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High-power semiconductor lasers based on AlGaInAs/InP heterostructures and emitting in the spectral range 1.9 – 2.0 μm are developed. Strain compensation in the active region makes it possible to use InGaAs quantum wells with a compressive strain of about 2.0% – 2.5%. The operation of a laser with an ultra-narrow waveguide at wavelengths increasing from 1.4 – 1.6 to 2.0 μm is studied. At room temperature, the semiconductor lasers with a stripe contact width of 100 μm demonstrates a cw output optical power of 1.0 W with a wavelength of 1.91 μm at a pump current of 6.5 A and with a wavelength of 1.98 μm at a pump current of 7.2 A.

Superluminescent diodes based on AlGaInAs/InP separate-confinement double heterostructures with strain-compensated quantum wells are investigated. The influence of elastic strains in the active region on the output characteristics of the devices is analysed. It is shown that such a design of a superluminescent diode allows an optical power of more than 5 mW, a radiation spectrum width of more than 60 nm, a degree of output radiation polarisation up to 30 dB to be obtained at the output of a single-mode fibre, and has a great potential for further improvement.

The room temperature dual-mode self-calibrating detector combines low-loss photodiodes with electrical substitution radiometry for determination of optical power. By using thermal detection as a built-in reference in the detector, the internal losses of the photodiode can be determined directly, without the need of an external reference. Computer simulations were used to develop a thermal design that minimises the electro-optical non-equivalence in electrical substitution. Based on this thermal design, we produced detector modules that we mounted in a trap structure for minimised reflection loss. The thermal simulations predicted a change in response of around 280 parts per million per millimeter when changing the position of the beam along the centre line of the photodiode, and we were able to reproduce this change experimentally. We report on dual-mode internal loss estimation measurements with radiation of 488 nm at power levels of 500 μW, 875 μW and 1250 μW, using two different methods of electrical substitution. In addition, we present three different calculation algorithms for determining the optical power in thermal mode, all three showing consistent results. We present room temperature optical power measurements at an uncertainty level approaching that of the cryogenic radiometer with 400 ppm (k = 2), where the type A standard uncertainty in the thermal measurement only contributed with 26 ppm at 1250 μW in a 6 hour long measurement sequence.

A scheme for instantaneous frequency measurement (IFM) using two parallel I/Q modulators based on optical power monitoring is proposed. The amplitude comparison function (ACF) can be constructed to establish the relationship between the frequency of radio frequency (RF) signal and the power ratio of two optical signals output by two I/Q modulators. The frequency of RF signal can be derived by measuring the optical power of the optical signals output by two I/Q modulators. The measurement range and measurement error can be adjusted by controlling the delay amount of the electrical delay line. The feasibility of the scheme is verified, and the corresponding measurement range and measurement error of the system under different delay amounts of the electrical delay line are given. Compared with previous IFM schemes, the structure of this scheme is simple. Polarization devices, a photodetector and an electrical power meter are not used, which reduces the impact of the environmental disturbance on the system and the cost of the system. In simulation, the measurement range can reach 0 GHz–24.5 GHz by adjusting the delay amount of the electrical delay line τ = 20 ps. The measurement error of the scheme is better at low frequency, and the measurement error of low frequency 0 GHz–9.6 GHz can reach –0.1 GHz to +0.05 GHz.

The terahertz (THz) amplitude modulation has been experimentally demonstrated by employing bilayer molybdenum disulfide (MoS2) on high-resistivity silicon (Si). The Raman spectroscopy and x-ray photoelectron spectra confirm the formation of bilayer MoS2 film. The THz transmission measurements are carried out using a continuous wave (CW) frequency-domain THz system. This reveals the higher modulation depth covering wide THz spectra of 0.1–1 THz at low optical pumping power. The modulation depth up to 72.3% at 0.1 THz and 62.8% at 0.9 THz under low power optical excitation is achieved. After annealing, the strong built-in electric field is induced at the MoS2–Si interface due to p-type doping in MoS2. This improves modulation depth to 86.4% and 79.7%, respectively. The finite-difference time-domain (FDTD) based numerical simulations match well with the experimental results. The higher modulation depth at low optical power, broadband response, low insertion losses, and simplicity in the design are the key attributes of this THz modulator.

