This PDF file contains the front matter associated with SPIE Proceedings Volume 11680

The work focuses on the modeling and simulation of plasmonic organic hybrid electro/optic modulators. Preliminary multiphysics-augmented simulations of the slot plasmonic waveguide phase modulator are presented. Instead of applying them to system-level models, they are combined with the results of 3D finite-difference time- domain (FDTD) simulations to achieve realistic physics-based simulations at moderate computational costs. The model is demonstrated on a Mach-Zehnder plasmonic modulator inspired to literature results and validated through a comparison with 3D-FDTD simulations of the entire device.

Nowadays, compound semiconductors are the main approach to detect mid-infrared (IR) light, such as HgCdTe and InAsSb, due to the bandgap tunability compared with Si. However, the epitaxy processes are expensive and energy-intensive. Also, compound devices are not compatible with Si-based IC manufacturing. To solve those problems, here, we apply inverted pyramid array structures (IPAS) to induce localized surface plasmon resonance (LSPR) for Si-based Schottky devices. While IR illuminates metal covered IPAS (metal-IPAS), the photo-electrons can accumulate photon energy repeatedly through IPAS induced LSPR. While the electron energy is large enough to overcome the Schottky barrier, so the photo-current is generated. Regarding device preparation and measurement, briefly, the IPAS were formed on n-type Si (n-Si) substrates through photolithography, dry etching, and wet etching. Afterward, 10-nm-thick Ag films and 100-nm-thick Ag grid anode were thermally deposited on the IPAS successively to form Schottky junctions. Finally, Al was thermally deposited on the back of n-Si wafers to be the cathode. After device fabrication, the devices were illuminated by a 4010 nm mid-IR pulse laser, generated from a 1064 nm pulse laser through an optical parametric generator. The photo-voltage of the device induced by the mid-IR was measured by an oscilloscope. Consequently, the oscilloscope showed a short pulse while the device was illuminated by the 4010 nm pulse laser. The rising time is 8 ns, and the amplitude is 10.2 mV. The result reveals that the metal-IPAS induced LSPR successfully detects mid-IR light with photon energy less than Schottky barrier height.

Despite the benefits that optics and photonics have brought to improving communications, there remains a lack of commercialized optical computing devices and systems, which reduces the benefits of using light as an information-carrying medium. We are developing architectures and designs of photonic logic gates for creating larger-scale functional photonic logic circuits. In contrast to other approaches, we are focusing on the development of logic devices which can be cascaded in arbitrary ways to allow for more complex photonic integrated circuit design. Additionally, optical computing often uses on-off keying, which fails to take advantage of denser encoding schemes often used to optically transmit data. We propose that devices that operate on phase-shift keying will not only be more efficient, but easier to cascade. To achieve the goal of cascadable devices operating on phase-shift keying, we have designed a plasmonic waveguide logic device using inverse design tools. These tools have allowed us to create a device with an arbitrary topology that has increased performance and reduced footprint compared to a conventional device with the same operation. In addition, inverse design simplifies the process of designing devices that operate with phase-shift keying, which can become complicated with conventional design methods. In order to implement inverse design tools for plasmonic devices and phase-shift keying, we used fully 3D FDTD simulations. We compare the inverse-designed devices to more conventional devices in order to characterize their performance.

Ghost metrology is a measurement modality exploiting correlation of photons. Recently, we have demonstrated ghost imaging and ghost spectroscopy by exploiting spatial and spectral photon correlations of amplified spontaneous emission light emitted by optoelectronic superluminescent diodes and erbium-doped fiber amplifiers. Here, we now exploit polarization correlations of so-called unpolarized light. We conceive and realize a novel communication scheme, - Ghost Polarization Communication (GPC) -, between two parties, Alice and Bob, which is based on the ultra-fast correlations of the polarization state of unpolarized classical light emitted by an erbium-doped fiber amplifier (EDFA) and which provides a measure of security directly on the physical layer. The light emitted by the EDFA is divided in to a reference arm which remains solely on Bob’s side and an object arm which is sent to Alice, who encodes a message onto the unpolarized light via a half-wave plate and sends it back to Bob. By determining the second-order correlation coefficient g⁽²⁾ on femtosecond timescale and using an agreed encoding table or keypad he uniquely extracts the message which has been camouflaged within the infinite number of polarization states on the Poincaré sphere. The investigated polarization correlation results are modelled within a theoretical approach based on the Stokes vectors dynamics and a Glauber protocol for g⁽²⁾ and the experimental results are in excellent agreement with this theory. We conclude with a proof-of-principle demonstration of a message transmitted by GPC and discuss real-world implementation and security issues of the proof-of-principle demonstration.

