fiber into the optical device. The tapered rib waveguide is integrated into the guiding rib atop a cutoff mesa type semiconductor device such as an expanded mode optical modulator or and expanded mode laser. The tapered rib acts to force the guided light down into the mesa structure of the semiconductor optical device instead of being bound to the interface between the bottom of the guiding rib and the top of the cutoff mesa. The single mode light leaving or entering the output face of the mesa structure then can couple to the optical fiber at coupling losses of 1.0 dB or less.

Analysis of enhanced-power solitons in dispersion-managed optical fibers.

Abstract: We analyze pulse propagation in an optical fiber employing a periodic dispersion map. Second-order averaging is used to determine a general evolution equation valid for both return-to-zero and non-return-to-zero pulses in dispersion-managed systems. The equation is then applied to the case of solitons, and an analytic expression for the power enhancement arising from the dispersion management is obtained.

Implications of fiber grating dispersion for WDM communication systems

Abstract: For high bit-rate dense wavelength-division multiplexed (DWDM) applications fiber grating dispersion for the transmitted adjacent channels is shown to be detrimental and ultimately leads to a penalty. We consider design criteria for fiber grating filters in DWDM systems using both Gaussian pulses and super-Gaussian pulses that approximate square pulses that are more common in nonreturn-to-zero (NRZ) systems.

New analytical results on fiber parametric gain and its effects on ASE noise

Abstract: Parametric gain (PG) in optical fibers may substantially enhance ASE noise, especially in long-haul amplified systems. We present new closed-form analytical results that permit to accurately characterize the effects of PG on ASE noise, as well as the interplay of PG and ASE noise with fiber dispersion in both the anomalous and normal dispersion regions. We introduce the concept of a PG transfer matrix that allows the easy analytical evaluation of ASE noise enhancement over chains of amplified fiber spans.

Mode coupling and equilibrium mode distribution conditions in plastic optical fibers

Abstract: The equilibrium mode distribution (EMD) condition is critical for optical fiber measurements. In this letter, we examine the achievement of EMD condition inside plastic optical fibers (POF's) under different launch conditions. Our pulse broadening measurements of step-index (SI) POF's as a function of fiber length show that the EMD condition can readily be achieved in an SI POF much shorter than in glass optical fibers. The observation of the EMD condition was also independently verified using the far-field pattern technique.

Novel network fiber to manage dispersion at 1.55μm with combination of 1.3μm zero dispersion single mode fiber

Abstract: New type of network fiber which has reverse dispersion and dispersion slope against 13 μm zero dispersion SMF was designed and fabricated The total dispersion was managed to be nearly zero and flat at 155 μm region by combining SMF with new fiber of approximately 1:1 length

Vertical mirrors fabricated by reactive ion etching for fiber optical switching applications

Abstract: We report on vertical mirrors fabricated by deep reactive ion etching of silicon In view of their application in fiber optical switches the mirror height is 75 /spl mu/m So the mirror covers well the fiber core of a single mode fiber, when the fiber is placed in a groove of the same depth and etched at the same time as the mirror A minimal mirror thickness of 23 /spl mu/m was achieved, resulting in an aspect ratio over thirty The verticality was better than 893/spl deg/ The surface roughness of the etched surface is 36 nm rms For an increased reflectivity the silicon mirrors are coated with aluminium Their reflectivity was measured to be 76% To obtain an uniform etch depth, etching is stopped on a buried oxide layer This allows to integrate at the same time mirrors with suspension and actuation structures as well as fiber-alignment grooves in one processing step Using this technology we have fabricated a fiber optical switch with promising performance: The coupling loss in the OFF position is 25 dB and 4 dB in the ON position The switching time is below 02 ms

Optical-Dipole-Force-Fiber Guiding and Heating of Atoms

Abstract: We present an experimental and theoretical investigation characterizing the flux of laser-guided atoms through hollow-core optical fibers and show how it depends on laser detuning from resonance, laser intensity, and fiber curvature. The guiding employs dipole forces arising from the interaction of the atoms with the optical field. Laser light is focused into the hollow region of 40-\ensuremath{\mu}m-inner-diam capillary fiber and guided through the fiber by grazing incidence reflection from the glass walls. The lowest-order mode is azimuthally symmetric with maximum intensity on the fiber axis and nearly zero intensity at the walls. Rubidium atoms are attracted to the high-intensity region along the axis when the laser is detuned to the red of resonance and consequently guided through the fiber. Of particular interest is the evolution of the atom-flux versus laser-detuning profile of increasing intensity. At low intensities the dipole guiding potential is purely conservative and the flux profile is roughly dispersion shaped. At high intensity, viscous dipole forces heat the atoms and ``burn a hole'' in the flux-detuning curve. We find that transverse heating of the atoms and the exponential attenuation of optical mode intensity limit the distance atoms may be guided to about 20 cm in a 40-\ensuremath{\mu}m-diam fiber. Bending the fiber can reduce the effects of heating on atom flux.

