Piotr Lesiak

Influence of temperature and electrical fields on propagation properties of photonic liquid-crystal fibres

The paper reports temperature and external electrical field effects on propagation properties of a photonic liquid-crystal fibre composed of a solid-core photonic crystal fibre filled either with a prototype nematic liquid crystal characterized by extremely low (of the order of ~0.05) material birefringence or with a typical nematic pentylo-cyano-biphenyl, PCB (birefringence of the order of ~0.2). The nematic liquid crystal was introduced into the micro holes of the photonic crystal fibre by the capillary effect. Depending on the liquid crystal material introduced into the micro holes and due to anisotropic properties of the photonic liquid-crystal fibre, switching between different guiding mechanisms controlled by temperature and an external electric field has been demonstrated. This creates great potential in fibre optic sensing and optical processing application.

Polarization effects in photonic liquid crystal fibers

In this paper we present experimental results of polarization properties of photonic liquid crystal fibers, also with permanent anisotropy achieved by using photo-aligning layers within the micro holes. Single-polarization propagation has been demonstrated in three ways: either by application of an external electric field, by using special aligning layers or by using an anisotropic host—commercially available highly birefringent Blazephotonics photonic crystal fiber infiltrated with liquid crystals. The possibility of thermal birefringence tuning in photonic liquid crystal fibers by using low-birefringence liquid crystals is also presented.

Photonic liquid crystal fibers : a new challenge for fiber optics and liquid crystals photonics

The paper reviews and discusses the latest developments in the field of the photonic liquid crystal fibers that have occurred for the last three years in view of new challenges for both fiber optics and liquid crystal photonics. In particular, we present the latest experimental results on electrically induced birefringence in photonic liquid crystal fibers and discuss possibilities and directions of future developments.

Phase and group modal birefringence of triple-defect photonic crystal fibres

We discuss the phase and group modal birefringence in photonic crystal fibres (PCFs) with an elongated core. Owing to large form birefringence, these two types of birefringence in such PCFs may not only have opposite signs, but their absolute value can also differ by several orders of magnitude. We also show that PCFs offer the unique possibility of having a large phase birefringence and a negligible polarization mode dispersion at the same time. Using a fully vectorial mode solver, we show how these parameters can be tailored by a proper choice of the geometry of the PCF. We demonstrate both numerically and experimentally the strong wavelength dependence of phase and group modal birefringence in triple-defect photonic crystal fibres (PCFs).

Polarization Optics of Microstructured Liquid Crystal Fibers

The present paper discusses polarization phenomena occurring in microstructrured liquid crystal fibers and in particular solid-core photonic crystal fibers infiltrated with liquid crystals. We report on the latest experimental polarization characteristics of microstructured photonic crystal fibers filled with prototype nematic liquid crystal guest materials characterized by either extremely low (of the order ∼ 0.05) or medium (of the order ∼ 0.2) material birefringence. Due to anisotropic properties of the microstructrured liquid crystal fibers switching between different guiding mechanisms as well as electrically and temperature-induced tuning of light propagation have been demonstrated. These preliminary results hold great potential for both fiber-optic sensing and in-fiber polarization mode dispersion control and compensation.

Interplay of form and material birefringence in photonic crystal fibers: application for sensing

We discuss how material anisotropy influences the modal birefringence of photonic crystal fibers. We introduce an efficient numerical method for the calculation of the modal structure which accounts for material anisotropy. The approach relies on solving the fully vectorial wave equation for the transverse magnetic field and the respective propagation constants within the general framework of plane-wave methods. This analysis is relevant to certain application areas, and, in particular, to fiber sensing, where material birefringence arises due to pressure or mechanical strain. We compare the sensitivity calculations with experimental data and discuss novel potentialities of photonic crystal fibers for sensing; the discussion includes the possibility of temperature insensitivity, a wide range of sensitivity tailoring options, and novel sensing mechanisms with the use of the photonic bandgap.

A Photonic Crystal Fiber and Fiber Bragg Grating-Based Hybrid Fiber-Optic Sensor System

A hybrid sensor that operates in the intensity domain by converting the polarization and wavelength information from the photonic crystal fiber sensor and fiber Bragg grating (FBG) sensor, respectively, into intensity variation is presented in this paper. The hybrid fiber-optic sensor system involves a combination of a polarimetric sensor based on a photonic crystal fiber and a FBG sensor and is used for simultaneous strain and temperature measurement. The strain sensitivity of the polarization maintaining photonic crystal fiber at different lengths and the corresponding slope required for the edge filter which converts the FBG wavelength information into intensity are studied and presented in this paper. The proposed sensor configuration has a wide range of applications in smart fiber-optic sensing.

Temperature tuning of polarization mode dispersion in single-core and two-core photonic liquid crystal fibers

In this paper we present numerical and experimental results of propagation and polarization properties of the photonic liquid crystal fibers (PLCFs) in which only selected micro holes were filled with nematic liquid crystal (LC) guest materials. As a host photonic crystal fiber (PCF) structure, we used a commercially available highly birefringent PCF (Blazephotonics, UK). A tunable laser operated at infrared has powered the PLCFs under investigation infiltrated by the 1550 nematic LC synthesized at the Military University of Technology. Temperature induced changes of the polarization mode dispersion (PMD) as well switching between fundamental and higher order modes and also single-core and two-core propagation were successfully demonstrated.

Optofluidic Photonic Crystal Fiber-Based Sensors

Over the last few years, there has been a growing interest in the field of microstructured optofluidic waveguides and especially those created by filling photonic crystal fibers with fluids. This paper presents an overview of sensing properties of optofluidic photonic crystal fiber-based sensors of temperature, pressure, electric/magnetic field, and refractive index that utilize photonic crystal fibers infiltrated with both isotropic and anisotropic liquids.

The influence of thermal expansion of a composite material on embedded polarimetric sensors

Some of the most critical issues of the influence of the thermal expansion of composite materials on embedded polarimetric sensors for measurements of strain and temperature are studied in this paper. A composite material sample with polarimetric fiber sensors embedded in two distinct layers of a multi-layer composite structure is fabricated and characterized. The polarimetric fiber sensors used in this study are based on Panda type fiber and polarization maintaining photonic crystal fiber (PM-PCF). The temperature sensitivities of polarimetric fiber sensors with acrylate buffer coated and buffer stripped polarization maintaining optical fibers are measured in free space and compared with those for sensors embedded in the composite material. It is found that a polarimetric fiber sensor with an acrylate coating embedded in the composite material shows the same response as the one in free space while the coating stripped fiber polarimetric sensor shows significant temperature sensitivity when embedded in the composite material. This is due to the stress induced change in birefringence created by the thermal expansion of the composite material, while in the case of a buffer coated fiber, the effect is considerably reduced as the thermal stress is largely eliminated by the buffer coating. The results obtained in this study demonstrated that thermal expansion of the composite material is the main source of error in strain and temperature measurement using embedded polarimetric fiber sensors and that more accurate strain and temperature measurements can be obtained with buffer coated polarimetric fiber sensors.