Widely tunable femtosecond soliton pulse generation at a 10-GHz repetition rate by use of the soliton self-frequency shift in photonic crystal fiber

We demonstrate a soliton self-frequency shift of approximately 120 nm in a fiber with 1.56-microm pulses generated at a 10-GHz repetition rate by an actively mode-locked laser. A highly nonlinear photonic crystal fiber with a length of only 12.6 m and a nonlinear coefficient of 62 W(-1) km(-1) is used to achieve such broadband operation. The wavelengths of the resulting sub-300-fs solitons can be tuned effectively by adjusting the input power. The maximum output power of the solitons exceeds 200 mW.     

Six-bit all-optical quantization using photonic crystal fiber with soliton self-frequency shift and pre-chirp spectral compression techniques

In this paper,we propose an optical quantization scheme for all-optical analog-to-digital conversion that facilitates photonics integration.A segment of 10-m photonic crystal fiber with a high nonlinear coefficient of 62.8 W 1/km is utilized to realize large scale soliton self-frequency shift relevant to the power of the sampled optical signal.Furthermore,a 100-m dispersion-increasing fiber is used as the spectral compression module for further resolution enhancement.Simulation results show that 317-nm maximum wavelength shift is realized with 1550-nm initial wavelength and 6-bit quantization resolution is obtained with a subsequent spectral compression process.     

Broadband coherent anti-Stokes Raman scattering spectroscopy using soliton pulse trains from a photonic crystal fiber

Pulse trains of fundamental soliton pulses with different center wavelengths and delay times from a photonic crystal fiber were generated and used as Stokes optical pulses in coherent anti-Stokes Raman scattering (CARS) spectroscopy. The pulse trains were created by shaping optical pulses with a pulse shaper and their waveforms were measured by a cross-correlation frequency-resolved optical gating method. By the use of pulse trains, the time required for obtaining broadband CARS signals was reduced to be about one third compared with our previous study without using pulse trains. With this setup, broadband CARS signals between 500 and 3100 cm⁻¹ of a single polystyrene bead sample have been measured and the most of the Raman peaks in this frequency range of samples have been observed clearly.     

Optimizational 6-bit all-optical quantization with soliton self-frequency shift and pre-chirp spectral compression techniques based on photonic crystal fiber

In this paper, we optimize a proposed all-optical quantization scheme based on soliton self-frequency shift(SSFS)and pre-chirp spectral compression techniques. A 10m-long high-nonlinear photonic crystal fiber(PCF) is used as an SSFS medium relevant to the power of the sampled optical pulses. Furthermore, a 10m-long dispersion flattened hybrid cladding hexagonal-octagonal PCF(6/8-PCF) is utilized as a spectral compression medium to further enhance the resolution. Simulation results show that 6-bit quantization resolution is still obtained when a 100m-long dispersion-increasing fiber(DIF)is replaced by a 6/8-PCF in spectral compression module.     

980 nm Yb-doped double-clad photonic crystal fiber amplifier and its frequency doubling

In this paper, we report on a large-mode-area double-clad 980 nm Yb-doped photonic crystal fiber (PCF) amplifier. In the experiment, an output power of 1.21 W at 980 nm with 2.5 nm bandwidth has been yielded when the PCF length was 40 cm. Through frequency doubling the 980 nm amplified laser with a BIBO crystal, an output power of 51 mW at 490 nm has been generated.     

Parametrically amplified ultrashort pulses from a shaped photonic crystal fiber supercontinuum

By seeding a noncollinear optical parametric amplifier with a photonic crystal fiber supercontinuum, temporally well-defined amplified output pulses have been generated with durations down to 13 fs. The phase of the supercontinuum seed has been characterized by the ZAP-SPIDER technique and can be tailored with a femtosecond pulse shaper. Thus, a very flexible source for arbitrarily shaped, amplified ultrashort laser pulses has been realized.     

Tuning the frequency of ultrashort laser pulses by a cross-phase-modulation-induced shift in a photonic crystal fiber

Femtosecond pulses of fundamental Cr:forsterite laser radiation are used as a pump field to tune the frequency of copropagating second-harmonic pulses of the same laser through cross-phase modulation in a photonic crystal fiber. Sub-100-kW femtosecond pump pulses coupled into a photonic crystal fiber with an appropriate dispersion profile can shift the central frequency of the probe field by more than 100 nm, suggesting a convenient way to control propagation and spectral transformations of ultrashort laser pulses.     

