This PDF file contains the front matter associated with SPIE Proceedings Volume 12904, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

VCSEL-based optical transceivers in data centers meet the increase in data traffic by increasing the data transmission rate. A single-channel PAM-4 data rate of >100 Gb/s is already in high demand. For 100Gb/s operation a low relative intensity noise (RIN) significantly gains importance. The challenge is to reduce the RIN without impeding the other static and dynamic VCSEL performance parameters. We demonstrate up to 20 dB/Hz RIN reduction of commercial VCSELs that are approaching the shot noise limit and give an outlook on datacom VCSELs for higher order modulation formats for single channel data rates of 100 Gb/s and beyond.

We measure the spectral emission and the small-signal modulation frequency response of our 980 nm VCSEL arrays across OM2 multiple-mode optical fiber (MMF) patch cords and for the first time across free space (air) via optical fiber collimators (small focusing triplet lenses with optical fiber connectors) separated by 0.4 m up to 10 m. The VCSELs in our arrays are electrically in parallel but optically uncoupled, with an aim toward mitigating scintillation and speckle loss mechanisms in high bit rate free space data streams. We measure the center (mean) wavelength and the root-mean-square spectral width of our VCSEL arrays as a function of forward bias current, both across MMF and across free space. We find the spectral results are nearly identical within fractions of a nanometer. We similarly measure the S21 (s-parameter) small signal modulation frequency response of our arrays from 0.05 to 40 GHz, across fiber and across free space, and extract and plot the -3 dB bandwidths as functions of forward bias current. We achieve bandwidths up to 25 and 30 GHz for 3-element arrays with 9 and 7 micrometer oxide aperture diameters (Φ), respectively, and find the bandwidths are nearly identical when comparing data transfers across OM2 MMF patch cords versus across the MMF plus a section of free space.

We report on the mode evolution of coupled dual-element laser arrays biased in the coherently coupled region, exploring both theoretical and experimental aspects. Utilizing a complex waveguide simulation, we identify two supermodes operating within the coherently coupled region. The formation of the supermodes leads to enhanced output power, visibility, and a photon-photon resonance frequency surpassing the carrier-photon resonance frequency. Such favorable attributes are facilitated by the formation of anti-guided cavities through current injection. Finally, we conduct a comparative analysis of mode characteristics under strong and weakly anti-guiding conditions to identify the impact on the supermode characteristics.

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.

The market for 100Gb/s per lane multimode (MM) vertical-cavity surface-emitting lasers (VCSELs) continues to be driven by the growing demand from data centers, cloud storage, and enterprise networks. Low cost and energy efficient VCSEL-based multimode links are especially suited for the high speed interconnections (HSI) that facilitate generative artificial intelligence (AI). The VCSEL technologies are largely shaped by the Fibre-channel and the Ethernet standards, and more recently by the Terabit Bidi MSA and InfiniBand requirements. In this paper, we present the development and performance of a 940nm multimode VCSEL with 3-dB small-signal modulation bandwidth exceeding 25GHz over temperature and relative intensity noise (RIN) below -145dB/Hz, suitable for 100Gb/s per lane data transmission. The VCSEL’s 940nm center wavelength is within the wavelength range directed by IEEE 802.3 VR4 and offers the advantages of higher differential gain and lower thermal impedance. Large-signal performance at 100 Gb/s as well as device reliability will also be presented.

We demonstrate a 3D integrated 2D addressable VCSEL array that integrates high power 2D VCSEL array on a circuit board with a built-in laser driver by flip-chip bonding, resulting in high optical power density of 1,500 W/mm2 and short pulse duration of 2 ns. Each VCSEL is designed to oscillate at 940 nm and has seven junctions, large optical aperture and Cu pillar bumps for individual driving. Compared to our previous report5 , the optical output power is improved from 45 to 80 W/channel by increasing filling factor which is the ratio of active area to chip size from 33 % to 59 % and decreasing operating voltage by changing donor in tunnel junction from Si to Te. Additionally, the optical pulse shape has short rise time 1 ns and a narrow pulse width of 2 ns thanks to low inductance in this unique structure, and highly uniform optical pulse shape was observed in the plane due to small deviation of inductance from various positions of VCSEL array. We also confirmed that there was no degradation after 1000 hours of operation at an ambient temperature of 105 °C and 40 V, and after 1000 cycles of temperature cycle test from -40 to 125 °C in the module configuration. We believe that this advanced 3D integrated 2D addressable VCSEL array is the candidate for a light source of advanced LiDAR system with "ROI" (region of interest) focusing and low power consumption due to its zone-emission characteristics.

