Hideaki Hiro-Oka

Fourier domain optical coherence tomography using optical demultiplexers imaging at 60,000,000 lines/s.

We describe high-speed Fourier domain optical coherence tomography (OCT) using optical demultiplexers (ODs) for spectral dispersion. The OD enables separation of a narrow spectral band of 14 GHz (0.11 nm) from a broadband incident light at 256 different frequencies in 25.0 GHz intervals centered at 192.2 THz (1559.8 nm). OCT imaging of 60,000,000 axial scans per second was achieved through parallel signal acquisition using 256 balanced photoreceivers to simultaneously detect all the output signals from the ODs in a Fourier domain OCT system. OCT imaging at a 16 kHz frame rate, 1100 A-lines per frame, 3 mm depth range, and 23 microm resolution was demonstrated using a resonant scanner for lateral scanning.

Spectral domain optical coherence tomography of multi-MHz A-scan rates at 1310 nm range and real-time 4D-display up to 41 volumes/second

An ultrafast frequency domain optical coherence tomography system was developed at A-scan rates between 2.5 and 10 MHz, a B-scan rate of 4 or 8 kHz, and volume-rates between 12 and 41 volumes/second. In the case of the worst duty ratio of 10%, the averaged A-scan rate was 1 MHz. Two optical demultiplexers at a center wavelength of 1310 nm were used for linear-k spectral dispersion and simultaneous differential signal detection at 320 wavelengths. The depth-range, sensitivity, sensitivity roll-off by 6 dB, and axial resolution were 4 mm, 97 dB, 6 mm, and 23 μm, respectively. Using FPGAs for FFT and a GPU for volume rendering, a real-time 4D display was demonstrated at a rate up to 41 volumes/second for an image size of 256 (axial) × 128 × 128 (lateral) voxels.

Optical frequency-domain reflectometry with a rapid wavelength-scanning superstructure-grating distributed Bragg reflector laser

Superstructure-grating distributed Bragg reflector lasers are particularly suited for optical frequency-domain reflectometry optical-coherence tomography with wide wavelength tunability and frequency agility. We report theoretical estimates of and experimental results for the data acquisition speed, the observable depth range, the resolution, and the dynamic range of an optical frequency-domain reflectometry system that uses a superstructure-grating distributed Bragg reflector laser whose wavelength can be tuned from 1533 to 1574 nm with a tuning speed of 10 micros/0.1-nm step.

Full-range imaging of eye accommodation by high-speed long-depth range optical frequency domain imaging

We describe a high-speed long-depth range optical frequency domain imaging (OFDI) system employing a long-coherence length tunable source and demonstrate dynamic full-range imaging of the anterior segment of the eye including from the cornea surface to the posterior capsule of the crystalline lens with a depth range of 12 mm without removing complex conjugate image ambiguity. The tunable source spanned from 1260 to 1360 nm with an average output power of 15.8 mW. The fast A-scan rate of 20,000 per second provided dynamic OFDI and dependence of the whole anterior segment change on time following abrupt relaxation from the accommodated to the relaxed status, which was measured for a healthy eye and that with an intraocular lens.

Two pion correlations as a possible experimental probe for disoriented chiral condensates

Abstract We discuss two-pion correlations as a possible experimental probe into disoriented chiral condensates. In particular, we point out that the iso-singlet squeezed states of the BCS type have peculiar two-particle correlations in the back-to-back and the identical momentum configurations which should be detectable experimentally. We motivate the examination of the squeezed state by showing that such state naturally appears in a final stage of nonequilibrium phase transitions via the parametric resonance mechanism proposed by Mrowczynski and Muller.

Numerical Compensation of Dispersion Mismatch in Discretely Swept Optical-Frequency-Domain-Reflectometry Optical Coherence Tomography

We propose a numerical method to compensate dispersion mismatch in optical coherence tomography (OCT) based on optical-frequency-domain reflectyometry (OFDR). Dispersion mismatch causes phase distortion in interferograms depending on wavelength and results in a loss of resolution. We introduce a method to perform the numerical compensation directly to experimental interferograms in real space. Experimental tests are performed for the case of the Mach–Zehnder type OFDR-OCT using a super-structured-grating distributed-Bragg-reflector (SSG-DBR) laser, in which the wavenumber of the optical source is swept discretely by equal interval. It is shown that the method is effective to improve images for layered transparency sheets. We also apply the method to OFDR-OCT imaging of a human nail.

Tissue imaging by OFDR-OCT using an SSG-DBR laser

Optical coherence tomography (OCT) system based on optical frequency-domain reflectometry (OFDR) has been developed using a superstructure-grating distributed Bragg reflector (SSG-DBR) laser, which can tune the wavelength from 1533 to 1574 nm stepwise with tuning speed of 10micro s per 0.1 nm step. Theoretical expressions of OCT imaging by the discretely swept OFDR-OCT system are described. OFDR-OCT images are demonstrated for a few biological tissues; an extracted canine, human skin, human nail, and anterior segment of enucleated porcine eye.

Improved sensitivity of optical frequency domain reflectometry-optical coherence tomography using a semiconductor optical amplifier

We demonstrate an approach to enhance the optical frequency domain reflectometry (OFDR)-optical coherence tomography (OCT) sensitivity using a semiconductor optical amplifier (SOA) and a superstructure grating-distributed Bragg reflector (SSG-DBR) laser. We find that the sensitivity of the OCT images of an extracted canine tooth increases as a function of SOA injection current due to amplification through stimulated emission. At the injection current of 150 mA, the sensitivity of the OCT image is increased to a factor of 22.8 dB when compared to the unamplified OCT. Furthermore, an 18 µm axial resolution of the OCT in dental tissue is achieved using the discrete wavelength-swept SSG-DBR laser with an axial scan rate of 0.25 kHz. The observed results suggest that the optical amplification by SOA can significantly enhance the sensitivity of the OFDR-OCT system with a high-resolution.

OFDR with an SSG-DBR laser

Recently, frequency-domain (FD) -optical-coherence-tomography (OCT) methods have been investigated extensively as more efficient and sensitive system compared with conventional time-domain (TD) -OCT. Superstructure-grating-distributed-Bragg-reflector (SSG-DBR) lasers are particularly suited for optical-frequency-domain-reflectometry (OFDR) -OCT with its wide wavelength tunability and frequency agility. We have made a discrete frequency OFDR-OCT system with an SSG-DBR laser, which can tune the wavelength from 1533 to 1574 nm with tuning speed of 10μs per 0.1 nm step. The theoretical expression of the discrete frequency OFDR-OCT is given. Utilizing near-transparent nature of enamel of teeth in the wavelength region of the SSG-DBR laser and long object range of the OFDR-OCT, we have carried out OCT measurements on teeth. Experimental OCT imaging of a canine are reported here.

A method of improving scanning speed and resolution of OFDR-OCT using multiple SSG-DBR lasers simultaneously

The superstructured-grating distributed-Bragg-reflector laser is a small (shorter than 1 mm in length) and relatively cheap swept source for optical-frequency-domain- reflectometry optical coherence tomography (OFDR-OCT), which practically enables use of multiple sources in a single OCT system. Simultaneous scanning of multiple sources over different wavelength regions and at different wavelength values in the same wavelength region enable improvement of the resolution and scanning speed, respectively. Those improvements have been demonstrated using C-band and L-band SSG-DBR sources.