Optical pulse compression based on stationary rescaled pulse propagation in a comblike profiled fiber

In this paper, optical pulse compression using a comblike profiled fiber (CPF) is theoretically and experimentally studied, in which highly nonlinear fibers and single-mode fibers are alternately concatenated. Stationary rescaled pulse (SRP), is the main focus, which is a recently discovered nonlinear stationary pulse in CPF. The fundamental characteristics of SRP are investigated, and SRP propagation is applied to the design of the CPF pulse compressor. Using the proposed design method, the specifications of the CPF can easily be controlled, such as the compression ratio per step of the CPF or the pedestal of the output pulse. Two experimental results of pulse compression using the CPF based on the proposed design method are shown: 1) pulse compression with a large compression ratio per step of the CPF and 2) low-pedestal and wideband wavelength-tunable compression. A parametric noise-amplification phenomenon occurring in a compression process for an optical pulse sequence is also numerically analyzed.     

Optimised one-step compression of femtosecond fibre laser soliton pulses around 1550nm to below 30 fs in highly nonlinear fibre

Optimised compression of femtosecond fibre laser pulses in highly nonlinear fibre is demonstrated. Specifically reported are compressed pulse durations below 30 fs using a simple setup where a single sub-10 cm segment of highly nonlinear fibre is directly spliced to the output pigtail of a commercial femtosecond fibre laser. The compressed pulse quality is confirmed through frequency resolved optical gating measurements.     

Impact of pumping configuration on all-fibred femtosecond chirped pulse amplification

Ultrashort pulse fibre lasers have been investigated for many applications, such as medical imagery, microsurgery, micromachining and terahertz generation. These applications often require high peak power and short pulse duration at the same time. Such specifications are generally difficult to obtain directly from a laser oscillator without using external amplification. However, amplification has to be performed with care, mainly because nonlinear effects can deteriorate the pulse shape. This is particularly relevant in small core optical fibres where the signal is guided through a section of just a few square micrometres. To reduce the impact of nonlinear effects, one solution is to use chirped pulse amplification (CPA) [1, 2]. The CPA method consists of stretching the optical pulses before amplification so that the peak power is below the nonlinear effects threshold. Optical pulses are first stretched, then recompressed up to their original duration after an amplification stage. There are two main ways to recompress the pulses: by using a bulk optical grating or by means of an optical fibre. Indeed the use of bulk optical gratings is effective [3] but, in this case, the laser must include some free-space optics, then losing the advantage of an all-fibred, more stable and compact approach. On the other hand, the use of an optical fibre presents the inconvenience of a potential enhancement of nonlinear effects. Fibres with large mode area (LMA) including photonics crystal fibres (PCF) [4, 5] can be used in order to reduce the detrimental impact of nonlinear effects or to compensate for chromatic dispersion. However, in such a case, particular care has to be taken in the design and fabrication of the laser regarding multimode operation and splicing issues.     

Nonlinear, dispersion-free 10 GHz optical pulse train transmission in distributed erbium-doped fibre

The transmission of a 10 GHz repetition rate optical pulse train over a 28.5 km long distributed erbium-doped fibre amplifier is reported. In the linear dispersion regime, the pulses broaden so that the tails of adjacent pulses overlap. However, given sufficiently high signal powers, the optical Kerr effect causes pulse narrowing back to the original 18 ps pulsewidth.<>     

Technique to generate equal amplitude, higher-order optical pulsesin rational harmonically modelocked fibre ring lasers

A novel technique of pulse amplitude equalisation in higher-order optical pulses in a rational harmonically modelocked fibre ring laser is proposed and demonstrated. The combination of intracavity optical filtering, and even-order modulation sideband generation using nonlinear characteristics of a Mach-Zehnder intensity modulator can effectively eliminate pulse amplitude instability at higher-order rational harmonic modelocking. The generated optical pulse trains exhibit equal amplitudes with a high degree of spectral purity in terms of a large suppression of supermode noise, low amplitude noise, phase noise, and timing jitter     

高阶孤子在色散渐减光纤环中的传输特性研究

研究了高阶孤子在对称结构和不对称结构的色散渐减光纤环形镜的脉冲传输特性,比较了不同耦合系数下的色散渐减光纤环形镜的开关性能及脉冲压缩性能.得出了使色散渐减光纤环具有良好脉冲输出的耦合器系数范围,对实验中参数的选取有一定的指导意义.发现不对称结构光纤环形镜亦能产生无基座超短脉冲.     

Pulse repetition rate multiplication in fibre laser using higher-order passive modelocking

A simple technique that allows for the repetition rate multiplication of optical pulse trains generated in passively modelocked fibre lasers is experimentally demonstrated. This is achieved by initiating higher-order passive modelocking by using both a dual-channel fibre Bragg grating and a Fabry-Perot filter inside the fibre cavity. Continuous dark pulse trains with a repetition rate of 60-GHz were generated, which is a four-fold multiplication of the Fabry-Perot free spectral range.     

