@article{61932,
  abstract     = {{<jats:p>Substantial improvements in the performance of optical interconnects based on multi-mode fibers are required to support emerging single-channel data transmission rates of 200 Gb/s and 400 Gb/s. Future optical components must combine very high modulation bandwidths—supporting signaling at 100 Gbaud and 200 Gbaud—with reduced spectral width to mitigate chromatic-dispersion-induced pulse broadening and increased brightness to further restrict flux-confining area in multi-mode fibers and thereby increase the effective modal bandwidth (EMB). A particularly promising route to improved performance within standard oxide-confined VCSEL technology is the introduction of multiple isolated or optically coupled oxide-confined apertures, which we refer to collectively as multi-aperture (MA) VCSEL arrays. We show that properly designed MA VCSELs exhibit narrow emission spectra, narrow far-field profiles and extended intrinsic modulation bandwidths, enabling longer-reach data transmission over both multi-mode (MMF) and single-mode fibers (SMF). One approach uses optically isolated apertures with lateral dimensions of approximately 2–3 µm arranged with a pitch of 10–12 µm or less. Such devices demonstrate relaxation oscillation frequencies of around 30 GHz in continuous-wave operation and intrinsic modulation bandwidths approaching 50 GHz. Compared with a conventional single-aperture VCSELs of equivalent oxide-confined area, MA designs can reduce the spectral width (root mean square values &lt; 0.15 nm), lower series resistance (≈50 Ω) and limit junction overheating through more efficient multi-spot heat dissipation at the same total current. As each aperture lases in a single transverse mode, these devices exhibit narrow far-field patterns. In combination with well-defined spacing between emitting spots, they permit tailored restricted launch conditions in MMFs, enhancing effective modal bandwidth. In another MA approach, the apertures are optically coupled such that self-injection locking (SIL) leads to lasing in a single supermode. One may regard one of the supermodes as acting as a master mode controlling the other one. Streak-camera studies reveal post-pulse oscillations in the SIL regime at frequencies up to 100 GHz. MA VCSELs enable a favorable combination of wavelength chirp and chromatic dispersion, extending transmission distances over MMFs beyond those expected for zero-chirp sources and supporting transfer bandwidths up to 60 GHz over kilometer-length SMF links.</jats:p>}},
  author       = {{Ledentsov, Nikolay N. and Ledentsov, Nikolay and Shchukin, Vitaly A. and Ledentsov, Alexander N. and Makarov, Oleg Yu. and Titkov, Ilya E. and Lindemann, Markus and de Adelsburg Ettmayer, Thomas and Gerhardt, Nils Christopher and Hofmann, Martin R. and Chen, Xin and Hurley, Jason E. and Dong, Hao and Li, Ming-Jun}},
  issn         = {{2304-6732}},
  journal      = {{Photonics}},
  number       = {{10}},
  publisher    = {{MDPI AG}},
  title        = {{{VCSELs: Influence of Design on Performance and Data Transmission over Multi-Mode and Single-Mode Fibers}}},
  doi          = {{10.3390/photonics12101037}},
  volume       = {{12}},
  year         = {{2025}},
}

@article{61931,
  abstract     = {{<jats:p>Recent research revealed that single-mode vertical-cavity surface-emitting lasers under spin injection (spin-VCSELs) have the potential to revolutionize laser technology for short-haul optical communications. While previous studies have focused solely on single-mode operation, this study introduces multimode spin-VCSELs. We experimentally demonstrate the existence of multi-resonant polarization dynamics when spin is injected, a phenomenon previously unobserved. The development opens the door to significantly faster and more efficient optical communication systems by harnessing the collective behavior of multiple laser modes. Furthermore, we lay the groundwork for understanding multimode operation through the extension of the single-mode spin–flip model, which forms the basis for present and future analyses of multimode spin-laser operation. This work is an important step toward realizing the full potential of spin-VCSELs and, thus, enables significantly improved performance of spin-VCSEL-based optical networks in the future.</jats:p>}},
  author       = {{Diiankova, Uliana and Drong, Mariusz and Pusch, Tobias and Michalzik, Rainer and Lindemann, Markus and Gerhardt, Nils Christopher and Hofmann, Martin R.}},
  issn         = {{2378-0967}},
  journal      = {{APL Photonics}},
  number       = {{10}},
  publisher    = {{AIP Publishing}},
  title        = {{{Multimode vertical-cavity surface-emitting lasers under spin injection}}},
  doi          = {{10.1063/5.0286998}},
  volume       = {{10}},
  year         = {{2025}},
}

