Vertical-cavity Surface-emitting Laser Technology Research Articles

Vertical Cavity Surface Emitting Laser technology: A comprehensive review

Vertical Cavity Surface Emitting Laser (VCSEL) technology has become an indispensable element in optical communication systems and optoelectronics due to its many advantages, and the unique characteristics of VCSELs, including vertical emission, high-speed operation, and low power consumption, have attracted much interest from researchers and industry professionals. This paper provides a comprehensive overview of VCSELs, explaining their basic principles and two commonly used structures. It also delves into the field of optical communications, highlighting the challenges faced in the current development, from which it introduces the significant progress made by VCSELs over the past decade in various applications such as high-speed data transmission, multi-mode communications, and long-distance networks. In addition, this study provides valuable insights into the future trajectory and potential evolution of VCSEL technology to facilitate further research and innovation in the field of communications. By providing a holistic analysis, this study is a valuable resource for scientists and researchers to help them realize the full potential of VCSELs in advancing optical communication technologies to meet the ever-changing needs of modern communication networks.

High Speed VCSEL Technology and Applications

Historically optical links up to 100–300m distances are served by light emitting devices in the 850 nm spectral range in combination with multimode glass fibers (MMF). As the silicon scaling continues, a single channel data rate is to double each 24 months. Light-emitting diodes had to be replaced by vertical cavity surface emitting lasers (VCSELs) and the data rate increased from 100 Mb/s to 10 Gb/s. At higher data rates problems with further scaling evolved. To avoid the collapse an anti-waveguiding VCSEL cavity design was invented, applied, and presently serves data links operating up to 50–100 Gb/s per channel. Another requirement in data communication is the bandwidth density scaling, with the number of channels per link increasing approximately 5-fold each 10 years, while keeping a similar space for connectors. A coarse short-wavelength division multiplexing allowing 850 nm, 880 nm, 910 nm, and 940 nm wavelengths in a single MMF is introduced. The bandwidth density increase is also possible by using multicore fiber (MCF) coupled to on-chip VCSEL arrays. The data rates up to 224 Gb/s are already reached by 850nm VCSELs. At such data rates significant transmission distance over MMF is only possible by applying ultra-narrow spectrum VCSELs minimizing the chromatic dispersion effects. On-chip mini-arrays of oxide-confined VCSELs allow a high coupling efficiency to MMFs, a narrow spectrum, a high power, a significant transmission distance at high data rates. Coherent lasing in such arrays allow photon-photon resonance engineering aimed at modulation bandwidths ∼50–100 GHz.

Advanced VCSEL photonics: Multi-level PAM for spectral efficient 5G wireless transport network

Transitions to 5G are accompanied by rapid increase in data traffics, creating exciting opportunities for competitive edges in 5G spectral efficiency (SE) solutions. We present the first reported vertical cavity surface emitting laser (VCSEL)-based heterodyne technique in context of four-level pulse amplitude modulation (PAM-4) over 15 km SMF fibre and 12 m radio frequency (RF) wireless link. Two low-cost temperature stabilized VCSELs with an extinction ratio (ER) of 4.6 dB and aggregated bit rate of 7 Gbps OOK data to meet the high data demands in wireless connectivity are heterodyned to dynamically generate low phase noise 37.9 GHz RF for 30 m wireless transmission link. PAM-4 modulation technique is adopted to maximize the RF carrier SE in transmission of 14 Gbps data over 12 m wireless link, doubling the network bit rate. It is the first time a VCSEL-based photonically generated RF carrier system is reported with a doubled network bitrate upgrade functionality in the contest of PAM-4. A receiver sensitivity of -23.19 dBm is attained on the 7 Gbps OOK data with a transmission penalty of 2.62 dB over a 30 m link. However, a 14 Gbps PAM-4 modulation incurred a 6.17 dB penalty over the 12 m wireless transmission link. Heterodyned VCSEL technology offer dynamic RF carrier flexibility while PAM-4 upgrades the RF carrier SE without replacing the network optics.

