Search

Photodiodes (PDs) which convert optical signals to electrical signals have been widely used in many fields. In contrast to pin PDs, in uni-traveling carrier (UTC) PDs, the absorption layer is p type doped and only photo-generated electrons are transported, which results in several superior characteristics including super high speed operation, high saturation current and low voltage operation. In this work, high speed InP based waveguide UTC-PDs have been fabricated by Zn diffusion doping for the first time to our knowledge, in contrast to the in situ doping of previous UTC-PDs. Diffusion doping will make it much easier for the UTC-PDs to be integrated with high quality passive waveguide and multi-quantum well (MQW) based active devices for photonic integrated circuit (PIC) applications. UTC-PDs with 3 × 15, 3 × 25 and 3 × 50 µm2 absorption areas are fabricated, all having over 50 GHz bandwidth at -1V bias voltage. At -3 V bias, the RF power at 40 GHz shows no saturation at up to 17 mA photocurrent for the 3 × 25 µm2 PD.

Rational design of bifunctional electrocatalysts to promote the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a fundamental challenge for the application of zinc-air batteries (ZABs). Herein, we propose a facile and cost-effective strategy to in situ grow N-doped carbon nanotubes with encapsulated FeCo alloy nanoparticles on carbon cloths (FeCo/N-CNTs@CC) as a self-supported air cathode for rechargeable ZABs. The bamboo-like FeCo/N-CNTs@CC catalyst with high nitrogen content (10.5 atom %) exhibits excellent electrocatalytic activities, including a half-wave potential of 0.816 V for ORR and an overpotential of 1.638 V for OER at 10 mA cm–² in alkaline medium. Impressively, the liquid-state ZAB based on the FeCo/N-CNTs@CC cathode demonstrates a remarkable power density of 132.0 mW cm–² and a stable cycling performance over 65 h. Furthermore, the flexible all-solid-state ZAB possesses outstanding performance retention under various bending conditions. The electrocatalyst presented in this work holds great potential as a self-supported air cathode for practical applications.

We report a high speed directly modulated widely tunable dual wavelength distributed feedback (DFB) laser for THz communication application. The wavelength separation between the two modes can be thermally tuned between 96 GHz and 1510 GHz. The device can be directly modulated by high speed data at up to 25 Gb/s data rate, which facilitates high speed data modulation in a THz communication system. The device emits at $1.3~\mu \text{m}$ wavelength, which helps to increase the transmission distance of high-speed baseband data in fibers and lowers the request for wavelength tuning range to obtain the same THz frequency when compared with $1.5~\mu \text{m}$ wavelength devices. The presented results show that our dual wavelength device is promising for future low cost and high capacity THz communication system.

We report data transmissions using a widely tunable InP-based distributed Bragg reflector (DBR) laser integrated monolithically with an electroabsorption modulator (EAM). The laser has a wavelength tuning range of over 12 nm that is obtained by current injection into the DBR section because the butt-jointed InGaAsP DBR material has a long bandgap wavelength. Data transmissions of 10 Gb/s nonreturn to zero (NRZ) at distances of up to 75 km of a single mode fiber have been demonstrated. A power penalty of less than 0.9 dB has been obtained when compared to the BtB condition. In addition, transmissions of 20 Gb/s four-level pulse amplitude modulation (PAM4) data at distances of up to 45 km have been conducted successfully. These results indicate that the EAM-modulated DBR laser is promising for long-reach low-cost WDM optical network applications.

A pair of homochiral coordination polymers, [Cu(DPT)]n (1M and 1P, HDPT = 3,5-di-4-pyridinyl–2H-tetrazole), were assembled from achiral precursors. Crystal structure analysis showed that they are c...

In Ethiopia, human schistosomiasis is caused by two species of schistosome, Schistosoma mansoni and S. haematobium, with the former being dominant in the country, causing infections of more than 5 million people and more than 37 million at risk of infection. What is more, new transmission foci for S. mansoni have been reported over the past years in the country, raising concerns over the potential impacts of environmental changes (e.g., climate change) on the disease spread. Knowledge on the distribution of schistosomiasis endemic areas and associated drivers is much needed for surveillance and control programs in the country. Here we report a study that aims to examine environmental determinants underlying the distribution and suitability of S. mansoni endemic areas at the national scale of Ethiopia. The study identified that, among five physical environmental factors examined, soil property, elevation, and climatic factors (e.g., precipitation and temperature) are key factors associated with the distribution of S. mansoni endemic areas. The model predicted that the suitable areas for schistosomiasis transmission are largely distributed in northern, central, and western parts of the country, suggesting a potentially wide distribution of S. mansoni endemic areas. The findings of this study are potentially instrumental to inform public health surveillance, intervention, and future research on schistosomiasis in Ethiopia. The modeling approaches employed in this study may be extended to other schistosomiasis endemic regions and to other vector-borne diseases.

