Category: Tunable Sources

We are developing a wide wavelength-swept fiber laser based on a dispersion tuning method for application to swept-source optical coherence tomography (SS-OCT) imaging. The tuning range of the laser is about 140 nm and the output power is 8 mW on average. We successfully obtained the in vivo OCT picture of the human skin at 1-kHz sweep rate.

Optical coherence tomography (OCT) in the 1060nm range is interesting for in vivo imaging of the human posterior eye segment (retina, choroid, sclera), as it permits a long penetration depth. Complementary to structural images, polarization-sensitive OCT (PS-OCT) images visualize birefringent, polarization-maintaining or depolarizing areas within the sample. This information can be used to distinguish retinal layers and structures with different polarization properties. High imaging speed is crucial for imaging ocular structures in vivo in order to minimize motion artifacts while acquiring sufficiently large datasets. Here, we demonstrate PS-OCT imaging at 350 kHz A-scan rate using a two-channel PS-OCT system in ...

The paper present the design and the construction of a novel 3-D micromirror optical scanner for use in a swept-source optical coherence tomography (SS-OCT) that is based on external-cavity tunable lasers. The 3D rotating octagonal micromirror consists of a rotary platform, onto which the micromirrors are assembled in an octagonal configuration. The 3D optical scanner was constructed in a two stage process. It was first fabricated using surface micromachining PolyMUMPs fabrication process, and then assembled using a robotic micromanipulator system. The microassembly process is a robotic-based process based on the PKMIL system.The methodology to construct the micromirror and the ...

Polarization sensitive optical coherence tomography (PS-OCT) is a functional imaging method that provides additional contrast using the light polarizing properties of a sample. This manuscript describes PS-OCT based on ultrahigh speed swept source / Fourier domain OCT operating at 1050nm at 100kHz axial scan rates using single mode fiber optics and a multiplexing approach. Unlike previously reported PS-OCT multiplexing schemes, the method uses a passive polarization delay unit and does not require active polarization modulating devices. This advance decreases system cost and avoids complex synchronization requirements. The polarization delay unit was implemented in the sample beam path in order to simultaneously ...

We present detailed investigations of chromatic polarization effects, caused by fiber spools used in FDML lasers and buffering spools for rapidly wavelength swept lasers. We introduce a novel wavelength swept FDML laser source, specially tailored for polarization sensitive optical coherence tomography (OCT) which switches between two different linear polarization states separated by 45°, i.e. 90° on the Poincaré sphere. The polarization maintaining laser cavity itself generates a stable linear polarization state and uses an external buffering technique in order to provide alternating polarization states for successive wavelength sweeps. The design of the setup is based on a comprehensive analysis ...

The Photonics Laboratories of Nippon Telegraph and Telephone Corporation (NTT) in Japan have developed a new swept light source operating at an A-line rate of 200 kHz. The swept light source was demonstrated at the 2012 BiOS exhibition, and received a favorable reception from OCT-relatedengineers. The swept light source is based on a Littman-Metcalf external cavity laser diode that incorporates an electro-optic (EO) KTN (KTa1-xNbxO3) deflector. The KTN deflector provides a fast and fairly large light deflection as a result of a non-uniform electric field generated by injected carriers. The deflector is a promising candidate for application to light sources ...

We propose the lateral integration scheme of an MEMS tunable VCSEL and a slow light amplifier for increasing single-mode power. The modeling result predicts the maximum output power over several tens mW for a compact slow light amplifier monolithically integrated with an MEMS VCSEL. In addition, the efficient excitation of slow light in the integrated slow light amplifier is shown. A high coupling efficiency and a radiation angle from the amplifier are almost constant during wide wavelength tuning

We present a detailed analysis of the optical field dynamics in a Fourier domain mode-locked (FDML) laser. We employ a numerical simulation based on the FDML evolution equation, describing the propagation of the optical light field. The temporal evolution of the instantaneous power spectrum at different points in the laser cavity is investigated. The results are carefully validated against experimental data, yielding good agreement. Deeper insight is gained into the role of the physical effects governing FDML dynamics, such as gain recovery and linewidth enhancement in the semiconductor optical amplifier, dispersion and self-phase modulation in the optical fiber, and the ...

