Feroza Begum

Broadband Dispersion Compensating Octagonal Photonic Crystal Fiber for Optical Communication Applications

We numerically report the design of a modified octagonal photonic crystal fiber (M-OPCF) for broadband dispersion compensation covering the C and L communication bands, i.e., wavelengths ranging from 1530 to 1625 nm. It was shown that the proposed broadband compensating PCF can be designed to simultaneously exhibit a high negative dispersion coefficient and a relative dispersion slope (RDS) close to that of a conventional single-mode optical fiber (SMF). From our results, it was found that the M-OPCF has a large negative dispersion [-226 to -290 ps/(nmkm)] over the C- and L-bands, and an RDS close to that of an SMF of about 0.0034 nm-1. In addition to this, the effective dispersion, residual dispersion, confinement loss, and polarization properties of the proposed PCF are also reported and discussed.

Novel Square Photonic Crystal Fibers with Ultra-Flattened Chromatic Dispersion and Low Confinement Losses

This study proposes a novel structure of index-guiding square photonic crystal fibers (SPCF) having simultaneously ultra-flattened chromatic dispersion characteristics and low confinement losses in a wide wavelength range. The finite difference method (FDM) with anisotropic perfectly matched layers (PMLs) is used to analyze the various properties of square PCF. The findings reveal that it is possible to design five-ring PCFs with a flattened negative chromatic dispersion of 0-1.5 ps/(nm.km) in a wavelength range of 1.27 μm to 1.7 μm and a flattened chromatic dispersion of 0±1.15 ps/(nm.km) in a wavelength range of 1.25 μm to 1.61 μm. Simultaneously it also exhibited that the confinement losses are less than 10 -9 dB/m and 10 -10 dB/m in the wavelength range of 1.25 μm to 1.7 μm.

Highly nonlinear dispersion-flattened square photonic crystal fibers with low confinement losses

A new simple structure of an index-guiding highly nonlinear dispersion-flattened square photonic crystal fiber (HNDFSPCF) with low confinement losses is proposed. The results reveal that it is possible to design five-rings HNDF-SPCFs with a flattened dispersion of 0.43 ps/(nm·km), low dispersion slope of -0:02 ps/(nm2·km), low confinement loss of approximately 103 dB/m, and a large nonlinear coefficient of approximately 35W-1 km-1 at 1.55 μm. It is also observed that the confinement loss is less than 10-1 dB/m in the wavelength range of 1.2 –1.7 μm.

Photonic Crystal Fiber for Medical Applications

Optical coherence tomography (OCT) is a new technology for noninvasive cross-sectional imaging of tissue structure in biological system by directing a focused beam of light at the tissue to be image [Bouma et al., 1995; Jiang et al., 2005; Ryu et al., 2005]. The technique measures the optical pulse time delay and intensity of backscattered light using interferometry with broadband light sources or with frequency swept lasers. It is analogous to ultrasound imaging or radar, except that it uses light rather than sound or radio waves. In addition, unlike ultrasound, OCT does not require direct contact with the tissue being imaged. OCT depends on optical ranging; in other words, distances are measured by shining a beam of light onto the object, then recording the optical pulse time delay of light. Since the velocity of light is so high, it is not possible to directly measure the optical pulse time delay of reflections; therefore, a technique known as low-coherence interferometry compares reflected light from the biological tissue to that reflected from a reference path of known length. Different internal structures produce different time delays, and crosssectional images of the structures can be generated by scanning the incident optical beam. Earlier OCT systems typically required many seconds or minutes to generate a single OCT image of tissue structure, raising the likelihood of suffering from motion artifacts and patient discomfort during in vivo imaging. To counter such problems, techniques have been developed for scanning the reference arm mirror at sufficiently high speeds to enable realtime OCT imaging [Tearnery et al., 1997]. OCT can be used where excisional biopsy would be hazardous or impossible, such as imaging the retina, coronary arteries or nervous tissue. OCT has had the largest impact in ophthalmology where it can be used to create crosssectional images of retinal pathology with higher resolution than any other noninvasive imaging technique. Now a days OCT is a prospective technology which is used not only for ophthalmology but also for dermatology, dental as well as for the early detection of cancer in digestive organs. The wavelength range of the OCT light source is spread from the 0.8 to 1.6 ┤m band. This spectral region is of particular interest for OCT because it penetrates deeply into biological tissue and permits spectrally resolved imaging of water absorption bands. In this spectral region, attenuation is minimum due to absorption and scattering. It should be noted that scattering decreases at longer wavelengths in proportion to 1/┣4, indicating that the scattering magnitude at 0.8 ~ 1.6 ┤m wavelengths is lower than at the visible wavelengths [Agrawal, 1995]. Ultrahigh-resolution OCT imaging in the spectral region from 0.8 to 1.6 ┤m requires extremely broad bandwidths because longitudinal resolution depends on the coherence length. The coherence length is inversely proportional to the bandwidth and proportional to square of the light source center wavelength. This can

