Up to now applications for singlemode VCSELs were in low volume and high prized applications like tunable diode laser absorption spectroscopy (TDLAS, [1,2]) or optical interferometers. Typical volumes for these applications are in the range of thousands of pcs per year, with pricing levels of several 100 USD/pcs. New applications for singlemode VCSELs in consumer markets require manufacturing in very high volumes and at very low cost. Examples are laser-based optical mouse sensors, optical encoders, and rubidium atomic clocks for GPS systems [3,4]. U-L-M photonics presents manufacturing aspects, device performance and reliability data for these devices. The first part of the paper is dealing with high volume manufacturing of 850 nm singlemode VCSEL chips with very high efficiency and low operation current. Special processing technologies have been developed to achieve yields on 3 inch wafers of more than 90%. Wafer qualification procedures are discussed as well. The second part of the paper covers high volume packaging in TO and SMT type packages where very high packaging yields must be achieved. In the last part of the paper reliability issues are discussed, focused on the very high susceptibility of these devices to electrostatic discharge.

After some thirty years of materials analyses into the failure behavior of III-V semiconductor lasers, manufacturers of these devices still regularly encounter new failure mechanisms. This is due mainly to the implementation of progressively more complex and refined designs in devices that are, moreover, often subjected to increasingly more stressful operating or environmental conditions. It is therefore incumbent upon commercial laser manufacturers to maintain a persistent effort to search out and understand these new failure mechanisms, preferably before they are uncovered by an unhappy customer. Below, we describe our pursuit of a thorough materials-level understanding of VCSEL behaviors and illustrate some of the positive effects of these efforts.

Beginning with 4 Gigabit/sec Fibre-Channel, 1310nm vertical-cavity surface-emitting lasers (VCSELs) are now entering the marketplace. Such VCSELs perform like distributed feedback lasers but have drive currents and heat dissipation like 850nm VCSELs, making them ideal for today's high-performance interconnects and the only choice for the next step in increased interconnection density. Transceiver performances at 4 and 10 Gigabits/sec over fiber lengths 10-40km are presented. The active material is extremely robust, resulting in excellent reliability.

Understanding of the noise characteristics of a long wavelength (LW) vertical cavity surface-emitting laser (VCSEL) under optical back reflection is crucial for its applications in optical fiber data communication. VCSELs at near 1.31μm are tested and the relative intensity noise (RIN) is measured in the presence of different levels of optical reflection intensity. Innovative LW VCSEL packaging solutions are demonstrated to achieve robust low cost error-free data communication systems.

Yield enhancement and reliability improvement are main requirements in todays industrial VCSEL manufacturing. This requires a thorough understanding of process tolerances and the effects resulting from design variations. So far, this has been done by statistical analysis of experimental data. In this work, we use a state-of-the art technology computer aided design (TCAD) tool to analyze device reliability and yield for multiple VCSEL designs. The starting point is a physics-based simulation model that is calibrated to temperature-dependent static and dynamic measurements for a set of single- and multi-mode VCSELs lasing at 850 nm. Applying statistical variations that result from design modifications and process fluctuations, yield and reliability data are extracted by means of simulation. The yield will be derived by compliance to selected device specifications (such available single-mode power), and the device reliability is determined from an analysis of the internal device properties. As example, the oxide aperture and metal aperture design will be discussed, and a robust design will be presented.

We report results on strained InGaAs quantum well Vertical Cavity Surface Emitting Lasers (VCSELs) for optical interconnection applications. The structure was grown by metalorganic vapour-phase epitaxy (MOVPE) and processed as top p-type DBR oxide-confined device. Our VCSELs exhibit low threshold currents and deliver up to 1.77 mW in continuous wave operation at room temperature. Fundamental mode continuous-wave lasing at wavelengths beyond 1300 nm is demonstrated at room temperature. The thermal behaviour of our devices is explained through the threshold current-temperature characteristics. Furthermore, the effective index model is used to understand the modal behaviour.

The spectroscopic technique of coherent population trapping (CPT) enables an all-optical interrogation of the groundstate hyperfine splitting of cesium (or rubidium), compared to the optical-microwave double resonance technique conventionally employed in atomic frequency standards. All-optical interrogation enables the reduction of the size and power consumption of an atomic clock by two orders of magnitude, and vertical-cavity surface-emitting lasers (VCSELs) are preferred optical sources due to their low power consumption and circular output beam. Several research teams are currently using VCSELs for DARPA's chip-scale atomic clock (CSAC) program with the goal of producing an atomic clock having a volume < 1 cm^3, a power consumption < 30 mW, and an instability (Allan deviation) < 1x10^-11 during a 1-hour averaging interval. This paper describes the VCSEL requirements for CPT-based atomic clocks, which include single mode operation, single polarization operation, modulation bandwidth > 4 GHz, low power consumption (for the CSAC), narrow linewidth, and low relative intensity noise (RIN). A significant manufacturing challenge is to reproducibly obtain the required wavelength at the specified VCSEL operating temperature and drive current. Data are presented that show the advantage of operating at the D1 (rather than D2) resonance of the alkali atoms. Measurements of VCSEL linewidth will be discussed in particular, since atomic clock performance is especially sensitive to this parameter.

