In-situ investigation of coupling between a fibre and a slab waveguide

The mode coupling between a fibre and a slab waveguide was experimentally investigated during the formation of the slab. A thin film has been deposited on a polished fibre close to the core-clad interface. By monitoring the optical transmittance of the fibre during the film deposition the coupling efficiency between the formed slab and the fibre has been studied as a function of the film thickness. Strong attenuation in the fibre output has been observed for thickness values at which the propagation constants of the optical mode in the fibre match those of the slab waveguide.<>     

锥形光纤与楔形光纤的耦合

用实验方法测量了楔形光纤与锥形光纤的耦合效率,作出耦合效率随楔形光纤的半楔角及锥形光纤半圆锥角的变化曲线。从实验结果可以看出,楔形与锥形光纤的耦合效率随半楔角增加而增大。当半楔角由15.0°增大到30.3°,半楔角由44.9°增大到55.2°时,耦合效率曲线呈较快的上升趋势;当半楔角由30.3°增大到44.9°时,耦合效率曲线上升趋势变缓。当锥形光纤半圆锥角增加时,耦合效率也随着增大;并且随着楔形与锥形光纤的间距的减小而增大,在间距由0.10mm减小到0.03mm时,耦合效率曲线呈较快的上升趋势;在间距由0.03mm减小到0.01mm时,耦合效率曲线呈下降趋势。     

Direct coupling from a GaAs laser into a single-mode fibre

Ways of coupling directly to a monomode fibre by neutralising the end reflection from the laser and then using the face of the fibre core as a cavity mirror are proposed. The condition is derived for the optimum transfer of power from the laser resonator to the fibre transmission line.     

Optical-fibre waveguide with a single-crystal core

Some properties of a new single-crystal optical fibre are described. The fibre is constructed with the nonlinear optical crystal meta-nitroaniline as its core. In its present configuration, the fibre acts as an effective polariser. Alternative configurations may yield a number of electro-optic fibre devices.     

Mutual injection locking of a fibre laser and a DFB semiconductorlaser

A fibre laser and a distributed feedback (DFB) laser are coupled through a 50:50 fibre coupler in such a way that the two lasers mutually injection-lock. The DFB laser forces the fibre laser to oscillate in a nearly single longitudinal mode. At the same time, the linewidth of the DFB laser is reduced to below 1.5 MHz because of mutual injection-loading     

The influence of a fibre structure on optical loss in a graded-index fibre

For designing a fibre structure, the influence of structural parameters on optical loss is investigated experimentally for a graded-index fibre. The fibre with large cladding/outer-layer index difference and small cladding thickness is found to have large excess loss near excitation points, such as a launching point and a splicing point.     

Wavelength dispersion in a single-mode fibre

Wavelength dispersion in a single-mode fibre has been evaluated by measuring propagation times of various-wavelength pulses transmitted through a 3.72 km-length fibre. Dispersion in a single-mode fibre is dominated by material dispersion, and is estimated to be 9.1 ps/? dkm at 0.85 ?m wavelength.     

Cutting optical fibres with a hot wire

A hot metal wire creates a knee in the fibre and a score in the hollow of the knee. The knee is used to introduce a nonuniform stress distribution across the fibre with a maximum at the score. Reproducible mirror-finished fibre ends were made by using a compact tool.     

Novel fibre optic gyroscope with a configuration combining Sagnac interferometer with fibre ring resonator

A novel fibre optic gyroscope, with a structure making use of the combination of a Sagnac interferometer with an active fibre ring-resonator, is proposed and analysed. The proposed gyroscope can be viewed as a generalised structure of the conventional Sagnac interferometric type fibre optical gyroscope. It has the advantages of both long fibre loop length and multipath interferences. By inserting a fibre amplifier in the loop to provide an optical gain of several dB, the relative maximum sensitivity is enhanced to approximately 30 times more than that of conventional Sagnac interferometric fibre optic gyroscopes.<>     

Cutoff frequencies of a parabolic-core W-type fibre

The cutoff frequencies of guided modes in a weakly guiding W-type fibre with parabolic core profile have been obtained. It is found that the cutoff frequency of the TE01-mode in such a fibre is much higher than for a homogeneous-core W-type fibre. This should allow greater ease in splicing.     

