Publications
28 results found
Dranczewski J, Fischer A, Tiwari P, et al., 2023, Plasma etching for fabrication of complex nanophotonic lasers from bonded InP semiconductor layers, Micro and Nano Engineering, Vol: 19, ISSN: 2590-0072
Integrating optically active III-V materials on silicon/insulator platforms is one potential path towards improving the energy efficiency and performance of modern computing. Here we demonstrate the applicability of direct wafer bonding combined with plasma etching to the fabrication of complex nanophotonic systems out of InP layers. We explore and optimise the plasma etching of InP, validating existing processes and developing improved ones. We explore the use of microdisk lasing as a way to evaluate fabrication fidelity, and demonstrate that we can create complex lasing systems of interest to us: coupled disk cavities and random network lasers.
Fischer A, Raziman TV, Dranczewski J, et al., 2023, Spectral Control of Coupled InP Nanolasers around Exceptional Points through Selective Excitation
Tunable on-chip nanolaser sources are indispensable for advances in optical data transmission and computing. One way to tune emission wavelength is through use of coupling between two nanolasers, and to exploit their non-Hermitian properties, such as single mode emission and exceptional points as a function of non-uniform gain distribution [1]. We experimentally study mode interactions between coupled, epitaxially-grown InP microdisks, with diameters in the micron range that support resonant whispering gallery modes (Fig. 1a) [2]. Through selective excitation, via a digital micromirror device (DMD), arbitrary pumping powers on each disk (P1, P2) can be reached (Fig. 1b). This enables the full exploration of the coupled mode landscape that is theoretically described by coupled mode theory [3] and includes PT-symmetric and PT-broken regimes, lasing gaps, and exceptional points. In specific regions of the mode landscape, a reversed pump dependence is observed, resulting in a counter-intuitive lasing gap [3]. When one of the microdisks is pumped above threshold (P1) and the pump on the second disk (P2) is increased from zero, hence increasing the total pump power, the lasing intensity decreases until the system is below threshold and in the lasing gap (Fig. 1c). Further increase in P2 is needed to close the lasing gap and drive the system above threshold at a shifted wavelength. When the power on the constantly pumped disk (P1) is increased, the lasing gap closes and the system reaches a virtual exceptional point.
Sapienza R, Barahona M, Saxena D, et al., 2022, Sensitivity and spectral control of network lasers, Nature Communications, Vol: 13, Pages: 1-7, ISSN: 2041-1723
Recently, random lasing in complex networks has shown efficient lasing over more than 50 localised modes, promoted by multiple scattering over the underlying graph. If controlled, these network lasers can lead to fast-switching multifunctional light sources with synthesised spectrum. Here, we observe both in experiment and theory high sensitivity of the network laser spectrum to the spatial shape of the pump profile, with some modes for example increasing in intensity by 280% when switching off 7% of the pump beam. We solve the nonlinear equations within the steady state ab-initio laser theory (SALT) approximation over a graph and we show selective lasing of around 90% of the strongest intensity modes, effectively programming the spectrum of the lasing networks. In our experiments with polymer networks, this high sensitivity enables control of the lasing spectrum through non-uniform pump patterns. We propose the underlying complexity of the network modes as the key element behind efficient spectral control opening the way for the development of optical devices with wide impact for on-chip photonics for communication, sensing, and computation.
Church SA, Al-Abri R, Parkinson P, et al., 2022, Optical characterisation of nanowire lasers, Progress in Quantum Electronics, Vol: 85, Pages: 1-26, ISSN: 0079-6727
Semiconductor nanowire lasers are single-element structures that can act as both gain material and cavity for optical lasing. They have typical dimensions on the order of an optical wavelength in diameter and several micrometres in length, presenting unique challenges for testing and characterisation. Optical microscopy and spectroscopy are powerful tools used to study nanowire lasers; here, we review the common techniques and analytical approaches often used and outline potential pitfalls in their application. We aim to outline best practise and experimental approaches used for characterisation of the material, cavity and lasing performance of nanowires towards applications in biology, photonics and telecommunications.
