All-Optical Fiber Photoacoustic Gas Sensor With Double Resonant Enhancement

An all-optical fiber photoacoustic gas sensor with double resonant signal enhancement is presented. The sensor uses a fiber-tip graphene nano-mechanical resonator operating at one of its resonances as the acoustic detector and a micro-acoustic resonant tube, whose resonant frequency is matched to that of the graphene resonator, as the PA gas cell. Compared with the single resonant detection with a graphene resonator, a five-fold signal enhancement is achieved. With 138-mW pump power and 1-s lock-in time constant, a noise equivalent concentration of ~25-ppb C
₂
H
₂
is achieved, corresponding to a normalized noise equivalent absorption of 1.29 × 10
^-8
cm
^-1
WHz
^-1/2
.