CdSe/TiO2NTs Heterojunction-Based Nonenzymatic Photoelectrochemical Sensor for Glucose Detection.

Compared with a single semiconductor, the heterojunction formed by two different semiconductors usually has higher light utilization and better photoelectric performance. By using stable TiO2 nanotubes as the main subject, CdSe/TiO2NTs heterojunctions were synthesized by a hydrothermal method. XRD, TEM, SEM, PL, UV-vis, and EIS were used to characterize the fabricated CdSe/TiO2NTs. Under visible light irradiation, CdSe/TiO2NTs heterojunctions exhibited a higher absorption intensity and lower degree of photogenerated carrier recombination than TiO2. The electrons and holes were proven to be effectively separated in this heterojunction via theoretical calculation. Under CdSe/TiO2NTs' optimal conditions, the glucose concentrations (10-90 µM) had a linear relationship with the photocurrent value, and the detection limit was 3.1 µM. Moreover, the CdSe/TiO2NTs sensor exhibited good selectivity and stability. Based on the experimental data and theoretical calculations, its PEC sensing mechanism was also illuminated.

Job-related stress associated with work-related upper extremity musculoskeletal disorders (UEMDs) in municipal waste collectors: the moderation and mediation effect of job support.

BACKGROUND: Since the policy of "keeping trash off of the ground" in Taiwan, long-term exposure to repetitive motion in waste collection process results in high risk of upper extremity musculoskeletal disorders (UEMDs). Thus, we assessed the moderation and mediation effects of job-related stress and job support on work-related UEMDs among municipal waste collectors. METHODS: A cross-sectional study was conducted in two cities located at northern Taiwan during 2018-2019. 626 municipal waste collectors voluntarily participated and anonymously filled out a structured questionnaire. The moderation and mediation effects of effort-reward imbalance (ERI) and social support on UEMDs were analyzed by Haye's Process Macro Model. RESULTS: Prevalence of UEMDs in municipal waste collectors were 43.4% for neck, 56.0% for shoulder, 24.1% for upper back, and 33.1% for hand/wrist. There was high prevalence of shoulder (72.2%), neck (48%), and upper back (30%) in female workers compared to male, most significantly in shoulders. In univariate and multivariate analysis, high ERI and low job support were significantly associated with ORs of 3.11 (95% CI:1.58-6.13) for elbow, 2.79 (95% CI:1.39-5.56) for shoulder, 3.39 (95% CI:1.64-7.00) for upper back and 3.83 (95% CI:1.98-7.41) for hand/wrist. Prevalent UEMDs were positively associated with high ERI in municipal waste collectors but negatively with job support. The moderation effects of ERI and job support on UEMDs, of which the measured synergy index exceeded one, were 18.24 for shoulder, 3.32 for elbow, and 2.45 for hand/wrist, but mediation effects were not significant. CONCLUSIONS: This study found municipal waste collectors with work-related upper extremity disorders were significantly associated with work-related psychological risk factors. Therefore, waste collection cannot only to be improved by semi-automatic and automatic processes but immediate intervention programs for the reduction of psychological risk factors is needed promptly.

Two CRISPR/Cas9 Systems Developed in Thermomyces dupontii and Characterization of Key Gene Functions in Thermolide Biosynthesis and Fungal Adaptation.

