This PDF file contains the front matter associated with SPIE Proceedings Volume 7952, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The demand for the on board intra-chip optical interconnection as the "Green interconnect" have been growing so rapidly in order to catch up the speed of the performance development of high performance computing systems. In this report, our continuous study results expanding to intra-chip application in terms with power consumption and reliability are shown for the "Green" 1060nm VCSEL arrays developed by Furukawa Electric¹. As the basic performance level, the clear eye opening up to 20Gbps was achieved with low power dissipation level of 160fJ/bit with voltage swing level of 130mVpp. This value would be considered as the same level of the 140fJ/bit in 10Gbps operation with 75mVpp. In the reliability test, our large scale FIT rate test had been reached up to 7.8E7 device hours and the estimated FIT rate of 30FIT/ch was obtained from no failure sample and confidence level of 90%. Our wear-out study was performed with high stress test of 170°C ambient temperature and estimated failure rate for 10years service time was 0.3FIT/ch for this mode. Our 1060nm VCSEL with low power consumption level of 140fJ/bit and high reliability of 30FIT/ch would be projected to a light source for intra-chip application.

In this paper we will discuss 14 Gb/s 850 nm oxide VCSEL performance and reliability. The device is targeted for the 16G Fibre Channel standard. The 14 Gb/s 850 nm oxide VCSEL meets the standard's specifications over the extended temperature range to support transceiver module operation from 0C to 85C.

In this paper, we summarize the recent VCSEL development effort at Emcore. The focus of this effort is on performance, reliability and manufacturability. We will report the performance of Emcore's 14Gbps VCSEL for the new fibre channel application. We will also present the work on manufacturing both singlet and various VCSEL arrays, with performance up to 10Gbps, using a universal mask set to deliver both high performance and high manufacturability. The reliability data and the work on wafer level burn-in will be updated as well.

Arrays of high power VCSELs offer a unique opportunity to create a target intensity distribution which is tailored to the needs of a specific application. The concept presented here images the near field of the VCSEL onto the target. This is achieved by a combination of micro-lenses and field lenses in order to superimpose many VCSELs in an array. The optical system can be simple and the freedom to realize a wide variety of different intensity distributions with one and the same optics is large. The total power can be scaled by using arrays of VCSELs and due to the superposition of many emitters the illumination pattern has low speckle and is robust against single emitter failures.

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.

It has been traditional in discussions of VCSEL reliability to consider it as having a single major wearout component, with known temperature and current acceleration. Beyond this major component all other causes of failure are lumped into a small random failure component with an assumed-but not characterized-lower activation energy. Because reliability testing to assess the wearout acceleration requires very long test times to generate failures in the lowest-stress conditions, it is often assumed that the model that has been successful describing reliability in 850-nm data communications VCSELs can be extended to VCSELs of other wavelengths without significant modifications. This paper examines that assumption with regard to several VCSELs of different designs, and with emission wavelengths from below 800 nm to above 900 nm. A careful analysis reveals that even well-behaved wearout degradation might have several components whose relative contributions differ somewhat for different designs, with different resulting performance effects.

Spin-controlled vertical-cavity surface-emitting lasers (VCSELs) have been intensively studied in recent years because of the low threshold feasibility and the nonlinearity above threshold, which make spin-VCSELs very promising for spintronic devices. Here we investigate the circular polarization dynamics of VCSELs on a picosecond time scale after pulsed optical spin injection at room temperature. A hybrid excitation technique combining continuous-wave (cw) unpolarized electrical excitation slightly above threshold and pulsed polarized optical excitation is applied. The experimental results demonstrate ultrafast circular polarization oscillations with a frequency of about 11 GHz. The oscillations last inside the first undulation of the intensity relaxation oscillations. Via theoretical calculations based on a rate equation model we analyze these oscillations as well as the underlying physical mechanisms.

