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Saturable absorption in single-walled carbon nanotubes at 1550 nm Ma, Robert Tak Fai

Abstract

Single-walled carbon nanotubes (SWNTs) provide an alternative to multi-quantum well (MQW) based saturable absorbers at optical communication wavelengths. This work is aimed at measuring the nonlinear absorption coefficient of SWNTs at 1550 nm and to compare the performance of SWNT based saturable absorbers with MQW based saturable absorbers. In this work, saturable absorption and optical bleaching in a SWNT sample at 1550 nm were observed by the Power-scan and the two-color pump-probe measurement methods. A measurement system capable of performing Z-scan, P-scan, and pump-probe measurements was developed. The filtration method was used to fabricate a thin film of SWNTs grown by the HiPco process onto a sapphire substrate. The experimental results obtained from the P-scan measurements were analyzed to estimate the nonlinear absorption coefficient of the SWNT sample. The estimated values are large compared to those of other nonlinear optical materials. Optical bleaching was observed in the pump-probe measurement. A figure of merit to compare the performance of saturable absorbers based on their modulation depth, saturation intensity, and recovery time is proposed. Using it, the figures of merit of the SWNT sample used in this work, those of several SWNT based saturable absorbers reported in the literature, and those of several MQW based saturable absorbers, also reported in the literature, were calculated. The calculations showed that the performance of SWNT based saturable absorbers is comparable to MQW based saturable absorbers. The optical properties of SWNTs, combined with the low cost of fabrication, demonstrate the potential of SWNT based devices to find a large number of optical applications.

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