We present a novel hybrid 800 nm laser with a wide tuning range, high optical power and ultra-narrow linewidth with ⪆kHz tuning speeds and a small footprint. Tunable, narrow linewidth hybrid lasers around 800nm serve as an attractive choice for e.g. OCT, LIDAR and atomic transition locking in e.g. atomic clocks. The laser has a microring resonator based optical cavity. The laser has a tuning range of 45 nm and a maximum output power of 5 dBm. The intrinsic linewidth of the laser is measured at 22 kHz.
Low NEP balanced receivers generally do not result in better sensitivity in a shot-noise-limited swept source OCT system. However, there is an advantage if RIN is significant. A lower NEP, even in the shot-noise-limited case, does allow for lower reference arm powers. This, in turn, reduces fixed pattern artifact signals caused by stray optical component reflections inside a swept source laser cavity. An NEP reduction of √10 allows the reference power to be reduced 10 dB while maintaining SNR. This reduces the pattern to noise ratio by 10 dB because pattern noise is directly detected (20 dB scaling per decade reference power), whereas the image signal is heterodyne detected (10 dB scaling per decade of reference power). We present sensitivity and fixed pattern measurements taken with six commercial balanced receivers, including an APD receiver. We also present an NEP survey of 23 commercial receivers over a wide range of bandwidths and transimpedances.
In this communication, we evaluate the suitability of Master-Slave (MS) optical coherence tomography (OCT) for processing of interferograms generated by an interferometer driven by an akinetic, electrically-tunable swept source from Insight with an ultra-large instantaneous coherence length. The akinetic source is programmed to sweep linearly, but within the sweep, at predictable times, the laser tuning introduces invalid regions in the interferogram, which are normally removed post-acquisition using a pre-calibration file. This makes sure that any optical frequency component is used once only and enables correct operation of a Fourier transform (FT). A FT applied to an unprocessed emitted spectrum leads to wide and numerous peaks in the A-scan. MS processing was introduced to avoid the necessary corrections demanded by conventional FT signal processing or its derivatives. The MS procedure consists of comparing photo-detected signals at the output of two interferometers, a Slave and a Master interferometer. The MS method was advanced along two avenues, either by using (i) electricallygenerated master signals (making use of the same interferometer twice) or (ii) optically-generated master signal via a recently introduced MS down-conversion procedure. We apply both avenues to the Insight source. Approach (i) tests the MS principle as an alternative to the Insight file correction while (ii) demonstrates near coherencelimited operation at a large axial range (>80 mm) for which a too-high sampling rate digitizer would have been needed. In this communication, we evaluate for the first time the suitability of the MS procedure to OCT measurements performed with the akinetic swept source commercialized by Insight. Two modalities are evaluated to implement the MS processing, based on: (i) digital generation of the master signals using the OCT interferometer and (ii) down conversion using a second interferometer driven by the swept source.
Studies have proven the relationship between cutaneous vasculature abnormalities and dermatological disorders, but to image vasculature noninvasively in vivo, advanced optical imaging techniques are required. In this study, we imaged a palm of a healthy volunteer and three subjects with cutaneous abnormalities with photoacoustic tomography (PAT) and optical coherence tomography with angiography extension (OCTA). Capillaries in the papillary dermis that are too small to be discerned with PAT are visualized with OCTA. From our results, we speculate that the PA signal from the palm is mostly from hemoglobin in capillaries rather than melanin, knowing that melanin concentration in volar skin is significantly smaller than that in other areas of the skin. We present for the first time OCTA images of capillaries along with the PAT images of the deeper vessels, demonstrating the complementary effective imaging depth range and the visualization capabilities of PAT and OCTA for imaging human skin in vivo. The proposed imaging system in this study could significantly improve treatment monitoring of dermatological diseases associated with cutaneous vasculature abnormalities.
We demonstrate a scheme for the interrogation of arrays of FBG sensors based on a Swept Laser Distributed Sensing
system which can achieve 1000 sensors or more in a single fiber, while retaining the sensitivity and repeatability
expected with FBG sensors of better than 0.5 μepsilon and 0.05 C. The system utilizes an ‘akinetic’ wavelength swept source
and an arrival time-dependent detection approach to allow potentially 1000s of very low reflectivity FBGs to be
monitored via a form of Wavelength-to-Time Domain Reflectometry. We demonstrate the interrogation of 250 gratings
in a system architecture designed to support 1000 gratings.
