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US 6,845,108 B1Granted
Tuning of laser wavelength in actively mode-locked lasers
AssigneeCalmar Optcom, Inc.
InventorsJian Liu, Yue Chen, Zheng Yan, Wynhdam Robertson, III, Hong Lin
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Abstract
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.
Claims21
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.
9 more elements
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.
6 more elements
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.
13 more elements
Dependencies are inferred from the claim text.