Showing papers by "Norihiko Nishizawa published in 2013"

Dispersion cancellation in high-resolution two-photon interference

Abstract: The dispersion cancellation observed in Hong-Ou-Mandel (HOM) interference between frequency-entangled photon pairs has been the basis of quantum optical coherence tomography and quantum clock synchronization. Here we explore the effect of phase dispersion on ultranarrow HOM dips. We show that the higher-order dispersion, the linewidth of the pump laser, and the spectral shape of the parametric fluorescence have a strong effect on the dispersion cancellation in the high-resolution regime with several experimental verifications. Perfect dispersion cancellation with a linewidth of 3 $\ensuremath{\mu}$m is also demonstrated through 25 mm of water.

Optical-Fiber-Type Broadband Cavity Ring-Down Spectroscopy Using Wavelength-Tunable Ultrashort Pulsed Light

Abstract: We proposed an optical-fiber-type broadband cavity ring-down spectroscopy system using wavelength-tunable ultrashort pulsed light. The absorbance of glucose in various concentrations in water was derived from the ring-down plots of intensities of the interference waveforms generated using a Mach–Zehnder interferometer with different optical delay path lengths, which were shifted by an automatic optical switching module. The absorption spectrum of glucose was obtained in the wavelength region from 1620 to 1690 nm by varying the wavelength using wavelength-tunable ultrashort pulsed light, which was generated from a femtosecond pulsed laser and polarization-maintaining fiber. The measurement error of concentration was improved using multiple linear regression analysis of absorption spectra. The results demonstrate that the optical-fiber-type cavity ring-down spectroscopy system has the potential to measure broadband absorption spectra with high sensitivity.

Temperature Measurement of Si Substrate Using Optical-Fiber-Type Low-Coherence Interferometry Employing Supercontinuum Light

Abstract: We have measured the temperature of a Si substrate using an optical low-coherence interferometer employing supercontinuum light (SC). The accuracy of temperature measurement and the minimum measurable thickness of a layer are determined by the maximum resolving power of the optical path length of the medium in low-coherence interferometry, which depends on the coherent length defined by the spectrum profile and the wavelength of the light source. Low-noise, ultraflat, and highly coherent SC, generated using ultrashort laser pulses and optical fibers, was used as a light source. The wavelength dispersion of SC on the Si substrate was compensated by using a silicon mirror as a reference mirror, resulting in shaper interference waveforms of SC at the front and back surfaces of Si substrate than those of the superluminescent diode (SLD) light used as a conventional low-coherence light source. The measurement accuracy of the temperature using SC was improved to be ±0.4 °C from ±1.0 °C for the case of using the SLD. The temperatures of the Si substrate and SiO2 thin film were simultaneously measured using SC on an 800-µm-thick Si substrate with an 8.55-µm-thick SiO2 film. The temperature of the thin film, the thickness of which is several micrometers, was measured using SC and a compensation technique of wavelength dispersion using the silicon reference mirror.

Optical frequency comb using dispersion managed Er-doped ultrashort pulse fiber laser using carbon nanotube polyimide film

Abstract: Optical frequency comb system based on Er-doped fiber laser with single wall carbon nanotube polyimide film was developed. Narrowing of fceo beat spectrum was achieved through dispersion management of fiber laser cavity.

Label-free observation of tissues by high-speed stimulated Raman spectral microscopy and independent component analysis

Abstract: We have developed a video-rate stimulated Raman scattering (SRS) microscope with frame-by-frame wavenumber tunability. The system uses a 76-MHz picosecond Ti:sapphire laser and a subharmonically synchronized, 38-MHz Yb fiber laser. The Yb fiber laser pulses are spectrally sliced by a fast wavelength-tunable filter, which consists of a galvanometer scanner, a 4-f optical system and a reflective grating. The spectral resolution of the filter is ~ 3 cm -1 . The wavenumber was scanned from 2800 to 3100 cm -1 with an arbitrary waveform synchronized to the frame trigger. For imaging, we introduced a 8-kHz resonant scanner and a galvanometer scanner. We were able to acquire SRS images of 500 x 480 pixels at a frame rate of 30.8 frames/s. Then these images were processed by principal component analysis followed by a modified algorithm of independent component analysis. This algorithm allows blind separation of constituents with overlapping Raman bands from SRS spectral images. The independent component (IC) spectra give spectroscopic information, and IC images can be used to produce pseudo-color images. We demonstrate various label-free imaging modalities such as 2D spectral imaging of the rat liver, two-color 3D imaging of a vessel in the rat liver, and spectral imaging of several sections of intestinal villi in the mouse. Various structures in the tissues such as lipid droplets, cytoplasm, fibrous texture, nucleus, and water-rich region were successfully visualized.

Octave spanning coherent supercontinuum generation by 51 fs pedestal free high power ultrashort pulse from similariton amplifier

Abstract: 51 fs, 4.4 nJ pedestal free high power ultrashort pulse was generated using Er-doped similariton amplifier. An octave spanning coherent supercontinuum broadened from 1.05 to 2.1 um was generated in highly nonlinear normal dispersive fiber.

