Highly stable oscillators are key components in many important applications where coherent processing is performed for improved detection. The optoelectronic oscillator (OEO) exhibits low phase noise at microwave and mmWave frequencies, which is attractive for applications such as synthetic aperture radar, space communications, navigation and meteorology, as well as for communications carriers operating at frequencies above 10 GHz, with the advent of high data rate wireless for high speed data transmission. The conventional OEO suffers from a large number of unwanted, closely-spaced oscillation modes, large size and thermal drift. State-of-the-art performance is reported for X- and K-Band OEO synthesizers incorporating a novel forced technique of self-injection locking, double self phase-locking. This technique reduces phase noise both close-in and far-away from the carrier, while suppressing side modes observed in standard OEOs. As an example, frequency synthesizers at X-Band (8 to 12 GHz) and K-Band (16 to 24 GHz) are demonstrated, typically exhibiting phase noise at 10 kHz offset from the carrier better than -138 and -128 dBc/Hz, respectively. A fully integrated version of a forced tunable low phase noise OEO is also being developed for 5G applications, featuring reduced size and power consumption, less sensitivity to environmental effects and low cost.
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