Bandwidths of single-mode and multimode optical fibre

An analysis is given of the effect of carrier spectral width on bandwidth of optical fibre transmission lines and a simple generalized expression is deduced relating carrier bandspread and maximum permissible pulse rate. It is shown that for the case of a semiconductor laser carrier source the bandwidth of a multimode fibre can be made to approach that expected from single-mode and graded-index fibres.     

Design of Broadband Single Fundamental Mode Hollow Core Bragg Fibre

The condition of the single fundamental mode （HE11） transmission in hollow core Bragg fibres is investigated theoretically by the transfer matrix method. The influences of core size and cladding parameters on the single HE11 mode bandwidth are analysed, showing that the maximal bandwidth is more sensitive to the core size than the cladding. The numerical results show that sufficiently broad bandwidth of single HE11 mode transmission can be achieved by proper fibre design. A simple and fast method based on improved hollow metal waveguide model is proposed to optimize fibre structure parameters for the maximal single HE11 mode bandwidth.     

一种信号光与泵浦光同时被反射的宽带双程分立式拉曼放大器的特性研究

对一种高效的宽带（80nm）双程分立式拉曼放大器的特性进行了理论及实验研究。该拉曼放大器中利用一端镀有金膜的光纤作为宽带反射镜，信号光及泵浦光均被反射而第二次经历增益光纤。与传统的前向泵浦的拉曼放大器相比，该拉曼放大器的增益提高了约150％。此外，分析了影响增益的几种因素，包括泵浦间的相互拉曼作用以及光纤的长度。     

Determination of the optimum electrical bandwidth for spectral slicing

The implementation of wavelength division multiplexing (WDM) in communication access networks is dependent upon the availability of low cost optical sources. One possible alternative to lasers is to employ slices of a broadband optical source obtained via optical filters, which may be tuneable. This paper considers the behaviour of such a spectrally sliced optical transmission system as a function of the bandwidth of a realistic receiver electrical filter for the first time. The treatment includes distortion from optical fibre dispersion over several kilometres of fibre. The optimum ratio between the electrical bandwidth and the optical bit rate is found to be ~0.6 for a fifth-order Bessel filter     

Demonstration of the possibility of >100 Gbit/s transmission over 77 km of standard fibre using a super-step-chirped fibre grating dispersion compensator.

3.8 ps pulses at 1556 nm are reconstructed after transmission over 77 km of standard fibre using a 20 cm long super-step-chirped fibre Bragg grating. We show that good results can be obtained despite the fact that the grating was untrimmed and unapodised, even when the full 1.5 nm reflection bandwidth of the grating is used.     

Design and analysis of a novel single-mode single-polarization photonic crystal fibre based on polarization-dependent coupling and absorption effect

A novel single-mode single-polarization (SMSP) photonic crystal fibre has been proposed and analysed based on the polarization-dependent coupling and absorption effect via a full-vector finite element method with perfectly matched layers. The numerical results predict that very efficient SMSP operation can be achieved with both high bandwidth and high extinction ratio at low loss penalty. Effects of the fibre structural parameters on the SMSP bandwidth and extinction ratio have been explored, which will provide useful guide for the design and fabrication of the fibre. The results obtained will be instructive for the realization of new SMSP fibres with high performance.     

Transmission properties of cabled multimode optical fibres

The study of real multimode fibres suggests a division into two main classes: very-low-dispersion fibres, employed in high-capacity transmission systems, for which a bandwidth limitation occurs in the repeater spacing; and other fibres. Surprisingly, for the fibres in the first class, the cabling process need not be too sophisticated and expensive, provided that no bandwidth limitations arise from material dispersion. In fact, in this case, the bandwidth limitation can be partly relaxed owing to the fibre perturbation.     

Low-pass filter characteristics of multimode graded index fibres

On the basis of ray model solutions, the response of a lossless multimode graded-index fibre to a modulated source is calculated. The results demonstrate great sensitivity of the bandwidth of the fibre to small variations in index profile.     

Enhanced Raman amplifier flatness with nonlinear broadening over non-standard transmission fibre

Nonlinear CW pump broadening over non-standard transmission fibre is used for the first time to achieve improved gain flatness in a single-pump broadband Raman amplifier. As an illustration of the benefits that can be obtained from this approach, a threefold increase in the bandwidth for 0.1 dB gain variation is reported when the broadened pump is used to produce 9.2 dB on-off gain over 25 km LEAF fibre.     

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.     

Fibre delay equalization by carrier drift in the detector

The transmission of optical multimode carriers via clad glass fibres has many advantages, but in general introduces severe signal distortion because of mode delay differences. We describe a simple semiconductor receiver capable of equalizing these delay differences at the fibre end. A tenfold increase in bandwidth (data rate) should be possible by this means if mode coupling in the fibre is not excessive.     

A simplified approach to digital optical receiver design

A simplified theory for the performance of a digital optical receiver is developed. The receiver sensitivity is calculated in terms of circuit parameters, received and equalized pulse shapes, photodiode parameters and bit-rate. An excellent agreement between this theory and a more complicated analysis by Personick [4] is demonstrated. It is shown that the receiver sensitivity may be improved by launching reduced-width pulses into the fibre, particularly if fibre bandwidth is a significant limitation. Reduced-width pulses bring benefits in source power consumption and lifetime, and in timing recovery.     

