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The optical losses and the refractive index change of optical planar waveguides formed by MeV ion implantation were correlated with the experimental ion implantation parameters. Direct ion implantation was performed by means of carbon, silicon and copper ion beams impinging on the substrate surface at normal incidence. The ions were accelerated at energies ranging from 3 to 12 MeV with fluences varying from 1 × 1012 to 2 × 1016 ion/cm2, according to the type of implanted ion. The modification of the substrate refractive index due to the ion irradiation‐induced damage was evaluated using the prism coupler method, and the refractive index profiles were determined by means of a reconstruction method using a multilayer structure approximation. The guiding properties of the waveguides were analysed using the fibre‐coupling technique to determine both the optical transmission and transversal modes at 635 nm. The main practical relevance of our research is the obtention of high‐quality waveguides at low current density MeV ion implantation (≤80 nA/cm2) without post‐implantation annealing. [ABSTRACT FROM AUTHOR]

The authors report a ductile dicing process for manufacturing optical‐quality facets in a multi‐layered silicon nitride platform without the need for polishing. A surface roughness (Sa) of 1.5 nm was achieved. This technique was extended to fabricate ridge waveguides, and the results and characterization are reported. [ABSTRACT FROM AUTHOR]

The authors proposed a flexible microresonator based on nanowires composed of Ⅱ–Ⅵ compounds to detect the small strain caused by external motion. The nanowire ring resonator is embedded in polydimethylsiloxane (PDMS) flexibility to improve the coupling efficiency. In this work, CdS nanowire is fabricated onto a PDMS flexible substrate. With the help of a fibre tip, the single nanowire is manipulated under a microscope, allowing the curved line to be a ring and making the litter overlapping. This overlap increases coupling efficiency and sensor performance. The ring cavity has the parameters of diameter 1 µm, length 75 µm and radius ∼10 µm. Experiments demonstrated the process of fabricating a strain sensor and detected peak shifts. This resonant wavelength appeared red‐shift and linear tuned when stretching the flexible substrate. The quality factor was about 2000 and the gauge factor was about 80 nm per stretching unit. Being a small structure and high sensitivity, the sensor can be integrated into the chip. This promotes the development of miniaturisation to some extent. As a result, this work is beneficial to optical manipulation, further being extended to the tunable light source. [ABSTRACT FROM AUTHOR]

In this work, the authors demonstrate the control of quality factor (Q‐factor) is laterally coupled vertical cavities. A 3 μm‐side‐length square cavity directly connected to a 1.5 μm‐width, 10 μm‐length Fabry–Perot (FP) cavity has been fabricated and measured. Dynamic tuning of the Q‐factor has been successfully observed by bringing the square cavity and FP cavity into resonance. The vertical‐cavity‐based Q‐factor control scheme provides a new choice for the modulation of light and holds potentials for applications associated with optical information processing. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) metasurface integrated with strip waveguide in silicon‐on‐insulator (SOI) has been designed to achieve high coupling efficiency for 3.8 μm wavelength. The optimisation in period and radius has been achieved using 3D finite‐difference time‐domain (FDTD). The calculated coupling efficiency in the in‐plane waveguide for the out‐of‐plane surface illumination is over 90% with a bandwidth of 1 μm. The design is consistent with the available lithography using 400 nm thick SOI for mid‐IR applications. Finally, monolithic integration can be achieved using standard multi‐project wafer run. [ABSTRACT FROM AUTHOR]

Synthesis of indium (III) oxide (In2O3) and chromium (Cr)‐doped In2O3 thin film (TF) by spin‐on technique was reported. The device showed the Schottky nature under dark and light illumination condition. The ideality factor of the diode showed an exponential increase with the decrease in temperature. The low ideality factor of ∼4 was calculated at 300 K. The barrier height of the device increased with temperature. The Cr‐doped In2O3 TF device possessed high sensitivity compared with undoped In2O3 TF at −2 V all over the temperature range from 10 to 300 K. The Cr‐doped In2O3 TF‐based device showed extremely high sensitivity toward ultraviolet (320 nm) light as compared with visible light. [ABSTRACT FROM AUTHOR]

