Synchronously pumped ring fiber Raman laser

A fiber optic apparatus, comprising:

• an optical fiber forming a loop for recirculating an optical signal in said loop, said optical fiber loop comprising an active material which emits photons at a first wavelength in response to optical pumping of said active material to an excited state by light at a second wavelength to generate light at said first wavelength;
• a fiber optic coupler for inputting a pump light signal at said second wavelength to said loop for propagation therethrough to optically pump said active material to said excited state and cause emission of said photons at said first wavelength, said coupler having a coupling ratio which is different for said first wavelength than for said second wavelength such that a first fraction of said light at said first wavelength exits said loop after propagation therethrough, and a second fraction of light at said wavelength exits said loop after propagation therethrough, said second fraction close to 1.0 and substantially greater than said first fraction;
• and
• a source of light for producing said pump light signal, said pump light signal comprising a series of energy bursts at a wavelength substantially equal to said second wavelength to cause said emission of said photons at said first wavelength and generate a series of corresponding energy bursts at said first wavelength at said lop, said energy bursts of said second wavelength spaced apart in time such that each of said energy bursts of said first wavelength arrives at said coupler at substantially the same time as said energy bursts of said second wavelength.

A fiber optic laser comprising:

• a source of pump optical energy at a pump frequency;
• means for modulating said pump optical energy to generate a series of pump pulses that are spaced apart in time by a selected time interval;
• a single, uninterrupted length of optical fiber, having an input end portion, an output end portion, and a loop portion disposed between said input end portion and said output end portion, said input end portion positioned to receive said pump optical energy from said source and to propagate said pump optical energy to said loop portion so that said pump optical energy propagates in said loop portion, said loop portion responsive to said pump optical energy propagating therein to emit stimulated optical energy at a laser frequency that is shifted in frequency from said pump frequency that is characteristic of said optical fiber;
• and
• means for coupling light from said input end portion to said loop portion, and from said loop portion to said output end portion, said loop portion having a length selected so that said pump optical energy traverses said loop portion in substantially the same amount of time as said selected time interval, said coupling means having a first coupling ratio at said pump frequency that is selected to prevent substantial amounts of the optical energy at said pump frequency from recirculating in said loop, said coupling means having a second coupling ratio at said laser frequency that is selected to cause a substantial portion of the optical energy at said laser frequency to recirculate in said loop as recirculating laser optical energy, said recirculating laser optical energy stimulating additional optical energy at said laser frequency in phase with said recirculating laser optical energy, the magnitude of the energy at said laser frequency thereby increasing with each recirculation until a steady-state magnitude is reached.

An apparatus, comprising:

• a loop of optical fiber for propagating light, said loop having a loop propagation time that is a function of the wavelength of light propagating therein;
• a source of light for generating a pump signal comprising a series of at least first and second adjacent optical energy bursts spaced apart in time by a time interval, and at least third and fourth adjacent optical energy bursts spaced apart in time by said time interval, said pump signal being at a first optical wavelength;
• and
• a coupler for coupling said pump signal into said optical fiber loop so that said pump signal propagates in said loop, said pump signal causing emission of optical energy in said fiber at a second optical wavelength, shifted from said first optical wavelength, to provide a laser signal at said second wavelength, said coupler recirculating said laser signal at said second wavelength in said loop and outputting a fraction of said laser signal from said loop to provide an output signal, said source of light timing said third and fourth energy bursts to arrive at said loop subsequent to said first and second energy bursts, respectively, by a time equal to a multiple of the loop propagation time for said second wavelength.

In a fiber optic device comprised of optical fiber, said device having an input end portion, a loop portion and an output end portion, and further comprising a coupler for coupling energy between said input end portion, said loop portion and said output end portion, a method of producing an optical output signal comprising the steps of:

• generating an optical pump signal at a pump frequency, said pump signal comprising bursts of optical energy spaced apart in time by a selectable time interval;
• inputting said optical pump signal to said input end portion to provide an input pump signal;
• coupling substantially all of said input pump signal to said loop portion to propagate in said loop portion so that said loop portion emits optical laser energy in response to said pump optical energy, said emitted optical laser energy being at a laser frequency that is characteristic of said optical fiber;
• coupling substantially all of said pump signal in said loop portion to said output end portion so that said pump signal does not recirculate in said loop portion;
• and
• propagating said emitted optical laser energy to said coupler and coupling a first portion of said emitted optical laser energy to said output end portion as an output signal at said laser frequency, and coupling a second portion of said emitted optical laser energy back to said loop portion to recirculate therein as a recirculating optical signal, said recirculating optical signal traversing said loop portion in a transmit time determined by the length of said loop portion and the wavelength of said optical signal;
• and
• selecting said time interval between said bursts of optical energy to be substantially equal to the transit time of said recirculating optical signal.

A method of generating an optical output signal, comprising the steps of:

• generating a pump signal comprising a series of at least first and second adjacent optical energy bursts spaced apart in time by a time interval, and at least third and fourth adjacent energy bursts spaced apart in time by said time interval, said pump signal being at a first optical wavelength;
• inputting said first and second energy bursts into a loop of optical fiber, said loop having a loop propagation time for light propagating therethrough, said propagation time being a function of the wavelength of said light;
• propagating said first and second energy bursts in said optical fiber loop to optically pump said fiber, and cause emission of optical energy in said optical fiber at a second optical wavelength, shifted from said first optical wavelength, to provide a laser optical signal at said second wavelength;
• inputting said third and fourth adjacent energy bursts into said loop;
• timing said third and fourth energy bursts to arrive at said loop subsequent to said first and second energy bursts, respectively, but a time equal to a multiple of the loop propagation time for said second wavelength;
• recirculating said laser optical signal at said second wavelength in said loop;
• and
• outputting a fraction of said laser optical signal from said loop to provide said output signal.