Integration Of Vertical-cavity Surface-emitting Lasers Research Articles

Hybrid Integration of VCSEL and 3-μm Silicon Waveguide Based on a Monolithic Lens System

We design an optical interface system for vertical coupling between vertical-cavity surface-emitting lasers (VCSELs) and 3-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> silicon waveguides. The system includes a photoresist lens and a total internal reflection mirror, which allows for passive alignment and flip-chip bonding (FCB) of VCSELs. The simulated coupling loss is 0.7 dB, in optimal conditions, which increases to 1 dB when 3- and 20-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> alignment tolerances are considered in lateral and longitudinal directions, respectively. The system is built by post-processing lens and metallic wiring on the backside of a 3-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> silicon photonic platform. After FCB and embedding of the VCSELs, the system performance is characterized, and VCSEL-to-waveguide coupling efficiency of &#x2212;7.5 dB is obtained.

Monolithic integration of VCSEL and coupled cavity RCEPD for short-reach single-fiber bi-directional optical interconnects

In this paper, we propose a monolithic integration of vertical-cavity surface-emitting laser (VCSEL) and coupled cavity resonant cavity enhancement photodiode (ccRCEPD). Based on this structure, a couple of matched chips is designed for single fiber bidirectional optical interconnects. That type of integration can easily put VCSEL and (photodiode) PD into one package, which not only reduces the costs of the device packages and even cut the costs of the optical system like beam splitter, but also can save the space in optical transceiver to make it tight. These chips’ VCSELs show a threshold current of 1.6 mA and 1.7 mA, and a slope efficiency of 0.74 W/A and 0.97 W/A. VCSELs’ modulation bandwidth is 9.5 GHz and 11.0 GHz, and PDs’ response bandwidth is 10 GHz. Furthermore, the modulation bandwidth can be higher if the material of the multiple quantum wells (MQWs) is transformed GaAs/AlGaAs to InGaAs/AlGaAs. And by optimizing, the 3dB bandwidth of PD will be higher.

Design and simulation of integration of vertical cavity surface emitting lasers and heterojunction bipolar transistor

Vertical cavity surface emitting lasers (VCSELs) are widely used in the field of short-range optical communication and optical interconnection because of their advantages such as low threshold current, large modulation bandwidth, easy two-dimensional integration, easy coupling with optical fibers and low cost. The VCSELs and heterojunction bipolar transistor (HBT) are longitudinal current devices, so they can be well integrated on the same wafer, and the output light power can be modulated by the HBT base current. Integration of VCSELs and HBT are designed in this paper. The VCSELs and PNP InGaP/GaAs HBT form a direct series structure. The reflectivity of DBR is 99.72% at a resonant wavelength of 850 nm and 99.57% after adding HBT separately. Therefore, the addition of HBT has little influence on the reflectivity of DBR at the resonant wavelength. The electro-optical characteristics of the integrated structure are simulated by using PICS3D software. An interim collector is added into the model in order to ensure that the simulation can be carried out smoothly. Firstly, HBT is conducted and the current flows from the emitter to the interim collector. Then, the voltage across the interim collector and the N-type electrode is increased to make VCSELs conducted and the current of the transition collector drop to zero. The interim collector can be removed from the actual structure because the current is zero. The simulation results show that the current gain coefficient is 400, and the maximum modulation rate of the base current to the output light power rises up to 280 mW/mA. The maximum temperature in the active region increases with the base current increasing, and the output light power first increases and then tends to be saturated. The ac optical gain characteristics of the integrated structure is simulated by PICS3D, and the simulation result shows that cutoff frequency exceeds 1 GHz. The addition of HBT limits the modulation rate of the integrated structure, and further optimization of HBT structure parameters and geometric dimension are needed to improve the modulation rate. The integrated structure and simulation method established in this paper can also be used to integrate LED, LD, DFB or other luminescent devices with HBT.

Monolithic vertical integration of VCSEL and RCEPD for bidirectional optical interconnects

In this letter, we demonstrate the monolithic vertical integration of vertical-cavity surface-emitting laser (VCSEL) with resonant cavity enhancement photodetector (RCEPD) for the application to bidirectional optical interconnect. Based on the optimal designed structure, the monolithic integrated device can realize optical decoupling and electrical isolation between its VCSEL unit and RCEPD unit. The VCSEL unit exhibits a threshold current of 1.65 mA, a slope efficiency of 0.58 W/A and 3 dB bandwidth of 12.8 GHz. Regarding the RCEPD unit, the width of its absorption quantum efficiency spectrum is 8 nm with a quantum efficiency of higher than 50%. The 3 dB response bandwidth of the RCEPD unit can be up to 65.7 GHz.

