All-polarization-maintaining Er-doped dual comb fiber laser using single-wall carbon nanotubes.

We demonstrated a bi-directional, Er-doped dual comb fiber laser consisting of all-polarization-maintaining fiber devices. Polyimide films in which single-wall carbon nanotubes (SWNTs) were dispersed were used as the in-line saturable absorber. In order to avoid synchronization of the two combs and associated damage to the SWNT film, a two-branch configuration with two SWNT films was employed. Soliton pulses with almost the same optical spectra were generated stably in each direction, and dual comb beats were observed simply by overlapping the two outputs. The repetition frequency was 28 MHz, and the frequency difference was 105-140 Hz. Thanks to the small frequency difference, dual comb beats corresponding to the whole optical spectrum were observed without any overlapping. Fourier transform spectroscopy using the developed dual comb source was examined, and the characteristics of an optical filter were successfully obtained.

Development of a high power supercontinuum source in the 1.7 µm wavelength region for highly penetrative ultrahigh-resolution optical coherence tomography.

We developed a high power supercontinuum source at a center wavelength of 1.7 µm to demonstrate highly penetrative ultrahigh-resolution optical coherence tomography (UHR-OCT). A single-wall carbon nanotube dispersed in polyimide film was used as a transparent saturable absorber in the cavity configuration and a high-repetition-rate ultrashort-pulse fiber laser was realized. The developed SC source had an output power of 60 mW, a bandwidth of 242 nm full-width at half maximum, and a repetition rate of 110 MHz. The average power and repetition rate were approximately twice as large as those of our previous SC source [20]. Using the developed SC source, UHR-OCT imaging was demonstrated. A sensitivity of 105 dB and an axial resolution of 3.2 µm in biological tissue were achieved. We compared the UHR-OCT images of some biological tissue samples measured with the developed SC source, the previous one, and one operating in the 1.3 µm wavelength region. We confirmed that the developed SC source had improved sensitivity and penetration depth for low-water-absorption samples.

Power scaling of dispersion-managed Er-doped ultrashort pulse fiber laser with single wall carbon nanotubes.

A high-power, passively mode-locked, Er-doped fiber laser with a single wall carbon nanotube polyimide film was demonstrated in dispersion-managed dissipative-soliton mode-locking operation. The average maximum power of 285 mW and a pulse energy of 8.1 nJ are the highest values yet achieved for single-pulse operation in a nanotube fiber laser. A high-power ultrashort pulse of 680 fs was generated by dispersion compensation at a repetition rate of 34.9 MHz. Passive mode-locking was numerically analyzed, and the dynamics and output properties are discussed.