Calculation of distortion performances of a given distributed feedback (DFB) laser for different frequency plans is a well-known problem when working with CATV AM-VSB optical links. One generally takes safety margins or performs measurements on the lasers with the requested frequency plans when it is possible. After investigating the most important theories proposed in the scientific literature, we have come to the conclusion that laser distortion can be described as the weighted contribution of two different distortion sources: leakage current and intrinsic distortion due to the laser oscillation mechanism itself. On the basis of the two preceding ideas we predict the evolution of the second-order two-tone intermodulation (IMD2) response as a function of frequency and operating point by cascading Volterra models of the laser leakage current and rate equations. The total composite second order (CSO) distortion can then be predicted with a '10.log' adding law and compared to distortion measurements, including clipping effects.

Chaotic stability of external cavity semiconductor laser under modulation is examined both theoretically and experimentally. When the modulation frequency is detuned below the cavity resonant frequency, the simulations show a two-frequency to three-frequency route to chaos, as depicted by the power spectrum and time series of the laser emission at different stages of detuning. This agrees with experimental observations of 1.3 micrometer wavelength distributed feedback (DFB) laser and ridge waveguide (RW) InGaAsP laser. The phase-space attractor of both DFB and RW lasers have well-defined structures at broadband chaotic state, which signifies the presence of dynamical determinism in this state.

The effect of coupling between quantum wells on the gain spectra, and on the differential gain is investigated assuming that the optical gain possess multiple peaks. The gain spectra showed many peaks located at the heavy-hole and light-hole transitions. Therefore, the lasers under investigation are being treated as multiple-level systems. It is shown that the dependence of these peaks is a function of the barrier thickness. Computer generated plots illustrate the use of analytic expressions for finding eigenvalues of the Schrodinger equation. Results and discussion for the gain spectra and for the differential gain are explained as bearing a relation to the bound-state energy eigenvalues. Such parameters of a GaInAsP-InP double quantum well laser are presented as a specific example.

Using small-signal analysis based on rate equations, the effect of carrier transport on the modulation bandwidth of multiple quantum well lasers (MQW) is analyzed. Based on effective transport time model, it is shown that there is an optimum value of the ratio between carrier capture time and escape time, at which the modulation bandwidth of MQW lasers achieves maximum. The theoretical results were compared with experimental data and satisfactory agreement has been found. Drift-diffusion approach has also been introduced, and some preliminary results are presented.

We report the first uncooled non-hermetic 1.3 micrometer InP-based communication lasers that have reliability comparable to their hermetically packaged counterparts for possible applications in fiber in the loop and cable TV. The development of reliable non-hermetic semiconductor lasers would not only lead to the elimination of the costs specifically associated with hermetic packaging but also lead the way for possible revolutionary low cost optoelectronic packaging technologies. We have used Fabry-Perot capped mesa buried heterostructure (CMBH) uncooled lasers with both bulk and MQW active regions grown on n- type InP substrates by VPE and MOCVD. We find that the proper dielectric facet passivation is the key to obtain high reliability in a non-hermetic environment. The passivation protects the laser from the ambient and maintains the proper facet reflectivity to achieve desired laser characteristics. The SiO facet passivation formed by molecular beam deposition (MBD) has resulted in lasers with lifetime well in excess of the reliability goal of 3,000 hours operation at 85 degrees Celsius/90% RH/30 mA aging condition. Based on extrapolations derived experimentally, we calculate a 15 year average device hazard rate of less than 300 FITs (as against the desired 1,500 FITs) for the combination of thermal and humidity induced degradation at an ambient condition of 45 degrees Celsius/50% RH. For comparison, the average hazard rate at 45 degrees Celsius and 15 years of service is approximately 250 FITs for hermetic lasers of similar construction. A comparison of the thermal only degradation (hermetic) to the thermal plus humidity induced degradation (non-hermetic) indicates that the reliability of these nonhermetic lasers is controlled by thermal degradation only and not by moisture-induced degradation. In addition to device passivation for a non-hermetic environment, MBD-SiO maintains the optical, electrical and mechanical properties needed for high-performance laser systems.