Stimulated Raman scattering in a potassium titanyl phosphate crystal: simultaneous self-sum frequency mixing and self-frequency doubling

A potassium titanyl phosphate crystal is used to achieve efficient stimulated Raman scattering conversion with simultaneous self-sum frequency mixing and self-frequency doubling. Inside a diode-pumped Nd:YAG Q-switched laser cavity, 1.03 W of 1129-nm second Stokes average output power and 0.25 W of 548-nm sum-frequency average power are simultaneously generated with a diode input power of 10 W at a pulse repetition rate of 10 kHz.     

White-light supercontinuum generation with 60-ps pump pulses in a photonic crystal fiber

The generation of a spatially single-mode white-light supercontinuum has been observed in a photonic crystal fiber pumped with 60-ps pulses of subkilowatt peak power. The spectral broadening is identified as being due to the combined action of stimulated Raman scattering and parametric four-wave-mixing generation, with a negligible contribution from the self-phase modulation of the pump pulses. The experimental results are in good agreement with detailed numerical simulations. These findings demonstrate that ultrafast femtosecond pulses are not needed for efficient supercontinuum generation in photonic crystal fibers.     

输出近百纳焦耳脉冲能量的光子晶体光纤锁模激光器

设计并搭建了一种支持百纳焦耳量级的单脉冲能量输出的锁模光纤激光器.激光器基于σ型腔结构,采用掺Yb偏振型大模场面积光子晶体光纤作为增益介质,利用半导体可饱和吸收镜实现自启动锁模.激光器内没有色散补偿机理,使其工作在全正色散锁模状态.通过在谐振腔内引入多通长腔使激光器的重复频率降低至11.1 MHz,直接获得了平均功率为1.08 W,单脉冲能量为 97 nJ,脉冲宽度为4.17 ps的稳定锁模脉冲输出,经腔外色散补偿,脉冲宽度压缩至740 fs.     

Electro-optic adiabatic wavelength shifting and Q switching demonstrated using a p-i-n integrated photonic crystal nanocavity

We demonstrate adiabatic wavelength shifting by electro-optic modulation, using a p-i-n integrated high-Q photonic crystal nanocavity. The wavelength of the trapped light is adiabatically shifted by modulating the resonance of the cavity faster than the photon lifetime. The cavity resonance is changed by injecting electrons through a p-i-n junction to reduce the refractive index. In addition, we employ adiabatic wavelength shifting in a demonstration of dynamic Q tuning by electro-optic modulation.     

Coherent anti-Stokes Raman scattering microscopy with a photonic crystal fiber based light source

A coherent anti-Stokes Raman scattering microscope based on a Ti:sapphire femtosecond oscillator and a photonic crystal fiber is demonstrated. The nonlinear response of the fiber is used to generate the additional wavelength needed in the Raman process. The applicability of the setup is demonstrated by imaging of micrometer-sized polystyrene beads.     

Linear effect of doubling of the laser pulse repetition rate in the laue geometry of bragg diffraction in a photonic crystal

It has been theoretically shown that, during Bragg diffraction of a picosecond laser pulse in the Laue geometry in a linear photonic crystal, the pulse, entering the crystal structure, may be split into two transmitted and two diffracted pulses. The time interval between these pulses can be controlled by varying the crystal thickness and the modulation depth of the refractive index.     

Distortion-free delivery of nanojoule femtosecond pulses from a Ti:sapphire laser through a hollow-core photonic crystal fiber

We demonstrate propagation of femtosecond pulses in the 800-nm range through a hollow-core photonic crystal fiber with preserved temporal and spectral profiles for pulse energies up to 4.6 nJ. Without the use of a prechirping unit, 170-fs pulses were transmitted essentially undistorted at 812 nm, near the zero-dispersion wavelength. Because of the air guidance of pulses, intensity-dependent nonlinear effects were minimal, with only 15% pulse broadening occurring at 350-mW average output power. This fiber thus is excellently suited for applications that require single-mode delivery of high-energy ultrashort pulses to the fiber output face such as, for example, miniaturized multiphoton microscopes.     

