Nondestructive optical fiber modulation using radiation mode coupling phenomena

We demonstrate a nondestructive optical fiber modulation technology based on a radiation mode coupling (RMC) interference effect that modulates the phase difference between a guided mode and recoupled radiation modes. Because of high sensitivity of the RMC effect in the buffer layer, deep signal modulation in frequency region to the order of MHz is successfully generated by applying slight lateral deformation of a few μm to the fiber with the piezoelectric device. Modulation index of 30 was achieved for an applied voltage of 14 V_pp and no signal fading was observed for all the states of polarization. This technique enables a free access modulation at any points along optical fibers with a wide frequency band response and low applied voltages and requires no complex composition such as polarization diversity