We report a study of the photoconductivity mechanism and transport paths of photoexcited charge carriers in the GeSn/Ge/Si heterostructures. The dark conductivity was studied as a function of temperature, which allowed to identify of the presence of deep levels at E_V+(100÷130) meV. We have established that point defects are the source of a band of electronic states and determine the photoconductivity response. The photocurrent dependencies on excitation intensity demonstrate that the main conduction occurs mainly through the Ge layer under low pumping and through the Si substrate under high one, since the GeSn top layer is much thinner has a much higher conductivity. This detailed understanding of the recombination processes is of critical importance for developing GeSn/Ge-based optoelectronic devices.

Printing polymer optical waveguides by means of combined printing processes has proven to be a challenging but effective way of producing waveguides with a loss less than 0.3dB/cm. In order to evaluate the optical performance of the produced waveguides, optical simulations have been carried out. In this work we show the influence on the optical performance by simulating droplets and enclosures in multimode waveguides with a proprietary raytracing algorithm. Critical waveguide parameters such as width and height variation will be evaluated. Finally, experimentally achieved optical performance is presented and compared with the simulation result.

Here, we introduce an integrated photonics-based tensor core unit by strategically utilizing i) photonic parallelism via wavelength division multiplexing, ii) high Peta-operations-per second throughputs enabled by 10’s of picosecond-short delays from optoelectronics and compact photonic integrated circuitry, and iii) near-zero static power-consuming novel photonic multi-state memories based on phase-change materials featuring vanishing losses in the amorphous state. Combining these physical synergies of material, function, and system, we discuss a design and performance of a 4-bit photonic tensor core unit.

Optical approaches to machine learning rely heavily on programmable linear photonic circuits. Since the performance and energy efficiency scale with size, a major challenge is overcoming scaling roadblocks to the photonic technology. Recently, we proposed an optical neural network architecture based on coherent detection. This architecture has several scaling advantages over competing approaches, including linear (rather than quadratic) chip-area scaling and constant circuit depth. We review the fundamental and technological limits to the energy consumption in this architecture, which shed light on the quantum limits to analog computing, which are distinct from the thermodynamic (e.g. Landauer) limits to digital computing. Lastly, we highlight a recent "digital" implementation of our architecture, which sheds light on the scaling challenges associated with controlling aberrations in the free-space optical propagation.

Deep neural networks exploit millions or more free parameters that are tuned to a requisite large and curated dataset. The black-box nature of these models masks interpretability and the ability to diagnose failures. Although astonishing performance gains are being achieved, these come at the expense of exponential rise in computation and memory utilization. This talk will review how the emerging convergence of physics and neural networks will confront these challenges, extend the rise of artificial intelligence, and create opportunities for scientific discoveries.

This work shows that optical feedback can either stabilize or destabilize quantum cascade lasers, depending on the alignment of the reflection mirror. On one hand, the laser is insensitive to the common well-aligned optical feedback, and the relative intensity noise has little change against optical feedback. Meanwhile, strong optical feedback well stabilizes the laser frequency and significantly narrows the spectral linewidth, instead of evoking chaotic oscillations. On the other hand, misaligned optical feedback with a tilt angle of the reflection mirror triggers multiple nonlinear dynamics including periodic oscillations, quasi-periodic oscillations, and low-frequency oscillations.

Optical feedback usually gives rise to rich nonlinear dynamics in semiconductor lasers, which are interesting for both physics and applications. In comparison with common quantum well lasers, the laser emission of mid-infrared interband cascade lasers relies on the interband transition of type-II quantum wells. This work experimentally explores the nonlinear dynamics of an interband cascade laser subject to optical feedback. It is found that the interband cascade laser exhibits both periodic oscillations and fully-developed chaos at different feedback ratios.

