Dongwook Park

Simple analysis of the energy density distribution of the diffracted ultraviolet beam from a fiber Bragg grating phase mask

The energy density distribution of the diffracted ultraviolet field from a phase mask used for fiber Bragg grating fabrication is efficiently analyzed at short-to-intermediate distances by application of a thin phase screen model and the angular spectrum decomposition method. A direct comparison with the results obtained from a rigorous coupled-wave model shows good agreement.

Analysis of Graded-Index Hollow Optical Fibers and Its Application to Atomic Waveguide Design

This paper presents a scalar analysis of hollow optical fiber (HOF) with a graded-index (GRIN) profile by using the modified Airy functions. A full-vectorial analysis based on finite element method is performed as well to confirm the validity of the scalar analysis results. Based on the results obtained, GRIN HOF is shown to offer a much steeper field gradient and thus a significantly stronger repulsive optical force within the hollow region compared to a conventional step-index HOF, improving the atomic guiding efficiency.

Analysis of Temperature Effects on Raman Silicon Photonic Devices

Recent research efforts on study of silicon photonics utilizing stimulated Raman scattering have largely overlooked temperature effects. In this paper, we incorporated the temperature dependences into the key parameters governing wave propagation in silicon waveguides with Raman gain and investigated how the temperature affects the solution of the coupled-mode equations. We then carried out, as one particular application example, a numerical analysis of the performance of wavelength converters based on stimulated Raman scattering at temperatures ranging from 298 K to 500 K. The analysis predicted, among other things, that the wavelength conversion efficiency could decrease by as much as 12 dB at 500 K in comparison to that at the room temperature. These results indicate that it is necessary to take a careful account of temperature effects in designing, fabricating, and operating Raman silicon photonic devices.

Mode analysis of DFB SE lasers

This paper presents theoretical results on mode characteristics of surface-emitting (SE) lasers utilizing an active second-order grating section. Based on a coupled-mode approach, longitudinal modes and the associated space-harmonic transverse modes are calculated via a numerical technique. From these, the lasing-mode spectrum, near- and far-field patterns of the radiation mode, and the surface-emission power efficiency are obtained. Effects of the substrate reflector and the grating parameters are also investigated. Finally, comparisons are made with conventional, edge-emitting DFB lasers. The results indicate that with a suitable choice of structural parameter values, DFB SE lasers can be made to possess both the spectral discrimination of the conventional DFB lasers and the advantages of SE lasers at the same time and also that the second lowest longitudinal mode may be preferred over the fundamental longitudinal mode for many applications due to its symmetric field distribution.

Modified Airy Function Method Applied to Optical Waveguides and Quantum Tunneling: A Critical Analysis

The validity of applying the Modified Airy Function (MAF) method to the problems of graded-index optical waveguides and graded potential barrier analysis was critically examined. In the former case, the method yielded very accurate results from the derived eigenvalue equations. In the latter case, however, the same method produced results that deviated significantly from exact numerical results for barriers with a smooth peak. The causes of the discrepancies were investigated in detail.

Numerical analysis of six-hole holey fibers

Mode properties of two different types of six-hole holey fibers were analyzed using the plane wave expansion (PWE) method. Calculated results suggest that a variety of waveguide dispersion characteristics may be obtained from these structures with a suitable choice of hole shape, size and pitch values. In addition, mode field diameter (MFD) and splice loss due to the MFD mismatch were calculated.

Lasing Modes of LD - Pumped Fiber Grating Lasers

Lasing modes of laser-diode-pumped fiber grating lasers are analyzed by coupled-mode theory. First, a power series solution of the coupled-mode equations is derived under the assumption of an exponentially-decreasing longitudinal modal gain profile for a laser-diode-pumped grating section, followed by determination of the transfer matrix for such a section. Based on these results, an eigenvalue equation for oscillation is then derived and solved numerically for the lasing modes of uniform and phase-shifted fiber grating lasers. Comparisons made with the uniform-gain results indicate that, surprisingly, the lasing mode characteristics are not as significantly altered as might be expected in most cases, even for a highly nonuniform gain profile. In the case of a phase-shifted grating, the phase-shift position appears to have a much greater impact on determining the threshold gain, the modal field distribution, and the front-to-back output power ratio.

A study on dispersion of long-period fiber gratings

Long-period fiber gratings (LPFG) have recently emerged as a candidate for a number of applications, including those related to wavelength-division-multiplexing (WDM) fiber-optic communication. Although some papers have presented analytical treatment of LPFG structures in the past, there has been no report thus far on theoretical calculation of the dispersion characteristics associated with LPFG devices, which could become a significant issue for high-bit-rate LPFG applications. The paper presents some group delay calculations for a wavelength region of 1.51-1.59 /spl mu/m for a variety of LPFG structures ranging from a simple uniform section to a cascaded multisection structure.