IPC분류정보
국가/구분 |
United States(US) Patent
등록
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국제특허분류(IPC7판) |
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출원번호 |
US-0146653
(2002-05-14)
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발명자
/ 주소 |
- Liu, Jian
- Chen, Yue
- Yan, Zheng
- Robertson, III, Wynhdam
- Lin, Hong
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출원인 / 주소 |
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대리인 / 주소 |
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인용정보 |
피인용 횟수 :
65 인용 특허 :
26 |
초록
▼
Techniques and designs for tunable and dynamically stabilized a laser wavelength in various lasers, including fiber lasers and actively mode-locked lasers. In an actively mode-locked laser, a dynamic wavelength tuning control and a dynamic cavity length control are implemented to maintain mode locki
Techniques and designs for tunable and dynamically stabilized a laser wavelength in various lasers, including fiber lasers and actively mode-locked lasers. In an actively mode-locked laser, a dynamic wavelength tuning control and a dynamic cavity length control are implemented to maintain mode locking during tuning of the laser wavelength.
대표청구항
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1. A tunable laser, comprising:a laser cavity enclosing a laser gain medium which produces an optical gain for laser oscillation within a laser gain spectral range; an optical modulator in said laser cavity responsive to a modulation control signal to modulate at least one of an amplitude and a phas
1. A tunable laser, comprising:a laser cavity enclosing a laser gain medium which produces an optical gain for laser oscillation within a laser gain spectral range; an optical modulator in said laser cavity responsive to a modulation control signal to modulate at least one of an amplitude and a phase of light in said laser cavity at a modulation frequency to lock optical modes of said laser cavity to produce laser pulses; a tunable optical bandpass filter in said laser cavity to selectively transmit light at a transmission wavelength, said optical bandpass filter tunable to vary said transmission wavelength in response to a filter control signal; and a wavelength control unit producing said filter control signal to tune said filter and coupled to receive a portion of a pulsed laser output from said laser cavity as an optical monitor beam and operable to determine a deviation of a laser wavelength of said optical monitor beam from a reference wavelength, said wavelength control unit operable to adjust said filter to reduce said deviation, wherein said wavelength control unit comprises: a wavelocker to receive said optical monitor beam and to determine said deviation, said wavelocker producing an output electronic signal indicative of said deviation; a wavelocker circuit coupled to receive said electronic signal and to produce an error signal; a filter control circuit producing said filter control signal to said filter; a laser wavelength identifier to produce a wavelength Signal to said filter control circuit to tune said filter; and a locking circuit coupled between said wavelocker circuit and said filter control circuit to feed said error signal to said filter control circuit to stabilize said laser wavelength after said filter is tuned to a selected laser wavelength by said laser wavelength identifier. 2. The laser as in claim 1, wherein said laser wavelength identifier includes an optical reference bandpass filter at a known laser wavelength, said optical reference bandpass filter coupled to receive a portion of said optical monitor beam.3. The laser as in claim 1, wherein said laser wavelength identifier includes an electronic circuit having a memory to store a lookup table with multiple tuning positions of said filter and corresponding transmission wavelengths of said filter.4. The laser as in claim 1, wherein said wavelocker includes a Fabry-Perot reference cavity having a free spectral range equal to a wavelength difference between two adjacent transmission wavelengths of said filter.5. The laser as in claim 1, wherein said filter includes an acousto-optic medium and an acoustic transducer engaged to said acousto-optic medium to generate an acoustic wave for spectrally filtering light.6. The laser as in claim 1, wherein said filter includes a Fabry-Perot filter with two opposing reflectors, said filter having a tuning mechanism to change an optical path length between said two opposing reflectors.7. The laser as in claim 6, wherein said tuning mechanism includes a piezo-electric transducer to shift one reflector relative to another reflector.8. The laser as in claim 6, wherein said tuning mechanism includes a MEMS transducer to shift one reflector relative to another reflector.9. The laser as in claim 6, wherein said tuning mechanism includes a liquid crystal material between said two reflectors to change a refractive index in response to a control voltage.10. The laser as in claim 1, further comprising a cavity length control mechanism operable to control a total optical path length of said laser cavity to maintain a phase matching condition for active mode locking where an integer multiple of a mode spacing of said laser cavity equals said modulation frequency to maintain mode locking when said filter is being tuned to