In this work, the authors present their recent progress in the development of a platform for the mid‐infrared wavelength range, based on suspended silicon waveguides with subwavelength metamaterial cladding. The platform has some intrinsic advantages, which make it a very promising candidate for sensing applications in the molecular fingerprint region. Specifically, it can cover the full transparency window of silicon (up to a wavelength of 8 μm), only requires one lithographic etch‐step and can be designed for strong light–matter interaction. Design rules, practical aspects of the fabrication process and experimental results of a complete set of elemental building blocks operating at two very different wavelengths, 3.8 and 7.7 μm, are discussed. Propagation losses as low as 0.82 dB/cm at λ0 = 3.8 μm and 3.1 dB/cm at λ0 = 7.7 μm are attained for the interconnecting waveguides. [ABSTRACT FROM AUTHOR]

An inverted lateral taper with one vertical discrete step was designed for a medium confinement silicon nitride waveguide platform in the C‐band, as a chip edge coupler, with a predicted insertion loss of 0.58 dB. The design is supported by an extensive study to evaluate the impact of fabrication process variations on the performance of such a coupler. The device was manufactured and measured, showing an insertion loss of 1.47 dB, which was traced back to fabrication process variations as cross‐checked with simulations. To the authors' knowledge, the reported edge coupler is the shortest and among the best performing found for silicon nitride platforms. [ABSTRACT FROM AUTHOR]

An eight‐channel hybrid‐integrated light source with 100 GHz channel spacing fabricated by a passive alignment technology is demonstrated. Side mode suppression ratios of better than 40 dB were obtained via grating couplers under eight‐channel simultaneous operation at a continuous wave current of 600 mA and 25°C. The surface slotted laser array fabricated by standard lithography butt‐joint with silicon photonic devices was demonstrated for the first time, to the best of the authors' knowledge. [ABSTRACT FROM AUTHOR]

In this Letter, high-uniformity 1 × 64 linear arrays of 4H-SiC avalanche photodiode (APD) are reported for ultraviolet detection. Multi-cycle inductively coupled plasma dry etching was adopted for the bevelled mesa formation, during which the wafers were rotated with a small angle for each cycle to suppress the process variation. As a result, a high pixel yield of 100% and a high-uniformity breakdown voltage with a fluctuation of smaller than 0.5 V are achieved for the fabricated 1 × 64 4H-SiC APD linear arrays, which is a great improvement for 4H-SiC APD arrays. Moreover, the dark currents at 95% of breakdown voltage are below 1 nA for all the 64 pixels. Besides, the pixels in the array show a multiplication gain of larger than 106 and a peak responsivity of 0.12 A/W at 285 nm (corresponding to a maximum quantum efficiency of 52%) at room temperature. [ABSTRACT FROM AUTHOR]

A highly selective and sensitive optical sensor based on localised surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) for the determination of a sulphide ion in aqueous solution is presented. The existence of sulphide is change the intensity of the LSPR band around 520 nm. In this sensor, sulphide ions were recognised and measured by UV–vis spectrophotometry. Three factors such as pH, time and concentration of AuNPs have been studied. The optimisation of effective parameters is done by one at a time method. This method was simple, rapid and cost efficient for the detection of sulphide. The linear range is 1.00–10.00 (4.16–41.63 µM) ppm with the correlation coefficient of 0.9874 and the detection limit of 0.54 ppm. The relative standard deviation of the reported method is 1.01%. [ABSTRACT FROM AUTHOR]