Low threshold optical differential amplification using a fibre amplifier in a nonlinear ring resonator

The basis for low threshold differential amplification in a nonlinear fibre resonator by incorporating an in-line fibre amplifier in the cavity is reported.<>     

Mode excitation in a multimode optical-fibre waveguide

For normal incidence of a Gaussian beam on a multimode optical fibre, theory predicts that only HE1m, modes are excited, and this is confirmed experimentally for a liquid-core fibre of normalised frequency v = 125. Discrete-mode propagation is observed, indicating that the amount of mode conversion due to fibre imperfections is thus very small.     

耦合半导体激光进入光纤

测量了半导体激光器的光束质量,对其光束的收集、准直、整形、聚焦和耦合进入光纤进行了实验研究。对于西门子5W diode bar的5个通道之一,采用微型柱面镜及光纤头处理技术,进入200μm光纤的耦合效率高达85.7%。同时还测量了整形系统和光纤的定位灵敏度。     

Tunable chirping of a fibre Bragg grating using a taperedcantilever beam

Continuously adjustable chirp of an optical fibre Bragg grating was produced by straining the fibre using a cantilever beam of nonuniform cross-section. A uniform shift in wavelength is also produced which can be eliminated by temperature control     

Light coupling from a semiconductor laser into a polarisation-maintaining single-mode fibre

For laser to polarisation-maintaining fibre coupling we propose the insertion of a short piece of normal single-mode fibre. As a result a power coupling loss of 2.8 dB is obtained, whereas additional crosspolarisation is very small compared with the unwanted polarisation excitation of the laser itself.     

Local field in a bent step index fibre

The local field and field shift in a bent step index single mode fibre are investigated by using local field theory. A simple approximate expression for the local field in a bent fibre is given here. The expressions for local field and field shift in the bent fibre are compared with numerical results     

Fields in a bent single-mode fibre

Gaussian functions are commonly used to approximate the fundamental mode field in a straight fibre. If used as a basis for perturbation theory in a bent fibre, then the perturbation terms can be summed to all orders to give a new expression for the field and propagation constant in a bent fibre. These expressions are not the usual first-order corrections to the unperturbed quantities, and not restricted by the magnitude of the perturbation. The expression for field shift is compared to experimentel results.     

Wideband gain flattened erbium fibre amplifier using a photosensitive fibre blazed grating

An erbium fibre amplifier with a highly flattened gain spectrum is demonstrated for the first time using an all fibre photosensitive Bragg grating. An ASE spectrum flattened to within +or-0.5 dB over a bandwidth of 35 nm in the 1550 nm window is achieved with a 3 mm long radiation coupling Bragg fibre grating.<>     

Optical fibres coated with a UV-curable material at a speed of 12 m/s

The letter reports the successful achievement of coating silica fibre at a rate of greater than 10 m/s. We draw 125 ?m-diameter fibres from silica rods and preforms, and coated in-line with UV-curable material. All fibres were proof-tested at two different stress levels of 0.7 and 1.4 GN/m2 We also checked the transmission properties of the fibre. It is found that the optical properties of the fibre remain the same while the mechanical properties are comparable to those of the fibres coated at a low speed.     

Strain-induced birefringence in a highly birefringent optical fibre

A simple theory to explain the strain-induced birefringence in a highly birefringent fibre with an arbitrary cross-sectional geometry is presented. The effects caused by the distributions of Young's modulus and Poisson's ratio in the fibre are highlighted. The phase difference due to the strain-induced birefringence is found to be approximately 20 times larger than that due to the change of fibre length for typical silica-based glass fibres.<>