Wavelength-to-time mapping (WTM)—stretching ultrashort optical pulses in a dispersive medium such that the instantaneous frequency becomes time-dependent—is usually performed using a single-mode fiber. In a number of applications, such as time-stretch imaging (TSI), the use of this single-mode fiber during WTM limits the achievable sampling rate and the imaging quality. Multimode fiber based WTM is a potential route to overcome this challenge and project a more diverse range of light patterns. Here, we demonstrate the use of a two-dimensional single-photon avalanche diode (SPAD) array to image, in a time-correlated single-photon counting (TCSPC) manner, the time- and wavelength-dependent arrival of different spatial modes in a few-mode fiber. We then use a TCSPC spectrometer with a one-dimensional SPAD array to record and calibrate the wavelength-dependent and mode-dependent WTM processes. The direct measurement of the WTM of the spatial modes opens a convenient route to estimate group velocity dispersion, differential mode delay, and the effective refractive index of different spatial modes. This is applicable to TSI and ultrafast optical imaging, as well as broader areas such as telecommunications.

中文翻译：

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使用单光子检测器阵列观察少数模式光纤中与模式有关的波长到时间的映射

波长到时间的映射（WTM）通常是在单模光纤上执行的，即在分散介质中拉伸超短光脉冲，使瞬时频率与时间相关。在许多应用中，例如时间拉伸成像（TSI），在WTM期间使用这种单模光纤会限制可实现的采样率和成像质量。基于多模光纤的WTM是克服这一挑战并投射出更多种类的光图案的潜在途径。在这里，我们演示了如何使用二维单光子雪崩二极管（SPAD）阵列以时间相关的单光子计数（TCSPC）方式对不同空间模式在时间和波长上的到达进行成像。几模光纤。然后，我们使用带有一维SPAD阵列的TCSPC光谱仪来记录和校准与波长有关和与模式有关的WTM过程。对空间模式WTM的直接测量为估算群速度色散，差模延迟和不同空间模式的有效折射率提供了一条便利的途径。这适用于TSI和超快光学成像以及电信等更广阔的领域。