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We propose a tunable multiwavelength-swept laser based on a nematic liquid crystal (NLC) Fabry–Perot (FP) etalon, which is embedded in the resonator of a wavelength-swept laser. We achieve the continuous wavelength tuning of the multiwavelength-swept laser by applying the electric field to the NLC FP etalon. The free spectral range of the fabricated NLC FP etalon is approximately 7.9 nm. When the...
We demonstrate a 1550nm band resonance Fourier-domain mode-locked (FDML) fiber laser with fiber Bragg grating (FBG) array. Using the FDML fiber laser, we successfully demonstrate real-time monitoring of dynamic FBG strain sensor interrogation for structural health monitoring. The resonance FDML fiber laser consists of six multiplexed FBGs, which are arranged in series with delay fiber lengths. It...
We present a tunable multiwavelength fiber laser based on nematic liquid crystal device (NLC) for fiber-optic electric field sensor. The lasing multiwavelength could be tuned over 18 nm by applying electric field to the NLC device.
We present a terahertz (THz) radiation pumped by a passively mode-locked Yb-doped fiber laser using two fiber-pigtailed log-spiral-based low-temperature-grown (LTG) InGaAs photoconductive antenna (PCA) modules. The mode-locked fiber laser produces over 220 mW of the average optical power with positively chirped of 1.49 ps pulses. In order to generate THz radiation using the fiber-pigtailed PCA modules,...
We measure the pitch variation of cholesteric liquid crystals (CLCs) according to the applied electric field using a wavelength-swept laser. While the electric field is applied to the CLC, the pitch of the CLC is elongated normal to the direction of electric field. Therefore, the reflection band is shifted to the longer wavelength. When the applied electric field to the CLC cell was over 1.52 V/μm,...
An Nd:YAG laser is generally used as the optical source for photoacoustic imaging (PAI) systems, which support a high-power pulsed laser. However, PAI systems based on Nd:YAG lasers have several disadvantages, such as instability against impact and vibration, poor mobility, and large size. To overcome the limitations, we demonstrate a PAI system using a master oscillator power amplifier (MOPA) fiber...
We analyze the relations of parameters in moving average method to enhance the event detectability of phase sensitive optical time domain reflectometer (OTDR). If the external events have unique frequency of vibration, then the control parameters of moving average method should be optimized in order to detect these events efficiently. A phase sensitive OTDR was implemented by a pulsed light source,...
We demonstrate a dynamic fiber Bragg grating (FBG) strain sensor interrogation using a 1550 nm band resonance Fourier domain mode-locked fiber laser. We successfully achieved a real-time measurement of the abrupt change of the applied frequencies to the FBG without any signal processing delay.
We report two kinds of wavelength-swept lasers based on semiconductor optical amplifier for dynamic optical fiber sensors. The wavelength-swept laser has a linear relationship that exists between wavelength and time. As an application using the wavelength-swept laser for dynamic optical fiber sensors, we measure a dynamic modulation frequency of the applied electric field using a nematic liquid crystal...
We report an Yb-doped mode-locked fiber laser at 1.03 μm for time-domain terahertz spectroscopy. The total cavity length is 21.4-m long including free space. The 3 dB optical bandwidth of the mode-locked fiber laser is ∼ 3.5 nm. It can be used as an optical source for compact and potable THz radiation source.
We report a measurement of effective refractive index of a nematic liquid crystal Fabry-Perot etalon according to the applied static electric field intensity. The effective refractive index decreases from 1.67 to 1.51 as the applied electric field intensity is increased.
We report a dynamic fiber-optic electric field sensor using a nematic liquid crystal (LNC) Fabry-Perot etalon and a wavelength-swept laser (WSL). The WSL has a linear relationship between the wavelength measurement and the time measurement. When a modulated electric field of the proper amplitude and frequency is applied to the NLC, the transmission wavelength peaks for the ordinary mode are maintained,...
We present experimental implementation of high-speed broadband frequency sweep of CW THz radiation applicable to high-speed THz spectroscopy and tomography. A wavelength-swept laser and a distributed-feedback laser diode constitute a high-speed frequency-swept optical beat source used for photomixing.
We have investigated the direct modulation characteristics of a phase-shifted 1.3-µm dual-mode laser diode. Stable dual-mode operation and high spectral purity are maintained under 2.5-Gbps direct modulation.
We characterize InGaAs Schottky barrier diodes (SBDs) with a variation in the anode size. High-efficiency terahertz (THz) pulse detection of the InGaAs SBDs is performed in the cases of anode diameters of 2 µm and 3 µm. The uniformity of the fabricated 1 × 20 InGaAs SBD array is measured to be fine. The THz imaging results using the 1 × 20 InGaAs SBD array are presented.
We report a continuously tunable dual-wavelength laser based on the polymer Bragg gratings for continuous wave terahertz optical beat source generation. The polymer Bragg gratings are used to wavelength selective components in the laser cavity. The measured wavelength tuning range is about 19 nm. The side mode suppression ratio is achieved more than 30 dB for dual wavelength.
We have developed a semiconductor optical amplifier integrated λ/4 phase-shifted 1.3-μm dual-mode laser as an optical beat source for continuous-wave (CW) terahertz (THz) generation. The CW THz system is also demonstrated with low-temperature-grown InGaAs photomixers.
We have developed the λ/4 phase-shifted 1.3-µm dual mode laser as an optical beat source of continuous-wave (CW) terahertz (THz) generation. The mode beat frequency is continuously tuned from 230 to 1485 GHz via integrated micro-heaters. The CW THz system is also demonstrated with low-temperature-grown InGaAs photomixers.
We demonstrate a portable terahertz (THz) spectrometer and imaging system. Absorption lines of water vapor in the free space are clearly observed by using the THz system. A THz imaging of a medical knife behind a poly-ethylene is finely measured by the same THz system as well.
We demonstrate a frequency swept optical beat source for high speed continuous wave THz generation. The range of the sweeping bandwidth is about 2.16 THz (17.3 nm). And we observe CW THz waveforms for several static optical beat sources using a fiber coupled CW THz measurement system in order to confirm the feasibility of our frequency swept optical beat source as a CW THz radiation source.
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