Trivedi M, Saxena D, Ng WK, et al., 2022, Self-organized lasers from reconfigurable colloidal assemblies, NATURE PHYSICS, Vol: 18, Pages: 939-+, ISSN: 1745-2473
Molkens K, Tanghe I, Saxena D, et al., 2022, Coupled Micro Ring Lasers based on Hybrid Integration of Colloidal Quantum Dots
Coupled and Random laser require flexible fabrication methods for photonic integration. Series of (random) coupled micro ring resonators were made with colloidal quantum dots and their unique properties investigated in both linear and lasing regimes.
Ta VD, Caixeiro S, Saxena D, et al., 2021, Biocompatible Polymer and Protein Microspheres with Inverse Photonic Glass Structure for Random Micro‐Biolasers, Advanced Photonics Research, Vol: 2, ISSN: 2699-9293
Ta VD, Caixeiro S, Saxena D, et al., 2021, Biocompatible polymer and protein microspheres with inverse photonic glass structure for random micro‐biolasers, Advanced Photonics Research, Vol: 2, Pages: 1-7, ISSN: 2699-9293
The miniaturization of random lasers to the micrometer scale is challenging but fundamental for the integration of lasers with photonic integrated circuits and biological tissues. Herein, it is demonstrated that random lasers with a diameter from 30 to 160 μm can be achieved by using a simple emulsion process and selective chemical etching. These tiny random laser sources are made of either dye-doped polyvinyl alcohol (PVA) or bovine serum albumin (BSA) and they are in the form of microporous spheres with monodisperse pores of 1.28 μm in diameter. Clear lasing action is observed when the microporous spheres are optically excited with powers larger than the lasing threshold, which is 154 μJ mm−2 for a 75 μm diameter PVA microporous sphere. The lasing wavelength redshifts 10 nm when the PVA microsphere diameter increases from 34 to 160 μm. For BSA microspheres, the lasing threshold is around 55 μJ mm−2 for a 70 μm diameter sphere and 104 μJ mm−2 for a 35 μm diameter sphere. The simple fabrication process reported allows for detail studies of morphology and size, important for fundamental studies of light–matter interaction in complex media, and applications in photonic integrated circuits, photonic barcoding, and optical biosensing.
Ta VD, Saxena D, Caixeiro S, et al., 2020, Flexible and tensile microporous polymer fibers for wavelength-tunable random lasing, Nanoscale, Vol: 12, Pages: 12357-12363, ISSN: 2040-3364
Polymer micro-/nanofibers, due to their low-cost and mechanical flexibility, are attractive building blocks for developing lightweight and flexible optical circuits. They are also versatile photonic materials for making various optical resonators and lasers, such as microrings, networks and random lasers. In particular, for random lasing architectures, the demonstrations to-date have mainly relied on fiber bundles whose properties are hard to tune post-fabrication. Here, we demonstrate the successful implementation of an inverted photonic glass structure with monodisperse pores of 1.28 μm into polymer fibers with diameter ranging from 10 to 60 μm. By doping organic dye molecules into this structure, individual fibers can sustain random lasing under optical pulse excitation. The dependence of lasing characteristics, including lasing spectrum and lasing threshold on fiber diameter are investigated. It is found that the lasing emission red-shifts and the threshold decreases with increasing fiber diameter. Furthermore, owing to the mechanical flexibility, the lasing properties can be dynamically changed upon stretching, leading to a wavelength-tunability of 5.5 nm. Our work provides a novel architecture for random lasers which has the potential for lasing tunability and optical sensing.
