Demonstration of a microwave spectrum analyzer based on time-domain optical processing in fiber

We demonstrate a novel method for spectral analysis of microwave signals that employs time-domain processing in fiber. We use anomalous dispersion in single-mode fiber to perform a Fresnel transform followed by a matched amount of dispersion-compensating fiber to perform an inverse Fresnel transform of an ultrashort pulse. After the Fresnel-transformed waveform is modulated by the microwave signal, the waveform at the output of the dispersion-compensating fiber represents the ultrashort pulse convolved with the microwave spectrum. An experimental system for spectral analysis of microwave signals in the range 6-21 GHz is demonstrated.     

DDF-based all-fiber optical source of femtosecond pulses smoothly tuned in the telecommunication range

The possibility of the creation of an optical source of femtosecond pulses that are smoothly tuned in the telecommunication range using a dispersion-decreasing fiber is demonstrated. The smooth tuning is based on the Raman frequency conversion of ultrashort pulses, which can be effectively tuned due to the compression mechanism for maintaining of a relatively high pulse intensity in the medium with a monotonically decreasing anomalous dispersion. The generation of a 90-fs soliton pulse whose spectrum is smoothly tuned in the wavelength range 1.6–1.8 μm is experimentally demonstrated.     

Fiber chromatic dispersion measurement based on wavelength-to-time mapping using a femtosecond pulse laser and an optical comb filter

A novel method for the measurement of chromatic dispersion of an optical fiber based on wavelength-to-time mapping using a femtosecond pulse laser (FSPL) and an optical comb filter is proposed and experimentally evaluated. In the proposed approach, the spectrum of an ultrashort optical pulse generated by an FSPL is sliced by an optical comb filter. The spectrum-sliced optical pulse is then coupled into the optical fiber under test. Thanks to the chromatic-dispersion-induced wavelength-to-time mapping in the optical fiber under test, a time-domain waveform similar to the sliced spectrum is generated at the output of the optical fiber, with different frequency components having different time delays. The time delay vs. frequency data are then recorded for the estimation of the chromatic dispersion by using least square fitting. Chromatic dispersions of two types of optical fibers with different lengths are tested. The measured dispersion values agree well with those measured by the conventional modulation phase shift (MPS) method.     

Measurement of UV absorption of single living cell for cell manipulation using NIR femtosecond laser

Optical UV absorption of single human living cells ranging from 200 nm to 360 nm was measured in situ for the study of cell manipulation using the near-infrared (NIR) femtosecond laser. Human breast living cells of MCF-10A, MCF-7, and MDA-MB-231 were used in this experiment. The selective photo-disruptions of single living cell and its sub-organelle (nucleus) were also demonstrated using the tightly focused 790 nm wavelength femtosecond laser with pulse duration of 110 fs. It was found that each living cell has its own absorption spectrum in UV wavelength ranges. It was also inferred that intrinsic absorption spectrum is attributed to the amount of DNA and protein of living cell. For the study of photo-disruption of single cell using the multi-photon absorption excited by the NIR femtosecond laser pulse, the origin UV absorption spectrum of targeted living cell is important and fundamental information to understand nonlinear interaction between NIR ultrashort, high-intensity laser light and transparent living cell.     

10 GHz, 2.4 ps pulse generation using a single-stage dual-drive Mach-Zehnder modulator

This Letter reports on picosecond pulse generation at a repetition of 10 GHz by using a single-stage electro-optic LiNbO(3) Mach-Zehnder modulator, stressing the simplicity of its setup. It is analytically and experimentally proved that dual-arm modulation with in-phase sinusoidal signals having slightly different amplitudes generated a highly coherent optical comb with a great spectral flatness and a parabolic phase relationship in its spectrum. The generated comb was Fourier synthesized and shaped into an ultrashort pulse train with an optical bandpass filter and a dispersive fiber. The pulse source was highly stable, exhibiting an ultralow timing jitter of less than 130 fs.     

Mode-locked fiber laser in the C-band region for dual-wavelength ultrashort pulses emission using a carbon nanotube saturable absorber

A saturable absorber is commonly employed to generate an ultrashort laser with a mode-locking scheme. In an erbium-doped fiber laser system, the laser regimes of either 1530 or 1550 nm wavelength are procured based on the absorption profile of the erbium-doped fiber. The absorption of the erbium-doped fiber is designed to emit at both wavelengths by controlling the net gain of the laser cavity. Subsequently, simultaneous erbium-doped fiber laser emission is attained at 1533.5 and 1555.1 nm with the pulse duration of 910 and 850 fs, respectively.Therefore, this work maximizes the output portfolios of a mode-locking fiber laser for dual-wavelength ultrashort pulses emission.     