This work theoretically investigates the optical noise characteristics of mutually-coupled quantum cascade lasers, which is achieved through the small-signal analysis of a set of rate equations with Langevin noise sources. It is shown that the stable locking range of the mutually-coupled lasers is on the order of several GHz. Within the stable locking range, the inphase mutual injection hardly changes the relative intensity noise of the lasers. In contrast, the frequency noise and the spectral linewidth of the coupled lasers can be reduced by about 10 dB.

Photonics integrated circuits on silicon are considered as a key technology for data centers and high-performance computers. Owing to the ultimate carrier confinement and reduced sensitivity to crystalline defects, semiconductor quantum dot lasers directly grown on silicon exhibit remarkable properties such as low threshold current, high temperature stability and robust tolerance to external reflections. This latter property is particularly important for achieving large-scale integrated circuits whereby unintentional back-reflections produced by the various passive/active optoelectronic components can hinder the stability of the lasers. In this context, it is known that quantum dot lasers are more resistant to optical feedback than quantum well ones thanks to the low linewidth enhancement factor, the large damping, and the possible absence of upper lasing states. In this work, we theoretically investigate the reflection sensitivity of quantum dot lasers directly grown on silicon by studying the peculiar role of the epitaxial defects, which induce nonradiative recombination through the Shockley-Read-Hall process. By using the Lang and Kobayashi model, we analyze the nonlinear properties of such quantum dot lasers through the bifurcation diagrams and with respect to the nonradiative lifetime. In particular, we show that the increase of the Shockley-Read-Hall recombination shrinks the chaotic region and shifts the first Hopf bifurcation to higher feedback values. We believe that these results can be useful for designing novel feedback resistant lasers for future photonics integrated circuits operating without optical isolator.

Time-delay reservoir computer (RC) based on semiconductor lasers provides a simple hardware implementation of the recurrent neural network. However, the data processing speed is limited by the length of the feedback loop. This work demonstrates a parallel RC scheme based on the wavelength division multiplexing (WDM) technique. This scheme is implemented on a Fabry-Perot quantum dot laser with multimode emission. It is shown that the four-channel WDM RC exhibits a better performance over the single-channel one, with the same number of virtual neurons. Meanwhile, the RC is accelerated by four times, owing to the shorter delay time. In addition, we show that the cross-gain saturation effect between the multimodes plays a crucial role on the RC performance.

This paper aims to characterise, both experimentally and theoretically, the dynamics which occur during the turn on transient of a long cavity semiconductor laser. The laser comprised of a semiconductor optical amplifier (SOA), centered around 1300nm, a tuneable narrow bandwidth filter, for wavelength selectivity, a polarisation controller, an output coupler and multiple single mode fibre isolators to ensure the unidirectional propagation of light within the ring cavity. The bias current driven to the SOA was periodically switched on and off in order to examine the laser dynamics within each cavity round trip. It is observed that the laser intensity builds up in a step-wise manner, with each step corresponding to one cavity round trip. By examining the space-time diagrams of the lasers intensity during the turn on, it is seen that the laser will initially randomly oscillate before transitioning into a semi-stationary state. After a certain amount of round trips the laser may develop one or more localised structures, characterised by their short and fast drops of intensity. In this paper we also aim to not only explain the formation of these localised structures but also expand on their development by examining the phase evolution of their electric field.

We present here a combined theoretical and experimental study to investigate the influence of external optical feedback in a semiconductor swept-source laser. The applied feedback is shown to transfer the coherence between the subsequent modes and retain it along the full sweep. As a result, the technique can act as a solution to the de-coherence during the mode-hops observed in this kind of swept-source lasers thus noticeable increasing the image quality of Optical Coherence Tomography systems.

Avalanche photodiodes (APDs) can provide high receiver sensitivity owing to their internal gain, however, the impact ionization gain mechanism is also a source of noise. Recently, AlxIn1-xAsySb1-y grown as a digital alloy has been used to fabricate APDs with excess noise as low as Si (k ~ 0.01). Operation of these APDs at telecommunication wavelengths (1300 nm to 1550 nm) or 2 µm has been achieved. This paper also discusses staircase APDs, which utilize compositional grading to mimic the dynodes of a photomultiplier tube, with a gain of 2x arising at each step providing extremely low noise avalanche gain.