To determine electro-optical characterization of laser diodes, various measurements are usually performed including LIV+λ (with spectrum) characterization. For VCSEL arrays with the existing solutions, it is hardly possible and timely expensive to perform these measurements since there are few up to some hundreds of single emitters within the array. VCSEL arrays are beneficial for technologies like structured light and Face ID, in which detailed characterization of individual emitters are required. Furthermore, polarized VCSEL arrays are unique and have potential applications, which then requires not only the LIV+λ but also polarization measurement of each emitter. Therefore, in this study, not only we extended the LIV+λ measurements to each individual emitters in a VCSEL array but also their polarization is measured. Our experimental design consists of a camera based radiant power and polarization measurement coupled to an array spectrometer. The system measures the absolute optical power, traceable to the standards. The VCSEL array mounted on a tempering system with a direct feedback loop. In order to characterize the stability of the VCSEL array in various environmental conditions, all the measurements were done further at multiple temperatures. Depending for which application the VCSEL will be, the valid range of the measured parameters of each emitter can be set. Therefore, non-functional emitters were determined. The design offers fast one-shot and comprehensive characterization of emitters of VCSEL arrays, allowing parallelization of the measurements to reduce overall measurement time and to determine damaged or out of spec VCSELs at early stage of the manufacturing process.

This paper investigates the evolving landscape of Vertical Cavity Surface Emitting Lasers (VCSELs) in consumer and optical communication technologies. With Apple's GaAs-based VCSEL adoption for facial recognition and augmented reality, the industry has seen leaders like Lumentum and Coherent shape the GaAs VCSEL market. A new entrant, Sony, into Apple's supply chain resulted in market share lose where it reached more than 50% for Lumentum and Coherent in their consumer 3D sensing business. The surge in demand for higher data rate 100G VCSELs for 800G optical transceiver, representing 10% of the total VCSELs expected to be shipped in 2024, for short-reach optical interconnects is mainly driven by AI applications. In addition, we have identified new trends in the VCSELs technology to achieve long-wavelength emission in the range of 13xx nm opening the path for under-display 3D sensing and single mode emission for data communications. With respect to all these facts, Yole group forecasts the VCSELs market to reach $1.4B in 2028 with a CAGR22-28 of 6% driven by consumer and datacom applications.

Increasing the number of active regions is an effective approach for scaling optical output power in vertical cavity surface emitting lasers (VCSELs). However, due to a more complex cavity structure, these devices can exhibit simultaneous stimulation of multiple higher order transverse modes. This issue is further exacerbated especially in oxide confined VCSELs, in which the possible differences in length, shape, thickness, and composition of each oxide layer can give rise to stimulation of a higher order mode. Moreover, due to cylindrical symmetry of the cavity structure, in addition to complete isotropy of the semiconductor gain material, VCSELs do not exhibit a stable and dominant polarization direction throughout their operation. In this paper, we report on design, fabrication, and characterization of single-mode single-polarization 8-junction 940nm VCSELs. Single-mode operation has been achieved by using a surface relief mode filter to preferentially reduce the effective mirror reflectivity for higher order transverse modes, and consequently, increase their threshold gain. Optimizing the shape and the size of the relief feature has shown to be effective in inducing a dominant polarization direction for the VCSELs, in which a non-circular relief feature can perturbate the cylindrical symmetry of the cavity structure. The effect of elliptical relief feature on stabilizing the polarization behavior of VCSELs has been investigated. Room-temperature continuous-wave (CW) L-I-V characteristics of a 5um VCSEL with such relief feature shows a single-mode output power of ~13.5mW at ~3mA bias current (sidemode suppression ratio >30dB) and polarization extinction ratio greater than 20dB. Moreover, this VCSEL remains reliably single-mode with stable polarization characteristics at different temperatures up to 95°C.

