Photonic integration enabling new multiplexing concepts in optical board-to-board and rack-to-rack interconnects

New broadband applications are causing the datacenters to proliferate, raising the bar for higher interconnection speeds. So far, optical board-to-board and rack-to-rack interconnects relied primarily on low-cost commodity optical components assembled in a single package. Although this concept proved successful in the first generations of optical-interconnect modules, scalability is a daunting issue as signaling rates extend beyond 25 Gb/s. In this paper we present our work towards the development of two technology platforms for migration beyond Infiniband enhanced data rate (EDR), introducing new concepts in board-to-board and rack-to-rack interconnects. The first platform is developed in the framework of MIRAGE European project and relies on proven VCSEL technology, exploiting the inherent cost, yield, reliability and power consumption advantages of VCSELs. Wavelength multiplexing, PAM-4 modulation and multi-core fiber (MCF) multiplexing are introduced by combining VCSELs with integrated Si and glass photonics as well as BiCMOS electronics. An in-plane MCF-to-SOI interface is demonstrated, allowing coupling from the MCF cores to 340x400 nm Si waveguides. Development of a low-power VCSEL driver with integrated feed-forward equalizer is reported, allowing PAM-4 modulation of a bandwidth-limited VCSEL beyond 25 Gbaud. The second platform, developed within the frames of the European project PHOXTROT, considers the use of modulation formats of increased complexity in the context of optical interconnects. Powered by the evolution of DSP technology and towards an integration path between inter and intra datacenter traffic, this platform investigates optical interconnection system concepts capable to support 16QAM 40GBd data traffic, exploiting the advancements of silicon and polymer technologies

Efficient optoelectronic de-embedding for VCSEL intrinsic response extraction

In this present work, we propose a new method to remove the parasitics contribution to the VCSEL chip response,in order to obtain the intrinsic transmission behavior. It has been observed that the S11 reflection coefficient of the chip is only due to the electrical access to the chip composed by the transmission line and cavity contacts. This allows us to decompose the chip into two cascaded subsystems representing the electrical access and the optical cavity respectively. An equivalent electrical circuit is developed for the electrical access behavior and, combined with the transfer matrix formalism, it becomes possible to remove the parasitics contribution from the measured S21 response. In this way, the intrinsic 3-dB bandwidth of the VCSEL can be determined

Dynamic properties of silicon-integrated short-wavelength hybrid-cavity VCSEL

We present a vertical-cavity surface-emitting laser (VCSEL) where a GaAs-based "half-VCSEL" is attached to a dielectric distributed Bragg reflector on silicon using ultra-thin divinylsiloxane-bis-benzocyclobutene (DVS-BCB) adhesive bonding, creating a hybrid cavity where the optical field extends over both the GaAs- and the Si-based parts of the cavity. A VCSEL with an oxide aperture diameter of 5 mu m and a threshold current of 0.4 mA provides 0.6 mW output power at 845 nm. The VCSEL exhibits a modulation bandwidth of 11 GHz and can transmit data up to 20 Gbps

Tunable MEMS VCSEL on Silicon substrate

We present design, fabrication and characterization of a MEMS VCSEL which utilizes a silicon-on-insulator wafer for the microelectromechanical system and encapsulates the MEMS by direct InP wafer bonding, which improves the protection and control of the tuning element. This procedure enables a more robust fabrication, a larger free spectral range and facilitates bidirectional tuning of the MEMS element. The MEMS VCSEL device uses a high contrast grating mirror on a MEMS stage as the bottom mirror, a wafer bonded InP with quantum wells for amplification and a deposited dielectric DBR as the top mirror. A 40 nm tuning range and a mechanical resonance frequency in excess of 2 MHz are demonstrated

Long wavelength VCSEL-by-VCSEL optical injection-Locking

VCSEL-by-VCSEL optical injection-locking to obtain high cut-off frequencies of 1.3 μm Vertical-Cavity Surface-Emitting Lasers (VCSELs) is demonstrated. A detailed physical explanation of the underlying mechanism is presented. VCSELs from the same wafer have been used in a master-follower configuration. Two probe stations are used in this experiment to power-up two VCSELs simultaneously. Polarization insensibility of the injection-locking is demonstrated and a novel architecture is proposed to achieve cut-off frequency doubling. For the first time a high cut-off frequency is achieved through optically injection-locking the satellite mode of a long wavelength VCSEL. Injection-locking spectra with variable injection-powers and variable detuning values have been obtained and methods have been proposed to obtain high cut-off and/or resonance frequencies. A rate-equation based model is presented. Simulations have been carried out using this model. Finally, a linear increases in the follower VCSEL cut-off frequency with increasing injected-power is demonstrated by using a semiconductor optical amplifier

