Single-Frequency, 2-cm, Yb-Doped Silica-Fiber Laser W. Guan and J. R. Marciante University of Rochester Laboratory for Laser Energetics The Institute of Optics Frontiers in Optics 2006 90th OSA Annual Meeting Rochester, NY 8 12 October 2006
Summary We have demonstrated a single-frequency, single-polarization, silica-fiber distributed Bragg reflector (DBR) laser Highly-doped fiber enables single-frequency operation from the short laser cavity. The laser shows excellent optical properties the output power reaches 35 mw the polarization extinction ratio (PER) is >20 db The laser has excellent noise properties the side-mode suppression ratio (SMSR) is >25 db the optical signal-to-noise ratio (OSNR) is >65 db The laser can be easily fabricated by fusion splicing from commercially available components. E14981
Single-frequency lasers are desirable for many applications Single-frequency lasers can be used in coherent communications, ranging, and interferometers. 1 3 Single polarization is desired in some applications. A single-frequency laser built with commercially available components is highly desirable. Higher power is always desirable. E14982 1D. Psaltis, Science 298, 1359 (2002). 2J. G. Williams, S. G. Turyshev, and D. H. Boggs, Phys. Rev. Lett. 93, 261101 (2004). 3A. Buonanno and Y. Chen, Class. Quantum Gravity 19, 1569 (2002).
Approaches for a single-frequency fiber laser A distributed-feedback (DFB) fiber laser generates single-frequency output. K B B A short DBR fiber laser generates single-frequency output by filtering out the single lasing mode with narrow-band fiber Bragg gratings (FBG s). Highly doped ytterbium fiber makes a short cavity possible and generates high output power. A short-cavity phosphate glass fiber laser has been previously demonstrated with 200-mW output power. 1 E14983 1C. Spiegelberg et al., J. Lightwave Technol. 22, 57 (2004).
The simple laser is built from commercially available components a Center Wavelength (nm) Parameters of FBG s* Reflectivity (%) Bandwidth (nm) SM FBG 1029.57 99 0.46 PM FBG 1029.30 55 0.05 E14984 *Vendor: O-E Land
The transmission spectrum of the PM FBG shows the polarization selectivity ASE source PM FBG Optical Spectrum Analyzer The two reflection peaks work in orthogonal polarizations. The reflection wavelength spacing is 0.3 nm. E14985
Single frequency is achieved through the overlapping of the spectrum of FBG s by temperature tuning E14986
The baseline performance of the laser has excellent optical and noise properties Optical Properties Noise Properties Output power: 35 mw OSNR: >65 db Wavelength: 1029.6 nm SMSR: >25 db Pump threshold: 10 mw RIN peak: < 105 db/hz Slope efficiency: 9% rms power: <0.9% Polarization extinction ratio: > 20 db P V wavelength: <0.02 nm E14994
The single-mode behavior has been verified with a scanning Febry Perot spectrometer The mode spacing of the laser cavity is approximately 5 GHz. The free spectral range (FSR) is 30 GHz and the finesse is ~150, giving a resolution of 200 MHz. The output modes can be resolved by the Febry Perot spectrometer. Only a single mode is observed. E14987
The optical signal-to-noise ratio (OSNR) and the side-mode suppression ratio (SMSR) of the laser output verify the single-mode behavior The OSNR over ASE is >65 db. The SMSR is >25 db (limited by the resolution of the OSA). E14988
The laser works in a single polarization state over all pump levels Laser Quarter-wave plate Polarizer Power meter The polarization extinction ratio of the laser output after a quarter-wave plate is >20 db under all pump levels. The quarter-wave plate is used to change the elliptical polarized output into linearly polarized output since the output of the laser went through a non-polarization-maintaining WDM. E14989
The relative intensity noise (RIN) is less than 105 db/hz The RIN is measured with an electrical spectrum analyzer (ESA). The RIN is shot noise limited beyond 20 MHz and less than 120 db/hz. The peak at 10 MHz is generated by the relaxation oscillation of the laser. E14990
The laser operates stably for two hours Peak-to-valley value is <6%; rms deviation is <0.9%. Peak-to-valley value is <0.02 nm; rms deviation is <0.004 nm. E14991
The laser frequency shifts under different pump levels due to thermal effects in FBG s m B Dm DT a = dm dt = 2nK B 1 dn = mb ca + m n dt 1 K dk dt = 0. 007 nmcc (Coefficient of thermal expansion) -1 The heat is generated in the ytterbium fiber and transferred to the two FBG s. The heat is due to the nonradiative transition of the ytterbium ions (i.e., quantum defect). E14992
Future improvements can enhance the laser performance More power can be generated by optimizing the reflectivity of the output FBG. The RIN peak can be reduced with feedback control circuits. Laser-frequency shifting can be eliminated with a temperature controller. Single linear polarization can be achieved by using a PM WDM. E14993
Summary/Conclusions We have demonstrated a single-frequency, single-polarization, silica-fiber distributed Bragg reflector (DBR) laser Highly-doped fiber enables single-frequency operation from the short laser cavity. The laser shows excellent optical properties the output power reaches 35 mw the polarization extinction ratio (PER) is >20 db The laser has excellent noise properties the side-mode suppression ratio (SMSR) is >25 db the optical signal-to-noise ratio (OSNR) is >65 db The laser can be easily fabricated by fusion splicing from commercially available components. E14981