Optoelectronic Microwave Oscillators David Yoo Center for Microwave and Lightwave Engineering Drexel University ECE-E641 – Fiber Optics and Optical Communications I 2/20/03 9/19/2018 David Yoo

Electronic Oscillators First developed by L. De Forest in 1912 Noise and stability limitations caused by ohmic and dispersive losses (e.g. in LC circuit) But these limits can be overcome by combining oscillator with a high Q resonator 9/19/2018 David Yoo

Loaded Quality Factor of Resonators General Definition of Q, the Loaded Quality Factor of a Resonator 9/19/2018 David Yoo

Optoelectronic Oscillators Convert continuous light energy from a laser to RF and microwave signals Use of fiber as an energy storage device results in signals with extremely low phase noise Phase noise practically independent of absolute oscillation frequency 9/19/2018 David Yoo

OEO Block Diagram Electro-Optic Modulator Optical Fiber Spool Optical Line Stretcher Laser Photodetector Microwave Output RF Coupler RF Bandpass Filter RF Amplifier Microwave Spectrum Analyzer 9/19/2018 David Yoo

Conditions for Oscillation Oscillation begins from noise In order to have self-sustained oscillation : Open loop gain of system must be greater than unity An integer number of half-wavelengths must be in the loop 9/19/2018 David Yoo

Loop Length and Frequency of Oscillation The OEO loop can produce a comb of frequencies that satisfy the conditions for oscillation The Free Spectral Range determines the distance between these frequencies FSR in loop Co is speed of light in vacuum n is index of refraction Lfiber is physical length of loop 9/19/2018 David Yoo

Phase Noise of OEOs Significant noises in an OEO (Yao & Maleki, 1996) Thermal noise Shot noise Intensity noise of laser (RIN) For high laser optical power, the phase noise of an OEO is limited by the laser’s relative intensity noise For low laser power, thermal noise tends to dominate Phase noises as low as -143 dBc/Hz at 10 kHz offset have been achieved for a 10 GHz carrier 9/19/2018 David Yoo

OEWaves TIDALWave Fixed frequency (up to 40 GHz) -143 dBc/Hz @ 10 kHz offset 10 dBm minimum output 10” x 10” x 4” 9/19/2018 David Yoo

Recent and Current Work on OEOs Development of Compact OEOs (1999) Use of semiconductor lasers and external modulators Multiloop OEOs (2000) The 2 fiber loops essentially act as the short and long cavities in a laser to select a single operation mode, and they also permit tunability Miniaturization of OEOs (currently ongoing) Replace fiber delay length with fused silica microspherical resonator Such resonators have Q’s of 107-1010 for optical frequencies Self Mode-Locking OEO (2002) 9/19/2018 David Yoo

Important Points to Remember Optoelectronic oscillators convert light energy from a laser into RF and microwave signals. The fiber delays in OEOs are high Q because of the extremely low attenuation rate of fiber. The phase noise of OEOs tends to be limited by the relative intensity noise of the system’s laser. 9/19/2018 David Yoo