Effect of copper impurity on the optical loss and Nd^(3+) nonradiative energy loss of Nd-doped phosphate laser glass

N31-type phosphate laser glasses doped with different concentrations of Cu were prepared. Their optical loss coefficient at 1053 nm wavelength and nonradiative transition rate from the Nd3＋ 4F3/2 state were determined and analyzed in detail. The optical loss coefficient per unit of Cu2＋ （cm–1/ppmw） and the fluorescence decay rate （Hz/ppmw） caused by Cu2＋ and Nd3＋ interaction were 0.0024 and 7.9, respectively. Cu impurity affected both optical loss at 1053 nm and fluorescent emission of Nd3＋ 4F3/2 state seriously in N31 laser glass.

Effect of optical losses on the transmission performance of a radio-over-fiber distributed antenna system

The effects of optical losses oil a directly-modulated radio-over-fiber （RoF） system used for distributed antenna networks are determined. The results show that with a properly designed bidirectional amplifier, the RoF link can tolerate over 20 and 16 dB of optical losses for down- and up-links, respectively. Simulation results are also consistent with the experimental data. These findings can contribute to tile design of RoF distributed antenna systems with different topologies.

QoS aware routing and wavelength allocation in optical burst switching networks using differential evolution optimization

The issue of burst losses imposes a constraint on the development of Optical Burst Switching （OBS） networks. Heavy burst losses strongly affect the Quality of Service （QoS） intended by end users. This article presents a QoS aware Routing and Wavelength Allocation （RWA） technique for burst switching in OBS networks. The RWA problem is modeled as a bi-objective Integer Linear Programming （ILP） problem, where objective functions are based on minimizing the number of wavelengths used and the number of hops traversed to fulfill the burst transmission requests for a given set of node pairs. The ILP model is solved using a novel approach based on a Differential Evolution （DE） algorithm. Analytical results show that the DE algorithm provides a better performance compared to shortest path routing, which is a widely accepted routing strategy for OBS networks.

Control of gain and thermal carrier loss profiles for mode optimization in 980-nm broad-area vertical-cavity surface-emitting lasers

Optical gain and thermal carrier loss distributions regarding current diffusion and various electric contact areas are investigated to improve the near-field modes from the ring-shape to a Gaussian-like configuration for extra-broad-area and oxide-confined vertical-cavity surface-emitting lasers. In this work an equivalent circuit network model is used. The resistance of the continuously-graded distributed Bragg reflectors （DBRs）, the current diffusion and the temperature effect due to different electric-contact areas are calculated and analyzed at first, as these parameters affect one another and are the key factors in determining the gain and thermal carrier loss. Finally, the gain and thermal carrier loss distributions are calculated and discussed.

Temperature-dependent optical properties of low-loss plasmonic SrMoO_(3)thin films

SrMoO_(3)(SMO)thin films are deposited on LaAlO_(3)substrates by magnetron sputtering.The effects of ambient temperature on the structural,electrical,and optical properties of the films are investigated.As the temperature increases from 23℃ to 800℃,the SMO film exhibits high crystallinity and low electrical resistivity,and the real part of dielectric functions becomes less negative in the visible and near-IR wavelength range,and the epsilon near zero(ENZ)wavelength increases from460 nm to 890 nm.The optical loss of the SMO film is significantly lower than that of Au,and its plasmonic performance is comparable to or even higher than TiN in the temperature range of 23℃ to 600℃.These studies are critical for the design of high-temperature SMO-based plasmonic devices.

850 nm Implant-confined VCSEL Temperature Characteristics

The temperature characteristics of VCSEL using proton implantation are described,compared with its edge-emitting counterpart.Implant-confined VCSEL operation has been realized up to 120 ℃.These records of high operating temperature are caused by high characteristic temperature. The relevant physical mechanisms including their dependence on temperature and carrier density are considered. The temperature sensitivity of the threshold current is not strongly increasing with higher temperature.