The essential performance parameters of present generations of Vertical Cavity Surface Emitting Lasers (VCSELs) like output power, f3dB cut-off frequency, are limited by extrinsic parameters. The most important among them is the shift of the gain maximum out of resonance with the DBR transmission due to increased heating of the active layer with increasing current, leading to a red shift of the emission. Another important limitation of f3dB is the unavoidable resistance by the p-type mirror and capacitance of the actual device generations. We present here a novel Multi-Hole Aperture (MuHA) VCSEL approach1 , based on variable aperture shapes and sizes, leading to increased output power for single/multi-mode emission, reduced series resistance, and larger f3dB of the devices. Holes in symmetric or asymmetric arrangements are etched from the top to the oxidizable layer(s). The aperture shape and size is realized by controlled oxidation of the oxidizable layer(s) through the holes. The holes are subsequently filled with gold, which effectively remove heat from the active layer. In MuHA VCSELs, the temperature of the active area for any given current is thus at least 50% lower than that of a comparable VCSELs processed using a “classical” design, resulting in larger rollover current, f3dB,… Combining MuHA to Multi-Aperture devices called Multi Aperture VCSELs (MAVs) is expected to lead to pseudo single mode emission with an output power of 8-10 mW across 50 μm Multi-Mode Fiber (MMF), enabling to cover much larger transmission distances than hitherto.

Single-mode VCSELs are almost perfect laser sources in terms of beam shape, spectral purity, and wavelength control. For many applications, e.g. tunable diode laser absorption spectroscopy (TDLAS), fiber coupling to single-mode fibers would offer additional benefits. In addition to the challenging 5 axis geometrical alignment on micron scale any mode field diameter mismatch between VCSEL and fiber is limiting the achievable coupling efficiency. Furthermore, temperature and current dependent emission angle could add to non-linearity of the coupled intensity. We present a detailed analysis of the dependencies of farfield angle with temperature, current, and laser aperture for surface relief stabilized single-mode VCSELs [1]. We describe the coupling to HP780 single-mode fiber, free of optical feedback, and finally present related performance parameters of an advanced single-mode VCSEL pigtail emitting at 760 nm wavelength. Coupling efficiencies better than 50 % and respective output power at the fiber connector exceeding 0.5 mW are reported. The built in microTEC allows for a wavelength tuning range of more than 6 nm. Such pigtail is perfectly suited for oxygen TDLAS or other applications that require wavelength tunable laser power from a single-mode fiber and a pre-defined optical interface determined by the optical fiber only.

Future space satellite systems will use high-speed 25 Gbps 850-nm multi-mode (MM) vertical cavity surface emitting lasers (VCSELs) for communications and 795-nm single-mode (SM) VCSELs for atomic clocks applications. The main advantage of deploying these VCSELs in space satellites over 850- or 795-nm edge emitting lasers is the absence of COMD (catastrophic optical mirror damage). In particular, VCSEL-based atomic clocks have a potential to significantly improve timekeeping accuracy and navigation positioning errors. Space satellite systems require stringent reliability of these VCSELs, but they are significantly lacking reliability data. We assess suitability of these VCSELs for high reliability applications through the physics of failure investigation to study reliability, failure modes, and degradation mechanisms. Also, this work is part of our efforts to understand the physical origin of degradation in oxide confined VCSELs under high current density operation. For the present study, we investigated reliability and failure modes of two state-of-the-art VCSEL types – 25 Gbps 850- nm MM oxide confined VCSELs and 795-nm SM oxide confined VCSELs. Accelerated life-tests of both VCSEL types were performed under varying stress conditions to model wear-out failures for reliability assessment. These life-tests were performed under ACC (automatic current control) mode. We also studied VCSELs that were exposed to ESD (electrostatic discharge). We employed optical beam induced current (OBIC), photocurrent spectroscopy, and electron beam induced current (EBIC) techniques for failure mode analysis (FMA). FMA was performed on life-tested VCSEL failures as well as on ESD tested VCSEL failures. Lastly, we employed plasma focused ion beam (PFIB) for removal of portions of top-DBR mirrors for EBIC and for slice-and-view techniques.