Two principal two‐stage switch architectures (cascaded and parallel), both of which are composed of two identical optical crossbar switches with an extra set of inputs and outputs, are compared in terms of their number of crosspoints, switch control complexities, and key optical performances, such as insertion loss and crosstalk power, through theoretical analysis. The authors begin by briefly introducing a known N × N cascaded optical crossbar switch with N2 /2 crosspoints, where N is the switch size, and present a new functional perspective based on quasi‐bitonic sorting. Subsequently, the authors derive two types of two‐stage parallel optical crossbar switches with reduced crosspoints from a conventional single‐stage parallel crossbar switch with N2 + 2N crosspoints. The first type uses two N /2 × N asymmetric switches in parallel, both of which are embedded in a single N /2 × N /2 crossbar switch. It has (N2 + 2N)/2 crosspoints and suffers from a complex switch control of O (N2). The second type is equivalent to a three‐stage Benes network and exploits bidirectional transmission to reduce the number of switching stages. It requires (N2 + 3N)/2 crosspoints, but has a dramatically reduced switch control complexity of O (N), and significantly improved optical performance. [ABSTRACT FROM AUTHOR]

In this Letter, a slope transfer method to fabricate vertical waveguide couplers is proposed. This method utilises wet etched Si as a mask, and takes advantage of dry etching selectivity between Si and SiC, to successfully transfer the profile from the Si master into SiC. By adopting this method, a <2° slope is achieved. Such a taper can bring the coupling efficiency in SiC waveguides to 80% (around 1 dB loss) or better from around 10% (10 dB loss) without taper. It further increases the alignment tolerance at the same time, which ensures the successful development of a plug‐and‐play solution for optical sensing. This is the first reported taper made in SiC. [ABSTRACT FROM AUTHOR]

4H‐SiC ultraviolet p‐i‐n photodiodes with four different epitaxial structures were fabricated. The experimental results prove that both a thin P+‐type Ohmic contact layer and a thick intrinsic layer were indispensible for a high‐performance ultraviolet p‐i‐n photodiode. A 4H‐SiC p‐i‐n photodiode with responsivity as high as 0.139 A/W at 278 nm incident wavelength was achieved. Meanwhile, within a certain wavelength range, the peak response wavelength of an ultraviolet p‐i‐n photodiode would be modulated by properly varying the thicknesses of P+‐type layer and the intrinsic layer. Moreover, the theoretical calculation was carried out to further authorise the experimental results. [ABSTRACT FROM AUTHOR]

Electrode‐less integrated optics lithium niobate (LiNbO3) asymmetric Mach–Zehnder interferometers (AMZIs) can be used as electric field (e‐field) sensors. Electrode‐less sensors are attractive for practical use as such devices do not perturb the sensed variable. A critical issue when using electrode‐less sensors is to ensure a linear sensing process. This requires the electro‐optic transfer function (EOTF) to be adjusted at its quadrature point. For this purpose, an electrode‐less sensor can be optically biased. However, an accurate optical bias is strongly limited by the fabrication tolerances of the AMZIs. Hence a linear sensing‐detection process is not actually ensured. To explore a linear e‐field sensing‐detection process, a simple linearising scheme is proposed in this Letter. The scheme is configured by cascading two optically matched AMZIs. The first AMZI is an electrode‐less sensor; the second one, which is provided of electrodes performs simultaneously as an optical demodulator and an EOTF tuner. The EOTF of the demodulating AMZI can be tuned to its quadrature point by a DC voltage on its associated electrodes. The sensing‐detection scheme is modelled and experimentally tested when illuminated either by coherent and incoherent light. The sensed e‐field is linearly recuperated only when incoherent light is used. [ABSTRACT FROM AUTHOR]

Holographic lithography has been widely used to the realisation of complex photonic structures such as photonic crystal and quasi‐photonic crystals. Dual‐beam multi‐exposure holographic technique was adopted for the fabrication of 18‐fold and 36‐fold sub‐microscopic rotational symmetric structures; the fabricated photonic quasi‐crystals examined by laser diffraction pattern, optical and scanning electron microscopes. Here, the authors have fabricated photonic quasi‐crystals in photoresist and the structure was transformed into metal, the transferred structure in metal could act as a substrate/or back reflector for the thin film solar cell. Further work on concentration of solar light by photonic quasi‐crystals is progressing. [ABSTRACT FROM AUTHOR]

