Integrated multi-wavelength lasers : a design study

Multi-wavelength lasers (MWLs) play an important role in wavelength division multiplexing networks, and also in photonic radar beam steering applications. In this paper we study different options for realizing such lasers, monolithically integrated with radio frequency (RF) modulators that can be modulated up to 40 GHz. Configurations of arrayed waveguide grating (AWG)-based MWLs integrated with Mach-Zehnder modulators are discussed. Depending on the application, they can have spatially separated modulated outputs or the modulated signals can be multiplexed onto a common output. A novel configuration, that exploits the reflection and transmission properties of on-chip reflectors is presented.

Accurate and efficient arrayed waveguide grating simulations for InP membranes

We analyze the Arrayed Waveguide Grating (AWG) response on indium phosphide (InP) membranes on silicon (IMOS) technology. The model is based on an analytical approach [1] that provides a better accuracy than the Gaussian approximation for similar simulation times

Integrated filtered-feedback tunable laser with enhanced control of feedback phase

Recently we presented a novel discretely tunable laser that consists of a Fabry-Perot laser which was forced to operate in single-mode condition by applying on-chip filtered feedback. The laser switches extremely fast (3 ns) and requires simple on/off control currents to switch the wavelength. In these first devices it was not possible to control the phase of the feedback light independently from the feedback intensity. In was solved by adding an extra electrode allowing us to control the phase separately. In this paper we present the new device and study the effect of the control ofthefeedbackphase in order to improve the performance ofthe original tunable laser concept

Integrated filtered-feedback tunable laser with enhanced control of feedback phase

Recently we presented a novel discretely tunable laser that consists of a Fabry-Perot laser which was forced to operate in single-mode condition by applying on-chip filtered feedback. The laser switches extremely fast (3 ns) and requires simple on/off control currents to switch the wavelength. In these first devices it was not possible to control the phase of the feedback light independently from the feedback intensity. In was solved by adding an extra electrode allowing us to control the phase separately. In this paper we present the new device and study the effect of the control ofthefeedbackphase in order to improve the performance ofthe original tunable laser concept

Perovskite-perovskite tandem photovoltaics with optimized bandgaps

We demonstrate four and two-terminal perovskite-perovskite tandem solar cells with ideally matched bandgaps. We develop an infrared absorbing 1.2eV bandgap perovskite, $FA_{0.75}Cs_{0.25}Sn_{0.5}Pb_{0.5}I_3$, that can deliver 14.8 % efficiency. By combining this material with a wider bandgap $FA_{0.83}Cs_{0.17}Pb(I_{0.5}Br_{0.5})_3$ material, we reach monolithic two terminal tandem efficiencies of 17.0 % with over 1.65 volts open-circuit voltage. We also make mechanically stacked four terminal tandem cells and obtain 20.3 % efficiency. Crucially, we find that our infrared absorbing perovskite cells exhibit excellent thermal and atmospheric stability, unprecedented for Sn based perovskites. This device architecture and materials set will enable 'all perovskite' thin film solar cells to reach the highest efficiencies in the long term at the lowest costs

Robot-Assisted Total Mesorectal Excision Versus Laparoscopic Total Mesorectal Excision:A Retrospective Propensity Score-Matched Cohort Analysis in Experienced Centers

BACKGROUND: The superiority of robot-assisted over laparoscopic total mesorectal excision has not been proven. Most studies do not consider the learning curve while comparing the surgical technique. OBJECTIVE: This study aims to compare laparoscopic with robot-assisted total mesorectal excision performed by surgeons who completed the learning curve of the technique. DESIGN: This is a multicenter retrospective propensity score-matched analysis. SETTINGS: The study was performed in 2 large, dedicated robot-assisted hospitals and 5 large, dedicated laparoscopic hospitals. PATIENTS: Patients were included if they underwent a robot-assisted or laparoscopic total mesorectal excision for rectal cancer with curative intent at a dedicated center for the minimally invasive technique between January 1, 2015, and December 31, 2017. INTERVENTIONS: We compared robot-assisted with laparoscopic total mesorectal excision. MAIN OUTCOME MEASURES: The main outcome was conversion to laparotomy during surgery. Secondary outcomes were postoperative morbidity and positive circumferential resection margin. RESULTS: A total of 884 patients were included and, after matching, 315 patients per treatment group remained. Conversion was similar between laparoscopic and robot-assisted total mesorectal excision (4.4% vs 2.5% (p = 0.20)). Positive circumferential resection margin was equal (3.2% vs 4.4% (p = 0.41)). Overall morbidity was comparable as well, although a lower rate of wound infections was observed in the robot-assisted group (5.7% vs 1.9% (p = 0.01)). More primary anastomoses were constructed in the robot-assisted group (50.8% vs 68.3% (p < 0.001)). Finally, more open procedures were performed in dedicated laparoscopic centers, with an overrepresentation of cT4N+ tumors in this group. LIMITATIONS: This is a retrospective multicenter cohort; however, propensity score matching was applied to control for confounding by indication. CONCLUSIONS: Robot-assisted and laparoscopic total mesorectal excision are equally safe in terms of short-term outcomes. However, with the robot-assisted approach, more primary anastomoses were constructed, and a lower wound infection rate was observed. See Video Abstract at http://links.lww.com/DCR/B677

The role of hole transport between dyes in solid-state dye-sensitized solar cells

