Window 영역을 갖는 laterally tilted SCH-SLD의 최적 설계

Abstract

In this study, It was proposed laterally-tilted SCH(Separate Confinement Heterostrucure)-SLD(Superluminescent Laser Diode) with a window region in order to apply to the fiber optic sensing systems, such as Mach-Zehnder fiber optic interferometer and fiber optic gyroscope(FOG). Theoretical analyses have been tried to design high power and stable operating SLD, especially, the SLD operating at 1.55㎛ wavelength range which is the lowest absorption wavelength in silica(SiO2) optical fiber. Therefore the materials and structures of active layer and SCH layer were chosen as conventional In_(1-x)Ga_x As_y P_(1-y) quaternary composition systems.

From the transverse mode and lateral mode analyses of waveguide, the optical power distributions and the optical confinement factor have been studied for single-mode high power operation. According to these analyses, it was calculated SCH layer composition and the thickness to obtain the maximum optical confinement factor.

For the stable superluminescent operation, the facet reflectivity of SLD has to be lowered than 10^-4. The AR coating condition has been investigated with three kinds of TiO₂/SiO₂ structures, such as single layer, one pair layer, and multiple layers.

Furthermore, in order to find to easy way to fabricate low values of reflectivity, several cases, such as using unpumped window region effects or tilted facet including above AR coating results, respectively, were calculated with the gaussian beam approximation and mode analysis.

From these researches, it was confirmed that several results to fabricate the efficient and stable SLD.

In case of using 1.3㎛ InGaAsP SCH composition layer, the layer thickness was obtained 0.08㎛ to get the maximum optical confinement factor.

In case of single layer coating, such as TiO₂ and SiO₂, to get the minimum reflectivity at 1.55㎛ wavelength, each layer thickness was obtained 1790Å, 2690Å respectively. And in case of TiO₂/SiO₂ one pair layer, to get below 1% reflectivity in AR coating, TiO₂, SiO₂ thickness is 1500∼2000Å, 1100∼1700Å respectively. And in case of TiO₂/SiO₂ multiple layers, the reflectivity was higher than other cases.

In case of using 0.2㎛ active layer thickness, 0.08㎛ SCH layer thickness, window region length is 100㎛ in without AR coating, 10㎛ in 1% AR coating to obtain about 10^-4 reflectivity. When the tilted angle is about 10∼15。, reflectivity is about 10^-3.

From these results, it was confirmed that it is possible to fabricate the stable SLD without AR coating analytically, if the window region length and tilted angle were controlled appropriately in given device structure.