Saturable absorption by carbon nanotubes on silica microtoroids

Tsutaru Kumagai, Naoya Hirota, Katsuya Sato, Koki Namiki, Hideyuki Maki, Takasumi Tanabe

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)


Saturable absorption is a key technology for shaping the waveform of light such as in passive mode-locking. The combination of high-Q optical microcavities with a saturable absorber allows stable lasing and soliton formation. This work describes saturable absorption by carbon nanotubes (CNTs) on silica microtoroids. CNTs, which are saturable absorbers capable of a fast response time and broadband absorption, were grown on silica microtoroids by chemical vapor deposition (CVD). Raman spectroscopy revealed that the CNTs are in good quality (G/D ratio ∼ 7) and about 1.0 nm in diameter, thus confirming that a sample for use in the telecommunication band can be prepared by CVD. A counter-propagating pump-probe experiment enabled us to investigate the characteristics of CNTs as saturable absorbers while suppressing thermo-optic bistability in a microcavity system. The results revealed a saturable absorption coefficient of 0.042 cm-1, a saturable intensity of 25.9 MW/cm2, and a modulation depth of 28%. This is the first step toward the demonstration of the robust mode-locking in a silica microtoroid consisting of CNTs.

Original languageEnglish
Article number233104
JournalJournal of Applied Physics
Issue number23
Publication statusPublished - 2018 Jun 21

ASJC Scopus subject areas

  • General Physics and Astronomy


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