【作者】 李卿；

【导师】 秦冠仕；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2018， 博士

【摘要】 光学频率梳(简称“光频梳”)在频域为具有等频率间隔的梳齿,在时域为具有固定重复频率的脉冲光。光频梳的应用已经从初期的频率测量,拓展到基本物理常数的精确测定、新一代的全球定位系统、超高精度分子动力学、地外生命的探测、宇宙膨胀的验证、超长距离的超高精度测量、超宽带光通信、光信息处理和激光雷达等方面。目前,光频梳的种类主要包括:基于锁模激光器的飞秒光频梳、基于腔内级联四波混频效应的微腔光频梳、基于电光调制器的光频梳、基于光纤中行波四波混频效应的光频梳等。对于前两种光频梳,由于器件腔长固定的原因,其梳齿间隔的调谐范围非常有限。对于基于电光调制器的光频梳,其梳齿间隔的调谐范围受限于所用调制器的带宽。而梳齿间隔大范围可调的光频梳在光通信、天文、精密测量等领域有着潜在应用。因此,为了进一步拓展光频梳的应用范围,研制梳齿间隔大范围可调的光频梳是很有必要的。在攻读博士期间,作者围绕着如何获得梳齿间隔大范围可调的光频梳以及如何进一步拓宽光频梳的光谱等方面进行了系统的研究,取得了以下研究结果:(1)利用双波长布里渊激光腔内的级联四波混频效应产生了梳齿间隔大范围可调、高信噪比光频梳。在实验上,使用两个工作波长位于C波段、频率间隔约为65 GHz、线宽约为150 kHz的单频激光作为产生双波长布里渊激光的泵浦光,利用500 m长的高非线性石英光纤作为增益介质,获得了线宽约为3 kHz的双波长布里渊激光,与泵浦光的线宽相比,输出布里渊激光的线宽被压窄了50倍;将泵浦光功率增大至306 mW时,获得了梳齿间隔约为65 GHz、高信噪比光频梳,光频梳光谱覆盖1500~1600 nm,其梳齿根数是基于光纤中行波四波混频效应光频梳的38倍;进一步通过调节泵浦光的频率间隔获得了梳齿间隔调谐范围覆盖40~1300 GHz的光频梳。(2)利用多波长布里渊激光腔内的级联四波混频和调制不稳定性效应获得了梳齿间隔大范围可调的孤子光频梳。在实验上,为了获得孤子光频梳,使用多个波长位于C波段、频率间隔相等的单频激光作为产生多波长布里渊激光的泵浦光,采用在C波段内为负色散的高非线性石英光纤作为增益介质,从而使得在多波长布里渊光纤激光腔内产生了强的调制不稳定性和级联四波混频效应,获得了梳齿间隔分别约为55、85、100、200、300 GHz的孤子光频梳,光频梳光谱范围覆盖1500~1600 nm,其脉冲呈现明显的腔孤子特征,对应的脉冲宽度分别约为770、650、540、310、300 fs。并通过求解非线性薛定谔方程对孤子光频梳进行了理论模拟,模拟结果和实验结果基本吻合。(3)为了进一步拓宽光频梳的光谱,设计出了在1500~1600 nm波段范围近零平坦色散、具有两圈空气孔结构的氟碲酸盐玻璃光纤,外圈大空气孔的作用是将光纤的零色散波长从2.16?m移动到1550 nm附近,内圈小空气孔的作用是使得光纤色散在1500~1600 nm波段范围内的值位于0.3 ps/km/nm与-0.5 ps/km/nm之间;通过求解非线性薛定谔方程研究了基于氟碲酸盐玻璃光纤的宽带光频梳产生,利用2 m长的近零平坦色散氟碲酸盐光纤作为非线性介质,使用平均功率为3 W、脉宽为890 fs、重复复频率可调(25~100 GHz)、中心波长为1550 nm的激光作为泵浦源,获得了光谱范围覆盖1300~2000 nm、梳齿间隔调谐范围覆盖25~100 GHz的光频梳。上述理论模拟结果表明,利用近零平坦色散氟碲酸盐光纤作为非线性介质可获得梳齿间隔大范围可调的宽带光频梳。(4)利用两个工作波长位于C波段、频率间隔约为176.32 GHz的单频激光作为产生双布里渊激光的泵浦光,通过控制布里渊激光腔中的级联布里渊散射效应和级联四波混频效应获得了频率间隔为9.28 GHz(布里渊频移)、光谱范围覆盖1500~1600 nm的多波长布里渊激光输出,其波长数目超过1000。(5)设计出了具有“倒L型”色散曲线形状的全正色散碲酸盐光纤,通过数值模拟研究了2?m飞秒激光脉冲在该光纤中的传输性质,发现输出激光的脉冲前沿变得陡峭,脉冲后沿变得平缓,这不仅抑制了自变陡效应引起的蓝移分量增加,而且增加了红移分量;进一步将2?m飞秒激光的峰值功率增大至30 kW时,获得了覆盖1250~5125 nm波段的超连续相干光源。上述结果表明,利用具有“倒L型”色散曲线形状的全正色散碲酸盐光纤作为非线性介质可实现高相干性的中红外超连续光源。更多还原

