# US 5,347,525 A · Generation of multiple stabilized frequency references using a mode-coupled laser > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,347,525 A - Document ID: US5347525A - Status: Granted - Kind: A - Application number: 08/019,980 - Filed: 1993-02-19 - Granted: 1994-09-13 - Earliest claimed: 1993-02-19 - Assignees: SRI International - Inventors: Gregory W. Faris - Web page: https://patentgrep.com/patent/US5347525A ## CPC - H04B 10/572: Wavelength control - H04B 10/50: Transmitters - H04B 10/504: {using direct modulation} - H04B 10/506: {Multiwavelength transmitters} - H04B: TRANSMISSION ## Abstract A technique for generating a large number of stabilized optical frequencies suitable for use in a wide variety of applications, including a multi-channel optical communications system, optical processing, optical computing, and heterodyne generation of stabilized RF frequencies. The technique contemplates stabilizing the cavity of a master laser and using the cavity modes as the carrier frequencies. Preferably, the modes are coupled, as by mode-locking, in order to prevent the modes from competing with each other for the laser gain, which would cause large amplitude variations. Since the cavity is stabilized, all of the cavity modes are stabilized. In one set of embodiments, the master laser is used directly as the laser source, the components at the different mode frequencies are spatially separated (demultiplexed) so that the component at each mode frequency can be individually amplified and modulated (e.g., by electro-optic (EO) modulators). In a second set of embodiments, a set of slave lasers is locked to respective modes. Each of these slave lasers may be individually modulated (e.g., by injection current modulation). The multifrequency source is useful even when the modes are not individually modulated, but serve only as heterodyne reference frequencies, as for example in radar applications. ## Claims ### Claim 1 A method of communicating information comprising the steps of: providing a mode-coupled master laser having a cavity capable of supporting a plurality of modes, said modes being characterized by respective mode frequencies that differ from one another; stabilizing said cavity so that said mode frequencies are stabilized; and modulating at least one of the mode frequencies with information to be communicated. ### Claim 2 (depends on 1) The method of claim 1 wherein said mode frequencies are separated by a frequency interval in the range of 50 MHz to 100 GHz. ### Claim 3 (depends on 1) The method of claim 1 wherein the information has a spectral content in the range of 1 KHz to 10 GHz. ### Claim 4 (depends on 1) The method of claim 1 wherein said master laser is a solid-state laser. ### Claim 5 (depends on 4) The method of claim 4 wherein said master laser has a monolithic cavity. ### Claim 6 (depends on 4) The method of claim 4 wherein said master laser comprises a body of erbium-doped glass. ### Claim 7 (depends on 1) The method of claim 1 wherein said master laser operates in the infrared. ### Claim 8 (depends on 1) The method of claim 1 wherein said cavity is a standing wave cavity. ### Claim 9 (depends on 1) The method of claim 1, and further comprising the steps of amplifying at least some of said modes. ### Claim 10 An optical source comprising: a mode-coupled master laser having a stabilized cavity capable of supporting a plurality of modes, said modes being characterized by respective mode frequencies that differ from one another; and a plurality of slave lasers, each locked to a different one of said modes to establish a respective frequency for that slave laser. ### Claim 11 (depends on 10) The source of claim 10 wherein each of said slave lasers is adapted to be optically coupled to a communications medium to define a respective communication channel for that slave laser characterized by the frequency for that slave laser. ### Claim 12 (depends on 11) The source of claim 11 wherein each of said slave lasers has an input terminal adapted to be coupled to a respective signal source that generates a respective signal for communication on that slave laser's respective channel. ### Claim 13 A transmitter system for coupling a plurality of N input signals to an optical communications medium comprising: a mode-coupled master laser having a stabilized cavity capable of supporting a plurality of at least N modes, said modes being characterized by respective mode frequencies that differ from one another; means for coupling optical power at said mode frequencies to the communications medium; and means for modulating said optical power at N of said mode frequencies according to the N input signals. ### Claim 14 (depends on 13) The transmitter system of claim 13 wherein said master laser is a solid-state laser. ### Claim 15 (depends on 14) The transmitter system of claim 14 wherein