Responsivity evaluation of photonics integrated photodetectors via pairwise measurements with an attenuation circuit

TL;DR

This paper presents a novel on-chip attenuation circuit and pairwise measurement method to accurately evaluate the responsivity of integrated photodetectors at low optical powers, improving calibration precision for optical technologies.

Contribution

It introduces a pairwise measurement approach combined with cascaded directional couplers for on-chip responsivity calibration at low powers, reducing uncertainties compared to traditional methods.

Findings

Pairwise measurement reduces calibration uncertainty from 1.21% to 0.22%.

The method achieves an expanded uncertainty of 10.13% (k=2).

Scattering noise and coupling errors limit measurement precision.

Abstract

Integrated photonics platforms offer a compact and scalable solution for developing next-generation optical technologies. For precision applications involving weak signals, the responsivity as well as the accurate calibration of the integrated photodetectors at low optical powers become increasingly important. It remains challenging to perform a calibration traceable to mW-level primary standards without relying on external attenuation setups. Here, we utilize an on-chip attenuation circuit, composed of a series of cascaded directional couplers (DCs), to evaluate the responsivity of integrated photodetectors (PDs) at uW optical power levels with mW inputs to the chip. Moreover, we show that a pairwise measurement method, involving the simultaneous measurement of the integrated PD photocurrent and an auxiliary optical output which is coupled off-chip, systematically improves the experimental uncertainties compared to a direct PD photocurrent measurement. For 3 cascaded DCs, the pairwise measurement improves the repeatability error from 1.21% to 0.22%, with an overall expanded calibration uncertainty (k=2) of 10.13%. The latter is dominated by the scattering noise floor and fiber-to-chip coupling errors, which can be significantly improved with better device fabrication control. Our method can be extended to a fully integrated calibration solution for waveguide-integrated single-photon detectors.