Takuji Amano

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.

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.

Reconstruction of three-dimensional structure of an extracted tooth by OFDR-OCT

We measure an extracted tooth by OFDR-OCT. Three-dimensional reconstruction is performed against OCT images. Non-telecentric scanning is reproduced in three-dimensions and refractive image distortions are corrected by ray tracing.

Enhancement of OFDR-OCT sensitivity using semiconductor optical amplifier

We propose a new method to increase the sensitivity of Optical Coherence Tomography (OCT) beyond the conventional shot noise limit using optical amplifiers. Criterion for effective use of optical amplifiers for OCT is discussed. Enhancement of OCT images is demonstrated with optical frequency domain reflectometry (OFDR) OCT.

Discretely swept optical-frequency domain imaging toward high-resolution, high-speed, high-sensitivity and long-depth-range

We have been developing a unique discretely swept optical frequency domain imaging (OFDI) using superstructured-grating distributed Bragg reflector (SSG-DBR) lasers. To increase resolution, four SSG-DBR lasers are being developed to obtain spectral coverage of 160 nm in total. To increase speed of D-OFDI imaging, simultaneous scanning of multiple sources with a parallel OFDI system and unique transversal scanning D-OFDI have been demonstrated. Introduction of an optical amplifier can increase sensitivity beyond the conventional shot noise limit. A deep 12 mm depth range has been demonstrated with the wavelength interval of 0.05 nm.

High-speed optical-frequency domain imaging by one frame imaging within one single frequency sweep

We demonstrate a novel imaging technique for high-speed optical-frequency domain imaging (OFDI)with a discretely swept laser source. In this technique, one frame of OCT data can be acquired within a single frequency sweep. Tomographic images consisting of 1550 A-lines are obtained at 21 frames per second. The method is explained and experimental results are demonstrated.