【Abstract】 Optical frequency combs(OFC)are comb teeth with equal frequency spacing in the frequency domain and pulsed light with a fixed repetition frequency in the time domain.The applications of optical frequency combs have been expanded from frequency measurement to the precise determination of basic physical constants,a new generation of global positioning systems,ultra-precision molecular dynamics,detection of extraterrestrial life,verification of the expansion of the universe,ultra-long distance ultra-high-precision measurement,ultra-wideband optical communications,optical information processing,and laser radar.At present,the types of optical frequency combs mainly include femtosecond optical frequency combs based on mode-locked lasers,micro-cavity optical frequency combs based on cascaded four-wave mixing in the cavity,optical frequency combs based on electro-optic modulators,and optical frequency combs based on travelling four-wave mixing effects in the optical fibers.For the first two types of optical frequency combs,the tuning range of the comb spacing is very limited due to the fixed cavity length of the device.For optical frequency combs based on electro-optic modulators,the tuning range of the comb spacing is limited by the bandwidth of the used modulator.The OFC with tunable frequency spacing has potential applications in many fields such as precision measurement,astronomy,optical clock and optical communication.Therefore,in order to further expand the application range of the optical frequency combs,it is necessary to develop OFC with a wide range of comb teeth spacing.During Ph.D.study,the author systematically studied how to obtain OFC with tunable comb spacing and how to further broaden the spectrum of the optical frequency comb,and achieved the following results:(1)OFC generation with large tunable frequency separation,wide bandwidth and high optical signal to noise ratio in a dual wavelength Brillouin laser cavity isproposed and domonstred.Experimentally,two single wavelength lasers withoperating wavelengths in the C-band,frequency spacings of approximately 65 GHz,and line widths of approximately 150 kHz were used as the pump light for generating dual-wavelength Brillouin lasers in the fiber cavity with 500 m long highly nonlinear fiber.Dual wavelength Brillouin lasers with reduced linewidth of 3 kHz(50 times narrower than the pump CW laser)and improved optical signal to noise ratios are generated in the direction opposite the pump laser.Cavity-enhanced cascaded four-wave mixing between dual wavelength Brillouin lasers occurs in the laser cavity,causing the generation of broadband optical frequency combs with step tunable mode spacing from 40 to 1300 GHz.Compared to the cavity-less case,the number of the comb lines generated in the dual wavelength Brillouin laser cavity is increased by nearly two order magnititude.The amplified spontaneous emission(ASE)from the fiber amplifer is suppressed in the OFC generation.(2)Cavity soliton and OFC generation in a multi-wavelength Brillouin laser cavity are proposed and demonstrated.Flatness and OSNR of the spectrum generated in the multi-wavelength Brillouin laser cavity are improved compared to that generated in the dual wavelength Brillouin laser cavity.Noting that,we observe the corresponding temporal pulse generated in the multi-wavelength Brillouin laser cavity turns to a cavity soliton with the significant feature.The profiles of the temporal pulse and spectrum can be fitted into the hyperbolic secant.The intensity enhanced resonant dispersive wave generated in the blue region of the spectrum is observed.By applying the numerical simulation based on Ikeda map,we understand and analyze the main physical mechnasim and feature of the cavity soliton and OFC generation in the multi-wavelength Brillouin laser cavity.(3)Short length fluorotellurite microstructured fibers with near zero flatted dispersion and high nonlinearity used as the nonlinear media for OFC generation are investigated.We present the design and fabrication of fluorotellurite microstructured fibers(FTMFs)with near zero flattened dispersion profiles in the wavelength range of1500-1600 nm.The fiber with the chromatic dispersion value between-0.5 and 0.3ps/nm/km in the wavelength range of 1500-1600 nm is achieved.Flat top OFC extending from 1500 to 1600 nm(3 dB bandwidth)with tunable mode spacing from25 GHz to 100 GHz can be generated in a 2 meter long fiber by using a 1550 nm laser with a pulse width of 0.85 ps and a peak power of 49 W(average pump power of 3 W)as the pump source through numerical simulations.Total bandwidth of OFC from1300-2000 nm is obtained by pumping the 25-50 GHz repetition pulse laser with average pump power of 3W.(4)Broadband bandwidth 1500-1600 nm multi-wavelength lasers with frequency separation of 9.28 GHz(more than 1000 tooth)are generated in the dual wavelength Brillouin laser cavity.The core to achieve the result is that we keep the dual wavelength pump laser,high order Brillouin lasers operating together with the dual wavelength first order Brillouin laser in the cavity,thus benefits the mechanism of not only cascaded four-wave mixing but also cascaded Brillouin scattering to generate the multi-wavelength lasers with frequency separation of Brillouin frequency shift.(5)Increased red frequency shift in coherent broadband mid-infrared supercontinuum generation in all normal dispersion(ANDi)tellurite microstructured fibers are proposed and investiaged through numerical simulations.The proposed tellurite microstructured fibers(PTMFs)have an inverted L-shaped ANDi profile in the wavelength range of < 5.2 μm.Interestingly,SPM induced spectral broadening is larger on the Stokes side than the anti-stokes side,since the trailing edge of laser pulse becomes smoother than its leading edge,and the effect of self-steepening(SS)on pulse shape is compensated by the effect of the dispersion in the PTMF.Since the trailing edge of output pulse is steeper than the leading edge of output pulse when SS occurs in previously reported ANDi fibers.As a result,coherent broadband mid-infrared supercontinuum light with long operating wavelength can be generated in the PTMF.更多还原