@article{64551,
  abstract     = {{<jats:p>Laterally coupled vertical-cavity surface-emitting lasers (VCSELs) can exhibit additional resonances at high modulation frequencies that can substantially increase the laser’s modulation bandwidth. State-of-the-art laterally coupled devices require non-standard manufacturing technology and precise tuning of the currents supplied to each cavity separately to form optical supermodes suitable for such resonances. Here, we report on a novel switching phenomenon in laterally coupled VCSEL structures having only a single common electric contact and manufactured in a standard oxide-confined VCSEL geometry. At lower currents, they can be operated in a weakly coupled (WCR) regime and, at higher currents, in an injection-locked (IL) regime, enabling fundamentally different spectral and dynamic features. In the WCR, both optical supermodes lase and a narrow tunable plasma-assisted peak at their beating frequency is observed for each of the apertures, with a current-dependent frequency tuning and anti-phase intensity oscillations in each of the cavities. In contrast, in the IL regimes, only one (anti-symmetric) supermode lases. This adds a broader resonance to the modulation response while the intensity oscillations in both cavities are in-phase. Only the IL regime can result in increased modulation bandwidth of the system. Measurements of the pulse responses and continuous modulation up to 70 GHz for both operational regimes are presented and compared with simulations of our distributed rate equation model whose parameters are extracted from full-wave electromagnetic simulations of the device, including the temperature distribution in the device. Excellent agreement is found and enables comprehensive understanding of the dynamics of supermodes in oxide-confined coupled cavity VCSELs.</jats:p>}},
  author       = {{Lindemann, M. and D’Alessandro, M. and Ledentsov, N. and Makarov, O. Y. and Ledentsov, N. N. and Tibaldi, A. and Gerhardt, Nils Christopher and Hofmann, M. R.}},
  issn         = {{0021-8979}},
  journal      = {{Journal of Applied Physics}},
  number       = {{5}},
  publisher    = {{AIP Publishing}},
  title        = {{{Laterally coupled vertical-cavity surface-emitting lasers with                    tunable resonance width and frequency}}},
  doi          = {{10.1063/5.0275622}},
  volume       = {{138}},
  year         = {{2025}},
}

@inproceedings{64293,
  author       = {{Gerhardt, Nils Christopher and Hofmann, Martin R. and Zens, Leon and Möller, Jens and Besaga, Vira}},
  booktitle    = {{Practical Holography XXXIX: Displays, Materials, and Applications}},
  title        = {{{Quantitative holography for the characterisation of semiconductor amplifieres and lasers}}},
  doi          = {{10.1117/12.3041318}},
  year         = {{2025}},
}

@article{64550,
  author       = {{Zens, Leon and Besaga, Vira and Möller, Jens and Gerhardt, Nils Christopher and Hofmann, Martin}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Holographic measurement of gain and linewidth enhancement factor in semiconductor waveguides}}},
  doi          = {{10.1364/oe.538741}},
  year         = {{2024}},
}

@article{64585,
  author       = {{Lindemann, Markus and Gerhardt, Nils Christopher and Dainone, Pambiang Abel and Renucci, Pierre and Bouché, Alexandre and Morassi, Martina and Devaux, Xavier and George, Jean-Marie and Jaffrès, Henri and Lemaitre, Aristide and Xu, Bo and Stoffel, Mathieu and Chen, Tongxin and Lombez, Laurent and Lagarde, Delphine and Cong, Guangwei and Ma, Tianyi and Pigeat, Philippe and Vergnat, Michel and Rinnert, Hervé and Marie, Xavier and Han, Xiufeng and Mangin, Stephane and Rojas-Sánchez, Juan-Carlos and Wang, Jian-Ping and Beard, Matthew C. and Žutić, Igor and Figueiredo Prestes, Nicholas and Lu, Yuan}},
  journal      = {{Nature}},
  number       = {{8005}},
  pages        = {{783 -- 788}},
  title        = {{{Controlling the helicity of light by electrical magnetization switching}}},
  doi          = {{10.1038/s41586-024-07125-5}},
  volume       = {{627}},
  year         = {{2024}},
}

@article{64549,
  author       = {{Zens, Leon and Besaga, Vira and Möller, Jens and Gerhardt, Nils Christopher and Hofmann, Martin}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Holographic measurement of gain and linewidth enhancement factor in semiconductor waveguides}}},
  doi          = {{10.1364/oe.538741}},
  year         = {{2024}},
}