said master laser has a monolithic cavity. ### Claim 16 (depends on 14) The transmitter system of claim 14 wherein said master laser comprises a body of erbium-doped glass. ### Claim 17 (depends on 13) The transmitter system of claim 13 wherein said master laser operates in the infrared. ### Claim 18 (depends on 13) The transmitter system of claim 13 wherein said cavity is a standing wave cavity. ### Claim 19 (depends on 13) The transmitter system of claim 13, and further comprising means for amplifying at least some of said modes. ### Claim 20 (depends on 19) The transmitter system of claim 19 wherein said means for amplifying comprises: a plurality of slave lasers, each locked to a different one of said modes. ### Claim 21 (depends on 13) The transmitter system of claim 13 wherein said means for coupling comprises: a plurality of slave lasers, each locked to a different one of said modes to establish a respective carrier frequency for that slave laser, said slave lasers being optically coupled to the communications medium. ### Claim 22 (depends on 21) The transmitter system of claim 21 wherein said means for modulating comprises: means for modulating the output of said slave lasers. ### Claim 23 A transmitter system for use with an optical communications medium comprising: a mode-coupled master laser having a stabilized cavity capable of supporting a plurality of modes, said modes being characterized by respective mode frequencies that differ from one another; and a plurality of slave lasers, each locked to a different one of said modes to establish a respective carrier frequency for that slave laser; each of said slave lasers adapted to be optically coupled to the communications medium to define a respective communication channel for that slave laser characterized by the carrier frequency for that slave laser; each of said slave lasers having an input terminal adapted to be coupled to a respective signal source that generates a respective signal for communication on that slave laser's respective channel. ### Claim 24 A receiver system for detecting signals on an optical communications medium having a plurality of N channels characterized by respective carrier frequencies that differ from each other, comprising: a mode-coupled master laser having a stabilized cavity capable of supporting a plurality of at least N modes, said N modes being characterized by N respective mode frequencies that have a predetermined relationship with the N carrier frequencies; and a plurality of N photodetectors, each having incident thereon light at a respective one of said mode frequencies and optical signals from the communications medium so as to provide an electrical signal representing signals on a respective channel. ### Claim 25 (depends on 24) The receiver system of claim 24, and further comprising: a plurality of N slave lasers, each locked to a different one of said modes; and means for directing light from each of said slave lasers onto a respective one of said photodetectors. ### Claim 26 A receiver system for use with an optical communications medium comprising: a mode-coupled master laser having a stabilized cavity capable of supporting a plurality of modes, said modes being characterized by respective mode frequencies that differ from one another; a plurality of slave lasers, each locked to a different one of said modes to establish a respective detection frequency; and a plurality of photodetectors, each having incident thereon light from a respective one of said slave lasers and optical signals from the communications medium so as to provide an electrical signal representing signals on a respective channel characterized by the detection frequency for the slave laser whose light is incident on that photodetector. ### Claim 27 Apparatus for monitoring, at a plurality of discrete frequencies, an input communication signal, the apparatus comprising: a mode-coupled stabilized multimode laser capable of providing a plurality of stabilized optical frequencies over a range; a signal laser having an output in the range of said stabilized multimode laser; means for modulating said signal laser with the input communication signal; and means for performing heterodyne detection between said signal laser and said stabilized multimode laser to provide a plurality of output signals. ### Claim 28 (depends on 27) The apparatus of claim 27 wherein said stabilized multimode laser comprises: a master laser having a cavity capable of supporting a plurality of modes, said modes being characterized by respective mode frequencies that differ from one another; and means for stabilizing said cavity so that said mode frequencies are stabilized. ### Claim 29 (depends on 27) The apparatus of claim 27 wherein said means for performing heterodyne detection comprises: a plurality of detectors; means for combining the output of said stabilized