Highly-Hermetic Feedthrough Fiber Pigtailed Circular To-Can Electro-Optic Sensor For Avionics Applications

CMC Electronics, An Esterline Company will present a paper titled, Highly-Hermetic Feedthrough Fiber Pigtailed Circular To-Can Electro-Optic Sensor For Avionics Applications, at the SPIE Defense Security & Sensing Exhibition, April 23 – 27, 2012 at the Baltimore Convention Center Baltimore, Maryland, USA.

By Jocelyn Lauzon, Lorrain Leduc, Daniel Bessette, Nicolas Bélanger
CMC Electronics, An Esterline Company
600 Dr. Frederik-Philips Blvd., Ville Saint-Laurent, Quebec, Canada H4M 2S9
Email: jocelyn.lauzon@cmcelectronics.ca

Abstract
Electro-optic sensors made of lasers or photodetectors assemblies can be associated with a window interface. In order to use these sensors in an avionics application, this interface has to be set on the periphery of the aircraft. This creates constraints on both the position/access of the associated electronics circuit card and the aircraft fuselage. Using an optical fiber to guide the light signal to a sensor being situated inside the aircraft where electronics circuit cards are deployed is an obvious solution that can be readily available. Fiber collimators that adapt to circular TO-can type window sensors do exist. However, they are bulky, add weight to the sensor and necessitate regular maintenance of the optical interface since both the sensor window and the collimator endface are unprotected against contamination. Such maintenance can be complex since the access to the electronics circuit card, where the sensor is sitting, is usually difficult. This interface alignment can also be affected by vibrations and mechanical shocks, thus impacting sensor performances.

As a solution to this problem, we propose a highly-hermetic feedthrough fiber pigtailed circular TO-can package. The optical element to optical fiber interface being set inside the hermetic package, there is no risk of contamination and thus, such a component does not require any maintenance. The footprint of these sensors being identical to their window counterparts, they offer drop-in replacement opportunities. Moreover, we have validated such packaged electro-optic sensors can be made to operate between -55 to 115°C, sustain 250 temperature cycles, 1500G mechanical shocks, 20Grms random vibrations without any performance degradations. Their water content is much smaller than the 0.5% limit set by MIL-STD-883, Method 1018. They have also been verified to offer a fiber pigtail strain relief resistance over 400g. Depending on the electronics elements inside these sensors, they can be made to have a MTBF over 50 000h at 100°C.

Summary
Electro-optic sensors for avionics applications such as LiDAR and laser range finding are used on many aircrafts today. Using window sensors is associated to field of view constraints that are not trivial on an aircraft. Fiber pigtailed components offer an elegant solution to the problem, but the current fiber collimator interface associated to these pigtails is bulky and requires regular maintenance, cleaning the collimator end-face regularly. We present a novel configuration made of a feedthrough fiber pigtailed circular TO-can electro-optic sensor that is lightweight, compact, resists vibration and shocks, is highly-hermetic and does not require any maintenance over an estimated 20 years lifetime.