Spectral linewidth analysis of semiconductor hybrid lasers with feedback from an external waveguide resonator circuit

We present a detailed analysis of a semiconductor hybrid laser exploiting spectral control from an external photonic waveguide circuit that provides frequency-selective feedback. Based on a spatially resolved transmission line model (TLM), we have investigated the output power, emission frequency, and the laser spectral linewidth. We find that, if the feedback becomes weaker, the spectral linewidth is larger than predicted by previous models that are based on a modified mean-field approximation, even if these take a strong spatial variation of the gain into account. The observed excess linewidth is caused by additional index fluctuations that are associated with strong spatial gain variations

Ultra-narrow linewidth hybrid integrated semiconductor laser

We demonstrate a hybrid integrated and widely tunable diode laser with an intrinsic linewidth as narrow as 40 Hz, achieved with a single roundtrip through a low-loss feedback circuit that extends the cavity length to 0.5 meter on a chip. Employing solely dielectrics for single-roundtrip, single-mode resolved feedback filtering enables linewidth narrowing with increasing laser power, without limitations through nonlinear loss. We achieve single-frequency oscillation with up to 23 mW fiber coupled output power, 70-nm wide spectral coverage in the 1.55 $\mu$m wavelength range with 3 mW output, and obtain more than 60 dB side mode suppression. Such properties and options for further linewidth narrowing render the approach of high interest for direct integration in photonic circuits serving microwave photonics, coherent communications, sensing and metrology with highest resolution.Comment: 13 pages, and 11 figure

Hybrid integrated semiconductor lasers with silicon nitride feedback circuits

Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth as well as compatibility for embedding into integrated photonic circuits are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback from low-loss silicon nitride (Si3N4 in SiO2) circuits, to provide sub-100-Hz-level intrinsic linewidths, up to 120 nm spectral coverage around 1.55 um wavelength, and an output power above 100 mW. We show dual-wavelength operation, dual-gain operation, laser frequency comb generation, and present work towards realizing a visible-light hybrid integrated diode laser.Comment: 25 pages, 16 figure

A Simulation-Based Method for Correcting Mode Coupling in CMB Angular Power Spectra

Modern CMB analysis pipelines regularly employ complex time-domain filters, beam models, masking, and other techniques during the production of sky maps and their corresponding angular power spectra. However, these processes can generate couplings between multipoles from the same spectrum and from different spectra, in addition to the typical power attenuation. Within the context of pseudo-$C_\ell$ based, MASTER-style analyses, the net effect of the time-domain filtering is commonly approximated by a multiplicative transfer function, $F_{\ell}$, that can fail to capture mode mixing and is dependent on the spectrum of the signal. To address these shortcomings, we have developed a simulation-based spectral correction approach that constructs a two-dimensional transfer matrix, $J_{\ell\ell'}$, which contains information about mode mixing in addition to mode attenuation. We demonstrate the application of this approach on data from the first flight of the SPIDER balloon-borne CMB experiment.Comment: 14 pages, 7 figure

Measuring outcome after cardiac arrest: construct validity of Cerebral Performance Category

Introduction: Approximately half of the survivors of cardiac arrest have cognitive impairments due to hypoxic brain injury. To describe the outcome after a cardiac arrest, the Cerebral Performance Category (CPC) is frequently used. Although widely used, its validity is still debatable. Objective: To investigate the construct validity of the Cerebral Performance Category in survivors of a cardiac arrest. Participants were 18 years and older that survived a cardiac arrest more than six months. Methods: Cross-sectional design. A method to administer the CPC in a structured and reproducible manner was developed. This 'Structured CPC' was administered by a structured interview. Construct variables were Cognitive Failure Questionnaire (CFQ), Barthel Index (BI), Frenchay Activity Index (FAI), Community Integration Questionnaire (CIQ) and Quality of Life after Brain Injury (Qolibri). Associations were tested based on Spearman correlation coefficients. Results: A total of 62 participants responded. In 58 (94%) patients the CPC was determined, resulting in CPC 1 (48%), CPC 2 (23%) and CPC 3 (23%). The CPC-scoring correlated significantly with the CFQ(r = -0.40); BI (r= -0.57); FAI (r= -0.65), CIQ(r = -0.53) and Qolibri (r= -0.67). Discussion and conclusions: In this study we developed the 'Structured CPC' to improve the transparency and reproducibility of the original CPC. A moderate correlation between the 'Structured CPC' and the constructs 'activities', 'participation' and 'quality of life' confirmed the validity of the 'Structured CPC'. Clinical message: The 'Structured CPC' can be used as an instrument to measure the level of functioning after cardiac arrest