InGaAs PIN detectors are extensively used for detection of photons in the wavelength range between 1000 nm and 1600 nm. Epitaxial InGaAs layers are commonly grown by MOCVD on InP substrates and layers of only a few micrometers are needed to fully absorb all IR radiation. In many applications, large area single- or multi-element InGaAs detectors are required with diameters ranging from 1 mm up to 5 mm. While useful for tracking large spots of IR light, their thin active layers have the disadvantage of a relatively large capacitance, which causes higher noise and reduced bandwidth. A PIN structure was designed with the purpose to reduce said capacitance by half and thus effectively double the value of the bandwidth when compared to standard values of catalog devices. The growth structure will be detailed, electro-optical measurement results will be presented and the next steps for specific markets such as laser spot tracking, semi-active laser guided precision-guided munitions or laser beam alignment over long distances will be presented. The new diodes have half the capacitance of regular PIN photodetectors leading to twice as much bandwidth at a low operating voltage. The combination of controlled epitaxial growth parameters with low defect density and low intrinsic doping in material have yielded new devices with proven reliability at high temperatures. Finally, it will be demonstrated that the change to the structure did not impact other parameters of the photodiode like dark current, breakdown voltage, responsivity or series resistance.

Here we report a new design for enlargement of the detection limit of a convention near infrare d InGaAs/InP photodetector to short wavelength infrared. In the new device configurations, we used GaAs _0.51Sb_{0 .49} as the p layer instead of InP layer because of its superiority in the hole lifetime. Also, by introducing different thickness of the GaAsSb in the absorption layer beside InGaAs, we engineered the electron and hole concentration in their corresponding interfaces of the absorption layer as well as the y component of the electric field to reach higher responsivity. The successful optimization of hybrid absorption layer photodetector with short wavelength infrared detection may accelerate the development of high-performance micro devices based on such configurations.

Many III-V digital alloy avalanche photodiodes have experimentally demonstrated very low excess noise. The presence of minigaps and enhanced valence band effective mass leads to the enhanced performance. Using first principle calculations and environment-dependent tight binding model we study the correlation of these properties with material parameters like stress. Furthermore, using NEGF formalism we study how these minigaps and mass enhancement impact the electron tunneling and phonon scattering processes in digital alloys. Based on our calculations, we propose some empirical inequalities for quantifying the effectiveness of such minigaps in making the device unipolar and thus high gain.

Transition metal dichalcogenides (TMDCs) have received a great deal of attention from the scientific community since the advent of graphene. Tungsten diselenide (2H-WSe₂) has particularly drawn-out attention of researchers because of its broadband spectral detection range. In this work, we have reported a halide assisted chemical vapor deposition (HA-LPCVD) technique for synthesis of large crystallites of 2H-WSe₂ with high crystalline perfection. The average crystallite size of synthesized 2H-WSe₂ was in the order of ~20 μm. We have reported device 2H-WSe₂ device fabrication using poly (methyl methacrylate) and electron beam lithography process to define titanium (Ti) metal contacts. A temperature (T) dependent analysis of the electronic transport reported here reveals a T-dependent conduction process existing at the interface of Ti and 2H-WSe₂ and an interfacial barrier height of ~ 0.35 eV was calculated at the thermionic emission regime. From the reported optoelectronic characterization, an on-off ratio (I_on/I_off) of ~9 was calculated. Furthermore, a responsivity (ℜ) of ~ 242 A/W was calculated for our 2H-WSe₂ based photodetector under broadband light excitation. The reported photodetector figures of merit will open avenues for use of monolayer 2H-WSe₂ with Ti metal contacts for high performance photodetection.

Semiconductor Nanowires (NWs) have revolutionized photonics by providing minimal footprint optoelectronic devices and coherent light sources. However, given their nanoscale dimensions, their integration with nanophotonic systems is a significant challenge. To overcome this issue, we have developed a hybrid nanofabrication technique, known as nanoscale transfer-printing, permitting the accurate integration of individually-selected NWs at target positions onto desired surfaces. Examples of nanophotonic systems enabled by our technique include 1D/2D NW laser arrays and on-chip waveguide-coupled NW laser systems. We have also recently demonstrated a nanophotonic circuit for THz signal detection formed by a 3D semiconductor NW network coupled with a metallic antenna structure.