Optical power splitter based on waveguide had been simulated numerically using Finite Difference Beam Propagation Method (FDBPM). Proposed waveguide was designed in the form of simple directional coupler waveguide. The waveguide was contained SnO2 nanomaterial as film or the guide part and the other supporting material as cladding with lower refractive index such as flint glasses. The waveguide used 2 μm of width to establish single-mode waveguide. The structure of waveguide is divided into three parts such as input, coupling and output part. While the waveguide was modified with angle in input and output parts to avoid coupling between waveguides. Furthermore, the proposed waveguide was analysed by varying the angle and coupling length. The analysed result shows that the waveguide has best performance in angle of 0.5 degrees and coupling length of 300 μm when the propagation loss was around 0.53%. Using the parameter, the output distribution percentage of waveguide approached 55%:44.5%. This performance indicated that the proposed waveguide can be used as optical power splitter. The application is very useful for optical telecommunication networking development.

Since it was proposed, memtransistors have been a leading candidate with powerful capabilities in the field of neural morphological networks. A memtransistor is an emerging structure combining the concepts of a memristor and a field-effect transistor with low-dimensional materials, so that both optical excitation and electrical stimuli can be used to modulate the memristive characteristics, which make it a promising multi-terminal hybrid device for synaptic structures. In this paper, a single CdS nanowire memtransistor has been constructed by the micromechanical exfoliation and alignment lithography methods. It is found that the CdS memtransistor has good non-volatile bipolar memristive characteristics, and the corresponding switching ratio is as high as 106 in the dark. While under illumination, the behavior of the CdS memtransistor is similar to that of a transistor or a memristor depending on the incident wavelengths, and the memristive switching ratio varies in the range of 10 to 105 with the increase of the incident wavelength in the visible light range. In addition, the optical power is also found to affect the memristive characteristics of the device. All of these can be attributed to the modulation of the potential barrier by abundant surface states of nanowires and the illumination influences on the carrier concentrations in nanowires.

Road traffic markings are made of glass beads embedded in paint. To analyze the effects of glass-bead radius, embedment depth, correlated color temperature of light sources, and incident angle on the reflective performance of glass beads, a numerical model is established using the geometric optics method, effective light conditions are analyzed, calculation methods for optical power devised, and non-standard planes of incident light calculated. Calculations were also carried out. Results show that the retroreflective properties of glass beads are positively correlated with the correlated color temperature of the light source and radius of the beads. The glass-bead radii, embedment depths, and incident angles have little effect on their reflective performance. Moreover, the correlated color temperature of the light source is an important factor affecting the accuracy of measuring glass-bead reflective performance. When using retro reflectometers, standard retro reflectance-measuring devices for retro reflectance measurement, and other equipment to evaluate the reflective performance of road traffic markings, the correlated color temperature of the light source of the equipment should be as close as possible to 2856 K.

This paper has demonstrated an experimental low power consumption underwater wireless optical communication (UWOC) system with 460-nm LZ1-00DB00 Blue LED and avalanche photodetector. With the LZ1-00DB00 Blue LED operating at a driving current of 1200 mA with an optical power of 5280 mW, UWOC link offering a data rate up to 20 Mb/s over a transmission range of 5 meters under an underwater channel link. The measured bit-error rate (BER) is 3 × 10-3 which pass well the forward error correction (FEC) threshold.

Objective. To design and implement a setup for ex-vivo optical stimulation for exploring the effect of several key parameters (optical power and pulse duration), activation features (threshold, spatial selectivity) and recovery characteristics (repeated stimuli) in peripheral nerves. Approach. A nerve chamber allowing ex-vivo electrical and optical stimulation was designed and built. A 1470 nm light source was chosen to stimulate the nerve. A photodiode module was implemented for synchronization of the electrical and optical channels. Main results. Compound neural action potentials (CNAPs) were successfully generated with infrared light pulses of 200–2000 µs duration and power in the range of 3–10 W. These parameters determine a radiant exposure for stimulation in the range 1.59–4.78 J cm−2. Recruitment curves were obtained by increasing durations at a constant power level. Neural activation threshold is reached at a mean radiant exposure of 3.16 ± 0.68 J cm−2 and mean pulse energy of 3.79 ± 0.72 mJ. Repetition rates of 2–10 Hz have been explored. In eight out of ten sciatic nerves (SNs), repeated light stimuli induced a sensitization effect in that the CNAP amplitude progressively grows, representing an increasing number of recruited fibres. In two out of ten SNs, CNAPs were composed of a succession of peaks corresponding to different conduction velocities. Significance. The reported sensitization effect could shed light on the mechanism underlying infrared neurostimulation. Our results suggest that, in sharp contrast with electrical stimuli, optical pulses could recruit slow fibres early on. This more physiological order of recruitment opens the perspective for specific neuromodulation of fibre population who remained poorly accessible until now. Short high-power light pulses at wavelengths below 1.5 µm offer interesting perspectives for neurostimulation.

