Polymer optical fibre Bragg gratings based fibre laser

For the first time the fibre laser constructed from a polymer optical fibre Bragg grating is reported. The single frequency laser with the peak power of −5 dBm and signal to noise ratio greater than 45 dB has been achieved. Further examination demonstrates the excellent characteristics of the fibre laser. First, the fibre laser can be easily tuned over 35 nm by the simple axial tension method. Second, the fibre laser has the high strain sensitivity of 1.48 pm/με with the dynamic measurement range as large as 2.37%.     

基于双折射效应的普通单模光纤频率偏移器和偏振控制器

本文介绍了利用普通单模光导纤维弯曲产生的双折射效应而研制成的频率偏移装置和偏振控制装置.频率偏移装置的单边带抑制达30dB以上,它与光纤偏振控制装置一起是构成全光纤功能型传感器比较理想的光纤元件.     

Beam delivery characteristics of optical fibres for carbon monoxide lasers

An experimental investigation has been conducted of the propagation characteristics of several types of optical fibres which are candidates for use in optical beam delivery systems for carbon monoxide lasers. Both solid core (chalcogenide) fibres and hollow core (with dielectric or dielectric coated metal) waveguides have been investigated. Such experiments have included an assessment of both the power transmission characteristics, and the effects of waveguide transmission on the optical quality of the beam at the exit of the fibre. The experiments indicated lowest loss for the chalcogenide solid core fibre with a value of 0.4 dB m⁻¹.     

Study of in-line single-mode optical fiber polarizer

The theoretical calculation method of multilayer metal-clad planar optical waveguide presented by Y. YAMAMOTO is greatly improved and transplant into the optical fiber and a suitable waveguide model of in-line single-mode optical fiber polarizer is set up to study its characteristics, the theorical analyses are in accordance with the experimental re suits. The polarizer whose extinction ratio is more than 30 dB at 0.633μm wavelength with an insertion loss of 0.5 dB is formed by grinding off the cladding on one side of a single-mode fibre and evaporating metal onto the polished durface in our Lab.     

基于新型长周期光纤光栅的掺铒光纤放大器

报道了基于高频CO₂激光脉冲写入的新型长周期光纤光栅的低噪音掺铒光纤放大器,这种新型长周期光纤光栅是用大约几千Hz的高频CO₂激光脉冲对光纤玻璃热冲击作用而形成的.在铒纤中插入一个长周期光纤光栅,会明显减少掺铒光纤放大器的放大自发辐射(ASE)噪音.报道了两种低噪音掺铒光纤放大器,作为前置放大器和线路放大器,它们的ASE噪音指数分别从4.0 dB减少到3.5 dB和从4.8 dB减少到4.3 dB,并且在作为线放时,其小信号增益从30 dB提高到37 dB,降噪及提高增益效应十分显著.     

Design of dual-core resonant leaky optical fibre based gain flattening filters for erbium doped fibre amplifiers

We propose optical fibre based filters employing dual-core resonant leaky structure for gain equalization of erbium doped fibre amplifier (EDFA). Spectral loss variation of the structure has been utilized to suppress gain peak and, thus, flatten overall gain profile in the C-band. We show 15.7 dB flat gain with ± 1.6 dB ripple in the wavelength range from 1525 nm to 1555 nm using a single filter and 18±0.7 dB gain using two cascaded filters.     

Fabrication and transmission experiments of distributed feedback laser modules for 2.5 Gb s-1 optical transmission systems

A distributed feedback (DFB) laser module has been developed for 2.5 Gbs^-1 optical transmission systems. The DFB laser has a multiple-quantum-well (MQW) active layer and a planar buried heterostructure (PBH) for a low threshold current and stable singlemode operation with low chirping. A PBH DFB laser module with a single-mode fibre pigtail and an optical isolator was designed and fabricated by employing a single lens and a laser welding method. The fabricated MQW PBH DFB laser module is shown to be a suitable light source for 2.5 Gb s^-1 optical transmission systems with a minimum received power of-33 dBm after 47 km conventional optical fibre transmission.     

