Widely tunable dual-pump parametric amplifiers with photonic crystal fibres

This paper theoretically studies the double-pumped fibre-optical parametric amplifiers (FOPAs) in photonic crystal fibres. Two distinct working regimes of FOPAs are researched, which depend on the dispersion at the central wavelength of the two pumps. Extremely broad tuning range can be obtained when the central pump wavelength is in the normal dispersion regime and is insensitive to the wavelength separation between the two pumps, while the tuning range is narrow in the anomalous dispersion regime and can be significantly enhanced by increasing the wavelength separation. Impacts of higher-order dispersions and temporal walk-off on the gain spectra are also discussed.     

Widely tunable femtosecond fiber optical parametric oscillator

The phase-matching condition in a fiber is discussed. A balance among the different orders of fiber dispersion can be found to achieve a widely tuning modulation instability gain for pumping around the normal dispersion regime. Three coupled nonlinear wave equations are used to simulate the femtosecond fiber optical parametric oscillator. The numerical results show that, through appropriate choice of dispersion, femtosecond pulses with a 180-nm tunable range can be generated when pump wavelength near a fiber’s zero-dispersion wavelength is tuned only 7 nm. Further tuning is limited by the walk-off between the pump and the signal pulses.     

基于色散调谐宽带扫频光纤激光器及其在光纤光栅解调中的应用

报道了一种基于色散调谐技术的宽带扫频掺铒光纤激光器。通过在主动锁模光纤激光器腔内引入较大色散,利用锯齿波电信号调制电光调制器的调制频率,可以实现激光器扫频输出。应用扫频激光器可将光纤光栅反射中心波长的变化转变为时域上信号间隔变化,适用于光纤光栅传感解调。搭建了扫频光纤激光器,利用掺铒光纤作为增益介质,研究了扫频范围的影响因素。通过优化实验参数,实验得到的扫频带宽达到43 nm,接近增益带宽,扫频速度为50 Hz。利用搭建的扫频激光器进行了光纤光栅传感解调,灵敏度约为0.68 ms/nm,验证了解调原理。     

Two-pump fiber optical parametric amplifiers using optimized photonic crystal fiber by genetic algorithm

In this paper, we investigate the gain spectra of fiber optical parametric amplifiers (FOPAs) consisting of dispersion-flattened fibers (DFFs) with different dispersion curves comparatively by means of the dispersion curve model of the DFFs. It is demonstrated that the broader gain spectrum of FOPAs can be achieved if the dispersion curve is lower and more flattened. Based on the preceding analyses, we propose to constitute FOPAs by using index-guiding photonic crystal fiber (PCF) with an anticipated ultra-flattened dispersion and ultra-low dispersion slope. The as-proposed PCF had different air-holes in the cladding rings. In total, four parameters of the PCF are optimized by using genetic algorithm. PACS 42.81.-i; 42.65.Hw; 42.65.Yj     

基于光纤简并四波混频的可调谐波长转换器的优化设计

分析了光纤零色散波长、光纤长度、信号光频率及泵浦功率对基于光纤简并四波混频的可调谐波长转换器调谐带宽和转换效率的影响.结果表明对应不同的零色散波长都存在唯一的最优信号光频使得调谐带宽达到最大,进而推导了最优信号光频和最大调谐带宽的解析表达式,给出了提高此类器件调谐带宽和泵浦效率,减少调谐中输出信号功率起伏的优化设计方法.与以往实验结果相比优化后同等泵浦功率下调谐带宽可增加10 nm,若保证同样的调谐带宽则可将泵浦功率降低4.6 dB.     

Wavelength-tunable prism-coupled external cavity passively mode-locked quantum-dot laser

A wavelength-tunable mode-locked quantum dot laser using an In As/Ga As quantum-dot gain medium and a discrete semiconductor saturable absorber mirror is demonstrated.A dispersion prism,which has lower optical loss and less spectral narrowing than a blazed grating,is used for wavelength selection and tuning.A wavelength tuning range of 45.5 nm(from1137.3 nm to 1182.8 nm) under 140-m A injection current in the passive mode-locked regime is achieved.The maximum average power of 19 m W is obtained at the 1170.3-nm wavelength,corresponding to the single pulse energy of 36.5 p J.     