The fabrication and modeling of bow-tie antenna integrated uni-traveling carrier photodiodes (UTC-PD) are presented. The experimental results show that a −10.68 dBm RF power can be obtained from the 4 × 50 μm2 area UTC-PD at 100 GHz. The device is modeled by high frequency simulation software. The trend of variation of the measured terahertz (THz) power with frequency matches well with the simulation results. Based on the model, the effects of the shape and the contact pads of the antenna on the THz power emission properties of the device are studied numerically, which helps to further optimize the device design.

Background In Ethiopia, schistosomiasis is caused by Schistosoma mansoni and S. haematobium with the former being widespread and more than 4 million people are estimated to be infected by S. mansoni annually with 35 million at risk of infection. Although many school- and community-based epidemiological surveys were conducted over the past decades, the national distribution of schistosomiasis endemic areas and associated socio-environmental determinants remain less well understood. In this paper, we review S. mansoni prevalence of infections and describe key biogeographical characteristics in the endemic areas in Ethiopia. Methods We developed a database of S. mansoni infection surveys in Ethiopia through a systematic review by searching articles published between 1975 and 2019 on electronic online databases including PubMed, ScienceDirect, and Web of Science. A total of 62 studies involving 95 survey locations were included in the analysis. We estimated adjusted prevalence of infection from each survey by considering sensitivity and specificity of diagnostic tests using Bayesian approach. All survey locations were georeferenced and associated environmental and geographical characteristics (e.g. elevation, normalized difference vegetation index, soil properties, wealth index, and climatic data) were described using descriptive statistics and meta-analysis. Results The results showed that the surveys exhibited a wide range of adjusted prevalence of infections from 0.5% to 99.5%, and 36.8% of the survey sites had adjusted prevalence of infection higher than 50%. S. mansoni endemic areas were distributed in six regional states with the majority of surveys being in Amhara and Oromia. Endemic sites were found at altitudes from 847.6 to 3141.8 m above sea level, annual mean temperatures between 17.9 and 29.8 ℃, annual cumulative precipitation between 1400 and 1898 mm, normalized difference vegetation index between 0.03 and 0.8, wealth index score between –68 857 and 179 756; and sand, silt, and clay fraction in soil between 19.1–47.2, 23.0–36.7, and 20.0–52.8 g/100 g, respectively. Conclusions The distribution of S. mansoni endemic areas and prevalence of infections exhibit remarked environmental and ecological heterogeneities. Future research is needed to understand how much these heterogeneities drive the parasite distribution and transmission in the region. Graphic Abstract

The Stratospheric Environmental respoNses to Solar stORms (SENSOR) campaign investigates the influence of solar storms on the stratosphere. This campaign employs a long-duration zero-pressure balloon as a platform to carry multiple types of payloads during a series of flight experiments in the mid-latitude stratosphere from 2019 to 2022. This article describes the development and testing of an acoustic anemometer for obtaining in situ wind measurements along the balloon trajectory. Developing this anemometer was necessary, as there is no existing commercial off-the-shelf product, to the authors' knowledge, capable of obtaining in situ wind measurements on a high-altitude balloon or other similar floating platform in the stratosphere. The anemometer is also equipped with temperature, pressure, and humidity sensors from a Temperature-Pressure-Humidity measurement module, inherited from a radiosonde developed for sounding balloons. The acoustic anemometer and other sensors were used in a flight experiment of the SENSOR campaign that took place in the Da chaidan District (95.37° E, 37.74° N) on 4 September 2019. The zonal and meridional wind speed observations, which were obtained during level flight at an altitude exceeding 20 km, are presented. This is the first time that in situ wind measurements were obtained during level flight at this altitude. In addition to wind speed measurements, temperature, pressure, and relative humidity measurements during ascent are compared to observations from a nearby radiosonde launched four hours earlier. Further analysis of the wind data will presented in a subsequent publication. The problems experienced by the acoustic anemometer during the 2019 experiment show that the acoustic anemometer must be improved for future experiments in the SENSOR campaign.

