【作者】 顾晓蓉；

【导师】 曾和平； 陆卫；

【作者基本信息】 华东师范大学 ， 光学， 2012， 博士

【摘要】 红外光子在光纤和大气中低损耗的传输特性使其在科学研究和实际生活中发挥着极其重要的作用,已广泛应用于国防科技和民用技术的多个层面。其关键技术——红外单光子灵敏探测,在量子信息处理与存储、量子保密通信、高分辨率分子光谱测量、大气污染与生物发光检测、非破坏性物质分析等诸多领域中都有重大的应用前景。然而,现有的红外探测器性能却不尽人意,半导体材料探测器探测效率低噪声大,超导探测器性能优越却造价昂贵且工作条件苛刻。频率上转换探测是一种新兴的红外单光子探测技术,该技术采用非线性和频过程将红外单光子“一对一”地转换到可见光波段,再通过性能卓越的硅探测器,实现高效率、低噪声的红外单光子探测,巧妙地规避了传统探测器在红外波段的性能不足。围绕着如何实现高效率、低噪声的红外单光子探测,本论文提出了时频域精密控制的单光子频率上转换探测方案。利用光纤激光技术,实现了信号光子与泵浦脉冲的时域同步和窄光谱匹配。在此基础上构建了以周期极化的铌酸锂晶体作为非线性介质,以全光同步的掺镱和掺铒锁模光纤激光器作为信号源和泵浦源的时频域精密控制的单光子频率上转换探测系统,实现了近红外单光子高效率低噪声探测。理论与实验相结合验证了多纵模系统中,转换后的可见光子与未转换的红外光子之间的关联性。并将这套平台应用于红外光子数可分辨探测和红外高分辨上转换成像系统中,拓展了单光子频率上转换探测的应用领域。另一方面本文将上转换信号光子的波长由近红外波段拓展到中红外波段,利用锁模脉冲泵浦中红外信号,在泵浦光包络内实现中红外信号的超灵敏探测。本文的主要研究成果和创新点概括如下：1.提出了全光同步的单光子频率上转换探测方案。该方案的优势在于,通过操控泵浦脉冲与信号光子在时域上高精度同步、频域上窄光谱匹配,极大地增强了非线性作用强度,从而保证了信号光的转换效率和系统整体的探测效率。同步脉冲泵浦方案将绝大部分的噪声限制在了泵浦脉冲的时间窗口内,极为有效地降低了系统的背景噪声。结合长波长泵浦方案,又进一步消除了由泵浦光的参量荧光产生的非线性背景噪声,从而实现了高效率、低噪声的单光子频率上转换探测,系统的转换效率为81.1%,探测效率为27.5%,相应的背景噪声为1.5kcounts/s。2.从理论上分析了多纵模单光子频率上转换系统中红外信号光子的量子特性保持问题,实验上验证了转换后的可见光子与红外信号光子的“一一对应”关系,并通过它们的符合计数测量验证了红外信号光子的相干光特性在上转换过程中保持不变。3.应用时频域精密控制的红外单光子频率上转换探测技术,实现了近红外光子数可分辨探测和近红外超灵敏成像。a)在时频域精密控制的单光子频率上转换技术的基础上,结合硅基多像素光子计数器,实现了波长为1.04μm的光子数可分辨探测,系统整体探测效率为3.7%,相应的背景噪声为0.0002/脉冲。b)在该系统基础上,信号光子通过空间强度调制,形成二维空间成像,再在强泵浦场作用下转换到可见光波段,转换效率为33.5%,再通过高性能电子增强型CCD采集可见光成像信号,实现1.04μm的灵敏上转换成像系统。4.利用锁模脉冲泵浦实现了中红外的单光子频率上转换探测,拓展上转换探测系统的信号光波长。信号光为连续输出的氦氖激光器,泵浦光为锁模掺镱光纤激光器,在泵浦光包络内实现了64%的转换效率,探测效率为6.1%,相应的背景噪声仅为400counts/s。更多还原

