A variety of commercial off-the-shelf options exist for extreme fiber applications such as military, avionics, shipboard, and space.
By Douglas A. Parker
There was a time when connector industry “experts” touted fiberoptics as the upcoming wave of the future with a fairly aggressive timeline for major replacement of copper data lines with fiber lines. Somehow, it didn’t quite happen as rapidly as predicted, but use of fiber is rapidly increasing in many new programs that require higher data-rate signal transmission. Along with increased use of fiber, RF signaling has advanced significantly toward higher data rates. Still, for the fastest data transmission needs, for safety and shielding issues, and for tremendous weight savings, fiberoptics is an excellent choice.
Military fiberoptic connector specifications have been very limited over the years, but the Navy recently rolled out a significant new specification called the Next Generation Connector (NGCon), intended to specify a family of harsh-environment fiberoptic connectors for military services. However, during the many years leading up to this NGCon connector, commercial off-the-shelf (COTS) connectors have been developed, tested, and used in military programs in the absence of adequate military-specified connectors. These continue to be available in a broad selection of choices while the NGCon connector goes through a period of testing and evaluation before it can be considered for use.
Fiberoptic standards efforts
Use of fiberoptic signal transmission for data routing in harsh environments has been gaining popularity these past few years. A few standards were written for particular fiberoptic connectors, but for the most part, connector manufacturers have developed their own solutions for fiberoptic applications. These have either stood the test of time on programs or have passed qualification testing required for military programs.
Many standardization efforts specify new fiberoptic connectors and outline testing and inspection criteria. The Navy’s NGCon is nearing design completion, paving the way for qualification testing. The SAE Fiberoptic Avionics Components group is nearing completion of the JELLI document on jumpers, endfaces, link loss, and inspection. ARINC has just approved release of several new fiberoptic documents for use in the airline industry. One ARINC specification, ARINC 801, standardizes fiberoptic connectors, including rectangulars, for use in aerospace applications. TIA/EIA continues to produce and update fiberoptic test procedures and optical fiber system test procedures. Only one of these, NGCon, is a military specification for a family of multi-channel fiberoptic connectors.
Past and present solutions
The U.S. military was on the forefront of fiberoptic research and program usage over 25 years ago and has continued to be a supporter and user of fiberoptic technology. Cooperation with industry standards organizations has been the rule for fiberoptic test procedures with frequent military adoption of TIA/EIA standards. Direct military standardization of fiberoptic connectors has been limited to avoid proliferation of approved/qualified designs. This was acceptable in early years of fiber usage, but as time passed, more and more military programs have selected COTS products, finding that they offered superior technical advantages over the few military standardized items.
In the past, the military used three basic approaches to fiberoptic connectors. The first approach was to use existing electrical connectors and put fiber into them. Examples of these are the Amphenol-developed FSMA single-channel fiberoptic connector and the multichannel MIL-C-38999 Series 3. The 38999 Series 3 electrical connector (unmodified) and MIL-T-29504 fiberoptic termini became a popular combination to implement multimode fiberoptics. Many companies offer these packages.
The second approach was to use existing electrical connector shells or coupling mechanisms and modify inserts for fiberoptic usage. An example is the Hughes (now Delphi) MIL-C-28876 (from MIL-C-28840). Deutsch Ltd., UK, developed the MC3 and MC5 connectors using 38999 Series 3 shells with precision fiber inserts.
The third approach was to design new fiberoptic connectors from scratch, such as the AT&T biconic connector and the fiberoptic ST bayonet connector. While these satisfied military fiberoptic needs for many years, by the 1990s, COTS harsh-environment fiberoptic connectors with improved technology offered far more in the way of precision alignment, resulting in significantly lower losses.
COTS fiberoptic solutions
Over the past ten to 15 years, many new fiberoptic connector products for harsh military, avionics, shipboard, and space applications have been proven in test programs and in active program usage. These fiberoptic interconnection products filled the void when military standard fiberoptic connectors were very few and limited. As new designs are being finalized and introduced, successful COTS components continue to serve in fiberoptic systems that require rugged reliability.
Connector companies recognized a need for fiberoptic connector solutions that went beyond the limited military specifications. Some companies went through the qualification process to be listed on the qualified products list for the few military connector specifications. Others, rather than try to qualify to produce the limited connectors covered by MIL-specs, developed their own solutions.