A wavelength-tunable chaotic optical signal generation and on-chip O/E conversion scheme based on an integrated laser-photodiode chip subject to filtered optical feedback is proposed and experimentally demonstrated. The integrated chip consists of a Fabry–Perot (FP) gain section and a photodiode, which was fabricated on an n-InP substrate with the same active material. By applying a filtered feedback signal to the FP gain section, wavelength-tunable chaotic carrier ranging from 1576 to 1587 nm was achieved. On-chip microwave chaotic signal generation with a standard bandwidth over 5.5 GHz was obtained using the integrated photonic chip.

Background China contributed 8.9% of all incident cases of tuberculosis globally in 2017, and understanding the spatiotemporal distribution of pulmonary tuberculosis (PTB) in major transmission foci in the country is critical to ongoing efforts to improve population health. Methods We estimated annual PTB notification rates and their spatiotemporal distributions in Sichuan province, a major center of ongoing transmission, from 2005 to 2017. Time series decomposition was used to obtain trend components from the monthly incidence rate time series. Spatiotemporal cluster analyses were conducted to detect spatiotemporal clusters of PTB at the county level. Results From 2005 to 2017, 976,873 cases of active PTB and 388,739 cases of smear-positive PTB were reported in Sichuan Province, China. During this period, the overall reported incidence rate of active PTB decreased steadily at a rate of decrease (3.77 cases per 100,000 per year, 95% confidence interval (CI): 3.28–4.31) that was slightly faster than the national average rate of decrease (3.14 cases per 100,000 per year, 95% CI: 2.61–3.67). Although reported PTB incidence decreased significantly in most regions of the province, incidence was observed to be increasing in some counties with high HIV incidence and ethnic minority populations. Active and smear-positive PTB case reports exhibited seasonality, peaking in March and April, with apparent links to social dynamics and climatological factors. Conclusions While PTB incidence rates decreased strikingly in the study area over the past decade, improvements have not been equally distributed. Additional surveillance and control efforts should be guided by the seasonal-trend and spatiotemporal cluster analyses presented here, focusing on areas with increasing incidence rates, and updated to reflect the latest information from real-time reporting. Electronic supplementary material The online version of this article (10.1186/s12879-019-4262-2) contains supplementary material, which is available to authorized users.

The design and preparation of highly efficient and durable electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is essential due to their applications in many green energy conversion devices, such as fuel cells and rechargeable metal–air batteries. Herein, we report a Co/Co9S8 composite catalyst, which is coupled with reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs) via a combined hydrothermal reaction with a calcination method. Benefiting from the unique porous scaffold structures and synergistic interactions between rGO/MWCNT and Co/Co9S8, the electrocatalyst (Co/Co9S8/rGO/MWCNT-800) exhibits high electrochemical activity for the ORR, showing a four-electron oxygen reduction pathway with an onset potential of 0.946 V (vs. RHE) in alkaline medium. Meanwhile, the electrocatalyst shows high electrochemical stability, excellent selectivity and methanol tolerance over the commercial Pt/C. It also exhibits good overall oxygen electrode activity (ΔE = EOER,10 − EORR,1/2 of 890 mV). The present work highlights a potential general strategy for developing carbon-based transition metal sulfide nanocomposites as cathodes with better performance in the ORR/OER.

We report data transmissions using a packaged two-section distributed Bragg reflector (DBR) laser, which has InGaAlAs multi-quantum wells as the gain material. The tunable DBR laser has a wavelength tuning range of 11.44 nm. The DBR laser has uniform 3-dB direct modulation bandwidth (over 12 GHz) within the over 11-nm wavelength tuning range; 10-Gb/s data transmissions are performed at up to 25-km distance and different wavelength emissions at 25 °C and 50 °C.

We report mode locking in lasers integrated with semiconductor optical amplifiers, using either conventional or phase-shifted sampled grating distributed Bragg reflectors (DBRs). For conventional sampled gratings with a continuous grating coupling coefficient of ∼80 cm−1, mode locking was observed at a fundamental frequency of 628 GHz and second harmonic of 1.20 THz. The peak output power was up to 142 mW. In the phase-shifted sampled grating design, the grating is present along the entire length of the reflector with π-phase-shifted steps within each sampled section. The effective coupling coefficient is, therefore, increased substantially. Although the continuous grating coupling coefficient for the phase-shifted gratings was reduced to ∼23 cm−1 because of a different fabrication technology, the lasers demonstrated mode locking at fundamental repetition frequencies of 620 GHz and 1 THz, with a much lower level of amplified spontaneous emission seen in the output spectra than from conventional sampled grating devices. High pulse reproducibility and controllability over a wide operation range was seen for both types of grating, but the π-phase-shifted gratings already demonstrate fundamental mode locking to 1 THz. The integrated semiconductor optical amplifier makes sampled grating DBR lasers ideal pump sources for generating terahertz signals through photomixing.