transmit from one laser wavelength to another laser wavelength.11. The laser as in claim 10, said cavity length control mechanism includes:a cavity length control element engaged to said laser cavity to control and adjust a cavity length of said laser cavity in response to a Cavity length control signal; a thermal control unit to control at least a temperature of a portion of said laser cavity in response to a temperature control signal; a thermal sensor coupled to measure a temperature of said portion of said laser cavity under control of said thermal control unit to produce a temperature signal to said thermal control unit; an optical detector receiving a portion of a laser output from said laser cavity to produce a detector output; an electrical signal mixer to mix a reference signal split from said modulation control signal with said detector output to produce a mixer output that includes an error signal indicating a frequency difference between said modulation frequency and a multiplicity of a longitudinal mode spacing of said laser cavity; a phase delay unit coupled to a signal path of said reference signal to cause a phase delay in said reference signal in response to a phase delay control signal; at least one bandpass filter, having a spectral bandwidth covering at least frequencies associated with energy relaxation processes in said laser cavity, and coupled to respectively receive and filter another portion of said detector output to produce a filter output signal indicating noise in said laser output; and a digital control module to digitally process said filter output signal to extract noise information of said laser output, to digitally process said error signal to extract said frequency difference caused by said laser cavity length, to digitally process said temperature signal to determine a measured temperature of said portion of said laser cavity, wherein said digital processor is operable to produce said cavity length control signal in response to said frequency difference, said temperature control signal, and said phase delay control signal in response to said noise information of said laser output. 12. The laser as in claim 10, wherein said laser cavity includes a fiber ring where said laser gain medium includes a doped fiber segment.13. The laser as in claim 10, wherein said laser cavity comprises:a polarizing beam splitter (PBS); a polarization-maintaining fiber loop having an input terminal coupled to one facet of said PBS to receive light in a selected polarization reflected from said PBS and an output terminal coupled to another facet of said PBS to output light in said selected polarization that transmits through said PBS; an optical isolator in said fiber loop to circulate said light directing from said input terminal to said output terminal and to suppress light in directing from said output terminal to said input terminal; a fiber segment having a first terminal and a second terminal, said first terminal coupled to said PBS to receive light from said output terminal of said fiber loop and to deliver light to said PBS a portion of which is reflected by said PBS into said input terminal of said fiber loop; and a Faraday rotator reflector coupled to said second terminal to reflect light with a rotation of polarization by about 90 degrees, wherein said fiber ring, said fiber segment, and said Faraday rotator reflector form said laser cavity. 14. A tunable laser, comprising:a laser cavity enclosing a laser gain medium which produces an optical gain for laser oscillation within a laser gain spectral range; a tunable optical bandpass filter in said laser cavity to selectively transmit light at a transmission wavelength, said optical bandpass filter tunable to vary said transmission wavelength in response to a filter control signal; and a wavelength control unit producing said filter control signal to tune said filter and coupled to receive a portion of a laser output from said laser cavity as an optical monitor beam and operable to determine a deviation of a laser wavelength of said optical monitor beam from a reference wavelength, said wavelength control unit operable to adjust said filter to reduce said deviation, wherein said wavelength control unit includes; a wavelocker to receive said optical monitor beam and to determine said deviation, said wavelocker producing an output electronic signal indicative of said deviation, a wavelocker circuit coupled to receive said electronic signal and to produce an error signal, a filter control circuit producing said filter control signal to said filter, a laser wavelength identifier to produce a wavelength signal to said filter control circuit to tune said filter, and a locking circuit coupled between said wavelocker circuit and said filter control circuit to feed said error signal to said filter control circuit to stabilize said laser wavelength after said filter is tuned to a selected laser wavelength by said laser wavelength identifier. 