Thermomyces dupontii, a widely distributed thermophilic fungus, is an ideal organism for investigating the mechanism of thermophilic fungal adaptation to diverse environments. However, genetic analysis of this fungus is hindered by a lack of available and efficient gene-manipulating tools. In this study, two different Cas9 proteins from mesophilic and thermophilic bacteria, with in vivo expression of a single guide RNA (sgRNA) under the control of tRNAGly, were successfully adapted for genome editing in T. dupontii We demonstrated the feasibility of applying these two gene editing systems to edit one or two genes in T. dupontii The mesophilic CRISPR/Cas9 system displayed higher editing efficiency (50 to 86%) than the thermophilic CRISPR/Cas9 system (40 to 67%). However, the thermophilic CRISPR/Cas9 system was much less time-consuming than the mesophilic CRISPR/Cas9 system. Combining the CRISPR/Cas9 systems with homologous recombination, a constitutive promoter was precisely knocked in to activate a silent polyketide synthase-nonribosomal peptide synthase (PKS-NRPS) biosynthetic gene, leading to the production of extra metabolites that did not exist in the parental strains. Metabolic analysis of the generated biosynthetic gene mutants suggested that a key biosynthetic pathway existed for the biosynthesis of thermolides in T. dupontii, with the last two steps being different from those in the heterologous host Aspergillus Further analysis suggested that these biosynthetic genes might be involved in fungal mycelial growth, conidiation, and spore germination, as well as in fungal adaptation to osmotic, oxidative, and cell wall-perturbing agents.IMPORTANCEThermomyces represents a unique ecological taxon in fungi, but a lack of flexible genetic tools has greatly hampered the study of gene function in this taxon. The biosynthesis of potent nematicidal thermolides in T. dupontii remains largely unknown. In this study, mesophilic and thermophilic CRISPR/Cas9 gene editing systems were successfully established for both disrupting and activating genes in T. dupontii In this study, a usable thermophilic CRISPR/Cas9 gene editing system derived from bacteria was constructed in thermophilic fungi. Chemical analysis of the mutants generated by these two gene editing systems identified the key biosynthetic genes and pathway for the biosynthesis of nematocidal thermolides in T. dupontii Phenotype analysis and chemical stress experiments revealed potential roles of secondary metabolites or their biosynthetic genes in fungal development and adaption to chemical stress conditions. These two genomic editing systems will not only accelerate investigations into the biosynthetic mechanisms of unique natural products and functions of cryptic genes in T. dupontii but also offer an example for setting up CRISPR/Cas9 systems in other thermophilic fungi.

[Therapeutic effect of tadalafil on lower urinary tract symptoms with erectile dysfunction].

OBJECTIVE: To investigate the therapeutic effect of low-dose tadalafil on BPH-induced lower urinary tract symptoms (LUTS) complicated with ED. METHODS: We randomly assigned 126 patients with BPH-induced LUTS and ED to receive daily administration of tadalafil (5 mg) plus tamsulosin hydrochloride sustained-release capsules (0.2 mg) (treatment group Ⅰ ［T-Ⅰ］, n = 42), tadalafil (5 mg) only (treatment group Ⅱ ［T-Ⅱ］, n = 42) or placebo (control group, n = 42), all for 12 weeks. Before and after 6 and 12 weeks of medication, and at 4 and 8 weeks after drug withdrawal, we recorded and compared the IPSS sub-item scores in the voiding stage and urinary storage symptoms, total IPSS, IIEF-5 scores, and the frequency of sexual activities among the three groups of patients. RESULTS: As for the IPSS sub-item scores in the voiding stage symptoms, T-Ⅰ showed statistically significant differences between any two of the five time points (P < 0.05), but not T-Ⅱ between the baseline and 6-week medication or 8-week withdrawal (P > 0.05), or between 6-week medication and 8-week withdrawal (P > 0.05), nor did the control group among the five time points (P > 0.05). Statistically significant differences were observed between any two of the three groups at 12 weeks of medication and 4 weeks after drug withdrawal (P < 0.05), but not between the T-Ⅱ and control groups at 6 weeks of medication or 8 weeks after withdrawal (P > 0.05). As to the IPSS sub-item scores in the urinary storage symptoms, there were significant differences between any two time points in T-Ⅰ and T-Ⅱ (P < 0.05), but not in the control (P > 0.05), nor between T-Ⅰ and T-Ⅱ at 6 or 12 weeks of medication or at 4 or 8 weeks after drug withdrawal (P > 0.05). With regard to the total IPSS, statistically significant differences were found between any two of the three groups at 6 and 12 weeks of medication and 4 and 8 weeks after drug withdrawal (P < 0.05), but not between 6-week medication and 8-week withdrawal in T-Ⅰ or T-Ⅱ (P > 0.05), nor among the five time points in the control group (P > 0.05). Concerning the IIEF-5 scores, there was no significant difference in the frequency of sexual activities between the three groups （Ｐ>0.05）.There were statistically significant differences between any two of the three groups at 6 weeks of medication and 8 weeks after drug withdrawal (Ｐ<0.05), but not between 6-week medication and 4- or 8-week withdrawal (P > 0.05) or between 4- and 8-week withdrawal (P > 0.05) in T-Ⅰ, nor between 6-week medication and 8-week withdrawal in T-Ⅱ (P > 0.05) or among the five time points in the control (P > 0.05), nor between T-Ⅰ and T-Ⅱ at 12 weeks of medication (P > 0.05) or 4 weeks after drug withdrawal (P > 0.05). CONCLUSIONS: Daily administration of tadalafil at 5 mg can effectively improve the IPSS sub-item scores in the urinary storage symptoms and IIEF-5 scores, with a persistent effect after withdrawal similar to that of its combination with other drugs, and therefore can be recommended for the treatment of BPH-induced LUTS complicated with ED.