Emerging quantum information technologies require a source that emits single photons at predetermined times under electrical pumping. Color centers in diamond attract considerable attention as a room-temperature single-photon source. However, their electroluminescence has been shown only in steady-state and not on-demand. Here, we show how to control the single-photon electroluminescence (SPEL) of SiV centers in a proposed diamond diode and switch SiV center SPEL rate from 2 cps to 1 Mcps and vice versa in less than 3 ns. Our findings bring closer on-demand electrically-driven single-photon sources operating at room temperature.

Aluminum nitride (AlN), which belongs to the family of the III-V semiconductors, is a material of great interest in the microelectronics industry due to its high decomposition temperature, good chemical stability, wide bandgap and CMOS compatibility. Moreover, AlN is known by its Pockels coefficients, which makes it very suitable for various non-linear optical devices. In this work, a study of a design space exploration of fundamental mode polarization in an AlN pedestal waveguide is proposed. The current work performs a dispersion analysis of this type of waveguide by varying the dimensions of the core and the pedestal. Lastly, electrode design for phase shifting analysis is also proposed. The data obtained with the exhibited work will allow the device designer to have a design space with light polarization control to stimulate the adequate electro-optic coefficient, with potential applications in modulators, switches, multiplexers, phase shifters, among others. A feasibility study will also be provided.

Under operating conditions, heterostructures can be exposed to high-energy radiation, for example, in space or at nuclear power or medical objects, which can lead to AlGaP LEDdegradation. Heterostructure resistance investigation is currently relevant and in the future will allow to create express method of predicting LED life time during their design and the possibilities for optimizing LEDs. Investigations of spectral parameters under irradiation cycles influence was carried out. It was detected that for increase life time and to decrease damage is need to use bulk substrates GaP.

Though AlGaN ultraviolet (UV) light-emitting diodes (LEDs) have been explored widely, their performance is still limited in the UV B and C regions due to several challenges. Electron leakage is one of the prominent reasons behind the poor performance of AlGaN deep UV LEDs. This problem can be mitigated by integrating the electron-blocking layer (EBL) between the active region and p-region to an extent, not entirely due to the own disadvantages of the EBL. In this regard, we report the achievement of high-performance EBL free AlGaN LEDs using a strip-in-a-barrier structure operating in the UV B and C regions, particularly at 254 nm and 292 nm wavelengths, respectively. Here, we have engineered each quantum barrier by integrating a 1 nm optimized intrinsic AlGaN strip layer in the middle of the QB. The resulting structure could significantly reduce the electron overflow and enhance the output power by ~1.87 times and ~1.48 times for 254 nm and 292 nm LEDs, respectively, compared to the conventional structure. Moreover, internal quantum efficiency droop is reduced notably in the proposed structure at 254 nm and 292 nm wavelengths.

We present a numerical model based on Coupled Mode Theory for modelling and optimization of thermally tuned semiconductor lasers used in digital coherent transceivers. This modular approach allows combinations of waveguides, gratings and microrings, and enables the quick simulation of longitudinal modes. Our comparative study shows that the combination of a phase-modulated DBR and a microring results in a promising, compact tunable laser diode for telecommunication and signal processing. It requires low tuning power due to the small footprint of microring. Wavelength tuning range is controlled effectively by the finite number of peaks of phase-modulated DBR, and the envelope of its reflectivity comb can be optimized numerically.

A quantum dots photonic CMOS device includes a quantum dot laser in the MOSFET drain region, and a photon sensor in the MOSFET drain / well regions. The MOSFET, quantum dot laser, and photon sensor are fabricated as one integral device. When a voltage is applied to the MOSFET gate, and a voltage is applied to the drain, both MOSFET and quantum dot laser are on. Light from the quantum dot laser is absorbed by the embedded photon sensors (which can be avalanche photo diodes (APD)), which produce a large light current flowing back to the drain and laser as part of total output current. When the MOSFET is off, both quantum dot laser and photon sensor are off. Quantum dot laser is well known for its near 0V laser diode forward voltage. As a field effective transistor, photonic CMOS is dominated by electric fiends and less dependent on temperatures. The embedded MOSFET, laser and APD form an amplifier that can substantially improve the external quantum efficiency of quantum dot lasers.