We have realized a highly efficient optical-coupling scheme and simple fabrication structure for laser-diode module by using a new assembly technique. In our module, laser-diode, GRIN rod lens, and single-mode fiber were hybridly integrated on a silicon platform by a passive alignment method. Accurate positioning of the laser in a lateral direction was achieved through the use of a center and side fiducial markers etched onto silicon dioxide film on the silicon platform. Lens and single-mode fibers were set into a V-groove in front of the center marker formed by an anisotropic etching process. The relative height in vertical direction between the lens and the fiber was determined by widths of the V-groove taking account of layer thickness of solder and the laser. Finally, axial positioning of the lens and the fiber were determined using markers on both sides of the V-groove, and the V-grooved lid was used to fix the lens and the fiber using PbSn solder. We attained a highly efficient coupling (coupling loss less than 3 dB) and simple assembly process using GRIN rod lens by a novel passive alignment, leading to low cost and excellent productivity.

We present data on the wide temperature operation of a high speed data link operating at nominally 1 micrometer wavelength. The single mode fiber packaged transmitter running at 1.2 GBit/s consists of a high speed laser diode packaged with a commercial laser driver chip. The laser is not cooled in any manner over the temperature range of operation and the link operates with low error rates without an optical isolator. The single mode fiber packaged receiver consists of a high speed photodiode packaged with a combination of a commercial transimpedance amplifier and a limiting amplifier.

An optical power of over 160 mW has been successfully achieved using 1.625-micrometer strained multiple quantum well lasers at a forward current of 800 mA in pulsed operation. Such high power is achieved by optimizing the separated confinement heterostructure layer thickness. The operating life of high power 1.625-micrometer lasers has been estimated from the results of accelerated aging at 45 degrees Celsius, and 300 mA and 500 mA under continuous-wave operation. No significant change in optical output power was observed up to 4500 hours. The mean-time-to-failure at driving currents of 300 mA and 500 mA, at an ambient temperature of 45 degrees Celsius, are estimated to be about 4.2 multiplied by 10⁴ hours and 3.5 multiplied by 10⁴ hours, respectively.

In order to meet the increasing market needs for uncooled lasers for such applications as fiber- in-the-loop, high efficiency, high power, and highly reliable 1.3 micrometer uncooled InGaAsP/InP strained multi-quantum well Fabry-Perot lasers were fabricated with 50 mm wafer processing. Slope efficiency as high as 0.39 W/A and peak power as high as 46 mW at 85 degrees Celsius was obtained by optimizing the device structure for high temperature operation. We have also demonstrated excellent uniformity and reproducibility over 6 wafers. Reliability was also shown to be very good. More than 10,000 chips sites are available on a 50 mm wafer, and the cost is expected to be low. Because of the high performance, these lasers are expected to be used for various applications.

An ultralow-threshold 1.3-micrometer InGaAsP/InP ten-element monolithic laser array has been grown on a p-InP substrate entirely by metal-organic vapor phase epitaxy. This was achieved by carefully optimizing the strained-MQW active layer, especially the amount of strain, the well thickness, the barrier thickness, the number of wells, and the active layer width. This array has a record-low threshold current, highly uniform threshold current characteristics (1.28 plus or minus 0.07 mA; slope efficiency of 0.37 plus or minus 0.01 W/A), extremely low operating current (14 mA under 5-mW output power), and long-term reliability. It is thus suitable as a practical light source in high-density parallel optical data-link applications. In addition, best-ever continuous-wave threshold currents of 0.58 mA at 20 degrees Celsius and 1.62 mA at 90 degrees Celsius, for a long-wavelength laser, were obtained by using a short cavity (100 micrometers) with high-reflection coatings. The reduced carrier lifetime and threshold current of an n-type modulation-doped strained-MQW laser were experimentally demonstrated to drastically reduce turn-on delay time.

Selective-area epitaxy over a patterned dual stripe oxide mask allows the fabrication of strained-layer buried heterostructure quantum well lasers in which the quantum well thickness and, hence, emission wavelength is defined anywhere on the wafer by the stripe width and spacing. This in-plane bandgap energy control allows the designer to fabricate devices with different wavelengths on the same wafer for integrated opto-electronic applications. Since no growth occurs on the oxide mask, the spacing between stripes defines the width of the lateral optical waveguide, and the width of the stripes defines the amount of growth rate and composition enhancement in the quantum well. A very wide range of emission wavelengths (i.e. 960 - 1060 nm) can be obtained over the wafer surface in a single growth. A number of novel and high performance photonic devices have been fabricated in this manner including sub-milliampere threshold current lasers, lasers integrated with waveguides, modulators, and detectors, multiple-wavelength WDM arrays, broad-band LEDs, and redundant sources.

