Tunable Sources

Electro-optically tunable single-frequency lasing from neodymium-doped lithium niobate microresonators

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Tunable light sources are a key enabling technology for many applications such as ranging, spectroscopy, optical coherence tomography, digital imaging and interferometry. For miniaturized laser devices, whispering gallery resonator lasers are a well-suited platform, offering low thresholds and small linewidths, however, many realizations suffer from the lack of reliable tuning. Rare-earth ion-doped lithium niobate offers a way to solve this issue. Here we present a single-frequency laser based on a neodymium-doped lithium niobate whispering gallery mode resonator that is tuned via the linear electro-optic effect. Using a special geometry, we suppress higher-order transverse modes and hence ensure single-mode operation. With an applied voltage of just 68 V, we achieve a tuning range of 3.5 GHz. The lasing frequency can also be modulated with a triangular control signal. The freely running system provides a frequency and power stability of better than Δ ( Read ...

Highly coherent, flat, and broadband time-stretched swept source based on extra-cavity spectral shaping assisted by a booster semiconductor optical amplifier

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We demonstrate a flat broadband time-stretched swept source based on extra-cavity spectral shaping. By adjusting the polarization-dependent gain profile and driving current of the booster optical amplifier (BOA), extra-cavity spectral shaping is optimized to generate output with a 1-dB bandwidth of ∼100 nm, 3-dB bandwidth of ∼140 nm and output power of ∼21.4 mW. The short-term and long-term stabilities are characterized. The average cross correlation of 183,485 round trips is 0.9997 with a standard deviation of 2×10 −5 , indicating high single-shot spectral similarity and high coherence. The noise floor of relative spectral energy jitter is −141.7 dB/Hz, indicating a high short-term spectral energy stability. The proposed highly stable flat broadband time-stretched swept source is applied to an optical coherence tomography (OCT) system. The axial resolution is 10.8 µm. The proposed swept source can serve as excellent light sources in ultra-fast co...

400 Hz Volume Rate Swept-Source Optical Coherence Tomography at 1060 nm Using a KTN Deflector

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In this Letter, a swept-source optical coherence tomography (SS-OCT) instrument employing an innovative scanning protocol for high-speed volumetric rate imaging is demonstrated. The optical source is a tunable laser based on a supercontinuum source pumped with femtosecond pulses, followed by a time-stretched delay fiber. The instrument is equipped with an ultra-fast lateral scanner, based on a KTN crystal, driven at 100 kHz. The letter proves the utility of combining an ultra-fast lateral scanner with an ultra-fast swept laser to provide A-scans at a repetition rate of 40 MHz and an unprecedented 3D-OCT volume acquisition rate of 400 Hz. ( Read Full Article )

Dual-comb based time-stretch optical coherence tomography for large and segmental imaging depth

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Optical coherence tomography based on time-stretch enables high frame rate and high-resolution imaging for the inertia-free wavelength-swept mechanism. The fundamental obstacle is still the acquisition bandwidth's restriction on imaging depth. By introducing dual-comb with slightly different repetition rates, the induced Vernier effect is found to be capable of relieving the problem. In our work, a dual-comb based time-stretch optical coherence tomography is proposed and experimentally demonstrated, achieving a 1.5-m imaging depth and 200-kHz A-scan rate. Moreover, about a 33.4-µm resolution and 25-µm accuracy are achieved. In addition, by adjusting the frequency detuning of the dual-comb, the A-scan rate can be further boosted to video-rate imaging. With enlarged imaging depth, this scheme is promising for a wide range of applications, including light detection and ranging. ( Read Full Article )

Optical Interference Measurement using High-Coherence Wavelength Swept Light Sources


Conventional contact measurement is replacing product shape inspection by non-contact optical measurement as part of the evolution of “smart factories”. Optical measurement includes various non-contact and non-destructive optical interferometry methods. Conventional methods feature accuracies ranging from nm to µm-order levels, but measurement distances are short, and high measurement accuracy is difficult to achieve due to meter-level measurement distances for targets with large surface areas. Our Wavelength swept light source with high coherence length supports accurate measurement over distances of several meters. This article explains the basic principles of OFDR as a typical optical interferometry measurement method and discusses the results of some actual measurement examples. A block gage with 2-µm or less surface level steps was measured with high accuracy by OFDR using this light source. To demonstrate long-distance measurement on relatively large ob...

Praevium Research Inc Receives NIH Grant for Next generation MEMS-VCSEL technology for ultra-low-cost dental and periodontal swept source optical coherence tomography imaging

Praevium Research Inc Received a 2022 NIH Grant for $275,001 for Next generation MEMS-VCSEL technology for ultra-low-cost dental and periodontal swept source optical coherence tomography imaging. The principal investigator is Vijaysekhar Jayaraman. Below is a summary of the proposed study. This proposal aims to enable a new generation of high-speed, low-cost, wavelength-flexible swept source optical coherence tomography (SS-OCT) imaging device technology targeting applications in dental imaging and based on microelectromechanical systems vertical cavity surface emitting lasers (MEMS-VCSELs) and planar lightwave circuits (PLCs). MEMS-VCSELs provide an unmatched combination of high and variable axial scan rate, dynamic single mode operation enabling long imaging range, and the potential for low-cost volume manufacturing through wafer scale fabrication and testing. The proposed effort involves a collaboration between Praevium Research, which pioneered MEMS-VCSELs for SS-OCT, and the Un...

