Publisher DOI: 10.1364/OL.44.000175
Title: Free-carrier detection in a silicon slab via absorption measurement in 2D integrating cells
Language: English
Authors: Fohrmann, Lena Simone 
Lotfi, Nima 
Alzein, Bilal 
Gaafar, Mahmoud Abdelazis 
Petrov, Alexander  
Eich, Manfred 
Issue Date: 1-Jan-2019
Source: Optics Letters 1 (44): 175-178 (2019-01-01)
Abstract (english): 
2D integrating cells provide long optical path lengths on a chip by multiple reflections at highly reflective mirrors similar to integrating spheres in free space. Therefore, they build a promising platform for integrated optical absorption sensing. Here, we present first absorption measurements of free carriers generated by a modulated pump laser inside a 2D integrating cell in a silicon slab. The results can be used to evaluate the lifetimes of free carriers in silicon slabs for integrated optics. Employing a silicon-on-insulator platform with a silicon thickness of 220 nm, we demonstrate measurements of the access free-carrier concentration on the order of 1 − 8 · 10 15 cm −3 with lifetimes on the order of 0.1–1 μs governed by surface recombination at the silicon interfaces. The measured lifetimes are dependent on free-carrier concentration, which confirms previous observations. The presented free-carrier absorption experiment verifies the sensitivity of 2D integrating cells to changes in the absorption coefficient and thus demonstrates the potential of 2D integrating cells for absorption sensing.
ISSN: 0146-9592
Journal: Optics letters 
Institute: Optische und Elektronische Materialien E-12 
Document Type: Article
Project: Mid infrared gas sensing 
Relativistische photonische Bandlückenspiegel in der integrierten Optik 
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