Leading-edge machine learning algorithms require large amounts of matrix multiplications, which absorb significant computational resources in modern digital electronic systems. Analogue optical computing systems consisting of light sources, modulators and receivers may perform these operations with much higher efficiency. We introduce an integrated device based on electro-optically modulated (EOM) vertical-cavity surface-emitting lasers (VCSELs) that can perform analog multiplication at >28 GHz and at <20 mW power consumption. Due to its monolithic integration, the EOM VCSEL may be used as a building block for integrated optical computing devices. Development of such devices can help create 3-dimensionally integrated computing and communication systems.
Vertical-cavity surface-emitting lasers (VCSELs) are of utmost importance as key components for high-speed datacom, sensor and free-space applications. Therefore, for a successful further optimization of their performance understanding their behavior during operation is of crucial importance. A set of 850 nm VCSEL samples employing different doping of the active cavity zone are studied during operation by means of reverse current-voltage (IV) characteristics as well as photocurrent spectroscopy (PCS) under reverse bias. Reverse IV characteristics exhibits avalanche breakdown which enables an estimation of the electric field in the active region as a function of applied bias. Photocurrent spectroscopy is a powerful, nondestructive technique which measures essentially the convolution of the top mirror and intrinsic region absorption spectra and reveals quantum well transitions which redshift with reverse bias due to quantum-confined Stark effect (QCSE). The VCSELs are characterised before and after high current operation. VCSELs with a controlled doping of the active cavity region do not alter neither avalanche breakdown nor the QCSE shift of the quantum well transitions during operation. However, VCSELs without doping of the active cavity region show a systematic shift in breakdown voltage towards lower values, which is accompanied by an operation-induced redshift of quantum well transitions observed by PCS. These results indicate an increase of the built-in electric field in the active cavity zone after high current operation which is discussed in terms of conceivable processes such as dopant diffusion, impurity electromigration, burn-in of contacts and/or the activation of dopants during operation.
We report high frequency (20-100 GHz range) optical field intensity oscillations in laterally-coupled-cavity verticalcavity surface-emitting lasers with several different techniques. The oscillation frequency is defined by the photon energy splitting of the coupled states. The resonance effect is stable in an extended current range and can enable modulation frequency resonances at higher frequencies as compared to the conventional relaxation oscillation frequency of the laser. This paves a way towards high-speed data transmission solutions at data rates beyond ~200 Gb/s with the advantage of better laser stability, as the resonance observed can reach high frequencies even at low current densities. A ~75 GHz intensity modulation between optical modes of a coupled-cavity VCSEL array was first reported by the authors in a two-aperture configuration in 2023 applying optical excitation [1]. Studies of 4- and 10-element coupled VCSEL arrays give further insight into the effects observed. New 3D numerical simulations and electrical modulation techniques have been applied to address the specific nature of the photon-photon resonance studies.
KEYWORDS: Vertical cavity surface emitting lasers, Resistance, Patents, Near field optics, Near field, Multimode fibers, Fiber lasers, Data transmission
Applying coherent arrays of muti-aperture lasers was proposed to improve data transmission over multimode fiber. We propose a novel compact a coherent and incoherent multi-aperture VCSEL array design in which multiple single-mode VCSEL apertures are electrically driven in parallel. Such approach allows a high output power as in standard multimode devices but shows significantly reduced spectral width not exceeding 0.2nm as well as high speed performance exceeding 25GHz with current density ~20kA/cm2 and beam divergence of 22O (1/e2). Moreover, we study the application of such devices for IM/DD 100Gbit/s PAM-4 and 50Gbit/s OOK.
VCSEL arrays can play an important role in the increasing the data throughput of VCSEL-based optical interconnects both due to the need to increase the channel density and due to new emerging technologies like optical wireless. In this work we show the progress in the development of high-speed VCSEL arrays suitable for multicore fiber transmission leading to an increase of the total throughput through single fiber to 600 Gbps. We also discuss a novel type of compact VCSEL mini-arrays capable of high-speed modulation and coherent emission at the same time. Photon-photon resonance and coherent effects can help increase the resonant frequency and the bandwidth of the VCSELs and enable devices capable of 100 GHz operation.
The paper presents the results of the research and development of 1300-nm vertical-cavity surface-emitting lasers, fabricated by wafer fusion technique for hybrid integration of an InAlGaAs/InP optical cavity with two AlGaAs/GaAs distributed Bragg reflectors using molecular-beam epitaxy. The active region is based on InGaAs/InAlGaAs superlattice, while current and optical confinement is provided by n++-InGaAs/p++-InGaAs/p++-InAlGaAs buried tunnel junction (BTJ). The proposed device design results in low internal loss (about 3.2 cm-1 at 20 °C). The devices with BTJ diameter of 5 μm demonstrate a stable single-mode lasing with threshold current less than 1.3 mA and output optical power more than 6 mW and operation in a wide temperature range. The measured -3 dB bandwidth is more than 8 GHz at 20 °C and about 5.5 GHz at 85 °C, the eye diagrams are open with a bit rate up to 20 Gbps using nonreturn-to-zero (NRZ) modulation standard. Using 5-tap feedforward equalizer, the NRZ transmission at 25 Gbps has been demonstrated up to 5km single-mode fiber.
