This PDF file contains the front matter associated with SPIE Proceedings Volume 12439, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Advancements to our VCSEL technology platform now allow to dynamically switch between two orthogonal polarization states on a single VCSEL-array chip. Here stable and linearly polarized emission is combined without change to the VCSEL optical characteristics. This is rendered possible by 90°-rotated surface-gratings for each channel to realize polarization locking in one of the two polarization directions. Similar high polarization extinction ratios, thresholds and output powers are attained for each channel. Furthermore, electrical routing enables the flexible definition of illumination zones consisting of sub-arrays of VCSELs with the same polarization orientation. Time-division polarization multiplexing is thus enabled by addressing different zones of the VCSEL array for dynamic illumination concepts.

In this paper, we report a high efficiency, addressable 940 nm Vertical-Cavity Surface-Emitting Laser (VCSEL) array with a tight pitch of 10 m for a compact, low-power sensing light source. High electrical resistance of a small diameter semiconductor DBR is a major issue to obtain a high-power conversion efficiency in achieving a tight pitch VCSEL array. We have developed a highly efficient back side emitted VCSEL with intracavity contacted structure, mesa diameter of 7.5 μm, and optical aperture of 3.0 μm. The power conversion efficiency exceeded 30% from 0.5 mW to 3.5 mW in the wide power range. We also report Tx module using this highly efficient VCSEL with a tight pitch of 10 μm. The tight pitch addressable 2D VCSEL array required sophisticated process techniques because they have a small spacing of 2–3 μm between mesas. To improve productivity, we developed a new device structure decreasing the process difficulty between mesas and demonstrated 2D addressable VCSEL array arranged 64 by 64 matrix and 4096 emitters. In addition, we demonstrated addressable operation with assembled sample using Si interposer.

Negative resistance millimeter wave semiconductor devices (including Tunnel, Gunn, IMPATT and, BARITT diodes) can generate high frequency microwave signals approaching the terahertz infrared regime for commercial telecommunications and military applications. These devices can be included in the drain or source regions of a MOSFET as one integral device to form Millimeter Wave to Terahertz Optoelectronic CMOS Transistors. Traditionally, VCSEL is not part of the CMOS transistors. In this paper, we will discuss CMOS VCSEL: a Vertical Cavity Surface Emitting Laser in the CMOS drain region, and photon sensors or avalanche photo diode in the CMOS drain / well regions. CMOS, VCSEL, and photon sensors are fabricated as one integral transistor. Millimeter wave generating diodes can also be fabricated in the drain region of the VCSEL MOSFET. We will discuss inversion mode and depletion mode CMOS VCSEL transistors.

We show that a photonic crystal triangular VCSEL array can lase in three possible coherent supermodes with three distinctive far-field beam profiles. To determine a dominant supermode at a given level of current injection, we define the peak ratio as the ratio between any sidelobe peak to the central peak of the Fourier transform of the far-field. The peak ratio and the number of sidelobes we show provides a numerical method to determine the dominant supermode in a coherent triangular VCSEL array. Coherent operation is found with approximately equal current injection into each element producing a single spectral resonance and structured far-field profile. We compare experimentally extracted peak ratios for an array nominally emitting at 850nm to those calculated from a complex waveguide modal simulation. This Fourier method based far-field analysis may be useful to determine a useful beam profile for target applications.

We report the design and manufacturing of a tunable VCSEL with an HCG MEMS mirror and an integrated detector oblique to the optical cavity for measuring output power without disturbing the laser cavity. This allows for a single laser device with integrated power monitoring capabilities that can be used in concert with external electronics to stabilize the power or monitor optical feedback of the device for sensing applications. The HCG tunable VCSEL is modified to incorporate a sacrificial layer capable of detecting light at the VCSEL’s operating wavelength. For the MEMS release process, the sacrificial layer is removed from the optical cavity defined by the VCSEL mirrors and active region. The release process is designed to create a cavern around the optical cavity and walls of such cavern are composed by sacrificial layer material. Thus, the sacrificial layer material is removed from the optical cavity, but is kept surrounding it. Light scattered at the interface semiconductor-air hits the cavern walls and modifies current through the MEMS terminals (I_det). Any change in VCSEL output power (P_out) is directly related to a change on I_det through MEMS terminal, creating a direct relationship of P_out vs. I_det. To the best of our knowledge, there is no previous report of a VCSEL with integrated oblique intracavity detector.