LncRNA THOR promotes human renal cell carcinoma cell growth.

BACKGROUND: Recent studies have characterized a novel but extremely conserved long non-coding RNA (LncRNA) THOR. THOR directly associates with insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) to promote mRNA stabilization of key pro-cancerous genes. RESULTS: Here, we show that THOR is expressed in human renal cell carcinoma (RCC) tissues and established/primary human RCC cells. It was not detected in normal renal tissues nor in HK-2 and primary human renal epithelial cells. THOR silencing (by targeted siRNAs) or CRISPR/Cas9 knockout inhibited RCC cell growth, viability and proliferation in vitro. Reversely, forced over-expression of THOR promoted RCC cell survival and proliferation. IGF2BP1-regulated genes, including IGF2, GLI1 and Myc, were downregulated by THOR silencing or knockout, but they were upregulated after THOR over-expression. In vivo, THOR-knockout 786-O tumors grew significantly slower than the control tumors in nude mice. CONCLUSION: THOR expression promotes RCC cell growth in vitro and in vivo. THOR could be a novel and important therapeutic target for human RCC.

Electrically-pumped plasmonic lasers based on low-loss hybrid SPP waveguide.

A low-loss surface plasmonic polariton (SPP) laser is designed as a candidate for the light-source in large-scale integrated (LSI) photonic circuits. Key design parameters of the laser are discussed and optimized to enhance the optical gain and minimize the metallic absorption loss. Performance of the laser is calculated to verify the device feasibility in the designed application.

Electro-optical switching at 1550 nm using a two-state GeSe phase-change layer.

New designs for electro-optical free-space and waveguided 2 x 2 switches are presented and analyzed at the 1.55 µm telecoms wavelength. The proposed devices employ a ~10 nm film of GeSe that is electrically actuated to transition the layer forth-and-back from the amorphous to the crystal phase, yielding a switch with two self-sustaining states. This phase change material was selected for its very low absorption loss at the operation wavelength, along with its electro-refraction Δn ~0.6. All switches are cascadeable into N x M devices. The free-space prism-shaped structures use III-V prism material to match the GeSe crystal index. The Si/GeSe/Si "active waveguides" are quite suitable for directional-coupler switches as well as Mach-Zehnder devices-all of which have an active length 16x less than that in the free-carrier art.

Electro-optical phase-change 2 × 2 switching using three- and four-waveguide directional couplers.

Theoretical modeling and numerical simulation have been performed at λ=2100 nm on silicon-on-insulator channel-waveguide directional couplers in which the outer two Si waveguides are passive and the central waveguide(s) are electro-optical (EO) "islands." The EO channel(s) utilize a 10 nm layer of Ge2Sb2Te5 phase-change-material sited at midlevel of a doped Si channel. A voltage-driven phase change produces a large change in the effective index of the TE(o) and TM(o) modes, thereby inducing crossbar 2×2 switching. A mode-matching method is employed to estimate EO switching performance in the limit of strong interguide coupling. Low-loss switching is predicted for cross-to-bar and bar-to-cross coupling lengths. These "self-holding" switches had active lengths of 500-1000 µm, which are shorter than those in couplers relying upon free-carrier injection. The four-waveguide devices had lower cross talk but higher loss than the three-waveguide devices. For the crystalline phase we sometimes used an active length that was smaller than that for the amorphous phase.