A terabit capacity passive polymer optical backplane based on a novel meshed waveguide architecture

An optical backplane based on a meshed polymer waveguide architecture enabling high-speed board-to-board optical interconnection is presented. This planar array of multimode polymer waveguides can provide passive strictly non-blocking links between server line cards fitted with optical transmitter and receiver arrays. This architecture offers a scalable and low-cost solution to the bandwidth limitations faced by electrical backplanes and is suitable for PCB integration. The reported backplane demonstrator uses a matrix of 100 waveguides each capable of 10 Gb/s operation to interconnect 10 cards for a total capacity of a terabit per second aggregate data rate in multicast mode. Characterisation of the backplane demonstrator reveals low link losses of 2 to 8 dB for a multimode fibre input and crosstalk values below −35 dB. Error free data transmission at 10 Gb/s is achieved with a power penalty of only 0.2 dB at a bit-error-rate of 10⁻⁹. Additionally, lossless operation of a Gigabit Ethernet link over the backplane is achieved even when using the worst-case highest loss links.     

Optical frequency-domain reflectometery

Experimental and simple analytical investigations have been performed on modulation-frequency-sweeping optical frequency-domain reflectometry (hereafter OFDR) technique for fibre diagnostic purposes. The experimental results are in good agreement with those obtained by computer simulations. Signal-to-noise-ratio improvement of more than 50 dB is expected by using a synchronous-detection type of filtering process. The results well confirm the diagnostic ability of the technique.     

Optical coding scheme for all-optical analog-to-digital conversion using asymmetrical Y-branch waveguide

The novel optical coding scheme for all-optical analog-to-digital conversion has been proposed, in which asymmetrical Y-branch waveguide structures have been introduced to achieve the desired optical power splitting. The optical performance has been simulated by using finite-difference beam propagation method (FD-BPM), which shows that the designed component exhibits good coding performance. Experimentally, the optical coding component has been fabricated and measured. The optical power contrast between bit code 1 and 0 at output port is more than 37 dB, and measured imbalance of output power is less than 1.5 dB for bit code 1.     

Chromatic-distortion compensation in splitting and focusing of femtosecond pulses by use of a pair of diffractive optical elements

We propose a simple optical system to compensate for chromatic distortion that occurs during fan-out of femtosecond pulses by diffractive optics. The proposed system comprises a pair of diffractive elements, one for splitting an incoming pulse and the other for focusing the split pulses. With an appropriate separation between the elements, chromatic distortion resulting from the spectral bandwidth of a femtosecond pulse is removed, and an array of focused pulses with the same dimensions can be obtained. The theory has been verified through optical and processing experiments with 100-fs, 800-nm pulses.     

Spatial uniformity of group delay in the IR diode radiation attained by short segment of optical fibre application

A simple method for obtaining high uniformity of group delay in the IR diode radiation by means of a short segment of optical fibre attachment is decribed and the results are presented.The experiments were done with edge emitting IR diode structures of over 3 ns ascertained group delay spatial inhomogeneity which, after application of the optical fibre decreased to below the 0.1 ns level.     

Uniform oscillations of supercontinua

Uniform oscillations of supercontinua, generated with microstructured fibre, have been observed and investigated. The oscillations are uniform in the sense that the optical power through the fibre changes with a regular and periodic waveform and the spectral bandwidth of the transmitted light changes correspondingly. The oscillations are continuous over periods of hours and the spectral width ranges from the octave-spanning condition (～310-THz wide at 20 dB below the maximum) to zero broadening of the input light. The corresponding contrast ratio of the fluctuating output light signal is as high as 0.75. Silica photonic crystal fibre with hexagonal air-hole structure and core diameter of 2.0 μm was used for the supercontinuum generation. The oscillations are produced when at least 15 mm of fibre is allowed to extend from the mount of the fibre launcher. Arguments in terms of thermal behaviour are used in an attempt to explain the fluctuations of light through the microstructured fibre. This appears to be the first occasion in which such behaviour has been reported.     