Perovskite solar cells are called to revolutionize the field of optoelectronic due to their intrinsic high absorption. Photonic structuration is widely reported as an efficient way to improve light harvesting. Nevertheless, little is known on the combination of photonic structuring and perovskite material. In this study, photonically-structured TiO2 is considered as photoanode layer for perovskite solar cells in a will to enhance light absorption through the excitation of quasi-guided modes within the photoactive perovskite material, while optimizing the charge collection and the global efficiency in the photovoltaic assemblies. Consequently, the photo-active layer is structured using opal-like perovskite layers (monolayers, bilayers or trilayers) made of perovskite (full or truncated) spheres, including hybrid uniform/structured layers, embedded in a TiO2 matrix. We present both numerical simulations and experimental results.

Optical singularities are dark regions of a light field that exhibit rich and nonintuitive behaviors such as local wavenumbers that far exceed the light field wavenumber. For example, helical beams have a one dimensional singularity along the axis of the optical vortex where the phase is undetermined. We demonstrate that both phase and polarization singularities can be engineered and that in addition to the common one-dimensional string-like topologies, we can produce a broader family of 0D (point) and 2D (sheet) singularities. As a potential application, we design an array of point singularities to serve as identical blue-detuned cold atom traps with three-dimensional confinement. Singularity engineering imbues microscale wavefront engineering tools with the ability to produce exotic forms of light deterministically and on-demand and has wide applicability to other wave-like systems in physics.

When engineering photonic integrated structures, there will be a time that one must consider coupling out the electromagnetic field to an external device. Often, this coupling is made through a single mode optical fibre. Due to the mismatch in mode field diameters between waveguide and fibre modes, the propagating mode inside the dielectric waveguide must undertake a spot-size conversion. It requires to be radially expanded, often laterally by a tapered waveguide and longitudinally through other means, to match the radial profile of the optical fibre mode. Then, the energy must be coupled out of its propagating path into the plane of the optical fibre, through a structure that possesses such functional purpose. In this work, we describe the design steps and optimization of a silicon nitride waveguide/fibre coupler operating in the visible range. To this end, we start by designing an optimized 3D taper waveguide, using Beam Propagation method, that performs as the spot-size converter. Next, through the Eigen Mode Expansion method, a 2D subwavelength grating is designed and optimized regarding substrate leakage and propagating plane energy coupling out, thus vertically validating the energy distribution of the outgoing profile. The required subwavelength grating apodization is accomplished, once more through the Eigen Mode Expansion method, and by carefully engineering a metamaterial that performs accordingly. The obtained diffraction grating is then expanded horizontally to create a 3D structure and laterally validated through Beam Propagation method. Finally, the whole 3D structure is optimized and validated through Finite Differences Time Domain simulations regarding energy profile coupling out, and overlap integral matching is established with the fibre mode profile.

In this study, we investigate dispersive effects of a wire-grid polarizer (WGP) in imaging polarimetry. Dispersion in periodic structures such as WGP may cause dispersive misregistration in images captured in the far-field imaging system. As a measure of performance, we defined off-axis non-uniformity (NT_off) and extinction ratio (ER_off) to evaluate non-uniformity induced by off-axis imaging scene. Similarly, we considered metrics to evaluate dispersive effects as wavelength-dependent non-uniformity in extinction ratio (NERλ) and transmittance (NTλ). Significant non-uniformity in the performance of a WGP was measured: the highest non-uniformity was obtained as |NT_off|_max = 0.93211 at Λ = 400 nm and |NER_off|_max = 0.93624 at Λ = 600 nm, while |NT_λ|_max = 0.84935 at Λ = 400 nm and |NER_λ|_max = 0.90139 at Λ = 300 nm. We also present images in imaging polarimetry that suffers from dispersive effects.