Long range mid-infrared propagation in Si and Ge hybrid plasmonic-photonic nano-ribbon waveguides.

We have investigated a hybrid plasmonic-photonic mode in Si and Ge channel waveguides over the 1.55-8.0 µm wavelength range. A 10-nm Cu ribbon was buried midway within a Si3N4 "photonic slot" centered in the semiconductor strip. For the TMo mode, propagation lengths L of several millimeters are predicted for a waveguide cross-section of about 0.7λ/n x 0.7λ/n which offers optical confinement mainly within the ~λ²/400-area slot. The L increased strongly with λ. For 0.4λ/n x 0.4λ/n channels, we found multi-centimeter propagation, but there ~60% of the propagating energy had leaked out into the thick, all-around Si3N4 cladding.

Insights into complex Berenger modes: a view from the weighted optical path distance perspective.

We present a simple and efficient approach for higher-order Berenger mode computation. We establish the physical mapping between radiation modes and complex Berenger modes, and theoretically prove that the higher-order substrate Berenger modes and cladding Berenger modes can converge to a cluster of complex modes with the same phase angle. This model can be explained by weighted optical path distance in both cladding and substrate, and can be implemented by adjusting parameters of perfectly matched layers. A germanium (Ge) photodetector is utilized to evaluate the merits of this method in terms of robustness, efficiency, and accuracy.

[Results of different postoperative adjuvant therapies for stage Ib-IIa cervical carcinoma with risk factors].

OBJECTIVE: To investigate the effects of postoperative adjuvant chemotherapy (CT) and chemoradiotherapy (CRT) or radiotherapy(RT) for Ib-IIa cervical cancer with risk factors. METHODS: From March 1995 to June 2010, there were 137 patients underwent radical hysterectomy and systematic pelvic lymphadenectomy for stage Ib-IIa cervical cancer admitted at Peking University First Hospital. These patients had risk factors, intermediate risk factors including bulky tumor ( > 4 cm) , lymph vascular space invasion, deep stromal invasion; high risk factors including positive surgical margin, parametrial invasion, lymph node involvement. Of the all patients, 79 cases of them were treated with CT, 58 of them were treated with RT or CRT. The 5-year survival and prognosis factors were analyzed retrospectively, the prognosis was compared between two adjuvant therapy groups. RESULTS: The univariate analysis shown that types of pathology, different grade of risk factors, stroma invasion and lymph node involvement were prognostic factors of 5-year overall survival. Patients with squamous cell carcinoma, intermediate risk factors, no parametrial invasion, and no lymph node involvement had better prognosis(P < 0.05). Whether patients with high-risk factors or intermediate-risk factors, the 5-year overall survival and 3-year disease-free survival had no difference between CT and RCT or RT groups respectively. Cox regression multivariate analysis of survival indicated that clinical stages, types of histology, different grade of risk factors were independent prognostic indicator. Patients with early stage, squamous cell carcinoma, intermediate risk factors had better prognosis. Univariate and multivariate analysis indicated that different postoperative adjuvant therapies had no effects on the prognosis. The 5-year overall survival was 88.6% in patients treated with CT, and 89.7% in patients treated with RT or CRT (P = 0.455) . CONCLUSION: There are equivalent therapeutic results between CT and RT or CRT for patients with risk factors after radical surgery, CT may be as one choice of postoperative adjuvant therapy for stage Ib-IIa cervical carcinoma with risk factors.

[Exploration of the theory of Renying Cunkou pulse method recorded in the Yellow Emperor's Inner Canon].

