This PDF file contains the front matter associated with SPIE Proceedings Volume 9001, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Avago’s 850nm VCSELs for applications requiring modulation at 25-28Gbps have been designed for -3dB bandwidths in excess of 19GHz over the extended temperature range of 0-85°C. The DBR mirrors have been optimized to minimize optical losses and thermal and electrical resistance. The active region is designed to provide superior differential gain for high optical bandwidth. In this paper we will describe the design for performance and manufacturability of Avago’s high speed 25-28Gbps VCSEL. Analysis of the high-speed modulation characteristics and results of wearout reliability studies will be presented. We will also discuss the manufacturability of this next generation of high performance, reliable lasers. The challenges of epitaxial growth and wafer fabrication along with the associated process control technologies will be described.

Principles of energy-efficient high speed operation of oxide-confined VCSELs are presented. Trade-offs between oxideaperture diameter, current-density, and energy consumption per bit are demonstrated and discussed. Record energyefficient error-free data transmission up to 40 Gb/s, across up to 1000 m of multimode optical fiber and at up to 85 °C is reviewed.

This paper presents recent development results of our 28-Gbps VCSELs featured with double intra-cavity structure and a lasing wavelength of 1060 nm. The double intra-cavity realizes very low cavity loss due to undoped semiconductor bottom DBR and dielectric top DBR layers. Compressively strained InGaAs MQW provides high differential gain that contributes to low power consumption and high reliability. Based on our 10-Gbps VCSEL structure, we carefully optimized MQW, selective oxide structure, cavity length, and doping profile in order to achieve high speed operation while maintaining high reliability and other laser performances. The developed VCSELs exhibit modulation 3 dB-bandwidth exceeding 20 GHz and D-factor of 10 GHz/(mA)^1/2. Typical threshold current and slope efficiency are 0.5 mA and 0.5 W/A, respectively. The paper also discusses static and dynamic characteristics of VCSELs with various oxide aperture sizes simultaneously fabricated on the same wafer. For a longer transmission distance and better optical coupling to a multimode fiber, optical lateral confinement is precisely controlled to reduce spectral width as well as far-field pattern. Clearly opened eye diagrams are obtained at a bit rate of 28 Gbps. Bit error rate tests are also performed and 28 Gbps error free transmission has been confirmed over 300 meters of multimode-fiber optimized for 1060 nm with a PRBS pattern length of 2³¹-1.

Even though the lane speed of VCSEL based AOC and transceivers has reached 25 Gbps and beyond [1-7], parallel optics are getting even more important in order to meet the increasing demand for aggregate bandwidths in upcoming applications, among others, 100 Gigabit Ethernet, Infiniband EDR, or EOM (embedded optical modules). As 100 Gbps can be achieved by, e.g., 4 times 25 Gbps using standard QSFP form factor, different approaches are using large scale 2D VCSEL arrays operating at lower lane speeds. Early work on 2D VCSEL based transceivers has already been presented beginning of this century [8] and recent work also addressed the potential of this technology [9,10]. In 2013, Compass EOS has introduced a 1.34 Tbps core router solution [11,12,13] that incorporates 2D VCSEL arrays of 14x12 emitters designed and manufactured by Philips U-L-M Photonics. The VCSEL array is mounted face down onto a CMOS ASIC, directly on top of the analog area. The emission wavelength of 1000 nm allows for substrate side emission and thus for flip-chip mounting as well as the possibility of integrating 2D microlens arrays onto the stack of CMOS and VCSEL array. After briefly introducing the router with regard to the incorporated VCSEL technology we discuss the design and performance of the VCSEL array. Finally, the assembly solution for this most compact and dense transceiver solution is presented.

A novel approach for bandwidth augmentation for direct modulation of VCSELs using transverse-coupled-cavity (TCC) scheme is raised, which enables us to tailor the modulation-transfer function. The base structure is similar to that of 3QW VCSELs with 980 nm wavelength operation. While the bandwidth of conventional VCSELs was limited by 9-10 GHz, the 3-dB bandwidth of TCC VCSEL with aperture diameters of 8.5×8.5𝜇m² and 3×3𝜇m² are increased by a factor of 3 far beyond the relaxation-oscillation frequency. Our current bandwidth achievement on the larger aperture size is 29 GHz which is limited by the used photo-detector. To the best of our knowledge this is the fastest 980 nm VCSEL.

