Noise measurements on optical detectors

Abstract

The main figure of merit for detectors whose output consists of an electrical signal that is proportional to the radiant signal power is the normalized detectivity $D^{\ast }$, which is directly proportional to the signal-to-noise ratio ($SNR)$. In order to have an accurate value for the signal-to-noise ratio of an optical detector, the noise level of the measurement system and the bias circuit should be small compared to the noise of the device under test. In this paper a low-noise setup to make noise measurements on optical detectors is analyzed and characterized for the specific case of an antenna-coupled microbolometer. The noise floor of the setup was calculated and measured at about 1.3 $\mathrm{nV}/\sqrt{\mathrm{Hz}}$, which gives detector-noise-limited measurements for microbolometers with resistances as low as 200 $\Omega.$ This measurement setup was used to characterize the noise of a 200 $\Omega $ antenna-coupled microbolometer made out of chrome. Measurements showed two $1/f^{k}$ components in this particular device.