Renying Cunkou pulse method is one of the classical pulse methods of acupuncture-moxibustion in the Yellow Emperor's Inner Canon, which is also a classical clinical paradigm for diagnosing and treating meridian diseases in the ancient times. Based on comprehensive review of literature and clinical practice, this paper reveals that this method compares the size of the neck Renying pulse with hand Cunkou pulse to determine the change of yin-yang and excess-deficiency identifying the affected meridians. The jing-well, xing-spring, and shu-stream points of the surface and interior meridians of affected meridians are mainly selected to regulate deficiency and excess through reinforcing and reducing methods. The Renying Cunkou pulse method possesses a simple and practical medical theory, easy diagnostic procedure, and clear meridian selection for acupuncture-moxibustion treatment, warranting further exploration of its essence and diagnostic therapeutic principles.

[Significance of serum procalcitonin levels in the evaluation of severity and prognosis of patients with systemic inflammatory response syndrome].

OBJECTIVE: To observe the dynamic changes in serum procalcitonin (PCT), C-reactive protein (CRP), and white blood cell (WBC) count in systemic inflammatory response syndrome (SIRS) and their implication in assessment of illness severity and prognosis. METHODS: A prospective case control study was conducted. Seventy-two patients with SIRS in Guangdong General Hospital were enrolled in intensive care unit (ICU) from May, 2010 to June, 2011. Parameters including PCT, CRP, and WBC count were determined on the 1st, 3rd, and 5th day after admission. The patients were divided into septic group (n=49) and non-septic group (non-infectious SIRS group, n=23) according to the presence or absence of infectious. Dynamic changes in all parameters were compared between the two groups and correlation analysis was carried out on the basis of differential indexes and sequential organ failure assessment (SOFA). The clinical outcome within 28 days after admission to ICU was observed, and the patients were divided into death group (n=19) and survival group (n=53). Dynamic changes in all parameters between the two groups were compared. Relevant parameters were analyzed with area under receiver operator characteristic curve (ROC curve, AUC) to predict 28-day survival. Logistic regression analysis of the multiple factors was used to screen independent risk factors for predicting death. RESULTS: PCT level (µg/L) on 1st, 3rd, 5th day after admission were all significantly higher in septic group than those in non-septic group (1st day: 2.5±0.3 vs. 0.9±0.2, 3rd day: 1.9±0.3 vs. 0.6±0.2, 5th day: 0.9±0.1 vs. 0.5±0.1, all P<0.05), while there was no statistically significant difference in CRP and WBC between two groups. PCT level in septic group was gradually decreased with time, there were statistically significant differences between septic group and non-septic group at the different treatment time (all P<0.05), but there was no correlation between PCT and treatment duration in non-septic group. Positive statistical correlation was found between PCT and SOFA score (r=0.979, P<0.05). PCT (µg/L) and CRP levels (mg/L) on 1st, 3rd, 5th day were significantly higher in death group than those of survival group (PCT on 1st day: 2.0±0.8 vs. 0.8±0.3, 3rd day: 2.2±0.7 vs. 0.6±0.3, 5th day: 2.4±1.0 vs. 0.4±0.1; CRP on 1st day: 422±45 vs. 411±44, 3rd day: 418±39 vs. 403±52, 5th day: 392±38 vs. 382±46, all P<0.05), but WBC count showed no statistically significant difference between two groups. PCT level in survival group showed a significant lowering along with treatment duration, and statistical difference was seen by paired comparison between every two time-points (all P<0.05). There was no correlation between PCT level and treatment duration in death group, and it maintained a rather high level. No significant difference was seen in CRP and WBC between two groups with passage of time. AUC was 0.824 and 0.720, respectively, when patient's 28-day survival was predicted by PCT and CRP (both P<0.01). Logistic regression analysis of the multiple factors revealed that PCT>2.23 µg/L was independent risk factor predicting the prognosis [odds ratio (OR) was 1.773, 95% confidence interval (95%CI) 1.033 to 3.214, P=0.015]. CONCLUSIONS: Serum PCT evaluation may be helpful in differentiating sepsis and non-sepsis at early stage of disease, and also in predicting the severity of the illness and prognosis of SIRS. PCT may be one of the independent risk factors for 28-day survival.