@inproceedings{64296,
  author       = {{Lindemann, Markus and Gerhardt, Nils Christopher and Hofmann, Martin R. and Ledentsov, N. N. and Shchukin, V. A. and Makarov, O. Y. and Zerova, V. and D’alessandro, M. and Tibaldi, A. and Turkiewicz, J. P.}},
  booktitle    = {{2024 IEEE 29th International Semiconductor Laser Conference (ISLC)}},
  title        = {{{Study of Electrically Excited Photon-Photon Resonances in Self-Injection-Locked Coupled-Cavity VCSELs}}},
  doi          = {{10.1109/islc57752.2024.10717381}},
  year         = {{2024}},
}

@article{64295,
  author       = {{Zens, Leon and Besaga, Vira and Möller, Jens and Gerhardt, Nils Christopher and Hofmann, Martin R.}},
  journal      = {{Optics express}},
  number       = {{1}},
  pages        = {{34 -- 49}},
  title        = {{{Holographic measurement of gain and linewidth enhancement factor in semiconductor waveguides}}},
  doi          = {{10.1364/oe.538741}},
  volume       = {{33}},
  year         = {{2024}},
}

@article{59663,
  abstract     = {{Controlling the intensity of emitted light and charge current is the basis of transferring and processing information1. By contrast, robust information storage and magnetic random-access memories are implemented using the spin of the carrier and the associated magnetization in ferromagnets2. The missing link between the respective disciplines of photonics, electronics and spintronics is to modulate the circular polarization of the emitted light, rather than its intensity, by electrically controlled magnetization. Here we demonstrate that this missing link is established at room temperature and zero applied magnetic field in light-emitting diodes2,3,4,5,6,7, through the transfer of angular momentum between photons, electrons and ferromagnets. With spin–orbit torque8,9,10,11, a charge current generates also a spin current to electrically switch the magnetization. This switching determines the spin orientation of injected carriers into semiconductors, in which the transfer of angular momentum from the electron spin to photon controls the circular polarization of the emitted light2. The spin–photon conversion with the nonvolatile control of magnetization opens paths to seamlessly integrate information transfer, processing and storage. Our results provide substantial advances towards electrically controlled ultrafast modulation of circular polarization and spin injection with magnetization dynamics for the next-generation information and communication technology12, including space–light data transfer. The same operating principle in scaled-down structures or using two-dimensional materials will enable transformative opportunities for quantum information processing with spin-controlled single-photon sources, as well as for implementing spin-dependent time-resolved spectroscopies.}},
  author       = {{Dainone, Pambiang Abel and Prestes, Nicholas Figueiredo and Renucci, Pierre and Bouché, Alexandre and Morassi, Martina and Devaux, Xavier and Lindemann, Markus and George, Jean-Marie and Jaffrès, Henri and Lemaitre, Aristide and Xu, Bo and Stoffel, Mathieu and Chen, Tongxin and Lombez, Laurent and Lagarde, Delphine and Cong, Guangwei and Ma, Tianyi and Pigeat, Philippe and Vergnat, Michel and Rinnert, Hervé and Marie, Xavier and Han, Xiufeng and Mangin, Stephane and Rojas-Sánchez, Juan-Carlos and Wang, Jian-Ping and Beard, Matthew C. and Gerhardt, Nils Christopher and Žutić, Igor and Lu, Yuan}},
  issn         = {{0028-0836}},
  journal      = {{Nature}},
  keywords     = {{Lasers, LEDs and light sources, Spintronics}},
  number       = {{8005}},
  pages        = {{783--788}},
  publisher    = {{Springer Science and Business Media LLC}},
  title        = {{{Controlling the helicity of light by electrical magnetization switching}}},
  doi          = {{10.1038/s41586-024-07125-5}},
  volume       = {{627}},
  year         = {{2024}},
}

@inproceedings{64298,
  author       = {{Lindemann, Markus and Gerhardt, Nils Christopher and Hofmann, Martin R. and Ledentsov, N. and Ledentsov, N. N. and Shchukin, V. A. and Chorchos, Ł. and Makarov, O. Yu and Kropp, J. R. and Titkov, I. E. and Kalosha, V. P. and Zerova, V. and D’Alessandro, M. and Torrelli, V. and Tibaldi, A. and Debernardi, P.}},
  booktitle    = {{Vertical-Cavity Surface-Emitting Lasers XXVIII}},
  title        = {{{Analysis of laterally-coupled-cavity VCSELs for ultra-high-frequency photon-photon resonance modulation}}},
  doi          = {{10.1117/12.3001177}},
  year         = {{2024}},
}