The short-term jitter and longer-term wander of the frequency sweep profile of a Vernier-Tuned Distributed Bragg Reflector (VT-DBR) laser at 1550 nm used in OCT applications is characterized in this work. The VT-DBR has demonstrated success in source-swept OCT (SSOCT), performing both intensity [1] and phase-sensitive [2] OCT. The purpose of this paper is to investigate one of the unique aspects of the VT-DBR laser that makes it successful in OCT: the stability of the linear optical frequency sweep of the source. Jitter measurements of the optical frequency sweep are recorded using a 3-cavity 100 GHz free spectral range (FSR) solid etalon. A gas absorption reference cell is used for wander characterization. We report that the VT-DBR jitters by no more than 82 MHz RMS in optical frequency while sweeping at an 8 kHz repetition rate. Longer-term wander provides insight into the accuracy of the VT-DBR selfcalibration routine which produces an intrinsically linear optical frequency sweep. Over an 8-hour data collection period, the system maintains a linear sweep with an optical frequency step of 105 MHz per 2.5 ns with +/- 3 kHz per 2.5 ns (+/- 0.03%) peak-to-peak deviation. We find that the absolute frequency drifts by 325 MHz (2.6pm) over the same 8- hour period with ambient temperature fluctuations of no more than 5 °C. Results show that using calibration with a gas reference cell, picometer absolute wavelength accuracy of the laser can be achieved at any time for a single sweep. Stability and accuracy limits are thought to be due to electronic drive circuitry in the current design.
Vernier-tuned distributed Bragg reector (VT-DBR) lasers in source swept OCT (SS-OCT) have previously been demonstrated at 1550 nm and 1600 nm.1 Many OCT applications prefer 1310 nm operation. This work describes the first demonstration of a VT-DBR operating at 1310 nm in the O-band, ideal for use in SS-OCT. This paper addresses the device characterization of such lasers, illustrating they are capable of fast amplitude and frequency sweeps necessary for SS-OCT applications. Equivalent circuit models for each of the five ports are also created to determine their electrical parasitics. Narrow linewidths of the VT-DBR indicate coherence length of several centimeters are possible during fast wavelength sweeps.
We demonstrate a new swept-wavelength laser for optical coherence tomography using a monolithic semiconductor
device with no moving parts. The laser is based on a Vernier-Tuned Distributed Bragg Reflector (VTDBR) structure. We
show highly-linear sweeps at 200 kHz sweep repetition rates, with peak output power of 20 mW. Using a test
interferometer, we demonstrate point-spread functions with 45-55 dB dynamic range. The source provides long
coherence length (> 40mm) at up to 200 kHz sweep rates. The laser system has sufficient linearity in optical frequency
and stability over time to provide an electronic sample trigger clock (an Electronic K-Clock) that denotes equal optical
frequency intervals during the sweep. The laser tuning mechanism is all-electronic, easily adjustable and programmable.
We demonstrate both flat and Gaussian power vs. wavelength profiles, programmable sweep rates with the same device,
and an adjustable duty cycle of up to 85% at full speed. Because the laser is a monolithic semiconductor structure based
on reliable, wafer-scale processes, the manufacturing cost of the laser will decrease rapidly in volume production.
A novel swept-wavelength laser for optical coherence tomography (OCT) using a monolithic semiconductor device with
no moving parts is presented. The laser is a Vernier-Tuned Distributed Bragg Reflector (VT-DBR) structure exhibiting a
single longitudinal mode. All-electronic wavelength tuning is achieved at a 200 kHz sweep repetition rate, 20 mW
output power, over 100 nm sweep width and coherence length longer than 40 mm. OCT point-spread functions with 45-
55 dB dynamic range are demonstrated; lasers at 1550 nm, and now 1310 nm, have been developed. Because the laser's
long-term tuning stability allows for electronic sample trigger generation at equal k-space intervals (electronic k-clock),
the laser does not need an external optical k-clock for measurement interferometer sampling. The non-resonant, allelectronic
tuning allows for continuously adjustable sweep repetition rates from mHz to 100s of kHz. Repetition rate
duty cycles are continuously adjustable from single-trigger sweeps to over 99% duty cycle. The source includes a
monolithically integrated power leveling feature allowing flat or Gaussian power vs. wavelength profiles. Laser
fabrication is based on reliable semiconductor wafer-scale processes, leading to low and rapidly decreasing cost of
manufacture.
InPhase Technologies is developing a holographic data storage drive with a target lifetime of at least 10 years. The laser
light source is a key component of the drive. Based on the limited lifetimes of early blue laser diodes, we made the laser a
modular and replaceable unit to minimize drive downtime and insure that the overall HDS drive meets the long lifetime goal.
Previously, we reported on one part of the laser module, the blue external cavity diode laser (ECLD) that we co-developed
with Nichia Corporation [1]. In this paper we report on the rest of the laser module, which prepares coherent, wavelength
tunable light from the ECLD for insertion into an HDS drive.
Nichia and InPhase have co-developed a Blue ECLD that works successfully in InPhase's Tapestry Holographic Data
Storage (HDS) drive [1]. In order to commercialize the HDS, InPhase and Nichia have moved into a production
development phase. In this paper we report on recent, dramatic improvements in ECLD reliability.
We consider a binary mixture of two overlapping Bose- Einstein condensates in two different hyperfine states of 87Rb with nearly identical magnetic moments. Such a system has been simply realized through application of radio frequency and microwave radiation which drives a two-photon transition between the two states. The nearly identical magnetic moments afford a high degree of spatial overlap, permitting a variety of new experiments. We discuss some of the conditions under which the magnetic moments are identical, with particular emphasis placed on the requirements for a time-averaged orbiting potential magnetic trap.
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