Moderating and Mediating Effects of Over-Commitment on the Association Between Effort-Reward Imbalance (ERI) with Upper Back and Hand/Wrist Disorders in Municipal Solid Waste Collectors.

PURPOSE: Despite repetitive activities and the frequency of high workload for municipal solid waste (MSW) collectors, the risks of work-related stress on upper extremity pain are inconclusive. The objective of this study is to assess the moderation and mediation effect of effort-reward imbalance (ERI) and over-commitment (OC) on upper back and hand/wrist disorders in MSW collectors. METHODS: A cross-sectional study was conducted with MSW collectors from two cities in Taiwan. Each participant was asked to anonymously fill out a structured questionnaire. Work-related stress, including ERI and OC, was assessed by a Chinese version of the Job Content Questionnaire (C-JCL). Upper back and hand/wrist disorders were assessed using the Nordic musculoskeletal questionnaire. Multivariate analysis was used to assess moderation and mediation effect of OC and ERI on upper extremity pain. RESULTS: The moderation effect of ERI and OC on upper back and hand/wrist disorders in MSW collectors was found. Disorders were higher in the group with both ERI ≥1 and high OC (OR (odds ratio) = 3.25 and OR = 3.00) than in the group with ERI ≥1 and low OC (OR = 2.66 and OR = 1.87) and in the ERI <1 and high OC group (OR = 2.27 and OR = 1.26). Synergy indexes were 0.77 and 1.77, respectively. Using multivariate analysis after adjusting for covariates, the mediation effect of OC was significant for the association between ERI and upper back and hand/wrist pains. The indirect effects of OC for upper back and hand/wrist pains accounted for 35% and 42%, respectively, and OC appears to mediate the relationship between ERI and upper back and hand/wrist disorders in MSW collectors. CONCLUSION: Work-related stress measured ERI and OC may play a role in moderating and mediating effects on upper extremity pain. Encouraging provisions of work modification and stress management is needed to mitigate the occurrence of upper extremities pain in MSW collectors.

CdS-Modified TiO2 Nanotubes with Heterojunction Structure: A Photoelectrochemical Sensor for Glutathione.

The formation of heterojunction structures can effectively prevent the recombination of photogenerated electron-hole pairs in semiconductors and result in the enhancement of photoelectric properties. Using TiO2 nanotubes (prepared using the hydrothermal-impregnation method) as carriers, CdS-TiO2NTs were fabricated as a photoelectrochemical (PEC) sensor, which can be used under visible light and can exhibit good PEC performance due to the existence of the heterojunction structure. The experimental results show that the prepared CdS-TiO2NTs electrode had a linear response to 2-16 mM glutathione (GSH). The sensor's sensitivity and detection limit (LOD) were 102.9 µA·mM-1 cm-2 and 27.7 µM, respectively. Moreover, the biosensor had good stability, indicating the potential application of this kind of heterojunction PEC biosensor.

Design and analysis of single mode Fabry-Perot lasers with high speed modulation capability.

The single mode Fabry-Perot (FP) semiconductor lasers are investigated systematically by a rigorous time-domain theoretical model based on the transfer matrix method. Static and high-speed dynamic performances under direct modulation and strong external optical feedbacks are simulated for both symmetric and asymmetric longitudinal structures of the lasers. Comparisons with the DFB and conventional FP lasers are made to confirm its effectiveness in achieving single-mode lasing with high spectrum purity under modulation and feedback conditions. Structural optimization is also carried out with respect to the key design parameters.

Complex coupled-mode theory for tapered optical waveguides.

