We report a compact, robust, and cost-effective ultra-short pulse fiber laser incorporating a NALM-based all-PM modelocked Yb fiber laser oscillator and an Yb-doped fiber amplifier. The Yb-doped fibers are pumped with a low-power laser diode. The laser generates 12 ps pulses at a repetition rate of 20 MHz, center wavelength of 1040 nm, spectral width of 20 nm and average power of 128 mW. We believe that this type of fiber laser is an ideal seed source for further high-power femtosecond fiber laser.
We report superiorities of a NALM-based all-PM fiber laser incorporating dual-bandpass filter instead of ordinal single narrow bandpass filter. The fiber laser starts mode-locking quickly with relatively low pump powers. Shorter wavelength bandpass window component of dual-BPF is used for inducing Q-switched mode-locking and enlarging amplitude noise. Longer wavelength bandpass window component is used for keeping CW mode-locking. Once the laser starts modelocking at longer wavelength window, spectrum components in shorter wavelength window are negligible. The laser produces various of ultra-fast pulses by adjusting longer wavelength window property.
We report an all-polarization maintaining fiber laser operating at central wavelength of 1020-1064 nm with pulse duration of 2-8 ps and the repetition rate of 6.12 MHz. The laser is mode-locked using a nonlinear amplifying loop mirror, and the wavelength can be tuned continuously by installing an electrically programmable optical filter into the cavity. Our ultrafast fiber laser will be attractive for various applications such as bio-imaging, laser micro-processing, optical measurements, medical treatment, and supercontinuum generation.
The optical dispersion can be obtained from the adjacent relative phase between neighbor peaks in the optical frequency comb. Thus, the dispersion measurement becomes possible by measuring the relative phase spectrum. Our group has experimentally confirmed the operation principle by parallel capturing of the dispersion spectrum using an arrayed waveguide grating. We have proposed a dual-heterodyne mixing that obtained relative phases (ΔΦ) by fitting data of beat intensity versus optical path length difference. The path difference was applied by a delay line. In this study, we removed the delay line to realize a fast measurement by measuring simultaneous three relative phases with path length differences corresponding to π⁄2 or π, with which we have measured the dispersion in millisecond speed (250 sec. in previous ). In general, it is effective to measured chromatic dispersion using high-speed signal transmission in the fundamental scientific research, such as the analysis of material properties and telecommunications. It is, however, that limit of cutoff frequency using measurement is the restriction on increasing of the speed. Our proposed method to observe it on a frequency domain is effective for the high-speed signal processing.
Novel two-dimensional single-shot imaging optical system based on Frequency-domain interferometry using a virtually imaged phased array is proposed. The VIPA simultaneously outputs incoherent optical frequency combs (OFCs) whose teeth interval are scanned as a function of its output angle. Teeth intervals of the OFCs only in a reference are spatially swept by using of a VIPA whose advantage compared to an optical resonator. Thus, the single-shot imaging system can be realized with the FSR scanned frequency-domain OFC interference monitored by CCD. This system enable high speed 2-dimensional tomographic image without mechanical moving part. And the axial measurement range is not limited by using multi-order interference that is generated by OFCs interferometry. We will present the operation principle with its confirmed results in terms of both simulation and experiment.
Pseudo optical frequency comb using a high-speed frequency laser scanner and an optical resonator is generated as a virtual broadband lightsource for the time-domain 2D single-shot tomography and profilometry. High-speed laser scanner (40 kHz) is realized using a broadband semiconductor optical amplifier (SOA) whose individual wavelengths are consequently picked up by a conventional grating setup and a high speed polygon mirror. The performance of the pseudo frequency comb is confirmed by a measurement of a reference step-height sample with an optical zooming operation.
We describe principle of spatially-resolved spectroscopy using swept source optical interferometry and demonstrate it using a multi-layered polypropylene and glass plates piled sample. The advantages of this technique compared to conventional spectroscopy technique are realizing spatially-resolved spectroscopy as transmittance spectra of each layer and obtaining tomographic image of the sample simultaneously. Moreover, potential for spectroscopy is the method we propose can calculate absorption coefficient of each mediums. In this demonstration, we could 1D tomographic image of multi-layered sample and characterize PP layer and glass layer by comparing transmittance spectra in near infrared region.
We propose a novel system for a two-dimensional (2-D) single-shot tomography and profilometry that can be realized by installing a Virtually Imaged Phased Array (VIPA) into a 2-D interferometer with a CCD. The VIPA simultaneously outputs incoherent optical frequency combs (OFC) whose teeth interval, such as free-spectral range (FSR), are scanned as a function of its output angle when the low-coherent light source is incident into the VIPA. Thus, the single-shot imaging can be realized with the FSR scanned Fourier-domain OFC interference monitored by the CCD. In other words, the fast imaging without mechanical moving part can be operated by the proposed OFC interferometry. And VIPA can use all of incident light. So this system enables to realize a high energy efficient interference measurement.
FSR of the output light of the VIPA is nonlinear with respect to the sweep direction. So we simulated the characteristics of the VIPA. As a result, we knew linearity optimal output angle depend on reflective index of the VIPA. And the VIPA can change the measurement range on the CCD by the number. In other word, the VIPA can zoom in and out no mechanical part. We will present the operation principle with its confirmed results in terms of both simulation and experiment.
We have developed a novel single-shot optical tomography and profilometry that is able to measure the tomograms and surface profiles of a sample in realtime with long measurable range. The system comprises of an optical frequency comb interferometry and a diffraction grating. The grating plays as a spatial phase modulator (SPM), so that the realtime interference images can be achieved by a CCD camera. Owing to the diffraction lights by the SPM, the axial zooming operation of the proposed system can be realized. The zooming range of the proposed system depends on how many diffraction orders are generated by the SPM. Measurements of a reference Gauge-block step-height sample at different diffraction orders are performed to evaluate the proposed system.
This paper demonstrates a novel fiber optic remote sensing system based on laser powering and a liquid-crystal optical modulator that transforms electrical signal of sensors into optical with low power consumption. A basic experiment for confirming the principle was conducted using a standard communication-grade semiconductor laser with the output of less than 20 mW both for laser powering and for sensor signal transmission. The sensor signal was transferred through 5-km-long optical fiber and detected with On/Off ratio of more than 15 dB.
3D common-path interferometer is proposed to obtain achromatic nulling for star coronagraphy. Common-path scheme compensates optical path difference (OPD) effectively and is stable to mechanical vibrations. 3D ray geometry involves polarization rotations ±90° in each interferometer arm and results in achromatic 180° phase shift for destructive interference for on-axial source. The interferometer throughput is obtained at nearly 100% for entire polarized light and nearly 50/50 ratio of light energy is split between Bright and Nulled ports for off-axial source. Theory, simulations and preliminary breadboard experiments are shown in reasonable agreement.
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