An electro-absorption modulator (EAM) integrated widely tunable distributed Bragg reflector (DBR) laser working at 1.5 µm is reported. By utilizing the RF resonance between the bonding wire and the EAM, a 28 GHz modulation bandwidth is obtained. The device is modulated with up to 50 Gb/s NRZ data. At 28 Gb/s, the power penalty to obtain a 10−10 bit error rate (BER) after a 5 Km standard single mode fiber transmission is less than 0.7 dB. Because the DBR material has a long bandgap wavelength, the wavelength tuning range of the laser is larger than 12 nm. The DBR laser is a promising low cost tunable light source for future high capacity wavelength division multiplexing (WDM) optical communication systems.

With the deployment of the fifth generation of mobile networks (5G), 25 and 100 Gb/s directly modulated lasers and modules will become the mainstream optical transmitters. A directly modulated InGaAlAs/InP distributed Bragg reflector (DBR) laser is fabricated by butt-joint technology. A 25 Gb/s data transmission over a single-mode fiber of up to 10 km is demonstrated, and a wavelength tuning range of 14.28 nm is achieved through injection current tuning of a DBR section and temperature control of a thermoelectric cooler (TEC), which is the best candidate of colorless light sources for wavelength-division-multiplexed passive optical network (WDM-PON) systems.

A 1.0 μm laterally-coupled dual-wavelength distributed feedback laser is reported, with a frequency separation of 1.1 THz and near-circular output beam with small divergence angle of 20.6° (H) × 22.8° (V).

High concentration rare earth doped, large mode area (LMA) step-index fibers, which feature a very high cladding absorption per unit length at the pump wavelength, high efficiency, and excellent beam quality, are ideal for high power pulsed fiber lasers/amplifiers where large effective mode areas and short device lengths are crucial in order to reduce detrimental nonlinear effects associated with high peak power operation. In this Letter, we realize low numerical aperture (NA) high absorption fibers, simply by employing a germanium (Ge)-doped cladding rather than a pure silica cladding to offset the high refractive index associated with using a high concentration of ytterbium (Yb) in the core. This approach allows us to separate the two inter-linked fiber design parameters of pump absorption and NA in a step-index fiber. Using a conventional modified chemical vapor deposition process combined with solution doping, a low NA (0.04), LMA ( 475 µ m 2 ) silica fiber is fabricated with a cladding absorption value of > 20 d B / m , which is the highest value among LMA step-index fibers with N A < 0.06 so far reported to the best of our knowledge. The fabricated Yb-doped fiber was tested in a high-power picosecond amplifier system and enabled the generation of 190 ps laser pulses with a 101 µJ pulse energy and 0.5 MW peak power at an average power of 150 W.

A DFB laser operating at wavelength of 1 μm has been demonstrated with a small divergence angle (17.8° × 25.5°), low threshold current of 16 mA and output power of 37 mW at 90 mA.

We present electroabsorption modulators integrated with distributed feedback lasers (EMLs) fabricated by a simple method, which combines the advantages of the selective area growth and double stack active layer techniques. The obtained EML device has a threshold current as low as 16 mA and optical power of larger than 10 mW at 85 mA laser current. Quite low chirp parameter of the fabricated EMLs is obtained. Negative chirp parameters can be obtained at only about 0.5 V reverse bias voltage. Open eye diagrams are demonstrated from the EML at both 10 and 20 Gb/s modulations with the driving voltage of only 0.65 V while securing high dynamic extinction ratio. The exhibited performance makes our device a very promising candidate as a simple light source in long distance and cost sensitive applications.

AlGaInAs electroabsorption-modulated lasers (EMLs) fabricated by identical epitaxial layer technique are demonstrated. The EML device shows an infinite characteristic temperature when the temperature ranges from 20 o C to 30 o C. The integrated modulator has static extinction ratios of larger than 20 dB at a reverse bias voltage of − 2 V. The small signal modulation bandwidth of the modulator is larger than 11 GHz. At 10 Gb/s data modulation, the dynamic extinction ratio is about 9.5 dB in a back to back test configuration. Because only a simple fabrication procedure is needed, our EMLs are promising low cost light sources for optical fiber transmission applications.