【Abstract】 Recently, high efficient infrared single-photon detectors draw a lot of attention due to their wide applications, such as astronomy, quantum key distribution, ultrasensitive spectroscopy, deep-space communication, laser sensing and ranging. The conventional infrared detectors as InGaAs avalanche photodiodes (APDs) show poor performance compared to that of Si APDs, which are available for visible single-photon detection. The superconductor detectors or the quantum dot detectors offer a superior performance for infrared single-photon detection, but they are prohibited from the widespread use by their high cost and extremely critical working conditions. Fortunately, single-photon frequency upconversion technique provides a novel solution. The infrared single photons could be converted to visible region with nearly unity efficiency under a strong pump field in a quadratic nonlinear medium, and then the converted photons can be handled by the Si APDs for high detection efficiency. Various infrared single-photon upconversion detectors have been realized in continuous-wave mode with high conversion efficiency. But the background noise mainly caused by the continuous-mode pump field limits the performance of those detectors.In order to achieve infrared single-photon upconversion detection with high efficiency and ultralow background noise, we developed a coincidence frequency upconversion detection scheme with a precise control in both temporal and spectral domains. With the help of fiber laser techniques, single-photon signals and the intense pump pulses are temporally synchronized while appropriately narrow spectra are obtained for approaching the acceptance bandwidth. The infrared signal and pump pulses were prepared experimentally by the synchronized mode-locked erbium doped fiber laser and ytterbium doped fiber laser, respectively. A periodically poled lithium niobate crystal (PPLN) was employed as the nonlinear media for frequency upconversion due to its wide transparent window, large nonlinear coefficient and long interaction length. With a specific concern about the temporal-and-spectral matching in frequency upconversion system, highly efficient single photon frequency upconversion detection was implemented with ultra-low background noise. Moreover, we demonstrated theoretically and experimentally that the converted visible photons were well temporally correlated with the unconverted infrared photons. Furthermore, the synchronously pulsed pumping frequency upconversion system was proved useful for photon-number-resolving detection and ultra-sensitive upconversion imaging. Additionally, the wavelength of single photon source in the frequency upconversion system was already extended from near infrared to mid-infrared regime.The main achievements and innovations of this thesis are summarized below:1. A single-photon frequency upconversion detection scheme based on the all-optical synchronization pumping technique was proposed. The conversion efficiency was significantly increased due to the temporal synchronization and spectral matching of the signal photons and pump pulses. Besides, the synchronous pump confines most of the noise within the ultra-short time window and the wavelength of the pump was chosen to be longer than that of signal, leading to effectively suppress of the background noise. Eventually, a high detection efficiency of80.5%has been realized with a corresponding low background noise of1.5kcps.2. The quantum features of the multi-longitudinal modes interaction during the upconversion process were analyzed theoretically. The experimental results indicated that the converted visible photon was in tight correlation with the unconverted infrared photon. The second-order temporal correlation was measured for proving the preservation of the coherence properties during the upconversion process.3. Benefited from the frequency upconversion system based on synchronously pulsed pumping, infrared photon-number-resolving detection and highly sensitive infrared imaging were achieved.a) Utilizing a Silicon multi-pixel photon counter, photon-number-resolving detection at1.04μm was realized. The total detection efficiency of the system was3.7%and the corresponding background noise probability was0.0002/pulse.b) The infrared object image was upconverted spectrally to the visible region with a conversion efficiency of33%using the frequency upconversion system mentioned above. The converted visible photons were then captured by a high performance electron multiplying CCDs, thus inferring the spatial information of the infrared object image.4. Mid-infrared single-photon frequency upconversion detection based on pulsed pumping was demonstrated experimentally. Specifically, the signal photons and the pump pulses came from a continuous-wave running He-Ne laser and a mode-locked ytterbium-doped fiber laser, respectively. The detection efficiency was measured to be6.1%, inferring a conversion efficiency of64%by correcting the transmittance of the filtering system. The background noise was reduced remarkably to400counts/s by the pulsed pump excitation.更多还原