This PDF file contains the front matter associated with SPIE Proceedings Volume 11300, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists

TriLumina develops and manufactures flip-chip VCSEL technology used in 3D sensing applications that must meet automotive grade 1 temperature range (-40˚C to 125˚C) performance and be tested to high reliability standards and criteria (AEC-Q102). Advances in VCSEL efficiency, performance and automotive qualification of TriLumina’s selfhermetic flip-chip VCSEL are discussed. TriLumina’s VCSEL-on-board (VoB), surface-mount technology VCSEL is introduced.

We have developed a solid-state LiDAR sensor with combination of pixelized laser beam sources and BCSCs (beam collimation and steering components). We utilized 2-Dimensional matrix addressable VCSEL arrays as Laser sources. Additionally two alternatives, combination of a microlens and a microprism plate and metalens plates, are tested as a candidate of the BCSC. This technology enables us to realize true solid-state LiDARs without mechanically moving part for scanning laser beams. We verified that our LiDAR can detect the objects which are in range of 100 meters and FOV (field of view) can be spanned up to 360o by combing of multiple sensor modules. The key components were fabricated semiconductor processing and paves the way for disruptive robust and mass-producible LiDAR sensors.

Long time being used in Datacom, in computer mice and cell phone, last decade VCSEL developments show that this laser source is an alternative to the long established edge emitter laser diodes (EELD), with attractive high power performance, better reliability, lower manufacturing costs and design flexibility. This paper will discuss the benefits of VCSEL compared to EELD and the importance to minimize parasitic inductance when used in LiDAR application were short pulses, high peak power are required¹. A theoretical analysis will be presented to show the advantage of multijunction VCSEL with better Power Conversion Efficiency (PCE) and Brightness than single junction VCSEL.

Low cost and compact 3D imaging for various applications like face-recognition, machine vision or LIDAR for automotive has introduced new requirements in terms of NIR light source characterization. These sources must comply safety regulations and must be verified rapidly and accurately during the fabrication process. In addition, precise characterization of the light source emissions within their entire angular aperture is mandatory to get accurate 3D images. The paper introduces a new Fourier optics system dedicated to this task.

We report on the design and characterization of multi-mirror vertical-cavity surface-emitting lasers (VCSELs) that achieve linewidths less than 2 MHz. We have fabricated all-semiconductor multi-mirror VCSELs at 850 nm that operate in a single mode and are suitable for high-resolution spectroscopy. Cold-cavity linewidth measurements confirm increased quality factors relative to standard VCSEL resonators. Frequency noise power spectral density measurements exhibit 1/f noise and white-noise floors consistent with Lorentzian linewidths less than 2 MHz.

Sophisticated control of beam patterns is attractive for applications including LiDAR, surveying, and 3D measurements. Light sources with beam pattern control on chips would enable simplicity and portability to systems, and this technology would prove useful in many fields. Therefore, we propose integrable spatial-phase-modulating surface-emitting lasers (iPMSELs) in which static arbitrary two-dimensional beam patterns are emitted from needle-tip sized sources. We present a demonstration of various static two-dimensional beam patterns including characters, multi-spots, lines, and even gray-scale pictures.
The basic structure of iPMSELs is similar to that of ordinary laser diodes. A novel phase modulating layer is introduced near the active layer. The holes in the phase modulating layer are systematically arranged in positions slightly shifted from the lattice point of square-lattice photonic-crystal. The layer contributes to two important operating mechanisms, “in-plane resonance” due to zero-group velocity at the photonic-band edge and “spatial-phase modulation” of output beam patterns due to the positional shift of holes designed using computer generated holograms. However, the prototype device shows not only target beam patterns but also subsidiary beam patterns including a strong central spot beam (zero order beam) attributable to vertical diffraction.
To address the issue, we improved the design and successfully removed the beam, demonstrating periodic beam patterns useful for 3D measurements. We also present a demonstration of electrical switching of beam patterns using arrayed iPMSELs where eight devices are integrated onto a TO-8 base. This enables applications including beam scanning or indications.

