Isolation of RF Signals using Optical Single Side Band Modulation Combined with Optical Filtering

A method for isolating RF signals in a system including a first port, a first 90 degree hybrid electrically connected to the first port, a second port, a second 90 degree hybrid in a complementary configuration with respect to the first 90 degree hybrid electrically connected to the second port, a laser, an optical modulator optically coupled to the laser and having a first and a second electrical waveguide, the first electrical waveguide electrically connected to a first output of the first 90 degree hybrid and a further electrically connected to a first output of the second 90 degree hybrid, the second electrical waveguide electrically connected to a second output of the first 90 degree hybrid and a further electrically connected to a second output of the second 90 degree hybrid, an optical notch filter optically connected to the optical modulator, and a photodetector optically connected to the optical notch filter, the method comprising:

• receiving a first RF signal at a first port;
• receiving a second RF signal at a second port;
• DC biasing the first and second waveguides to produce single side band optical outputs of the first and second RF signals on opposite sides of an optical carrier frequency;
• upconverting the received first RF signal to the optical carrier frequency with the optical modulator to create a single side band optical output of the first RF signal and co-propagate the optical output of the first RF signal with an optical field of the laser;
• upconverting the received second RF signal to the optical carrier frequency with the optical modulator to create a single side band optical output of the second RF signal and counter-propagate the optical output of the second RF signal with the optical field of the laser;
• removing one of the single side band optical outputs of the first and second RF signals with the optical notch filter;
• and
• converting the other of the single side band optical outputs of the first and second RF signals to an electrical signal by the photodetector.