Monolithic multiple wavelength ridge waveguide laser array fabricated by Nd:YAG laser-induced quantum well intermixing

Coronagraph designs that use photonic integrated circuits have the highest theoretical throughput for off-axis signals, and therefore the highest potential exoplanet yield for future high-contrast direct imaging campaigns. Using the rejected starlight, the photonic integrated circuit may also provide simultaneous wavefront sensing, allowing for the correction of non-common-path aberrations. This work considers how a photonic circuit should be configured to maximize its sensitivity to phase aberrations. Two cases are considered: in the first, the photonic circuit is coupled directly to an electric field in a piecewise manner, while in the second, the circuit is coupled to the field via an optical mode sorter. In either case, this work constructs a unitary matrix, which can be applied by a photonic circuit to produce maximum sensitivity.

This paper proceeds from basic research on carrier dynamics to applications in high-speed laser devices. Different retardation mechanisms are studied experimentally and theoretically providing input for the design of high-speed laser devices. Optically detected carrier dynamics in III/V semiconductor quantum well (QW) heterostructures perpendicular to the interfaces is studied. Photoluminescence emissions originating from different semiconductor layers are recorded time-resolved to probe the carrier dynamics between these layers. High spatial and temporal resolution is obtained experimentally, partly even in the nm and sub-ps ranges, respectively. Retardation effects are separated and studied experimentally and theoretically by corresponding model calculations. A material comparison shows that GaInAsP is beneficial due to considerable advantages in technological implementation processes and AlGaInAs is superior from a physical point of view enabling higher modulation band-widths due to larger conduction band discontinuities. The equalization of the carrier densities in the individual wells is found to be mainly retarded by hole thermionic emission. Hole transport in the p-sided confinement layer and electron capture from the p-sided confinement layer is also found to be also a limiting factor. These results are used to optimized AlGaInAs/InP lasers with asymmetric confinement layers. The p-sided confinement layer is reduced on the costs of the n- sided confinement layer to obtain (1) a faster hole transport across the p-sided confinement layer and (2) to accelerate the capture of electrons from the p-sided confinement layers being uncaptured during the transfer across the QWs. In our experiments a modulation bandwidth of 26 GHz is obtained. Even higher values are found in corresponding theoretical model calculations demonstrating an interesting development potential.

The aim of this paper is to present detailed experimental and theoretical investigations of the behavior of ridge-waveguide (RW) lasers emitting at 670 nm under injection of sub-ns current pulses with high amplitudes. The RW lasers are based on strained GaInP double quantum wells embedded in an asymmetric AlGaInP/AlInP waveguide structure. The width of the ridge is 15 μm and the cavity length 3 mm. The laser diode is mounted on an in-house developed laser driver with a final stage based on GaN transistors, which generates nearly rectangular shaped current pulses with amplitudes up to 30 A and widths down to 300 ps. The pulse width can be varied electronically between 300 ps and 1.2 ns with a repetition frequency up to 1 MHz, which results in a variation of the pulse width of the emitted optical pulses between 200 ps and 1.2 ns. The maximum pulse power depends on the electrical pulse width and reaches 7.2 W for a ridge width of 15 μm. At high pulse current amplitudes the pulse power saturates. Time-dependent simulations with the drift-diffusion simulator WIAS-TeSCA reveal that accumulation of excess electrons under the ridge is the root cause for the power saturation, limiting the maximum achievable output power.

The metalorganic chemical vapor deposition of a highly strained InGaAsN quantum-well (QW) surrounded by (In)GaAsP direct barrier layers is investigated. We found that growth pause annealing with AsH3, performed immediately before and after the growth of the QW, significantly improves the optical quality of InGaAsN QW with (In)GaAsP direct barriers. The utilization of larger band gap barrier materials, such as InGaAsP or GaAsP, will potentially lead to reduced carrier leakage from the QW laser structures.

Integrated lithium niobate (LN) photonic circuits have recently emerged as a promising candidate for advanced photonic functions such as high-speed modulation, nonlinear frequency conversion, and frequency comb generation. For practical applications, optical interfaces that feature low fiber-to-chip coupling losses are essential. So far, the fiber-to-chip loss (commonly >10 dB/facet) has dominated the total insertion losses of typical LN photonic integrated circuits, where on-chip losses can be as low as 0.03-0.1dB/cm. Here we experimentally demonstrate a low-loss mode size converter for coupling between a standard lensed fiber and sub-micrometer LN rib waveguides. The coupler consists of two inverse tapers that convert the small optical mode of a rib waveguide into a symmetrically guided mode of a LN nanowire, featuring a larger mode area matched to that of a tapered optical fiber. The measured fiber-to-chip coupling loss is lower than 1.7dB/facet with high fabrication tolerance and repeatability. Our results open the door for practical integrated LN photonic circuits efficiently interfaced with optical fibers.

