IEEE Transactions on Applied Superconductivity
Branching-Ratio-Based Detection Efficiency Calibration of Transition-Edge Sensors at C-Band Wavelengths
Tetsuya Tsuruta, Takeshi Jodoi, M. Rajteri, Daiji Fukuda
Abstract
We characterize a detection efficiency calibration system with a wavelength-tunable pulsed photon source for single photon detectors or photon number resolving detectors covering the telecommunication range from 1510 nm to 1570 nm, with measurements performed at the representative wavelength of 1550 nm. The source employs an external cavity diode laser and acousto-optic modulator for pulse generation with controlled mean photon number. By implementing a branching-ratio monitoring scheme instead of direct power monitoring, we achieved a relative Allan deviation below 0.02% at an averaging time of 10000 seconds, representing a tenfold improvement in long-term stability. This stability enables extended calibration measurements while maintaining consistent photon flux determination. Using photon-number-resolving detection with transition edge sensors, we measured second- and third-order intensity correlation functions from single datasets. The light source maintained Poisson distribution at repetition rates below 1 MHz, with weak bunching (g⁽²⁾ ≈ 1.05,g⁽³⁾ ≈ 1.16) observed at higher frequencies. The measured correlations satisfied the theoretical relation for weak bunching, indicating a single dominant mechanism, likely background light from the finite AOM extinction ratio. While we cannot entirely exclude potential contributions from the detector's response characteristics, the systematic frequency dependence and consistency with the weak bunching model strongly suggest the light source as the primary factor. The demonstrated stability and characterized photon statistics confirm the suitability of this source for detector calibration at repetition rates up to 1 MHz. These performance metrics meet the requirements for calibrating photon-number resolving detectors used in quantum state characterization and quantum information applications.