Bitapered fiber coupling characteristics between single-mode single-core fiber and single-mode multicore fiber

By splicing and tapering at the fusion point of one-core single-mode fiber and three- or four-core single-mode fiber, an effective bitapered fiber coupling technique is implemented. Based on the beam propagation method, the bitapered coupling characteristics between the one-core fiber and the multicore single-mode fiber are simulated and analyzed. The theoretical prediction is confirmed by the experimental results, and the difference between the simulation and the experimental results is also discussed.     

Low-cost optical amplitude modulator based on a tapered single-mode optical fiber

A new, to our knowledge, modulator based on a tapered single-mode optical fiber is introduced. The electro-optic device consists of a tapered optical fiber placed on a resonator made of a piezoelectric material. An electrical signal applied to the piezoelectric material makes the taper bend, and that displacement produces a modulation in the intensity of the optical signal traveling through the fiber. This device is very easy to build and is low in cost. Because of its nature, this new device might be very useful in optical fiber sensors. Its performance is analyzed, and the results are discussed.     

Supercontinuum generation in a single-mode optical fiber with novel dispersion profile

A novel dispersion model different from the conventional one is introduced to enhance supercontinuum generation in dispersion-flattened/decreasing fiber. The results show that supercontinuum spectrum generated in this fiber is by far wider than that in the conventional one,whose flat width can be nearly 1000 nm. The results further show that both the fiber parameters such as peak chromatic dispersion, dispersion differential constant and dispersion decreasing coefficient and the pump pulse parameters including pulse width, soliton order, frequency chirp are crucial to the flat ultra-wideband supercontinuum spectrum generated in this fiber.     

Fabrication and modeling of uniform-waist single-mode tapered optical fiber sensors

We report the fabrication and modeling of single-mode tapered optical fiber sensors. The fabrication technique consist of stretching a section of fiber with an oscillating flame torch. Such a process allows controllable fabrication of lossless tapered fibers with a uniform waist. The sensor transmittance is modeled with a simple ray optics approach. In the model, all the taper parameters are taken into account. Our results indicate that sensor sensitivity can be adjusted with the taper waist diameter. As an example a gold-coated tapered fiber is theoretically and experimentally analyzed.     

Mode-field diameter of single-mode optical fiber by far-field scanning

I use the direct far-field method to measure the mode-field diameter of a single-mode fiber with an expanded uncertainty of 30 nm, with a coverage factor of 2. For a step-index fiber with a mode-field diameter of approximately 9 mum, the major sources of uncertainty are nonlinearity in the electronics, angular errors and scattered light in the apparatus, and the polarization and noncircularity of the mode of the fiber. The paper concludes by showing an inconsistency in the derivation of the far-field expression for mode-field diameter.     

Tailoring the time delay of optical pulse/sequence employing cascaded SOA and band-pass filter

Abstract

A tunable time delay for a 100-ps pulse is achieved via a SOA cascaded band-pass filter, which can be tailored by tuning the filter or changing the SOA injection current. For a single pulse, when the pulse propagates through the cascaded system, a delay of 99.6 ps and an advance of 42.6 ps can be achieved by altering the SOA injection current at two different wavelengths located in the red band and blue band of the filter, respectively. The corresponding tunable delay range is 165 ps, and the maximum delay-bandwidth product (DBP) is 1.65. For an optical sequence, to our knowledge, it is the first time that the time delay is tailored over 145.6 ps corresponding to a DBP of 1.46 by tuning the wavelength from 1556.075 to 1556.955 nm, and 45.2 ps (95.6 ps) advance (delay) by tuning the injection current from 100 to 500 mA at 1556.155 nm (1556.955 nm). The dependence of the time delay on the injection current and filtering configuration has been discussed based on plenty of experiments data. Based on SOA’s fast switching, this device can be used for signal synchronization and bit-by-bit signal processing in a communication system.     

Surface plasmon resonance in a metal-coated single-mode optical fiber with decreased normalized frequency

We have numerically simulated the excitation of surface plasmon resonance in a bent metal-coated single-mode optical fiber with decreased normalized frequency. It is established that an optimum combination of the normalized frequency, bending radius, and film thickness favors effective energy transfer from guided radiation to a plasmon-polariton wave excited on the surface of a metal film deposited onto the optical cladding. It is shown that, using this effect, it is possible to measure the refractive index (RI) of an external medium with a spectral sensitivity of 70 δm/RI unit and a resolution of up to 3 × 10⁻⁷ RI unit.

     

Enhanced two-photon excitation through optical fiber by single-mode propagation in a large core

Multiphoton excitation through optical fibers is limited by pulse broadening caused by self-phase modulation. We show that for short fiber lengths (approximately 2 m) two-photon excitation efficiency at the fiber output can be substantially improved by single-mode propagation in a large-area multimode fiber (10-microm core diameter) instead of a standard 5.5-microm core fiber. Measurements and numerical simulations of postfiber spectra and pulse widths demonstrate that the increase in efficiency is due to a reduction of nonlinear pulse broadening. Single-mode propagation in a large-core fiber is thus suitable for multiphoton applications for which pulse recompression is not possible at the fiber end.     