multimode laser and the output of said signal laser; and a wavelength demultiplexer receiving the combined output and directing components near the stabilized frequencies to respective ones of the detectors. ### Claim 30 (depends on 27) The apparatus of claim 27 wherein said means for performing heterodyne detection comprises: a plurality of detectors; a wavelength demultiplexer receiving the output from said stabilized multimode laser and providing spatially separated components at a plurality of the stabilized frequencies; means for dividing the output from said signal laser to provide a corresponding plurality of output portions; and means for combining said components from said wavelength demultiplexer and said output portions at respective ones of said detectors. ### Claim 31 (depends on 27) The apparatus of claim 27 wherein said means for performing heterodyne detection comprises: a plurality of detectors; a plurality of slave lasers, each locked to a different one of said stabilized frequencies; means for dividing the output from said signal laser to provide a corresponding plurality of output portions; and means for combining outputs from said slave lasers and said output portions at respective ones of said detectors. ### Claim 32 (depends on 27) The apparatus of claim 27 wherein the input communication signal is a microwave signal. ### Claim 33 Apparatus for performing spectral analysis of an input optical signal comprising: a stabilized mode-coupled multimode laser capable of providing a plurality of stabilized optical frequencies over a range; and means for performing heterodyne detection between the input optical signal and said stabilized multimode laser to provide a plurality of output signals. ### Claim 34 (depends on 33) The apparatus of claim 33 wherein said stabilized multimode laser comprises: a master laser having a cavity capable of supporting a plurality of modes, said modes being characterized by respective mode frequencies that differ from one another; and means for stabilizing said cavity so that said mode frequencies are stabilized. ### Claim 35 (depends on 33) The apparatus of claim 33 wherein said means for performing heterodyne detection comprises: a plurality of detectors; means for combining the output of said stabilized multimode laser and the input optical signal; and a wavelength demultiplexer receiving the combined output and directing components near the stabilized frequencies to respective ones of the detectors. ### Claim 36 (depends on 33) The apparatus of claim 33 wherein said means for performing heterodyne detection comprises: a plurality of detectors; a wavelength demultiplexer receiving the output from said stabilized multimode laser and providing spatially separated components at a plurality of the stabilized frequencies; means for dividing the input optical signal to provide a corresponding plurality of output portions; and means for combining said components from said wavelength demultiplexer and said output portions at respective ones of said detectors. ### Claim 37 (depends on 33) The apparatus of claim 33 wherein said means for performing heterodyne detection comprises: a plurality of detectors; a plurality of slave lasers, each locked to a different one of said stabilized frequencies; means for dividing the input optical signal to provide a corresponding plurality of output portions; and means for combining outputs from said slave lasers and said output portions at respective ones of said detectors. ### Claim 38 A spread spectrum communication system for communicating an input signal on an optical communications medium comprising: a first mode-coupled master laser having a stabilized cavity capable of supporting a plurality of modes, said modes being characterized by respective mode frequencies that differ from one another; means for coupling optical power at at least some of said mode frequencies to the communications medium; means for modulating said optical power according to the input signal; a second mode-coupled master laser having a stabilized cavity capable of supporting a plurality of modes having mode frequencies having a predetermined relationship with the mode frequencies coupled to the communications medium; and a photodetector having incident thereon (a) light from said second master laser, and (b) optical signals from the communications medium so as to provide a detectible electrical signal representing the input signal. ### Claim 39 A master oscillator comprising: a mode-coupled solid state laser having a cavity capable of supporting a plurality of modes, said modes being characterized by respective mode frequencies that differ from one another; and means for stabilizing said cavity so that said mode frequencies are stabilized. ### Claim 40 (depends on 39) The master oscillator of claim 39 wherein said solid state laser has a monolithic cavity.