An electro‐optic filter based on guided‐mode resonance for optical communication has been designed and fabricated. The rigorous coupled‐wave analysis is used to calculate the reflection spectra of the designed filter. The grating structure of the filter is patterned by interference lithography with two ultraviolet laser beams. The polymer‐dispersed liquid crystal is injected into the gap between the glass substrate and the bottom of the grating to fabricate the electro‐optic filter. The measured spectra of the fabricated filter exhibit a 38.7 nm shift of the resonant reflected wavelength by controlling the applied voltage. [ABSTRACT FROM AUTHOR]

The InAs/AlSb quantum cascade lasers (QCLs) operating ∼11 µm in the continuous wave (cw) regime at room temperature are reported. The lasers with cleaved Fabry–Perot resonators demonstrated pulsed threshold current densities below 1 kA/cm2 at 300 K and operated in a cw up to 320 K that is the maximum temperature of such regime of operation for InAs‐based QCLs. Distributed feedback lasers fabricated from the same wafer exhibited single frequency emission near 11 µm and operated in the cw regime up to 295 K. [ABSTRACT FROM AUTHOR]

Consolidation of flame hydrolysis deposition silica soot with a 9.3 µm CO2 laser has been demonstrated. A range of laser parameters were investigated and the surface roughness of the resulting silica layers were characterised with a stylus profiler and white light interferometer. The surface roughness parameters were Ra = 68.9 nm, Rq = 83.8 nm perpendicular to the trajectory of the translated laser beam for a speed of 300 mm s−1 and an average laser power of 42.5 W, and Ra = 29.5 nm, Rq = 36.18 nm along the trajectory of the translated laser beam for a speed of 250 mm s−1 and an average laser power of 35.8 W. [ABSTRACT FROM AUTHOR]

A microring resonator realised by femtosecond laser two‐photon photopolymerisation in an epoxy‐based negative photoresist (SU‐8) is proposed and demonstrated, which is further proved to be capable of temperature and refractive index sensing by monitoring the shift of the resonance wavelength of the interferometric pattern. The experimental results indicate refractive index sensitivity of 12.50 nm/refractive index unit (redshift) and temperature sensitivity of −9.51 × 10−2 nm/oC (blueshift), respectively. [ABSTRACT FROM AUTHOR]

The high‐quality factors (Q‐factors) of nanocavities in three‐dimensional photonic crystals were experimentally demonstrated by increasing the in‐plane area of the structure. Entire structures made of GaAs were fabricated by a micro‐manipulation technique, and the nanocavities contained InAs self‐assembled quantum dots that emitted near‐infrared light. The obtained Q‐factor was improved to 93,000, which is 2.4 times larger than that in a previous report of a three‐dimensional photonic crystal nanocavity. Due to this large Q‐factor, a lasing oscillation from this cavity mode was successfully observed. [ABSTRACT FROM AUTHOR]

The authors have developed a new heterogeneous‐integration method for fabricating semiconductor lasers with high modulation efficiency on Si substrates. The method employs the direct bonding of an InP‐based active layer to the SiO2 layer of a thermally oxidised Si substrate (SiO2 /Si substrate), followed by the epitaxial growth of InP to form a buried heterostructure (BH). By using the InP membrane, the authors realise epitaxial growth of an InP on the InP membrane directly bonded to Si without crystal quality degradation. Both a theoretical estimation and photoluminescence measurements revealed that the total laser thickness must be less than the critical thickness determined by the applied thermal strain. The authors confirmed that the crystal quality of the BH is comparable to that fabricated on an InP substrate when using a 250‐nm‐thick InP‐based membrane. A distributed feedback laser fabricated on a SiO2 /Si substrate exhibited continuous‐wave operation up to 100°C and was directly modulated by a 40 Gbit/s non‐return‐to‐zero signal with a bias current of 15 mA. These results indicate that epitaxial growth using a directly bonded InP‐based active layer on a SiO2 /Si substrate allows us to achieve lasers with high modulation efficiency and to use a large‐scale Si wafer as a fabrication platform, resulting in low‐cost fabrication. [ABSTRACT FROM AUTHOR]

