Liquid Crystal Polarization Controller Arrays on Planar Lightwave Circuits

Katsuhiko HIRABAYASHI  Chikara AMANO  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E86-C   No.5   pp.753-761
Publication Date: 2003/05/01
Online ISSN: 
DOI: 
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Joint Special Issue on Recent Progress in Optoelectronics and Communications)
Category: OECC Awarded Paper
Keyword: 
polarization control,  polarization mode dispersion,  liquid crystal,  planar lightwave circuit,  variable optical attenuators,  

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Summary: 
We have formed simple polarization-controller arrays by inserting liquid crystal (LC) in trenches cut across planar lightwave circuits (PLCs). We fabricated LC layers for use as polarization controllers on PLCs in two ways; in one, the ultra-thin layer of LC is held in a cell that is inserted into a trench on the PLC while in the other, the trench is directly filled with the LC. The ultra-thin LC cell can change the phase of 1.55-µm light from 0 to 3π while the LC filling can change the phase of light at the same wavelength from 0 to 12π below 5Vrms. Two former parallel-aligned ultra-thin LC cells, where the directions of alignment of the liquid crystals are rotated by 45 relative to each other, are capable of converting light with an arbitrary input polarization to TE or TM polarization. Ultra-thin cells of twisted nematic LC can switch the polarization between TE and TM modes with an extinction ratio of -15dB. The array we fabricated had a pitch of 1 mm and 5 elements, but an array with more than 100 elements and a pitch below 125µm will easily be possible by using finely patterned transparent electrodes. We have also applied our techniques to the fabrication of LC-based variable optical attenuators (VOA) on the PLC.