The SIG (chalcogenide glass) developed by Sunny Infrared Optics is suitable for all kinds of thermal lenses, especially for molding lenses. It has competitive price and several advantages including stable refractive index, low softening temperature, great material uniformity. However, SIG is relatively soft and easy to be scratched. Sunny Infrared Optics has developed HD (high-durable) coating for SIG to protect the lenses from environmental damage. HD coating combines the best attributes of DLC coating(diamond-like carbon) and AR coating(anti- reflection), while minimizing their disadvantages. For one thing, HD coating is harder and more durable than AR coating, for another, the transmittance of HD coating is higher than DLC coating. HD coating on SIG is becoming a more popular solution for security application from fire protection to border defense.

The need for rapid, compact, and accurate biosensing capability has increased dramatically in recent times in biomedical and environmental applications. Optical biosensing is one of the most promising methods for virus and chemical substance detection. With analytes or substance binding to the ligands that are attached to the surface or nanoparticles, the optical spectra shift accordingly resulting in detection of a specific substance. Localized surface plasmon resonance (LSPR) technique can be applied to enhance the detection sensitivity, providing an improvement on optical biosensor devices. However, the literature on wide bandgap GaN-based optical biosensor utilizing LSPR is limited, even though GaN-based visible optoelectronic devices have been widely implemented in various applications. Thus, it is important to design and optimize the GaN-based biosensors for their use in optical biosensing applications. In this work, optical properties of GaN-based structure with LSPR effect are investigated using the Finite-Difference-Time-Domain (FDTD) simulation method. GaN-based structures are constructed with nanoparticles coated on GaN surface. The nanoparticles are designed taking into consideration the size and metal elements such as gold, silver, and titanium. A modified refractive index-varying layer is incorporated to mimic the substance attachment on the structure surface. Electric field spectra show that optimizing the GaN-based structures will lead to the LSPR effect, confirming its potential for biosensing applications In addition, the optical spectra of the GaN-based sensor structures show sharp shifts (~ 4 nanometers per .01 refractive index change) when the refractive index of the substance layer is tuned. Additional investigations on the GaN-based sensor with various optimized design parameters will be discussed in further detail.

The hardness of rigid electronic devices limits its application scope. People use flexible scheme to improve it, so the design of flexible circuit structure is very important. Some special structures, such as island bridge structure, mesh structure and serpentine structure, can make the circuit have the ability of deformation. However, people cannot get good results from using a single structure, but the multi-level structures may improve the flexibility. Inspired by the softness of the net in our life, combined with the honeycomb structure, we design a 2-D honeycomb mesh structure. When the mesh is stretched, the 2-D hole is deformed by stress, and the local large strain converts to the small strain of the whole structure to avoid fracture. The stretch-ability of the single-level honeycomb mesh structure is 6.77%. Then, in order to further improve the flexibility, the serpentine structure is applied to the edge of the honeycomb structure to form a two-level structure. When the primary-level honeycomb structure is stretched, the second-level serpentine structure is also appropriately stretched to improve the flexibility. Finite element analysis shows the stretch-ability is 8.3%, which is better than single-level structure. Next, we also simulate the bending angle and twist angle of the structure, which has 120 degree bending (bending radius 1.55mm), 54 degree twisting and no plastic deformation occurs. It is clear that the multi-level microstructure has better flexibility, which provides a new scheme for the fabrication of flexible electronic devices and circuit microstructure design.

The InAs/InAsSb superlattices are attractive materials for the replacement of both RoHS restricted bulk HgCdTe and strongly Shockley-Read (SR) generation limited InAs/GaSb superlattices. Two main factors limit the performance of InAs/InAsSb photodiodes: the rate of the SR processes, especially in the depletion region, which is the source of the large dark current and a short vertical diffusion length of charge carriers in superlattice absorbers which results in poor responsivity. In this paper, we report on the status of HOT LWIR detectors based on InAs/InAsSb superlattices at VIGO System S.A. The uncooled and Peltier cooled LWIR photoconductors are the most successful devices developed so far. The practical InAs/InAsSb SL-based photoconductors have been fabricated by MBE heteroepitaxial growth on buffered 3” wafers. The design of the devices, material composition and doping, has been optimized for operation at temperatures from 200 to 300 K at a spectral range up to 18 μm. Some of the detectors were supplied with immersion microlenses formed in the GaAs substrates. The devices were characterized by measurements of the spectral responsivity and frequency-dependent noise density. The measured spectral detectivities of the best SL devices were found to be close or better compared to the HgCdTe counterparts operating at the same conditions. The devices are now offered as commercial products. Vigo present efforts are focused on the development of HOT LWIR photodiodes including monolithic cascade devices and thin absorber devices with the plasmonic enhancement of absorption. The development roadmap of advanced HOT devices is also sketched.