Near-noiseless amplification of light by a phase-sensitive fibre amplifier

We report near-noiseless (noise figure of 0.4 dB, which is an improvement over the theoretical limit of 1.2 dB for a conventional laser amplifier with the same gain of 1.7 dB) optical amplification of laser light in a phase-sensitive fibre amplifier.     

Flat Supercontinuum Generation at 1550 nm in a Dispersion-Flattened Microstructure Fibre Using Picosecond Pulse

The generation of a flat supercontinuum of over 80nm in the 1550nm region by injecting 1.6ps 10 GHz repetition rate optical pulses into an 80-m-long dispersion-flattened microstructure fibre is demonstrated. The fibre has small normal dispersion with a variation smaller than 1.5 （ps·nm^-1·km^-1） between 1500 and 1650nm. The generated supercontinuum ranging from 1513 to 1591 nm has the flatness of ±1.5 dB and it is not so flat in the range of several nanometres around the pump wavelength 1552nm. Numerical simulation is also used to study the effect of optical loss, fibre parameters and pumping conditions on supercontinuum generation in the dispersion-flattened microstructure fibre, and can be used for further optimization to generate flat broad spectra.     

Sinusoidal modulation of a CW GaAs laser from 9 MHz to 1.1 GHz

Sinusoidal modulation and its detection of a room-temperature cw GaAs laser from 9 Mhz to 1.1 GHz is reported. A 25 dB signal-to-noise ratio with 20 dB harmonic rejection is obtained at 35 mA bias above threshold with a useful power output for optical fibre measurements. Possible extension of the frequency range and the application to sweep-frequency measurements in optical fibre waveguides are discussed.     

Dynamic imaging and hydrodynamics study of high velocity, laser-accelerated thin foil targets using multiframe optical shadowgraphy

The main aim of the study of thin target foil–laser interaction experiments is to understand the physics of hydrodynamics of the foil acceleration, which is highly relevant to inertial confinement fusion (ICF). This paper discusses a simple, inexpensive multiframe optical shadowgraphy diagnostics developed for dynamic imaging of high velocity laser-accelerated target foils of different thicknesses. The diagnostic has a spatial and temporal resolution of 12 μm and 500 ps respectively in the measurements. The target velocity is in the range of 10⁶–10⁷ cm/s. Hydrodynamic efficiency of such targets was measured by energy balance experiments together with the measurement of kinetic energy of the laser-driven targets. Effect of target foil thickness on the hydrodynamics of aluminum foils was studied for determining the optimum conditions for obtaining a directed kinetic energy transfer of the accelerated foil. The diagnostics has also been successfully used to study ablatively accelerated targets of other novel materials.     

A high performance backscattering set-up using multimode light channels

The utilization of multimode ion-exchanged waveguides to form an optical directional coupler for multimode fibre backscattering measurements is discussed. The optical properties of the integrated branching element are described in detail. A very high directivity of 70 dB was obtained with this new device. The dynamic range in the backscattering measurement was 23 dB fibre one-way loss.     

Side-polished fiber based gain-flattening filter for erbium doped fiber amplifiers

A simple and accurate novel normal mode analysis has been developed to take into account the effect of the non-uniform depth of polishing in the study of the transmission characteristics of optical waveguide devices based on loading of a side-polished fiber half-coupler with a multimode planar waveguide. We apply the same to design and fabricate a gain-flattening filter suitable for fiber amplifiers. The wavelength dependent filtering action of the overall device could demonstrate flattening of an EDFA gain spectrum within ±0.7 dB over a bandwidth of 30 nm in the C-band. Results obtained by the present analysis agree very well with our experimental results. This present analysis should be very useful in the accurate design and analysis of any SPF-MMOW device/component including side-polished fiber based sensors.