We present data transmission using a directly modulated distributed Bragg reflector (DBR) laser having an integrated Ti thin film heater in the DBR section and butt-jointed InGaAsP as DBR material. By combining DBR current tuning and thermal tuning effects, an over 16 nm wavelength tuning range is obtained. 5 Gb/s data transmissions are conducted at up to 25 km distance and different wavelengths. In the fabricated device, the butt-jointed InGaAsP material is also used for the formation of an integrated photodiode for monitoring the light power of the device.

Synchronized dual-wavelength narrow-linewidth lasers and a wideband frequency-tunable optoelectronic oscillator are simultaneously realized using mutual-injection-locked distributed feedback (DFB) lasers. The two laser modes serve as the seeding light and a microwave photonic filter for the optoelectronic oscillation. Mutual-injection locking between the two DFB lasers through a delay fiber loop results in synchronized narrow-linewidth operation. Microwave tuning from 19 to 41 GHz has been obtained through thermal-tuning of the DFB lasers, with the single-sideband phase noises below -100 dBc/Hz at a 10-kHz frequency offset from the carrier. Laser linewidth has been reduced from several-MHz to kHz with a linewidth reduction factor over 104.

Methanol oxidation is a very important reaction in diret methanol fuel cells. Developing stable and efficient Pt-based catalysts with a convenient method has been on the stage recently. Herein, we employed a convenient one-pot method to synthesize Pt nanoparticles encapsulated by polyoxometalates (POMs) spreading on a few layers of graphene oxide with a nickel foam as a conductive substrate. Four kinds of samples with different Pt loadings were finally obtained by adjusting the H2PtCl6 concentration, named as PPGN-n (n = 1, 2, 3, 4). The microscopic structure of the sample was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. It was proved that small-sized Pt nanoparticles with a diameter of ca. 2.47 nm spreaded on graphene oxide (GO) with the nickle foam support were successfully synthesized. The synthesized electrocatalysts exhibited higher electrocatalytic activities than commercial Pt/C for methanol oxidation in electrocatalytic tests. The mass activity of PPGN-1 of 250.6 mA mg−1 can be achieved. During the synthesis, POM was used as a bifunctional reagent; as a reductant for reducing chloroplatinic acid and a stabilizer for the regulation of the Pt nanoparticle size simultaneously. POM cooperated rapid synthesis of Pt nanoparticles can offer a new route for designing and synthesising electrocatalysts.

We report 1.3 µm InGaAlAs/InP lasers integrated with laterally tapered spot size converter (SSC) in reverse mesa shape. Because the top width is significantly larger than the bottom width for the reverse mesa ridge, high quality SSCs having narrow tip width can be fabricated through conventional photolithography with a high reproductivity. The Threshold current of the fabricated 1000 µm long SSC integrated device is 25 mA and 44 mW single facet optical power can be obtained at 300 mA current. The lateral and vertical divergence angles are as low as 8 ° and 11°, respectively.

We demonstrate a widely tunable InGaAs quantum-wells (QWs) distributed Bragg reflector (DBR) laser, in which the DBR section was realized by using butt-jointed InGaAsP ( λ = 1 . 46 μ m ) material. In the device process, we explored an optimal chemical etchant applied in the butt-jointed active–passive integration technology. A wide tuning range of 10.7 nm with 19 consecutive channels is obtained with a single tuning current at room temperature (RT). With the help of the heat sink temperature, the tuning range is expanded to 16 nm. A side mode suppression ratio (SMSR) of higher than 34 dB is obtained for all channels at 5 °C to 45 °C. A six-wavelength laser array that can cover a wavelength tuning range of 41.6 nm at 20 °C with a side mode suppression ratio higher than 37 dB in all channels is demonstrated by varying the grating periods. It is a promising light source for methane or multispecies gas detection.

The design and fabrication of an evanescently coupled waveguide InGaAs unitraveling-carrier photodiode (PD) are presented. Through doping the InGaAs absorption layer gradedly, a large built-in electric field can be obtained. As a result, a 4- $\mu \text{m}$ -wide 15- $\mu \text{m}$ -long PD has a bandwidth larger than 21 GHz at zero bias. Passive input waveguide is integrated monolithically with the PD by a simple process, which eases the integration of PD with other optical components.