Chromatic Dispersion Properties of A Decagonal Photonic Crystal Fiber

This paper presents dispersion characteristics of a decagonal photonic crystal fiber (D-PCF) for the first time. The finite difference method (FDM) with an anisotropic perfectly matched boundary layer (PML) is used to investigate the chromatic dispersion characteristics. It is shown through numerical simulation results that D-PCFs can be used as a dispersion compensating fiber for their high negative dispersion slope characteristic. The dependency of chromatic dispersion with pitch, wavelength and air-hole diameters are also presented. Moreover, dispersion properties of D-PCF have been compared with that of the octagonal PCF (O-PCF) and hexagonal PCF (H-PCF), respectively.

Decagonal Photonic Crystal Fibers with Ultra-Flattened Chromatic Dispersion and Low Confinement Loss

Decagonal PCFs with extremely low dispersion of 0 plusmn 0.26 ps/(nm-.km) in the wavelength range of 1.40 mum to 1.60 mum with confinement loss less than 10-6 dB/km is presented.

An unique design of ultra-flattened dispersion photonic crystal fibers

We report that it is possible to control chromatic dispersion of photonic crystal fibers in wide wavelength range by using elliptical air-holes located at core disposed perpendicular alternately. Using this arrangement, a newly PCFs with ultra-low and ultra-flattened dispersion are designed with flattened dispersion of 0.23 [ps/km-nm] from 1.5 mum to 1.8 mum wavelength with the confinement loss less than 10-13 dB/m in the wavelength range shorter than 1.8 mum.

A novel ultra-flattened chromatic dispersion using defected elliptical pores photonic crystal fiber with low confinement losses

This paper reports a novel design in photonic crystal fiber (PCF) with nearly zero ultra flattened dispersion characteristics. We describe the chromatic dispersion controllability taking non-uniform air hole structures into consideration. Through optimizing non-uniform air hole structures, the ultra flattened zero dispersion PCF can be efficiently designed. We show numerically that the proposed triple non-uniform air cladding structure successfully achieves flat dispersion characteristics as well as extremely low confinement loss. As an example, the proposed PCF with flattened dispersion of plusmn0.28 ps/km/nm from 1.5 mum to 1.8 mum wavelength with extremely low confinement loss of less than 10-11 dB/m.

Broadband Supercontinuum Spectrum Generated Highly Nonlinear Photonic Crystal Fiber Applicable to Medical and Optical Communication Systems

Optical-fiber-based supercontinuum (SC) light sources have attracted much research attention in recent years. High-quality nonlinear optical fibers allow us to readily implement stable and practical SC sources. In this work, we present a highly nonlinear photonic crystal fiber (HN-PCF) in optical coherence tomography (OCT) and telecommunication windows that can generate SC spectra. The finite difference method with an anisotropic perfectly matched layer boundary condition is used to calculate different properties of the proposed HN-PCF. From numerical simulation results, it is found that the HN-PCF nonlinear coefficients are more than 108.0, 74.0, and 53.0 (Wkm)-1 at 1.06, 1.31, and 1.55 µm, respectively. The flattened chromatic dispersion is 0 to -4.0 ps/(nmkm) in the wavelength range of 1.06 to 1.7 µm (640 nm bandwidth), and the confinement loss is lower than 10-2 dB/km in the entire wavelength range. The generated supercontinuum bandwidths are 295.0, 408.0, and 590.0 nm at 1.06, 1.31, and 1.55 µm, respectively. The calculated longitudinal resolutions for biomedical imaging are 1.2, 1.2, and 1.1 µm at 1.06, 1.31, and 1.55 µm, respectively.

High Power Highly Nonlinear Holey Fiber with Low Confinement Loss for Supercontinuum Light Sources

The high power holey fiber is an efficient supercontinuum light source by using picosecond pulse, which is a less expensive laser source compared with low power and expensive femtosecond laser sources. In this paper, a high power highly nonlinear holey fiber (HN-HF) with a low confinement loss is proposed for supercontinuum light sources. The finite difference method is used to calculate the different properties of the proposed HN-HF. High nonlinear coefficients are obtained at 1.06 μm, 1.31 μm, and 1.55 μm wavelengths with flattened chromatic dispersion and low confinement losses simultaneously. Moreover, numerical simulation results show that high power broad supercontinuum spectra with very short length of the proposed photonic crystal fiber are achieved.