Multicast-enabled high-speed VCSEL technology for flexible data center networks

We experimentally demonstrate the multiple signal modulation on a single class 10 G vertical cavity surface emitting laser (VCSEL) carrier at 1 310 nm for next generation multicast-enabled data center networks. A 10 Gbit/s data signal is directly modulated onto a single mode VCSEL carrier. To maximize carrier spectral efficiency, a 2 GHz reference frequency (RF) clock tone is simultaneously modulated on the VCSEL phase attribute. The inherent VCSEL orthogonal polarization bistability with changing bias current is further exploited in transmission of a polarization based pulse per second (PPS) timing clock signal. Therefore, we simultaneously transmit a 10 Gbit/s directly modulated data, 2 GHz phase modulated RF and a polarization- based PPS clock signals using a single mode 10 GHz bandwidth VCSEL carrier. It is the first time that a single class 10 G VCSEL carrier is reported to transmit a directly modulated data, phase modulated RF clock and polarization based PPS timing signal simultaneously in a single wavelength. A of G.652 single mode fibre (SMF) transmission over 3.21 km is experimentally attained. A receiver sensitivity of −15.60 dBm is experimentally obtained for the directly modulated 10 Gbit/s data signal. A 3.21-km-long SMF transmission introduces a penalty of 0.23 dB to the data signal. The contribution of a 2 GHz phase modulated RF and a polarization-based PPS clock signal to this penalty is found to be 0.03 dB. An RF single- side band (SSB) phase noise values of −82.36 dBc/Hz and −77.97 dBc/Hz are attained without and with simultaneous directly modulated data and polarization-based PPS clock signals respectively for a 3.21-km-long SMF transmission. This work provides an alternative efficient and cost effective technique for simultaneous high-speed multiple information transmission to different network nodes within a data center network through shared network infrastructure.

Advanced VCSEL Technology: Self-Heating and Intrinsic Modulation Response

Experimental data and modeling results are presented for a new type of vertical-cavity surface-emitting laser (VCSEL) that solves numerous problems with oxide VCSELs. In addition, the new oxide-free VCSEL can be scaled to small size. Modeling shows that this small size can dramatically increase the speed of the laser through control of self-heating. Modeling compared with both the oxide and the new oxide-free VCSEL predict intrinsic modulation speed for room temperature approaching 80 GHz, indicating the potential for > 100-Gb/s data speed from directly modulated VCSELs. The modeling is one of if not the first to include self-heating and spectral detuning between the gain and the cavity resonance that results from self-heating. The modeling results accurately accounts for the saturation in modulation speed in very high-speed oxide VCSELs operating at high temperature and accounts for the temperature of differential gain and photon density in limiting speed. Saturation of the photon density is found to limit the ultimate intrinsic speed. Differential gain decreases with increasing temperature but with sufficiently weak temperature dependence that it is not found to limit the VCSEL speed.

Vertical-cavity surface-emitting laser sources for gigahertz-bandwidth, multiwavelength frequency-domain photon migration.

.Frequency-domain photon migration (FDPM) uses modulated laser light to measure the bulk optical properties of turbid media and is increasingly applied for noninvasive functional medical imaging in the near-infrared. Although semiconductor edge-emitting laser diodes have been traditionally used as miniature light sources for this application, we show that vertical-cavity surface-emitting lasers (VCSELs) exhibit output power and modulation performance characteristics suitable for FDPM measurements of tissue optical properties at modulation frequencies exceeding 1 GHz. We also show that an array of multiple VCSEL devices can be coherently modulated at frequencies suitable for FDPM and can improve optical power. In addition, their small size and simple packaging make them an attractive choice as components in wearable sensors and clinical FDPM-based optical spectroscopy systems. We demonstrate the benefits of VCSEL technology by fabricating and testing a unique, compact VCSEL-based optical probe with an integrated avalanche photodiode. We demonstrate sensitivity of the VCSEL-based probe to subcutaneous tissue hemodynamics that was induced during an arterial cuff occlusion of the upper arm in a human subject.

Impact of Damping on 50 Gbps 4-PAM Modulation of 25G Class VCSELs

We present an investigation into the effects of photon lifetime and the associated damping of the modulation response on 50 Gbps 4-pulse-amplitude modulation (4-PAM) signal generation with directly modulated 25G class vertical-cavity surface-emitting lasers (VCSELs). While 4-PAM benefits from higher slope efficiency and output power, it is shown that the greater impact of intensity noise and dynamic nonlinearities implies that a VCSEL with a longer photon lifetime and more damped response is needed when transitioning from existing 25 Gbps OOK to 50 Gbps 4-PAM using the 25G VCSEL technology.