We report the fabrication of a ten channel electroabsorption modulated DFB laser (EML) array. Different emission wavelengths of the laser array are obtained by selective area growth (SAG) technique, which is also used for the integration of electroabsorption modulators (EAM) with the lasers. An arrayed waveguide grating (AWG) combiner is integrated monolithically with the laser array by butt-joint regrowth (BJR) technique. A buried ridge waveguide structure is adopted for the AWG combiner. A self aligned fabrication procedure is adopted for the fabrication of the waveguide structure of the device to eliminate the misalignment between the laser active waveguide and the passive waveguide. A Ti thin film heater is integrated for each laser in the array. With the help of the heaters, ten laser emissions with 1.8 nm channel spacing are obtained. The integrated EAM has a larger than 11 dB static extinction ratios and larger than 8 GHz small signal modulation bandwidths. The light power collected in the output waveguide of the AWG is larger than −13 dBm for each wavelength.

We report a novel passively mode-locked quantum-well laser, which have an asymmetric colliding pulse mode-locked structure. The saturable absorber (SA) multi-quantum wells (MQWs) of the laser have bandgap, which is gradually varied along the ridge direction realized by selective area growth technique, forming a broadband absorber. As a result, light pulses are obtained at a repetition frequency of 226 GHz with a minimum pulse width of 605 fs under an appropriate current bias. Because of the continuous variation of the SA MQW bandgap, the SA absorption peak covers a wide range of wavelength, which makes the device more immune to SA bandgap change resulted from SA reverse bias or light absorption-induced heating of the SA, compared with traditional MQW mode-locked lasers.

Oriented growth of thin films of covalent organic frameworks (COFs) has attracted significant interest as the anisotropically aligned channels provide ideal nanoscopic domains that can facilitate mass transport or charge percolation. Despite some experimental progress in achieving oriented COF thin films, little is known about the kinetics and thermodynamics associated with the orientation or control over the solution-based growth process. We performed a systematic study of the thin film growth of an imine-based COF as a function of concentration and growth time. Grazing incidence wide-angle X-ray scattering (GIWAXS) was used to reveal the orientation and evolution of crystallization within the thin films at sequential growth stages. An unusual re-entrant transition from an oriented to disoriented to reoriented state was discovered, which correlates with the kinetics associated with independent surface- and solution-based nucleation and growth processes, as well as reorganization of disoriented COF crystallites.

Multiwavelength laser arrays with 25-GHz channel spacing have been fabricated by upper separate confinement heterostructure (SCH) layer selective area growth (SAG) technique. The reconstruction equivalent chirp (REC) technique is used to introduce an equivalent phase shift into the grating structure, so that a high single longitude mode yield of lasers can be ensured. Because different emission wavelengths are realized through thickness modulation of the upper SCH layer by SAG, the sampling period in the REC technique is the same for all the lasers in an array, which may alleviate the effects of the facet phase on the emission wavelength. The fabricated laser arrays have less than 0.051 nm standard deviation of wavelength deviations. Only conventional photolithography process is needed, helping to lower the fabrication cost of the laser arrays.

We report 10 Gb/s data transmission over 30 km using a packaged two-section InGaAsP distributed Bragg reflector (DBR) laser. The tunable DBR laser has a wavelength tuning range over 12 nm.

Boron and Nitrogen co-doped carbon nanotubes incorporated iron carbide (Fe3C) nanoparticles (Fe3C@BN-C) were successfully prepared by one-step pyrolysis method employing melamine, ferric chloride and boric acid as precursors. Characterizations indicate that the catalyst has large specific surface area (258.17–305.74 m2/g) and abundant defect sites, which are closely related to the adsorption performance and catalytic efficiency of the catalysts. In the presence of peroxymonosulfate (PMS), the removal rates of Fe3C@BN-C-7, Fe3C@BN-C-8 and Fe3C@BN-C-9 for doxycycline hydrochloride (DOX-H) are 87.0%, 91.9% and 86.0% within 120 min. Fe3C nanoparticles, oxygen-containing functional groups, pyridinic N, pyrrolic N, graphite N and B, N dopants play a vital role in the improvement of catalytic activity. Quenching experiments and electron paramagnetic resonance (EPR) studies show that singlet oxygen (1O2) is dominant reactive oxygen species, demonstrating that the degradation reaction predominantly follows the non-radical oxidation pathway. The possible degradation pathway of DOX-H is proposed and 14 intermediate products are reported for the first time. This work not only provides a novel and valuable catalyst for pharmaceutical wastewater treatment, but also reveals a new perspective for the study of activated PMS dominated by non-radical pathway.