Single-channel connectors include FC connectors, DIN/AVIM, and probably the most ruggedized, the RSC, developed by Deutsch Ltd., UK. Later entrants included the 3M ROC and SC for less rugged data transfer. Still later, the “small-form-factor,” 1.25-mm ferrule Lucent LC demonstrated higher density without degrading performance.
All of the recently developed fiberoptic connector products for the U.S. military offer small-form-factor termini for higher density. Most products use the 1.25-mm, small-form-factor terminus, made relatively inexpensive by Lucent’s pioneering of the LC connector compared to the more expensive MIL-T-29504 size 16 terminus. Most also feature identical termini in both socket and pin inserts, spring loading on both sides, precision guide-pin aligned inserts, and a removable front socket insert for cleaning, all pioneered by Deutsch Ltd., UK.
Several companies offer high-quality fiberoptic connector products being used or being considered for use in military programs. Fifteen years ago, Deutsch Ltd., UK, developed a special fiberoptic insert package for the MIL-C-38999 Series 3 connector (MC3) that makes it a superior fiberoptic connector for single-mode and multimode applications. The features mentioned above lowered losses and allowed ease of cleaning and inspection, along with an optional “active alignment” (Diamond SA) termini. A later composite shell version (MC5) makes use of the small-form-factor, 1.25-mm ferrules to increase density (see Fig. 1). Military programs have selected the Deutsch Ltd., UK, connectors, recognizing the technical advantages over standard MIL-C-38999.1
The ITT Cannon PHD series was developed as a relatively low-cost, high-performance, densely packaged replacement for optical-ribbon-fiber interconnect designs. The PHD series termini include keyed options for single-mode and polarization-maintaining repeatability (see Fig. 2).2
 FIGURE 2. The PHD-series MIL/COTS 1.25-mm fiberoptic termini feature polarization-maintaining repeatability. |
The Molex LumaCore series offers very high density, plus keyed termini used in circular, multi-channel and LC2 connectors. The LC2 is a ruggedized all-metal LC connector for high-density, rack-mounted, single-channel fiberoptic applications (see Fig. 3).3
 FIGURE 3. The MIL/COTS ruggedized LC2 connector is used for single-channel fiberoptic applications. |
New harsh-environment fiberoptic applications at Boeing extensively use Radiall’s LuxCis connector family, which includes keyed termini for circulars and rectangulars (see Fig. 4). They can also be used in hybrid configurations (electrical and fiber in the same connector), and are in compliance with the soon-to-be released ARINC 801 standard.4
 FIGURE 4. Radiall’s LuxCis rectangular connector family, used by Boeing, will satisfy the ARINC 801 standard. |
Amphenol Aerospace produces upgraded its MIL-C-38999 series 3 connectors for fiberoptics with size 16 and size 20 termini. In the 80s, Amphenol and G&H Technology developed special fiberoptic connectors for the International Space Station.5 Glenair has also produced several fiberoptic harsh-environment connector products that have found their way into Lockheed military programs.6
Fiberoptics is being used increasingly in harsh-environment applications requiring high data rates along with the need for ruggedization. In the absence of military specification connectors for fiber, commercial companies have developed excellent products that have provided military shipboard, avionics, and ground program engineers with high-quality fiberoptic options. The Navy’s new NGCon connector family may prove to be a fine addition to the list offered by connector companies, but in any case, newer and better COTS products continually emerge from innovative suppliers.
DOUGLAS A. PARKER is program manager, Connections, at Tempo Research Corporation, 80 Wood Road #202, Camarillo, CA 93010. He also serves as secretary for the International Institute for Connectors and Interconnection Technology (IICIT), and as the chairman of the SAE AS3C3 JELLI inspection standard. Tel: (805) 384-1834; Email: dparker@tempo.textron.com.
REFERENCES
- www.deutschltd.com, 2005.
- Novacoski, J., www.ecnmag.com, Aug. 2005.
- www.molex.com, 2005.
- Radiall Catalog D6 F206 CE, Apr. 2005.
- www.amphenol-fiberoptics.com, 2005.
- www.glenair.com, 2005.