@article{64302,
  author       = {{Lindemann, Markus and Jung, Natalie and Gerhardt, Nils Christopher and Hofmann, Martin R. and Manrique‐Nieto, Nicolas and Pusch, Tobias and Michalzik, Rainer}},
  journal      = {{Electronics letters}},
  number       = {{13}},
  title        = {{{Polarization dynamics in spin‐VCSELs with integrated surface grating for high birefringence splitting}}},
  doi          = {{10.1049/ell2.12827}},
  volume       = {{59}},
  year         = {{2023}},
}

@article{59668,
  abstract     = {{<jats:title>Abstract</jats:title><jats:p>Spin‐controlled lasers are highly interesting photonic devices and have been shown to provide ultrafast polarization dynamics in excess of 200 GHz. In contrast to conventional semiconductor lasers their temporal properties are not limited by the intensity dynamics, but are governed primarily by the interaction of the spin dynamics with the birefringent mode splitting that determines the polarization oscillation frequency. Another class of modern semiconductor lasers are high‐<jats:italic>β</jats:italic> emitters, which benefit from enhanced light–matter interaction due to strong mode confinement in low‐mode‐volume microcavities. In such structures, the emission properties can be tailored by the resonator geometry to realize for instance bimodal emission behavior in slightly elliptical micropillar cavities. This attractive feature is utilized to demonstrate and explore spin‐lasing effects in bimodal high‐<jats:italic>β</jats:italic> quantum dot micropillar lasers. The studied microlasers with a <jats:italic>β</jats:italic>‐factor of 4% show spin‐laser effects with experimental polarization oscillation frequencies up to 15 GHz and predicted frequencies up to about 100 GHz, which are controlled by the ellipticity of the resonator. These results reveal appealing prospects for very compact, ultrafast, and energy‐efficient spin‐lasers and can pave the way for future purely electrically injected spin‐lasers enabled by short injection path lengths.</jats:p>}},
  author       = {{Heermeier, Niels and Heuser, Tobias and Große, Jan and Jung, Natalie and Kaganskiy, Arsenty and Lindemann, Markus and Gerhardt, Nils Christopher and Hofmann, Martin R. and Reitzenstein, Stephan}},
  issn         = {{1863-8880}},
  journal      = {{Laser &amp; Photonics Reviews}},
  number       = {{4}},
  publisher    = {{Wiley}},
  title        = {{{Spin‐Lasing in Bimodal Quantum Dot Micropillar Cavities}}},
  doi          = {{10.1002/lpor.202100585}},
  volume       = {{16}},
  year         = {{2022}},
}

@inproceedings{64306,
  author       = {{Heermeier, Niels and Jung, Natalie and Lindemann, Markus and Gerhardt, Nils Christopher and Hofmann, Martin R. and Heuser, Tobias and Große, Jan and Kaganskiy, Arsenty and Reitzenstein, Stephan}},
  booktitle    = {{Spintronics XV}},
  title        = {{{Spin lasing in high-beta bimodal quantum dot micropillar cavities }}},
  doi          = {{10.1117/12.2632687}},
  year         = {{2022}},
}

@article{64307,
  author       = {{Gurevich, Evgeny L. and Hofmann, Martin R. and Gerhardt, Nils Christopher and Neutsch, Krisztian}},
  journal      = {{Nanomaterials}},
  number       = {{3}},
  title        = {{{Investigation of laser-induced periodic surface structures using synthetic optical holography}}},
  doi          = {{10.3390/nano12030505}},
  volume       = {{13}},
  year         = {{2022}},
}

@article{59686,
  abstract     = {{The monolithic growth of III–V materials directly on Si substrates provides a promising integration approach for passive and active silicon photonic integrated circuits but still faces great challenges in crystal quality due to misfit defect formation. Nano-ridge engineering is a new approach that enables the integration of III–V based devices on trench-patterned Si substrates with very high crystal quality. Using selective area growth, the III–V material is deposited into narrow trenches to reduce the dislocation defect density by aspect ratio trapping. The growth is continued out of the trench pattern and a box-shaped III–V nano-ridge is engineered by adjusting the growth parameters. A flat (001) GaAs nano-ridge surface enables the epitaxial integration of a common InGaAs/GaAs multi-quantum-well (MQW) structure as an optical gain medium to build a laser diode. In this study, a clear correlation is found between the photoluminescence (PL) lifetime, extracted from time-resolved photoluminescence (TRPL) measurements, with the InGaAs/GaAs nano-ridge size and defect density, which are both predefined by the nano-ridge related pattern trench width. Through the addition of an InGaP passivation layer, a MQW PL lifetime of up to 800 ps and 1000 ps is measured when pumped at 900 nm (only QWs were excited) and 800 nm (QWs + barrier excited), respectively. The addition of a bottom carrier blocking layer further increases this lifetime to ∼2.5ns (pumped at 800 nm), which clearly demonstrates the high crystal quality of the nano-ridge material. These TRPL measurements not only deliver quick and valuable feedback about the III–V material quality but also provide an important understanding for the heterostructure design and carrier confinement of the nano-ridge laser diode.}},
  author       = {{Shi, Yuting and Kreuzer, Lisa C. and Gerhardt, Nils Christopher and Pantouvaki, Marianna and Van Campenhout, Joris and Baryshnikova, Marina and Langer, Robert and Van Thourhout, Dries and Kunert, Bernardette}},
  issn         = {{0021-8979}},
  journal      = {{Journal of Applied Physics}},
  number       = {{10}},
  publisher    = {{AIP Publishing}},
  title        = {{{Time-resolved photoluminescence characterization of InGaAs/GaAs nano-ridges monolithically grown on 300 mm Si substrates}}},
  doi          = {{10.1063/1.5139636}},
  volume       = {{127}},
  year         = {{2020}},
}