Optical time-domain reflectometry (OTDR) is an effective technique for locating faults in fiber communication links. The fact that most OTDR measurements are performed manually is a significant drawback, because it makes them too costly for use in many short-distance networks and too slow for use in military avionic platforms. Here we describe and demonstrate an automated, low-cost, real-time approach to fault monitoring that can be achieved by integrating OTDR functionality directly into VCSEL-based transceivers. This built-in test capability is straightforward to implement and relevant to both multimode and single mode networks. In-situ OTDR uses the transmitter VCSEL already present in data transceivers. Fault monitoring is performed by emitting a brief optical pulse into the fiber and then turning the VCSEL off. If a fault exists, a portion of the optical pulse returns to the transceiver after a time equal to the round-trip delay through the fiber. In multimode OTDR, the signal is detected by an integrated photodetector, while in single mode OTDR the VCSEL itself can be used as a detector. Modified driver electronics perform the measurement and analysis. We demonstrate that VCSEL-based OTDR has sufficient sensitivity to determine the location of most faults commonly seen in short-haul networks (i.e., the Fresnel reflections from improperly terminated fibers and scattering from raggedly-broken fibers). Results are described for single mode and multimode experiments, at both 850 nm and 1.3 μm. We discuss the resolution and sensitivity that have been achieved, as well as expected limitations for this novel approach to network monitoring.

Vertical cavity surface emitting lasers (VCSELs) designed for 10 G Ethernet over 300 m graded index multimode fiber in general have optical aperture diameters of 7 to 10 μm; cavities of these sizes support multiple transverse modes. The circularly symmetric structures are assumed to have no polarization selection, however, we show that orthogonally polarized lasing modes are often present and cause polarization partition noise which degrades the link bit error rate (BER). When a polarization selector was used in the link to allow only one polarization, the BER improved by two-order of magnitude even with the loss of more than 32 percent of the VCSEL average emitted power.

We report on a 1060 nm single transverse mode operation of an end-pumped vertical external cavity surface emitting laser (VECSEL). End-pumping scheme is enabled by capillary bonding of a VECSEL chip with a diamond heat spreader followed by a GaAs substrate removal by selective wet etching. The VECSEL structure is consisted of 10 periods of resonant periodic gain with an 8 nm InGaAs single quantum well at the antinodes of the standing wave optical field and a 35 pair AlAs/AlGaAs bottom distributed Brag reflector (DBR). Optical pump efficiency through the bottom mirror is enhanced by a modified DBR structure with a reduced reflectance in 808 nm pump wavelength region. A low threshold pump density of 433 W/cm² and over 45 W/W optical to optical conversion efficiency are achieved with reflectivity of 94 % output coupler at the heat spreader temperature of 20°C. The laser operates in a circular TEM₀₀ mode (M²<1.5) up to 7 W, and maximum power of 9.1 W is limited by our pump laser power.

A new concept is presented for realizing midwave-infrared vertical- cavity lasers based on an interband-resonant-tunneling-diode (I-RTD). Model equations are derived in terms of material and structure parameters for predicting the output power in an I-RTD laser device constructed of InAs/AlGaSb layers. Simulation made for midwave- infrared lasers suggest that the radiation output density power in this I-RTD laser can be achieved of the order of 40 W/cm².

An active photonic lattice is characterized by cross-cavity gain modulation (hole-burning) due to carrier depletion from adjacent cavity interactions. A VCSEL array offers a generic example for studying the physics of these, inherently nonlinear, active photonic lattices. The interplay between the non-linear frequency pulling, which allows phase locking over the array, and the coupling among the individual slow cavity oscillations, creates a rich behavior involving both steady-state and dynamic effects.

Two-dimensional photonic lattices with a low-index defect have been studied. Simulations demonstrate that this type of structure has potential for realizing single-spatial mode operation from a relatively large emitting aperture, making it ideal for fiber coupling applications. A 2-D finite difference model is used to calculate the radiation loss of the modes in various low-index defect based two-dimensional photonic lattices. The simulation results are also compared to the results from a comprehensive the 3-D bi-directional beam propagation model. These calculations have been used to guide mask design and the experimental realization of the defect VCSEL devices.

Phase-coupled arrays of vertical cavity surface emitting lasers (VCSELs) constitute a particular class of two-dimensional photonic crystal (PhC) structures in which the refractive index varies periodically in the plan normal to the beam propagation direction. The relatively simple implementation of these structures via lithography techniques permits the exploration of novel PhC configurations and the realization of novel spatial-mode-controlled VCSEL array structures. We review here the properties of VCSEL-based PhC structures realized using Bragg mirror patterning. Design and control of the photonic envelope functions in these devices using a variety of PhC homostructures and heterostructures are demonstrated and discussed. Potential applications of these structures in high power VCSELs, dynamic beam switching and optical image processing are mentioned.

