1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-03-01a71 Center Point of Contact: GSFCa71 Submitted by: Wil HarkinsSubject: Optical Fiber Cable Terminations Techniques and Procedures Practice: Practice: Apply approved requirements and assembly techniques and procedures in
2、the termination of optical fiber cables used in spaceflight applications.Programs that Certify Usage: Programs That Utilize Practice: GSFC X-Ray Timing Explorer Mission (XTE); GSFC Tropical Rainfall Measuring Mission (TRMM)Center to Contact for Information: GSFCImplementation Method: This Lessons Le
3、arned is based on Reliability Practice No. PD-EC-1110 from NASA Technical Memorandum 4322A, NASA Reliability Preferred Practices for Design and Test.Benefits:This practice ensures the performance reliability of optical fiber cable assemblies by requiring the selection of optical fiber cable componen
4、ts that have been tested and approved for spaceflight use and by specifying approved assembly and acceptance inspection and test procedures.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Implementation:The termination of optical fiber cables used in
5、 spaceflight applications is performed in accordance with the GSFC approved training document, Ref. 1, which defines approved material requirements and detailed assembly techniques and procedures. Ref. 1 is used by engineers, senior technicians and those involved in training personnel in the techniq
6、ues of terminating optical fiber cable. The procedures defined in the Ref. 1 training document are applicable to the following items from the MIL-STD-975 NASA Standard Electrical, Electronic, and Electromechanical Parts List, (NSPL), and the GSFC Preferred Parts List-20, (PPL-20):1. MIL-T-29504/4 co
7、urse hand polishing and a two step machine fine polishing procedure. Refer to the polishing procedures in Ref. 1. The connector assembly is inspected for excess adhesive on the fiber endface and other parts of the connector, as defined in the engineering documentation, which could interfere with pro
8、per operation of the connector. Excessive adhesive on the connector endface can flake off over time and create contamination which can affect performance. Excess adhesive on other connector parts can prevent springs and other mechanisms from operating properly or fitting properly together. The optic
9、al fiber is back-lit using a flashlight from the opposite end of the cable assembly without touching the fiber when inspecting a finished fiber optic connector for cracks in the fiber. The polishing process produces a “flat“ polish and the use of an interferometer is recommended to measure the profi
10、le of a fiber endface. The amount of fiber protrusion and the amount of fiber undercut is specified in the engineering documentation. Physical contact connectors, angle polished connectors, or other specialized polished endfaces have specific requirements for endface finishing. The amount of fiber p
11、rotrusion, amount of fiber undercut, connector endface geometry parameters and tolerances, such as flatness, radius of curvature, vertex offset, or angle, as a minimum, are specified in the engineering documentation.Final Polish VerificationVisual examination of the polished, bonded terminus is perf
12、ormed to ensure that the finished termination is of high optical quality and free of unacceptable defects, such as chips, contamination, cracks, scratches, pits, or hackles. A 200X hand held microscope is used and because of the high magnification, the microscope lens and terminus adapter and the po
13、lished terminus must be clean. Loose debris or dust is removed by using dry nitrogen. Care is used to insure that lenses of the microscope and the polished terminus are not scratched. Cleaning and inspection is accomplished in accordance with the step by step procedures of Ref. 1.Provided by IHSNot
14、for ResaleNo reproduction or networking permitted without license from IHS-,-,-Acceptance CriteriaThe following define the acceptance criteria:1. The terminus must have a smoothly polished face and glass fiber free of visible scratches and imperfections which affect optical performance or reliabilit
15、y.2. No visible scratches on the terminus ceramic face.3. No fiber edge chips, scratches, pits, or hackles.4. No contamination.5. No fiber cracks or cracks anywhere in the ceramic ferrule.6. No excess epoxy around the fiber or spots of apoxy anywhere on the ceramic face.Optical Performance Verificat
16、ion The optical fiber cable has been terminated on both ends and conforms with all acceptance criteria up to this point. Optical performance verification is performed by conducting a power loss measurement in accordance with a test setup and the procedure defined in Ref. 1. The first step is to perf
17、orm power loss measurements without the optical fiber cable in the test setup to establish reference measurement values. The second step is to insert the cable to be verified into the test setup without changing anything else in the test setup and repeating the power loss measurement. The difference
18、 in the two power loss measurements, is the power loss of the optical fiber cable. Power Loss Acceptance Criteria Power losses of -1.0 dB per terminus or -2.0 dB per cable is the acceptable value for the two termini of each completed cable. In addition acceptable cable length losses for cables less
19、than 34 feet long is 0.1 dB. Acceptable cable length losses for cables longer than 34 feet are based on -0.003 dB per foot of cable length. Cables that fail the power loss acceptance criteria may be repaired by cleaning or additional fine polishing of an terminus or by replacement of a defective ter
20、minus if the cable length permits replacement of a terminus. Connector Installation A terminated optical fiber cable is installed into a MIL-C-38999 connector before it is used in a spacecraft harness assembly. The optical fiber terminus is installed into the connector in the same way that a wire co
21、ntact is installed. Care is exercised to ensure that the termini ends are not touched, contaminated, or scratched during installation. Standard contact extraction tools for the MIL-C-38999 connector are used if the termini are to be removed from the connector. Mechanical strain relief backshells are
22、 used as appropriate. Socket termini have springs which allow for movement inside a connector when optical termini are mated together. Care is exercised to ensure that the strain relief allows for a slight movement of all socket termini cables in the harness. Provided by IHSNot for ResaleNo reproduc
23、tion or networking permitted without license from IHS-,-,-Optical fiber cable connector terminations are inspected and cleaned if necessary before each mate. Under no circumstances are 100 mate and demate cycles exceeded without cleaning the fiber optical termination to ensure consistent optical per
24、formance. Dust caps which are non-outgassing in laboratory or room environments are used as covers for optical assemblies. Vinyl dust covers are not used.Technical Rationale:The use of components, materials, and techniques used in the fabrication of optical fiber cables that have not been tested and
25、 approved for spaceflight use could result in significant loss of performance during the mission. Outgassing of contaminates in space can be a serious problem with optical fiber systems. Also, space radiation can cause significant loss in performance of certain optical fibers. Nicks in the small and
26、 fragile glass fiber can result in latent optical defects and failures.References:1. GSFC Document No. 733-FO-29504-TERM-TRAINING Entitled “Optical Fiber Cable Termination Procedures For Spaceflight Applications Using MIL-T-29504 Optical Fiber Termini“Impact of Non-Practice: Impact of Nonpractice: F
27、ailure to select approved materials and to follow the fabrication and inspection procedures of this practice can result in limited initial performance and further significant degradation during space flight. This degradation could result in mission failure.Related Practices: N/AAdditional Info: Prov
28、ided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2000-03-01a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