15. The laser as in claim 14, wherein said laser wavelength identifier includes an optical reference bandpass filter at a known laser wavelength, said optical reference bandpass filter coupled to receive a portion of said optical monitor beam.16. The laser as in claim 14, wherein said laser wavelength identifier includes an electronic circuit having a memory to store a lookup table with multiple tuning positions of said filter and corresponding transmission wavelengths of said filter.17. A tunable laser, comprising:a laser cavity enclosing a fiber loop to guide light and a laser gain medium which is in said fiber loop and produces an optical gain for laser oscillation within a laser gain spectral range; an optical modulator in said laser cavity responsive to a modulation control signal to modulate at least one of an amplitude and a phase of light in said laser cavity at a modulation frequency to lock optical modes of said laser cavity to produce laser pulses; a tunable optical bandpass filter in said laser cavity to selectively transmit light at a transmission wavelength, said optical bandpass filter tunable to vary said transmission wavelength in response to a filter control signal; a wavelength control unit producing said filter control signal to tune said filter and coupled to receive a portion of a pulsed laser output from said laser cavity as an optical monitor beam and operable to determine a deviation of a laser wavelength of said optical monitor beam from a reference wavelength, said wavelength control unit operable to adjust said filter to reduce said deviation; and a cavity length control mechanism operable to control a total optical path length of said laser cavity to maintain a phase matching condition for active mode locking where an integer multiple of a mode spacing of said laser cavity equals said modulation frequency to maintain mode locking when said filter is being tuned to transmit from one laser wavelength to another laser wavelength, wherein said cavity length control mechanism comprises: a cavity length control element engaged to said laser cavity to control and adjust a cavity length of said laser cavity in response to a cavity length control signal; a thermal control unit to control at least a temperature of a portion of said laser cavity in response to a temperature control signal; a thermal sensor coupled to measure a temperature of said portion of said laser cavity under control of said thermal control unit to produce a temperature original to said thermal control unit; an optical detector receiving a portion of a laser output from said laser cavity to produce a detector output; an electrical signal mixer to mix a reference signal split from said modulation control signal with said detector output to produce a mixer output that includes an error signal indicating a frequency difference between said modulation frequency and a multiplicity of a longitudinal mode spacing of said laser cavity; a phase delay unit coupled to a signal path of said reference signal to cause a phase delay in said reference signal in response to a phase delay control signal; at least one bandpass filter, having a spectral bandwidth covering at least frequencies associated with energy relaxation processes in said laser cavity, and coupled to respectively receive and filter another portion of said detector output to produce a filter output signal indicating noise in said laser output; and a digital control module to digitally process said filter output signal to extract noise information of said laser output, to digitally process said error signal to extract said frequency difference caused by said laser cavity length, to digitally process said temperature signal to determine a measured temperature of said portion of said laser cavity, wherein said digital processor is operable to produce said cavity length control signal in response to said frequency difference, said temperature control signal, and said phase delay control signal in response to said noise information of said laser output. 18. The laser as in claim 17, wherein said fiber loop includes a first fiber segment and a second fiber segment that exhibits a chromatic dispersion opposite to a chromatic dispersion of said first fiber segment.19. The laser as in claim 17, wherein said laser cavity includes a dispersion control unit to produce a variable chromatic dispersion to control a chromatic dispersion in said laser cavity.20. The laser as in claim 17, wherein said laser cavity includes a first cavity portion and a second cavity portion, and wherein said thermal control unit includes a powered thermal control element to control said first cavity portion and a passive thermal control element coupled to said second cavity portion to negate an effect of thermal expansion without receiving power from a power supply.21. The laser as in claim 17, wherein said wavelength control unit includes:a wavelocker to receive said optical monitor beam and to determine said deviation, said wavelocker producing an output electronic signal indicative of said deviation; a wavelocker circuit coupled to receive said electronic signal and to produce an error signal; a filter control circuit producing said filter control signal to said filter; a laser wavelength identifier to produce a wavelength signal to said filter control circuit to tune said filter; and a locking circuit coupled between said wavelocker circuit and said filter control circuit to feed said error signal to said filter control circuit to stabilize said laser wavelength after said filter is tuned to a selected laser wavelength by said laser wavelength identifier.
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