Dynamic response of optical-fiber modulator by using magnetic fluid as a cladding layer

An in-line optical-fiber modulator that uses magnetic fluid as a cladding layer has been developed to control transmission loss generated from external magnetic fields. In this work, we investigate the instant variation in the transmission loss of an optical-fiber modulator after an external magnetic field has been turned on (referred to as the charging operation) or turned off (referred to as the discharging operation). Research showed that when the external field was turned on/off, the transmission loss of the optical-fiber modulator did not change until after 10 ms. Successively, the transmission loss varied exponentially. Thus, two kinds of characteristic time were observed to describe quantitatively the instant variation in the transmission loss: retarding time and response time. It was found that both the retarding time in a charging/discharging operation increased with the length of the magnetic-fluid cladding over a critical level, whereas the response time in a charging/ discharging operation was cladding length independent.