Demonstration of a 16×10-Gb/s OTDM system

A 16×10-Gb/s optical time-division-multiplexing (OTDM) system was demonstrated experimentally with a well-designed ultrashort pulse source based on an electro-absorption modulator (EAM) and nonlinear fiber compressor. The obtained 10-GHz stable and pedestal-free pulse train has 2-ps width, high extinction ratio, and low timing jitter. An ultrafast demultiplexer based on a nonlinear optical loop mirror (NOLM) including a commercially available highly nonlinear fiber (HNLF) is employed to demultiplex data signal from 160 to 10 Gb/s. A back-to-back error-free demultiplexing experiment is carried out to verify the system performance.     

Modified spectrum autointerferometric correlation (MOSAIC) for single-shot pulse characterization

A method for generation of the modified spectrum autointerferometric correlation that allows single-shot pulse characterization is demonstrated. A sensitive graphical representation of the ultrashort pulse phase quality is introduced that delineates the difference between the presence of temporal and spectral phase distortions. Using these schemes, full-field reconstruction of ultrashort laser pulses is obtained in real time using an efficient iterative technique.     

超短脉冲掺Yb3+光纤激光器实验研究

报道了掺Yb3+光纤激光器产生超短脉冲的实验研究超短脉冲激光器抽运源采用波长为976 nm的半导体激光器,采用非线性偏振旋转相加脉冲锁模技术,通过调节偏振控制器的方向,实现了掺Yb3+光纤激光器的稳定锁模输出,获得了最大输出功率为7.02 mW,脉冲激光光谱宽度为6 nm,重复频率为13.7 MHz.     

Carboxyl graphene oxide solution saturable absorber for femtosecond mode-locked erbium-doped fiber laser

The carboxyl-functionalized graphene oxide(GO-COOH) is a kind of unique two-dimensional(2 D) material and possesses excellent nonlinear saturable absorption property and high water-solubility. In this paper, we prepare saturable absorber(SA) device by depositing GO-COOH nanosheets aqueous solution on a D-shaped fiber. The modulation depth(MD) and saturable intensity of the SA are measured to be 9.6% and 19 MW/cm~2, respectively. By inserting the SA into the erbium-doped fiber(EDF) laser, a passively mode-locked EDF laser has been achieved with the spectrum center wavelength of 1562.76 nm. The pulse duration, repetition rate, and the signal-to-noise ratio(SNR) are 500 fs, 14.79 MHz, and 80 dB,respectively. The maximum average output power is measured to be 3.85 mW. These results indicate that the GO-COOH nanosheets SA can be used as a promising mode locker for the generation of ultrashort pulses.     

In situ third-order interferometric autocorrelation of a femtosecond deep-ultraviolet pulse

The interferometric measurement of an ultrashort optical pulse is demonstrated using three-photon ionization of Xe in a time-of-flight mass spectrometer (MS). This approach allowed measurement of the third-order fringe-resolved autocorrelation trace of an ultrashort optical pulse in the deep-ultraviolet (DUV) region. The pulse can be measured in situ using the same MS that is employed in ultrafast spectroscopy. Sensitivity (>3×10⁷ W) was sufficient to measure a DUV pulse used in such applications. This setup has the potential to measure the temporal duration of a broadband (204–306 nm) ultrashort optical pulse with no additional distortion in the temporal characteristics.     

Surface-emitted THz generation using a compact ultrashort pulse fiber amplifier at 1060 nm

Generation of InAs-surface-emitted terahertz radiation by application of an ultrashort pulse 1060 nm parabolic fiber amplifier source is reported for the first time. The fiber amplifier delivers 100 fs pulses at a repetition rate of 75 MHz and an average power of maximum 12 W. This new excitation laser for surface-emitters generates high brightness broadband THz radiation ranging from 100 GHz to over 2.5 THz. THz detection is demonstrated based on two-photon absorption at low-temperature-grown GaAs dipole receivers.     

Author index to volume 54

It has been experimentally shown that when light pulses propagate in active neodymium glass fibers, a decrease of amplified pulse length almost by a factor of two is observed at a fiber length of 1 m. The study of the amplification process of an ultrashort laser pulse train by a glass fiber quantum amplifier showed that the main reason of the nanosecond light pulse compression is a recombination of the short-lifetime colouring centers due to the absorption of the front of the light pulse. Experimental results are presented concerning light pulse compression at various excitation levels of active glass fibers.     

基于全正色散光子晶体光纤的超连续谱光源

利用预估校正分步傅里叶法数值求解非线性薛定谔方程, 模拟超短激光脉冲在全正色散光子晶体光纤中传输时的演化情况, 分析了不同脉宽和能量的脉冲对产生的超连续谱的影响. 结果表明: 无啁啾高斯脉冲在此全正色散光子晶体光纤中传输时, 始终保持单个脉冲特性, 提高脉冲峰值功率可进一步展宽获得的超连续谱.模拟结果同时表明, 利用中心波长为1060 nm, 脉宽和能量分别为50 fs, 15 nJ的脉冲抽运此光纤, 当传输12 cm 后便可获得具有较好的光谱连续性和光谱平坦度的超连续谱. 进一步模拟结果表明, 采用棱镜对对其进行脉冲压缩, 可获得脉宽约15 fs, 谱宽约700 nm的理想超连续谱光源. 关键词： 超连续谱 光子晶体光纤 全正色散     

Pulse characterisation of a quantum-well mode-locked laser diode by two-photon absorption frequency-resolved optical gating

The intensity and phase of ultrashort optical pulses from a 40-GHz monolithic InGaAsP quantum-well heterostructure laser diode are retrieved for the first time from two-photon absorption pulse spectrograms. The pulse traces showing the mode-locked pulses from the laser are distorted due to ultrafast absorption saturation associated with quantum-confined Stark excitons. It is suggested from comparison between experimental time-integrated spectrum and reconstructed pulse spectrum that the mode-locked pulses are formed only from a part of the longitudinal modes in the laser cavity.     

