Higher-order Soliton Compression Research Articles

Early optical soliton research at Imperial College London

The early work of the Femtosecond Optics Group at Imperial College on optical soliton generation in fibres is reviewed that commenced with studies of ultrashort pulse generation using high order soliton compression for the production of pulses of 18 fs. Also described are seminal studies of soliton Raman generation using long pulse pumping where evolution from modulational instability led to continuum generation and tunable femtosecond generation. Early investigations of seeding modulational instability for enhanced soliton generation and spectral extension are described, as is the work on seeding of noise, soliton generation from noise bursts and soliton generation from amplified noise bursts. The first study of femtosecond soliton amplification in Er fibre amplifiers is described as well as synchronous Raman amplification of solitons. Various schemes reviewing our investigations of adiabatic soliton compression and amplification are included for the generation of pulsewidth and wavelength tunable soliton sources in fully fibre integrated geometries.

Dispersive wave generation at 4 µm in a dispersion-engineered fluorotellurite fiber pumped by a 1.98 µm femtosecond fiber laser

We demonstrate dispersive wave generation at 4 µm in a dispersion-engineered fluorotellurite fiber pumped by a 1.98 µm femtosecond fiber laser. All-solid fluorotellurite fibers with a core diameter of ∼2.6 µm are fabricated by using a rod-in-tube method. The fluorotellurite fibers have two zero-dispersion wavelengths (ZDWs). The first ZDW is 1.328 µm and the second one is 3.551 µm. As the pump laser is launched into the fluorotellurite fiber, firstly, tunable mid-infrared Raman solitons are generated through higher order soliton compression, soliton fission and soliton self-frequency shift. Then, red-shifted dispersive wave at 4 µm is generated as those Raman solitons meet the second ZDW (∼3.551 µm) and soliton self-frequency shift cancellation occurs. Our results show that dispersion-engineered fluorotellurite fibers are promising nonlinear media for constructing all-fiber 4 µm light sources

Numerical investigation of a real-time temperature sensor based on high-order soliton compression

Temperature sensors based on photonic crystal fibers (PCFs) have attracted considerable attentions due to their desirable advantages. However, the real-time temperature sensing in the temporal region is rarely studied. Here, an all-fiber real-time high-sensitivity temperature sensor is fabricated based on the high-order soliton compression process. A 1560 nm femtosecond fiber laser is used as the injected pulse source and the alcohol-filled silica PCF is adopted as the temperature sensitive device. Temperature sensing can be realized by detecting the peak values of temporal profiles with an oscilloscope at the change of temperature. The oscilloscope possesses faster response rate than the optical spectrum analyzer and can record the variation of the single pulse. Through numerical simulations, a real-time temperature sensor with the sensitivity of 4.91 W °C−1 is achieved at the fiber length of 21 cm. Our simulated results show that the designed temperature sensors with low cost, compact all-fiber structure and real-time response are competitive for application in temperature measurement devices.

Cascaded single-mode fibers for higher-order soliton compression at 2 µm.

We present the design of single-mode fibers for two-stage higher-order soliton compression at 2 µm wavelength and achieve high-degree pulse compression in cascaded single-mode fibers. The compression performance for the initial input pulse width from 1 to 50 ps is also investigated. For the initial third-order soliton of 10 ps, a compression factor of 75.7 has been achieved, and the pedestal energy is only 46.66%.

Broadband supercontinuum generation from 600 to 5400 nm in a tapered fluorotellurite fiber pumped by a 2010 nm femtosecond fiber laser

We demonstrate broadband supercontinuum (SC) generation from 600 to 5400 nm in a tapered fluorotellurite fiber pumped by a 2010 nm femtosecond fiber laser. All-solid fluorotellurite fibers with a core diameter of ∼6 μm are fabricated by using a rod-in-tube method. Tapered fluorotellurite fibers with an untapered region length of ∼2 cm and a tapered transition region length of ∼1.05 cm are prepared by employing an elongation machine. By using the tapered fiber as the nonlinear medium and a 2010 nm femtosecond fiber laser as the pump source, SC generation from 600 to 5400 nm is obtained, the 30 dB bandwidth of the generated SC light is about 3600 nm, and the corresponding output power is about 0.85 W for a launched average pump power of ∼1.57 W. The spectral broadening in the tapered fiber is caused by higher order soliton compression, Raman soliton, and blue-shifted and red-shifted dispersive wave generation. Our results show that fluorotellurite fibers are promising nonlinear media for generating broadband SC light expanding from visible to 5400 nm.

172 fs, 24.3 kW peak power pulse generation from a Ho-doped fiber laser system.

We demonstrate a high-peak-power femtosecond fiber laser system based on single-mode holmium (Ho)-doped fibers. 833fs, 27.7MHz pulses at 2083.4nm generated in a passively mode-locked Ho fiber laser are amplified and compressed to near transform-limited 172fs, 7.2nJ pulses with 24.3kW peak power. We achieve this performance level by using the soliton effect and high-order soliton compression. To the best of our knowledge, this is the first demonstration of sub-200fs pulses, with peak power exceeding 10kW from a Ho-doped single-mode fiber laser system without using bulk optics compressors.

