Hybrid Integration of RF Photonic Systems

Radio-frequency (RF) photonics is demonstrating superior performance in communication systems using discrete components. As systems establish an upgrade path balancing challenging bandwidth requirements with size, weight, and power constraints, the time is ripe for transition to a more efficient and cost-effective hybrid manufacturing technology. This technology has been applied to the construction of an optical coherent receiver for the down conversion of RF signals from 10-18 to 2 GHz. Light from a distributed feedback semiconductor laser is split between two lithium niobate Mach-Zehnder modulators, driven either by a tunable local oscillator tone or an RF signal coming, for example, from a receiving antenna. The modulated light signals are combined with an optical coupler and filtered by two fiber Bragg gratings that select one optical sideband from each signal. Detection of the filtered light by a balanced photo-detector produces an electrical signal at an intermediate frequency equal to the beat difference between the frequencies of the RF signal and the local oscillator. Packaging of optical and opto-electronic components within a common enclosure where light routing is performed by micro-optics has allowed a significant decrease in the size, weight, and power consumption of the receiver.