An asymmetric dual-gate (DG) MoS2 field-effect transistor (FET) with ultrahigh electrical performance and optical responsivity using atomic-layer-deposited HfO2 as a top-gate (TG) dielectric was fabricated and investigated. The effective DG modulation of the MoS2 FET exhibited an outstanding electrical performance with a high on/off current ratio of 6 × 108. Furthermore, a large threshold voltage modulation could be obtained from −20.5 to −39.3 V as a function of the TG voltage in a DG MoS2 phototransistor. Meanwhile, the optical properties were systematically explored under a series of gate biases and illuminated optical power under 550 nm laser illumination. An ultrahigh photoresponsivity of 2.04 × 105 AW−1 has been demonstrated with the structure of a DG MoS2 phototransistor because the electric field formed by the DG can separate photogenerated electrons and holes efficiently. Thus, the DG design for 2D materials with ultrahigh photoresponsivity provides a promising opportunity for the application of optoelectronic devices.

In order to improve the indoor positioning accuracy and reduce the impact of a reflected light on the positioning performance, based on the analysis of the existing RSS positioning algorithm, an improved positioning algorithm based on K-means clustering is proposed. According to the indoor visible light communication system model and optical power distribution, 10*10 receiving points are uniformly selected on the receiving surface of 5m*5m. Through the collection of the received optical power of each receiving point, the K-means clustering algorithm is used to classify 100 receiving points: the first cluster of points is less affected by a reflected light, and the second cluster of points is greatly affected by a reflected light. The second cluster of receiving points is weighted after classifying, and the simulation results show that the algorithm significantly reduces the room edge positioning error, and the positioning performance of the entire room is improved by 28%.

Experimentally resolving the microscopic energy dissipation and redistribution pathways in a molecular-scale junction, the smallest possible nanoelectronic device, is of great current interest. Here we report measurements of the vibrational pumping and light emission processes in current-carrying molecular junctions using surface enhanced Raman spectroscopy. We show that the heating of vibrational modes exhibits distinct features when the molecular junctions are driven by electrical bias or optical power. We further discuss the hot carrier origin of the broadband continuum emission observed in the Raman scattering spectrum.

In this work, we review the viability and precision of the photon-momentum-based optical power measurement method that employs an amplification effect caused by a multi-reflected laser beam trapped in an optical cavity. Measuring the total momentum transfer of the absorbed and re-emitted photons from a highly reflective surface (reflection of the laser beam from an optical mirror) as a force provides the possibility of measuring the optical power with direct traceability to SI units. Trial measurements were performed at two different metrology laboratories: the laboratory for mass/force at the Technical University of Ilmenau, and the clean room laser radiometry laboratory at PTB, with a portable force measurement setup consisting of two electromagnetic force compensation balances. We compared the results of the optical power measurements performed with the force measurement setup, via the photon-momentum-based method, with those performed using a calibrated reference standard detector traceable to PTB’s primary standard for optical power, the cryogenic radiometer. The comparison was carried out for an optical power range between 1 W and 10 W at a wavelength of 532 nm, which corresponds to a force of approximately 2000 nN at the upper limit, yielding approximately 2.3% relative standard uncertainty in the case of 33 reflections. Thus, conflating the high-precision force metrology technique at μN to nN levels with the optical setup required to achieve specular multi-reflection configuration of the laser beam, where a macroscopic optical cavity with ultra-high reflective mirrors (>99.995%) can adjustably be suspended from the force sensors, depending on required geometry of reflections, we show that the uncertainty of the optical power measurements upon further increase of the nominally applied optical power, the number of laser beam reflections, or the reflectivity coefficient of the mirrors can be markedly reduced.

The pursuit of optoelectronic devices operating in mid-infrared regime is driven by both fundamental interests and commercial applications. The narrow bandgap (0.3 eV) of layered Bi2Se3 makes it a promising material for mid-infrared photodetection. However, the weak absorption of mid-infrared optical power and high dark current level restrict its performance. Here, a supply-control technique is applied to modulate the growth mode of Bi2Se3 crystal, and Bi2Se3 crystals with various morphologies are obtained. The nanoplates pattern transits from maze to freestanding when source mass was tuned. Due to the strong infrared absorption and photoelectric conversion efficiency of vertical Bi2Se3 nanoplates, the as-prepared vertical Bi2Se3 nanoplates/Si heterojunction shows excellent photoresponse and extremely low dark current. Among these devices based on different Bi2Se3 morphologies, freestanding nanoplates show the optimal mid-infrared characteristics, namely a photo-to-dark ratio of 2.0 × 104, a dark current of 0.21 pA, a response time of 23 ms, a specific detectivity of 6.1 × 1010 Jones (calculated) and 1.2 × 1010 Jones (measured) under 2.7 μm illumination and at room temperature. Notably, the specific detectivity of our devices are comparable to commercial InGaAs photodetectors. With the tunable- morphology growing technique and excellent photoresponding characteristics, Bi2Se3 nanomaterials are worth attention in optoelectronic field.

