We have theoretically and experimentally investigated the dual-peak feature of tilted fiber gratings with excessively tilted structure (named as Ex-TFGs). We have explained the dual-peak feature by solving eigenvalue equations for TM0m and TE0m of a circular waveguide, in which the TE (transverse electric) and TM (transverse magnetic) core modes are coupled into TE and TM cladding modes, respectively. Meanwhile, in the experiment, we have verified that one of the dual peaks at the shorter wavelength is due to the TM mode coupling whereas the other one at the longer wavelength arises from TE mode coupling when a linearly polarized light launched into the Ex-TFG. We have also investigated the peak separation of TE and TM cladding mode for different surrounding medium refractive indexes (SRI), revealed that the dual peaks separation is decreasing as increasing of SRI, which agrees very well with the theoretical analysis results.
We report all-fiber polarization interference filters, known as Lyot and Lyot-Őhman filters, based on alternative concatenation of UV-inscribed fiber gratings with structure tilted at 45°and polarization maintaining (PM) fiber cavities. Such filters generate comb-like transmission of linear polarization output. The free spectral range (FSR) of a single-stage (Lyot) filter is PM fiber cavity length dependent, as a 20 cm long cavity showed a 26.6 nm FSR while the 40 cm one exhibited a 14. , and laser [6][7] systems. Because of unavailability of in-fiber components, the majority reported Lyot and Lyot-Őhman filters were constructed using bulk polarizers with a polarization maintaining (PM) fiber, inducing not just high insertion loss but also the chunky structure, which is not compatible with all-fiber systems. Tilted fiber gratings (TFGs) were firstly reported by Meltz et al. in 1990 [8]. Owing to their unique polarization function, TFGs have been applied as polarimeter, polarization dependent loss equalizer and so on [9][10]. Recently, we have demonstrated in-fiber polarizers with a high polarization extinction ratio (PER) based on 45°-TFGs UV-inscribed in single mode telecom and photosensitive fibers [11,12]. We have also demonstrated that the 45°-TFGs can be UV-inscribed into PM fibers along the fast or slow axis, leading to linear polarization light output. In this Letter, we propose and demonstrate all-fiber Lyot and Lyot-Őhman filters that are implemented by alternatively concatenating 45°-TFGs and PM fiber cavities with fiber axis at 45°to each other. The bandwidth of the filter is easily controlled by changing the length of PM fiber cavity, while the FSR of transmission bands can be freely tailored by using multistage Lyot filters.The configuration of an all-fiber Lyot filter using two 45°-TFGs is illustrated in Fig. 1(a). In this structure, the two 45°-TFGs created in PM fiber along the fast axis are used as linear polarizers, and a section of PM fiber is used as a BM with its fast axis aligned 45°to that of the two polarizers.The working principle of this all-fiber Lyot filter is as follows: the light that passes the first 45°TFG is linearly polarized and then enters the PM fiber at 45°direction and is resolved into two beams with equal intensity travelling along the fast-and slow-axis of the PM fiber, respectively. Because of the birefringence of the PM fiber, there is a relative phase difference between these two beams; thus when they arrive at the second 45°-TFG, the combined beam will generate interference output of linear polarization state. Figure 1(b) shows a 3-stage all-fiber Lyot-Őhman filter, which can be formed by concatenating four 45°-TFGs spaced by three PM fibers with a length ratio 4∶2∶1 and all aligned at 45°to the fast axis of the PM fibers that are hosting 45°-TFGs. In this 3-stage Lyot-Őhman filter, only the light at the wavelengths in phase (i.e., the phase difference is a multiple of 2π) will be constructive and pass the filter. The final output spectrum thus consists of a serial of...
A 1.05 μm picosecond pulsed fiber master oscillator power amplifier system delivering an average power of over 100 W was used to pump a 5 m long commercially available photonic crystal fiber and a 49.8 W supercontinuum spanning from around 500 nm to above 1700 nm was generated. Strictly single mode operation of the all-fiber supercontinuum source across the whole spectral range was verified through the quantitative measurement of the beam quality.
An all-fiber normal-dispersion Yb-doped fiber laser with 45°-tilted fiber grating (TFG) is, to the best of our knowledge, experimentally demonstrated for the first time. Stable linearly-chirped pulses with the duration of 4 ps and the bandwidth of 9 nm can be directly generated from the laser cavity. By employing the 45° TFG with the polarization-dependent loss of 33 dB, output pulses with high polarization extinction ratio of 26 dB are implemented in the experiment. Our result shows that the 45° TFG can work effectively as a polarizer, which could be exploited to singlepolarization all-fiber lasers. Pivtsov, "Gamma-shaped long-cavity normal-dispersion mode-locked Er-fiber laser for sub-nanosecond highenergy pulsed generation," Laser Phys. Lett. 9(1), 59-67 (2012). "Measuring ultrashort laser pulses in the time-frequency domain using frequency-resolved optical gating," Rev. ©2012 Optical Society of America
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