Performance of a 40 GHz RF photonic balanced link using a polarization modulator

Fiber optic links are commonly employed for high bandwidth applications. Analog RF photonic link applications often have critical sensitivity and linearity requirements, as such the noise figure (NF) and spurious free dynamic range (SFDR) are key performance parameters for these links. There has been considerable research dedicated to developing improved components and link designs to yield improvement in NF and SFDR. A single output intensity modulator based on an AlGaAs polarization modulation (PolM) design with half wave voltage Vπ≅3 V at 1 GHz, 3 dB roll off at 40 GHz, and optical insertion loss ≅3 dB has been reported and is commercially available. [1,2] If the linear polarizer at the output of this device is replaced with a polarizing beam splitter (PBS), dual complementary outputs similar to a dual output Mach Zehnder modulator (MZM) are provided. This allows for an intensity modulated direct detection balanced link (IMDD-BL) design to be implemented which provides multi-octave operation and common mode suppression (CMS) of laser relative intensity noise (RIN) to improve the link NF.[3] Such a IMDD-BL using a PolM, a single fiber from transmitter to receiver, and the PBS preceded by a polarization controller located at the receiver has been demonstrated at 2 GHz showing common mode suppression of RIN similar to a link using a standard lithium niobate (LN) MZM.[4]