Fiber Stretcher Research Articles

Distributed fiber-optic intrusion sensor system

A distributed sensor system for detecting and locating intruders based on the phase-sensitive optical-time-domain reflectometer (/spl phi/-OTDR) is described. The sensing element is a cabled single-mode telecommunications fiber buried along the monitored perimeter. Light pulses from a continuous-wave Er:fiber Fabry-Pe/spl acute/rot laser with a narrow (/spl ap/3 kHz) instantaneous linewidth and low (few kilohertz per second) frequency drift are injected into one end of the fiber, and the backscattered light is monitored with a photodetector. The effect of phase changes resulting from the pressure of the intruder on the ground immediately above the buried fiber are sensed by subtracting a /spl phi/-OTDR trace from an earlier stored trace. In laboratory tests with fiber on reels, the effects of localized phase perturbations induced by a piezoelectric fiber stretcher on /spl phi/-OTDR traces were observed. In field tests, people walking on the ground above a buried fiber cable induced phase shifts of several-/spl pi/ radians.

New design of a high-power femtosecond 800-nm laser

A new simple design of a femtosecond laser is proposed, which consists of a 1550-nm erbium-doped fibre laser, a fibre stretcher, a BBO crystal parametric amplifier converting the input radiation to the 800-nm radiation, a Ti:sapphire or a BBO amplifier, and a diffraction grating compressor.

Compensation of nonlinear phase shifts with third-order dispersion in short-pulse fiber amplifiers

We show that nonlinear phase shifts and third-order dispersion can compensate each other in short-pulse fiber amplifiers. This compen-sation can be exploited in any implementation of chirped-pulse amplification, with stretching and compression accomplished with diffraction gratings, single-mode fiber, microstructure fiber, fiber Bragg gratings, etc. In particular, we consider chirped-pulse fiber amplifiers at wavelengths for which the fiber dispersion is normal. The nonlinear phase shift accumulated in the amplifier can be compensated by the third-order dispersion of the combination of a fiber stretcher and grating compressor. A numerical model is used to predict the compensation, and experimental results that exhibit the main features of the calculations are presented. In the presence of third-order dispersion, an optimal nonlinear phase shift reduces the pulse duration, and enhances the peak power and pulse contrast compared to the pulse produced in linear propagation. Contrary to common belief, fiber stretchers can perform as well or better than grating stretchers in fiber amplifiers, while offering the major practical advantages of a waveguide medium.

Comments on “Wavelength-tunable add/drop multiplexer for dense wavelength division multiplexing using long-period gratings and fiber stretchers”

Comments on “Wavelength-tunable add/drop multiplexer for dense wavelength division multiplexing using long-period gratings and fiber stretchers”

Promising compact wavelength-tunable optical add-drop multiplexer in dense wavelength-division multiplexing systems.

We design and model a highly compact and tunable optical add-drop multiplexer (OADM) device that consists of long-period gratings and piezoelectric ceramic fiber stretchers. The proposed OADM shows that 50 dense wavelength-division multiplexing channel signals can be selected in the wavelength range from 1526.25 to 1563.75 nm with 0.75-nm channel spacing, which covers the whole C-band gain spectrum of an erbium-doped fiber amplifier. The cross talk between channels is less than -39 dB, and the total insertion loss of the device is approximately 0.24 dB, which includes the splicing losses, the mode mismatching loss, and the expected losses in the two side-by-side coupled fibers.

Phase-locked, erbium-fiber-laser-based frequency comb in the near infrared.

A phase-locked frequency comb in the near infrared is demonstrated with a mode-locked, erbium-doped, fiber laser whose output is amplified and spectrally broadened in dispersion-flattened, highly nonlinear optical fiber to span from 1100 to >2200 nm. The supercontinuum output comprises a frequency comb with a spacing set by the laser repetition rate and an offset by the carrier-envelope offset frequency, which is detected with the standard f-to-2f heterodyne technique. The comb spacing and offset frequency are phase locked to a stable rf signal with a fiber stretcher in the laser cavity and by control of the pump laser power, respectively. This infrared comb permits frequency metrology experiments in the near infrared in a compact, fiber-laser-based system.

All fiber chirped-pulse amplification system based on compression in air-guiding photonic bandgap fiber

We report on the experimental demonstration of an all fiber CPA system based on a step-index fiber stretcher and an air-guiding photonic crystal fiber compressor. The ultrafast fiber laser system producing an average power of 6.0 W with 100-fs pulses at 73 MHz, what corresponds to a peak power out of the compressor fiber of 0.82 MW. This completely fiber integrated approach has the potential to be scaled to significantly higher peak powers.

Wavelength-tunable add/drop multiplexer for dense wavelength division multiplexing using long-period gratings and fiber stretchers

We have designed and configured a novel wavelength-tunable add/drop multiplexer (ADM) device that employs long-period gratings (LPGs) and piezoelectric ceramic fiber stretchers. The modeling for this ADM predicts that 50 International Telecommunication Union (ITU) dense wavelength division multiplexing (DWDM) channel signals could be selected in the wavelength range from 1526.25 to 1563.75 nm with 0.75-nm channel spacing, which covers the whole C-band gain spectrum of erbium-doped fiber amplifiers. The cross-talk between channels is less then −39 dB, and the total insertion loss of the device is about 0.24 dB which includes the splicing losses, the mode mismatching loss, and the expected losses in the two side-by-side coupled fibers. The tuning of add/drop channels within a limited region can be provided by changing the voltage, which is applied to the piezoelectric ceramic fiber stretchers. This technique is suitable for the in-line implementation of optical communication networks.