A theoretical study of nano‐plasmonic couplers constructed using aluminium arsenide (AlAs) and alumina (Al2 O3) is presented. The analysis has been done using the finite difference time domain technique. The dependence of coupling efficiency on the width of the air layer of silver–air–silver waveguide has been investigated to determine the optimal width of air. Coupling efficiency with the variation in input signal wavelength, reflection coefficient and return loss have been calculated numerically in order to characterise the performance of AlAs and Al2 O3 as nano‐plasmonic couplers. The resonant peaks have also been obtained for both AlAs and Al2 O3. The couplers provide appreciable performance at 1550 nm wavelength and have simple rectangular shape with no tapering which provides advantage in the fabrication process. It also offers broadband operation. [ABSTRACT FROM AUTHOR]

Quantum well laser diodes with low far‐field divergence remain a requirement for many applications such as optical interconnects and data networks, pump sources and next generation holographic red–green–blue displays requiring compact, high power, visible light sources with high spatial and spectral coherence. Many designs exist, but the structure must be easy to grow reproducibly, which has commercial advantages. The authors' low far‐field divergence design widens the vertical mode in such a way as to decrease the far‐field divergence without significantly reducing the confinement factor, thus keeping threshold current lower. In this study, the authors calculate the sensitivity of their design, which has high refractive index mode expansion layers inserted in the cladding, to unintentional variations in layer thickness and composition during growth. They obtain consistency in measured far‐fields for three wafers grown over an interval of a year, with a full‐width‐half‐maximum vertical far‐field divergence of 17° for a narrow design (Design A) and just under 13° for a very narrow design (Design B). They have demonstrated a useful, reproducible design, adding to the range of versatile semiconductor lasers available for every application. [ABSTRACT FROM AUTHOR]

The authors report 1.3‐μm InAs/GaAs quantum‐dot (QD) lasers monolithically grown on a Si substrate by optimising the dislocation filter layers (DFLs). InAlAs/GaAs strained layer superlattices (SLSs) have been presented as DFLs in this study. A distinct improvement in the InAs/GaAs QDs was observed when using InAlAs/GaAs SLSs because of the effective filtering of threading dislocations. Consequently, a laser with a threshold current density of 194 A/cm2 at room temperature and an operating temperature as high as 85°C is successfully demonstrated. These results show the potential for integrating III–V QD materials on a Si platform via InAlAs/GaAs SLSs as DFL. [ABSTRACT FROM AUTHOR]

A microsquare dual wavelength laser has been fabricated and applied to sub‐THz emission by beating two modes. An 18 × 18 μm square AlGaInAs/InP microsquare laser combined with an optimised uni‐travelling‐carrier photodiode has demonstrated stable emission at 103.2 GHz. [ABSTRACT FROM AUTHOR]

GaSb‐based type‐I quantum wells cascade diode lasers with nearly diffraction limited output beam were fabricated using methane–hydrogen dry etching plasma process. Rapid thermal annealing was shown to be a necessary step to reverse the effect of hydrogen plasma on conductivity of AlGaAsSb cladding alloy. Annealed two‐step narrow ridge lasers confined both optical field and current in lateral direction and demonstrated operating voltage, threshold current density and slope efficiency comparable to those of reference wide ridge devices. [ABSTRACT FROM AUTHOR]

Continuous wave (CW) operation of high‐power blue laser diodes (LDs) with polished facets on semi‐polar (202̅1̅) gallium nitride (GaN) substrates is demonstrated. Ridge waveguide LDs were fabricated using indium GaN waveguiding layers and GaN cladding layers. At a lasing wavelength of 452 nm, the peak two‐facet CW output power from an LD with uncoated facets was 1.71 W at a current of 3 A, corresponding to an optical power density of 32.04 MW/cm2 on each facet. The dependence of output power on current did not change with repeated CW measurements, indicating that the polished facets did not degrade under high‐power CW operation. These results show that polished facets are a viable alternative to cleaved or etched facets for high‐power CW semi‐polar LDs. [ABSTRACT FROM AUTHOR]

