Chilas develops off-the-shelf laser sources based on hybrid integration of Photonic Integrated Chips (PICs). Combining the high optical powers of semiconducting optical amplifiers (SOAs) with low-loss wavelength tunable mirror structures on Si3N4 PICs results in compact and robust tunable laser sources. These extended cavity diode lasers (ECDLs) exhibit unique characteristics like wide tuning ranges (>100 nm), ultra-narrow linewidths (<1 kHz) and high output powers. Here we present up to 162.5 mW of optical output power by combining two SOAs inside a single cavity, thereby scaling the output power without the need of additional optical amplification on the output port. The presented laser operates inside the telecom C-band, but the strategy can be tailored to other wavelengths like 850 nm, 780 nm and 690 nm, where Si3N4 plays a key role. This new generation of hybrid integrated ECDLs, exhibiting high optical output powers, wide wavelength tuning ranges and ultra narrow linewidths, opens up a wide range of applications.
SignificanceIn handheld laser speckle contrast imaging (LSCI), motion artifacts (MA) are inevitable. Suppression of MA leads to a valid and objective assessment of tissue perfusion in a wide range of medical applications including dermatology and burns. Our study shines light on the sources of these artifacts, which have not yet been explored. We propose a model based on optical Doppler effect to predict speckle contrast drop as an indication of MA.AimWe aim to theoretically model MA when an LSCI system measuring on static scattering media is subject to translational displacements. We validate the model using both simulation and experiments. This is the crucial first step toward creating robustness against MA.ApproachOur model calculates optical Doppler shifts in order to predict intensity correlation function and contrast of the time-integrated intensity as functions of applied speed based on illumination and detection wavevectors. To validate the theoretical predictions, computer simulation of the dynamic speckles has been carried out. Then experiments are performed by both high-speed and low-framerate imaging. The employed samples for the experiments are a highly scattering matte surface and a Delrin plate of finite scattering level in which volume scattering occurs.ResultsAn agreement has been found between theoretical prediction, simulation, and experimental results of both intensity correlation functions and speckle contrast. Coefficients in the proposed model have been linked to the physical parameters according to the experimental setups.ConclusionsThe proposed model provides a quantitative description of the influence of the types of illumination and media in the creation of MA. The accurate prediction of MA caused by translation based on Doppler shifts makes our model suitable to study the influence of rotation. Also the model can be extended for the case of dynamic media, such as live tissue.
Wavelength stabilization of external cavity lasers is a of key importance to exploit their sub-kHz intrinsic linewidth. In this work we demonstrate < 20 dB optical phase noise reduction at acoustic frequencies using a simple off-the-shelf electronic feedback loop. The novelty here is that we exploit an on-chip optical frequency discriminator (OFD) in Si3N4 (TriPleX), based on an aMZI with a path length difference of 1.4 m, having less than 10 dB loss. The used setup has a bandwidth of approximately 1 MHz, allowing for wavelength modulation depth in the order of tens of MHz.
We have developed a compact PIC external cavity laser consisting of a hybrid integrated InP gain section and SiN tunable mirror, with a superior combination of characteristics. The laser has shown a narrow linewidth < 5 kHz, broad tuning range of 140 nm over the S-, C- and L- band, from 1473 nm to 1612 nm, and high single mode output power of 60 mW. The laser frequency can be modulated at frequencies < 10 MHz having a wavelength modulation depth of < 20 MHz.
Progress has been made in laser speckle contrast imaging (LSCI) of microcirculatory blood flow for biology and medicine. However, the underlying reason for occurrence of movement artefacts (MA) that compromises effective use of LSCI remains largely unexplored. Here, employing a dual-camera setup for both speckle imaging and movement tracking, we validate our analytical model that is based on optical Doppler effect for predication of speckle contrast drop as a function of applied translational speed. We perform both motorized and handheld experiments where planar and scrambled wave illumination schemes have been examined. Experimental data points fairly match the theoretical predictions. These findings indicate that the vision-based movement detection during handheld LSCI is a preferable option. Moreover, the proposed analytical model is promising for further exploration of MA in order to realize a reliable handheld LSCI.
Movement artefacts distort handheld measurements of laser speckle contrast imaging (LSCI). Enabling a robust LSCI in handheld use brings convenience for both patients and clinical staff. However, there is a lack of a comprehensive model that can predict and potentially compensate the amount of movement artefacts occurring during a handheld LSCI measurement. Here, we propose an analytical-numerical model based on the optical Doppler effect for handheld LSCI in case of translation on a high scattering static surface. The model incorporates the type of illumination as well as the imaging geometry by taking into account the spread of wavevectors for illumination and detection. We validate the theoretical model by simulated dynamic speckles and experiments for the cases of (1) planar and spherical waves illumination and (2) scrambled waves illumination. Results of the speckle simulation are in agreement with predictions of the numerical model for semi-circular form of the density functions of the incoming and outgoing wavevectors.
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