Impurity-induced disordering in vertical-cavity surface-emitting lasers (VCSELs) has demonstrated enhanced performance such as higher modulation speeds, reduced series resistance, and higher-order mode suppression for singlemode operation. Initiated by the diffusion of Zn, impurity-induced disordering intermixes discrete AlGaAs-based distributed Bragg reflectors (DBR) pairs which leads to lower mirror power reflectivity and increased optical loss. When formed into an aperture where the center is non-disordered, suppression of higher-order transverse modes for high-power single-mode operation can be achieved. For maximal mode suppression, deep disordering apertures are desirable. However, due to the isotropic nature of diffusion, these apertures are limited to the lateral diffusion encroaching onto the fundamental mode. By tailoring the film stress of the SiN_x diffusion mask, the capability to modify the diffusion front of the disordering aperture is demonstrated. Defined by their lateral-to-vertical (L/V) diffusion ratios, an L/V ratio of 3.7 to 0.90 is measured for corresponding SiN_x diffusion mask strains ranging from a compressive -797 MPa to a tensile +347 MPa. This demonstrates that tensile strained diffusion masks limit the amount of lateral diffusion. To further reduce the lateral encroachment, increasingly tensile diffusion masks are deposited by modifying the SiH₄/NH₃ flow ratios. This diffusion mask is employed to fabricate high-power single-mode VCSELs designed for 850 nm emission. Compared to VCSELs fabricated with non-optimized disordering apertures, enhanced transverse-mode control is achieved and singlemode output power in excess of 3.8 mW with a side mode suppression ratio greater than 30 dB is measured.

76X nm single-mode and single-polarization VCSELs with extended tuning range of 10 nm are presented, which prove very suitable for the Tunable Diode Laser Absorption Spectroscopy (TDLAS) application. The broad tuning range covers both major absorption line bands for Oxygen around 761 nm and 763 nm. The VCSELs are discussed in terms of design, manufacturing, performance, and reliability aspects. Tuning coefficients are 0.5 nm/mA and 0.053 nm/K, typical for small aperture oxide confined VCSELs and the AlGaAs material system, respectively. The wide operating temperature range of up to 150 K, e.g., output power of more than 0.1 mW and threshold currents below 0.9 mA between -30°C and +120 °C, in combination with a sophisticated two stage thermo-electrical element (TEC) in a compact TO39 package, which allows for wide range temperature control, is an excellent match to the requirements set by TDLAS oxygen sensing.

We demonstrate multimode 940 nm flip chip VCSELs with >20dB polarization suppression and small signal modulation bandwidth > 25 GHz (3dB) in 2x4 arrays for 50 Gbit/s/channel NRZ transmission. The VCSELs have surface gratings for polarization suppression. The high bandwidth operation is achieved in part by using a relatively small oxide aperture. The arrays are comprised of pairs of VCSELs with orthogonal polarizations, which enable cold sparing; if a primary (P-polarized) VCSEL fails, a system turns on a secondary (S-polarized) VCSEL. The light beam is routed through optics to the same 50 μm core fiber for both polarizations thus keeping the link integrity intact.

We investigate triple and septuple electrically parallel, optically uncoupled 980 nm vertical-cavity surface-emitting laser (VCSEL) arrays with varying intra-array VCSEL-to-VCSEL spacings and oxide aperture diameters. We demonstrate 20 to 40 gigabit-per-second back-to-back data transmission with a bit error ratio of 1x10^-13. Our VCSELs enable optical wireless communication for a plethora of sensors, smartphones, and other Internet of Things gadgets.

