Highly sensitive ultrafast all-optical light modulation by complex refractive-index changes in guided mode geometry composed of a photoresponsive polymer and a low-refractive-index polymer

Nagamura, Toshihiko; Matsumoto, Ryuji; Naito, Atsushi; Nagai, Yasuyuki
July 2005
Applied Physics Letters;7/25/2005, Vol. 87 Issue 4, p041107
Academic Journal
Highly sensitive ultrafast all-optical light modulation is proposed on the basis of photoinduced complex refractive-index changes in composite guided wave mode (GWM) geometry composed of a low-refractive-index polymer and a photoresponsive polymer. Both calculated and observed results indicated that reflectance, which was unity at an extinction coefficient k=0, decreased rapidly with increasing k until a certain value (kc), and increased again after that. The kc-value and the GWM dip width decreased with increasing the thickness of both polymer layers. The real-part changes shifted the GWM dip very sensitively. The low-refractive polymer contributed great improvements, such as high sensitivity and durability against a repeated femtosecond laser. The present device can give highly enhanced changes of probe light as compared with simple transmission-type devices or the GWM geometry on a metal thin film. A photoelectrochromic polymer was employed in this geometry to demonstrate ultrafast reflectance control upon femtosecond laser excitation.


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