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Deep Submergence Electro-Optical Hybrid Connector and Cable Assembly
BIRNS Millennium Series Offers High and Low-Voltage Capacity, Fiber Optic Connections and Design That Withstands Open-Face Pressure


Eric Birns
President and Chief Executive Officer
Amy Brown
Director of Corporate Communications
Oxnard, California
A key driver of the subsea connector industry is the need for both more and less: more power, performance and capability while requiring less space, cost and time.

Today's leading connectors can deliver compact, robust, highly complex solutions—all in one system—for applications that would have required several connectors less than a decade ago.

BIRNS Inc. was recently called upon to deliver a custom hybrid electro-optical connector and cable assembly for the Naval Facilities Engineering Command/Engineering Service Center (NAVFAC ESC) at Naval Base Ventura County in Port Hueneme, California.

The hybrid connector needed to be low profile and high performance, with high and low-voltage conductors only a quarter-inch away from numerous optical ferrules.

The requirements necessitated a precise, strategic approach in design, production, electrical/optical termination and testing methodology.

General Connector Requirements
One NAVFAC ESC group develops low-frequency acoustics systems, which tend to be enormous and thus require specialized handling equipment.

The group's engineers needed a solution for a new low-frequency active sonar (LFAS) system that would be deployed from an 11-meter rigid inflatable boat (RIB). LFAS was originally developed to generate low-frequency (100 to 1,000 hertz), intense (more than 240 decibels) sound capable of traveling vast distances for long-range detection of underwater vehicles.

In the past, this particular project might have required a much larger vessel and three separate connections: high-voltage alternating current power, low-voltage control signals and multiple optical fiber lines. Typical systems of this type were exponentially bigger and operated with dedicated surface ships—naval vessels 200 meters or larger—that did not use connectors, instead passing power and signals through penetrators that were permanently affixed to the systems.

In order to deploy the system from a small craft, NAVFAC ESC requested that BIRNS design a connector system that could achieve multiple operational requirements. The team was to install and break down the equipment before and after each use, so connectors were necessary, yet typical connectors would have added unacceptable size and intricacy. The design team was driven to seek miniaturization and hybridization due to the stringent size requirement, as the system stretched the length of the 11-meter RIB, so there was not space for factoring in multiple connectors.

The final Millennium series electro-optical cable assembly with a mating flange receptacle. The connector has two multimode optical fibers, eight 2.5-kilovolt conductors and four 600-volt conductors. (Photo courtesy of BIRNS Inc.)
BIRNS Millennium Series
The BIRNS Millennium™ series was developed to deliver all requisite high-performance attributes in one low-profile system. The system consists of an electro-optical cable assembly (3T-H02012-CP) with a mating flange receptacle (3T-H02012-FR). The assembly has two multimode optical fibers, eight 2.5-kilovolt conductors and four 600-volt conductors. Triple multimode optical loss testing of the mated assembly at 850 nanometers confirmed connector repeatability of less than two decibels. The cable assembly is rated to 2,000 meters, able to withstand open-face pressure to 200 bar and, while mated, to 600 bar (6,000 meters' depth).

The Millennium system differs from other electro-optical connectors available, as it is capable of carrying both high and low voltages to power and control the sensor package. Thus, the single connector can provide power and control signals to the device and carry sensor data back. It was tailored to deliver fast data rates while providing the NAVFAC ESC a reduction in both cost and system complexity.

High-Voltage Parameters
The NAVFAC ESC required a sophisticated system with extremely high-voltage conductors to power the underwater sonar. From a design standpoint, the pin configuration of the connectors had to allow for high-voltage contacts up to 3.6 kilovolts, separated by more than 0.03 inch. The pins also needed sufficient dielectric insulation, which BIRNS achieved using glass-reinforced epoxy (GRE) with a rated resistance value of 400 volts per 0.001 inches.

Because these eight 2.5-kilovolt conductors would be in close proximity to the low-voltage pins, BIRNS developed a specially tapered GRE insulator to seal the bottom of the recess, which would prevent possible short circuits by closing off the metal deep inside the dielectric insulated material. Thus, superior pin engagement was crucial; each pin had to engage the socket deep enough to provide ample current-carrying capacity while avoiding interference with the surrounding low-voltage pins. The rounded tips of these pins are electrically nonfunctional, and the larger the pin, the larger the end radius, so a bigger pin would need to go deeper into the socket, as it loses more linear engagement distance to its larger tip radius.

The Millennium series can use coax, 22, 20, 16, 14 and/or 10 American Wire Gauge contacts in the same connector.