In the recent decade, the growth of data centers is being driven by spreading of cloud computing and its relevant technologies. As of now, 100 Gbit/s optical interconnects have been widely used in the data-centers, and the trend is about to be switched to 400 Gbit/s data-rate. Multi-mode VCSELs are employed for the reasons of the lower cost and power consumption in a short-distance range. 400 Gbit/s transceivers are equipped with an 1×8 or a pair of 1×4 VCSEL arrays. Especially, 400GBASE-SR4.2 (BiDi) uses two different wavelengths for each 1×4 array. In such case, sufficient uniformity in terms of optical output, bandwidth, relative intensity noise (RIN) and spectral width properties could be keys to success in 400 Gbit/s applications. Variations of optical output and bandwidth over a processed wafer can be suppressed by maturing the epitaxial growth and fabrication procedures. In contrast, spectral and noise properties are strongly coupled to transverse mode properties of VCSELs, which are controlled by a shape of the oxide aperture. In this work, we report uniform spectral and noise characteristics of 1×4 VCSEL arrays by introducing a rotationally-asymmetric oxide aperture. The rotationally-asymmetric aperture VCSELs show less variation in root-mean-square (RMS) spectral width and RIN compared with circular-aperture VCSELs. The rotationally-asymmetric aperture is capable of splitting degenerated modes in spectral domain. Uniformity in the performance of optical output, 3dB bandwidth and RIN are verified in 1×4 arrays for both 850 nm and 910 nm VCSELs. 53.125 Gbit/s PAM-4 modulation is then performed with different temperatures of 25 and 90℃, which shows the capability of our VCSEL arrays for 400 Gbit/s applications.

This paper will review the VCSEL performance requirements and link length limitations to support next generation 53Gbaud line rates with PAM-4 modulation for 100G per lane multi-mode optical links for both active optical cables and transceivers. VCSEL performance with bandwidth in excess of 25GHz and relative intensity noise lower than -145dB/Hz will be needed to enable this next generation of multi-mode links. VCSEL device performance and associated wear out life data will be included.

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.

We design, produce, characterize, and compare 850 nm vertical cavity surface emitting lasers (VCSELs) with one and two oxide aperture layers, and with cavity optical thicknesses of 0.5λ and 1.5λ. We process five VCSEL wafers side by side with varying oxide aperture diameters from about 4 to 16 m and perform on-wafer static and dynamic testing. From optical output power-current-voltage characteristics we extract and compare threshold currents, differential series resistances, and wall plug efficiencies. We measure the dynamic 2-port scattering parameters (S11 and S21) to determine the small signal modulation frequency response of the VCSEL and the combined VCSEL and photodetector optical link. By extracting and comparing the D-factor, modulation current efficiency factor, -3 dB bandwidth, and resistanceinductance- capacitance (RLC) circuit elements we find only a small difference in the static and dynamic performance characteristics of the five VCSEL designs, with slightly higher bandwidth for the half-lambda cavity VCSELs with two top oxide apertures.

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.

We’ve developed a next-generation MOCVD platform for high-performance, commercial VCSEL production. The tool is capable of achieving total population uniformity >95% yield in +/- 3nm bin on 6” GaAs. In addition, the tool is capable to go >300 runs between maintenance while maintaining very fast growth rate up to 4.2micron / hr and low [C] impurity <2E17 cm-3. Another parameter critical to VCSEL is defectivity, where <0.5 defects / cm2 @ >2 micron size have been demonstrated. Correlation of epi and VCSEL device parameters such as threshold current density (Jth) and power conversion efficiency will be discussed.

Over the last two years, our group has reported the first room-temperature continuous-wave (RTCW) fixed wavelength VCSELs operating above 3 microns, in both optically pumped and electrically pumped devices. Our optically pumped 3.3um devices employ one or two wafer-bonded GaAs/AlGaAs mirrors, in conjunction with a type I InGaAsSb/AlInGaAsSb quantum well active region. Our electrically pumped 3.3um devices employ a bottom waferbonded GaAs/AlGaAs mirror, top deposited ZnSe/ThF4 mirror, and type II interband cascade (ICL) active region. These fixed wavelength devices lay a foundation for tunable devices in the spectrally rich 3-5um region. Narrowly tunable devices can use thermal tuning, by variation of pump power (optically pumped devices), bias current (electrically pumped devices), or device temperature (both electrically and optically pumped devices). In this paper, we describe tunable CW optically pumped devices with >4nm of tuning near 3.3um using variation of pump power. CW electrically pumped devices show ~2nm tuning near 3.3um using variation of bias current. These results are a critical first step towards an inexpensive and high-speed methane sensing source. A first generation of MEMS-tunable optically pumped devices has achieved 70nm tuning range near 3.34um.