VLC(Visible Light Communication) is a new and emanating technique which uses light for communication. For indoor wireless ommunications, it is considered as a promising scheme for both information bearing communication as well as illumination. It provides high data rate performance at reduced cost. The aim of this paper is the analysis of optical power distribution and signal to noise ratio in an indoor VLC system. Analysis of power distribution and SNR is done by changing the direction of LEDs. It is observed that the noise in the optical channel link between the LED and photodetector dominates the data transmitted. Finally, simulation results and various parameters affecting the performance of VLC is also studied

We report the design and analysis of a non-blocking microring resonator-based optical switched router, which can be used as a switch node to construct a large photonic routing network on chips. The proposed optical router has sixteen microrings, fourteen crossings and four 90° waveguide bends, which could be tuned through the thermo-optic (TO) or electro-optic (EO) effect. Compared with a previously described 5 × 5 optical switching router, our router comprises fewer microring resonators (MRRs), crossings and bends, which results in a more compact design, a higher switching speed, a lower loss and a lower optical power consumption. In addition, all the rings operate at the same wavelength making it scalable to a network of any size.

A comparison down to sub-100-fW optical power level was carried out between a low-noise Silicon photodiode and a low optical flux measurement facility based on a double attenuator technique. The comparison was carried out via a silicon single-photon avalanche diode (Si-SPAD), which acted as transfer standard. The measurements were performed at a wavelength of 770 nm using an attenuated laser as a radiation source at optical power levels between approximately 86 fW and approximately 1325 fW, corresponding to approximately 330 000 photons s−1 and approximately 5.2 × 106 photons s−1, respectively. The mean relative deviation of the detection efficiencies of the Si-SPAD, determined by the Si-photodiode and the low optical flux measurement facility, i.e. between two completely independent traceability routes, was < 0.2%, thus well within the combined standard uncertainty of the two measurements. To our knowledge, this is the first comparison for the detection efficiency of a single photon detector using a direct optical flux measurement by a conventional Si-photodiode at such low power levels.

A visible laser-based vibration compensation interferometer has recently been designed for the EAST tokamak and the bench test has been finished. The system was optimized for its installation on EAST. The value of the final optical power before the detectors without plasma has been calculated from the component bench test result, which is quite close to the measured value. A nanometer level displacement (of the order of the laser's wavelength) has been clearly measured by a modulation of piezoelectric ceramic unit, proving the system's capability.

The effect of power limiting for optical radiation at a wavelength of 660 nm with a pulse duration of 10 ms and operation threshold of 2.2 – 3.1 mJ cm-2 is observed in ensembles of colloidal Ag2S quantum dots (QDs). Using the z-scanning method in an open-aperture scheme it is found that the power is limited mainly due to reverse saturable absorption caused by two-photon optical transitions that involve energy levels of Ag2S photoluminescence centres, related to structural impurity defects in colloidal Ag2S QDs. At the same time, the z-scanning in a closed-aperture scheme demonstrates the formation of a thermal dynamic lens.

Laser diodes based on AlGaInAs/InP heterostructures with an ultra-narrow waveguide are developed. It is shown that the use of this waveguide in conjunction with profiled doping ensures a balance between internal optical losses and heat resistance. Laser diodes with a stripe contact 100 μm wide demonstrate at room temperature an output optical power exceeding 4 W in a continuous-wave mode and exceeding 20 W in a pulsed mode.

The traceability of measurements of the parameters characterizing single-photon sources, such as photon flux and optical power, paves the way towards their reliable comparison and quantitative evaluation. In this paper, we present an absolute measurement of the optical power of a single-photon source based on an InGaAs quantum dot under pulsed excitation with a calibrated single-photon avalanche diode (SPAD) detector. For this purpose, a single excitonic line of the quantum dot emission with a bandwidth below 0.1 nm was spectrally filtered by using two tilted interference filters. Since high count rates are essential for many metrological applications, we optimized the setup efficiency by combining high overall transmission of the optical components with a geometrical enhancement of the extraction efficiency of a single quantum dot by a monolithic microlens to reach photon fluxes up to 3.7 ⋅ 10 5 photons per second at the SPADs. A relative calibration of two SPAD detectors with a relative standard uncertainty of 0.7% was carried out and verified by the standard calibration method using an attenuated laser. Finally, an Allan deviation analysis was performed giving an optimal averaging time of 92 s for the photon flux.