Demonstration of Raman-based, dispersion-managed VCSEL technology for fibre-to-the-hut application

Abstract For the first time, we experimentally investigate the use of vertical cavity surface emitting lasers (VCSELs) in the fibre-to-the-home (FTTH) flavour for Africa, known as fibre-to-the-hut. Fibre-to-the-hut is a VCSEL based passive optical network technology designed and optimized for African continent. VCSELs have attracted attention in optical communication due to its vast advantages; low power consumption, relatively cheap costs among others. A 4.25 Gb/s uncooled VCSEL is used in a dispersion managed, Raman assisted network achieving beyond 100 km of error free transmission suited for FTTHut scenario. Energy-efficient high performance VCSEL is modulated using a 27-1 PRBS pattern and the signal transmitted on a G.655 fibre utilizing the minimum attenuation window.

Impact of the Oxide-Aperture Diameter on the Energy Efficiency, Bandwidth, and Temperature Stability of 980-nm VCSELs

New oxide-confined 980-nm vertical-cavity surface-emitting lasers (VCSELs) with record temperature-stable small-signal bandwidths of 25.6 to 23.0 GHz at 25 to 85 °C are designed, fabricated, and characterized. Technology-based device parameters essential for system-level models of VCSEL-based short-reach and ultrashort-reach optical interconnects are extracted. These parameters include key intrinsic figures-of-merit, including the -3-dB modulation bandwidth, the bandwidth-to-electrical power ratio, and device input impedance, all as functions of temperature, oxide-aperture diameter, and desired range of bias current or current density. Further, the M-factor, relating the intrinsic VCSEL bandwidth to the error-free bit rate for a given external systems configuration and application, is introduced. Our present 980-nm VCSEL technology is capable of 40 Gb/s operation at 85 °C at a simultaneously low current density of 10 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with an energy of only 100 fJ per bit.

Ultrahigh speed endoscopic optical coherence tomography using micromotor imaging catheter and VCSEL technology

We developed a micromotor based miniature catheter with an outer diameter of 3.2 mm for ultrahigh speed endoscopic swept source optical coherence tomography (OCT) using a vertical cavity surface-emitting laser (VCSEL) at a 1 MHz axial scan rate. The micromotor can rotate a micro-prism at several hundred frames per second with less than 5 V drive voltage to provide fast and stable scanning, which is not sensitive to the bending of the catheter. The side-viewing probe can be pulled back to acquire a three-dimensional (3D) data set covering a large area on the specimen. The VCSEL provides a high axial scan rate to support dense sampling under high frame rate operation. Using a high speed data acquisition system, in vivo 3D-OCT imaging in the rabbit GI tract and ex vivo imaging of a human colon specimen with 8 μm axial resolution, 8 μm lateral resolution and 1.2 mm depth range in tissue at a frame rate of 400 fps was demonstrated.

Reproducibility of a Long-Range Swept-Source Optical Coherence Tomography Ocular Biometry System and Comparison with Clinical Biometers

To demonstrate a novel swept source optical coherence tomography (SS-OCT) imaging device using a vertical cavity surface-emitting laser (VCSEL) capable of imaging the full eye length and to introduce a method using this device for noncontact ocular biometry. To compare the measurements of intraocular distances using this SS-OCT instrument with commercially available optical and ultrasound biometers. To evaluate the intersession reproducibility of measurements of intraocular distances using SS-OCT. Evaluation of technology. Twenty eyes of 10 healthy subjects imaged at the New England Eye Center at Tufts Medical Center and Massachusetts Institute of Technology between May and September 2012. Averaged central depth profiles were extracted from volumetric SS-OCT datasets. The intraocular distances, such as central corneal thickness (CCT), aqueous depth (AD), anterior chamber depth (ACD), crystalline lens thickness (LT), vitreous depth (VD), and axial length (AL), were measured and compared with a partial coherence interferometry device (IOLMaster; Carl Zeiss Meditec, Inc., Dublin, CA) and an immersion ultrasound (IUS) A-scan biometer (Axis-II PR; Quantel Medical, Inc., Cournon d'Auvergne Cedex, France). Reproducibility of the measurements of intraocular distances, correlation coefficients, and intraclass correlation coefficients. The standard deviations of the repeated measurements of intraocular distances using SS-OCT were 6 μm (CCT), 16 μm (ACD), 14 μm (AD), 13 μm (LT), 14 μm (VD), and 16 μm (AL). Strong correlations among all 3 biometric instruments were found for AL (r > 0.98). The AL measurement using SS-OCT correlates better with the IOLMaster (r=0.998) than with IUS (r=0.984). The SS-OCT and IOLMaster measured higher AL values than ultrasound (175 and 139 μm, respectively). No statistically significant difference in ACD between the optical (SS-OCT or IOLMaster) and ultrasound methods was detected. High intersession reproducibility of SS-OCT measurements of all intraocular distances was observed with intraclass correlation coefficients >0.99. The SS-OCT using VCSEL technology enables full eye length imaging and high-precision, noncontact ocular biometry. The measurements with the prototype SS-OCT instrument correlate well with commercial biometers. The SS-OCT biometry has the potential to provide clinically useful comprehensive biometric parameters for pre- and postoperative eye evaluation.