1.1 MW peak-power, 7 W average-power, high-spectral-brightness, diffraction-limited pulses from a photonic crystal fiber amplifier

We report a large-core, Yb-doped photonic crystal fiber amplifier generating diffraction-limited (M2 = 1.04), approximately 0.45 ns, approximately 8 GHz linewidth pulses with energies of 540 microJ, peak power in excess of 1.1 MW, and average power of approximately 7.2 W at a repetition rate of 13.4 kHz. The pulse peak spectral brightness exceeds 10 kW/(sr Hz cm2) and is the highest generated by a fiber source, to our knowledge.     

在远离光子晶体光纤零色散波长的正常色散区入射飞秒脉冲产生四波混频及孤子效应的实验研究

在远离光子晶体光纤零色散波长的正常色散区入射飞秒脉冲,实验产生了一对由四波混频引起的信号波带和闲频波带,及一对由脉冲内拉曼散射和非孤子辐射引起的孤子和色散波带,并观察到功率饱和现象.利用有限元法理论模拟了光纤的色散和非线性特性,用四波混频的相位匹配条件模拟了光纤在满足相位匹配条件下所产生的信号波带和闲频波带出现的可能位置,并与实验结果符合得很好.结果表明:即使在光子晶体光纤的正常色散区抽运激光脉冲亦可以产生四波混频和孤子效应;研究发现四波混频的产生是由四阶色散参量引起的;并进一步从理论上解释了孤子及色散波的产生原因.     

Mid-infrared supercontinuum and optical frequency comb generations in a multimode tellurite photonic crystal fiber

We numerically investigate the mid-infrared(MIR) supercontinuum(SC) and SC-based optical frequency comb(OFC) generations when the three optical modes(LP01, LP02, and LP12) are considered in a multimode tellurite photonic crystal fiber(MM-TPCF). The geometrical parameters of the MM-TPCF are optimized to support the multimode propagation and obtain the desired dispersion characteristics of the considered three optical modes. When the pump pulse with center wavelength λ = 2.5 μm, width T = 80 fs, and peak power P = 18 k W is coupled into the anomalous dispersion region of the LP01, LP02, and LP12 modes of the MM-TPCF, the-40-d B bandwidth of the generated MIR SCs can be up to2.56, 1.39, and 1.12 octaves, respectively, along with good coherence. Moreover, the nonlinear dynamics of the generated SCs are analyzed. Finally, the MIR SCs-based OFCs are demonstrated when a train of 50 pulses at 1-GHz repetition rate is used as the pump source and launched into the MM-TPCF.     

Ultrashort pulse compression and delivery in a hollow-core photonic crystal fiber at 540 nm wavelength

We have fabricated a bandgap-guiding hollow-core photonic crystal fiber (PCF) capable of transmitting and compressing ultrashort pulses in the green spectral region around 532 nm. When propagating subpicosecond pulses through 1 m of this fiber, we have observed soliton-effect temporal compression by up to a factor of 3 to around 100 fs. This reduces the wavelength at which soliton effects have been observed in hollow-core PCF by over 200 nm. We have used the pulses delivered at the output of the fiber to machine micrometer-scale features in copper.     

Ultrafast tilting of the dispersion of a photonic crystal and adiabatic spectral compression of light pulses

We demonstrate, by theory and experiment, the ultrafast tilting of the dispersion curve of a photonic-crystal waveguide following the absorption of a femtosecond pump pulse. By shaping the pump-beam cross section with a nanometric shadow mask, different waveguide eigenmodes acquire different spatial overlap with the perturbing pump, leading to a local flattening of the dispersion by up to 11%. We find that such partial mode perturbation can be used to adiabatically compress the spectrum of a light pulse traveling through the waveguide.     

Dynamics of self-similar light pulses of limiting pulse width and energy in a fiber laser

We investigate dynamics of the formation of high-power ultrashort self-similar light pulses (similaritons) in a fiber laser in the regime of positive dispersion. The physical factors limiting the energy and the pulse width of such pulses are revealed. We specify regimes where a laser system based on an ytterbium-doped fiber can generate self-similar pulses with an energy of about 80 nJ compressible to a pulse width of about 150 fs through extracavity linear chirp compensation.