A photonic integrated circuit for full duplex spectrum monitoring in cognitive radio

We show preliminary results on a photonic integrated circuit (PIC) designed to enable a cognitive radio (CR) to constantly monitor its environment even while transmitting. Cognitive radios were conceived to combat the inefficiencies and underutilization of the radio-frequency spectrum that were created by the allocation of static frequency bands to “licensed users”. Cognitive radios enable secondary users to recycle underutilized spectrum by temporarily accessing an unused band. However, these radios must constantly monitor the band to ensure that a licensed user does not come online during a transmission. Moreover, monitoring the band introduces overhead because a radio must stop transmitting to monitor the band; otherwise, their own strong transmitted signal would mask the weaker signals coming from distant nodes, a problem known as self-interference.