Erbium-doped-fiber-based broad visible range frequency comb with a 30 GHz mode spacing for astronomical applications.

We have realized a comb system with a 30 GHz mode spacing, 62 % available wavelength coverage in the visible region, and nearly 40 dB spectral contrast by combining a robust erbium-doped-fiber-based femtosecond laser, mode filtering with newly designed optical cavities, and broadband-visible-range comb generation using a chirped periodically-poled LiNbO ridge waveguide. Furthermore, it is suggested that this system produces a spectrum with little change over 29 months. These features of our comb will contribute to fields requiring broad-mode-spacing combs, including astronomical observations, such as exoplanet exploration and the verification of the cosmic accelerating expansion.

Iodine-stabilized laser at telecom wavelength using dual-pitch periodically poled lithium niobate waveguide.

We demonstrate the third harmonic generation of a 1542-nm laser using a dual-pitch periodically poled lithium niobate waveguide with a conversion efficiency of 66%/W. The generated 514-nm light is used for saturation spectroscopy of molecular iodine and laser frequency stabilization. The achieved laser frequency stability is 1.

Multi-branch fiber comb with relative frequency uncertainty at 10 using fiber noise difference cancellation.

In multi-branch combs, the comb outputs from the branches suffer from different fiber noises, which often limit the uncertainty of the combs referring a highly-stable optical frequency. To overcome this limitation, we introduced fiber noise difference cancellation to multi-branch fiber combs. We detected and phase-locked the beat notes between the branch outputs and a common 1542 nm continuous wave laser.

Direct generation of 12.5-GHz-spaced optical frequency comb with ultrabroad coverage in near-infrared region by cascaded fiber configuration.

We generated a 12.5-GHz-spacing optical frequency comb that can be resolved over 100 THz, from 1040 to 1750 nm, without spectral mode filtering. To cover such a broad spectrum, we used electro-optic modulation of single frequency light and line-by-line pulse synthesis to produce a clear pulse train and subsequent spectral broadening in highly nonlinear fibers (HNLFs).

Dark soliton synthesis using an optical pulse synthesizer and transmission through a normal-dispersion optical fiber.

We precisely generate dark solitons using an optical pulse synthesizer (OPS) at a repetition rate of 25 GHz and experimentally investigate soliton transmission through a normal-dispersion fiber. Because of their particular waveform, there are not many experimental studies. The OPS provides frequency-domain line-by-line modulation and produces arbitrary pulse waveforms.

Background suppression in synthesized pulse waveform by feedback control optimization for flatly broadened supercontinuum generation.

We demonstrate a method of background component suppression of synthesized pulses for flatly broadened supercontinuum (SC) generation. An adaptive pulse shaping in frequency domain achieved a 26 dB contrast between pulse center and background level in auto-correlation trace by combining two fitness functions during feedback-controlled pulse shaping. The pulse was used as a SC pump, and the spectral peak of the SC at the pump wavelength was suppressed by 5 dB using the combination scheme.

Deposition of carbon nanotubes around microfiber via evanascent light.

Optical devices based on carbon nanotubes (CNTs) have been realized with several fabrication methods in different structures, such as free-space, fiber-end, waveguide, and fiber structures. Most of waveguide- and fiber-type devices utilize evanescent coupling between the guided light and CNT layers, and offer very high optical damage threshold and high third-order nonlinearity. However, the conventional fabrication methods require complicated processes and waste much of CNTs.

In-situ monitoring of optical deposition of carbon nanotubes onto fiber end.

Carbon nanotubes (CNTs) emerged as an attractive material for nonlinear optical devices. Their quasi-one-dimensional structure provided their unique nonlinear characteristics. However, one of their drawbacks is the handling method.

Optically formed carbon nanotube sphere.

Carbon nanotubes (CNTs) offer vast possibilities for future ultra-fast photonic devices. One of the biggest challenges to realize the devices is handling of carbon nanotubes. To achieve efficient handling, we have proposed and demonstrated the optical deposition of CNTs onto optical fiber ends.