3D sensing is being widely adopted in consumer, industrial and automotive markets. As an illumination source, VCSELs provide a combination of high efficiency, miniaturized packaging, fast pulse rise times and minimal spectral shift with temperature. This paper will describe advances in VCSEL technology that address the requirements of 3D sensing and LiDAR applications. 3D Sensing based on structured light requires power efficient VCSELs with a narrow beam divergence, compatible with the optics that produce a spot pattern in the far field. Time of Flight or LiDAR also requires high power efficiency, as well as fast rise times for good resolution in the 3rd dimension. For consumer applications, compactness of the illumination module is important, while all versions of 3D sensing benefit from the VCSEL’s narrow spectrum and low spectral shift with temperature. In this paper we will describe recent advances in VCSEL technology that enable improvements in 3D sensing systems. This includes efficiency improvements (greater than 60% power conversion efficiency), multi-junction VCSEL designs (up to 5 junctions in a device), and flip-chip back-side emitting VCSELs that enable miniaturization of illumination modules and large-scale addressability. In addition, we will describe module level integration of illumination sources, particularly for Time of Flight (TOF) and LiDAR applications, that incorporate VCSEL, driver, monitor diode, eye safety measures and optics.
Vixar presents a novel monolithic tunable vertical cavity surface emitting laser (VCSEL) design with a demonstrated tunable wavelength range of 41 nm in the near-infrared. This design combines a microelectromechanical system (MEMS) top mirror over a gallium arsenide based VCSEL cavity, and a monolithic construction which side steps any complex external cavity structures needed for tuning. We will present results which show the electro-thermally tunable mirror physically and reproducibly moving up to 400 nm, which corresponds to potential tuning range of over 50 nm in output wavelengths. These results also illustrate the use of this single mode, continuous wave, tunable VCSEL as a light source for biological tomographic imaging. Data taken in collaboration with Notre Dame presents the use of such tunable light sources for diffuse optical spectroscopic imaging (DOSI) of breast tumors and other anomalous tissue inclusions. Previous work confirms the viability of this design as an optical source for DOSI instruments and the work presented here shows improved results with even greater tuning capabilities and higher optical power. In conjunction with past work centered at 775 nm, current work at 940 nm, and future proposed VCSEL examples at 905 nm, Vixar expects to show that this design is capable of supporting tomographic imaging spanning 765 -782 nm, and 885 – 955 nm in total. Above and beyond these immediate imaging goals, these results continue to enable future visions of many possible applications for which a monolithic tunable light source might be ideal.
We present a near-infrared tunable vertical cavity surface emitting laser (VCSEL) based upon a unique electrothermally tunable microelectromechanical systems (MEMS) topside mirror designed for tissue imaging and sensing. At room temperature, the laser is tunable from 769-782nm with single mode CW output and a peak output power of 1.3mW. We show that the tunable VCSEL is suitable for use in frequency domain diffuse optical spectroscopy by measuring the optical properties of a tissue-simulating phantom over the tunable range. These results indicate that tunable VCSELs may be an attractive choice to enable high spectral resolution optical sensing in a wearable format.
VCSELs (Vertical Cavity Surface Emitting Lasers ) provide a very versatile optical source for Low Light Therapy
applications. This talk will discuss performance characteristics and packaging demonstrations for VCSELs primarily
operating in the 680nm and 850nm regimes. At 680nm individual VCSELs produce >10mW, while >0.35W can be
provided from a 0.4mm2 emission area. Spectral width is typically 1-2nm even for a multi-mode or array device. At
850nm these numbers increase to >30mW and >0.8W. Even higher powers can be achieved under pulsed modulation,
i.e. 0.55W for a 680nm VCSEL or 1.2W for an 850nm VCSEL. While we report on results achieved at 680nm and
850nm, extension to wavelengths ranging from 660nm to 1000nm is easily achieved.
The packaging flexibility of VCSELs also makes them of significant interest to the Low Light Therapy community. We
will report on the incorporation of VCSELs into surface mount packages, including typical LED packages such as the
PLCC, or ceramic chip carriers. VCSELs in PLCC packages have been attached to flexible circuits to provide a broad
area illumination. We will also report on a unique chip on board package which easily allows for the addition of optical
elements such as diffusers, diffraction gratings or lenses. This package is 2mm on a side, sufficiently small for
incorporation into catheters or implantation.
Vixar has been developing VCSELs at both shorter (680nm) and longer (1850nm) wavelengths. This paper reports on
advances in technology at both of these wavelengths. 680nm VCSELs based upon the AlGaAs/AlGaInP materials
system were designed and fabricated for high speed operation for plastic optical fiber (POF) based links for industrial,
automotive and consumer applications. High speed testing was performed in a “back-to-back” configuration over short
lengths of glass fiber, over 42 meters of POF, with and without I.C. drivers and preamps, and over temperature.
Performance to 90°C, 10 Gbps and over 40 meters of plastic optical fiber has been demonstrated. Reliability testing has
been performed over a range of temperatures and currents. Preliminary results predict a TT1% failure of at least 240,000
hours at 40°C and an average current modulation of 4mA. In addition, the VCSELs survive 1000 hours at 85% humidity
85°C in a non-hermetic package. 1850nm InP based VCSELs are being developed for optical neurostimulation. The
goals are to optimize the output power and power conversion efficiency. 7mW of DC output power has been
demonstrated at room temperature, as well as a power conversion efficiency of 12%. Devices operate to 85°C. Over
70mW of pulsed power has been achieved from a 35 VCSEL array, with a pulse width of 10μsec.
