# US 9,435,839 B2 · Discrimination of low power RF signals using phase modulation with injection locked lasers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,435,839 B2 - Document ID: US9435839B2 - Status: Granted - Kind: B2 - Application number: 14/693,327 - Filed: 2015-04-22 - Published: 2016-04-07 - Granted: 2016-09-06 - Earliest claimed: 2014-10-07 - Assignees: The United States of America as represented by the Secretary of the Air Force - Applicants: The United States of America, as represented by the Secretary of the Air Force - Inventors: Preetpaul S Devgan; Nicholas G Usechak - Web page: https://patentgrep.com/patent/US9435839B2 ## CPC - G01R 29/0892: {Details related to signal analysis or treatment; presenting results, e.g. displays; measuring specific signal features other than field strength, e.g. polarisation, field modes, phase, envelope, maximum value} - G01J 1/42: using electric radiation detectors (optical or mechanical part G01J1/04; by comparison with a reference light or electric value G01J1/10) - H04B 10/90: Non-optical transmission systems, e.g. transmission systems employing non-photonic corpuscular radiation - G01J 2001/4242: {Modulated light, e.g. for synchronizing source and detector circuit} - H04B 2210/006: Devices for generating or processing an RF signal by optical means - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) - H04B: TRANSMISSION ## Abstract An apparatus is provided for RF signal discrimination. A master laser of the apparatus is connected to an optical input of an optical phase modulator. The optical phase modulator is configured to receive a plurality of RF signals at an RF input and further configured to receive an output from the master laser at an optical input. A slave laser operating below a lasing threshold is configured to receive a modulated output from the optical phase modulator. An optical filter is configured to receive a mixed signal generated inside the slave laser. A photodetector receives the filtered mixed signal and is configured to recover a RF signal from the plurality of RF signals, where a frequency of a sideband of the recovered RF signal corresponds to a mode of the slave laser. ## Claims ### Claim 1 A RF signal discrimination apparatus, comprising: a master laser; an optical phase modulator configured to receive a plurality of RF signals at an RF input and further configured to receive an output from the master laser at an optical input; a slave laser operating below a lasing threshold configured to receive a modulated output from the optical phase modulator; an optical filter configured to filter a received mixed signal generated by the slave laser; and a photodetector receiving the filtered mixed signal and configured to recover a RF signal from the plurality of RF signals, wherein a frequency of a sideband of the recovered RF signal corresponds to a mode of the slave laser. ### Claim 2 (depends on 1) The RF signal discrimination apparatus of claim 1, further comprising: an optical circulator positioned between the optical phase modulator, the slave laser, and the optical filter, wherein the optical circulator is configured to receive the modulated output from the optical phase modulator and output the modulated output to be received at the slave laser, and wherein the optical circulator is further configured to receive the mixed signal from the slave laser and output the mixed signal to be received by the optical filter. ### Claim 3 (depends on 1) The RF signal discrimination apparatus of claim 1, wherein RF signals of the plurality of RF signals not having a sideband with a frequency corresponding to a mode of the slave laser are suppressed. ### Claim 4 (depends on 1) The RF signal discrimination apparatus of claim 1, wherein the mode of the slave laser provides a gain to the sideband with the frequency corresponding to the mode. ### Claim 5 (depends on 1) The RF signal discrimination apparatus of claim 1, wherein the slave laser is a multi-mode laser. ### Claim 6 (depends on 1) The RF signal discrimination apparatus of claim 1, wherein the slave laser is a single mode laser. ### Claim 7 (depends on 1) The RF signal discrimination apparatus of claim 1, wherein the maser laser is configured to sweep a plurality of frequencies. ### Claim 8 (depends on 1) The RF signal discrimination apparatus of claim 1, wherein the master laser is a first master laser, the apparatus further comprising: a second maser laser; the optical phase modulator configured to receive an output from the second master laser at the optical input. ### Claim 9 (depends on 8) The RF signal discrimination apparatus of claim 8, wherein the optical modulator is configured to receive the optical output from the second master laser at an alternate optical input. ### Claim 10 (depends on 1) The RF signal discrimination apparatus of claim 1, wherein the photodetector is a square-law optical detector. ### Claim 11 (depends on 1) The RF signal discrimination apparatus of claim 1, wherein the slave laser is a first slave laser and the optical filter is a first optical filter, the apparatus further comprising: a second slave laser operating below a lasing threshold and configured to receive the modulated output from the optical phase modulator; a second optical filter configured to filter a received mixed signal generated by the second slave laser; and the photodetector configured to receive the filtered received mixed signals from the first and second optical filter. ### Claim 12 A method of discriminating an RF signal, the method comprising: optically modulating a received plurality of RF signals onto an optical carrier generated by a master laser via a phase modulator; injecting the optically modulated plurality of RF signals into an optical output of a slave laser, filtering a mixed signal containing the optically modulated plurality of RF signals from the slave laser with an optical filter; and recovering an RF signal from the filtered mixed signal containing the optically modulated plurality of RF signals, wherein a frequency of a sideband of the recovered RF signal corresponds to a mode of the slave laser. ### Claim 13 (depends on 12) The method of claim 12, further comprising: suppressing RF signals of the plurality of RF signals from the mixed signal containing the optically modulated plurality not having a sideband with a frequency corresponding to the mode of the slave laser. ### Claim 14 (depends on 12) The method of claim 12, wherein recovering an RF signal comprises: recovering an RF signal having an imbalance in a magnitude of upper and lower sidebands of the RF signal; and suppressing an RF signal having balanced magnitudes of the upper and lower sidebands of the RF signal. ### Claim 15 (depends on 14) The method of claim 14, further comprising: thresholding recovered RF signals to eliminated unwanted RF signals not suppressed. ### Claim 16 (depends on 14) The method of claim 14, further comprising: providing a gain to a sideband of an RF signal with a frequency corresponding to the mode of the slave laser to create an imbalance in the magnitudes of the upper and lower sidebands of the RF signal.