In dye-sensitized solar cells (DSSCs) photogenerated positive charges are normally considered to be carried away from the dyes by a separate phase of hole-transporting material (HTM). We show that there can also be significant transport within the dye monolayer itself before the hole reaches the HTM. We quantify the fraction of dye regeneration in solid-state DSSCs that can be attributed to this process. By using cyclic voltammetry and transient anisotropy spectroscopy, we demonstrate that the rate of interdye hole transport is prevented both on micrometer and nanometer length scales by reducing the dye loading on the TiO₂ surface. The dye regeneration yield is quantified for films with high and low dye loadings (with and without hole percolation in the dye monolayer) infiltrated with varying levels of HTM. Interdye hole transport can account for >50% of the overall dye regeneration with low HTM pore filling. This is reduced to about 5% when the infiltration of the HTM in the pores is optimized in 2 μm thick films. Finally, we use hole transport in the dye monolayer to characterize the spatial distribution of the HTM phase in the pores of the dyed mesoporous TiO₂

Comparison of three-year oncological results after restorative low anterior resection, non-restorative low anterior resection and abdominoperineal resection for rectal cancer

Introduction: Oncological outcome might be influenced by the type of resection in total mesorectal excision (TME) for rectal cancer. The aim was to see if non-restorative LAR would have worse oncological outcome. A comparison was made between non-restorative low anterior resection (NRLAR), restorative low anterior resection (RLAR) and abdominoperineal resection (APR). Materials and methods: This retrospective cohort included data from patients undergoing TME for rectal cancer between 2015 and 2017 in eleven Dutch hospitals. A comparison was made for each different type of procedure (APR, NRLAR or RLAR). Primary outcome was 3-year overall survival (OS). Secondary outcomes included 3-year disease-free survival (DFS) and 3-year local recurrence (LR) rate. Results: Of 998 patients 363 underwent APR, 132 NRLAR and 503 RLAR. Three-year OS was worse after NRLAR (78.2%) compared to APR (86.3%) and RLAR (92.2%, p < 0.001). This was confirmed in a multivariable Cox regression analysis (HR 1.85 (1.07, 3.19), p = 0.03). The 3-year DFS was also worse after NRLAR (60.3%), compared to APR (70.5%) and RLAR (80.1%, p < 0.001), HR 2.05 (1.42, 2.97), p < 0.001. The LR rate was 14.6% after NRLAR, 5.2% after APR and 4.8% after RLAR (p = 0.005), HR 3.22 (1.61, 6.47), p < 0.001. Conclusion: NRLAR might be associated with worse 3-year OS, DFS and LR rate compared to RLAR and APR

Laparoscopic Versus Robot-Assisted Versus Transanal Low Anterior Resection:3-Year Oncologic Results for a Population-Based Cohort in Experienced Centers

BACKGROUND: Laparoscopic, robot-assisted, and transanal total mesorectal excision are the minimally invasive techniques used most for rectal cancer surgery. Because data regarding oncologic results are lacking, this study aimed to compare these three techniques while taking the learning curve into account. METHODS: This retrospective population-based study cohort included all patients between 2015 and 2017 who underwent a low anterior resection at 11 dedicated centers that had completed the learning curve of the specific technique. The primary outcome was overall survival (OS) during a 3-year follow-up period. The secondary outcomes were 3-year disease-free survival (DFS) and 3-year local recurrence rate. Statistical analysis was performed using Cox-regression. RESULTS: The 617 patients enrolled in the study included 252 who underwent a laparoscopic resection, 205 who underwent a robot-assisted resection, and 160 who underwent a transanal low anterior resection. The oncologic outcomes were equal between the three techniques. The 3-year OS rate was 90% for laparoscopic resection, 90.4% for robot-assisted resection, and 87.6% for transanal low anterior resection. The 3-year DFS rate was 77.8% for laparoscopic resection, 75.8% for robot-assisted resection, and 78.8% for transanal low anterior resection. The 3-year local recurrence rate was in 6.1% for laparoscopic resection, 6.4% for robot-assisted resection, and 5.7% for transanal procedures. Cox-regression did not show a significant difference between the techniques while taking confounders into account. CONCLUSION: The oncologic results during the 3-year follow-up were good and comparable between laparoscopic, robot-assisted, and transanal total mesorectal technique at experienced centers. These techniques can be performed safely in experienced hands

Comparison of laparoscopic versus robot-assisted versus transanal total mesorectal excision surgery for rectal cancer:a retrospective propensity score-matched cohort study of short-term outcomes

BACKGROUND: Laparoscopic total mesorectal excision (TME) surgery for rectal cancer has important technical limitations. Robot-assisted and transanal TME (TaTME) may overcome these limitations, potentially leading to lower conversion rates and reduced morbidity. However, comparative data between the three approaches are lacking. The aim of this study was to compare short-term outcomes for laparoscopic TME, robot-assisted TME and TaTME in expert centres. METHODS: Patients undergoing rectal cancer surgery between 2015 and 2017 in expert centres for laparoscopic, robot-assisted or TaTME were included. Outcomes for TME surgery performed by the specialized technique in the expert centres were compared after propensity score matching. The primary outcome was conversion rate. Secondary outcomes were morbidity and pathological outcomes. RESULTS: A total of 1078 patients were included. In rectal cancer surgery in general, the overall rate of primary anastomosis was 39.4, 61.9 and 61.9 per cent in laparoscopic, robot-assisted and TaTME centres respectively (P < 0.001). For specialized techniques in expert centres excluding abdominoperineal resection (APR), the rate of primary anastomosis was 66.7 per cent in laparoscopic, 89.8 per cent in robot-assisted and 84.3 per cent in TaTME (P < 0.001). Conversion rates were 3.7 , 4.6 and 1.9 per cent in laparoscopic, robot-assisted and TaTME respectively (P = 0.134). The number of incomplete specimens, circumferential resection margin involvement rate and morbidity rates did not differ. CONCLUSION: In the minimally invasive treatment of rectal cancer more primary anastomoses are created in robotic and TaTME expert centres