Septiadi D, Barna V, Saxena D, et al., 2020, Biolasing from individual cells in a low-Q resonator enables spectral fingerprinting, Advanced Optical Materials, Vol: 8, Pages: 1-8, ISSN: 2195-1071
Lasing from cells has recently been subject of thorough investigation because of the potential for sensitive and fast biosensing. Yet, lasing from individual cells has been studied in high‐quality resonators, resulting in limited dependence of the lasing properties on the cellular microenvironment. Here, lasing is triggered by cells floating in a low quality factor resonator composed of a disposable poly(methyl methacrylate) (PMMA) cell counting‐slide, hence in absence of conventional high‐reflectivity optical cavities. The exceptional spectral narrowing and the steep slope increase in the input–output energy diagram prove occurrence of laser action in presence of cells. The observed biolasing is an intrinsically dynamic signal, with large fluctuations in intensity and spectrum determined by the optical properties of the individual cell passing through the pump beam. Numerical simulations of the scattering efficiency rule out the possibility of optical feedback from either WGM (whispering gallery mode) or multiple scattering within the cell, and point to the enhanced directional scattering field as the crucial contribution of cells to the laser action. Finally, principal component analysis of lasing spectra measured from freely diffusing cells yields spectral fingerprints of cell populations, which allows discriminating cancer from healthy Rattus glial cells with high degree of confidence.
Zhang Y, Davis G, Fonseka HA, et al., 2019, Highly Strained III-V-V Coaxial Nanowire Quantum Wells with Strong Carrier Confinement., ACS Nano, Vol: 13, Pages: 5931-5938
Coaxial quantum wells (QWs) are ideal candidates for nanowire (NW) lasers, providing strong carrier confinement and allowing close matching of the cavity mode and gain medium. We report a detailed structural and optical study and the observation of lasing for a mixed group-V GaAsP NW with GaAs QWs. This system offers a number of potential advantages in comparison to previously studied common group-V structures ( e. g., AlGaAs/GaAs) including highly strained binary GaAs QWs, the absence of a lower band gap core region, and deep carrier potential wells. Despite the large lattice mismatch (∼1.7%), it is possible to grow defect-free GaAs coaxial QWs with high optical quality. The large band gap difference results in strong carrier confinement, and the ability to apply a high degree of compressive strain to the GaAs QWs is also expected to be beneficial for laser performance. For a non-fully optimized structure containing three QWs, we achieve low-temperature lasing with a low external (internal) threshold of 20 (0.9) μJ/cm2/pulse. In addition, a very narrow lasing line width of ∼0.15 nm is observed. These results extend the NW laser structure to coaxial III-V-V QWs, which are highly suitable as the platform for NW emitters.
Zhang Y, Saxena D, Aagesen M, et al., 2019, Toward electrically driven semiconductor nanowire lasers., Nanotechnology, Vol: 30
Semiconductor nanowire (NW) lasers are highly promising for making new-generation coherent light sources with the advantages of ultra-small size, high efficiency, easy integration and low cost. Over the past 15 years, this area of research has been developing rapidly, with extensive reports of optically pumped lasing in various inorganic and organic semiconductor NWs. Motivated by these developments, substantial efforts are being made to make NW lasers electrically pumped, which is necessary for their practical implementation. In this review, we first categorize NW lasers according to their lasing wavelength and wavelength tunability. Then, we summarize the methods used for achieving single-mode lasing in NWs. After that, we review reports on lasing threshold reduction and the realization of electrically pumped NW lasers. Finally, we offer our perspective on future improvements and trends.
Gaio M, Saxena D, Bertolotti J, et al., 2019, A nanophotonic laser on a graph, Nature Communications, ISSN: 2041-1723
Nanophotonic architectures for classical and quantum optical technology canboost light-matter interaction via sculpturing the optical modes, formingcavities and designing long-range propagation channels. Conventional photonicschemes minimise multiple scattering to realise a miniaturised version ofmacroscopic beam-splitters, interferometers and optical cavities for lightpropagation and lasing. Here instead, we introduce a nanophotonic network builtfrom multiple paths and interference, to control and enhance light-matterinteraction via light localisation beyond single scattering. The network isbuilt from a mesh of subwavelength waveguides, and can sustain localised modesand mirror-less light trapping stemming from interference over hundreds ofnodes. When optical gain is added, these modes can easily lase, reaching$\sim$100 pm linewidths. We introduce a graph solution to the Maxwell'sequation which describes light on the network, and predicts lasing action. Inthis framework, the network optical modes can be designed via the networkconnectivity and topology, and lasing can be tailored and enhanced by thenetwork shape. Nanophotonic networks pave the way for new laser devicearchitectures, which can be used for sensitive biosensing and on-chip opticalinformation processing.