Low-Voltage Requirements
The project's four low-voltage conductors supply power to the small sensors, which are primarily used to report on the status and effectiveness of the entire underwater array.

Compared with the high-voltage conductors, the system's low-voltage contacts did not require as deep of a recess, but they still needed an integral mechanical stress reducer at the base of each pin to prevent stress cracking at that interface. For further security in long-term electrical performance, BIRNS designed heat-treated beryllium-copper sockets to provide sufficient spring memory to maintain socket spring pin retention strength, particularly during ongoing coupling and uncoupling, as the system was to be broken down and reassembled by the engineering team after each use.

The final Millennium series electro-optical cable assembly with a mating flange receptacle. The connector has two multimode optical fibers, eight 2.5-kilovolt conductors and four 600-volt conductors. (Photo courtesy of BIRNS Inc.)
Fiber Optic Requirements
The LFAS system was designed so that data could be returned from the sensors to the computers topside via two multimode optical fibers. Naturally, in creating these tailored connectors, finesse was needed in the alignment of delicate optical ferrules so that they met exactly with no gap between the fibers.

The tiniest differential in position could result in huge signal losses, which could severely interfere with the accuracy of data being reported back to the crew. In order to achieve optical losses of less than two decibels, it took precision placement of eight-micrometer-diameter single-mode or multi-mode optical fibers and a design that avoided macrobending losses. Since the LFAS system was initially planned for depths of approximately 600 feet, these fibers were sealed from possible open-face pressure using miniscule 0.125-inch-diameter O-rings in both ferrules' assembly. BIRNS also designed a dry, 101.3-kilopascal fiber chamber in a permanently encapsulated cable plug back shell to ensure alignment and provide ferrule 'spring action' as an engagement enhancement device.

Another major advantage of the system was that it could be used while under way by project laymen who did not have comprehensive fiber optic training.

Insert and Termination Technology
In order to achieve superior fiber alignment, BIRNS did not mold the optical ferrules into the insert; rather, they were installed, thus requiring a precision hole for each one. Precision was also required in the molding of each individual insert to ensure a perfect seal for the demanding offshore environment and to resist mechanical impact damage during repeated deployment of the LFAS system. BIRNS developed features for the insert to provide absolute hydrostatic sealing with complete absence of any parting lines, total circularity, a specially molded 15° lead-in chamfer angled to ensure the dual O-rings' longevity and reliability, and self-guiding keys.

Each BIRNS connector had positive stainless steel stops to prevent over-tightening, dual stainless steel keys for precision alignment and unique anti-rotation locks to ensure that the system would remain in place during in-use vibration. Each solder pot was insulated with GRE partway up the shaft and after termination.

Heat shrink tubing was placed over the entire conductive area for a completely insulated termination, which prevented electrical interference between pins.

The inserts were developed to be replaceable, providing the option for simple changes to circuitry if needed as the LFAS project matured. Electrical wires were soldered in, and each fiber was epoxied into a ferrule, oven-baked and polished so that all excess epoxy was removed, except for a minute curvature at the end, polished with ultrafine one-micrometer diamond lapping film.

Testing Requirements
To meet the NAVFAC ESC teams' project performance requirements, BIRNS electrical technicians (certified IPC specialists per J-STD-001) performed in-house electrical testing per MIL-STD-1344 to five kilovolts and hydrostatic pressure testing per MIL-STD-202 to 20,000 pounds per square inch.

Triple optical-loss testing was carried out by BIRNS' ETA-I certified optical technicians to ascertain repeatability. A power meter and a light source were applied to opposite ends of the connector and cable system and then tested three times in each direction to monitor signal loss.

Conclusions The BIRNS Millennium hybrid electro-optical connectors were created specifically to push the technological barriers inherent in transmitting significant amounts of real-time data for subsea observatories, towed data acquisition devices, remotely operated vehicle projects or any use of underwater electro-optical systems.

The Millennium series is a huge leap forward: Other optical connectors either cannot carry electrical power, cannot handle high voltages or cannot withstand open-face pressure. The hybrid connectors are smaller and more powerful than their predecessors and provide users with high-density, deep-submergence connectors that meet a wide range of specific requirements.

Eric Birns is president and chief executive officer of BIRNS Inc., an ISO 9001:2008 certified global leader in the design and manufacturing of high-performance lights, connectors, penetrators and custom cable assemblies for the subsea, military, commercial diving and nuclear power industries since 1954. He also founded and managed the engineering and manufacturing firm BIRNS (UK) Ltd. in Scotland.

Amy Brown is director of corporate communications for BIRNS Inc., responsible for developing and managing the company's strategic external marketing, media relations and internal communications programs.

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