Parity-time-symmetric optoelectronic oscillator based on higher-order optical modulation

Area of Science:

• Photonics and Optics
• Microwave Engineering
• Nonlinear Dynamics

Background:

• Optoelectronic oscillators (OEOs) are crucial for generating high-frequency microwave signals.
• Achieving single-frequency operation in OEOs typically requires ultra-narrow filters, which can be complex and costly.
• Parity-time (PT) symmetry offers a novel approach to controlling oscillation modes in coupled systems.

Purpose of the Study:

• To propose and demonstrate a single-frequency optoelectronic oscillator (OEO) based on broken parity-time (PT) symmetry.
• To achieve stable single-frequency microwave generation without relying on ultra-narrow passband filters.
• To investigate the performance of the proposed PT-symmetric OEO in terms of signal purity and stability.

Main Methods:

• Implemented broken PT symmetry within a single physical loop of the OEO using higher-order modulation.
• Configured equivalent gain and loss loops through optical carrier and sideband beating at a photodetector.
• Controlled gain and loss coefficients by adjusting incident light power and modulator bias voltage to break PT symmetry.

Main Results:

• Successfully generated a single-frequency microwave signal at 9.997 GHz from a 10.1 km OEO.
• Achieved a high sidemode suppression ratio of 55 dB.
• Demonstrated excellent phase noise performance of -142 dBc/Hz at a 10 kHz offset frequency.
• Observed stable operation with no mode hopping over a 5-hour measurement period.

Conclusions:

• The proposed PT-symmetric OEO effectively generates single-frequency microwave signals with high spectral purity and stability.
• This approach eliminates the need for external ultra-narrow filters, simplifying OEO design.
• The demonstrated PT-symmetry breaking in a single-loop OEO offers a promising pathway for advanced microwave signal generation.