Monolithically Integrated Opto-Electronic Frequency Synthesizer in Silicon Photonics

Low jitter signal sources are in widespread use for object detection, navigation systems, and ultra-high speed data communication systems. The jitter of the signal sources is dominated by the reference signal source which is a Surface Acoustic Wave (SAW) or a quartz oscillator. While these reference oscillators are standard for communication systems, the optical pulse train generated by a Mode Locked Laser (MLL) can have a better jitter performance by 2-3 orders of magnitude. It has also been shown that by using an electro-optical locking scheme, a microwave signal can be locked to an MLL [4]. Such Opto-Electronic Phase Locked Loops (OEPLL) have a great potential for a new class of low jitter frequency synthesizers.

Phase noise comparison of different technologies

The main drawbacks of these OEPLLs are their bulky and expensive optical components. Electronic-photonic integrated circuits based on silicon photonics technology offer the potential for extreme miniaturization of these optical components as well as integration of optics and low cost.

The goal of this project is to implement a monolithically integrated OEPLL with extremely low phase noise. In cooperation with our project partners at the Ruhr University of Bochum, we develop the next generation of low jitter microwave signal sources. This type of signal source employs a PLL that uses an MLL as a reference. In order to fully take advantage of the reference signal in the optical domain, the phase detection is done electro-optically using a Mach-Zehnder Modulator (MZM).

Block diagram of the opto-electronic frequency synthesizer

In the first phase, the whole system will be implemented using modular components. In the second phase, the MZM and the electronics will be integrated into a single silicon chip. The work is accompanied by theoretical investigation which will be validated by measurements.

The additive jitter of the OEPLL is expected to be less than the reference MLL jitter. The microwave signal then would have an in-band jitter which surpasses conventional electronic PLLs.

References:

[1] Kim et al, “Sub-100-as timing jitter optical pulse trains from mode-locked Er-fiber lasers,” Optics letters, vol. 36, no. 22, pp. 4443-4445, 2011.

[2] “Ultra Low Phase Noise Oven Controlled Crystal Oscillator,” Vectron, Datasheet OX-305.

[3] “Voltage Controlled SAW Oscillator Surface Mount Model,” Synergy Microwave, Datasheet HFSO1000-5.

[4] Jung et al, “Subfemtosecond synchronization of microwave oscillators with mode-locked Er-fiber lasers,” Optics letters, vol. 37, no. 14, pp. 2958-2960, 2012