A comparative analysis of the properties of vertical light‐emitting diodes (VLEDs) fabricated using different surface treatment schemes was conducted. Compared with a conventional VLED, a light output power increase of 24.8% for an injection current of 350 mA was achieved by an n‐type‐gallium nitride (GaN)‐based VLED with a thin undoped GaN layer and microsized protrusions produced by krypton fluoride laser irradiation using an energy density of 600 mJ/cm2. This was accomplished without noticeable degradation of the electrical properties of the device. Further, potassium hydroxide wet etching of the VLED surface increased the light output power gain to 47.3% for the same injection current. [ABSTRACT FROM AUTHOR]

The fabrication of orange‐emitting semiconductor laser on interdiffused InGaP/InAlGaP structure is reported. The lasers lased at 22°C at a wavelength as short as 608 nm with threshold current density of 3.4 KAcm−2 and a maximum output power of ∼46 mW. This is the shortest wavelength electrically pumped semiconductor laser emission from the InGaP/InAlGaP structure. [ABSTRACT FROM AUTHOR]

A novel fabrication method of buried‐heterostructure (BH) mid‐infrared quantum cascade lasers (QCLs) by using non‐selective regrowth of iron‐doped indium phosphide (InP) (Fe:InP), around deeply etched laser ridges, via metal‐organic chemical vapour deposition (MOCVD) and planarisation via chemical polishing is reported. Owing to better heat dissipation, the fabricated 4.75 μm emitting QCLs exhibit about three‐fold enhancement in maximum output power under continuous‐wave operation at room temperature (T = 20°C) compared with that from lasers without the regrown InP. The demonstrated fabrication method provides a more flexible route to realising BH QCLs by removing strict requirements on the etched‐ridge sidewall profile, as well as on the physical dimensions of the dielectric mask for the regrowth via MOCVD. The method can be further employed for making large‐emitting aperture, closely packed arrays of QCLs, with planarised geometry, for coherent‐power scaling. [ABSTRACT FROM AUTHOR]

Narrowband filters based on Bragg gratings (BGs) in subwavelength grating (SWG) waveguides in silicon‐on‐insulator are reported. The SWG BGs are fabricated using electron beam lithography with a single etch. For SWG BGs 1.12 mm in length, the measured 3 dB bandwidths are ∼0.5 nm, and they have a peak reflectivity as high as 94.4% in the C‐band. [ABSTRACT FROM AUTHOR]

An eight‐wavelength hybrid Si/AlGaInAs/InP microring laser array coupled with an underlying silicon waveguide has been fabricated based on the bonding technique, with the radii varying from 15 to 15.14 μm at a step of 20 nm and with a microring width of 2 μm. Continuous‐wave (CW) electrically injected operation is obtained at 280 K, with threshold currents of about 6 mA, channel spacing of about 2 nm and sidemode‐suppression ratios above 20 dB. [ABSTRACT FROM AUTHOR]

In the authors' previous work, the effect of a plasmonic metal hole array (MHA) as integrated on the infrared (IR) photodetector was demonstrated and its performance particularly at a normal incidence was analysed. However, in IR imaging, the associated optics or lens focuses and collimates the light to the detector, which in turn causes the incident light to bend with various angles. Since the MHA is integrated on top of the detector, it is critical to investigate its sensitivity against the angle of incidence and how it impacts the overall sensing capability. The splitting of the surface plasmon polariton (SPP) resonances due to MHA is reported here, since the incident angle varies. In the experiment, the SPP structure has been fabricated by a two‐dimensional (2D) square array of subwavelength circular holes penetrating the gold film. The transmission spectra of the SPP structure in a mid‐IR range have been measured for various incident angles. An interesting phenomenon is observed here, that is, the first‐ and second‐order bimodal plasmonic spectra split into three or more peaks as the incident angle increases. Consistency in the experimental results with the simulation is found. [ABSTRACT FROM AUTHOR]