Vixar has recently developed VCSELs at 1850nm, a wavelength of interest for neural stimulation applications. This
paper discusses the design and fabrication of these new long-wavelength lasers, and reports on the most recent
performance results. The VCSELs are based on InP-compatible materials and incorporate highly strained InGaAs
quantum wells to achieve 1850nm emission. Current confinement in the VCSEL is achieved by ion implantation,
resulting in a planar fabrication process with a single epitaxial growth step. Continuous wave lasing is demonstrated
for aperture sizes varying from 8 to 50μm with threshold currents of 1-17mA. The devices demonstrate peak power
of 7mW at room temperature and CW operation up to 85°C.
Neural stimulation using infrared optical pulses has numerous potential advantages over traditional
electrical stimulation, including improved spatial precision and no stimulation artifact. However,
realization of optical stimulation in neural prostheses will require a compact and efficient optical
source. One attractive candidate is the vertical cavity surface emitting laser. This paper presents
the first report of VCSELs developed specifically for neurostimulation applications. The target
emission wavelength is 1860 nm, a favorable wavelength for stimulating neural tissues. Continuous
wave operation is achieved at room temperature, with maximum output power of 2.9 mW. The
maximum lasing temperature observed is 60° C. Further development is underway to achieve
power levels necessary to trigger activation thresholds.
Red VCSELs are of interest for medical and industrial sensing, printing, scanning, and consumer electronics
applications. This paper will describe the optimization of red VCSEL design to achieve improved output power and a
broader temperature range of operation. We will also discuss alternative packaging approaches and in particular will
describe non-hermetic packages and performance of the VCSELs in a humid environment.
Record output power of 14mW CW and a record maximum temperature of operation of 105°C have been achieved at an
emission wavelength of 680nm. The achievement is the result of attention to many details including resonance cavitygain
peak offset, material choices, current and mode confinement approaches, and metal aperture design. We have also
demonstrated lifetimes >1000 hours for non-hermetic packages in an 85% humidity environment. A chip on board
approach has been used to create a large scale linear array of VCSELs for a scanning application.
Although vertical cavity surface emitting lasers (VCSELs) have traditionally found their place in high-speed
communication links, the recent advancements of VCSELs emitting in the visible spectrum has sparked interest
for new applications in scanning and imaging. Compared to other lasers, VCSELs have many advantageous
characteristics including compact size, low power requirements, low cost, and high reliability. VCSELs also offer
the unique ability to be fabricated in one- or two-dimensional arrays, making it possible for multiple VCSELs on
a single chip to perform the same function as a mechanically scanned beam. One such application is computed
radiography (CR), which provides an efficient solution for digitizing and electronically storing x-ray images. In
this work, we demonstrate a 1-inch prototype CR scanner based on high-density VCSEL arrays. The device is
capable of generating very fast scans with no moving parts, and has the potential to increase throughput, stability,
and image quality. In this paper, we discuss the design and performance of this scanner and demonstrate X-ray
image acquisition with resolution exceeding 5 line pairs per millimeter (lp/mm).
In this paper, we report on the latest advances in implementation of the photonic integrated circuits (PICs) required for optical routing. These components include high-speed, high-performance integrated tunable wavelength converters and packet forwarding chips, integrated optical buffers, and integrated mode-locked lasers.
We demonstrate 10Gbit/s operation of two different types of monolithic photocurrent driven wavelength converters (PD-WC). These photonic integrated circuits use a Semiconductor Optical Amplifier (SOA)-PIN photodetector receiver to drive an Electro-absorption (EA), or Mach-Zehnder (MZ) modulator that is integrated with a SGDBR tunable laser. We demonstrate improvements in optical bandwidth, insertion losses, device gain, and modulation efficiency.
The evolution of optical communication systems has facilitated the required bandwidth to meet the increasing data rate demands. However, as the peripheral technologies have progressed to meet the requirements of advanced systems, an abundance of viable solutions and products have emerged. The finite market for these products will inevitably force a paradigm shift upon the communications industry. Monolithic integration is a key technology that will facilitate this
shift as it will provide solutions at low cost with reduced power dissipation and foot-print in the form of highly functional optical components based on photonic integrated circuits (PICs). In this manuscript, we discuss the advantages, potential applications, and challenges of photonic integration. After a brief overview of various integration techniques, we present our novel approaches to increase the performance of the individual components comprising highly functional PICs.
An InP-based tunable wavelength converter is investigated which monolithically combines a waveguide photodetector with a sampled-grating distributed Bragg reflector laser diode. We employ advanced device simulation to study internal physical mechanisms and performance limitations. Our three-dimensional finite-element model self-consistently combines carrier transport, optical waveguiding, and nanoscale many-body theory to accurately account for optical transitions within the quantum wells. Good agreement with measurements is achieved. The validity of several model simplification options is discussed.
Wavelength converters are seen as important to the scalability, flexibility, and cost of future optical networks. These devices have opportunities for deployment in optical switches, routers and add/drop multiplexers. This talk will outline the latest results of monolithic and hybrid photocurrent-driven wavelength converters (PD-WC) based on either the direct modulation of a bipolar cascade SGDBR laser or by external modulation using an Electro-absorption (EA), or Mach-Zehnder (MZ) modulator using integration building blocks such as a semiconductor optical amplifiers (SOA), SGDBR lasers, PIN detectors and EA and MZ modulators. As the input and output waveguides are separate in this configuration of wavelength converter, an optical filter is not required to reject the input signal at the output which is desirable particularly with wavelength tunable applications where the response time of a filter could limit system performance.