High-speed characteristics at high input optical power of GaInAsPelectroabsorption modulators

High-speed characteristics at high input optical power levels of GaInAsP double heterostructure electroabsorption modulators are investigated. It is shown that the bandwidth degradation due to high input optical power is strongly dependent on the absorption coefficient. A design to maintain high-speed characteristics under milliwatt range output power operation, and experimental results including a 100 km single-mode fibre pulse transmission experiment are demonstrated     

Demonstration of passive modelocking through dissipative four-wavemixing in fibre laser

Experimental observation of passive modelocking by dissipative four-wave mixing in an erbium-doped fibre laser containing a dual-peak fibre Bragg-grating filter is reported. The laser operates in the normal dispersion regime and generates optical dark pulse trains with a repetition rate of 80 GHz     

Simple technique to improve the spectral quality of gain-switchedpulses from a DFB laser

The authors show that by coupling the output from a gain-switched DFB laser to a fibre loop mirror the spectral quality of the gain-switched pulse can be greatly improved. The SMSR of a gain-switched 1.5 μm DFB has been increased by 25 dB, and also the chirp has been reduced, by using this technique. This spectral improvement is vitally important in systems where the gain-switched pulses will pass an optical filter     

Generation of 1 THz repetition rate, 97 fs optical pulse train based on comb-like profiled fibre

Experimentally generated is a 1 THz, 97 fs optical pulse train at 1.55 cm wavelength region based on a comb-like profiled fibre, which consists of 15 pairs of highly nonlinear fibres (HNLFs) and standard singlemode fibres. Such high-repetition rate pulse generation in the 100 fs regime was made possible by the HNLF with high nonlinearity and small dispersion slope.     

320/640 GHz high-quality pulse sources based on multiple four-wave mixing in highly nonlinear optical fibre

Ultra-high repetition rate quality pulse trains have been generated in a highly nonlinear optical fibre through the compression of a dual-frequency beat-signal based on a multiple four-wave mixing process. FROG analyses show that 500 and 300 fs transform-limited pulses have been generated at 320 and 640 GHz, respectively, over a 20 nm wavelength range.     

Generation of high-repetition-rate optical pulse using cascaded long-period fibre gratings

The generation of high-repetition-rate optical pulses using cascaded long-period fibre gratings is proposed. The pulse multiplication is realised by exploiting the difference in the propagation constant of the core and a cladding mode in a standard singlemode fibre. Two, four and eight times pulse multiplication have been successfully implemented with a minimum repetition period of 2.4 ps.     

Highly flat super-continuum generation from 2 ps pulses using 1 km-long erbium-doped fibre amplifier

A method for generating a supercontinuum (SC) that uses a long optical fibre amplifier is proposed. In this method, the distributed optical gain and the long interaction length enable one to generate the flat SC generation from picosecond pulses used in telecommunication systems. Flat SC generation over 34 nm from a 2 ps pulse train using a 1 km-long erbium-doped fibre is experimentally demonstrated.     

High-intensity fibre-coupled diode laser array

An optical fibre that can couple more than 80% of the power from a 100 ?m-wide 10-stripe diode laser array to a 50 ?m core diameter and 0.3 NA optical fibre is demonstrated. Output powers of 850 mWCW and 2.8 W pulsed (200 ns pulse width at 10 kHz repetition rate) are achieved from the output end of the fibre.     

Brillouin fibre laser enhanced by Raman amplification

A multiple-wavelength Brillouin fibre laser is demonstrated, with channel spacings of /spl sim/10.5 GHz, using Raman amplification in dispersion-shifted optical fibre. More than 20 frequency lines with /spl sim/2 kHz linewidths are obtained using a 14.5 km length of fibre and a 1.3 MHz linewidth Brillouin pump. Gain depletion due to amplified spontaneous emission limits the total number of cascaded Brillouin lines. At high Raman pump powers, the laser produces a pulse train at the repetition rate corresponding to the cavity round-trip time.     

Pulse response of a graded-index optical fibre

An analysis has been made of pulse dispersion in an optical fibre having a continuous radial variation of refractive index. Solutions are presented for Selfoc fibre showing the effects of mode and material dispersion and of group delay. The predicted dispersions range from very low values up to about 1 ns/km, depending on the launching conditions.     

New type of optical fibre analogue SSB data communication system using edge‐emitting LED coupled to single‐mode optical fibre

This paper describes a single‐mode(SM) optical fibre SSB data communication system for use in place of power‐line data transmission. In the optical transmitter, SSB data is fed through the squarewave frequency (SWFM) modulator to the edge‐emitting LED (ELED) module. The light beam of the ELED module is fed to the SM optical fibre having a length of 12km. In the optical receiver, the light beam received through the SM optical fibre is detected by the PIN photodiode module, and fed to the SWFM detector to obtain the double‐pulse frequency modulation (DPFM) signal voltage. The DPFM signal voltage at the output of the SWFM detector is fed to the low‐pass filter (LPF) to obtain analogue SSB data. When the transmission was experimentally carried out, the spurious component was as low as −50–−70 dB and the SNR of SSB data as high as more than 65–70 dB. The optical transmitter and receiver were attached to the conventional analogue SSB data communication system to constitute a new optical fibre analogue SSB data communication system. During the field test utilizing the new system, the crosstalk and SNR were 60–70 dB and 60–70 dB on each channel, respectively. Copyright © 1999 John Wiley & Sons, Ltd.     

General formalism for the study of nonlinear pulse propagation in optical fibres

A general formalism for the study of nonlinear pulse propagation in optical fibres is presented. It is then applied to study the time evolution of a Gaussian laser pulse in a fibre with cubic and fifth-order nonlinearity in the index of refraction. The results are presented and discussed.     

Degree of polarisation in a birefringent single-mode optical fibre

We examine the evolution of the polarisation of a field propagating in a birefringent single-mode optical fibre. The explicit dependence of the degree of polarisation on pulse duration, coherence time of the source and chromatic delay of the fibre is derived.