Reliability and characterization of 850 nm 25 Gbit/s (25G) InGaAs/AlGaAs vertical-cavity surface-emitting lasers (VCSELs) with oxide apertures, fabricated at OEpic Semiconductors, Inc., are presented. These 25G VCSELs have demonstrated a threshold current of <1.0 mA and a slope efficiency of 0.45 W/A. An optical output power of >;5.0 mW and rise and fall times of 18 and 25 ps, respectively, have been achieved. The non-hermetically sealed VCSELs were stress tested at 85o C under bias for up to 1200 hours to achieve accelerated failure modes to predict atmospheric-ambient reliability for applications such as board-to-board data communications. VCSEL failures are likely due to a combination of factors including the propagation of dislocation defects from the oxide layers, the incorporation of ambient oxygen into and near the active region, as well as layer cracking and separation near the active regions due to stress from the mechanical strain induced by the oxide layers. Our high-speed VCSELs use 0.5λ optical cavity lengths and oxide layers that are as close as 126 nm to the active region. OEpic’s design uses two or more oxide apertures to increase current confinement, allowing for greater overall current density. The proximity of the oxide layers to the active region, coupled with the increased heating of the active region due to a higher current density, likely results in a non-radiative recombination-based lasing failure. An increase of the optical cavity length, a decrease of the selective oxidation rate, and a reduction of the oxide layer thickness are measures that are expected to improve the VCSEL reliability.
We are reporting the first successful fabrication of 850-nm buried tunnel junction (BTJ) VCSELs. Multiple parameters were considered for the design. First, n-type dopants other than silicon had to be considered for an abrupt junction. Second, proper layer thickness had to be chosen. Finally, compatibility with regrowth and processing had to be ensured. In this paper the successful fabrication and performance of 850-nm BTJ VCSELs with tunnel junctions comprised of GaAs and AlGaAs materials is demonstrated. Key achieved parameters include a significant improvement in the slope efficiency from approximately 0.45 W/A in an oxide-aperture VCSEL to over 0.6 W/A.
We establish an empirical model to project the highest power output from a photovoltaic power converter (PPC). This model helped us achieve over one watt electrical output power from a single fiber channel. A total of 1.2W electrical power output from two parallel connected 8-segment devices was obtained from a well heat-sunk package with 4W laser illumination from a single fiber. To the best of our knowledge, this is the first time that, over one watt electrical power has been delivered by a single fiber channel. Over 30% power conversion efficiency was maintained in this high power conversion process, whereas the power conversion efficiency was over 40% at low laser input power. This high electrical power output enables more applications in sensing, safing, or arming that could not be achieved before due to less available power. It also further strengthens the position of this unique solution of providing isolated power in harsh, noisy and high-voltage environments.
In this work, we report a highly efficient Photovoltaic Power Converter (PPC) suitable for 920 nm to 970 nm InGaAs MQW lasers for the first time. The epitaxial layers were grown by low pressure MOCVD on the semi-insulting GaAs substrate. The epi layers consist of a p-n junction of In0.12Ga0.88As and the window layer of p+ AlInGaAs. The device is made of seven or eight pie-segments of equal area series-connected by means of air-bridges. Under 500mW of 940nm laser illumination, the open-circuit voltage of the eight-segment InGaAs chip is 6.7V. The short-circuit current is 29.7mA. Its maximum delivered electrical power is 171.2mW, equal to a 34.2% overall power conversion efficiency. We also demonstrate the high temperature characteristic and stability of the device.
Photovoltaic power converters transform optical power into electrical power, which is inherently immune to RF, EMI, high voltage, and lightning effects. Capable of powering electronic circuitry directly over optical fiber in a wide variety of applications, this technology has been validated in industries such as electric power, communications, remote sensing and aerospace. From no more than a laboratory curiosity less than fifteen years ago, power-over-fiber, or photonic power, has established itself in thousands of industrial operations worldwide. Optical energy for pre-amplifiers or low-power transmitters as well as switches and relays can be efficiently delivered through noise immune and non-conductive optical fiber. These advantages are also readily available for safe and arm applications since optical fiber is immune to electrical noise, magnetic fields and conduction of unexpected electrical currents. Since it is made from glass, a dielectric fiber is impervious to electromagnetic interference. High optical power is readily delivered through fiber, and conversion of optical to electrical energy at the remote site with efficient photovoltaic converters is routine.
Optical power provides a novel and often superior way of delivering power to electronic sensors and transducers. Total immunity to lightning and other electromagnetic interference comes from the use of fiber optics to provide power and data communication. The key element in any optically powered sensor or transducer is a photovoltaic power converter developed by Photonic. This device converts light into electrical energy for powering of the sensor and associated circuitry. Pertinent design issues include, choice of light source, minimization of power consumption, single vs. dual fiber, data protocol and level of integration. In addition to a discussion of these issues, a brief outlook on the future of optically powered systems is presented.
Using an uncoated monolithic single-contact distributed feedback (DFB) laser, transmission of 2 Mb/s data at a subcarrier frequency of 35 GHz over 2.2 km of optical fiber by resonant modulation is demonstrated. Modulation response of 60 MHz with more than 1 GHz of enhancement at round trip frequency, carrier-to-noise ratio and bit-error-rate results are reported. The tolerance of the resonant round-trip frequency to the DFB facet cleaving process and the device length uncertainty due to cleaving is also addressed in detail by computer simulation.