We propose and demonstrate a programmable high-speed, frequency-swept laser for swept-source optical coherence
tomography (SS-OCT). This new technique is based on Vernier effect of two pieces of Fabry-Perot electro-optic
modulators. This technique offers a non-mechanical optical filter with high resolution and wide tuning range. By
applying it to a Fourier domain mode-locked laser, such sweeps are generated. The Vernier effect filter can be modulated
by arbitrary wave forms, thus this laser source can eliminate the rescaling process which is the main bottle-neck of the
operation time in SS-OCT by applying frequency sweep to equidistant spacing in frequency. Effective repetition
frequencies of 100kHz~1MHz are demonstrated with a tuning range of 17THz (140nm) at 1550nm center wavelength.
OCT imaging of <i>in vivo </i>human sweat duct with A-line rate of 100kHz and 300kHz are also demonstrated. The resolution
of 12μm~ is realized without rescaling process. We present an analysis which suggests design approaches for
We review here the historical development of an optical comb generation technology. In 1991, an optical comb as wide as 1 THz was generated for the first time for the purpose of the optical frequency measurement, and the difference frequency between two lasers was measured. The measured difference frequency was only 500 GHz at that time. However, measurable difference frequency has been increased by thousand times in nine years. Finally, absolute frequency measurement of laser has become possible.
In-situ patterning of nano-scale Zn dots and lines has been succeeded by photodissociation of a gas-phase diethylzinc in optical near-field. By using an optical fiber probe with the aperture diameter of 60 nm, dots with full width at half maximum of approximately 60 nm and approximately 70 nm, closely separated by 100 nm were fabricated. It implies that finer patterns of a metal can be fabricated by using optical fiber probe with smaller aperture, allowing control of the size and position of nano-scale structures. Consequently, the technique is the one of most suitable for nano-photonic device fabrication.
We applied a super-wavelength apertured fiber probe to phase-change recording/readout. Though the fiber probe had a super-wavelength aperture, the spot size at the aperture was as small as 150 nm (< λ/5). An as-deposited SiO<SUB>2</SUB>/AgInTe<SUB>2</SUB>/glass substrate was used as a recording medium. For recording, a laser diode with a pulsewidth of 2 μs (λ=850 nm) was used. By scanning the probe for reading, we obtained resolved images of the recorded dot with a width of 250 nm.
We propose and demonstrate a new optical near-field slider with a planar apertured probe array for optical memory. The slider was fabricated by utilizing anisotropical etching of a silicon membrane and anodic bonding of a silicon membrane and glass substrate. We also present for the first time a subwavelength-sized phase-change recording/reading by using the planar apertured probe array. Apertures were fabricated at the bottom end of the pyramidal grooves. A SiO<SUB>2</SUB>/AgInTe<SUB>2</SUB>/glass substrate was used as the recording medium. By scanning the planar apertured probe array, we obtained resolved images with line width of 250 nm.
ZnO nanodots have been successfully fabricated on a (001) Al<SUB>2</SUB>O<SUB>3</SUB> substrate by photo-enhanced chemical vapor deposition (PE-MOCVD) combined with near-field optical technology. The optical near-field generated from an optical fiber probe tip allowed ZnO dots to selectively grow on the irradiated substrate surface, with a size smaller than the wavelength of the light source (λ=244 nm). The crystallinity and composition of ZnO were evaluated from planar films using x-ray diffraction analysis, optical transmittance and x-ray photoelectron spectroscopy. The planar films were grown using PE-MOCVD with a direct irradiation by an ultraviolet light source without probe tip. Above a deposition temperature of 150°C, stoichiometric ZnO films (R O:Zn=1), strongly the c-axis oriented and exhibiting a band gap of about 3.3 eV were obtained.
We have successfully fabricated an extremely high throughput probe for near-field optics introducing a triple-tapered structure to reduce the loss in a tapered core, to focus the light, and to excite effectively the HE<SUB>11</SUB> mode. A focused ion beam and selective chemical etching were used for fabrication. Over 100 times increase in the throughput of the triple-tapered probe with the aperture diameter D < 100 nm was realized in comparison with the conventional single-tapered probe. Furthermore, due to the third taper with a small cone angle, the localized optical near-field on the triple-tapered probe with D equals 60 nm has been confirmed.
We proposed and demonstrated a novel silicon planar apertured probe array as a near-field optical head for optical memory. In comparison with the conventional fiber probe, the apertured probe array has durability, higher read-out data transmission rate and it allows us to overcome difficulty of precise mechanical tracking of the single fiber probe because it can be used for reading data as a surface information. The probe array was fabricated by utilizing wet etching technique of a silicon wafer. Inverted pyramids were formed on the silicon plate, and apertures were fabricated at the tops of the inverted pyramids. An aperture with a size less than 100nm was realized. By scanning the probe array we obtained resolved images of the lines in corrugation which was made on a metal thin film. The observed line width was 250 nm. Furthermore, we put spherical lens inside the inverted pyramids to focus the propagating light at the apertures automatically. The near- field intensity at an aperture was 16 times larger than that without a spherical lens.
A waveguide type optical frequency comb generator was developed at 1.5 micrometers wavelength region by utilizing a waveguide type phase modulator. It was confirmed that the envelope of sideband spectrum had a width of 4.3 THz. A multiplex optical frequency comb generation system was assembled, and modulation sidebands were generated on a space as wide as 10 THz. A heterodyne signal between two OFCs whose central frequencies are separated as large as).4 THz was detected. By utilizing the signal, a frequency offset locked loop system was realized between the two OFCs.
For highly accurate optical frequency measurement in 1.5 micrometers wavelength region, an optical frequency comb (OFC) generator was realized by using a high frequency LiNbO<SUB>3</SUB> electro-optic phase modulator which was installed in a Fabry-Perot cavity. By using the OFC generator, we demonstrated the frequency difference measurement up to 0.5 [THz] with a signal-to-noise ratio higher than 61 [dB], and the heterodyne optical phase locking with a heterodyne frequency of 0.5 [THz] in which the residual phase error variance was less than 0.01 [radian<SUP>2</SUP>]. The maximum measurable frequency difference, which was defined as a sideband frequency with the signal-to-noise ratio of 0 [dB], was estimated to be 4 [THz].