Wavelength Tunable Soliton Pulse Research Articles

Tunable quasi-supercontinuum generation in a 1.7 µm spectral band for spectral domain optical coherence tomography

We present a system for generating a 1.7 µm quasi-supercontinuum (SC) as what we believe to be a new broadband light source for spectral domain (SD) optical coherence tomography (OCT). The quasi-SC source, whose spectral range and spectral shape can be arbitrarily changed, is based on wavelength-tunable soliton pulse generation and high-speed intensity modulation. A Gaussian-shaped quasi-SC was introduced into an SD-OCT system. A maximum axial resolution of 14 µm in air (corresponding to 10 µm in tissue) and an imaging sensitivity of 94 dB was obtained. We also demonstrated high-resolution imaging for tape stack, human nail and pig thyroid gland samples using a quasi-SC. From these results, we confirmed the usefulness of a quasi-SC for SD-OCT imaging.

Kelly sideband suppression and wavelength tuning of a conventional soliton in a Tm-doped hybrid mode-locked fiber laser with an all-fiber Lyot filter

We demonstrate a stable conventional soliton in a Tm-doped hybrid mode-locked fiber laser by employing a homemade all-fiber Lyot filter (AFLF) and a single-wall carbon nanotube. The AFLF, designed by sandwiching a piece of polarization-maintained fiber (PMF) with two 45° tilted fiber gratings inscribed by a UV laser in PMF with a phase-mask scanning technique, shows large filter depth of ∼9 dB and small insertion loss of ∼0.8 dB. By optimizing the free spectral range of the AFLF, the Kelly sidebands of a conventional soliton centered at 1966.4 nm can be dramatically suppressed without impairing the main shape of the soliton spectrum. It gives the pulse duration of 1.18 ps and bandwidth of 3.8 nm. By adjusting the temperature of the PMF of the AFLF from 7°C to 60°C, wavelength tunable soliton pulses ranging from 1971.62 nm to 1952.63 nm are also obtained. The generated soliton pulses can be precisely tuned between 1971.62 nm and 1952.63 nm by controlling the temperature of the AFLF.

Novel super-continuum fiber lasers and wavelength-tunable soliton pulses

Advances in ultrashort laser pulse technology have recently generated several new applications in fields as diverse as laser processing, medical and bio-optics, opto-electronics, etc. However, ultrashort-pulse lasers require quiet laboratory environments and water cooling which prevents their use for practical applications. Spectroscopic applications also require a wavelengthtunable ultrashort pulses. The tuning range, however, is generally limited by the gain bandwidth of the laser. Since these pulses are generated with wavelength conversion using nonlinear crystals and mechanical tuning, it is difficult to generate wideband tunable pulses. Of significant interest is the recent development of compact ultrashort-pulse fiber lasers. Since these lasers consist of fiber-optic devices, they produce stable pulses and water cooling is not required. Fiber lasers are also maintenance-free and can work wherever there is electricity. The wavelength of the output pulses, however, can only be changed within the gain bandwidth of the fiber amplifier and the bandwidth is less than 100nm. In our work, we investigate all-fiber wideband utrashort-pulse sources based on ultrashort-pulse fiber lasers and study nonlinear effects in optical fibers. Specialty fibers, such as highly nonlinear fibers and photonic crystal fibers, were recently developed. Their characteristics are determined by their structure and they have demonstrated high energy density and dispersion tunability. Using ultrashort-pulse lasers and suitable specialty fibers, we can generate ultrawideband optical spectra, referred to as a super continuum. All-fiber super-continuum sources have also been reported. However, their noise level is generally high and the super continuum is characterized by excessive fine structure. To date, no practical Figure 1. Optical spectra of wavelength-tunable soliton pulses that were generated through nonlinear effects. As the fiber input power is increased, the center wavelength is continuously red-shifted. We can tune the wavelength from 1.55 to 2.0μm.

640-Gb/s OTDM Signal Measurement With High-Resolution Optical Sampling System Using Wavelength-Tunable Soliton Pulses

We have demonstrated an optical sampling system using wavelength-tunable soliton pulses produced by a highly nonlinear polarization-maintaining (PM) fiber. We successfully observed a 640-Gb/s optical signal with the system. The wavelength of the sampling pulses was shifted to 1736 nm by employing a 40-m-long PM fiber, and the sampling pulsewidth was 210 fs. The system achieved high temporal resolution of 280 fs and high sensitivity by employing a 2-mm-thick periodically poled LiNbO/sub 3/ crystal. The system jitter was estimated to be 80 fs.