We fabricated a high output power large-scale 2D addressable VCSEL array and demonstrated a small footprint transmitter (Tx) module for true solid-state LiDAR. The module integrated VCSEL array and laser diode driver built-in circuit board in three dimensions. Each used VCSEL had five junctions, large optical aperture, and bump for individual driving. The wavelength of light output through a substrate was 940 nm. VCSELs were arranged in 48×48 matrix wherein 2,304 emitters can be individually driven. The array chip was assembled on the circuit board by flip-chip bonding via bump. All VCSELs were connected to the driver with very short current path caused by the three-dimensional integration. Short current path and small current loop resulted in small resistance and inductance, which facilitated driving of VCSELs with short current pulse. The transmitter module can generate high peak power with short pulse duration for time-of-flight measurement without RF input. Each VCSEL can be sequentially driven by trigger pulse input. The footprint of the module was 17.3 mm square. We confirmed that all VCSELs emit with sequential driving mode; the peak output power was over 45 W and pulse width was approximately 4 ns. The pulse shapes and widths were nearly identical at the center and edge of the array, which is generally unusual for a Tx module with two-dimensional integration where VCSEL and laser driver are integrated side by side. The divergence of output was less than 10°.

Multijunction VCSELs with up to eight active regions are fabricated with integrated surface relief features for transverse mode suppression. Using this approach, we demonstrate a single mode 940nm VCSEL with a record high power of 14.2 and SMSR >30dB during room temperature, continuous wave operation.

Flip-chip VCSELs with backside emission and lenses directly etched into the GaAs substrate are the most compact way to integrate optics with the VCSEL (ViBO = VCSEL with integrated Backside Optics). Beam shapes with lens structures enabling collimation as well as the uniform illumination of a defined field of view have been realized. Superior to separate optical elements the integrated optics avoids the need for individual alignment of laser die and optics and makes them an irremovable part of the chip. The realization of both contacts on the epitaxy side enables flip-chip assembly without the need for wire bonds, thus enabling ultra-short pulse operation. VCSELs are preferred for LiDAR applications due to their thermal stability and reliability. The required high brilliance can be achieved by micro-optics. Scaling the power into the kilowatt range requires stacked junctions and multi-chip concepts. This paper presents a new LiDAR system concept exploiting the potential of VCSELs with integrated optics.

LUMENTUM’s multi-channel VCSEL arrays in combination with SPAD (Single photon avalanche photodiode) receivers can make up the primary components of a “true” Solid-State Electronic Scanning LIDAR. The light from VCSELs reflects off an object, and is detected by an SPAD array receiver, that contains depth information, allowing for line scanning and 3D imaging of surrounding objects. The current system has 1D addressability and can perform line scanning in a single direction. The novel optics design consisting of collimating lenses and a horizontal diffuser allows for pairing of VCSELs with SPAD arrays of different sizes and aspect ratios and illuminating different field of views. The VCSEL has 57 channels with 7J epi architecture, with each channel emitting up to 248W at pulsewidths of 5-6ns, DC of 0.03%, making them optimal for short to medium range LIDAR. Wafer level testing of VCSELs at pulsewidths of 100ns, shows very good uniformity in power, voltage, wavelength, divergence and near field uniformity, between different channels. The channel to channel leakage between the anode pads is negligible and in the order of nano-amperes. In this paper, we will focus on VCSEL part of the system and present wafer level test results and initial module data at high speed.

