Erlend Rønnekleiv, Sigurd W. Løvseth, and Jon T. Kringlebotn ..... Meeting on Bragg Gratings, Photosensitivity, and Poling in Glass Waveguides, paper ThE4,.
Invited Paper
(UGRSHGILEHUGLVWULEXWHGIHHGEDFNODVHUV± SURSHUWLHVDSSOLFDWLRQVDQGGHVLJQFRQVLGHUDWLRQV Erlend Rønnekleiv, Sigurd W. Løvseth, and Jon T. Kringlebotn Optoplan AS, Norway $%675$&7 Fiber distributed feedback (F-DFB) lasers have proven to be attractive devices for interrogation of optical sensors with high frequency resolution, due to their very low frequency noise/narrow linewidth, low relative intensity noise (RIN), robust mode-hop free tunability, compact size, and flexible and accurate wavelength setting. It has also been demonstrated that F-DFB lasers can act as sensor elements for high resolution measurements of physical quantities causing strain, refractive index, or birefringence changes in the laser fiber. It has been demonstrated that F-DFB lasers can be used as fast tunable sources for high resolution and high accuracy spectral component characterization. They may also find applications in dense WDM transmission systems utilizing their potentials for accurate wavelength setting, easy wavelength tuning, semiconductor pump redundancy, or multiple wavelength operation. In this paper properties and applications of F-DFB lasers will be discussed, with emphasis on modeling, design and characterization of the devices. In particular, RIN and frequency noise properties, requirements on grating and gain medium quality, the design requirements for achieving singlemoded or (intentionally) multimoded laser operation, and the output characteristics of single- versus multimoded F-DFB laser devices will be treated. Keywords: Fiber lasers, distributed feedback lasers, Bragg grating lasers, erbium doped fibers, optical sensors
,1752'8&7,21 Single mode Er-doped Fiber Bragg grating (FBG) lasers, and in particular fiber distributed feedback (F-DFB) lasers [1], rely on the fiber Bragg grating [2–3] and fiber amplifier [4] technologies. These technologies have been developed to mature commercial levels during the last 15 years [5–8] mainly driven by the demand for signal filtering and amplification in telecom systems. Important features of F-DFB lasers are their compact in-fiber design, narrow linewidth, flexible and accurate wavelength setting during production, robust mode-hop free wideband tunability by strain or temperature tuning, and a potential for manipulating the number of longitudinal and polarization modes through grating design. It is also possible to create multiple wavelength sources by serial laser multiplexing along a single fiber, using a single diode pump laser. Advantages of the π phase-shifted DFB laser geometry, as compared to the distributed Bragg reflector (DBR) geometry where two Bragg gratings are separated by a gain section, are that the DFB lasers can be made shorter, and that they provide more robust single longitudinal mode operation [9]. On the other hand, investigation of Er-doped fiber DFB lasers has shown that the UV-exposure of the gain medium during grating fabrication causes degradation of the gain medium, and thus of the laser noise and output power efficiency [10,11]. It is therefore a potential advantage of the DBR geometry that the gain section is not exposed to UV. The use of longer cavities also reduces the frequency noise contribution from fundamental thermal fluctuations [12].
3523(57,(6$1'$33/,&$7,216 )5(48(1&