Coherent transverse coupling in 2×2 arrays of defect cavities in photonic crystal (PhC) vertical cavity surface emitting lasers (VCSELs) is reported. Modification of the effective index and optical loss by design of the photonic crystal hole pattern results in evanescent coupling between the multiple defect cavities of a PhC VCSEL. Fabrication processes for these devices are discussed. Far field measurements are utilized to demonstrate both the out-of-phase and in-phase results. Room temperature continuous wave operating characteristics for the devices are provided, and a quantitative description of the coherently coupled operation is presented. The resulting agreement between the simulated and observed far fields is shown.

We designed and demonstrated a unique C-shaped nanoaperture (C-aperture) Vertical-Cavity Surface-Emitting Laser with an estimated maximum net power of 113 μW coming from a 70nm C-aperture. Simulation shows the near-field FWHM spot size at 30nm away from the C-aperture is 94nm and 108nm in X and Y direction. We estimate the peak near-field intensity from the C-aperture VCSEL to be as high as 13.7mW/μm². This high intensity and small spot size is promising to realize high-density near-field optical data storage.

We have optimized a resonant gain structure of a 920 nm vertical external cavity surface emitting laser. We found that a long saturated carrier lifetime in shallow quantum well (QW) under a high injection level restricts the laser performance. An insertion of non-absorbing laser in the middle of barrier layers with multi QWs is effective to reduce the saturated carrier lifetime and, therefore, to enhance the laser performance. With the optimized laser structure, which has 10 periods of triple In_0.09Ga_0.91 As QWs located at the anti-standing wave optical field with A_l0.3Ga_0.7As non-absorbing layers in the middle of GaAs barrier, we achieved 4.9 W operation at 920nm. Subsequently blue laser was achieved by employing an intra-cavity frequency doubling crystal LBO. As a result, we demonstrated 2 W single transverse mode operation in blue (460 nm) with a 20 W pump laser power. The conversion efficiency from 808 nm pump laser to the blue laser is measured to be 10 %.

The vertical cavity surface emitting laser (VCSEL) based on graded distributed Bragg reflectors (DBR) consisted of a top mirror of 20 pairs of Al_xGa_1-xAs/Al_yGa_1-yAs (x=0~0.9, y=0~0.12) quarter-wave stacks and a bottom mirror of 34 pairs of Al_yGa_1-yAs/Al_xGa_1-xAs quarter-wave stacks has been demonstrated. Using two proposed transfer matrix methods, the simulation of DBR reflectivity depending on temperature refractive index of Al_xGa_1-xAs and Al_yGa_1-yAs are discussed and investigated. The simulation results could be achieved to well predicted the DBR performance under operating temperature variances, i.e., the temperature on varying reflectivity and full width half maximum (FWHM), wavelength stop-band shifts of the laser reflector, where using the multi-layer films evolution software of essential Macleod and modified transfer matrix method, respectively. Under our simulation, assuming the physically VCSEL device feature such as the linear grading DBR structure sandwiched with a n-type GaAs substrate and air films, we have systematically studied the temperature effects on the key parameters of top and bottom DBR schemes. In contrast with the temperature dependent DBR on the 850nm-VCSEL characteristics simulated with the above two transfer methods, the temperature varying spectra of VCSEL are agreed with the our simulated results presented in this paper. Also the temperature dependent model of DBR based on refractive index of graded multi-Al_xGa_1-xAs/ Al_yGa_1-yAs has been proposed. So, a series of optoelectronic measurements experimentally confirm our results again. The maximum reflectivity of the top and bottom DBRs are 96.4 and 99.98%, respectively. The central wavelengths of the bandwidth spectra in the top and bottom DBR are same. i.e., 840nm. These results can be obtained the criteria for the high performance VCSEL design. The far-field patterns of transverse electromagnetic fields confined in <15μm active-layer aperture of selectively oxidized VCSEL have been observed.

Vertical-cavity surface-emitting lasers with variant compressively strained InGaAlAs quantum wells have been investigated. The valence band structures, optical gain spectra, and threshold properties of InGaAlAs/AlGaAs quantum wells are compared and analyzed. The simulation results indicate that the characteristics of InGaAlAs quantum wells can be improved by increasing the amount of compressive strain in quantum well. Furthermore, the properties of VCSELs with these compressively strained InGaAlAs quantum wells are studied numerically. The results of numerical calculations show that the threshold current and maximum output power can be enhanced by using higher compressively strained InGaAlAs quantum well. However, when the compressive strain is larger than about 1.5%, further improvement of the laser performance becomes minimal. The effects of the position and aperture size of the oxide-confinement layers on the laser performance are also investigated. Variation of the oxide layer design is shown to affect the current distribution which makes the temperature in the active region different. It is the main reason for the power roll-off in the VCSEL devices.