A coupled-mode formulation based on complex local modes is developed for tapered and longitudinally varying optical waveguides. Different from the conventional coupled-mode theory that requires integration over the entire spectrum of radiation modes, the new formulation treats the radiation fields via discrete complex modes similarly to the guided modes. Accuracy, convergence, and scope of validity for the solutions of the complex coupled-mode equations are investigated in detail for a typical single-mode waveguide taper. It is demonstrated that the complex coupled-mode theory has overcome the difficulties of the conventional theory in simulation of radiation field effects while preserving the simplicity and intuitiveness of this popular method.

Compact Bragg grating with embedded metallic nano-structures.

A compact Bragg grating with embedded gapped metallic nano-structures is proposed and investigated theoretically. The Bragg grating consists of periodic planar metallic strips embedded in a dielectric waveguide. The grating exhibits distinct polarization characteristics due to its underlying working mechanisms of the metallic nano-strips. The grating can be considered as insulator-metal-insulator surface plasmonic polariton waveguide grating with improved light confinement for TM polarized waves. For the TE waves, significant field mismatch between metal and non-metal sections of the grating results in strong reflection. Comparison with the conventional deeply-etched grating on the same waveguide structures reveals interesting characteristics. It is concluded that the two types of grating structures share similar guidance, reflection and loss mechanisms for the TE modes. The spectral characteristics and their dependences on grating duty cycle are drastically different for the TM modes, mainly due to the SPP effect for the metal. Although the proposed grating performs slightly worse comparing to the deeply-etched grating for TE waves, its fabrication process should be easier since there will be no narrow trench (in sub-microns) deep-etching process (up to a few microns in depth) involved.

Acceleration of FDTD mode solver by high-performance computing techniques.

A two-dimensional (2D) compact finite-difference time-domain (FDTD) mode solver is developed based on wave equation formalism in combination with the matrix pencil method (MPM). The method is validated for calculation of both real guided and complex leaky modes of typical optical waveguides against the bench-mark finite-difference (FD) eigen mode solver. By taking advantage of the inherent parallel nature of the FDTD algorithm, the mode solver is implemented on graphics processing units (GPUs) using the compute unified device architecture (CUDA). It is demonstrated that the high-performance computing technique leads to significant acceleration of the FDTD mode solver with more than 30 times improvement in computational efficiency in comparison with the conventional FDTD mode solver running on CPU of a standard desktop computer. The computational efficiency of the accelerated FDTD method is in the same order of magnitude of the standard finite-difference eigen mode solver and yet require much less memory (e.g., less than 10%). Therefore, the new method may serve as an efficient, accurate and robust tool for mode calculation of optical waveguides even when the conventional eigen value mode solvers are no longer applicable due to memory limitation.

New insight into quasi leaky mode approximations for unified coupled-mode analysis.

To facilitate the analysis of radiation mode couplings, quasi leaky mode approximations were utilized in coupled-mode analysis. The key to effectively and accurately apply this approach is how to well approximate radiation modes by the quasi leaky modes in an equivalent closed waveguide model. In this paper, the principle, applicability and accuracy of the approximations are demonstrated, and the detailed implementation is also suggested by applying a unified coupled-mode analysis to fiber gratings. First of all, based on a thorough study on the characteristics of the complex modes, for the first time, quasi leaky modes are classified into guided-mode-like inner-cladding and radiation-mode-like outer-cladding leaky modes so as to explicitly establish equivalence relationships between the discrete leaky modes and the continuous radiation modes. With this new insight, the whole analysis process especially for some of the practically tricky issues such as the criteria for developing the proper equivalent waveguide model and the subsequent mode expansion basis are better understood and easier to be dealt with for different problems where radiation modes come into play. Moreover, as essential preconditions to extend the conventional coupled mode analysis to the present unified one, the couplings between the guided core mode and a leaky mode are studied in a systematic and consistent manner. An intuitive and then a deep understanding on the roles of complex modes on mode coupling and power exchanging are thus gained for further simulations. Lastly, the transmission spectra of fiber gratings with different surrounding indices are simulated. The simulated results agree well with those obtained theoretically and experimentally in the literatures, which strongly validate the principle of quasi leaky mode approximations and its implementation on the unified coupled-mode analysis expounded in this paper.