Fig. 1: 1/f-noise-free optical sensor.
From: 1/f-noise-free optical sensing with an integrated heterodyne interferometer
a A low-frequency light scattering signal induced by a nanoparticle buried in noise background (i), and the principle of 1/f-noise-free detection (ii). Blue peak: original light scattering signal; green peak: the first amplified signal after optical up-conversion process; red peak: the extracted signal after electrical amplification and down-conversion processes. b Experimental set-up. BPD balanced photodetector, S1 and S2 signal generators with fRF = 80.15 MHz and fLO = 80.18 MHz, respectively; AOM acousto-optic modulator, Amp. radio-frequency amplifier, PS 90∘ power splitter, DAQ data acquisition system. c Power spectra of \({A}_{{\rm{beat}}}^{{\rm{I}}}\) at low frequency region when both probe and local light are off (gray curve) or on (red curve). The low-frequency noise floor is fitted by 1/f (dashed curves). d The sampling noise amplitude versus bias frequency Δf. Red circles: experimental data; black curve: 1/f0.61 fitting below the corner frequency. Error bars represent the standard deviation of repeated measurements. e Beat intensity Ibeat for the conventional lock-in amplifying scheme (Δf = 0, blue curve) and the 1/f-noise-free regime (Δf = 30 kHz, red curve).
