Juanjuan Hu

Low-loss air-core polarization maintaining terahertz fiber

We propose a low-loss air-core polarization maintaining polymer fiber for terahertz (THz) wave guiding. The periodic arrangement of square holes with round corners in the cladding offers a bandgap effect for mode guiding. Numerical simulations show that the bandgap effect repels the modal power from the absorbent background polymers, resulting in a significant suppression of absorption loss of the polymers by a factor of more than 25. The phase-index birefringence of the proposed THz fiber is in the order of 10(-3).

Polarization Maintaining Air-Core Bandgap Fibers for Terahertz Wave Guiding

A polarization-maintaining air-core bandgap polymer fiber is proposed for low-loss terahertz (THz) wave guiding. The polarized guided modes are confined in an asymmetric core by a bandgap of periodic arrangement of square holes with round corners in the cladding. The guiding properties, including transmission bandwidth, numerical aperture, phase-index birefringence, modal absorption loss, and bend loss, are systematically investigated. The influence of background polymers on guiding properties is demonstrated in detail. Numerical simulations reveal that, while maintaining a relatively high phase-index birefringence (of the order of 10-3 ), the THz fiber shows a significant suppression of absorption loss of the background polymers (by a factor of more than 25) due to the bandgap effect that repels the modal power from the absorbent polymers. The proposed THz fiber has potential for guiding intense THz waves for polarization-sensitive applications.

Polarization-Dependent Bandgap Splitting and Mode Guiding in Liquid Crystal Photonic Bandgap Fibers

A theoretical investigation is presented for nematic liquid crystal photonic bandgap fibers (LCPBGFs), in which the rotation angle of liquid crystals director n could be arbitrarily controlled by external electric field. Based on the investigation on the polarization effect of photonic bands, we propose two orthogonal polarization-dependent bandgap maps to describe the mode guiding behavior. The symmetry properties analysis of photonic band structure reveals that the bandgap map of LCPBGFs is approximately independent of the rotation angle of director. The guiding properties of LCPBGFs including the position and width of high transmission windows, single-mode single-polarization or ultrahigh birefringence guiding, confinement loss, and coupling loss are investigated. Specifically, the high loss peaks due to the coupling between guided mode and polarization-dependent photonic bands will greatly narrow the transmission windows of the LCPBGFs. The polarization axis of the guided mode is determined by the rotation angle of the director, which could be controlled by external electric field.

Study of Polarization-Dependent Bandgap Formation in Liquid Crystal Filled Photonic Crystal Fibers

The mechanism of polarization-dependent bandgap formation for nematic liquid crystal filled photonic crystal fibers (LCPCFs) is presented. The total polarization-independent bandgap map is not applicable for describing the mode guiding in LCPCF. We propose the formation of two orthogonal polarization-dependent bandgap maps to describe the mode guiding behavior. The formation of polarization-dependent bandgap caused by the high index difference between the ordinary and the extraordinary dielectric indexes of liquid crystal offers single-mode single-polarization or ultrahigh birefringence guiding for LCPCFs.

Fabrication of all-solid photonic bandgap fiber coupler

We report the fabrication of a tunable all-solid photonic bandgap fiber coupler based on the side-polishing technique. This device is believed to be the first demonstration of a photonic bandgap fiber coupler to eliminate the contamination of the open air holes. By adjusting the length of the interaction section, the tunable coupling ratio as much as 92.5% at 1550 nm is achieved. The investigation of the spectrum properties shows that the coupler has excellent tunability properties, for which the coupling ratio can be smoothly and continuously controlled.

Silica-based Low Loss All-solid Bandgap Fiber

We report the fabrication of a new designed all- solid bandgap fiber. The low loss transmission (as low as 2 dB/km at 1310 nm) has been realized with a bandwidth of over 700 nm.

Investigation on optimized launch power in the distributed Brillouin fiber sensor design

Distributed sensors, based on Brillouin effect in the optical fiber, provide an excellent method for measuring temperature and strain over long distances. There are two types of such sensors. The first type is based on spontaneous Brillouin scattering, and is called Brillouin optical time domain reflectometer (BOTDR). It measures the Brillouin frequency shift or Brillouin power or Brillouin gain bandwidth to get the temperature and strain information. The second type of sensor is based on stimulated Brillouin amplification. It is called Brillouin optical time domain analyzer(BOTDA). Normally, it uses one laser at each fiber ends, one as pump and the other as a probe light. The probe light will experience Brillouin amplification. Through the analysis of Brillouin gain spectrum (BGS), we can get the temperature and strain information. Both the two types of sensors are attracting attention all over the world, and temperature resolution of less than 1 degree and strain resolution up to 5 με was reported. The fiber distances of up to 150km was presented while other papers reported a spatial resolution of the order of 1cm with frequency domain techniques or correlation techniques. We proposed and analyzed our design, it is an improvement of BOTDA with a single end laser, which make it easy to implement in field. Through simulations, optimized launch power has been found for a certain design.

Bandgap splitting in liquid crystal photonic bandgap fibers

The polarization dependent bandgap splitting for nematic liquid crystal photonic bandgap fibers (LCPBGFs) is investigated. We proposed two orthogonal polarization dependent bandgap for guiding linear-polarized fiber modes of LCPBGFs.

Polarization maintaining air-core bandgap terahertz fiber

We proposed a novel polarization maintaining air-core bandgap polymer fiber for terahertz (THz) wave guiding. The periodic arrangement of square holes with round corners in cladding offers bandgap effect for mode guiding. The guiding properties including transmission bandwidth, numerical aperture, phase-index birefringence, modal absorption loss and bend loss are systematically investigated. Numerical simulations show that the bandgap effect repels the modal power from the absorbent background polymers, resulting in a significant suppression of absorption loss of polymers by a factor of more than 25. The phase-index birefringence of the proposed THz fiber is on the order of 10-3.

Investigation of nanosize waveguide and nanofiber coupler

Long interaction region coupler and racetrack resonator constructed by nanosize waveguide and nanosize optical fiber are investigated. Several components are investigated separately by using theoretical methods or simulation methods. For planar waveguide and coupler, analytical solution of parallel waveguides pair is investigated, by solving Maxwell equation, instead of weakly guiding approximation. The input field is distributed onto the complete set of solutions of the coupler super-modes, which propagate separately inside coupler. At the output port, the superposition of each mode is directly related with the coupler output. The field distribution at the output of parallel waveguides pair is calculated theoretically. After verified the method, for nanofiber, the propagation constant is got by numerical simulation, and then the nanofiber coupler could be investigated as the same way. Based on the analysis of coupler, the racetrack resonator could be investigated.