Advances in optically nonlinear materials and single mode fiber technology have led to a renewed interest in integrated optics. For coherent communication fiber systems, integrated optics offer the possibility of an entirely monolithic implementation with narrow linewidth lasers, modulators, detectors, frequency shifters and optical switches. With III-V semiconductors, optical functions and associated electronics for drivers and detectors can be on the same opto-electronic chip. Recent advances in nonlinear integrated optics also hold promises for applications in ALL-OPTICAL processing and interfacing of fiber signals. Power dependent nonlinear couplers, nonlinear distributed feedback gratings, optically tunable filters, bistable integrated gratings and logic gates are all possible applications of integrated optics in communication systems resulting from a better understanding of nonlinear guided mode behavior. New organic (such as liquid crystals) or semiconductor materials (multiple quantum wells (MQW) for example) in an integrated optics context may provide the properties needed to make all-optical processing viable in the next generation devices. As an example we present some of our work on all-optical modulation and logic gates in silicon based channel waveguides at wavelengths of 1.32 and 1.55 micrometers. PicoJoule switching energies and subpicosecond initiation times make these waveguide devices attractive for single fiber systems since the lack of resonators ensures good stability in actual operation.

Selective modification of the band gaps of GaInNas/GaAs structures by quantum well intermixing techniques

The simulation of double quantum well (QW) GaInNAs ridge-waveguide (RW) lasers is performed over a wide range of cavity lengths and operating temperatures using a comprehensive in-house 2D laser simulator that takes into account all of the major device physics, including current spreading, capture escape processes, drift diffusion in the QW, 2D optical modes and fully resolved lasing spectra. The gain data used by the simulator were fitted to experimental gain spectra measured by the segmented contact method. The gain model includes the band-anticrossing model for the conduction band and a 4×4 k·p model for the valence band. Using a carrier density-dependent and temperature-dependent linewidth broadening parameter, a good fit with experiment over a temperature range of 300–350 K was obtained. A Shockley–Read–Hall (SRH) lifetime of 0.5 ns and an Auger recombination coefficient of 1×10−28 cm6/s, were extracted from the calibration of the laser simulator to experimental device characteristics of broad-area (BA) devices. Using the same set of parameters for BA devices, except for a reduced SRH lifetime of 0.45 ns underneath the etch, 2D simulation results were found to agree well with the measured RW laser operating characteristics. The impact of the various recombination processes in the RW laser at threshold has also been identified using the calibrated laser simulator.

Photonic integrated circuits (PICs), implementing optical functions such as light generation, modulation, routing and detection on a single chip, are emerging as a powerful platform to realize miniaturized optical systems. These chips find applications in various fields, ranging from high-speed optical transceivers to disposable biosensors, LiDARs for detection and ranging, spectroscopic analytical sensors, etc. Silicon photonics is the field that is using silicon fabrication technologies, developed over the last decades for advanced electronic integrated circuits, to realize PI Cs. Using this approach advanced PICs can be realized on 200 mm or 300 mm wafers in high volume and at low cost. On the silicon photonics platform many device structures are readily available: Si or SiN waveguides, micro-heaters for tuning/switching, Si or Ge based modulators and photodetectors. However, other optical functions such as light generation require the integration of III-V semiconductors on the silicon wafers. This can be realized using different approaches ranging from hybrid assembly over die-towafer bonding to monolithic integration. Every approach has its advantages and disadvantages. An interesting approach that we are developing is the use of microtransfer- printing technology for the integration of III-V semiconductor devices on a silicon photonic wafer, which is a scalable and minimally-invasive approach.

Photonic integrated circuits (PIC) have been established for miniaturized, on-chip optical systems. Current approaches for producing PICs mostly rely on semiconductor processing technologies, which are complex and costintensive. A promising alternative with the potential to revolutionize PIC fabrication is additive manufacturing (AM), which offers the opportunity to develop tailored and customized waveguide designs for functionalities needed in fast-evolving modern applications like the Internet of Things. Here, an AM technology called laser glass deposition (LGD) is presented for the production of on-chip core-cladding waveguides based on fused silica. Commercially available glass fibers with a diameter of 125 μm are fused onto a quartz glass substrate using a CO2-laser in a 2.5D-printing process. Test series are performed to determine the process window to reach a stable connection between fiber and substrate while maintaining the fiber´s optical functionality. To enable efficient light coupling into the waveguide, the fiber end facets are laser cleaved after the deposition within the same process environment. Again, parameter studies are performed to reach a high surface quality. Both the waveguides and the cleaved surfaces are characterized using different imaging techniques. In addition, the optical properties of the generated waveguides are analyzed.