The entry of 100G 850 nm VCSELs enables the replacement of copper by multimode fiber in switch-to-server links, and facilitates the upgrade of switch-to-switch links in enterprise networks and data centers. This paper will present the key features and characteristics of multimode VCSELs that enable direct modulation at 100 Gb/s suitable for multimode Ethernet and Fibre Channel standards. Beyond 100G, a bidirectional link using VCSELs of two wavelengths is one potential solution to double the aggregate data rate on duplex fiber links. Elements of both 850 and 910 nm VCSELs that would enable the next generation data links are described.

Emerging markets for optical interconnects with VCSEL-based transceivers require VCSELs with superior wide temperature performance. One of the prime parameters controlling the temperature dependence of VCSEL performance is wavelength detuning. We study the impact of detuning on the performance of 25 Gbaud class 850 nm VCSELs over a temperature range of -40 to 125°C, as applicable to e.g. automotive optical networking. Two VCSELs with different detuning, but otherwise identical, are compared. Basic static and dynamic performance parameters and their temperature dependencies are extracted. The results show that with appropriate detuning, sufficient performance at the temperature extremes and improved tolerance to temperature variations can be achieved. Excessive detuning to meet the more challenging high temperature performance requirements leads to insufficient low temperature performance.

Remarkable progress made in performance characteristics and reliability of high-speed (> 10 GHz) 850-nm multi-mode (MM) oxide-confined vertical cavity surface emitting lasers (VCSELs) during the last decade has led them to find applications in space satellite systems. The main advantage of deploying high-speed VCSELs in space satellites over directly modulated 850-nm edge emitting lasers is the absence of COMD (catastrophic optical mirror damage). In recent years, leading VCSEL manufacturers introduced higher speed (~ 20 GHz or 25 Gbps) VCSELs with encouraging characteristics. However, little has been reported on reliability and failure modes of these state-of-the-art VCSELs although it is crucial to understand failure modes and degradation mechanisms in these VCSELs through physics of failure investigation and subsequently develop VCSELs that exceed lifetime requirements for space satellite systems. For the present study, we performed short-term and long-term accelerated life-tests on 25 Gbps oxide-confined MM VCSELs to study reliability of these devices. Our goal is to extract credible reliability model parameters (thermal activation energy and current exponent factor) from these life-tests to determine suitability of these lasers for future space satellite systems. We also performed failure mode analysis on VCSELs at different stages of degradation using various techniques. We employed nondestructive techniques including optical beam induced current (OBIC) and electron beam induced current (EBIC) techniques as well as destructive techniques including focused ion beam (FIB) and high-resolution TEM techniques. Our detailed reliability and failure mode analysis results are reported along with our understanding on the physical origin of degradation in high-speed VCSELs with strained InGaAs quantum wells.

Laser diodes are of paramount importance for on-chip telecommunications applications, and a wide range of sensing devices that require near-infrared sources. In this work, the devices under test are vertical-cavity silicon-integrated lasers (VCSILs) designed for operation at 845 nm in photonic integrated circuits (PICs). We focus on the analysis of the degradation of the optical performance during aging. To investigate the reliability of the devices, we carried out several stress tests at constant current, ranging from 3.5 mA to 4.5 mA representing a highly accelerated stress condition. We observed two different degradation modes. In the first part of the experiments, the samples exhibited a worsening of the threshold current, but the sub-threshold emission was unaffected by degradation. We associated this behavior to the diffusion of impurities that, from the p-contact, were crossing the upper mirror implying a worsening of the DBR optical absorption. In the second stage of the stress test, the devices showed a higher degradation rate of the threshold current, whose variation was found to be linearly correlated to the worsening of the sub-threshold emission. We related this second degradation mode to the migration of the same impurities degrading the top DBR that, when reaching the active region of the laser, induced an increase in the non-radiative recombination rate. In addition to that, we related the two degradation modes to the change in series resistance, which was ascribed to the resistivity increment of the top DBR first and of oxide aperture afterwards.