With the use of SiO₂/SiC based movable MEMS-DBR, the continuous tuning range of electrically pumped MEMS-VCSEL can be extended to > 140 nm. The high refractive index contrast of Δn > 1 between SiO₂ and SiC reduces the needed number of layers (11 layers) and broadens the spectral width of the reflectivity (448nm for R > 99.5 %) by more than a factor of two compared to the material system SiO₂/Si₃N₄ (23 layers / 216nm for R > 99.5 %), which has been used for the current world record continuous tuning range of 100nm of an electrically pumped MEMS-VCSEL. The smaller number of needed DBR-layers enables a significant reduction of the overall mirror thickness, which enables a further miniaturization of the device and thus an increase of the free spectral range (FSR), the ultimate limit for continuous wavelength tuning. In this paper we evaluate the performance advantages of using SiO₂/SiC based MEMS-DBR for tunable VCSEL by using Transfer-matrix method simulations.

A novel concept to form a photo-detector integrated VCSELs using transverse-coupled-cavity (TCC) scheme is demonstrated. In our configuration one cavity suppressed by the reverse bias voltage at 1volt, while the other cavity used as a laser. Proton-implantation was used in order to prevent the current leakage. The formation aperture diameter of each cavity gives us multimode and quasi-single mode condition. Our preliminary results on L-I indicate the possibility of continues tracking of photocurrent in the range of 0.7- 10 mA, which is limited by the threshold and saturation level of the laser side cavity.

We show numerically that many recently proposed GaN-based VCSEL cavities, with DBR mirrors deposited onto the current aperture, balance dangerously close to the border between the guided and antiguided regime. A guided cavity is often preferred because of its lower optical loss, but a strongly antiguided cavity offers built-in modal discrimination favoring single fundamental mode operation. We show that very small changes in the VCSEL structure are sufficient to strongly change the guiding character of the VCSEL cavity, and that thermal lensing caused by device self-heating under operation can dramatically reduce the optical loss but not the modal discrimination in the antiguided cavities.

Via experimental results supported by numerical modeling we report the energy-efficiency, bit rate, and modal properties of GaAs-based 980 nm vertical cavity surface emitting lasers (VCSELs). Using our newly established Principles for the design and operation of energy-efficient VCSELs as reported in the Invited paper by Moser et al. (SPIE 9001-02 ) [1] along with our high bit rate 980 nm VCSEL epitaxial designs that include a relatively large etalonto- quantum well gain-peak wavelength detuning of about 15 nm we demonstrate record error-free (bit error ratio below 10^-12) data transmission performance of 38, 40, and 42 Gbit/s at 85, 75, and 25°C, respectively. At 38 Gbit/s in a back-toback test configuration from 45 to 85°C we demonstrate a record low and highly stable dissipated energy of only ~179 to 177 fJ per transmitted bit. We conclude that our 980 nm VCSELs are especially well suited for very-short-reach and ultra-short-reach optical interconnects where the data transmission distances are about 1 m or less, and about 10 mm or less, respectively.

Over the last 20 years, nearly 1 billion VCSELs have been shipped, the vast majority of them emitting at 850nm using GaAs active regions, and primarily used in data communications and optical tracking applications. Looking to the future, the ever increasing speed of data communications is driving the VCSEL to evolve with more complex active regions, optical mode control, and alternate wavelengths to meet the more stringent requirements. We will discuss the current state of VCSELs for 28Gbps, and higher speeds, focusing on evolution to more complex active regions and alternate wavelength approaches, particularly as the market evolves to more active optical cables. Other high volume applications for VCSELs are driving improvements in single mode and optical power characteristics. We will present several evolving market trends and applications, and the specific VCSEL requirements that are imposed. The ubiquitous 850nm, GaAs active region VCSEL is evolving in multiple ways, and will continue to be a viable optical source well in to the future.

In this paper, we will present the development progress of 850-nm VCSELs operating at 25 Gbit/s and beyond at Sumitomo Electric Device Innovations USA. With improved growth of indium-containing quantum wells, we have demonstrated low-power-consumption VCSELs that can operate at 25 – 28 Gbit/s with reduced current density and enhanced reliability. We will also present recent progress on the improved performance of the new device in EDR cables.

For infrared illumination with wavelength range of 808nm-1064nm, vertical-cavity surface-emitting lasers (VCSELs) offer many advantageous properties including superior beam quality (such as low divergence, circular shape beam and speckle-free image), increased eye safety, high reliability and low manufacturing cost. We report our progress on highpower high-efficiency VCSELs and two dimensional (2D) VCSEL arrays for such illumination applications. GaAs-based VCSEL wafers are grown by MOCVD and processed into either top-emitting or bottom-emitting devices depending on the emission wavelength and applications. Results from both single devices and arrays are presented. In particular, record-high power conversion efficiency (PCE) of 63.4% with 300mW output was achieved from VCSELs at 1064nm. Such VCSELs also operate with <55% PCE at 50C. For a 2mm by 10mm array, 56.4% PCE with 150W output was demonstrated. Using those VCSELs and arrays as building blocks, various high power illuminators ranging from a few Watts to over 100 kiloWatts have been fabricated.

