METAL BULKHEAD 



EPOXY BOND 



LOW-PRESSURE 

 ENVIRONMENT 



OPTICAL FIBER 



HIGH-PRESSURE 

 ENVIRONMENT 



DEMOUNTABLE 

 CONNECTOR 



1/2-PITCH 

 SELFOC ROD 



INDIUM 

 SOLDER SEAL 



Figure 17. Optical fiber high-pressure penetrator schematic. 



A CJRIN lens of one-halt" pitch length has the property of relaying an image, inverted 

 and at unity magnitlcation, from one face to the opposite face. This allows the light from a 

 fiber-optic connector to be imaged onto a conjugate connector with very low insertion loss. 

 The glass rod is sealed into the bulkhead to serve as a pressure window as well as perform the 

 relay lens function (ref 15). 



As a result of a development program carried out at NOSC in FY 80 under Internal 

 Hxploratory Development funding (ref 16), we are confident that practical, high-performance 

 tlber-optic pressure penetrators are entirely realizable, and that practical production devices 

 are possible to manufacture if suitable fabrication techniques are employed. Prototype 

 demountable penetrator units developed at NOSC, which use the one-half pitch GRIN lens 

 window concept combined with refinements related to positional rod location and connector 

 transverse alignment, exhibit approximately 1-1.5 dB optical insertion loss, which makes 

 them optically comparable to many of the better fiber-optic connectors themselves. Intrinsic 

 insertion loss of the GRIN lens is on the order of 0.4-0.5 dB, which would permit a very low 

 level of insertion loss to be realized in nondemountable designs as well. Units have been 

 tested to hydrostatic pressures in excess of 10 000 psi (corresponding to maximum depths of 

 more than 95% of the ocean floor) without failure. No degradation in opfical performance 

 was observed after high-pressure "soaks" lasting several days, which indicates that inconse- 

 quential positional creep in rod position was taking place as the result of long-term apphed 

 stress. Temperature cycling over a range from -40°C to +100°C caused no glass spalUng as a 

 result of mismatch of temperature coefficients between glass and metal. A prototype fiber- 

 optic penetrator is shown in figures 18 and 19. 



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