Observing mode-dependent wavelength-to-time mapping in few-mode fibers using a single-photon detector array

Abstract

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.

All-Fiber Source and Sorter for Multimode Correlated Photons

“…We can therefore map the arrival times of the photons to their modal decomposition, up to modal degeneracy in symmetric fiber cores. Although this sorting scheme is quite common in classical optics [34], it was only recently demonstrated at the single photon regime for weak coherent pulses [35]. Here we use the same principle for entangled state.…”

Linear dispersion (GDD) design using grating group

“…Dispersion plays distinct and crucial roles in various application scenarios. Therefore, precise measurement and control of the dispersion of optical signals through a medium is essential, which is particularly critical in fields such as spectral measurement, [1][2][3][4] frequency modulation signal generation, [5][6][7][8] optical time-stretch technology, [9][10][11] dispersion compensation, [12][13][14][15] and ultrafast measurement, [16][17][18][19] offering broad prospects for applications.…”

Ultrafast photonic time-stretch imaging using an optically transparent medium

“…Secondly, frequency-to-time transformation, also referred to as timestretch dispersive Fourier transform (TS-DFT), maps the broadband spectrum of an optical pulse into a temporal waveform using particular temporal dispersion devices, allowing the temporal detection of an optical spectrum with ultrahigh speed. [3][4][5][6][7] Traditional photosensitive imaging apparatuses (e.g., CCD or CMOS), the most widely deployed optical imaging technologies, make fundamental trade-offs between sensitivity and speed. 8,9) Pump-probe techniques can achieve a high time resolution, but they do not operate in real time.…”