Vertical-cavity surface-emitting lasers (VCSELs) are well established as light sources in integrated photonics or for communication purposes. We investigate the VCSELs for their utilization as highly sensitive topography sensor. The system is based on creating a coupled resonator configuration with the VCSEL as a central element. In this context, the back reflection of a sample surface affects the internal resonator conditions of the VCSEL resulting in a change of the emitted wavelength and operating current, respectively, if the operating voltage is kept constant. Hereby, the signal change is mainly affected by the sample’s reflectivity and the length of the coupled resonator which offers the potential for different types of applications. Our experimental findings show that a measurable and reproducible change of the operating current can be detected when moving the sample by a few nm in vertical direction. The first experiments required additional bulky objective lenses to focus the emitted beam on the sample surface. To avoid such optical elements in the setup we printed a customized lens on the emission window of the VCSEL using a two-photon polymerization systems to realize a stand-alone integrated sensor. We will present our recent experimental and simulation results, show first topography measurements and discuss both possible future application in precision metrology as well as how the capability of the coupled resonator to change the emission wavelength enables a sensing concept without expensive electronic devices by using a glass substrate pre-structured with selective laser etching

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.

LUMENTUM’s multi-channel VCSELs in combination with SPAD (Single photon avalanche photodiode) receivers can perform “true” solid-state scanning in a single direction. The multi-channel VCSEL along with collimating lens and a horizontal diffuser can be matched with SPAD arrays of different sizes and aspect ratios. In this paper, we show the characterization results of the multi-channel VCSEL with 57 channels and 7J epi architecture, at 5ns pulse width, 0.1% duty cycle from temperature range of -40°C to 125°C. The L-I tests at 25°C yield a threshold current of 0.57A, optical power of 140W, and slope efficiency of 7.21W/A at 20A. The optical power, slope efficiency decreased by only 20% from -40°C to 125°C. The FF divergence at 25°C is about 25° and varies by 1.9° from -40°C to 125°C. The leakage current between different anodes/channels at 85ºC is only 0.27μA for a voltage difference of 50V between the channels. We continue to develop higher current drivers to characterize the VCSELs at higher currents. The next generation VCSELs will have higher junction-count epi, allowing for even higher power and slope efficiency. This scheme of addressable high speed and high power VCSELs tailored for operation with SPAD arrays is a very crucial step towards building allelectronic scanning automotive grade LIDARs.

We design, fabricate, characterize, and compare 980 nm vertical cavity surface emitting lasers (VCSELs) with monolithic high contrast gratings (MHCGs) as top coupling mirrors. The MHCG is a series of parallel, rectangular stripes etched into a uniform GaAs epitaxial surface layer via electron-beam lithography and inductively coupled reactive ion etching, with specific grating period, height, and fill factor (defined as the grating bar width divided by the grating period). To boost the MHCG’s optical power reflectance at 980 nm and the width of the optical stopband we add a 5.5-period p-doped distributed Bragg reflector (DBR) beneath the MHCG grating, thus forming a composite DBR plus MHCG top coupling mirror. The bottom n-doped DBR is a conventional all-semiconductor AlGaAs/GaAs DBR with 37-periods on a GaAs substrate. We fabricate single 980 nm DBR MHCG VCSELs with two oxide aperture diameters on quarter wafer pieces from starting 3- inch diameter VCSEL epitaxial wafers. Each quarter wafer contains six complete unit cells, and each unit cell is a twodimensional array of single VCSELs in 16 rows and 15 columns. We for example set a constant but different grating period in five of the unit cells and vary the grating fill factors from column to column and we vary the oxide aperture diameters from 1 to 9 Pm in the rows, thus yielding a large variety of VCSEL diodes with differing MHCG parameters for us to compare. We perform room temperature on-wafer probe testing of the static optical output power-current-voltage (LIV) characteristics and emission spectra and compare the impact of the grating designs on these test results. We report record static LIV performance for our DBR MHCG VCSELs with threshold current below 1 mA and optical output power exceeding 1.3 mW. We observe room temperature bias current dependent mode emission for example single mode wavelength tuning ranges up to 12 nm.