An electro‐optic (EO) polarisation conversion type modulator for short‐wavelength light using periodically poled MgO:LiNbO3 is fabricated and the characteristics are evaluated using a tunable GaN laser. High‐quality domain‐inverted gratings with 3.6 μm were obtained over a 1.0 × 1.0 mm2 area. The maximum conversion efficiency, as high as 91%, was obtained. The wavelength bandwidth was 0.7 nm, which was in good agreement with the calculated value, and high wavelength selectivity was obtained. [ABSTRACT FROM AUTHOR]

An electro‐optic (EO) polarisation conversion type modulator for short‐wavelength light using periodically poled MgO:LiNbO3 is fabricated and the characteristics are evaluated using a tunable GaN laser. High‐quality domain‐inverted gratings with 3.6 μm were obtained over a 1.0 × 1.0 mm2 area. The maximum conversion efficiency, as high as 91%, was obtained. The wavelength bandwidth was 0.7 nm, which was in good agreement with the calculated value, and high wavelength selectivity was obtained. [ABSTRACT FROM AUTHOR]

Terahertz (THz) detectors imaging is an attractive technology that has been widely adopted in various imaging applications, but the low response has always been a critical problem for THz detectors. Here, the authors present some antenna‐coupled 2.58 THz detectors fabricated using 55 nm CMOS process technology for the terahertz wave detection well beyond the device cut‐off frequency, each detector consists of a patch antenna and one or few short‐channel metal–oxide–semiconductor field‐effect‐transistors (MOSFETs). The authors demonstrated two drain‐driven detectors different from the commonly used configurations, and proved that this structure can effectively improve the response to the quantum cascade laser. The output signal is extracted with a lock‐in amplifier under room temperature. [ABSTRACT FROM AUTHOR]

Mesa‐type and ridge‐type InGaAs/InAlAs double‐channel quantum cascade lasers (QCLs) emitting 8.15 μm wavelength were fabricated by using metal–organic chemical vapour deposition and inductively coupled plasma reactive ion etching techniques. The output power, threshold current, characteristic temperature (T0), and slope efficiency were compared. The smooth and vertical sidewall profile enabled mesa‐type QCL to exhibit the higher output power, the lower threshold current, and the higher slope efficiency than the ridge‐type QCL. [ABSTRACT FROM AUTHOR]

The first laterally‐coupled distributed feedback (DFB) laser with first‐order sidewall gratings fabricated by optical interference lithography is experimentally demonstrated. The gratings were first etched into a dielectric mask on the planar top surface of an InP/AlGaInAs laser epiwafer, and then transferred to both sidewalls of a 2 µm deep ridge‐waveguide structure using a novel self‐aligned process. DFB ridge‐waveguide lasers with a cavity length of 650 µm and width of 2.6 µm (with 300 nm gratings on both sidewalls) achieved single longitudinal mode continuous‐wave operation, with a sidemode suppression ratio of 37 dB. The threshold current density is 1.7 kA/cm2 at room temperature, and the slope efficiency is 0.14 mW/mA per facet (uncoated). [ABSTRACT FROM AUTHOR]

The first room‐temperature operation of a transistor vertical‐cavity surface‐emitting laser (T‐VCSEL) is demonstrated. Fabricated using an epitaxial regrowth process, the T‐VCSEL is electrically a pnp‐type bipolar junction transistor and consists of an undoped AlGaAs/GaAs bottom DBR, an InGaAs triple‐quantum‐well active layer, an Si/SiO2 dielectric top DBR, and an intracavity contacting scheme with three electrical terminals. The output power is controlled by the base current in combination with the emitter‐collector voltage, showing a voltage‐controlled operation mode. A low threshold base‐current of 0.8 mA and an output power of 1.8 mW have been obtained at room temperature. Continuous‐wave operation was performed up to 50°C. [ABSTRACT FROM AUTHOR]