Simultaneous wavelength conversion and optical phase conjugation of 200 Gb/s (5x40 Gb/s) WDM signal using a highly nonlinear fiber four-wave mixer

Abstract: A simultaneous wavelength conversion of 200 Gb/s (5×40 Gb/s) WDM signal over the entire gain band of an Er-doped fiber amplifier (EDFA) is demonstrated by a four-wave mixing in a dispersion arranged 750-m highly nonlinear dispersion-shifted fiber with a nonlinear coefficient of 20.4 W-1 km-1. Simultaneous optical phase conjugation is also demonstrated with successful dispersion compensation in a 200 Gb/s (5×40 Gb/s) WDM transmission through a 105 km conventional single-mode fiber.

Experimental demonstration of soliton transmission over 28 Mm using mostly normal dispersion fiber

Abstract: We report on stable soliton propagation experiments in a fiber transmission system consisting of more than 90% normal dispersion fiber. The transmission system has a dispersion map much like that used in nonreturn-to-zero (NRZ) pulse transmission but with a path-average anomalous dispersion of +0.1 ps/nm-km. A stable soliton pulse train at 8 GHz has been observed after 28 Mm of propagation in a 108-km recirculating fiber-optic loop. A significant enhancement in the average soliton power required for stable transmission in a dispersion map with alternating signs of dispersion is experimentally demonstrated for the first time. Theoretical modeling of our experiment is in good agreement with our findings.

Measurement of transverse strains with fiber Bragg gratings

Abstract: In this paper, we present a method to measure two components of transverse strain in an optical fiber using a single Bragg grating written into high-birefringent, polarization- maintaining (PM) fiber The reflected spectrum from this grating contains two peaks corresponding to the two orthogonal polarization modes of the fiber If the axial strain and temperature in the fiber is known, then two components of transverse strain can be computed from the changes in wavelength of the two peaks A Bragg grating written near 1300 nm in PM fiber was loaded in diametrical compression, and the changes in wavelength of the Bragg peaks were monitored using an optical spectrum analyzer Transverse strains were computed from the changes in wavelength using available strain-optic coefficients for low-birefringent optical fiber These strains are compared to finite element analysis predictions, and it is shown that the observed sensor response is greater than the response predicted by the low-birefringent analysis A calibration factor is developed for the sensor to allow the determination of transverse strains from the measured wavelength shifts

Theoretical and experimental considerations for a single-mode fiber-optic bend-type sensor

Abstract: A novel single-mode bend fiber-optic sensing principle is presented. The design makes use of the translucent protective sheath that encases a typical fiber as a means of locating the position of a small bend present on an otherwise straight fiber. We can simultaneously determine bend magnitude by measuring the reduction in the fiber's core light. The theoretical model presented and the experimental results obtained are in excellent agreement, suggesting that a single-point sensor system is feasible with the proposed technique.

Wavelength division multiplex communication link for optical transmission

Abstract: The invention provides a wavelength division multiplex communication link for optical transmissions, which is able to provide a ultra high bit-rate wavelength division multiplex communication at a 1550nm wavelength band using the existing 1300nm band zero dispersion of a single mode fiber network. A dispersion compensating fiber DCF having a negative dispersion value at a 1550nm wavelength band is connected to a single mode fiber SMF of the existing 1300nm band zero dispersion of a single mode fiber network with a line length which compensates the dispersion slope of the single mode fiber to zero. And, a dispersion flat fiber which makes the dispersion slope zero is further connected, with a line length which makes the remaining dispersion value zero, to the terminal end of a connection link of the single mode fiber SMF and dispersion compensating fiber DCF, whereby both the dispersion slope of a single mode fiber and dispersion value thereof can be adjusted to be zero at the terminal end of the dispersion flat fiber DFF.