Retinal, anterior segment and full eye imaging using ultrahigh speed swept source OCT with vertical-cavity surface emitting lasers

We demonstrate swept source OCT utilizing vertical-cavity surface emitting laser (VCSEL) technology for in vivo high speed retinal, anterior segment and full eye imaging. The MEMS tunable VCSEL enables long coherence length, adjustable spectral sweep range and adjustable high sweeping rate (50–580 kHz axial scan rate). These features enable integration of multiple ophthalmic applications into one instrument. The operating modes of the device include: ultrahigh speed, high resolution retinal imaging (up to 580 kHz); high speed, long depth range anterior segment imaging (100 kHz) and ultralong range full eye imaging (50 kHz). High speed imaging enables wide-field retinal scanning, while increased light penetration at 1060 nm enables visualization of choroidal vasculature. Comprehensive volumetric data sets of the anterior segment from the cornea to posterior crystalline lens surface are also shown. The adjustable VCSEL sweep range and rate make it possible to achieve an extremely long imaging depth range of ~50 mm, and to demonstrate the first in vivo 3D OCT imaging spanning the entire eye for non-contact measurement of intraocular distances including axial eye length. Swept source OCT with VCSEL technology may be attractive for next generation integrated ophthalmic OCT instruments.

VCSEL Technology for Green Optical Interconnects

State-of-the-art vertical-cavity surface-emitting laser (VCSEL) technology will be reviewed in terms of power consumption and reliability to realize the energy-efficient high-performance computing (HPC) and data centers. Intermediate wavelength (between short and long wavelength) VCSELs emitting at 1060 nm are promising candidates for the upcoming higher performance computing with energy saving.

Emerging applications for vertical cavity surface emitting lasers

Vertical cavity surface emitting lasers (VCSELs) emitting at 850 nm have experienced explosive growth in the past decade because of their many attractive optical features and incredibly low-cost manufacturability. This review reviews the foundations for GaAs-based VCSEL technology as well as the materials and device challenges to extend the operating wavelength to both shorter and longer wavelengths. We discuss some of the applications that are enabled by the integration of VCSELs with both active and passive semiconductor elements for telecommunications, both in vivo and in vitro biosensing, high-density optical storage and imaging at wavelengths much less than the diffraction limit of light.

Photonic crystal vertical-cavity surface-emitting lasers with true photonic bandgap

By calculating the band diagrams for the distributed Bragg mirrors of vertical-cavity surface-emitting lasers (VCSELs) with triangular two-dimensional lattice of etched holes we show that true photonic bandgap (PBG) confinement is possible for TE-like polarized light. We confirm this true PBG confinement for a low-index line defect as well as for a low-index cavity mode. Such PBG-VCSELs are compatible with the VCSEL technology and do not require a complicated assembly of three-dimensional photonic crystals.

Advances in photoreflectance characterisation of photonic (resonant‐cavity) and transistor epiwafers

AbstractAdvances in the application of non‐contact photoreflectance (PR) spectroscopy to the characterisation of epiwafer device materials are presented. The study examines both vertical cavity surface emitting laser (VCSEL) and heterojunction bipolar transistor (HBTs) device structures. Emphasis is placed on the technologically important applications of VCSEL device material characterisation, for which PR offers the only true non‐destructive testing capability, as well as upon the measurement of electric fields in device epiwafers for rf application transistors such as HBTs. This paper demonstrates the application of non‐destructive and rapid techniques for evaluation and control of compound semiconductor materials for both VCSEL and HBT technology. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)