掺Er3+氟化物光纤振荡器中红外超短脉冲的产生

基于非线性薛定谔方程建立了氟化物(ZrF₄-BaF₂-LaF₃-AlF₃-NaF, ZBLAN)光纤振荡器中产生中红外超短脉冲的理论模型, 在此基础上研究了中红外超短脉冲在氟化物光纤振荡器中形成的物理机理, 数值模拟了氟化物光纤振荡器中中红外超短脉冲的演化过程. 分析了腔内净色散和小信号增益系数对振荡器中锁模脉冲产生的影响, 并给出了参数设置范围. 研究发现: 当掺Er³⁺氟化物光纤长度, 小信号增益系数, 不饱和损耗为一定值时, 腔内净色散在一定范围内才会出现稳定的锁模脉冲, 且随着腔内净色散增加脉冲宽度变宽, 光谱变窄, 峰值功率降低; 当掺Er³⁺氟化物光纤长度及不饱和损耗一定, 腔内净色散量为合理值, 小信号增益系数在合理的范围时可以得到稳定的锁模脉冲, 且随着小信号增益系数的增加脉冲宽度变宽, 光谱变宽, 峰值功率增加.     

双包层掺Bi光纤的制备及其光谱特性研究

用改进的化学气相沉积方法和溶液掺杂方法制备了掺Bi双包层石英基光纤. 测试了掺Bi光纤预制棒切片的吸收光谱和掺Bi光纤在特定波长下的吸收系数,在不同波长的激光激发下, 研究了掺Bi光纤的近红外荧光光谱. 掺Bi光纤在976 nm激光激发下,其荧光光谱范围在1000---1400 nm之间, 荧光峰的峰值位于1140 nm附近,半高宽约为130 nm;在793和808 nm激光激发下得到了 1000---1700 nm的超宽带近红外荧光,半高宽超过250 nm.通过对掺Bi光纤预制棒切片进行900 ℃ 保温1 h的热处理后,发现在808 nm激光 激发下预制棒切片的荧光强度增加了近4倍.研究结果表明,具有超宽带荧光特性的双包层掺Bi光纤 有望作为超短脉冲激光器和可调谐激光器的增益介质.     

Anomalies in the Absorption and Reflection of a High-Power Ultrashort Laser Pulse by a Plasma with a Solid-State Density

The patterns of absorption and reflection of an ultrashort laser pulse by a plasma with a solid-state density, which are realized in the mode of the normal skin effect, are studied. It is shown that a decrease in low-power pulse duration shorter than the period corresponding to the fundamental frequency of radiation leads to an increase in the absorption coefficient. If the pulse power is so high as to provide electron heating during a time shorter than the reciprocal fundamental frequency, nonlinear suppression of absorption takes place and the spectrum of the reflected radiation contains odd harmonics of the fundamental frequency.     

大模场面积光子晶体光纤耗散孤子锁模激光器

研制了一种基于掺Yb3+的双包层大模场面积偏振光子晶体光纤的耗散孤子锁模激光器.利用数值模拟分析了光纤激光器中耗散孤子动力学过程,与全正色散锁模激光器相比,脉冲窄化机理更加丰富,半导体可饱和吸收镜(SESAM)的非线性吸收,啁啾脉冲的光谱滤波以及光纤的增益色散同时起作用,这些因素使耗散孤子锁模更加容易实现,并且稳定运行.其中,光谱滤波的耗散过程是稳定锁模机制的主导因素,滤波片能够在频域和时域同时窄化脉冲,并且去除脉冲啁啾,限制脉冲在腔内始终小于1ps.在实验上实现了无色散补偿腔中直接输出脉冲宽度777fs,最高平均功率达到1W,重复频率48·27MHz,对应单脉冲能量20nJ的飞秒激光.     

Ultrashort pulse generation using fiber FM laser

Ultrashort optical pulse generation using a fiber FM laser is presented and analyzed in detail. Fiber FM laser operation is realized using a fiber ring with an internal phase modulator and an erbium-doped fiber amplifier. To compress FM laser pulses, an external dispersive single-mode fiber is employed. Furthermore, by external intensity modulation, the pulse background is removed. The background ratio of the generated ultrashort pulse is calculated and compared with the experimental results. The experimental results show an output optical pulse width of 1.77 ps and a spectral bandwidth of 0.5 THz.