UC Santa Barbara

Beginning from their bulky and power-hungry implementations in the early 20th century, microwave synthesizers have now progressed to occupying nearly every aspect of our lives. Despite initially finding a place only in military and fringe scientific applications, these synthesizers can now be found, in some shape or form, in every electronic device we use.

Optical frequency synthesizers (OFS) find applications in the field of metrology, molecular spectroscopy, navigation, optical communication, and LiDAR. These synthesizers have the same technological disrupt potential that microwave synthesizers did in the previous century, however, most demonstrations of frequency synthesizers often involve unwieldy implementations that reside on expensive optical benches and consume several Watts of power.

To increase their applicability, it is important to reduce their Size, Weight and Power consumption (SWaP). Silicon Photonics technology, which is compatible with Complementary Metal Oxide Semiconductor (CMOS) foundry processes, offers a viable solution to this problem of integration and mass production; however, miniaturizing these devices also makes them prone to fabrication variation and environmental fluctuations during operation.

This works focuses on the challenges faced during the design and implementation of the electronics required to stabilize and control these intricate systems, and discusses three specific implementations of OFS that involve varying degrees of integration. It first presents a Printed Circuit Board (PCB) prototype that demonstrates laser frequency synthesis with parts-per-trillion stability. It then two Application Specific Integrated Circuits (ASICs) designed in 130nm and 55nm CMOS processes, that attempt to tackle the SWaP limitations of the board level prototype. Finally, it discusses the difficulties that arise during the design and fabrication of these ASICs, and addresses the challenges faced during the testing of these circuits in conjunction with complex optical systems to achieve synthesis. Hardware and software solutions are presented at every level of the system – beginning from the PCBs that house these ASICs, continuing through the Digital Signal Processing (DSP) implemented on Field Programmable Gate Arrays (FPGA) and finally to the Graphical User Interface (GUI) designed to make interfacing with these systems easier.

The final part of this research then shifts focus to an alternative and novel method of OFS that attempts to relatively stabilize two laser systems with offsets up to THz in frequency, without the use of high-speed electronics. A board level prototype of this system achieves this feat, accompanied by a software interface that allows turn key operation of this system, enabling production of arbitrary microwave frequency signals with the click of a button.