C-band three-port tunable band-pass thin film optical filter with low polarization-sensitivity

According to the oblique incidence characteristics of thin film narrowband filter, the stack of 100 GHz DWDM four cavities angle-tuned thin film filter has been designed and optimized. The two polarization modes’ central wavelengths of the thin film filter can be centered at the same one in oblique incidence, and it has a stable tuning range of 20 nm without the phenomenon of polarization central wavelength separation. Using this kind of angle-tuned thin film filter and the polarization beam-splitters, the tuning range of the angle-tuned thin film filter can be further expanded due to the reason that it can transmit only the s-polarization light. In this paper we also developed a three-port bandpass tunable filter device with new structure, which tuning range can cover the whole C-band and its adjacent channel isolation degree is high. The experiments show that the three-port tunable filter has an effective tuning range of 33 nm, and its adjacent channel isolation degree is more than 35 dB. It has a bright application opportunity for its flexibility and effective performance.     

基于光纤简并四波混频的可调谐波长转换器的优化设计

分析了光纤零色散波长、光纤长度、信号光频率及泵浦功率对基于光纤简并四波混频的可调谐波长转换器调谐带宽和转换效率的影响．结果表明对应不同的零色散波长都存在唯一的最优信号光频使得调谐带宽达到最大,进而推导了最优信号光频和最大调谐带宽的解析表达式,给出了提高此类器件调谐带宽和泵浦效率,减少调谐中输出信号功率起伏的优化设计方法．与以往实验结果相比优化后同等泵浦功率下调谐带宽可增加10nm,若保证同样的调谐带宽则可将泵浦功率降低4．6dB．     

Wavelength tunable subpicosecond pulse generation with a fiber grating Raman laser

Operation of a wavelength tunable fiber grating Raman laser working in the 1.1 m regime is demonstrated. The pumping mechanism utilizes the process of stimulated perpendicular Raman scattering, possible in fibers for which birefringence can compensate dispersion. A total tuning range of 40 nm with a minimum output pulse duration of 0.8 ps is achieved by using two optical fibers and controlling their birefringence thermally.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

双泵浦光子晶体光纤参量放大研究

利用光子晶体光纤在不同零色散波长附近具有不同色散的特性,研究了在零色散波长为780 nm和1550 nm附近的双泵浦光子晶体光纤参量放大过程.在780 nm附近,讨论了零色散波长变化对双泵浦光子晶体光纤参量放大的影响.数值模拟结果表明:当零色散波长发生微小的变化时,信号增益谱带宽会发生很大的变化.当两泵浦光之间的波长差值减小时,零色散波长的变化对参量放大的影响在很大程度上可以得到抑制,但是增益带宽会有一定的减小.依据这一原理,在1550 nm附近设计光子晶体光纤中的色散平坦光纤参量放大,在5 m长的光子晶体光纤中,当峰值功率为10 W时,得到了增益为65 dB,带宽达到420 nm且极为平坦的增益谱.     

宽调谐范围垂直腔面发射激光器特性分析及设计

运用光学传输矩阵和有限元方法对波长可调谐垂直腔面发射激光器(VCSELs)的波长调谐范围进行了研究.对中心波长为980nm的可调谐VCSELs的波长调谐特性和微电子机械系统(MEMS)悬臂梁结构进行了设计，并进行了实验研究.结果表明，MEMS可调谐VCSELs调谐特性同时受到光波谐振腔结构和悬臂梁最大位移的共同影响.在悬臂梁几何尺寸和激光器有源区结构一定的条件下，通过优化可调谐VCSELs的牺牲层厚度可实现大范围波长调谐.同时，对可调谐VCSELs整体结构进行了设计，计算结果显示波长调谐范围达到30nm以 关键词： 悬臂梁 可调谐垂直腔面发射激光器     

