Harold Hager

VCSEL optical subassembly for avionics fiber optic modules

With the growing maturation of vertical cavity surface emitting laser (VCSEL) technology as a source of commercial off-the-shelf components, the question of VCSEL suitability for use in avionics-qualifiable fiber-optic systems naturally follows. This paper addresses avionics suitability from two perspectives. First, measured performance and burn-in reliability results, determined from characterization of Honeywell VCSELs, are compared with application-based military and commercial avionics environmental requirements. Second, design guidelines for developing a cost-effective VCSEL optical subassembly (VCSEL/OSA) are outlined.

Potential opportunities for utilizing commercial optoelectronics in avionics fiber-optic networks

Industry studies indicate the feasibility of using both MCM-L/COB and silicon microbench passive alignment technology in harsh, high reliability environments such as military and commercial avionics systems. Moreover, in many cases, if proper design, materials, and packaging approaches, and assembly and quality assurance procedures are utilized, both MCM-L/COB and silicon microbench passive alignment technologies may actually enable design ad manufacturing of low cost avionics optoelectronics modules. Silicon microbench passive alignment packaging technology has been demonstrated for LED, PIN photodiode, VCSEL and edge emitting laser diode packaging. Although MCM-L/COB and silicon microbench passive alignment technologies have been shown to be ruggedizable for the avionics environment, additional reliability testing and infrastructure development work is required before they are implemented in real avionics systems. VCSELs and edge-emitting diode lasers can be reliably used in systems with excursions to high temperature avionics environments) if the total time-at-high temperature is kept modest. Simple temperature measuring circuits and laser diode drive current monitoring circuits for onboard diagnostics and maintenance could be implemented to ensure reliable operations of high-speed laser-based transmitters in the avionics environment.

Optoelectronic devices for fiber-optic sensor interface systems

A standardized interface for fiber-optic sensor systems based on wavelength-division- multiplexing (WDM) has been successfully demonstrated using a novel broad-spectrum quantum-well LED and a high-resolution waveguide spectrograph. This efficient interface allows a 40-decibel system loss in 20 sensor channels. The new broadband LED and slab- waveguide spectrograph represent key enabling components for the WDM interface system. The LED produces a spectral width a factor of 3 times larger than that from conventional edge emitting LEDs in the 750-900 nm range. The compact slab-waveguide spectrographs channel resolution (4-5 nm) and grating efficiency (>50%) compare favorably with other multimode WDM elements.

Wireless optical links for avionics applications

Recently there has been strong interest in wireless optical (WO) communication link applications in airplanes and avionics platforms for size, weight, power, cost, and electromagnetic interference (EMI) reduction. Wireless optical link has additional advantage of providing network security because the optical signal from wireless optical link is well confined within an airplane or avionics vehicle. In this paper we discuss some potential wireless optical link applications in commercial airplanes and the challenges in the implementation of wireless optical links for these applications. We will present our experimental results on using white LED (WLED), visible laser source and free-space small-form-factor (SFF) optical transceivers to demonstrate the viability of applying wireless optical links in avionics platforms.

Universal detachable optical connector for military and commercial aerospace fiber optic modules

Packard-Hughes Interconnect has developed a detachable connector for plugging to military and commercial aerospace fiber-optic modules. The connector comprises floating spring loaded fiber-optic termini with 1-mm ceramic ferrules, all contained within a 0.136-in thick, low-profile connector plug body. The connector is mated to the package via a patented retention clip mechanism which secures the plug body to metal posts attached to the package sidewall. Optical alignment between the connector plug terminus and the package is accomplished by an alignment sleeve and mating 1-mm ceramic ferrule mounted in the package nosetube. Connector demating is performed by actuating a release button mechanism integral to the connector plug body. The fiber-optic termini in the connector plug body are easily maintained without replacing the entire connector. This makes the repair/replacement process for a broken fiber pigtail or damaged terminus endface a low cost, fast, and simple operation. The insertion loss for a simplex connector mated to a Boeing FDDI Transmitter receptacle package using 100/140 micrometers graded index optical fiber is less than 0.5 dB at 1.3 micrometers wavelength.

Design of InGaAs strained quantum-well lasers for high-temperature operation

The effect of high temperature on the threshold gain and threshold current density of an InGaAs (GaAs based) strained quantum well laser is examined both theoretically and experimentally. It is shown that designing a quantum well laser for low threshold gain through the use of a long laser cavity and/or high reflectivity facet coatings will reduce the temperature induced threshold current increase. This result is related to the nonlinear dependence of quantum well gain and current density on carrier density. The high temperature characteristics of strained InGaAs and GaAs QWs are also compared.

Hermetic fiber optic modules for avionics applications

In the past, Boeing had successfully developed and produced the hermetic ARINC 636 fiber optic transmitter and receiver modules for the PLANET System in the Boeing 777 commercial airplanes. These hermetic fiber optic modules had demonstrated over 4 millions aggregate flight hours with zero failure; the hermetic fiber seal technology is a key contributor to this outstanding reliability record. Recently, we have investigated failure mechanisms in commercial-off-the-shelf (COTS) hermetic mini-dil (dual-in-line) laser diode modules; and developed new hermetic fiber seal process for low cost mini-dil form factor packages. In addition, we are also developing cost effective hermetic multi-channel fiber optic array modules technology for aerospace applications.

Low-cost high data rate white LED (WLED) transceiver development

Recently there has been strong interest in wireless white LED (WLED) communication link applications in airplanes and avionics platforms for size, weight, cost, and electromagnetic interference (EMI) reduction. Wireless WLED link has additional advantage of providing network security because the optical signal from WLED link is well confined within an airplane or avionics vehicle. In this paper we discuss and analyze commercial-off-he-shelf WLED design and color measurement results. An experimental implementation of a low cost WLED transceiver which shows error free freespace operation at 10Mb/s is successfully demonstrated. The feasibly of implementing free space optical link which meets both lighting and communication requirements using WLED array is analyzed by mathematical modeling using MATLAB simulation technique.

Hermetic fiber optic modules for aerospace

The authors presented the challenges to produce hermetic fiber optic module for flight critical avionics applications. We have provided viable approaches to produce hermetic fiber optic modules for different aerospace platform applications.

Radiation effect in quantum well optoelectronic devices

The survivability for satellite applications of two classes of quantum-well-based fiberoptic light sources was evaluated by MeV-proton space-environment simulation studies. The first was an InGaAs/GaAs strained-layer quantum-well (QW) laser; the second was a broad-band light-emitting diode (LED) based on dual asymmetric quantum wells in the InGaAs/GaAs/AlGaAs system. In contrast to earlier reports comparing bulk active-region heterostructure LEDs with similarly structured laser diodes, these QW LEDs were more tolerant of proton irradiation (-3dB power at ~3xl013 protons/cm2) than the QW lasers (- 3dB power at ~3xl012 protons/cm2). The LEDs were operated far into gain saturation with a high-loss cavity structure, while the lasers were operated in a region where gain was more sensitive to current density. Therefore, atomic displacement-related recombination sites had a greater detrimental effect upon the lasers than the LEDs. The lasers held constant slope efficiency, and current thresholds increased linearly with proton fluence, while both LED power and slope efficiency decreased with proton fluence. The degradation was similar to that predicted from a universal damage relation for GaAs electronic devices, and extends that relation to include these QW photonic devices.