UC Santa Barbara

Communication needs have grown tremendously over the past few decades and will continue to increase in the future. In order to address these needs, 5G mobile communication systems are moving towards higher carrier frequencies in the millimeter wave (mmW) regime (30 – 300 GHz). Unlike traditional microwave frequencies, which have a relatively isotropic radiation pattern, the highly directional free space propagation characteristics of mmWs requires beemsteering and tracking between transmitters and receivers. One technology that is promising for future mobile communication systems is optical beam forming networks (OBFN). This technology uses photonic components to provide wide bandwidth and eliminate beam squint associated with RF methods to drive phased array antennas. The optical signals from the OBFN are down-converted using high speed photodiodes, which require high bandwidth, efficiency and RF output power. Here we present results on waveguide uni-traveling-carrier photodiodes integrated with mode converters for efficient coupling to a silicon nitride OBFN photonic integrated circuit (PIC). We demonstrate greater than 67 GHz bandwidth and extract efficiency limitations due to the space charge effect of the high carrier density under large optical input power.

In addition to communication, highly directional beams can be used for free space sensors including LIDAR. While various frequency ranges provide benefits for specific applications, by increasing the frequency from the mmW regime to the near infrared (~193 THz), beam size can be further reduced to provide high resolution imaging and sensing. We present an indium phosphide transceiver PIC that incorporates a tunable laser, frequency discriminator, and receiver that can be used for frequency modulated continuous wave (FMCW) LIDAR when integrated with an optical phased array for 2D beamsteering. The transceiver provides wavelength tuning over 40 nm, a method for stabilizing the lasing frequency and imparting frequency modulation, and a balanced receiver for coherent detection. The components of the PIC will be discussed along with experimental verification of the functionality of this transceiver.