Enhancing performance of GaN-based LDs by using GaN/InGaN asymmetric lower waveguide layers

The effects of Ga N/In Ga N asymmetric lower waveguide(LWG)layers on photoelectrical properties of In Ga N multiple quantum well laser diodes(LDs)with an emission wavelength of around 416 nm are theoretically investigated by tuning the thickness and the indium content of In Ga N insertion layer(In Ga N-IL)between the Ga N lower waveguide layer and the quantum wells,which is achieved with the Crosslight Device Simulation Software(PIC3D,Crosslight Software Inc.).The optimal thickness and the indium content of the In Ga N-IL in lower waveguide layers are found to be 300 nm and 4%,respectively.The thickness of In Ga N-IL predominantly affects the output power and the optical field distribution in comparison with the indium content,and the highest output power is achieved to be 1.25 times that of the reference structure(symmetric Ga N waveguide),which is attributed to the reduced optical absorption loss as well as the concentrated optical field nearby quantum wells.Furthermore,when the thickness and indium content of In Ga N-IL both reach a higher level,the performance of asymmetric quantum wells LDs will be weakened rapidly due to the obvious decrease of optical confinement factor(OCF)related to the concentrated optical field in the lower waveguide.

Optimized design and fabrication of nanosecond response electro optic switch based on ultraviolet-curable polymers

A nanosecond response waveguide electro-optic （EO） switch based on ultraviolet （UV） sensitive polymers of Norland optical adhesive （NOA73） and Dispersed Red 1 （DR1） doped SU-8 （DR1/SU-8） is designed and fabricated. The absorption properties, refractive indexes, and surface morphologies of NOA73 film are characterized. The single-mode transmission condition is computed by the effective index method, and the percentage of optical field distributed in EO layer is optimized to be 93.78 %. By means of spin-coating, thermal evaporation, photolithography, and inductively coupled plasma etching, a Mach-Zehnder inverted-rib waveguide EO switch with micro-strip line electrode is fabricated on a silicon substrate. Scanning electron microscope characterization proves the physic-chemical compatibility between NOA73 cladding and DR1/SU-8 core material. The optical transmission loss of the fabricated switch is measured to be 2.5 dB/cm. The rise time and fall time of switching are 3.199 ns and 2.559 ns, respectively. These results indicate that the inverted-rib wave- guide based on UV-curable polymers can effectively reduce the optical transmission loss and improve the time response performance of an EO switch.

Improved all-optical OR logic gate based on combined Brillouin gain and loss in an optical fiber

Improved all-optical OR gates are proposed, using a novel fiber nonlinearity-based technique, based on the principles of combined Brillouin gain and loss in a polarization-maintaining fiber （PMF）. Switching contrasts are simulated to be between 82.4%-83.6%, for two respective configurations, and switching time is comparable to the phonon relaxation time in stimulated Brillouin scattering （SBS）.

Photonic bands,gap maps,and intrinsic losses in three-component 2D photonic crystal slabs

We obtain the photonic bands and intrinsic losses for the triangular lattice three-component two- dimensional （2D） photonic crystal （PhC） slabs by expanding the electromagnetic field on the basis of waveguide modes of an effective homogeneous waveguide. The introduction of the third component into the 2D PhC slabs influences the photonic band structure and the intrinsic losses of the system. We examine the dependences of the band gap width and gap edge position on the interlayer dielectric constant and interlayer thickness. It is found that the gap edges shift to lower frequencies and the intrinsic losses of each band decrease with the increasing interlayer thickness or dielectric constant. During the design of the real PhC system, the effect of unintentional native oxide surface layer on the optical properties of 2D PhC slabs has to be taken into consideration. At the same time, intentional oxidization of macroporous PhC structure can be utilized to optimize the design.