We present results on the electrical characterization of commercial fiber pigtailed 1. 55 μm 2.5 Gb/s VCSEL based on InAlGaAs active region, tunnel junction (TJ), air-gap aperture and InAlGaAs/InAlAs mirrors. The current-voltage (I-V) characteristics were measured and the results were fitted to the analytical expressions of an equivalent circuit considering the TJ in series with the active junction and a series resistance. Carrier capture/escape effects were considered in order to account for the reduced value of the drop in the measured differential resistance at threshold. The electrical parameters of both junctions were determined, showing that the TJ was responsible for most of the voltage drop at threshold. High frequency electrical impedance measurements were used to determine internal parameters as well as the role of external parasitics. The results were analyzed using a small signal equivalent circuit which includes the TJ, carrier capture/escape effects, the cavity parasitics, and the electrical access. A good agreement between the experimental and the equivalent circuit impedances at different bias was obtained by considering the differential resistances of the active and tunnel junctions extracted from the I-V characteristics, yielding reasonable values of the dynamic time constants and of the recombination coefficients.

Results of single mode and tunable GaSb-based VCSELs, with emission wavelengths above 2μm, are presented. Devices are aimed at trace gas sensing applications and operate in two important spectral windows - 2.3 μm and 2.6 μm. The first one is suitable for CO detection and in the second one strong absorption lines of H₂S and H₂O lie. VCSELs emitting at 2.33 μm operate in continuous-wave (CW) up to heatsink temperatures of 90 °C and deliver the maximum single-mode output power of 0.8 mW at 0°C with an aperture diameter of 6μm. With the introduction of inverted surface relief on top of the processed device, single mode operation has been extended up to 12 μm large aperture devices. The maximum wavelength tuning range of 20 nm has been achieved. VCSELs emitting at 2.6 μm operate in CW mode up to 55 °C, with the maximum single-mode output power of 0.4 mW, at -20 °C. They offer single transverse mode emission up to 9 μm large apertures. The maximum wavelength tuning of 10 nm is presented. Finally, first applications to trace gas sensing are also presented for 2.3 μm GaSb-based VCSELs.

We report on designs for compact VCSEL sensors for use in hydrogen gas detection. We discuss 980nm VCSELs coated with Pd, which has been proven to react with hydrogen. During this reaction, the device undergoes hydrogen induced lattice expansion (HILE) which causes two distinct effects that can be detected at the output. These two effects are a red-shift in the emission wavelength and a decrease in the output power. The compact VCSELs will be positioned into a 2D array with varying mesa diameters and palladium thickness in order to distinguish and track the specific level of hydrogen present in the atmosphere.

Continuous monitoring of methane emissions has assumed greater significance in the recent past due to increasing focus on global warming issues. Many industries have also identified the need for ppm level methane measurement as a means of gaining carbon credits. Conventional instruments based on NDIR spectroscopy are unable to offer the high selectivity and sensitivity required for such measurements. Here we discuss the development of a robust VCSEL based system for accurate low level measurements of methane. A possible area of application is the measurement of residual methane whilst monitoring the output of flare stacks and exhaust gases from methane combustion engines. The system employs a Wavelength Modulation Spectroscopy (WMS) scheme with second harmonic detection at 1651 nm. Optimum modulation frequency and ramp rates were chosen to maintain high resolution and fast response times which are vital for the intended application. Advanced data processing techniques were used to achieve long term sensitivity of the order of 10^-5 in absorbance. The system is immune to cross interference from other gases and its inherent design features makes it ideal for large scale commercial production. The instrument maintains its calibration and offers a completely automated continuous monitoring solution for remote on site deployment.