The authors report the design, growth and optical properties of InAsP/InGaAsP and InAsP/InGaP lasers with compressively-strained quantum wells. Both tensile-strained and lattice-matched quaternary barriers were investigated. Strain-compensated structures, i.e. those with tensile-strained barriers, show narrow photoluminescence and X-ray diffraction linewidths indicating high crystalline quality. These devices were subsequently processed into ridge waveguide lasers and a threshold current of ~1 kA/cm2 was obtained for a strain-compensated five well structure.

A design framework to implement non-unitary input–output operations to a practical unitary photonic integrated circuit is described. This is achieved by utilising the cosine-sine decomposition to recover the unitarity of the original operation. The recovered unitary operation is decomposed into fundamental unitary building blocks, forming a photonic integrated circuit network based on directional couplers and waveguide phase shifters. The individual building blocks are designed and optimised by three-dimensional full-wave simulations and scaled up using a circuit approach. The paper investigates the scalability and robustness of the design approach. Our study demonstrates that the proposed approach of performing unitary matrix completion can be applied to any arbitrary matrices. This design approach allows for implementation of non-unitary operations to perform various linear functions in neuromorphic photonics for computing, sensing, signal processing and communications.

One of the key challenges in Silicon based optical interconnect system remains to be the efficient coupling of optical signals from the submicron size on-chip waveguides to standard single mode (SM) fibers with low insertion loss (IL) and relaxed alignment tolerance. Large optical alignment tolerance allows optical connectors to be attached to on-chip waveguides passively using standard semiconductor pick-and-place assembly tools that have placement accuracies of 10- 15μm. To facilitate the assembly, optical fiber coupling elements need to be modular and compact. They have to also have low profile to avoid blocking air flow or mechanical interference with other elements of the package. In this paper we report the development of a two-dimensional (2D) SM optical fiber coupling architecture that consists of Si based photonic lightwave circuit (PLC) substrate and a high-density micro-lensed fiber optic connector. The system is compact, efficient and has large optical alignment tolerance. At 1300nm an insertion loss of 2.4dB and 1.5dB was measured for the PLC module and the fiber optic connector, respectively. When the PLC module and connector was aligned together, a total insertion loss of 7.8dB was demonstrated with x,y alignment tolerance of 40μm for 1dB optical loss. The SM optical coupling architecture presented here is scalable, alignment tolerant and has the potential to be manufactured in high volume. To our knowledge, such a system has not been reported in the literature so far.

Efficient photonic circuit simulation tools are essential for the design and optimization of photonic integrated circuits (PICs). However, the computational speed of current commercial simulators remains insufficient to support large-scale circuit optimization and statistical verification. In this paper, a multimode scattering matrix computation method based on a multimode subnetwork growth approach (referred to as MSG) for efficiently calculating the frequency-domain response of photonic circuits is proposed. The presented method starts with accurate photonic devices modeling leveraging the multimode scattering matrix. It then utilizes the established multimodal models to precisely characterize component parameters and topology information of the arbitrarily interconnected multiport photonic circuit. By employing an iterative strategy that connects only two subnetworks at each step, the global response is progressively computed, which significantly reduces the complexity of matrix inversion. The sequence of network connections is optimized using a suboptimal ordering algorithm, further minimizing the total computational cost. Benchmark results demonstrate that our approach enables fast multimode simulation, delivering over twice the speed of commercial simulators and strong engineering applicability.

Achieving high external quantum efficiency (EQE) in AlGaN-based ultraviolet-B (UVB) light-emitting diodes (LEDs) remains a persistent challenge due to strong polarization-induced electric fields and poor electron–hole wave function overlap in strained quantum wells. Here, we report a decisive enhancement in carrier dynamics and optical efficiency by precisely engineering the QW thickness in a 40% relaxed AlGaN-based UVB LED grown on sapphire. Structural analyses confirm that controlled strain relaxation in the AlGaN quantum well effectively suppresses polarization fields, while compositional grading and optimized quantum-well thickness significantly improve carrier confinement and overlap. Systematic optimization of QW width mitigates the quantum-confined Stark effect, reducing the internal electric field from −0.97 to −0.32 MV cm–1, thereby strengthening the electron–hole wave function overlap via a 7 nm thick QW and enhancing radiative recombination. A moderately Mg-doped p-type multiquantum-barrier electron-blocking layer and a partially relaxed n-type AlGaN electron injection layer further improve carrier confinement and injection efficiency. These combined effects yield an internal quantum efficiency of 80% and a predicted high external quantum efficiency exceeding 12%, nearly doubling that of conventional devices. This study establishes QW thickness modulation and polarization field management as practical and scalable strategies to overcome intrinsic polarization effects, enabling high-efficiency, mercury-free UVB emitters for next-generation disinfection, water purification, and smart-agriculture applications.