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.
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.
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.
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.
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.
Two classes of quantum-well-based fiber-optic light sources were evaluated for degradation under 5.5-MeV proton irradiation as part of an evaluation of the survivability of fiber optic components for satellite applications. The first was an InGaAs/GaAs strained-layer quantum- well laser; the second was a broad-band light-emitting diode based on concurrent multiple- state transitions from two asymmetric quantum wells in the GaAs/AlGaAs system. In contrast to earlier reports comparing bulk active-region heterostructure light-emitting diodes with similar structured laser didoes, it was found here that these quantum-well light-emitting diodes are more tolerant of proton irradiation than the quantum-well-based lasers. Analysis revealed the quantum-well light-emitting diode allows operation far into gain saturation with the more lossy cavity structure as compared to quantum-well lasers. The lasers, in contrast, operate in a region where gain is more sensitive to current density, and therefore, the introduction of energetic proton-induced atomic displacement-related recombination sites have a greater effect than in similar structured light-emitting-diodes. In addition, it was found that the laser maintained constant slope efficiency, while current thresholds increased linearly with proton fluence. In contrast, both light-emitting-diode output-power and slope efficiency decreased with fluence. Experimental damage constants were determined for performance parameters and found to be similar to those previously reported for carrier removal rates on other GaAs- based electronic structures.
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.
Two classes of quantum-well-based fiber-optic light sources are examined for degradation under 5.5-MeV proton irradiation as part of an evaluation study for satellite applications. Contrary to previous experience with bulk active area heterostructure light-emitting diodes and laser diodes, it was found that these quantum-well light-emitting diodes are more tolerant of proton irradiation than quantum-well-based lasers. This is the case when the quantum-well light-emitting diode structure allows operation far into gain saturation and the cavity is lossy compared with the quantum-well lasers where gain is more sensitive to current density and with low-loss cavities. Experimental damage factors were measured for performance parameters of these quantum-well photonic devices and found to be similar to those previously reported for carrier removal rates in GaAs-based electronic structures.
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.
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 spectrograph's channel resolution (4-5 nm) and grating efficiency (>50%) compare favorably with other multimode WDM elements.
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