The development of technologies of hybrid structures with combined three-dimensional (3D) and two-dimensional (2D) materials is being recognised as a highly attractive opportunity to create new optoelectronic devices with unique properties originating from the atomic thin structures. In the present study, a novel approach in the direct synthesis of MoS2 2D-layers on p-Si was proved to be acceptable for fabricating a photovoltaic effect-driven photodetector based on a hybrid 2D/3D heterojunction that included an atomically thin n-MoS2 film and crystalline p-Si substrate. It was demonstrated experimentally that the heterojunction with the top and bottom contacts was highly sensitive to illumination between 650 and 1200 nm. The experimental study proved that the response to light was originated by the photovoltaic effect in the sample devices without an external power supply. The maximum sensitivity of the 2D/3D heterostructures to the optical power of the illumination was up to 210 V W-1 and was practically independent of the wavelength. The analysis of experimental I-V, C-V characteristics, Raman spectra and AFM surface images allowed us to construct a flat band model of the hybrid 2D/3D n-p-heterojunction that explained the electrical properties of the n-MoS2/p-Si photodetectors. The photovoltaic effect-driven light detectors offer highly promising possibilities in the development of autonomous photonic systems.

Supercontinuum (SC) from optical fibres [1-3] has recently gained significant interest in the development of new broadband optical sources for applications requiring a tunable, bright source operating in the pico- to nano-second range for communications. Typically, ultra-short pulses are generated using bulk laser systems such as Titanium-Sapphire (Ti-Sapphire) lasers, but require critical optical alignment and many other sophisticated optical techniques, thus making these systems complicated, expensive and not suitable for laboratories with a limited budget. An alternative approach is to generate these short pulses using rare-earth doped fibres, which would allow for the development of cheap, compact, stable and easy to maintain sources for SC generation [4, 5]. Such a system will also find applications in the areas of optical coherence tomography [6], spectroscopy [7] and frequency metrology [8]. The process of SC generation is normally done in a non-linear fibre, whereby SC is a complex nonlinear phenomenon that is characterized by the dramatic spectral broadening of intense light pulses passing through a nonlinear medium. Recently, more attention has been paid to nonlinear fiber with longer infrared transmission windows such as Highly Nonlinear Fiber (HNLF), Photonic Crystal Fiber (PCF) and Chalcogenide Fiber. Therefore, the Few Mode Fiber (FMF) is the alternative fiber for infrared transmission window. This fiber possess a high refractive index and can support high optical power than Single Mode Fiber (SMF). In this book, the feasibility of FMF transmission systems by studying the supercontinuum generation in two modes is presented. In most reported experiments, SC generation is observed by higher-order mode excitation in other nonlinear fiber. However, broad tunable soliton and associated dispersive wave sources by two modes in FMF is also investigated.

All-fiber optical current transformer (FOCT) based on Magneto-optical Faraday effect plays a pivotal role in current metering and protection of smart grid. However, the fault diagnosis of FOCT is one of the most critical issues to be solved. In order to ensure the proper functioning of FOCT, a fault diagnosis system is presented by monitoring the intensity variation of the light interference with Square wave bias modulation of FOCT, which is measured by digital signal processing unit using correlation detection technology. Afterwards, the faulty types of FOCT are recognized by the amount of the optical power variation. The experimental results show that the system can effectively detect these kinds of fault types, such as the broken of optical fiber, the increasing loss of optical fiber and the breakdown of light source in FOCT.

Photovoltaic (PV) cells used for optical power transmission convert laser light incident from limited directions to electricity. This illumination condition is in contrast to that for solar cells. A combination of an angular selective filter consisting of a dielectric multilayer on the front surface and a diffuse reflector on the rear surface significantly traps both the incident laser light into and radiation from the PV cell. This light trapping effect can improve the monochromatic conversion efficiency of a GaAs PV cell by 9% (absolute) compared with that for the ×4n2 trapping, under 872 nm and 1 W cm−2 laser illumination.

The effects of buried oxide (BOX) layer on the capacitance of SiGe heterojunction photo-transistor (HPT), including the collector–substrate capacitance, the base–collector capacitance, and the base–emitter capacitance, are studied by using a silicon-on-insulator (SOI) substrate as compared with the devices on native Si substrates. By introducing the BOX layer into Si-based SiGe HPT, the maximum photo-characteristic frequency f t,opt of SOI-based SiGe HPT reaches up to 24.51 GHz, which is 1.5 times higher than the value obtained from Si-based SiGe HPT. In addition, the maximum optical cut-off frequency f β,opt, namely its 3-dB bandwidth, reaches up to 1.13 GHz, improved by 1.18 times. However, with the increase of optical power or collector current, this improvement on the frequency characteristic from BOX layer becomes less dominant as confirmed by reducing the 3-dB bandwidth of SOI-based SiGe HPT which approaches to the 3-dB bandwidth of Si-based SiGe HPT at higher injection conditions.