Comparable gain can be obtained in semiconductor optical amplifiers (SOAs) with either bulk or strained-layer multiple quantum well (MQW) active layer. Their polarization dependence and saturation power are affected by strain and structure designs. In this study, SOAs with compressively strained MQWs have exhibited highest gain and saturation power, while buried waveguide SOAs with large optical cavity have lower polarization sensitivity than the ridge waveguide SOAs.

In this paper we report on the combination of a precision cleaved large spot laser and a silicon micromachined optical bench to achieve high coupling efficiencies by purely passive alignment. Coupling efficiencies of over 50% have been obtained by passively aligning precision cleaved large spot sized lasers to singlemode fiber on a silicon micromachined substrate. This is the highest known coupling figure reported for passive alignment. The packaging of semiconductor laser chips has always presented a range of technical problems due to the sub-micron tolerances required to obtain optimum coupling of the small laser spot size to the larger spot size of a singlemode fiber. Lasers have been developed that can ease these tolerances by matching the laser spot size to that of cleaved fiber. This is achieved by tapering the active layer to adiabatically expand the laser mode size. A method of controlling the physical size of laser diode chips to sub-micron accuracy has enabled these lasers to be bonded against substantial alignment features on a silicon micro-engineered optical bench which also includes a V-groove into which a cleaved single-mode optical fiber can be fixed. Results are also discussed for an alternative ferrule-based, non-hermetic laser packaging design which utilizes the relaxed alignment tolerances of the large spot lasers to give simple package assembly suitable for automation. Both of the packaging technologies discussed offer a viable route to obtaining the very low cost optoelectronic components required for fiber to the home networks.

Reliable non-hermetic photodiodes are expected to reduce the cost of optoelectronics used in fiber to the home and cable TV system. However, all reports to date indicate non-hermetic InGaAs/InP photodiodes do not have sufficient reliability for use in the systems. In this paper, we report the first data that conclusively shows, properly designed and manufactured non- hermetic InGaAs/InP photodiodes can be made with reliability sufficient to use in telecommunication systems. We have produced non-hermetic photodiodes whose hazard rate at 15 years of field use at 45 degrees Celsius and 50% RH is less than 100 FITs, the requirement for telecommunication systems.

Local access fiber optic systems and distributed gain fiber amplifier systems require low-cost and highly stable laser diode packages with high coupling efficiencies. These systems may use uncooled packaged lasers from the central office to the subscriber units in discrete or integrated transceiver packages. Low cost and high volume manufacturing technologies must be developed in order to produce these laser packages. A simple alternative to existing technologies is described in this paper. AT&T Bell Laboratories has been developing silicon optical bench (SiOB) technology for use as an integrated packaging platform for lasers, photodetectors and passive optical components. In this paper we describe an integrated optical sub-assembly for use in high volume and low cost laser packaging. The assembly integrates bond sites for a laser, a backface monitor photodetector and a metallized lensed fiber onto a single silicon optical sub-assembly. The approach allows for low cost batch processing, assembly and testing of components using the silicon wafer as a carrier and the use of automated pick and place machines for assembly.

Pulsed laser welding has proven to be the preferred bonding method that best facilitates the automated fiber alignment and bonding process of optoelectronic devices. However, a combination of considerations regarding (1) the high capital investment for a laser welding workstation (LWWS), (2) acquiring and developing the packaging technology for laser welding, and (3) the undeveloped demand in the market place have caused hesitation by many manufacturers in adopting the process. Typically, the majority of packages manufactured with laser welding have been higher-end priced devices. Further understanding and improvement of technical challenges, such as 'post-weld-shift' control, material selection, and package design, along with development of a cost-effective semi-automated LWWS are presenting a greater opportunity for a broader range of packages to be designed for laser welding, especially for low-cost singlemode datacom packages. The focus of the current work is to design a broad range of OE packages and develop a nanometer precision automation process for laser welding technology. The solution is recognized to be the combination of understanding the laser welding process, designing packages for laser welding, and developing an automation capability for manufacturing.

This paper describes the development of laser transmitter arrays for analog optoelectronic link applications up to 2 GHz. These modules have been developed in an attempt to utilize passive assembly and alignment operations for the purpose of reducing costs. To this end, silicon waferboard integration platforms and semiconductor laser arrays have been fabricated with special alignment features that allow passive assembly of flip-chip laser arrays to single-mode optical fiber arrays.