In this study, the MnCo2O4/g-C3N4 (CMCN2) is used to activate peroxymonosulfate (PMS), for treating nitrobenzene (NB) and industrial wastewater containing nitrobenzene homologue. Different from traditional sulfate radical-based advanced oxidation processes (SR-AOPs), high-valent metal-oxo species (MIV(O)/MV(O)) is a major reactive component via dimethyl sulfoxide (DMSO) as a verify compound. The mechanism is speculated that the bond of nitrogen–metal = oxygen (N–M = O) activates PMS to form MIV(O)/MV(O) during sacrificial oxidation. The quenching experiments and electron spin resonance (ESR) confirm that CMCN2 activated PMS to form OH and SO4 –. The Langmuir-Hinshelwood model conforms to the NB degradation curve, and the best removal efficiency is 96.7% in 240 min. The CMCN2/PMS system has excellent stability between pH 3–10. Also, the CMCN2/PMS system exhibited satisfactory removal of NB in the presence of inorganic anions and natural organic matters. The treatment effect of industrial wastewater containing phenyl homologues shows that CMCN2/PMS has a high mineralization capacity. This study details the electron transfer during the formation of active components and provides new ideas for selecting active ingredients that degrade phenyl pollutants in the field of advanced oxidation.

We report the application of two widely tunable directly modulated distributed Bragg reflector (DBR) lasers to cover over 20 nm wavelength. 10 Gb/s data are transmitted up to 30 km distance at different wavelengths with the wavelength range. The results indicate that the DBR lasers are promising light sources for the next generation high capacity wavelength division multiplexed passive optical network (WDM-PON) systems.

The effects of doping in the multiquantum well (MQW) active region on the properties of InP-based long wavelength deep ridge transistor lasers (TLs) are numerically studied. Doping in the MQWs is shown to lead to a decrease of the slope efficiency and a notable increase of the current gain of the TLs, which makes MQW doping a useful tool for facilitating the design of TLs. When there are nonradiative recombination centers on the exposed MQW side walls of the TLs, doping in the MQWs is found to be able to enhance the performance of the TLs by reducing the threshold current and increasing the current gain greatly. With doping in the MQWs, the carrier diffusivity is decreased, making the defects less effective in consuming the carriers. The results show that doping in the MQWs helps to obtain high-quality TLs. The reduced carrier diffusion that results from doping also helps to improve the quality of a normal diode laser in case a deep ridge structure is needed.

We demonstrate a four-wavelength distributed feedback (DFB) diode laser array integrated with a semiconductor optical amplifier (SOA) for widely tunable terahertz (THz) mode-beating generation. The InP-based monolithically integrated chip consists of DFB laser diodes, an SOA, and a multimode interference (MMI) coupler. Microheaters and electrode plates are integrated on top of each DFB section for continuous and independent wavelength tuning. By heterodyning the output from the DFB lasers on a Uni-Traveling Carrier Photodiode (UTC-PD) integrated antenna, a continuous THz radiation ranging from 0.1 to 2.25 THz was obtained.

We report 10 Gb/s data transmissions using a packaged two-section InGaAsP/InP distributed Bragg reflector (DBR) laser. The tunable DBR laser has a wavelength tuning range of 12.12 nm. The DBR laser has greater than 10.84 GHz 3-dB direct modulation bandwidth within the wavelength tuning range. The 10 Gb/s data transmissions are performed at up to a distance of 30-km.

We report a novel single-cavity dual-wavelength laser that has two distributed Bragg reflector (DBR) gratings at each side of a gain section for THz communication applications. By varying the inject current of one of the DBR gratings, the optical beat frequency of the laser can be widely tuned. In the device, a high-speed electro-absorption modulator (EAM) is also integrated and can be used for up to 25 Gb/s data modulation.

InP-based photonic integrated circuits (PICs) have aroused great interest in recent years to meet the needs of future high-capacity and high-performance optical systems. With the advantages of small size, low power consumption, low cost, high reliability, InP-based PICs are promising solutions to replace the multiple discrete devices used in various systems. In this paper, we will review the design, fabrication, key integration technology and performance of several kinds of InP-based monolithically integrated transmitters developed in our group in recent years. Particular attention will be paid to the electro-absorption modulated laser (EML), multi-wavelength distributed feedback (DFB) laser arrays, widely tunable distributed reflector (DBR) lasers and their arrays, integrated amplified feedback lasers (AFL), and few-mode transmitters.