Single mode fibers for two stage higher-order soliton compression

Abstract Practical fiber designs for two stage third-order soliton compression with single mode fibers are presented. Fiber design rules as well as influences of higher-order dispersion and splicing loss are discussed. A compression factor of 85.92 is achieved with only 60.39% pedestal energy.

Cascaded photonic crystal fibers for three-stage soliton compression.

Cascaded higher-order soliton compression in photonic crystal fibers (PCFs) is demonstrated, where both the hyperbolic secant and Gaussian input pulses are considered. Detailed fiber designs for three-stage higher-order soliton compression where soliton order is three or non-integer are presented. A highest compression factor of 221.32 has been achieved with only 49.48% pedestal energy.

금 증착 측면연마 광섬유를 이용한 1.93㎛ 모드잠금 펨토초 전광섬유 MOPA 레이저

We experimentally demonstrate the use of a gold-deposited side-polished fiber as a 2-μm-band polarizing device to produce mode-locked pulses from a thulium/holmium-codoped fiber ring cavity. The mode-locking effect was induced by nonlinear transmission caused by the gold-deposited side-polished fiber, due to nonlinear polarization rotation of the oscillated beam within the fiberized cavity. It is also shown that ~558-fs pulses with a peak power of ~6.7 kW could readily be produced at a wavelength of 1935 nm through subsequent thulium/holmium-codoped fiber amplification, due to the higher-order soliton compression effect.

Mode-locked pulse generation from an all-fiberized, Tm-Ho-codoped fiber laser incorporating a graphene oxide-deposited side-polished fiber

An in-depth experimental investigation was conducted into the use of a graphene oxide-based saturable absorber implemented on a side-polished fiber platform for femtosecond pulse generation in the 2 μm region. First, it was experimentally shown that an all-fiberized thulium-holmium (Tm-Ho)-codoped fiber ring laser with reduced cavity length can produce stable femtosecond pulses by incorporating a graphene oxide-deposited side-polished fiber. Second, the measurement accuracy issue in obtaining a precise pulse-width value by use of an autocorrelator together with a silica fiber-based 2 μm-band amplifier was investigated. It showed that the higher-order soliton compression effect caused by the combination of anomalous dispersion and Kerr nonlinearity can provide incorrect pulse-width information. Third, an experimental investigation into the precise role of the graphene oxide-deposited side-polished fiber was carried out to determine whether its polarization-dependent loss (PDL) can be a substantial contributor to mode-locking through nonlinear polarization rotation. By comparing its performance with that of a gold-deposited side-polished fiber, the PDL contribution to mode-locking was found to be insignificant, and the dominant mode-locking mechanism was shown to be saturable absorption due to mutual interaction between the evanescent field of the oscillated beam and the deposited graphene oxide particles.

Broadband and low amplitude noise supercontinuum generated by using compressed pulse

In this paper, enhancement of bandwidth of supercontinuum generated in a normal dispersion-flattened microstructured fiber by using compressed pulse is demonstrated experimentally and numerically. Using high-order soliton compression effect, the standard single mode fiber is used as a pulse compressor. The experimental measured −10dB spectral width is broadened from 75nm to more than 140nm by adding a 20m long standard single mode fiber. Numerical analysis shows that using pulse compressed by a certain length fiber can increase the spectral bandwidth without making extra amplitude noise.

All-fiber design of erbium-doped laser system for tunable two-cycle pulse generation

We report a simple all-fiber design of an Er-doped laser system that is capable of generating widely tunable two-cycle pulses. In particular, 13-fs pulses at a wavelength of 1.7 μm are produced. The mechanism of pulse shortening is identical to the higher-order soliton compression and is supported by modeling based on the slowly evolving wave approximation, which is well suited for down to single-cycle pulse propagation in nonlinear dispersion-shifted fibers.

Cascaded higher-order soliton for non-adiabatic pulse compression

Non-adiabatic pulse compression of cascaded higher-order optical soliton is investigated. We demonstrate high degree compression of pulses with soliton orders N=2, 3, 4, and 5 in two or three nonlinear fibers with different second-order dispersion coefficients. Each fiber length is shorter than half of its soliton period. This compression technique has significant advantages over the widely reported adiabatic and higher-order soliton compression.

All-polarization-maintaining Er-doped ultrashort-pulse fiber laser using carbon nanotube saturable absorber

We present an all-polarization-maintaining Er-doped ultrashort-pulse fiber laser using a single-wall carbon nanotube polyimide nanocomposite saturable absorber. The maximum average power for single-pulse operation is 4.8 mW, and the repetition frequency is 41.3 MHz. Self-start and stable mode-locking operation is achieved. The RF amplitude noise is also examined and it is confirmed that the noise figure is as low as that of a solid-state laser. Using a polarization-maintaining anomalous dispersive fiber, a 314 fs output pulse is compressed to 107 fs via higher-order soliton compression. The peak power of the compressed pulse is up to 1.1 kW.