Ultrahigh resolution optical coherence tomography using high power fiber laser supercontinuum at 1.7 μm wavelength region

Abstract: Optical coherence tomography (OCT) is a non-invasive optical imaging technology for micron-scale cross-sectional imaging of biological tissue and materials. We have been investigating ultrahigh resolution optical coherence tomography (UHR-OCT) using fiber based supercontinuum (SC) source. Although UHR-OCT has many advantages in medical equipments, low penetration depth is a serious limitation for wider applications. Recently, we have demonstrated high penetration depth UHR-OCT by use of fiber based Gaussian shaped SC source at 1.7 μm center wavelength. However, the penetration depth has been limited by the low power of SC source. In this paper, to realize deeper penetration imaging, we have developed the high power Gaussian shaped SC source at 1.7 μm wavelength region based on the custom-made Er-doped ultrashort pulse fiber laser with single-wall carbon nanotube and nonlinear phenomena in fibers. This SC source has 43.3 mW output power, 242 nm full-width at half maximum bandwidth, and 109 MHz repetition rate. The repetition rate and average power were almost twice as large as those of previous SC source. Using this light source, 105 dB sensitivity and ultrahigh resolution of 4.3 μm in tissue were achieved simultaneously. We have demonstrated the UHR-OCT imaging of pig thyroid gland and hamster’s cheek pouch with this developed SC source and compared the images with those measured by the previous SC source. We have observed the fine structures such as round or oval follicles, epithelium, connective tissue band, and muscular layer. From the comparison of the UHR-OCT images and signals, we confirmed the improvement of imaging contrast and penetration depth with the developed SC source.

Ultrahigh-resolution optical coherence tomography imaging of protein crystals using gel inclusion technique

Abstract: Protein crystals are required for X-ray crystallography to determine three-dimensional structures of proteins at atomic resolution. The conventional microscopy is currently used for observation and screening of protein crystals. However, the three-dimensional imaging, which is important for automated treatment of protein crystals, is generally difficult by light microscopy. In addition, the protein crystals in the media are frequently difficult to identify by conventional light microscopy owing to the appearance of salt crystals or amorphous materials. In this work, we successfully demonstrated micro-scale, non-invasive, three-dimensional cross-sectional imaging of protein crystals using ultrahigh resolution optical coherence tomography (UHR-OCT). A low noise, Gaussian like, high power supercontinuum at wavelength of 800 nm was used as the light source. The axial resolution of 2 um in sample and the sensitivity of 95 dB were achieved. Since the protein crystal has homogeneous nano-structure, the optical scattering is negligibly small. Therefore, we used gel-inclusion technique to enhance the intensity of scattered signals, and clear, sharp 3D cross-sectional images of protein crystals were successfully observed. As the gel concentration was increased, the OCT signal intensity was increased. Using this method, the protein crystals surrounded by substantial amount of precipitates could be visualized, which is difficult by conventional light microscopy. The discrimination of protein and salt crystals was also demonstrated by the OCT signal intensity. The wavelength dependence of OCT imaging for protein crystal was examined at wavelength of 800-1700 nm regions. It was confirmed that the finest images were observed using 800 nm wavelength system.

285 mW high power, dissipative-soliton mode-locked, Er-doped fiber laser using carbon nanotube

Abstract: Dissipative soliton mode-locked Er-doped ultrashort pulse fiber laser using carbon nanotube polyimide film was investigated both experimentally and numerically. The highest output power of 285 mW was achieved for passively mode-locked nanotube fiber laser.

Three-dimensional ultrahigh-resolution optical coherence tomography imaging of lung tissues

Abstract: We have been investigating ultrahigh resolution optical coherence tomography (UHR -OCT) imaging of lung tissues using fiber based super continuum (SC) sources. The high pow er, low -noise, Gaussian shaped SC generated with ultrashort pulses and optical fibers at several wavelength regions were used as the broadband light sources for UHR -OCT. Since the lung con sists of tiny alveoli which are separeted by thin wall, the UHR -OCT is supposed to be effective for lung ima ging. The normal and disease d lung tissues were observed without invasive procedures to the lung itself. The clear images of alveoli were observed with index matching effect by saline. In this work, we investigated t he three -dimensional UHR -OCT imaging of lung structure. The lung s of rat s inflated with 10% formalin at 5 cmH 2 O, 15 cmH 2 O, and 20 cmH 2 O pressure were prepared as the sample for investigation of size and shape of the lung structure. T hese samp les were fixed with 10% formalin . T he inter alveolar sept a, thin walls separat ing the alveoli , w ere clearly observed. The difference of size and shape of alveoli and thier three -dimensional network was clearly observed from the UHR -OCT images. The clear images of alveoli were observed with index matching effect of 10% formalin . We investigated the wavelength dependence of 3D UHR -OCT image of lung structure at 800 nm, 1060 nm, and 1 700 nm wavelength regions . The 3D UHR -OCT images of structure of rat lung were clearly obser ved in all wavelength regions and wavelength dependence of imaging was discussed . Keywords: optical coherence tomography, super continuum, ultra -high resolution, lung

High-resolution quantum optical coherence tomography by broadband parametric fluorescence

Abstract: Quantum optical coherence tomography (QOCT) can achieve high-resolution imaging with dispersion tolerance by virtue of quantum entanglement. We demonstrate advantages of high-resolution QOCT by comparison with classical optical coherence tomography.

Generation of high-quality supercontinuum using ultrashort pulse fiber laser system with carbon nanotube

Abstract: Widely broadened high-quality supercontinuum is generated using high power soliton from ultrashort pulse fiber laser system with carbon nanotube. Temporal distribution of generated SC was directly observed using cross-correlated frequency resolved optical gating technique.

110 MHz soliton mode-locked high power Er-doped fiber laser using carbon nanotube polyimide film

Abstract: 110 MHz high repetition rate soliton mode-locked fiber laser with 40 mW high average power was demonstrated using carbon nanotube polyimide film. Super continuum at 1.7 um was generated and ultrahigh resolution OCT was demonstrated.