Method and apparatus for generating ultrashort pulses with adjustable repetition rates from passively modelocked fiber lasers
First Claim
1. A passively modelocked laser comprising:
- means for optical pumping of the modelocked laser;
an optical cavity for adjusting the energy of said laser;
means for initiating and sustaining the production of short optical pulses in said cavity;
an optical fiber gain medium for transmitting said optical pulses, said optical pulses having a repetition rate of integer multiples of the fundamental cavity frequency;
means for outputting laser energy from said cavity;
means for maximizing the separation of said pulses inside the cavity, including at least one semiconductor saturable absorber with a carrier life time shorter than the fundamental cavity round-trip time and longer than one hundredth of the cavity round-trip time; and
means for providing optical limiting in the cavity to minimize pulse amplitude fluctuations.
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Abstract
The generation of ultrashort pulses with adjustable repetition rates from passively modelocked fiber lasers is demonstrated. By inserting semiconductor saturable absorbers with life-times of the order of 10 nsec into fiber lasers with cavity round-trip times of the order of 100 nsec, passive harmonic modelocking is obtained, leading to the stable generation of pulses at integer multiples of the fundamental cavity frequency. For polarization states that allow for optical limiting of the lasers, pulses are obtained in a frequency range between 20 and 500 MHz., where different repetition rates can be simply selected by changing the pump power level to the cavity. The pulse jitter within one cavity round-trip time is measured to be between 300 psec and 50 psec, where side bands in the frequency domain may be suppressed by up to 70 dB. The saturable absorber acts to both stabilize the cavity repetition rate and to initiate passive modelocking, where nonlinear-polarization evolution is used to sustain modelocking and to suppress amplitude fluctuations of the pulses by providing for optical limiting. Practical embodiments can be obtained by employing environmentally stable cavity designs in polarization preserving single-clad and double clad fibers, where the latter fiber designs allow the pumping of the fiber lasers with broad area-diode array lasers.
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Citations
42 Claims
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1. A passively modelocked laser comprising:
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means for optical pumping of the modelocked laser; an optical cavity for adjusting the energy of said laser; means for initiating and sustaining the production of short optical pulses in said cavity; an optical fiber gain medium for transmitting said optical pulses, said optical pulses having a repetition rate of integer multiples of the fundamental cavity frequency; means for outputting laser energy from said cavity; means for maximizing the separation of said pulses inside the cavity, including at least one semiconductor saturable absorber with a carrier life time shorter than the fundamental cavity round-trip time and longer than one hundredth of the cavity round-trip time; and means for providing optical limiting in the cavity to minimize pulse amplitude fluctuations. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42)
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Specification