In this paper, we report on design optimization, design, and fabrication of single-junction red VCSELs emitting at the wavelength of ~650nm with improved power and temperature performance. This has been achieved through redesigning the VCSEL epitaxial structure by optimizing the number of top and bottom mirror pairs to reduce the optical losses, optimizing p-DBRs’ doping concentration levels, changing the oxide layer thickness and position relative to the active region, and adjusting the wavelength detuning between peak wavelength of the gain medium and the Fabry-Perot dip wavelength. Moreover, several changes have been implemented to improve the carrier confinement in the active region to improve the performance of these devices at higher temperatures. These include optimizing the net strain across the active region, modifying the electron blocking layers, and also optimizing the number and thickness of InGaP-based multiple quantum wells. The CW characterization results indicate a record-high output optical power of 4.25mW at room temperature for a 14μm VCSEL. The temperature-variable L-I-V characterization results indicate a maximum lasing temperature of 50°C for the 14μm VCSEL, while the 5μm device has shown to be lasing up to 80°C. All devices have shown to be highly multi-mode spectrally, but with different far-field beam profiles. Moreover, the results indicate that the output light from these devices are strongly polarized in the <011> direction. Overall, the results depict a promising roadmap into developing high brightness red VCSELs which have superior performance over a broad temperature range

Polarization-sensitive optical coherence tomography (PS-OCT) is a non-destructive and three-dimensional imaging technique that can provide polarization properties, e.g., phase retardation and the optical axis, as well as architectural information similar to conventional OCT from the sample. In this study, we have developed a high-speed PS-OCT imaging engine by using a novel wavelength-swept laser light source based on a high-contrast grating vertical-cavity surface-emitting laser (HCG-VCSEL). Example PS-OCT imaging including the human fingernail junction, 3D plastic printing material, and the chicken breast tissue demonstrated the depth-resolved measurement of the multifunctional information of the sample with PS-OCT and HCG-VCSEL light source at an A-scan rate of 250 kHz.

We investigated a novel sensor concept based on a coupled resonator configuration and the employment of vertical-cavity surface-emitting laser (VCSEL) sources. Hereby, the back reflection of a sample which is placed next to the emission window of the semiconductor based laser source affects the internal resonator conditions of the VCSEL. If the operating voltage is kept constant, the internal interaction results in a change of the emitted wavelength and operating current, respectively. First experiments show a reproducible change of the operating current when the sample is moved in vertical direction by a few nm. This behavior was previously verified with a simulation based on ANSYS Lumerical by creating distributed Bragg reflection (DBR) stacks with different layers and quantifying the influence of the movable third resonator surface on the emission wavelength.

Vertical-cavity surface-emitting lasers (VCSELs) with low power consumption and high efficiency offer excellent characteristics for many applications. In this report, we design and demonstrate GaAs-based 940 nm VCSEL devices with different output mirror reflectivity values demonstrating slope efficiency from 0.97-1.16 (W/A) and show near unity internal quantum efficiency and low internal loss of 6.6 (cm^-1) at room temperature by using WIN Semiconductor 6-inch GaAs VCSEL wafer foundry service. Furthermore, the high temperature reliability test results guarantee quite long equivalent 14.6 years of operating time and stability.

The performance of the oxide-confined surface relief (SR) structure vertical-cavity surface-emitting laser (VCSEL) is simulated and analyzed by using the Finite Difference Frequency Domain (FDFD) microcavity model available in the PICS3D simulation package. Using the full vectorial microcavity model enables an accurate analysis of both the dominant and higher order modes, thus more insight into the cavity structural parameters can be investigated. In this proceeding, the impact of the oxide layer and the SR layer on both the emitting laser as well as the far field characteristics is investigated. The simulated Surface Relief (SR) VCSEL shows a threshold current increase to 1.2mA compared to 1.0mA without the SR layer, and far field divergent angles decrease to almost 10°.