This paper reports a wavelength-stabilized high-power diode laser emitting up to 14 W CW in the 9xx nm range. Wavelength stabilization is achieved by a distributed Bragg reflector (DBR) monolithically integrated in the diode laser chip. Key features are identical layer epitaxy (ILE) and the use of a multiple-order electron beam lithography (EBL) optical confining grating. ILE avoids any regrowth or complex technology processes, while EBL multiple-order grating allows narrow-band back reflection and effective lateral optical confinement, and makes it possible to stabilize multiple wavelengths on the same wafer using a manufacturable and reliable technology. DBR diode lasers with different pitches, whose wavelengths were 3 nm spaced, were fabricated and high spectral purity (95% optical power within about 0.6 nm) and wavelength stability were measured. Moreover, the high uniformity of performances across the wafer with different emitted wavelengths demonstrates the maturity of the proposed technology for high-yield, high-volume laser diode production for wavelength-stabilized applications. A multi-emitter module, including ten DBR diode lasers, collimating and focusing optics, showed 100 W CW wavelength-stabilized output power at 14 A in a 135 μm core optical fiber within 0.17 NA. Single diode lasers, or multi-emitter modules, can be used to combine high-power optical beams by wavelength division multiplexing (WDM) using dichroic optics, scaling up beam power to the kW range and maintaining optical beam quality.

A new type of VCSEL (Vertical-Cavity Surface-Emitting Laser) which uses Pt1000 as a temperature sensitive component and non-magnetic heating membrane as a temperature actuator is designed for SERF (Spin-Exchange Relation-Free) atomic magnetometer, which can decrease the magnetic interference produced while heating or cooling VCSEL. Therefore a low noise driver for this kind of VCSEL is necessary. A driver for the novel VCSEL is designed in this paper. The output current is adjustable from 0 to 4.5 mA, and RMS (Root Mean Square) noise of current is less than 80 nA. The operating temperature of the VCSEL is adjustable between 30-110 °C and RMS noise of temperature is less than 0.6 mK. So that it can be ensured that the VCSEL outputs a laser with stable optical power and wavelength.

Modern optical variosystems include lenses with a fixed and tunable focal length, which can also move relative to each other according to a certain law. The method of dimensional synthesis of the variosystems converting incoherent radiation and laser Gaussian beams is considered. Examples of the calculation of optical variosystems are presented.

We have studied the effect of laser cavity parameters on the light–current characteristics of lasers based on the AlGaInAs/GaInAsP/InP solid solution system that emit in the spectral range 1400 – 1600 nm. It has been shown that optimisation of cavity parameters (chip length and front facet reflectivity) allows one to improve heat removal from the laser, without changing other laser characteristics. An increase in the maximum output optical power of the laser by 0.5 W has been demonstrated due to cavity design optimisation.

We report an experimental study of power characteristics of semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures with a broadened waveguide as functions of cavity length, stripe contact width and mirror reflectivities. It is shown that at high current pump levels, the variation of the cavity parameters of a semiconductor laser (width, length and mirror reflectivities) influences the light – current (L – I) characteristic saturation and maximum optical power by affecting such laser characteristics, as the current density and the optical output loss. A model is elaborated and an optical power of semiconductor lasers is calculated by taking into account the dependence of the internal optical loss on pump current density and concentration distribution of charge carriers and photons along the cavity axis of the cavity. It is found that only introduction of the dependence of the internal optical loss on pump current density to the calculation model provides a good agreement between experimental and calculated L – I characteristics for all scenarios of variations in the laser cavity parameters.

We have developed a fully-lithographic electrical-substitution planar bolometric-radiometer (PBR) that employs multiwall vertically-aligned carbon nanotubes (VACNT) as the absorber and thermistor, micro-machined Si as the weak thermal link and thin-film Mo as the electrical heater. The near-unity absorption of the VACNT over a broad wavelength range permits a planar geometry, compatible with lithographic fabrication. We present performance results on a PBR with an absorption of 0.999 35 at 1550 nm, a thermal conductance of 456 µW K−1 at 4 K and a time constant (1/e) of 7.7 ms. A single measurement of approximately 100 µW optical power at 1550 nm achieved in less than 100 s yields an expanded uncertainty of 0.14% (k = 2). We also observe an elevated superconducting transition temperature of 3.884 K for the Mo heater, which opens the possibility of future devices incorporating more sensitive thermistors and superconducting thin-film wiring.