Radiative characteristics of a two-section laser structure based on a δ-doping superlattice

Spectral characteristics of a two-section laser structure with δ-doping active regions are studied theoretically. The wide range of tuning of the lasing wavelength is primarily related to specific characteristics of the gain spectra of n-i-p-i crystals: the dependence of the effective band-gap width of the superlattice on the level of excitation, the character of variation of the overlap integrals of the electron and hole wave functions, and broadening of the electronic spectra due to fluctuations of the electrostatic potential. Depending on the pumping currents in sections of the laser structure, the lasing wavelength can be tuned over a wide spectral range of the IR region in regimes of cw lasing, the transient regime, and the regime of regular pulsations. In the regime of self-sustaining pulsations, lasing is also possible at two wavelengths spaced well apart.     

Efficient femtosecond optical parametric oscillator with dual-wavelength operation

We demonstrated on a synchronously pumped femtosecond optical parametric oscillator with dual-signal-wavelength operation. Our results showed that the dual-wavelength oscillation is not determined by the net-zero dispersion but rather by the balance of phase matching and group-velocity mismatching caused by the nonlinear crystal between the two signals. With a MgO-doped periodically poled lithium niobate as the nonlinear crystal, total signal power up to 530 mW was obtained by using a 2.6 W femtosecond Ti:sapphire laser at the central wavelength of 808 nm as the pump source, corresponding to a conversion efficiency of 20.4%. By slightly adjusting the cavity length, the signal wavelength can be broadly tuned from 1001 to 1438 nm and the dual-wavelength tuning range is from 1001 to 1204 nm.     

金微纳阵列表面等离激元中红外波段光谱特性

表面等离激元是金属表面自由电子在入射光激发下产生的电子集体振荡行为及其相应的电磁场分布。目前，金微纳颗粒表面等离激元除了在可见光波段内被大量研究和应用外，在中红外波段内也显示出独特的光谱特性，具备设计生产优良传感器的潜力，因而同样备受瞩目。研究表明，在中红外波段内设计表面等离激元传感器的关键问题在于如何有效地调节共振谱的共振波长、峰值吸收率以及半峰宽等主要特征参数。相比于单个微纳颗粒而言，阵列结构由于拥有良好的周期性，从而能够在上述参数的宽光谱调节方面具有独特的优势。基于此，提出一种基于金微纳颗粒组成的阵列结构，利用时域有限差分方法，在4～18 μm波段范围内，通过分别改变该阵列的结构参数，包括颗粒半径、高度、间距及颗粒形状等，系统地研究了该微纳阵列结构在中红外波段对入射光的反射光谱、透射光谱和吸收光谱等特性的影响。研究发现，在8～10 μm光谱内，入射光能够与其所激发的金微纳阵列表面等离激元产生共振效应，表现出明显的共振峰特性。可以通过分别改变上述结构参数来有效调节吸收率谱线共振峰的共振波长、峰值吸收率和半峰宽等主要特征参数。研究结果对中红外光谱内基于金微纳阵列结构传感器的科学研究和实际设计具有独特的理论应用价值。     

Dual‐wavelength optical parametric oscillator using antiresonant ring interferometer

A novel technique for coupling of two resonant optical cavities using an antiresonant ring (ARR) interferometer is reported. By deploying two synchronously‐pumped femtosecond optical parametric oscillators (OPOs), it is shown that the use of an ARR can provide an intracavity common path for the two oscillating fields, but without gain coupling between the two nonlinear media. The new technique permits the generation of two signal (idler) wavelengths, which can be independently and arbitrarily varied across the OPO tuning range. The absence of gain coupling also enables unrestricted and uninterrupted tuning through wavelength degeneracy at any arbitrary point within the OPO tuning range. It is shown that signal wavelength pairs tunable across 1500–1580 nm, corresponding to a frequency separation from ∼ 10 THz down to exact degeneracy, can be generated from the coupled OPOs, limited only by the reflectivity of the available mirrors.     