Athermalization and on-chip multi-wavelength integration of VCSELs employing thermally actuated micromachined mirrors

An athermal multi-wavelength vertical cavity surface emitting laser (VCSEL) array is demonstrated using a thermally actuated cantilever structure with different cantilever lengths. The cavity length of each VCSEL is precisely controlled via the deflection of the cantilever due to difference in the lattice constant of GaAlAs layers. Also, the thermally induced actuation of the cantilever reduces the cavity length as the ambient temperature increases, which compensates the thermal wavelength drift of the VCSEL. The wavelength drift could be reduced within ±0.017 nm/K, which is 4 times smaller than that of conventional VCSELs. The proposed multi-wavelength VCSEL array enables four wavelength channels with 2.5 nm spacing under uncooled operations.

Lateral integration of vertical-cavity surface-emitting laser and slow light Bragg reflector waveguide devices

We present the modeling and the experiment on the lateral integration of a vertical-cavity surface-emitting laser (VCSEL) and slow light Bragg reflector waveguide devices. The modeling shows an efficient direct-lateral coupling from a VCSEL to an integrated slow light waveguide. The calculated result shows a possibility of 13 dB chip gain and an extinction ratio over 5 dB for a compact slow light semiconductor optical amplifier (SOA) and electroabsorption modulator integrated with a VCSEL, respectively. We demonstrate an SOA-integrated VCSEL, exhibiting the maximum output power over 6 mW. Also, we fabricate a sub-50-μm long electroabsorption modulator laterally integrated with a VCSEL. An extinction ratio of over 15 dB for a voltage swing of 2.0 V is obtained without noticeable change of threshold. In addition, we demonstrate an on-chip electrothermal beam deflector integrated with a VCSEL.

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.

High-Power Single Transverse Mode Vertical-Cavity Surface-Emitting Lasers With Monolithically Integrated Curved Dielectric Mirrors

We report the monolithic integration of vertical-cavity surface-emitting lasers (VCSELs) with curved dielectric mirrors. The laser structure has an InGaAs/GaAs gain region and incorporates a photoresist pattern fabricated on the substrate side. A dielectric distributed Bragg reflector is applied on the curved photoresist surface which provides sufficient optical feedback for laser operation. On-wafer measurements at room temperature show single transverse mode output powers up to 15.0 mW under continuous wave operation.

A method to tune the cavity-mode wavelength of resonant cavity-enhanced photodetectors for bidirectional optical interconnects

A method to tune the cavity-mode wavelength of resonant cavity-enhanced photodetectors (RCE-PDs) is proposed. The proposed method can enable monolithic integration of vertical-cavity surface-emitting lasers and RCE-PDs to be a cost-competitive choice for bidirectional optical interconnection by reducing the amount of component and packaging costs presently involved. The properly tuned cavity-mode wavelengths remain effectively aligned within a temperature range of -10/spl deg/C/spl sim/50/spl deg/C.

Monolithic integration of vertical-cavity surface-emitting lasers with in-plane waveguides

The ability to couple light from a vertical-cavity surface-emitting laser into a planar, on-chip waveguide creates new opportunities for achieving higher levels of integration and functionality. Here we propose to use a strong grating etched into a waveguide defined into the top layer of the epitaxially grown structure, so that epitaxial regrowth is not required. By introducing a defect mode into the cavity we were able to achieve a 40% coupling efficiency even though light is coupled through a ninety degrees bend. We also show that polarization control of the vertical-cavity surface-emitting laser is enhanced by coupling to the defect mode. Calculations were performed using the finite-difference time-domain method.

A 36-channel parallel optical interconnect module based on optoelectronics-on-vlsi technology

We describe the packaging and testing of a two-dimensional array parallel-optics module with 36 channels with each channel operating up to 3.3 Gb/s. This represents the first commercial module based on direct integration of vertical-cavity surface-emitting lasers (VCSELs) onto silicon very large scale integration (VLSI) circuits using a hybrid optoelectronic-VLSI technology. The module eliminates wire bonds between the driver/receiver chips and the corresponding VCSELs thereby reducing crosstalk and power dissipation, simplifying packaging and alignment, and simultaneously improving bandwidth and total link jitter performance.

Monolithic integration of vertical-cavity surface-emitting laser and diffractive optical element for advanced beam shaping

We have demonstrated a vertical-cavity surface-emitting laser (VCSEL) with a monolithically integrated diffractive optical element (DOE) for advanced beam shaping. The DOE is a two-level surface relief, etched into the GaAs substrate beneath a bottom-emitting VCSEL. The combination generates a 4/spl times/4 array of focused spots 10 mm from the substrate with spot sizes down to less than 400 /spl mu/m, almost at the diffraction limit. Diffraction efficiencies of 29% and uniformity errors of 14% were measured.