High-power VCSEL systems with multi kilowatt output power require a good electro-optical efficiency at the point of operation i.e. at elevated temperature. The large number of optimization parameters can be structured in a way that separates system and assembly considerations from the minimization of electrical and optical losses in the epitaxially grown structure. Temperature dependent functions for gain parameters, internal losses and injection efficiency are derived from a fit to experimental data. The empirical description takes into account diameter dependent effects like current spreading or temperature dependent ones like voltage drops over hetero-interfaces in the DBR mirrors. By evaluating experimental measurements of the light output and voltage characteristics over a large range of temperature and diameter, wafer-characteristic parameters are extracted allowing to predict the performance of VCSELs made from this material in any array and assembly configuration. This approach has several beneficial outcomes: Firstly, it gives a general description of a VCSEL independent of its geometry, mounting and detuning, secondly, insights into the structure and the underlying physics can be gained that lead to the improvement potential of the structure and thirdly the performance of the structure in arrays and modules can be predicted. Experimental results validate the approach and demonstrate the significantly improved VCSEL efficiency and the benefit in high power systems.

Spin polarized lasers, especially spin polarized vertical-cavity surface-emitting lasers (VCSEL) provide improved performance when compared to conventional, purely charge-based lasers. Advantages of these spin-enhanced devices lie in their reduced laser threshold, increased emission intensity, amplification of spin information, chirp control and possibilities for ultrafast modulation due to their faster dynamics. Utilizing a commercially available conventional VCSEL and additional spin polarized optical pumping we are able to enhance the modulation dynamics of a conventional VCSEL with new spin effects. Our experiments show polarization oscillations in the spin-photon system that result in oscillations of the circular polarization of the VCSEL emission. The resulting polarization oscillations are of significantly higher frequency than the direct modulation bandwidth of the VCSEL and persist for durations longer than the spin lifetime in the active region. Simulations based on a rate-equation model show that with an improved VCSEL layout it should be possible to reach oscillation frequencies well above 100 GHz. Here, we show that with multiple optical spin polarized pulses these oscillations can be coherently excited, amplified and also stopped. Using this excitation scheme, polarization oscillations faster than the purely charge-based dynamics can be achieved with half-cycle to multi-cycle duration. Various influences of unpolarized electrical bias, optical excitation power and delay between pulses will be discussed both theoretically and experimentally. Additionally, we analyze the qualification of this new concept for ultrafast optical communication.

We present the optimization of the carrier injection, heat flow and optical confinement aimed at single mode operation in anti-guiding long-wavelength VCSEL arrays. The analyzed structure incorporates InP/AlGaInAs quantum wells within an InP cavity. The cavity is bounded by GaAs/AlGaAs DBRs. The tunnel junction is responsible for carrier funneling into the active region. The air-gap etched at the interface between cavity and top DBR provides the confinement of the lateral modes. To rigorously simulate the physical phenomena taking place in the device we use a multi-physical model, which comprises three-dimensional models of optical (Plane Wave Admittance Method), thermal and electrical (Finite Element Method) phenomena. We perform an exhaustive modal analysis of a 1x3 VCSEL arrays. In the analysis we investigate the influence of the size and the distance between the emitters. As the result we illustrate the complex competition of the modes and determine the geometrical parameters favoring specific array modes in the considered array designs.

We report on the numerical analysis of the electrical and optical properties of current-injected III-N based vertical-cavity surface-emitting lasers (VCSELs) with three types of current confinement schemes: the conventional planar-Indium Tin Oxide (ITO) type, the AlN-buried type without ITO, and the hybrid type. The proposed hybrid structure, which combines an ITO layer and an intracavity AlN aperture, exhibits not only a uniform current distribution but also an enhanced lateral optical confinement. Thus, the hybrid type design shows a remarkably better performance including lower threshold current and series resistance compared with the planar-ITO type and the AlN-buried type. Furthermore, the multi-transverse mode lasing behavior induced by strong index guiding of the AlN aperture is suppressed to single transverse mode operation by reducing the aperture size. Such design provides a powerful solution for the high performance III-N based VCSELs and is also viable by using current state of the art processing techniques.

In this work we have proposed chaotic synchronization system using two identical electro-optical nonlinear delayed feedback systems (NDFS) utilizing VCSEL. This first time proposal has high potential to perform more sensitive chaotic dynamics for improvement of encrypted communications quality. In this system we have demonstrated the reduction of robustness to prevent tapping by someone else attaining higher correlation but only if the feedback gain is the same value. We have also demonstrated the variations of correlation if feedback gain has the slight difference. Moreover, we have demonstrated applications to encrypted communications using VCSEL.