Visible continuum generation using a femtosecond erbium-doped fiber laser and a silica nonlinear fiber

Supercontinuum extending to visible wavelengths is generated in a hybrid silica nonlinear fiber pumped at 1560 nm by a femtosecond, erbium-doped fiber laser. The hybrid nonlinear fiber consists of a short length of highly nonlinear, germano-silicate fiber (HNLF) spliced to a length of photonic crystal fiber (PCF). A 2 cm length of HNLF provides an initial stage of continuum generation due to higher-order soliton compression and dispersive wave generation before launching into the PCF. The visible radiation is generated in the fundamental mode of the PCF.

Enhanced compression of high-order solitons in dispersion decreasing fibers due to the combined effects of negative third-order dispersion and Raman self-scattering

We propose an improved method to compress high-order femtosecond solitons, which combines effects of negative third-order dispersion and Raman self-scattering in the fibers. Based on the results of the numerical simulations, we can conclude that given a dispersion decreasing parameter, the higher the soliton order is, the shorter the optimum fiber length is needed, and the greater the relative peak intensity is. For a given initial soliton width and a given dispersion decreasing parameter, there exist both an optimum dispersion decreasing fiber (DDF) length and an optimum value of the negative third-order dispersion coefficient of the DDF at which the enhancement in higher-order soliton compression is maximum. We have also studied the dependence of the compression enhancement on both the initial soliton width and the dispersion decreasing parameter and found for a certain input pulse, the relative peak intensity will increase with the dispersion decreasing parameter. It is also shown that both Gaussian pulses and solitons are favorable for the highest quality compression in fibers with slowly decreasing dispersion.

Wavelength tunable 10-GHz 3-ps pulse source using a dispersion decreasing fiber-based nonlinear optical loop mirror

We experimentally demonstrate the use of a dispersion decreasing fiber (DDF) based nonlinear optical loop mirror for the generation of 10 GHz, wavelength tunable soliton-like pulses. 12 ps Gaussian pulses from an electro-absorption modulator (EAM) followed by 125 m of DCF are compressed into 3 ps pedestal-free pulses using both high-order soliton compression and nonlinear switching effects within an 8.5 km DDF based loop mirror. Wavelength tuning of the compressed pulses over a /spl sim/15 nm bandwidth is also demonstrated.

Ultrashort soliton generation through higher-order soliton compression in a nonlinear optical loop mirror constructed from dispersion-decreasing fiber

A novel technique to generate ultrashort fundamental solitons is proposed and demonstrated numerically. The technique utilizes both the multisoliton pulse-compression effect and the switching characteristics of a nonlinear optical loop mirror constructed from dispersion-decreasing fiber. We show that, in contrast to the conventional soliton-effect pulse compression in which compressed pulses are always accompanied by broad pedestals, the proposed technique can completely suppress pulse pedestals, and the compressed pulses propagate like fundamental solitons. Unlike the adiabatic-compression technique based on dispersion-decreasing fibers that are limited to input pulse widths <5 ps, the proposed technique does not require the adiabatic condition and therefore can be used to compress long pulses by use of reasonable fiber lengths. Furthermore, the scheme is more tolerant of initial frequency chirps than the adiabatic-compression technique, and it is shown that positive chirps are beneficial to ultrashort soliton generation. The influences of higher-order effects such as Raman self-scattering and third-order dispersion on soliton generation are also investigated, and it is found that Raman self-scattering can significantly enhance pulse compression under certain conditions.

Higher-order soliton compression with pedestal suppression in nonlinear optical loop mirrors constructed from dispersion decreasing fibers

Compression of higher-order solitons in nonlinear optical loop mirrors (NOLMs) constructed from dispersion decreasing fibers (DDFs) is investigated numerically. Results show that when compared to a soliton-effect pulse compressor in which only a piece of DDF is used, a NOLM constructed from a DDF not only suppresses pulse pedestals but also significantly reduces frequency chirps of the compressed pulse. Furthermore, since both compression and pedestal suppression are realized in the same loop, the novel compressor not only is simpler and more compact but also less affected by higher-order effects as compared with the recently reported techniques based on DDF. For a given input pulse, there is an optimum loop length at which the best trade-off among the compression factor, pulse quality, and output peak power can be obtained. The proposed scheme works well for a broad range of input soliton orders.

270–360 GHz tunable beat signal light generator for photonic local oscillator

A new millimetre- and submillimetre-wave generation method is proposed. The method employs three techniques, namely the modulation of CW light by an electroabsorption modulator, pulse spectrum expansion through higher-order soliton compression, and spectrum filtering by using tunable fibre Bragg gratings. With this method, a continuously tunable beat signal from 270 to 360 GHz with no frequency fluctuation was obtained experimentally. In addition, the method requires only one laser source, and generates a beat spectrum with a linewidth of less than 10 Hz. By using optical filters with a sufficiently wide tuning range, it is possible to generate a beat signal at any frequency from 100 GHz to 1 THz.