Theory and simulation of subwavelength high contrast gratings and their applications in vertical-cavity surface-emitting laser devices

This work intends to fully explore the qualities and applications of subwavelength gratings. Subwavelength gratings are diffraction gratings with physical dimensions less than the wavelength of incident light. It has been found that by tailoring specific dimension parameters, a number of different reflection profiles can be attained by these structures including high reflectivity or low reflectivity with broad and narrow spectral responses. In the course of this thesis the physical basis for this phenomenon will be presented as well as a mathematical derivation. After discussion of the mechanics of the reflection behavior, the methods used in modeling subwavelength gratings and designing them for specific functions will be explored. Following this, the fundamentals of vertical-cavity surface-emitting lasers (VCSELs) will be discussed, and the applications of subwavelength gratings when used with these lasers will follow. Several devices, both theoretical proposals and fabricated examples, will be presented in addition to the available performance measurements. Finally, the fabrication challenges that restrict subwavelength gratings from adoption as standard components in VCSEL design will be considered with regard to ongoing fabrication research

Noise and signal modeling of various VCSEL structures

Current evolution in Datacoms and Gigabit Ethernet have made 850nm Vertical Cavity Surface Emitting Lasers(VCSEL) the most important and promising emitter. Numerous different structures have been growth, to obtain bestcurrent confinement and then to control the emitted light modal behavior. We have developed a small signal equivalent electrical model of VCSEL including Bragg reflectors, active area, chip connection and noise behavior. Easy tointegrate with classical software for circuit studies, this model which is widely adaptable for different structures takesinto account the complete electrical environment of the chip. An experimental validation for RF modulation up to 10GHz has been realized on oxide confined VCSEL, demonstrating that the model could be used to get realistic valuesfor the VCSEL intrinsic parameters.Including Langevin noise sources into the rate equations and using the same electrical analogy, noise current andvoltage sources can be added to the model. It allows good prediction for the RIN function shape up to 10GHz formonomodal emitter

GaAs-based subwavelength grating on an AlOx layer for a vertical-cavity surface-emitting laser

© 2020 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.A GaAs-based subwavelength grating on a thick (∼3/4*λ at 1300 nm) AlOx layer is designed, fabricated, and characterized. The AlOx layer as a low-index medium is oxidized from a 640-nm Al0.9Ga0.1As layer. The layer contraction of the Al0.9Ga0.1As layer after wet oxidation to AlOx is 4.9%. We fabricated GaAs-based subwavelength gratings on the AlOx layer showing a high reflectivity of 90% in the 1300-nm wavelength range, consistent with the simulation results. Such GaAs-based subwavelength gratings can be used as high-contrast grating mirrors for narrow-linewidth VCSELs, improving the mechanical stability and simplifying the device fabrication

Equivalent Circuit Model of High-Performance VCSELs

In this work, a general equivalent circuit model based on the carrier reservoir splitting approach in high-performance multi-mode vertical-cavity surface-emitting lasers (VCSELs) is presented. This model accurately describes the intrinsic dynamic behavior of these VCSELs for the case where the lasing modes do not share a common carrier reservoir. Moreover, this circuit model is derived from advanced multi-mode rate equations that take into account the effect of spatial hole-burning, gain compression, and inhomogeneity in the carrier distribution between the lasing mode ensembles. The validity of the model is confirmed through simulation of the intrinsic modulation response of these lasers.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeDFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Fabrication and characterization of integrable GaAs-based high-contrast grating reflector and Fabry-Pérot filter array with GaInP sacrificial layer

Integrable GaAs-based high-contrast gratings (HCGs) are fabricated and characterized, targeting applications in high-speed vertical-cavity surface-emitting lasers (VCSELs). A Ga 0.51 In 0.49 P sacrificial layer beneath the GaAs layer is employed to create a low index surrounding HCG strips by selective etching. Experimental results show that the finite-size HCG has a reflectivity of 93% from 1270 to 1330 nm for the transverse magnetic polarization, which is consistent with the calculated results. An HCG-based Fabry-Perot filter array formed by the different HCGs, air gap, and GaAs substrate is demonstrated. The measured resonance wavelengths of the filter arrays are consistent with the theoretical results, which implies that the resonance wavelength of such filters can be tuned by parameters of the HCG itself