分布反馈式光纤激光器的光热调谐方法

针对现有光纤激光器调谐方法通常不能兼顾调谐幅度和调谐速率的问题,提出了一种基于光热效应的调谐方法,有效兼顾了调谐幅度和调谐速率的要求。分析了光纤激光器的输出波长随泵浦功率变化而改变的实验现象,并以980 nm泵浦源自身调谐为例,进行了静态和动态实验,结果表明:基于光热效应的分布反馈式光纤激光器静态调谐幅度达392 MHz/100 mA,动态调谐速率超过2 kHz,验证了光纤激光器光热调谐方案的可行性。     

Experimental study on the Stokes effect in disordered birefringent microstructure fibers

In this paper, a 120-fs pulse transmission experiment is carried out using disordered birefringent microstructure fibers with cladding ventages. Through this experiment, it is found for the first time that remarkable Stokes and anti-Stokes waves can also be produced when the central wavelength of the incident pulse is in the normal dispersion regime of the microstructure fiber. The generation of the two waves can be explained by the four-wave mixing phase matching theory. Properties of the two waves under the action of femtosecond laser pulses with different parameters are studied. The results show that the central wavelength of anti-Stokes waves and Stokes waves produced under the two orthogonal polarization states shift by 63 nm and 160 nm, respectively. The strengths and central positions of the two waves in birefringent fibers can be controlled by adjusting the phase match condition and the polarization directions of incident pulses.     

Generation of Broadband Near-Infrared (2–2.5 μm) Radiation from an Optical Parametric Amplifier Driven by a Cr:Forsterite Laser Near Dispersion Anomalies of Tuning Curves

Pulses with a spectral width of 450 nm at a wavelength of 2.2 μm are generated in a parametric amplifier based on a type-I BBO crystal pumped by the second harmonic (620 nm) of a Cr:forsterite laser. Such a broadband radiation is obtained in a specific regime of the group velocity matching near the vertical region of the tuning curve. The generated pulses can be compressed to a duration of about 2.5 optical cycles (34 fs) in a medium with positive group-velocity dispersion.     

Numerical modelling of the pump-to-signal relative intensity noise transfer in two-pump fibre optical parametric amplifiers

An accurate numerical model to investigate the pump-to-signal relative intensity noise (RIN) transfer in two-pump fibre optical parametric amplifiers (2-P FOPAs) for low modulation frequencies is presented. Compared to other models in the field, this model takes into account the fibre loss, pump depletion as well as the gain saturation. As a result, the model allows to include a wide range of practical circumstances, both in and beyond the undepleted pump regime, related to different applications of FOPAs. In the small-signal or undepleted pump regime, the model predicts the ripples of the RIN spectrum very well and yields better results than those of other models. It is shown that beyond the small-signal regime, pump power variations do not remain unchanged over the length of the amplifier and for high signal powers, when the FOPA saturates, minimum pump-to-signal RIN transfer occurs. The results of the model are also compared with the available experimental data in the field and a very good agreement can be seen.     

Tunable optical properties in engineered one-dimensional coupled resonator optical waveguides

In this paper, the optical properties in finite size tilted and engineered one dimensional coupled resonator optical waveguide have been investigated. The large dependence of the optical transmittance, dispersion parameter and its higher order slope such as transmittance group delay, third order dispersion and intrinsic waveguide induced loss on the oblique incidence and fraction factor, as the ratio of the optical thicknesses of two adjacent layers, have been studied. Our results showed that as a consequence of changing the fraction factor, at normal incidence, photonic band gap zone, flat portion of third order dispersion curve and maximum magnitude of the transmission group delay can be tuned in long range of wavelength (red shift) slightly. Despite of slight tuning the optical properties in one dimensional coupled resonator optical waveguide by changing the fraction factor, incidence angle has a significant large magnitude of tunability in the overall region of operational wavelength. This fact yields us by changing the incidence from 30 to 60, the operational wavelength can be tuned between two main optical communication windows, while by changing the fraction factor, dispersion and its higher order can be fine tuned in each of optical communication windows which are very useful in wavelength division multiplexing systems and planar lightwave circuits.