Infrared illumination is used in the commercial and defense markets for surveillance and security, for high-speed imaging, and for military covert operations. Vertical-cavity surface-emitting lasers (VCSELs) are an attractive candidate for IR illumination applications as they offer advantageous properties such as efficiency, intrinsically low diverging circular beam, low-cost manufacturing, narrow emission spectrum, and high reliability. VCSELs can also operate at high temperatures, thereby meeting the harsh environmental requirements of many illuminators. The efficiency and brightness of these VCSELs also reduce the requirements of the power supply compared to, for example, an LED approach. We present results on VCSEL arrays for illumination applications, as well as results on VCSEL-based illumination experiments. These VCSELs are used in illuminators emitting from a few Watts up to several hundred Watts. The emission of these VCSEL-based illuminators is speckle-free with no interference patterns. Infra-red illumination at up to 1,600ft (500m) from the source has been demonstrated using VCSEL-based illumination, without any optics.

The progressive penetration of optical communication links into traditional copper interconnect markets greatly expands the applications of vertical cavity surface emitting lasers (VCSELs) for the next-generation of board-to-board, moduleto- module, chip-to-chip, and on-chip optical interconnects. Stability of the VCSEL parameters at high temperatures is indispensable for such applications, since these lasers typically reside directly on or near integrated circuit chips. Here we present 980 nm oxide-confined VCSELs operating error-free at bit rates up to 25 Gbit/s at temperatures as high as 85 °C without adjustment of the drive current and peak-to-peak modulation voltage. The driver design is therefore simplified and the power consumption of the driver electronics is lowered, reducing the production and operational costs. Small and large signal modulation experiments at various temperatures from 20 up to 85 °C for lasers with different oxide aperture diameters are presented in order to analyze the physical processes controlling the performance of the VCSELs. Temperature insensitive maximum -3 dB bandwidths of around 13-15 GHz for VCSELs with aperture diameters of 10 μm and corresponding parasitic cut-off frequencies exceeding 22 GHz are observed. Presented results demonstrate the suitability of our VCSELs for practical high speed and high temperature stable short-reach optical links.

As the density of transistors in CMOS integrated circuits continues to roughly double each two years the processor computational power also roughly doubles. Since the number of input/output (I/O) devices can not increase without bound I/O speed must analogously approximately double each two years. In the Infiniband EDR standard (2011) a single channel bit rate of 26 Gb/s is foreseen. The maximum reliable and efficient copper link length shrinks at bit rates above 10 Gb/s to a few meters at best. At higher bit rates the length of a given multimode fiber link must also shrink, due to both modal and wavelength dispersions. Although the modal dispersion in modern multimode OM3 and OM4 fibers that are optimized for 850 nm vertical-cavity surface-emitting lasers (VCSELs) is reduced, the wavelength dispersion remains a serious issue for standard multimode VCSELs. An ultimate solution to overcome this problem is to apply single-mode VCSELs to extend and ultimately maximize the link length. In this paper we demonstrate recent results for single-mode VCSELs with very high relaxation resonance frequencies. Quantum well 850 nm VCSELs with record high 30 GHz resonance frequencies are demonstrated. Additionally single-mode data transmission at 35 Gb/s over multimode fiber is demonstrated. For comparison we also present specific device modeling parameters and performance characteristics of 850 nm single-mode quantum dot (QD) VCSELs. Despite a significant spectral broadening of the QD photoluminescence and gain due to QD size dispersion we obtain relaxation resonance frequencies as high as 17 GHz.

The impedance characteristics and the effects of photon lifetime reduction on the performance of high-speed 850 nm VCSELs are investigated. Through S₁₁ measurements and equivalent circuit modeling we show that the parasitic mesa capacitance can be significantly reduced by using multiple oxide layers. By performing a shallow surface etch (25 - 55 nm) on the fabricated VCSELs, we are able to reduce the photon lifetime by up to 80% and thereby significantly improve both static and dynamic properties of the VCSELs. By optimizing the photon lifetime we are able to enhance the 3dB modulation bandwidth of 7 μm oxide aperture VCSELs from 15 GHz to 23 GHz and finally demonstrate errorfree transmission at up to 40 Gbit/s.