Alanis JA, Lysevych M, Burgess T, et al., 2019, Optical Study of p-Doping in GaAs Nanowires for Low-Threshold and High-Yield Lasing, NANO LETTERS, Vol: 19, Pages: 362-368, ISSN: 1530-6984
Parkinson P, Alanis JA, Peng K, et al., 2018, Modal refractive index measurement in nanowire lasers-a correlative approach, NANO FUTURES, Vol: 2
Alanis JA, Saxena D, Mokkapati S, et al., 2017, Large-Scale Statistics for Threshold Optimization of Optically Pumped Nanowire Lasers, NANO LETTERS, Vol: 17, Pages: 4860-4865, ISSN: 1530-6984
Saxena D, Jiang N, Yuan X, et al., 2016, Design and Room-Temperature Operation of GaAs/AlGaAs Multiple Quantum Well Nanowire Lasers, NANO LETTERS, Vol: 16, Pages: 5080-5086, ISSN: 1530-6984
Burgess T, Saxena D, Mokkapati S, et al., 2016, Doping-enhanced radiative efficiency enables lasing in unpassivated GaAs nanowires, NATURE COMMUNICATIONS, Vol: 7, ISSN: 2041-1723
Saxena D, Wang F, Gao Q, et al., 2015, Mode Profiling of Semiconductor Nanowire Lasers, NANO LETTERS, Vol: 15, Pages: 5342-5348, ISSN: 1530-6984
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- Citations: 69
Mokkapati S, Saxena D, Jiang N, et al., 2015, An Order of Magnitude Increase in the Quantum Efficiency of (AI)GaAs Nanowires Using Hybrid Photonic-Plasmonic Modes, NANO LETTERS, Vol: 15, Pages: 307-312, ISSN: 1530-6984
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- Citations: 18
Gao Q, Saxena D, Wang F, et al., 2014, Selective-Area Epitaxy of Pure Wurtzite InP Nanowires: High Quantum Efficiency and Room-Temperature Lasing, NANO LETTERS, Vol: 14, Pages: 5206-5211, ISSN: 1530-6984
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- Citations: 172
Mokkapati S, Saxena D, Jiang N, et al., 2014, Plasmonic cavities for increasing the radiative efficiency of GaAs nanowires, Conference on Optoelectronic and Microelectronic Materials and Devices (COMMAD), Publisher: IEEE, Pages: 244-245, ISSN: 1097-2137
Mokkapati S, Saxena D, Nian-Jiang, et al., 2014, III-V semiconductor nanowire lasers, 24th IEEE International Semiconductor Laser Conference (ISLC), Publisher: IEEE COMPUTER SOC, Pages: 217-218, ISSN: 2326-5442
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- Citations: 1
Saxena D, Mokkapati S, Parkinson P, et al., 2013, Optically pumped room-temperature GaAs nanowire lasers, NATURE PHOTONICS, Vol: 7, Pages: 963-968, ISSN: 1749-4885
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- Citations: 452
Tan HH, Jiang N, Saxena D, et al., 2013, III-V Nanowires for Optoelectronic Applications, Symposium on Semiconductors, Dielectrics, and Metals for Nanoelectronics 11 held during the 224th Meeting of the Electrochemical-Society, Publisher: ELECTROCHEMICAL SOC INC, Pages: 93-98, ISSN: 1938-5862
Tan HH, Jiang N, Lee YH, et al., 2012, III-V Nanowires for Optoelectronic Applications, 5th International Conference on Computers and Devices for Communication (CODEC), Publisher: IEEE
Wang H, Parkinson P, Tian J, et al., 2012, Optoelectronic properties of GaAs nanowire photodetector, Conference on Optoelectronic and Microelectronic Materials and Devices (COMMAD), Publisher: IEEE, Pages: 139-140, ISSN: 1097-2137
Saxena D, Mokkapati S, Tan HH, et al., 2012, Designing single GaAs nanowire lasers, Conference on Optoelectronic and Microelectronic Materials and Devices (COMMAD), Publisher: IEEE, Pages: 101-102, ISSN: 1097-2137
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- Citations: 5
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