Vertical-cavity surface-emitting lasers (VCSELs) are of utmost importance as key components for high-speed datacom, sensor and free-space applications. Therefore, for a successful further optimization of their performance, understanding their aging behavior is of crucial importance. Photocurrent spectroscopy (PCS) is a powerful, nondestructive technique which can be used to analyze semiconductor materials. Applying it on VCSELs makes it a powerful tool to investigate these tiny devices. In this work, we present room temperature high-resolution PCS analyses of fresh vs. aged 850 nm VCSELs. These VCSELs are characterized before and after aging by means of PCS, which measures essentially the convolution of the top mirror and intrinsic region absorption spectra. Heavy hole and light hole quantum well transitions are revealed and the related quantum-confined Stark effect is studied. The VCSELs used in this study are mounted on a standard V-connector and were intentionally aged at extreme conditions to accelerate their degradation till reaching optical damage. It was found that in these VCSELs, a reduced PCS current is observed, which is possibly caused by nonradiative recombination centers generated by the aging-related processes. Moreover, we observe that aging of the devices at very high current densities results in the evolution of defect related states, which modify the IV-curve under reverse bias. Degraded devices also show a systematic shift in breakdown voltage towards lower values, indicating a possible shrinkage of the undoped region by impurity electromigration and diffusion. Interestingly, these changes are minimal in stable devices that were aged under normal conditions.
Strain-induced birefringence in GaAs-based oxide-confined VCSELs (Vertical-Cavity Surface-Emitting Laser) can split the optical modes into orthogonally polarized components. A polarization switching at very high frequencies can occur between these components, which is of great interest for optical communication systems of the future. In this study, we focus our investigation on the frequency characteristics of the polarization switching between the optical modes, which is caused by polarization self-modulation (PSM) in fiber-coupled systems. Moreover, we analyze the PSM that is originating in different optical modes of the VCSEL and compare multi-mode and single-mode VCSELs.
In this paper, we perform a comparison of three modulation formats: NRZ, duo binary and DMT in combination with the state of the art 850 and 910nm VCSELs for their application in short reach high speed optical links. The system for NRZ and DB utilizes feasible for deployment equalization including a 9-tap finite impulse response filter and raised cosine filtering in the transmitter and a 7-tap UI-spaced feed forward equalizer in the receiver. The 100 Gbit/s net link with DB modulation can be realized without applying receiver equalization. For DMT the highest gross data rate of 224 Gbit/s/lambda is achieved.
We report on vertical cavity surface emitting lasers (VCSELs) having a -3dB modulation bandwidth above 30 GHz and a narrow spectrum down to single mode (SM) operation. The 850 nm and 910 nm SM VCSELs in combination with the IN5612 VCSEL driver from Inphi Corporation allowed to reach 106 Gb/s PAM4 with the TDECQ values of only 1.5 dB. For the multimode VCSELs, TDECQ of ~2.6 dB were achieved in combination with the same driver chip. VCSELs with the reduced spectral width allow to cover transmission distance over multimode fiber reaching 1.0-2.5 km at 50 Gbaud. Furthermore, reduction of the aperture size to a certain limit allows to reach ultimate modulation bandwidths at the same current density as applied in the large aperture VCSELs but at lower total currents and thus much lower current-induced overheating. The latter enables a significant improvement in the reliability of the devices and stimulates further research in novel types of VCSEL-based devices.
New applications in sensing, automotive and on-board applications require vertical-cavity surface-emitting lasers (VCSELs) operating at high data rates up to very high ambient temperatures. We study temperature stability of the 850 nm Quantum-Dot (QD) VCSELs and benchmark them to Quantum-Well (QW) VCSELs of similar design.
QD VCSELs enable extension of the temperature stability and demonstrate threshold currents below 1 mA for operation range from 30°C to 200°C. The role of gain to cavity detuning is discussed in details. 25 Gbit/s NRZ multi-mode fiber transmission with QD VCSELs is realized at temperatures up to 180°C. Pulsed operation of QD VCSELs with 8 μm oxide aperture diameter is studied at temperatures from 30°C to 125°C and 1 W peak power is realized on 100 ns pulses at room temperature.
KEYWORDS: Vertical cavity surface emitting lasers, Polarization, Birefringence, Near field optics, Switching, Near field, Multimode fibers, Data transmission, Receivers, Modulation
We report high-frequency polarization self‐modulation (PSM) in high speed vertical-cavity surface emitting lasers (VCSELs) connected to the stress-induced birefringence in oxide-confined aperture VCSELs. Polarization oscillations up to 45 GHz were captured. We analyze the far and the near field of the device and show how the fiber-coupling conditions induce optical feedback, affect emission properties of the device and influence the polarization switching phenomenon. In conditions where the PSM was suppressed, we demonstrate NRZ high-speed multi-mode fiber data transmission up to 90 Gbit/s.
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