Significance Optically pumped far-infrared (OPFIR) lasers are one of the most powerful continuous-wave terahertz sources. However, such lasers have long been thought to have intrinsically low efficiency and large sizes. Moreover, all previous theoretical models failed to predict even qualitatively the experimental performance at high pressures. Here, we have developed an innovative model that captures the full physics of the lasing process and correctly predicts the behavior in the high-pressure regime. Validated against experiments, our model shows that nearly all previous OPFIR lasers were operating in the wrong regime and that 10 × greater efficiency is possible by redesigning the terahertz cavity. Our results reintroduce the use of OPFIR lasers as a powerful and compact source of terahertz radiation.

640 GHz THz signals were generated based on 1.55 μm operating wavelength sampled grating distributed-Bragg-reflector mode locked laser diodes and photomixing techniques which will pave a way to provide compact low-cost, robust THz sources.

Synchronized dual-wavelength narrow-linewidth laser and high-quality microwave signal generation is demonstrated using mutual-injection-locked DFB lasers with optoelectronic feedback. Two synchronized lasers with linewidth down to kHz and beating frequency of 23.3 GHz is realized.

A novel passively mode-locked quantum-well laser, which saturable absorber (SA) has gradually varied bandgap, is fabricated. Light pulses are obtained at a repetition frequency of 226 GHz with a minimum pulse width of 605 fs under an appropriate mono current bias.

A buried ridge stripe (BRS) structure InGaAsP-Si hybrid laser based on selective area metal bonding (SAMB) method is demonstrated. This novel hybrid laser structure combines the SAMB method's advantage of low bonding requirements and great flexibility and the BRS lasers' low threshold, high thermal performance, and good optical field and carrier confinement. The 300-$\mu $ m-long hybrid laser has a threshold current of 14 mA and a maximum single-facet output power of 5.4 mW at room temperature, with a slope efficiency of 0.17 W/A. The laser has a characteristic temperature of 50 K, with continuous wave operation at temperature >50 °C.

We report the fabrication details of a monolithically integrated electro-absorption modulated distributed feedback laser (EML) based on the ion-implantation induced quantum well intermixing (QWI) technique. To well-preserve material quality in the laser region, thermal-oxide SiO2 is deposited before implantation and the ion-implantation buffer layer is etched before annealing. Thirteen pairs quantum well and barrier are employed to compensate deterioration of the modulator’s extinction ratio (ER) caused by the QWI process. The fabricated EML exhibits an 18 dB static ER at 5 V reverse bias. The 3 dB small signal modulation bandwidth of modulator is over 13.5 GHz indicating that this EML is a suitable light source for over 16 Gb/s optical transmission links.

We present the fabrication of a low-cost multiwavelength laser array monolithically integrated with a passive optical combiner for optical line terminals (OLTs) in wavelength-division multiplexing (WDM) passive optical networks (PONs). By combining the upper separate confinement heterostructure layer selective area growth technique and the bundle integrated guide technique, both multiwavelength emission with highly uniform spacing and low-loss passive-waveguide material can be obtained in a single metal–organic chemical vapor deposition (MOCVD) growth step, which greatly simplifies the fabrication of the device. A prototype laser array, which has four distributed feedback (DFB) laser elements and a multimode interference coupler as combiner, is successfully fabricated. The shallow ridge structure of the DFB lasers and the deep ridge structure of the passive waveguides are obtained by a single dry etching step, which further eases the device fabrication. The properties of the device are measured and discussed. The results indicate that our method is promising for fabricating cost-effective OLT light sources for WDM-PONs.

The focus of this work was to study the photothermal effect of a silica-gold-silica nanocomposite in the near-infrared (NIR) region. The NIR region is considered a biological window because living cells and tissues have low light scattering and adsorption in this region. Both a laser source and a tungsten lamp source were used in this study. The critical parameters for photothermal efficiency, including nancomposite concentration and irradiation time, were evaluated. The penetration of the nanocomposites into mammalian cells was also investigated. With laser irradiation, the nanocomposite showed a significant photothermal effect in the NIR region. The maximal temperature that the nanocomposites could reach was 51.9 °C. Vybrant assays showed that 5 min of laser irradiation along with the nanocomposite caused target cell death through both apoptosis (59%) and necrosis (31%), while controls showed minimal effects. The nanocomposite may be a potential light-absorbing agent for NIR fluorescence-guided photothermal therapy.