Towards phase-stabilized Fourier domain mode-locked frequency combs

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Fourier domain mode-locked (FDML) lasers are some of the fastest wavelength-swept light sources, and used in many applications like optical coherence tomography (OCT), OCT endoscopy, Raman microscopy, light detection and ranging, and two-photon microscopy. For a deeper understanding of the underlying laser physics, it is crucial to investigate the light field evolution of the FDML laser and to clarify whether the FDML laser provides a frequency comb structure. In this case, the FDML would output a coherent sweep in frequency with a stable phase relation between output colours. To get access to the phase of the light field, a beat signal measurement with a stable, monochromatic laser is performed. Here we show experimental evidence of a well-defined phase evolution and a comb-like structure of the FDML laser. This is in agreement with numerical simulations. This insight will enable new applications in jitter-free spectral-scanning, coherent, synthetic THz-generation and as metrologic...

Praevium Research Receives NIH Grant for Swept source retinal visible optical coherence tomography using broadly tunable frequency doubling of NIR MEMS-VCSELs

Praevium Research Received a 2022 NIH Grant for $369,999 for Swept source retinal visible optical coherence tomography using broadly tunable frequency doubling of NIR MEMS-VCSELs. The principal investigator is Kirill Larin. Below is a summary of the proposed work. This proposal aims to develop a new generation of swept source optical coherence tomography (SS-OCT) technology operating at visible wavelengths near 530-600nm for retinal imaging and oximetry. This work will develop the first swept sources and SS-OCT systems in the visible wavelength range, enabling increased sensitivity, imaging range and speed compared to current visible spectral domain OCT (SD-OCT) systems with supercontinuum laser sources. Our approach uses novel dispersion engineered, periodically poled Lithium Niobate (PPLN) waveguides to achieve broadly tunable second harmonic generation of wavelength swept near infrared (NIR) laser emission from micro-electro-mechanical systems vertical cavity surface emitting las...

Visual field simulation using optical coherence tomography and optical coherence tomographic angiography

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Disclosed herein are methods for simulating the results of a visual field (VF) test using an optical coherence tomography (OCT) system. The disclosed methods may utilize structural information extracted from OCT image datasets, such as thickness measurements, or may utilize functional information, such as blood perfusion measurements, extracted from OCT angiography (OCTA) image datasets. Other embodiments may be described and claimed. ( Read Full Article )

Bonded tunable VCSEL with bi-directional actuation


A MEMS tunable VCSEL includes a membrane device having a mirror and a distal-side electrostatic cavity for displacing the mirror to increase a size of an optical cavity. A VCSEL device includes an active region for amplifying light. Then, a proximal-side electrostatic cavity is defined between the VCSEL device and the membrane device is used to displace the mirror to decrease a size of an optical cavity. ( Read Full Article )

Dual resonance akinetic dispersive cavity swept source at 900 kHz using a cFBG and an intensity modulator

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In this paper, a fast dual resonance akinetic optical swept source operating at 1550 nm is demonstrated. Instead of modulating the optical amplifier gain reported in our previous studies, here we employ a fiber intensity modulator as a mode-locking element. A chirped fiber Bragg grating is used to provide sufficient dispersion in the laser cavity. A tuning range of 25 nm is obtained for a sweep frequency of ≈900 kHz with a 6-dB drop-off in sensitivity at 2.6-mm optical path difference. ( Read Full Article )

Photonic integrated receiver


A wavelength tunable laser device includes a gain element positioned in an optical cavity that provides optical gain to an optical signal. A frequency shifter that generates a frequency shift as a function of time is positioned in the optical cavity. The optical cavity is configured so that a magnitude of the frequency shift as a function of time generated by the frequency shifter is substantially equal to a frequency separation of a cavity mode of the cavity such that an output of the cavity generates laser light having a wavelength that tunes as a function of time. ( Read Full Article )

Digitizer for an optical coherence tomography imager

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A digitizer and processor device for a swept-source optical coherence tomography (SS-OCT) imaging system, comprising: an input configured to receive an OCT signal; a control input configured to receive a k-clock signal; a combiner unit (130) receiving the OCT signal and the k-clock signal configured to output a composite signal; a digitizing unit (60) arranged to convert the composite signal into a digital composite signal (69); a data processing unit (70) arranged to determine a profile of optical density in a sample that generated the OCT signal based on the digital composite signal (69). 2012/0162659 June 2012 Goldberg 2015 ... ( Read Full Article )

Ultra-broadband wavelength-swept Ti:sapphire crystal fiber laser

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An ultra-broadband wavelength-swept laser (WSL) was generated using glass-clad Ti:sapphire crystal fiber as the gain media. Due to the low signal propagation loss of the crystal fiber, the swept laser has a tuning bandwidth of 250 nm (i.e., 683 nm to 933 nm) at a repetition rate of 1200 Hz. The steady-state and pulsed dynamics of the WSL were analyzed. The 0.018-nm instantaneous linewidth corresponds to a 3-dB coherence roll-off of 7 mm. When using the laser for swept-source optical coherence tomography, an estimated axial resolution of 1.8 µm can be achieved. ( Read Full Article )

Fourier Domain Mode Locked Laser and Its Applications

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The sweep rate of conventional short-cavity lasers with an intracavity-swept filter is limited by the buildup time of laser signals from spontaneous emissions. The Fourier domain mode-locked (FDML) laser was proposed to overcome the limitations of buildup time by inserting a long fiber delay in the cavity to store the whole swept signal and has attracted much interest in both theoretical and experimental studies. In this review, the theoretical models to understand the dynamics of the FDML laser and the experimental techniques to realize high speed, wide sweep range, long coherence length, high output power and highly stable swept signals in FDML lasers will be discussed. We will then discuss the applications of FDML lasers in optical coherence tomography (OCT), fiber sensing, precision measurement, microwave generation and nonlinear microscopy. ( Read Full Article )


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