Actively mode-locked, single-polarization, picosecond optical fiber laser

Abstract

An optical fiber laser source comprising a polarization-maintaining loop and a birefringence-compensating branch preferably operatively connected to a length-stabilizing element is disclosed. The optical fiber laser source provides soliton pulse compression to reduce the duration of the pulses of the output pulse train to 1.3 ps or less.

What we claim is: 
     
       1. An optical fiber laser source comprising: a lasing material having a length in the range of about 0.5 m to about 100 m and input and output sections;   a source for activating the lasing material to produce light at said output stage of said lasing material;   a frequency signal generator for providing a modulating signal;   a modulator having input and output stages and a control terminal for receiving the modulating signal provided by said frequency signal generator, said modulator being responsive to said modulating signal for developing a carrier signal at its output stage that is varied and in sympathy with said modulating signal, said carrier signal being applied to said input section of said lasing material;   anomalous-dispersion fiber having a length in the range of about 10 m to about 10 km and an input and an output with said input of said anomalous-dispersion fiber coupled to said output stage of said lasing material;   dispersion-compensating means having a length in the range of about 1 m to about 100 m and an input and an output with said input of said dispersion-compensating means coupled to said output of said anomalous-dispersion fiber; and   a first coupler having first fiber means for coupling to said output of said isolator and applying a predetermined ratio of a signal thereat, said first coupler also having second fiber means for applying said signal at said output of said isolator to said input stage of said modulator.   
     
     
       2. The optical fiber source according to claim 1, wherein said dispersion-compensation means is selected from the group consisting of dispersion-compensating fiber and grating means. 
     
     
       3. The optical fiber laser source according to claim 1, wherein said lasing material, said anomalous-dispersion fiber, said dispersion-compensating means, said first fiber means, and second fiber means are selected from the group consisting of polarization-maintaining fibers and non-polarization-maintaining fibers. 
     
     
       4. The optical fiber laser source according to claim 3, wherein said lasing material, said anomalous-dispersion fiber and said dispersion compensating means are non-polarization-maintaining fiber. 
     
     
       5. The optical fiber laser source according to claim 1 further including: an isolator coupled to said output of said anomalous-dispersion fiber.   
     
     
       6. The optical fiber laser source according to claim 5 further comprising: a beamsplitter having a first polarized section for receiving the carrier signal at the output stage of the modulator and a second polarized section and a trunk stage for distributing signals in predetermined proportions, said trunk stage having means for coupling to said input section of said lasing material;   one or more couplers including said first coupler coupled to said second section of said beamsplitter for extracting a predetermined portion of signal thereat and allowing the remaining portion of said extracted signal to be directed to said input stage of said modulator after being intercepted by a phase shifter so that said remaining portion is shifted in phase by about 90 degrees;   a phase sensitive detector having couplers for coupling to said modulating signal and to said extracted predetermined portion of said signal at said beamsplitter for developing an error signal whose value is proportional to the difference in phase between said modulating signal and said extracted predetermined portion of said signal at said beamsplitter; and   a compensator connected to said output section of said lasing material and responsive to said error signal.   
     
     
       7. The laser source according to claim 1, wherein said modulator is selected from the group consisting of Mach-Zehnder, electro-optic, acousto-optic amplitude and phase modulator types. 
     
     
       8. The laser source according to claim 4, wherein said lasing material is a gain fiber having a dopant comprising an Erbium material. 
     
     
       9. The laser source according to claim 4, wherein said lasing material is a gain fiber having a co-dopant comprising Erbium and Ytterbium. 
     
     
       10. The laser source according to claim 4, wherein said lasing material is a gain fiber comprising other lasing materials. 
     
     
       11. The laser source according to claim 6 further comprising a laser diode interposed between the output section of said lasing material and said compensator responsive to an error signal. 
     
     
       12. The optical fiber laser source according to claim 6, wherein said beamsplitter is a single-polarization type. 
     
     
       13. The optical fiber laser source according to claim 5 further comprising: an optical circulator having a first polarized section for receiving the carrier signal at the output stage of the modulator and a second polarized section and a trunk stage for distributing signals in predetermined proportions, said trunk stage having means for coupling to said input section of said lasing material;   one or more couplers including said first coupler coupled to said second section of said optical circulator for extracting a predetermined portion of signal thereat and allowing the remaining portion of said extracted signal to be directed to said input stage of said modulator after being intercepted by a phase shifter so that said remaining portion is shifted in phase by about 90 degrees;   a phase sensitive detector having couplers for coupling to said modulating signal and to said extracted predetermined portion of said signal at said beamsplitter for developing an error signal whose value is proportional to the difference in phase between said modulating signal and said extracted predetermined portion of said signal at said beamsplitter; and   a compensator connected to said output section of said lasing material and responsive to said error signal.   
     
     
       14. The laser source according to claim 6, wherein said one or more couplers for extracting comprise said first optical coupler having a coupling ratio so that said extracted predetermined portion of said signal is a first percentage of said signal of said second section of said beamsplitter and said remaining portion of said extracted signal is a second selected percentage of said signal of said second section of said beamsplitter. 
     
     
       15. The laser source according to claim 14 wherein said one or more couplers are located anywhere within the laser source. 
     
     
       16. The laser source according to claim 14, wherein said isolator is connected to said second section of said beamsplitter and is a single polarization type. 
     
     
       17. The laser source according to claim 14 further comprising a second optical coupler receiving said first percentage of said signal from said first coupler predetermined portion of said signal from said first coupler and having a coupling ratio so that a preselected percentage of said first percentage extracted predetermined portion of said signal is allowed to pass therethrough, and the preselected percentage of said first percentage extracted predetermined portion of said signal is transferred and serves as a signal output therefrom. 
     
     
       18. The laser source according to claim 17 further comprising a third optical coupler receiving said extracted predetermined portion of said signal passed by said second coupler and having a coupling ratio so that said extracted portion of said signal from said second optical coupler is allowed to pass therethrough and a portion of said extracted portion of said signal from said second optical coupler is transferred and serves as a diagnostic signal therefrom.