Smart integration and packaging of 2D VCSEL's for high-speed parallel links

This paper reviews recent progress in the integration and packaging of two-dimensional (2D) vertical-cavity surface-emitting laser (VCSEL) arrays being developed for the use in high-speed parallel optical interconnections. It reviews the smart integration of VCSEL's with detecting, switching and latching functions through the integration of a VCSEL-thyristor and double-cavity phototransistor. It also describes self-alignment-packaging technologies for 2D VCSEL module that can be used in high-density parallel links. Various system applications, such as a distributed fiber switch used to enable crossbar interconnections with address switching functions and hyper-parallel transmission using an image fiber, are also examined.

Hybrid integration of VCSEL's to CMOS integrated circuits

Three hybrid integration techniques for bonding vertical-cavity surface-emitting lasers (VCSELs) to CMOS integrated circuit chips have been developed and compared in order to determine the optimum method of fabricating VCSEL based smart pixels for optical interconnects and free-space optical processing. Each of the three bonding techniques used different ways of attaching the VCSEL to the integrated circuit and making electrical contacts to the n- and p-mirrors. All three techniques remove the substrate from the VCSEL wafer leaving an array of individual VCSELs bonded to individual pixels. The 4/spl times/4 and/or 8/spl times/8 arrays of bonded VCSELs produced electrical and optical characteristics typical of unbonded VCSELs. Threshold voltages down to 1.5 V and dynamic resistance as low as 30 /spl Omega/ were measured, indicating good electrical contact was obtained. Optical power as high as /spl sim/10 mW for a VCSEL with a 20-/spl mu/m aperture and 0.7 mW with a 6-/spl mu/m aperture were observed. The VCSELs were operated at 200 Mb/s (our equipment limit) with the rise and fall times of the optical output <1 nS.

Thermal analysis of closely-packed two-dimensional etched-well surface-emitting laser arrays

A self-consistent thermal-electrical model of etched-well surface-emitting GaAs-AlGaAs lasers is applied to study thermal properties of two-dimensional (2-D) arrays. Temperature profiles across small- and moderate-size arrays are generated. Thermal problems associated with integration of vertical-cavity surface-emitting lasers (VCSEL's) into closely packed 2-D arrays are addressed. In particular, thermal crosstalk between elements of the array is investigated. The results indicate severe thermal crosstalk, even at relatively low pumping currents, with strong individual-element temperature-profile nonuniformities. The asymmetry of individual waveguides caused by skewed temperature distributions can be exploited for controlling supermode structure in phase-locked arrays. Optimization of 2-D etched-well laser array designs is presented, aimed at maximizing the optical output power density from the array. We find that the highest output power density is strongly increasing for arrays of small diameter emitters, and that the optimal center-to-center spacing between emitters is equal to /spl sim/2.5-3 times their diameter. >

Low-threshold 1.57-&amp;#x03BC;m VC-SEL's using strain-compensated quantum wells and oxide/metal backmirror

We present an electrically-pumped long wavelength vertical cavity surface-emitting laser (VC-SEL) using strain-compensated multiple quantum well gain medium and an oxide/metal backmirror. Design flexibilities such as using oxide/metal mirrors are possible because of the exceedingly high optical gain provided by strain-compensated multiple quantum wells. The gain medium is bonded to various substrates, including InP and Si, prior to device processing. This substrate transfer process facilitates heat sinking, and can be useful in the integration of VC-SEL's with other devices. The device operates at a single wavelength of 1.57 μm, and has a minimum threshold of 12 mA at room temperature under pulse pumping.

Demonstration of the n-channel vertical-cavity double-heterostructure optoelectronic switching laser and heterostructure field effect transistor

Optoelectronic integration of vertical-cavity surface-emitting lasers would be highly desirable for future optical interconnect and preprocessing applications. Configuring the double-heterostructure optoelectronic switch (DOES) as such a laser offers the potential for integration and utilization of the bistable switching action for thresholding and photonic switching operations. The authors present the initial results of fabricating the DOES as a simple, two-terminal, surface-emitting laser and as a heterostructure field-effect transistor (HFET). Pulsed threshold currents of 10 mA are obtained in conjunction with excellent, high-voltage contrast switching. The HFET had a peak transconductance of 40 mS/mm and a peak drain to source current density of 120 mA/mm. >

Inverting and latching optical logic gates based on the integration of vertical-cavity surface-emitting lasers and photothyristors

Inverting optical logic gates based on the monolithic integration of a vertical-cavity surface-emitting laser (VCSEL) with a heterojunction photothyristor (PNPN) are described. Logic functions INVERT, NAND, and NOR are experimentally demonstrated for the first time using latchable and cascadable PNPN/VCSEL switches, which can be triggered with very low optical energy, while producing high optical gain and optical contrast. These gates are integrable on a single epitaxial structure to provide multifunctional logic and memory arrays. >