Recently, optical waveguides designed by utilizing metal-insulator-metal (MIM) are widely used because of its excellent ability to limit surface plasmons to a deep sub-wavelength scale. In this paper, combined design of OR and universal NAND logic gates is proposed using the switching property of non-linear effect of plasmonic-MIM waveguide-based Mach–Zehnder interferometer. The footprint of proposed Feynman logic gate is 42μm*9μm, extinction ratio is 9.03dB for NAND gate and 11.25dB for OR gate. An insertion loss of -0.705dB for NAND gate and -0.655 dB for OR which is much better as compared to electro-optic based structures.The simulation is done using a finite-difference time-domain (FDTD) method and mathematical modeling of the device that has been verified by using MATLAB.

In this study, we have investigated the effect of varying In-concentration in the barrier material of Stranski-Krastanov (SK) on sub-monolayer (SML) InAs quantum dots (QDs). Four different heterostructures (A, B, C, and D) have been modeled using Nextnano software. Structures A, B, C, and D with the barrier material of GaAs, In_0.15Ga_0.85As, In_0.25Ga_0.75As, and In_0.35Ga_0.65As respectively have been taken into consideration. The barrier thickness has been kept constant at 7.5 nm for all the structures. The matrix material of In_0.15Ga_0.85As has been considered for InAs SML QDs. The biaxial and hydrostatic strain have been computed and compared. Lower magnitude of hydrostatic strain governs more carrier confinement in conduction band whereas, higher biaxial strain provides more splitting of heavy-hole and light-hole band. This results in more red-shifted photoluminescence. From the simulation results, it is observed that the biaxial strain is improved by 0.3704 % and the magnitude of hydrostatic strain is improved by 1.623 % in the InAs SK region of structure D as compared to that of structure A. Similarly, the biaxial strain is improved by 0.7677 % and the magnitude of hydrostatic strain is improved by 2.301 % in the InAs SML region of structure D as compared to that of structure A. The observed PL emission wavelength of structures A, B, C, and D were approximately 1549 nm, 1561 nm, 1572 nm, and 1584 nm respectively. Hence, the structure D provides the highest PL emission wavelength for LWIR telecommunication applications and optimal strain distribution among the other heterostructures.

The InAs quantum dots (QDs) with dot-in-well (DWELL) structure are preferable than the conventional InAs QD heterostructures because of the carrier funneling mechanism in the DWELL structure. There are few reports on the InAs DWELL quantum dot infrared photodetectors (QDIPs). However, a complete study on the optimization of the well structure and thickness is still missing in the literature. Here, we report the optimization of InAs DWELL heterostructure for superior structural and optical properties. We have simulated the DWELL heterostructures by varying the thickness of In_0.15Ga_0.85As well in both sides of the InAs QD. The symmetric DWELLs with 2/2, 4/4, 6/6, 8/8, and 10/10 nm InGaAs well are considered. For the asymmetric DWELL, the underlying well is kept fixed at 2 nm, whereas the upper well thickness is varied as 4, 6, 8, and 10 nm. A decrease (increase) in the hydrostatic (biaxial) strain is observed as the well thickness is increased in both symmetric and asymmetric DWELL structures. There is a redshift in the absorption peak with thicker wells, but a cutoff in the absorption coefficient value is obtained as the well thickness is increased beyond 6 nm in both cases. The probability density functions of the carriers in the case of 6/6 nm symmetric DWELL are high, which attributes to higher oscillator strength. Thus, the 2/6 nm asymmetric DWELL is the optimum one and hence the corresponding QDIP is grown. The photoluminescence result has good match with the simulated result and the QDIP showed a mid-wave infrared (MWIR) photoresponse.