We present the concept of a dual-mode primary standard cryogenic detector, utilizing a predictable quantum efficient silicon photodiode, and demonstrate the behaviour of the detector from room temperature down to 30 K. The detector absorbs visible radiation generating either heat or photocurrent, dependent on the selected mode of operation. In effect, this detector links optical power to fundamental constants through the two different routes of operation in the one artefact. Forward biasing of the photodiode is used in lieu of resistive heating to provide the electrical substitution power. The detector has a thermal time constant of 50 s and a sensitivity of 1.39 K mW−1. Using an LED source, we measure equivalence between the two modes of operation of 1.5% at 50 K, limited principally by our knowledge of the wavelength of the emitted radiation of the source.

Lateral force measurement using a cantilever ruler-beam (CRB) sensor based on linear chirp fiber Bragg grating (LCFBG) is proposed and experimentally demonstrated. The lateral force is determined by altering the reflection optical power of LCFBG of which an axial-strain gradient along its sensing is induced. The reflection spectrum intensity responds linearly and monotonically with lateral force increasing from 0 to ≍ 0.6 N. Experimental results demonstrate that the CRB force sensor can successfully achieve lateral forces prediction with less than 0.0015 N resolution using simply Thorlabs PM100USB optical power meter. And can accomplish an adequate accuracy with RMS error < 0.04N of full scale (0-0.749N). The CRB is chosen in one way or another to resemble steerable catheter flexibility as our intention is to developing catheter force sensor based on temperature-insensitive contact force measurement.

We proposed a multiport T-shaped 1 x 8 balanced optical power splitter design based on asymmetric vertical silicon slot waveguides working on the principle of coupled-mode theory (CMT). The scheme of the power splitter is unique which offers strong field confinement of TE-polarized light and delivers the light to four ports each on two opposite side of the chip. By shifting the slot towards the outer sideline of the bend, the bending losses are reduced to 80% as compared to standard symmetric slot waveguide.

For the practical Faraday mirror (FM) in a continuous-variable quantum key distribution (CVQKD) system there exists a rotation angle deviation that can lead to a loss of photon number when a light message passes through the polarization beam splitter. Here we employ the entanglement-based model to research the influence of the FM's imperfection. Based on parameter estimation, the imperfection can introduce a loophole for Eve to obtain information. The secret key rate of the CVQKD will be impaired. Finally, a novel method is proposed to ensure system performance by compensating optical power, and we further study the relationship between the secret key rate and the modulation variance.

PbS colloidal quantum dots (QDs) are a promising material for the realization of low-cost, high-responsivity near-infrared photodetectors. Previously reported attempts showed high responsivity but a fast performance decay in air-exposed devices, demanding encapsulation of the photodetectors. Conversely, devices with very high air stability have been demonstrated but the low trap-state density hinders photoconductive gain and reduces overall responsivity. In this paper, photoconductive devices prepared with partially tetrabutylammonium iodide exchanged PbS QDs are presented with enhanced air stability and high responsivity at low voltage, low optical power.

An optical switch that routes optical signals without converting them into electrical signals is a key component used in optical fiber communications. It is required to exhibit low loss, low crosstalk, and low power consumption. A 1 × N arrayed-waveguide optical switch has an advantage whose circuit size is small. In a design of the 1 × N arrayed-waveguide optical switch, we employ some window functions other than a conventional Gaussian distribution. We show that slight modification of the optical power ratio between the arrayed-waveguides effectively suppresses the crosstalk to unrouted output ports.

We analyzed the theoretical characteristics of horizontal slot waveguides that consist of two Nb2O5 layers and a narrow gap. The slot waveguides strongly confine light in the low index region in the narrow horizontal slot. The obtained peak optical power density of the horizontal slot waveguides is approximately 3.8 times higher than that of the conventional rib-type waveguide. The dependency of the peak optical power density on the structural parameters was investigated. In addition, the coupling between the rib-type waveguides and the horizontal slot waveguide was simulated. The influence of fabrication tolerances for optical power density was calculated in order to estimate the fabrication tolerances. As a preliminary experiment, a horizontal slot in an Nb2O5 waveguide structure was fabricated. An air slot region less than 30 nm thick was successfully obtained.

Graphene nano-mechanical resonators integrated over waveguides provide a powerful sensing platform based on the interaction of graphene with the evanescent wave. An integrated actuation scheme that does not compromise this interaction is required for optimal usage of the ultra-sensitive platform. Conventional electrical and optical actuation techniques are not favorable towards efficient utilization of the near-field interaction. We propose tuning and actuation of these resonators using on-chip optical gradient force due to the guided wave as an alternative to these conventional techniques. We have used the fundamental quasi-TM optical mode in a silicon waveguide in a finite-element model. We obtain a force-distribution that is spatially correlated with the fundamental mechanical mode of the graphene nano-mechanical resonator. We demonstrate that for an evanescent continuous-wave (CW) optical power of 8 mu W, the resonant frequency of the device can be tuned by about 24.5%. With an intensity-modulated optical power

We demonstrate narrow-line green laser emission at 513.85 nm with a linewidth of 31 pm and side-mode suppression ratio of 36.9 dB, operating under continuous-wave injection at room temperature. A high-order (40th) distributed-feedback surface grating fabricated on multimode InGaN-based green laser diodes via a focused ion beam produces resolution-limited, single-mode lasing with an optical power of 14 mW, lasing threshold of 7.27 kA cm−2, and maximum slope efficiency of 0.32 W A−1. Our realization of narrow-line green laser diodes opens a pathway toward efficient optical communications, sensing, and atomic clocks.