High efficiency, dual-wavelength fibre Raman pump laser for U-band fibre Raman amplifiers

A dual-wavelength, continuous wave, high efficiency fibre Raman ring laser for pumping U-band (1625–1675 nm) fibre Raman amplifiers is demonstrated. Two fibre Bragg gratings were used as wavelength-selective elements resulting in lasing lines at 1529.7 and 1558.7 nm with respective maximum powers of 209.0 and 390.9 mW. A simple U-band Raman amplifier was constructed to test the dual-wavelength pump laser and on:off gain with a peak of 7.3 dB and a 3-dB bandwidth of 73 nm was obtained.     

A Novel Design of Grating Couplers for Efficient Broadband Coupling between Silicon-on-Insulator Nanophotonic Waveguides and Fibres

A novel design of out-of-plane grating couplers is proposed for coupling between silicon-on-insulator nanophotonic waveguides and single-mode fibres. The coupler with the first-order diffraction coupling to the optical fibre is actually a second-order reflected grating with two times of period of the first-order grating. To enhance outcoupled power, a back hole is designed to form in the silicon substrate and a kind of metals is placed on the top acting as a reflection layer. The coupler is optimized using coupled-mode-based simulations, showing that the coupling efficiency to and from tapered optical fibre can be as high as 85% with 1dB bandwidth about 23 nm.     

Polarimetric fibre laser sensors using Er-doped fibre

A polarimetric fibre laser sensor with narrow polarization mode beat frequency bandwidth is demonstrated using a polarization-maintaining Er-doped fibre. The slope coefficients of 124kHz°C^-1 cm^-1 and 137kHz m^-1 are obtained for temperature change and longitudinal strain measurements, respectively. A new configuration of polarimetric fibre laser sensor is also demonstrated using a conventional Er-doped fibre as a gain medium and a short length of polarization-maintaining fibre as a sensing part.     

面向下一代航电系统的数据块填装性能

结合光分组交换(OPS)网络和光纤通道(FC)技术的优势, 提出一种下一代航电系统组网方案——基于光分组交换网络的光纤通道技术(FC over OPS)。建立了数学仿真模型, 研究了一种数据块填装算法与网络实时性之间的关系, 分析不同的参数如发送带宽、最低效率门限、发送定时的选取对网络实时性的影响。进一步完成硬件原型设计和仿真, 比较了软件仿真与硬件仿真的结果, 并分析该数据块填装算法的性能。     

Pulse Evolution Characteristics in Self-Similar Mode-locked Fibre Laser

A self-similar mode locked fibre laser is studied based on a numerical model. By introducing a dimensionless factor k to characterize the pulse shape, the self-similar pulse evolution, formation and the temporal and spectral shape changes due to the elements in the cavity are investigated throughout the laser cavity. The results show that in the self-similar mode locked fibre laser, self-similar pulse is first formed in the single-mode fibre, which is then amplified in the gain fibre. Gain bandwidth has a small influence on pulse shape, so high energy self-similar pulse can be obtained after amplification. Because net cavity dispersion directly influences the pulse width as well as peak power after compression by a pair of gratings, which can determine the pulse self-similar evolution, it is very important to control the net cavity dispersion to a certain range to obtain self-similar pulses.     

Transfer function of a multimode step-index fibre: a geometrical optical investigation

The transfer function of a multimode step-index fibre has been calculated by means of geometrical optics taking into account mode coupling and leaky rays. The light source may have axial symmetry (light emitting diode) or be line shaped (semiconductor laser). Radial displacement of the line source relative to the fibre axis is allowed. Calculations performed for a large numerical aperture fibre (N.A.=0.475) with a coupling length of 2 km show that leaky rays and radial displacement of the line source are significant for fibre lengths shorter than 200m. The influence of the width of the entrance beam is significant for lengths up to 5 km.Varying coupling length and steady state angle for a fibre length of 150 m calculations show that the bandwidth varies between 15 and 95 MHz for penalty losses between 8 and 18 dB.Calculations have been compared with direct baseband frequency measurements for a high-loss fibre with a large numerical aperture and excellent agreement has been found.     

A novel highly efficient grating coupler with large filling factor used for optoelectronic integration

A novel highly efficient grating coupler with large filling factor and deep etching is proposed in silicon-on-insulator for near vertical coupling between the rib waveguide and optical fibre.The deep slots acting as high efficient scattering centres are analysed and optimized.As high as 60% coupling efficiency at telecom wavelength of 1550-nm and 3-dB bandwidth of 61 nm are predicted by simulation.A peak coupling efficiency of 42.1% at wavelength 1546-nm and 3-dB bandwidth of 37.6 nm are obtained experimentally.     

Origin of the variability of the mechanical properties of silk fibres: 3. Order and macromolecule orientation in Bombyx mori bave,hand‐stretched strings and Nephila madagascarensis spider fibres

The comparison of the low wavenumber of polarized Raman spectra (50–300 cm^–1) from Bombyx mori (fresh cocoons fibres, hand‐stretched ‘Crins de Florence’ strings from the gland content, dried gland, regenerated silk films) and Nephila madagascarensis silks reveals the high polarisation of fibre modes and the absence of polarisation for dried gland and regenerated silk films. This is consistent with X‐ray diffraction measurements. The orientation of the fibroin/spidroin chains is due to the stretching during production, as for advanced synthetic fibres. The bandwidth of the ‘ordered chains’ signature is almost the same for the different fibres. However, the degree of polarisation seems to be higher in the case of spider fibre. The huge bandwidth of low wavenumber components of regenerated films indicates high disorder. Measurements along the fibre point out conformation changes with a periodicity (~20 mm) related to the silkworm head motion during the fabrication of the cocoon. Copyright © 2012 John Wiley & Sons, Ltd.