A tunable laser includes an optical gain medium, a first resonator, a periodically tunable optical filter, and a second resonator in which light of a laser wavelength exhibits a round trip time T. The optical filter is arranged between the first resonator and the second resonator and is tuned with a period t. The period t is governed by t=(n/m) T, where n and m are integers and m/n is not an integer.

Optical coherence tomography (OCT) in the 1060nm range is interesting for in vivo imaging of the human posterior eye segment (retina, choroid, sclera) due to low absorption in water and deep penetration into the tissue. Rapidly tunable light sources, such as Fourier domain mode-locked (FDML) lasers, enable acquisition of densely sampled three-dimensional datasets covering a wide field of view. However, semiconductor optical amplifiers (SOAs)-the typical laser gain media for swept sources-for the 1060nm band could until recently only provide relatively low output power and bandwidth. We have implemented an FDML laser using a new SOA featuring broad gain bandwidth ...

A new light source for swept-source optical coherence tomography (SSOCT) is presented, namely, an external-cavity LD equipped with a KTN electro-optic deflector. The KTN deflector is unique in being very fast and simultaneously providing an appreciable deflection caused by injected carriers.Being free frommechanical resonance, the 1.3 μm laser exhibits a scanning range of almost 80 nm up to 200 kHz with a + 400 V deflector driving voltage. Preliminary SS-OCT images of a human fingernail and finger skin have been obtained using the swept light source.

We demonstrate the acquisition of densely sampled wide-field 3D OCT datasets of the human retina in 0.3s. This performance is achieved with a multi-MHz Fourier domain mode-locked (FDML) laser source operating at 1050nm. A two-beam setup doubles the 3.35MHz laser sweep rate to 6.7MHz, which is 16x faster than results achieved with any non-FDML source used for retinal OCT. We discuss two main benefits of these high line rates: First, large datasets over an ultra-wide field of view can be acquired with a low probability of distortions. Second, even if eye movements occur, now the scan rate ...

This paper demonstrates new wavelength swept light source technology, MEMS tunable VCSELs, for OCT imaging. The VCSEL achieves a combination of ultrahigh sweep speeds, wide spectral tuning range, flexibility in sweep trajectory, and extremely long coherence length, which cannot be simultaneously achieved with other technologies. A second generation prototype VCSEL is optically pumped at 980nm and a low mass electrostatically tunable mirror enables high speed wavelength tuning centered at ~1310nm with ~110nm of tunable bandwidth. Record coherence length >100mm enables extremely long imaging range. By changing the drive waveform, a single 1310nm VCSEL was driven to sweep at speeds from ...

MEMS tunable vertical cavity surface emitting laser (MEMS-VCSEL) development, over the past two decades, has primarily focused on communications and spectroscopic applications. Because of the narrow line-width, single-mode operation, monolithic fabrication, and high-speed capability of these devices, MEMS-VCSELs also present an attractive optical source for emerging swept source optical coherence tomography (SSOCT) systems. In this paper, we describe the design and performance of broadly tunable MEMS-VCSELs targeted for SSOCT, emphasizing 1310nm operation for cancer and vascular imaging. We describe the VCSEL structure and fabrication, employing a fully oxidized GaAs/AlxOy mirrors in conjunction with dielectric mirrors and InP-based multi-quantum well ...

In this work the use of two identical QD SOAs to enhance the performance of swept laser system for OCT applications is discussed, resulting in an increase in bandwidth up to 94nm. The combination of GaAs based QD SOAs and InP based QW SOAs for realizing broad bandwidth sources for OCT system is described. For the swept laser source a 154nm spectral bandwidth from 1193nm to 1347nm and an average power of 8mW is obtained and for the filtered ASE source a 225 nm bandwidth is demonstrated