We report the demonstration of a fully micro-fabricated vertical-external-cavity surface-emitting laser (VECSEL) operating at wavelengths near 850 nm. The external-cavity length is on the order of 25 microns, and the external mirror is a dielectric distributed Bragg reflector with a radius of curvature of 130 microns that is micro-fabricated on top of the active semiconductor portion of the device. The additional cavity length, relative to a VCSEL, enables higher output power and narrower laser linewidth, and micro-fabrication of the external mirror preserves the manufacturing cost advantages of parallel lithographic alignment.

We have been investigating the use of coaxial multimode VCSEL/PD (vertical cavity surface emitting laser/photodiode) pairs for positional sensing with emitter to target mirror distances on the order of 1mm. We have observed large variations in signal levels due to the strong optical feedback in these close-coupled systems, employing either heterogeneously integrated commercial components or our own monolithically integrated devices. The feedback effect is larger than anticipated due to the annular geometry of the photodetector. Even though there is very little change in the measured VCSEL total output power, the optical feedback induces variations in the transverse mode distributions in these multimode VCSELs. The higher order modes have a larger divergence angle resulting in changes in the reflected light power incident upon the active detector area for a large range of emitter/mirror separations. We will review the experimental details and provide strategies for avoiding these variations in detected power.

An experimental investigation of the modal selection induced by optical injection in 1550 nm multitransverse-mode VCSELs is performed. The free-running VCSEL emits in two transverse modes that are linearly polarized in a direction referred as parallel. We consider the situation in which parallel polarized laser light is injected in the VCSEL in order to select its fundamental transverse mode. We analyze the dependence of the modal selection process on the wavelength detuning between the externally injected signal and the fundamental mode. The injected power needed to select the fundamental mode as a function of the wavelength detuning is measured for several values of the bias current. This injected power exhibits a minimum at a positive wavelength detuning. The curves obtained for different bias currents are very close for positive and large wavelength detuning, while they are very separated for smaller detuning. The selection of the fundamental mode can be obtained with a value of the injected power that changes only slightly with the bias current when the wavelength detuning is large and positive. These results indicate that operation at large and positive wavelength detuning is of interest in the long-distance single-mode fiber transmission of multimode injection-locked VCSELs because the selection of the fundamental mode is obtained with an injected power that is almost independent on the VCSEL bias current. Both, the minimum injected power and the wavelength detuning at which it appears increase with the VCSEL bias current. We describe the relation between transverse mode selection and injection locking by comparing the dependence of both phenomena on the wavelength detuning. Modal selection is accompanied by injection locking only for large and positive values of the wavelength detuning. For small detuning values, with the VCSEL biased with a low (high) current, the injected power required for modal selection is lower (higher) than that needed for injection locking.

Data are presented demonstrating lithographic vertical-cavity surface-emitting lasers (VCSELs) and their scaling properties. Lithographic VCSELs have simultaneous mode- and current-confinement defined only by lithography and epitaxial crystal growth. The lithographic process of these devices allows getting uniform device size throughout a wafer and easy scaling to manufacture very small lasers. The semiconductor's high thermal conductivity enables the small lithographic VCSEL to have lower thermal resistance than an oxide-aperture VCSEL, while the lithographic fabrication produces high VCSEL uniformity even at small size. Very dense packing is also possible. Devices of 3 μm to 20 μm diameters are fabricated and scaling properties are characterized. 3 μm lithographic VCSELs produce output power of 4.1 mW, with threshold current of 260 μA and slope efficiency of 0.76 W/A at emission wavelength of ~980 nm. These VCSELs also have single-mode single-polarization lasing without the use of a surface grating, and have >25 dB sidemode- suppression-ratio up to 1 mW of output power. Lifetime tests demonstrate that 3 μm VCSEL operates for hundreds of hours at high injection current level of 85 kA/cm² with 3.7 mW output power without degradation. Scaling properties and low thermal resistance of the lithographic VCSELs can extend the VCSEL technology to manufacturable and reliable small size lasers and densely packed arrays with long device lifetime.