Broadband wavelength-to-time mapping
For broadband wavelength-to-time measurements, the supercontinuum was spectrally narrowed to within the 500 nm to 600 nm range using short and long pass filters. Wavelength-to-time mapped spectra were then obtained in two ways, one measurement with and one measurement without a rotating diffuser plate. The wavelength-to-time calibration was performed by recording the arrival time of spectrally narrow pulses within the 500nm to 600nm region. By fitting a 4th order polynomial to these arrival times, we obtained a set of equations for each core-SPAD combination that could be used to convert arrival time into wavelength for the broadband measurements. The spectrum of the light entering the photonic lantern (USB2000_Broadband_Measurement) was also recorded with a conventional spectrometer (USB2000 - Ocean Optics).
For the measurement without the diffuser plate (TCSPC_Broadband_No_Diffuser), the supercontinuum was focused directly into the multimode end of the photonic lantern. When injecting the light into the photonic lantern in this manner, it was observed that each core at the end of the 290 m long multicore emitted light with very different spectra; the result of wavelength dependent coupling in the multimode end of the photonic lantern.
For the second measurement(TCSPC_Broadband_With_Diffuser) a rotating diffuser plate was inserted into the beam path before the multimode end of the multicore fibre. The diffuser plate ensured that all modes in the multimode end of the photonic lantern were equally excited in a time-averaged manner.
For both TCSPC_Broadband_No_Diffuser and TCSPC_Broadband_With_Diffuser, the data consists of a 1024 x 1024 matrix with columns representing pixel number and row representing time bin. To convert time bin into time(s), multiply bin number with the resolution, 53ps e.g. bin number 100 = 100x53e-12s.
To process the TCSPC data, all the hot pixels (TCSPC_Hot pixels) should be set to 0.