Prof. Hongpu Li
Prof. Hongpu Li
Shizuok University, Japan
Title: Enhancement of high-order azimuthal mode couplings in a single-helix helical long-period fiber grating by using the phase-sampling method

Key words:  Fiber optics, fiber optics components, helical long-period fiber grating, optical vortices.

As is known that, in a single-helix helical long-period fiber grating (SHLPG), due to the inherent one-fold azimuthal symmetric structure of the fiber core (i.e., in general, the high-order Fourier expansion coefficients of the core boundary profile is extremely small), it is very hard to efficiently obtain the high-order azimuthal mode couplings. In this study, we have proposed and demonstrated a phase-sampling approach to overcome this obstacle, which is realized by periodically inserting phase shifts in the transverse direction of the SHLPG. As results of the proposed method, high-efficient couplings between the fundamental mode and the second- and third-order azimuthal modes in a SHLPG have been successfully demonstrated. The proposed method can be applied to generate and convert high-order orbital angular momentum (OAM) modes even with the SHLPG.


1.    H. Xu and L. Yang, “Conversion of orbital angular momentum of light in chiral fiber gratings,” Opt. Lett. 38(11), 1978-1980 (2013).

2.    M. Napiorkowski and W. Urbanczyk, “Rigorous simulations of coupling between core and cladding modes in a double-helix fiber,” Opt. Lett. 40(14), 3324–3327 (2015).

3.    L. Xian, P. Wang, and H. Li, “Power-interrogated and simultaneous measurement of temperature and torsion using paired helical long-period fiber gratings with opposite helicities,” Opt. Express 22(17), 20260–20267 (2014).

4.    P. Wang and H. Li, “Helical long-period grating formed in a thinned fiber and its application to a refractometric sensor,” Appl. Opt. 55(6), 1430–1434 (2016).

5.    H. Zhao, P. Wang, C. Zhu, S. Ramanathan, and H. Li, “Analysis for the phase-diffusion effect in a phase-shifted helical long-period fiber grating and its pre-compensation,” Opt. Express 25(16), 19085–19093 (2017).

6.    H. Zhao, C. Zhu, R. Subramanian, and H. Li, “Comprehensive analysis for the consecutively-cascaded single-helix long-period fiber gratings with opposite helicities,” IEEE J. Quantum Electron., Vol. 54, No. 1, p. 6800606 (2018).

7.    H. Li, Y. Sheng, Y. Li, and J. Rothenberg, “Phased-only sampled fiber Bragg gratings for high channel counts chromatic dispersion compensation.” J. Lightwave Technol. 21(9), 2074-2083 (2003).

8.    H. Li, M. Li, Y. Sheng, and J. Rothenberg, “Advances in the design and fabrication of high-channel-count fiber Bragg gratings.” J. Lightwave Technol. 25(9), 2739-2750 (2007).

Hongpu Li received the B.S. and M.S. degrees from Huazhong University of science and technology, Wuhan, China, in 1985 and 1988, respectively, and received the Ph.D. degree from Shizuoka University, Hamamatsu, Japan in 2000. From 2000 to 2003, first, he was with the NEC Research Institute, NJ, then the Phaethon Communication Inc., CA, USA, and then the Laval University, Canada. In April of 2003, he joined to the Shizuoka University, Japan. Now he is a full professor working at the Faculty of Engineering, Shizuoka University with decades of experiences in photonics areas. His present research interests include the nonlinear fiber optics, photonic signal processing, fiber gratings, fiber sensors, and nanophotonics, etc. He has authored more than 250 publications in top scientific journals and leading technical conferences. He has also held several U.S. patents. He is a Member of IEICE, OSA, and IEEE Photonics Society.