In our paper, the design of a high contrast grating is optimized to obtain a wider reflectivity bandwidth. HCGs present an incidence angle dependence that can affect the reflectivity bandwidth. This dependence was mitigated by reducing the duty cycle of the HCG. A further optimized model was done by matching the reflectivity phase with the phase of the incident Gaussian wavefront. The broader bandwidth of the new designs was calculated using simulations. Subsequently the MEMS VCSELs with the new designs of HCG were fabricated. The highest tuning range obtained for the focusing design was 45nm and for the low duty cycle design 38nm. These ranges are lower than the standard design due to differences from the design. Further improvements in the fabrication process are required to demonstrate the new designs proposed.

Renewed interest in vertical-cavity surface-emitting lasers (VCSELs) operating in the regions of 1300 and 1550 nm has come as a result of the desire for so-called ‘eye-safe’ lasers (>1400 nm) in consumer applications, for below-screen sensing in mobile devices (>1380 nm) and for light detection and ranging (LiDAR). Current VCSELs have a host of applications, including printing, bar code reading, data communications and facial recognition systems. Typical (In)GaAs quantum-well VCSEL active-regions are sub-optimal for reaching telecoms and ‘eye-safe’ wavelengths because of the large strain accompanying the increased In fraction required. Here, a case is made for the use of GaSb quantum rings (QRs) over other materials in VCSEL active regions for devices across the telecoms range. The design and fabrication of two prototype quantum ring VCSELs is discussed and provisional results are presented for continuous operation at room temperature and at 77 K. The origin of background emission is considered and a sub-milliamp threshold current achieved for emission at 1257 nm.

We study high-power high bit rate single-mode 1550 nm vertical-cavity surface-emitting lasers fabricated using wafer-fusion. The optical cavity was grown on an InP wafer, and the two AlGaAs/GaAs distributed Bragg reflectors were grown on GaAs wafers, all three by molecular-beam epitaxy. The active region is based on thin InGaAs/InAlGaAs quantum wells and a composite InAlGaAs tunnel junction. To confine current and optical radiation, we use a lateral-structured buried tunnel junction with ≈ 6 µm diameter and an etching depth of ≈ 20 nm. These VCSELs demonstrate up to 5 mW single-mode continuous-wave output power and a threshold current of ≈ 2 mA at 25 °C. Even at an ambient temperature of 85 °C, the maximum optical output power is larger than 1 mW. The lasers demonstrate a 34 Gbps non-return-to-zero data transfer rate and 42 Gbps (21 GBaud) using 4-level pulse amplitude modulation at 25 °C back-to-back conditions with ≈ 934 fJ/bit power consumption per bit, which is amongst the lowest values reported for this wavelength range and bit rate.

We study the dynamics of a multimode VCSEL with an elliptical oxide aperture for datacom applications. We simulate the laser dynamics through a set of coupled rate equations for the modal components of the electric field and the carrier density, accounting for coherent mode mixing and spatial hole burning. Our simulations show what are the relevant frequency detuning configurations to control in order to improve noise performance. Simulations with NRZ PRBS performed in order to explore the applications of these devices in short-reach data transmission show potentially reachable transmission speeds of 65 Gbit/s.

The design and analysis of the Photonic Crystal Vertical Cavity Surface Emitting Laser (PCVCSEL) device are discussed and simulated using the 3D Finite Difference Frequency Domain (FDFD) microcavity model, available in the PICS3D simulation package. The 3D full vectorial microcavity model provides an accurate analysis of complex 3D structures, offering insights into mode complexity and modal parameters. In this paper, we investigate the effect of the photonic crystal unit cell on both the lasing power and the far-field pattern. The simulation results demonstrate a lasing power of almost 5mW with a threshold current of 0.2mA.

We propose a Particle Swarm Optimization (PSO) algorithm for the extraction of Vertical-Cavity Surface-Emitting Laser (VCSEL) parameters compatible with a rate equation based model that takes into account the thermal effects. PSO is an evolutionary algorithm that drastically reduces the computational cost and time with respect to traditional brute-force approaches, thanks to the "swarm intelligence" of the agents of the optimization (called "particles"). With an optimal choice of the hyperparameters of the algorithm, the method is shown to predict parameters that accurately reproduce the non-linear behavior of the device, as well as its complicated thermal effects.