Characterization of a Raman-based distributed fiber optical temperature sensor in liquid nitrogen

Distributed Temperature Sensor(DTS)based on Raman scattering have a promising application in temperature monitoring and quench detection of high‐temperature superconducting(HTS)fiber optic cable.In this paper,a series of mechanical property tests were carried out on fiber optical cables with different encapsulation materials to select the best material for the engineering environment.This was followed by loss testing of fiber optic cables with different outer diameters under liquid nitrogen(LN_(2))and the optimal outer diameter to meet measurement accuracy and engineering practicability was determined.Finally,the temperature measurement of fiber optic cables laid on HTS fiber optic cables were calibrated using thermocouple as a reference.The results of this research results provide a suitable fiber optic cable for engineering applications.At the same time,it provides a reference for the selection of optical cable structure parameters in HTS optical cable projects.

Design and growth of GaN-based blue and green laser diodes

GaN-based laser diodes(LDs)extend the wavelength of semiconductor LDs into the visible and ultraviolet spectrum ranges,and are therefore expected to be widely used in quantum technology,bio&medical instruments,laser displays,lighting and materials processing.The development of blue and green LDs is still challenging,even though they are based on the sameⅢ-nitride materials as GaN-based lightemitting diodes.The challenges and progress of GaN-based blue and green LDs are reviewed from the aspects of epitaxial growth and layer structure design.Due to large differences in lattice constants and growth conditions for InN,GaN,and AlN,considerable effort is required to improve the quality of InGaN multiple quantum well(MQW)gain medium for blue and especially green LDs.p-type doping profiles,conditions and layer structures are critical to reduce the internal losses and to mitigate the degradation of InGaN MQWs.Hole injection is also a key issue for GaN-based LDs.

GaInN light-emitting diodes with omni-directional reflector using nanoporous SnO_2 film

Enhancement of light extraction in a GaInN light-emitting diode （LED） employing an omni-directional reflector （ODR） consisting of GaN, SnO2 nanorod and an Ag layer was presented. The ODR comprises a transparent, quarterwave layer of SnO2 nanorod claded by silver and serves as an ohmic contact to p-type GaN. Transparent SnO2 sols were obtained by sol-gel method from SnCl2·2H2O, and SnO2 thin films were prepared by dip-coating technique. The average size of the spherical SnO2 particles obtained is 200 nm. The refractive index of the nanorod SnO2 film layer is 2.01. The GaInN LEDs with GaN/SnO2/Ag ODR show a lower forward voltage. This was attributed to the enhanced reflectivity of the ODR that employs the nanorod SnO2 film layer. Experimental results show that ODR-LEDs have lower optical losses and higher extraction efficiency as compared to conventional LEDs with Ni/Au contacts and conventional LEDs employing a distributed Bragg reflector （DBR）.

Perovskite/Si tandem solar cells: Fundamentals, advances,challenges, and novel applications

The world record device efficiency of single-junction solar cells based on organic–inorganic hybrid perovskites has reached 25.5%.Further improvement in device power conversion efficiency(PCE)can be achieved by either optimizing perovskite films or designing novel device structures such as perovskite/Si tandem solar cells.With the marriage of perovskite and Si solar cells,a tandem device configuration is able to achieve a PCE exceeding the Shockley–Queisser limit of single-junction solar cells by enhancing the usage of solar spectrum.After several years of development,the highest PCE of the perovskite/Si tandem cell has reached 29.5%,which is higher than that of perovskite-and Si-based singlejunction cells.Here,in this review,we will(1)first discuss the device structure and fundamental working principle of both two-terminal(2T)and four-terminal(4T)perovskite/Si tandem solar cells;(2)second,provide a brief overview of the advances of perovskite/Si tandem solar cells regarding the development of interconnection layer,perovskite active layer,tandem device structure,and lightmanagement strategies;(3)third,discuss the challenges and opportunities for further developing perovskite/Si tandem solar cells.This review article,on the one hand,provides a comprehensive understanding to readers on the development of perovskite/Si tandems.On the other hand,it proposes various novel applications that may bring such tandems into the market in a near future.