We report the fabrication of a simple and inexpensive device based on diffractive optics for spectrally resolved imaging. A brass surface manufactured on a metal lathe and a deformable, reflecting diffraction grating guarantee spatially and spectrally resolved images without the need for other optical elements. The grating is a metal-polymer nanocomposite replica of a plastic grating: reflectivity of the transparent dielectric substrate is obtained by the implantation of gold clusters, hence preserving deformability. The brass surface is a portion of a rotation ellipsoid, on which the deformable grating adheres to gain optical power. According to the optical tests performed on the system, the achieved spatial resolution of the system is ∼80 μm, whereas limiting spectral resolution of about 3 nm is observed. Reflectivity of the zero-order reflection and the first order diffraction approaches 45% and 5% respectively. We detail the results for the reconstruction of an on-axis and off-axis pointlike source, and a vertically extended slit-like source with a 110 μm obstruction.

We demonstrate a photo-induced high modulation depth terahertz (THz) modulator based on a VO x /Si/VO x hybrid structure. The thickness of the embedded high resistance silicon substrate is 510 µm and two layers of VO x films are 100 nm, respectively. Compared with other THz modulators based on the phase transition of vanadium oxide which were fabricated by complex chemical vapor deposition and sputtering processes, the VO x film in this device is fabricated using a simple spin coating process of VO x solution. The sample is characterized using a THz time-domain-spectroscopy system. In the test experiment, the insulator–metal-transition of the VO x is induced by two oblique incident pump lasers with a central wavelength of 650 nm from two sides. The experimental results show that it can be optically modulated in a wide frequency range from 0.2 to 2.0 THz, and the maximum modulation depth of 93% is realized when the optical power is 120 mW. Film theory and Drude theory are introduced to interpret the mechanism of modulation. This modulator has broadband, a simple fabrication process and very low optical power, which are important for broadband THz communication and all-optical THz systems.

We report on a new and simple approach for continuous wave supercontinuum generation in optical fibers. Our new approach uses the effect of stimulated Stokes Raman scattering in a low loss fiber ring laser. By continuously pumping this ring laser with up to 19 W optical power we excited up to six Stokes orders and covered a wavelength range of 500 nm. Due to the feedback mechanism of the ring layout additional nonlinear effects occurred next to the plain generation of individual Stokes peaks. Eventually, these effects broaden and merge the separated Stokes peaks and create a single, connected continuous supercontinuum. By using the effect of stimulated Stokes Raman scattering, we do not rely on anomalous dispersion and modulation instability as typically required for continuous wave supercontinuum generation.

A high-performance wavelength-switchable single-longitudinal-mode (SLM) fiber laser with ultra-narrow linewidth and high stability in C-band was proposed and demonstrated, mainly benefiting from the use of a wide-band chirped Moire fiber Bragg grating (WB-CM-FBG) with 41 ultra-narrow channels. By combining the WB-CM-FBG with a manual tunable bandpass filter and using a subring cavity with a length of only 34 cm to efficiently stabilize the SLM lasing, we achieved switchable lasing operation among 41 wavelengths, with a switching-step of ~0.96 nm from 1526.592 nm to 1565.126 nm, covering the whole C-band, and obtained sub-kHz linewidth at every lasing wavelength. The high stability was validated by the measured slight fluctuations of lasing wavelength and optical power of

Nano-optomechanical systems actuated by optical forces enable many interesting scientific and technological applications. They are vulnerable to the effects of surface stress and Casimir forces. Therefore, calculation of optical forces is essential for the reliability applications of these advanced devices. In this paper, an approximate and explicit expression is developed for the evaluation of the optical force existing between a waveguide and a substrate through the effective refractive index. The influences of surface stress and Casimir forces on the pull-in instability of a silicon nano-optomechanical device actuated by optical forces are investigated. It is found that if neglecting the effect of surface stress, the maximum size, which indicates the device can be safely fabricated, will be over-predicted. The surface stress reduces the critical optical power and its effect is more significant for a slender waveguide.