A hollow‐waveguide‐output uni‐travelling‐carrier photodiode (UTC‐PD) module operating at frequencies from 400 to 900 GHz has been developed. The module consists of a UTC‐PD, a photodiode‐to‐waveguide coupler, and a metallic package with a waveguide rectangular (WR)‐1.5 rectangular waveguide. The coupler is monolithically integrated with the UTC‐PD chip. The fabricated module exhibits the output power as high as −19 dBm at 500 GHz and the 3 dB bandwidth of 340 GHz, which is the widest among ever‐reported photodiode modules. [ABSTRACT FROM AUTHOR]

Distributed‐feedback ridge‐waveguide lasers emitting around 670 nm have been fabricated and experimentally characterised. Wavelength stabilisation is provided by 40th Bragg order surface gratings dry‐etched into the p‐GaAs–AlGaAs–AlGaInP layer structure. The large grating period of 4.2 µm allows the injection of the current between the grooves of the grating without sacrificing the electrical and optical properties noticeably. The 1.5 mm long devices achieve an output power of 50 mW at an injection current of 180 mA. The side mode suppression ratio is 50 dB at 150 mA. [ABSTRACT FROM AUTHOR]

We demonstrate, for the first time, a single section passively mode‐locked InAs/InGaAs quantum dot laser directly grown on on‐axis (001) GaP/Si substrate. The laser has a continuous‐wave threshold current of 34 mA at 20°C. By forward biasing the laser gain section current at 470 mA, 490 fs pulse generation with 31 GHz repetition rate can be obtained. This simple femtosecond pulse generation structure with CMOS fabrication compatibility makes the laser a promising light source candidate in future large‐scale silicon photonic applications. [ABSTRACT FROM AUTHOR]

The design and fabrication of metamorphic periodic heterostructures containing InAsSb layers with controllable modulated Sb composition and well‐regulated band alignments are reported. The bandgap energy of ordered alloy can be much smaller than that in bulk InAsSb with any Sb content. The modulation period is determined by the thicknesses of the strain compensated InAsSbx/InAsSby pairs grown on a virtual GaInzSb substrate with a given lattice constant. The experiment shows that the deviation of the modulation period from ∼2.3 to ∼5.5 nm leads to the shift of the maximum of 20 K photoluminescence from 12.9 to 19.6 µm. It is concluded that the growth of strain compensated InAsSbx/InAsSby on virtual substrates allows developing narrow bandgap III–V materials with various bandgap energies. [ABSTRACT FROM AUTHOR]

Three‐element in‐phase coherently coupled arrays of vertical cavity surface‐emitting lasers (VCSELs) were fabricated using proton implantation. The arrays show excellent beam quality with a far‐field divergence of 4°, while maintaining a stable in‐phase mode until a maximum output power of 4 mW under continuous‐wave condition. The process for the arrays is simple and the cost is low. [ABSTRACT FROM AUTHOR]

The first compact electroabsorption modulators integrated with distributed‐feedback (EADFB) laser array module using flip‐chip interconnects have been fabricated for a 400 Gbit/s transceiver. Eight 50 Gbit/s EADFB lasers and an optical multiplexer were monolithically integrated on one chip in an area of only 3.2 × 4.8 mm. The flip‐chip interconnects provide a higher modulation bandwidth. Clear eye opening was achieved for all eight lanes under 50 Gbit/s operation. [ABSTRACT FROM AUTHOR]

A Si wire arrayed waveguide grating designed to reduce the noise and transmission peak width and avoid systematic phase error generated at the curved waveguides is reported. A slab waveguide structure to remove stray light is used. 200 GHz spacing 16 channel devices were fabricated by ArF immersion. An improved crosstalk of −23 dB was obtained. [ABSTRACT FROM AUTHOR]

An edge‐coupled high‐speed photodiode based on strained InGaAs quantum wells for detection at 2000nm is demonstrated. The fabricated device shows a leakage current as low as 120nA at −3V bias voltage and a responsivity of around 0.3A/W at 2000nm. The high‐speed butterfly packaging of the device is presented which shows a 3dB bandwidth of more than 10GHz. The device shows similar high‐speed performance at 1550nm. [ABSTRACT FROM AUTHOR]