tailieunhanh - Advances in Optical and Photonic Devices 2011 Part 3

Tham khảo tài liệu 'advances in optical and photonic devices 2011 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | A Tunable Semiconductor Lased Based on Etched Slots Suitable for Monolithic Integration 41 slot such as slot position slot depth to which it is etched and slot width. Even though the slot is not etched into the active waveguiding regions it will still interact with the mode of the electric field and magnetic field of the waveguide as the mode profile is not fully confined to the active region and will expand into the surrounding cladding regions. The one-dimensional first order electric field mode profile modelled using the finite difference time domain FDTD technique for a simple laser structure with active region depth of 1 pm upper cladding region of 1 pm and lower cladding of 1 pm with active region refractive index of and cladding region refractive index which are normal values for an InGaAsP active region sandwiched between InP cladding regions are shown below in Fig. 1. Fig. 1. Mode profile of the fundamental mode and refractive index profile through the laser structure. From Fig. 1 the fundamental mode is seen to penetrate into the cladding region so any perturbation in this area will influence the mode profile of the laser diode. The scattering matrix method SMM is a simple and accurate technique which can be used to determine the reflection and transmission from slots etched into the laser cavity. Numerous texts deal with the SMM of which Buus Amann et al. 2005 is a good introduction. Of particular importance in a laser structure is the ability to determine loss using the SMM method. This is an important advantage of the SMM over that transmission matrix method TMM . A F-P laser with one etched slot can be described as three cavities with different interface reflections and transmissions as described below in Fig 2. Fig. 2. Schematic description of single slot laser diode. 42 Advances in Optical and Photonic Devices In fig. 2 ni refers to the effective refractive index in these section of the laser structure while ri refers to the reflection .