Some characteristics of an extremely-short-external-cavity laser diode realized by butt coupling a Fabry-Perot laser diode to a single-mode optical fiber

When butt coupling a Fabry-Perot laser diode to an extremely closely spaced waveguide (separation less than or equal to a few times the Rayleigh range of the laser beam), there is a trade-off between the optimal power coupling and the variation of the coupled laser diode's operational characteristics. Changes in the butt-coupling configuration parameters influence the coupling efficiency, as well as the strength of the feedback into the laser diode. Using a previously reported phenomenological model that treats the butt-coupled laser diode as an extremely short external-cavity (ESEC) device, we quantitatively describe how the butt-coupling parameters can be used to control the output power, threshold current, wavelength, and relative intensity noise of the ESEC laser diode. Our analyses are supported by experimental results. The importance of choosing the correct coordinate plane for evaluation of the overlap integrals that are used in the model is also discussed.     

Excess loss of single-mode jacketed optical fiber at low temperature

This paper describes excess loss of single-mode jacketed optical fibers at low temperature. A structural model is proposed for the jacketed fiber in order to investigate the relationship between the structure and excess loss. This model clarifies the excess loss increase mechanism that any initial irregularity existing in the jacketed fiber increases due to shrinkage of the jacket and causes excess loss. These results show that reducing the buffer diameter and controlling the fiber deformation inside the jacket are effective in suppressing excess loss at low temperature.     

Supraluminal velocity of a pulse envelope maximum in amplifying optical fiber

Frequency-modulated Gaussian pulse propagation in an amplifying fiber is described within the framework of a linear model with an allowance for the second-order dispersion effects. It is demonstrated that the presence of an imaginary part in the group velocity dispersion parameter of the single-mode optical fiber with luminous gain leads to the possibility of the pulse envelope at a supraluminal velocity.     

Dynamic thermal response of single-mode optical fiber for interferometric sensors

The dynamic temperature phase sensitivity of a three-layer optical fiber is calculated for unjacketed as well as Al- and Hytrel-coated fibers. The calculations include both the variation of the refractive index with temperature and the thermally induced axial and radial strains. The calculated phase sensitivity indicates that it is currently possible to measure a 1-microdegree C temperature change at frequencies exceeding 50 kHz with 1 cm of a metal coated optical fiber.     

Optical time-domain reflectometry in optical fiber with reflection delay time matched to the period of the optical frequency modulation

A method of optical time-domain reflectrometry in optical fiber is described that uses a single distributed feedback diode laser and a reference reflector. When the period of the frequency modulation of the laser matches the time difference between the reference reflection and the reflection of interest an increase in the noise at the detector occurs. The locations of reflections within the fiber are then mapped to frequencies at which the noise at the detector increases. A sinusoidal frequency modulation is analyzed, and an experiment is described in which the system is used to measure the location and the wavelength of two Bragg gratings located 10 cm apart in an optical fiber. Wavelength measurement is accomplished by temperature tuning the diode laser.     

Differential group delay prediction in optical fiber links

We simulate the time evolution of differential group delay (DGD) in a fiber link in the hinge model with time series forecasting procedures, in particular, autoregressive (AR) models with Kalman filter, pattern imitation, and a Taylor expansion. In these studies, the furthest prediction horizon was attained with the AR accompanied by the Kalman filter procedure. We further discuss the influence of measurement noise on the prediction horizon. We also apply these methods to the measured DGD on 40 Gb/s fiber links and discuss the results.     

Reflowed solgel spherical microlens for high-efficiency optical coupling between a laser diode and a single-mode fiber

To improve the coupling efficiency between a laser diode and a single-mode fiber, we propose a two-microlens coupling scheme that uses two solgel spherical microlenses for high coupling efficiency. The conventional reflow technique was employed and extended to the inorganic-organic hybrid SiO2/ZrO2 solgel material to form the microlenses. Preliminary results show that the coupling efficiency was increased to--1.28 dB (74.5%) by the proposed scheme, compared with a coupling efficiency of--10.13 dB (9.7%) by the butt-joint method. The proposed fabrication technique demonstrates that use of a reflowed solgel spherical microlens is a cost-effective mass-production approach to application of micro-optical elements in optical communication.     

Highly efficient wideband continuum generation in a single-mode optical fiber by powerful broadband laser pumping

By pumping a single-mode optical fiber with a powerful broadband nonselective dye laser, we obtain a high-efficiency wideband continuum (530-930 nm) with nonlinear conversion efficiency exceeding 90%. Experimental conditions for a coherent regime of broadband stimulated Raman scattering are created, which in combination with the broadband self-phase modulation and the four-photon parametric processes leads to a spectral broadening and to the continuum formation. The influence of the pump laser spectral linewidth on the nonlinear conversion efficiency is analyzed and investigated by comparative experiments at narrow-band and broadband laser excitations.