Reducing noise in higher-frequency oscillators is one way to achieve reliable, high-data-rate communications, although noise tends to rise with increasing frequency. All sorts of oscillators and frequency-synthesis techniques have been applied in recent years in attempts to trim phase-noise levels at microwave frequencies. Many of these approaches have been electrical in nature.
Taking a different tack, Synergy Microwave Corp. and Drexel University jointly developed a line of frequency synthesizers that leverage optical circuit techniques to help achieve lower-noise microwave signals at X- and K-band frequencies. In these low-noise frequency synthesizers, optoelectronic transmission lines and optoelectronic oscillators (OEOs) are part of the solution for reducing both close-in and far-from-the-carrier phase noise in microwave signal sources.
The latest line of low-noise frequency synthesizers from Synergy Microwave Corp. (Fig. 1) builds upon OEOs to produce tunable, low-noise output signals at X- and K-band frequencies. They use long fiber-optic delay lines to reduce phase noise close to the carrier. The synthesizers also employ self-phase-locked-loop (SPLL) and self-injection-locking (SIL) techniques to reduce phase noise otherwise located close-in and far-from the carrier, respectively.
1. Shown in two views, this line of rack-mountable frequency synthesizers employs different techniques and technologies to trim phase noise at X- and K-band frequencies.