相互相関周波数分解光ゲート法を用いた光ファイバにおける超短パルス光の伝搬特性の解析

Characteristics of ultrashort pulse propagation in optical fibers at the wavelength region of 1.55 μm are experimentally analyzed using the cross-correlation frequency resolved optical gating (X-FROG) technique. In the anomalous dispersive fibers, widely wavelength tunable femtosecond soliton pulse is generated. The spectrogram of almost transform limited soliton pulse around 2 μm is observed. In the dispersion shifted fibers, the wavelength tunable soliton pulse and anti-stokes pulse are generated. As the results of X-FROG measurement, it is clarified that the anti-stokes pulse is overlapped with the soliton pulse and trapped by the soliton pulse. In the highly nonlinear optical fibers, 1.2-2.1 μm ultra-widely broadened super continuum and 1.46-1.68 μm linearly chirped one are generated. The spectrograms of generated super continuum are observed. The phenomenon of pulse trapping is also observed in generated super continuum.

Widely wavelength-tunable ultrashort pulse generation using polarization maintaining optical fibers

Characteristics of widely wavelength tunable ultrashort pulse generation using several types of polarization maintaining fibers have been experimentally analyzed. Using the diameter reduced type of polarization maintaining fibers, the wavelength tunable soliton pulse is generated from 1.56 to 2.03 /spl mu/m. It is confirmed that the almost transform-limited 340-fs soliton pulse is generated at a wavelength of around 2 /spl mu/m using a frequency-resolved optical gating method. When low-birefringence fibers are used, it is observed that the orthogonally polarized small pulse spectrum is trapped by the soliton pulse and is also shifted toward the longer wavelength side in the process of soliton self-frequency shift. The wavelength of the orthogonally polarized pulse spectrum is 40-50 nm longer than that of the soliton pulse, and the birefringence of the fiber is compensated by the chromatic dispersion. Finally, a polarization maintaining highly nonlinear dispersion-shifted fiber is used as the sample fiber. When the fiber input power is low, the wavelength-tunable soliton and anti-Stokes pulses are generated. As the fiber input power is increased, the pulse spectra are gradually overlapped and the 1.1-2.1 /spl mu/m widely broadened supercontinuum spectra are generated by only 520 pJ pulse energy.

Wavelength Tunable Ultrashort Pulse Fiber Laser.

Compact system of wavelength tunable ultrashort soliton pulse generation has been demonstratedusing modelockedfemtosecond fiber laser and polarization maintaining (PM) fiber. The wavelengths of generated pulsescan be changed continuously by merely varying fiber input power. The generated pulses are almost transformlimited ideal soliton pulses. Two-colored soliton pulses can be generated simultaneously usingthe birefringenceof PM fibers. Using the dispersion shifted PM fibers, in addition to the soliton pulse, the anti-stokespulse is generated at the shorter wavelength side. Using the diameter reduced PM fibers and dispersion shiftedPM fibers, the wavelength tunable ultrashort pulses can be generated in the wide wavelength region of 1.3-2.0μm. In this paper, the characteristics of wavelength tunable soliton pulse are described withthe principles and applications.

Measurement of Chromatic Dispersion of Optical Fibers Using Wavelength-Tunable Soliton Pulses

The chromatic dispersion of optical fibers is measured using a compact wavelength-tunable soliton pulse generation system. In this system, an ultrashort optical pulse can be generated in a wide wavelength region and the wavelengths of the optical pulses can be changed simply by varying the fiber input power. Since the system is compact and changing the wavelength is very easy, measurement of the chromatic dispersion can be demonstrated easily using a simple setup. The magnitudes of the second- and third-order dispersions in the optical fibers are measured in the wide wavelength region from 1.32 to 1.93 µm. Since the pulse width of the soliton pulse is as narrow as 200 fs, the dispersion of the fiber can be measured in an optical fiber as short as 10 m.

Measurement of Timing Jitter in Wavelength Tunable Femtosecond Soliton Pulses

We investigated the root mean square (RMS) timing jitter and RMS intensity noise of the wavelength tunable femtosecond soliton pulses using the technique of radio-frequency spectrum analysis. We obtained interesting results that the generated solitons have almost constant RMS timing jitter and RMS intensity noise of approximately 410 fs and 0.03% in the wavelength region of 1600-1750 nm. It is therefore believed that the magnitudes of the jitter and noise are not greatly increased in the process of wavelength tunable soliton pulse generation. The wavelength tunable soliton pulse is confirmed to be stable and useful for practical applications.

Analysis of Widely Wavelength Tunable Femtosecond Soliton Pulse Generation Using Optical Fibers

Characteristics of wavelength-tunable femtosecond (fs) soliton pulse generation using optical fibers in a negative dispersion region are investigated both experimentally and numerically. The extended nonlinear Schrödinger equation, in which the wavelength dependence of parameters is considered, is used to analyze the characteristics of widely wavelength-tunable soliton pulses. The wavelength of the soliton pulse can be almost linearly shifted from 1.56–1.86 µm for a 220 m fiber merely by varying the fiber-input power. Ideal mono-colored fs soliton pulses of 90–300 fs are generated stably, and the generated pulses are nearly transform-limited fundamental soliton pulses. The numerical results fit the experimental ones well. The numerical analysis revealed that the wavelength of the soliton pulse can be shifted up to 2.2 µm in this system.