This manuscript summarizes the work presented at the meeting. A more complete paper has already been submitted to a journal. In an effort to adapt the analysis of coupling lenses to the use of optical design software, we demonstrate that the coupling efficiency of a system can be related to an apodized and normalized point spread function. This approach allows the evaluation, optimization and tolerancing of systems which contain a fair amount of aberration. Comparison of theoretical predictions with experimental results shows good agreement

A ray tracing model has been developed to optimize the design of a low cost polymer molded fiber optic coupling device for data communication applications. Important features of the model are (1) power tracking of each ray through each interface, (2) multi-dimensional optimization algorithms, (3) inclusion of large-angle rays, and (4) graphical ray path representation. Measured butt coupling of an LED to a 62.5 micrometer core multimode fiber was used for verification of the model. The fiber optic coupling device was then designed and good agreement between calculations and measured values was obtained.

Ball lenses are frequently used in low to mid-cost laser packages where coupling efficiency is not a major concern. As a single element, the low cost, high precision, and high symmetry of ball lenses offer considerable advantages in packaging. When moderately higher coupling efficiencies are necessary, two-lens designs (in which the first lens is spherical) are often used successfully. Since the aberrations scale with lens diameter, the coupling efficiency generally increases as the diameter of the ball lens decreases. However, placement tolerances become more critical as the lens diameter is reduced and can limit the minimum practical ball diameter. A compromise between higher coupling efficiency and workable tolerances is often encountered when the ball lens diameter is on the order of 500 micrometers. As a result, higher coupling packaging schemes often abandon ball lenses in favor of high NA molded aspheric elements which eliminate spherical aberrations altogether. However, high NA molded aspheres are relatively expensive, and since aberrations are only corrected for a small region on axis, the alignment and bonding of these lenses become critical. We analyze the problem of pupil distortion and spherical aberrations produced by ball lenses and propose potentially cost- effective designs for downstream aberration compensation.

We describe a design tool for analyzing coupling between laser diodes and waveguides. The calculation includes adding system aberration information from a ray trace to a diffraction calculation in order to estimate the distribution of light incident on the waveguide. The overlap integral is used to calculate coupling efficiency. A simple example is given that analyzes coupling from a single-mode laser diode to a single-mode fiber using a ball lens. Calculations are compared with experimental results.

Diffractive optical elements (DOEs) have many advantages over refractive optical elements including the ability to implement exotic function (such as flat-tops, line generators and splitting and combining functions), the ability to easily incorporate a variety of functions in to one element, lower volume and less weight. In addition to these advantages, diffractives offer 3 potential positive characteristics which are sometimes cited as drawbacks. These are: diffraction efficiency, dispersion and cost. In some applications, such as wavelength division multiplexing (WDM) or other applications in which it is desirable for different wavelengths of light to be affected in different manners, the highly dispersive nature of diffractives is an advantage. In other applications when the spectral width of the illumination is large (e.g. laser diodes when the case temperature varies over a wide range), the dispersion of DOEs can be a disadvantage. Diffraction efficiency, defined as the power diffracted into the desired diffraction order divided by the power incident on the DOE, can be very high or low depending on the application and design procedure. This paper focuses on these 3 potential advantages of diffractives. In the remainder of this paper each characteristic is discussed individually in order to show how the negative effects of each can be minimized and the positive effects enhanced.

The coupling efficiency of an optical transceiver module is calculated over a wide range of tolerances for the key design parameters. The yield of the manufacturing process depends upon the minimum acceptable coupling efficiency for the module. The sensitivity of yield in the presence of various tolerances is illustrated. Tradeoffs between two key lensed-fiber parameters are developed in order to maximize the yield.

Examples are presented of the application of Lawrence Livermore National Laboratory's expertise in photonics packaging. Several examples of packaged devices are described. Particular attention is given to silicon microbenches incorporating heaters and their use in semiconductor optical amplifier fiber pigtailing and packaging.

We describe advances in the development of high-power diffraction-limited lasers for single- mode fiber-coupled sources. The development of the tapered amplifier has led to the realization of a monolithic MOPA diode laser, which provides up to 3 W cw of single-spatial- mode output power. We further describe the implementation of the MOPA in fiber-coupled architectures that provide up to 1.2 W cw coupled into a single-mode optical fiber and some of the optical considerations unique to devices based on tapered amplifiers.

A method of improving the coupling efficiency of an elliptical light beam into an optical fiber is achieved with a novel cylindrical concave microlens. Coupling efficiencies of 87% from single transverse mode diode lasers into single-mode optical fiber have been achieved with this microlens when used in conjunction with a pair of bulk optic asphere lenses. The microlens is amenable to production processes, is effective for a wide range of beam aspect ratios and represents a significant improvement over the 60 - 65% coupling efficiency which is typical of volume fiber coupling techniques to date.