@article{59685,
  abstract     = {{Introducing spin-polarized carriers in semiconductor lasers reveals an alternative path to realize room-temperature spintronic applications, beyond the usual magnetoresistive effects. Through carrier recombination, the angular momentum of the spin-polarized carriers is transferred to photons, thus leading to the circularly polarized emitted light. The intuition for the operation of such spin-lasers can be obtained from simple bucket and harmonic oscillator models, elucidating their steady-state and dynamic response, respectively. These lasers extend the functionalities of spintronic devices and exceed the performance of conventional (spin-unpolarized) lasers, including an order of magnitude faster modulation frequency. Surprisingly, this ultrafast operation relies on a short carrier spin relaxation time and a large anisotropy of the refractive index, both viewed as detrimental in spintronics and conventional lasers. Spin-lasers provide a platform to test novel concepts in spin devices and offer progress connected to the advances in more traditional areas of spintronics.}},
  author       = {{Žutić, Igor and Xu, Gaofeng and Lindemann, Markus and Faria Junior, Paulo E. and Lee, Jeongsu and Labinac, Velimir and Stojšić, Kristian and Sipahi, Guilherme M. and Hofmann, Martin R. and Gerhardt, Nils Christopher}},
  issn         = {{0038-1098}},
  journal      = {{Solid State Communications}},
  publisher    = {{Elsevier BV}},
  title        = {{{Spin-lasers: spintronics beyond magnetoresistance}}},
  doi          = {{10.1016/j.ssc.2020.113949}},
  volume       = {{316-317}},
  year         = {{2020}},
}

@article{59684,
  abstract     = {{<jats:p>In this paper, we present a confocal laser scanning holographic microscope for the investigation of buried structures. The multimodal system combines high diffraction limited resolution and high signal-to-noise-ratio with the ability of phase acquisition. The amplitude and phase imaging capabilities of the system are shown on a test target. For the investigation of buried integrated semiconductor structures, we expand our system with an optical beam induced current modality that provides additional structure-sensitive contrast. We demonstrate the performance of the multimodal system by imaging the buried structures of a microcontroller through the silicon backside of its housing in reflection geometry.</jats:p>}},
  author       = {{Schnitzler, Lena and Neutsch, Krisztian and Schellenberg, Falk and Hofmann, Martin R. and Gerhardt, Nils Christopher}},
  issn         = {{1559-128X}},
  journal      = {{Applied Optics}},
  number       = {{4}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Confocal laser scanning holographic microscopy of buried structures}}},
  doi          = {{10.1364/ao.403687}},
  volume       = {{60}},
  year         = {{2020}},
}

@inproceedings{64361,
  author       = {{Neutsch, Krisztian and Hofmann, Martin R. and Gerhardt, Nils Christopher and Schnitzler, Lena and Tranelis, Marlon J.}},
  booktitle    = {{Practical Holography XXXIII: Displays, Materials, and Applications}},
  title        = {{{Three-dimensional particle localization with common-path digital holographic microscopy}}},
  doi          = {{10.1117/12.2509448}},
  year         = {{2019}},
}

@inbook{64360,
  author       = {{Gerhardt, Nils Christopher and Žutić, Igor and Lee, Jeongsu and Gøthgen, Christian and Farla, Paulo E., Junior and Xu, Gaofeng and Sipahi, Guilherme M.}},
  booktitle    = {{Nanoscale spintronics and applications}},
  pages        = {{499 -- 540}},
  title        = {{{Semiconductor spin-lasers}}},
  year         = {{2019}},
}