980 nm VCSELs with different numbers of top dielectric DBR periods added to a 5.5-period top semiconductor DBR and with various oxide aperture diameters are investigated to determine the impact of the added dielectric DBR’s impact on the static and dynamic properties of the VCSELs. For VCSELs with the same oxide aperture diameter we observe smaller small-signal modulation bandwidth and lower D-factor for the VCSELs with more pairs of dielectric DBRs. For the VCSELs with 4 μm oxide aperture diameters with 8 and 12 periods of added top dielectric DBRs we measured bandwidths of 29 and 26 GHz, respectively.

We report recent advances in electrically-pumped 1050 nm and 1550 nm micro-electro-mechanically-tunable verticalcavity surface emitting-lasers (MEMS-VCSELs). We demonstrate a single-mode, continuous, mechanical tuning range of 73 nm with high output power and low threshold current performance for the 1050 nm devices. To the best of our knowledge, 73 nm is a record tuning value for an electrically-pumped tunable VCSEL with a tuning speed >250 kHz, making them highly desirable for next generation OCT and other swept source applications. 10 Gbps 1550-nm DWDM tunable SFP+ modules based on an HCG-VCSEL are demonstrated with an embedded communications channel for automatic wavelength tuning and locking for low cost FTTx and front haul network applications.

In recent years, MEMS-tunable VCSELs have emerged as a leading swept source for optical coherence tomography imaging. At the ophthalmic imaging wavelength of 1050nm, optically pumped MEMS-VCSELs (MEMS-oVCSELs) have previously achieved >100nm tuning range and repetition rates approaching 1Mhz, enabling high-resolution and high-speed eye imaging. Electrically pumped MEMS-VCSEL technology (MEMS-eVCSEL) is a critical need for many emerging low-cost high-volume applications, but thus far tuning range has lagged substantially behind optically pumped devices. In this work, we demonstrate 97nm continuous tuning range in a MEMS-eVCSEL operating near 1050nm, and >100nm total tuning range, representing the widest tuning ranges achieved to date, and rivaling the performance of optically pumped devices. Our devices employ a strain-compensated InGaAs/GaAsP gain region disposed on a wideband fully oxidized GaAs/AlxOy back mirror. A deposited top mirror rests on a flexible dielectric membrane separated by a variable airgap from the underlying gain region. Application of voltage between the dielectric membrane and a bottom actuator contact on the top of the gain region creates an electro-static force which pulls the suspended mirror down, contracting the airgap and tuning the device to shorter wavelengths. In this 3-terminal device, the bottom actuator contact doubles as the laser anode. Current injection proceeds from the anode to the cathode at the back of the GaAs substrate through a lithographically defined low-loss current aperture, enabling reproducible aperture size and reproducible single-mode performance. These devices offer promise for many emerging high-volume imaging applications.

We show our latest results on electrically-driven VCSELs incorporating a monolithic high contrast grating (MHCG) mirror. Via optimized processing techniques we achieve a 3-fold improvement in threshold current and optical output power and a 2-fold improvement in the small-signal modulation bandwidth frequency with respect to the first generation of our MHCG VCSELs.

Vertical-cavity surface-emitting lasers (VCSELs) with single-mode, single-polarization emission at a wavelength of 894.6 nm was demonstrated for miniaturized atomic clocks. Utilizing the direct-etched surface grating on the surface of VCSELs, the state of polarization of VCSELs was controlled and pinned over the whole current range. The Modal properties of VCSELs with grating structures was studied using a finite difference time domain (FDTD) method. We investigate modal loss behavior with respect to the variation of grating structural parameters for the optimization of VCSELs polarization characteristics.