Round-trip time and dispersion optimization in a dual-wavelength actively mode-locked Er-doped fiber laser including nonchirped fiber Bragg gratings

Round-trip time and intracavity dispersion were optimized in a dual-wavelength actively mode-locked Er-doped fiber laser including two nonchirped fiber Bragg gratings. This optimization allowed to generate nearly transform-limited pulses as short as 16 and 13 ps at 1547 and 1562 nm, respectively, at a 3-GHz repetition rate only limited by the modulator bandwidth. In the experiment, the round-trip time difference between pulses at two wavelengths was adjusted using a fiber stretcher. Intracavity dispersion was managed at each wavelength separately.

WDM channel selector based ontransmissive chirped moiré fibre grating

A novel tunable optical fibre filter design is presented to be used as a channel selector in wavelength division multiplexing systems, based on a chirped moire fibre grating assembled on a fibre stretcher. It is specifically designed to operate in the transmission mode.

Polarization control in a large-stroke optical fiber delay line

In the context of an optical fiber delay-line implementation by use of silica fiber stretching capability, we experimentally demonstrate that highly birefringent fibers preserve their ability to maintain the polarization coherence in spite of the high magnitude of the stresses applied to them during large stretching. Two experimental demonstrations are presented. In the first, polarization cross coupling versus stretching is characterized. This stretching induces a variation of group delay in the span 0-45 cm. The second is a test of the fiber stretcher in an interferometric application.

A stabilised fibre-optic Mach-Zehnder interferometer filter using an independent stabilisation light source

We have demonstrated a stabilised scheme of fibre-optic Mach-Zehnder interferometer-type optical filter for application in periodic wavelength dividing filters. The stabilised scheme is based on controlling one arm length of the interferometer with electronically fedback fibre stretcher and utilizes an independent control light source and a voltage amplifier. This filter turns out to be useful for optical inputs not only of discrete spectra but also of broadband spectra. The output characteristics including stability, extinction ratio and transmission period are discussed.

Rapid acquisition of in vivo biological images by use of optical coherence tomography

The development of techniques for high-speed image acquisition in optical coherence tomography (OCT) systems is essential for suppressing motion artifacts when one is imaging living systems. We describe a new OCT system for performing micrometer-scale, cross-sectional optical imaging at four images/s. To achieve OCT image-acquisition times of less than 1 s, we use a piezoelectric fiber stretcher to vary the reference arm delay. A Kerr-lens mode-locked chromium-doped forsterite laser is employed as the low-coherence source for the highspeed OCT system. Dynamic, motion-artifact-free in vivo imaging of a beating Xenopus laevis (African frog) heart is demonstrated.

Birefringent effect measurement and compensation in a highly birefringent fiber optical path modulator

We describe the principle and the experimental tests of a fiber stretcher generating the same optical path modulation along the two polarization axes of a highly birefringent fiber with a 50 μm stroke. Firstly, we study the birefringence modification of the optical path modulator under stretching. Secondly, this fluctuation is cancelled by the implementation of a HB fiber Babinet compensator.

Grating compensation of third-order material dispersion in the normal dispersion regime: Sub-100-fs chirped-pulse amplification using a fiber stretcher and grating-pair compressor

We describe a method for compensating large amounts of second- and third-order material dispersion, and we present two simple, compact and robust stretcher-compressor systems for microjoule-and millijoule-level chirped-pulse amplification. These systems, which use dispersive material to stretch and a modified grating pair to compress the pulse, provide expansion and compression with full cubic-phase compensation. Unlike previous fiber-stretcher systems which were limited to picosecond pulse durations, these systems can be used effectively with 50-fs microjoule pulses or 100-fs millijoule pulses. The results of our model are described, including the quartic-phase limitations for both systems. We discuss other applications of this grating pair to other areas of ultrafast optics, including intracavity dispersion compensation for femtosecond oscillators. >

Optically generated true-time delay in phased-array antennas

This tutorial review paper deals with various methods for solving a basic problem of wideband phased arrays, i.e. beam squinting, using optical technologies. The problem of beam squinting in phased arrays is analyzed and the concept of true-time delay is introduced. The advantages of realizing variable delay lines by optical rather than by microwave means are reviewed, together with principles of operation. Among the techniques described are switched-path length delay lines, fiber stretchers, tunable lasers with highly dispersive fiber, and coherent techniques incorporating dispersive delay. Recent experimental results are discussed in the light of practical system requirements. >

Linear optical path modulation with λ/200 accuracy using a fibre stretcher

The Letter reports the experimental generation of a linear optical path modulation of 20 λ range with an accuracy of λ/200 (λ = 633 nm) using a servo control system driving an optical fibre stretcher. The error signal is provided by mixing interferometric signals with an electronic oscillator.

Pseudo-heterodyne detection scheme for the fibre gyroscope

The results of a preliminary investigation of a phase-swept pseudo-heterodyne scheme suitable for use with all-fibre versions of the fibre gyroscope are presented. The output carrier, which is phase-modulated by the Sagnac shift, is generated by employing a sinusoidal phase modulation via a piezoelectric fibre stretcher in combination with selective detector gating