On-chip coherent detection with quantum limited sensitivity

Heterodyne spectrometer sensitivity limit for quantum networking

Optical heterodyne detection-based spectrometers are attractive due to their relatively simple construction and ultrahigh resolution. Here we demonstrate a proof-of-principle single-mode optical-fiber-based heterodyne spectrometer that has picometer resolution and quantum-limited sensitivity around 1550 nm. Moreover, we report a generalized quantum limit of detecting broadband multispectral-temporal-mode light using heterodyne detection, which provides a sensitivity limit on a heterodyne detection-based optical spectrometer. We then compare this sensitivity limit to several spectrometer types and dim light sources of interest such as spontaneous parametric downconversion, Raman scattering, and spontaneous four-wave mixing. We calculate that the heterodyne spectrometer is significantly less sensitive than a single-photon detector and is unable to detect these dim light sources, except for the brightest and narrowest-bandwidth examples.

Compensation for the Decoherence Effect in Heterodyne Detection of Rough Targets and a Target Vibration Characteristic Measurement System

In practical applications of signal detection, the roughness of a target surface significantly affects detection efficiency. In this paper, we propose a signal processing method that improves the sensitivity of a detection system by up to 100 times. In experiments, the target vibration measurement system successfully captured an automotive vibration power spectrum using the proposed signal processing method. This technology opens a new avenue for development in the field of rough surface target detection and recognition.