Single-Fibre BCR Bulkhead Underwater Fibre Optic Connector — Dry Box, 6,000m Depth, Expanded Beam

Single-Fibre Underwater Fibre Optic Connector — BCR (Bulkhead) — Overview

This single-fibre bulkhead (BCR) underwater fibre optic connector is a panel-mount fibre penetration solution for pressure housings, junction boxes, and instrument chassis rated to 6,000 metres standard depth. The BCR (Bulkhead) configuration mounts through the housing wall with a threaded fitting, providing a depth-rated optical feedthrough for a single fibre circuit — single-mode or multi-mode — using expanded beam ball lens technology.

The dry-box BCR is designed for installations where the inboard side of the connector remains in a dry, atmospheric-pressure environment — typical of instrument pressure housings, junction boxes, and shallow-rated systems where a pressure-balanced internal environment is maintained. The expanded beam design eliminates the precision polishing and contamination sensitivity of physical contact fibre penetrations.

Key Design Features

• BCR bulkhead (panel-mount) configuration — threaded housing wall penetration; installs directly into instrument chassis, junction box, or pressure housing
• Dry-box design — inboard side remains at atmospheric pressure within the dry housing; depth pressure acts on the external connector face only
• Single fibre — single-mode or multi-mode — flexible fibre type selection for high-speed data, video, or sensor telemetry
• 6,000 metre standard depth rating — covers commercial ROV, AUV, and deep scientific instrument applications
• Expanded beam ball lens — no physical contact between optical surfaces; tolerates contamination and allows field cleaning without removing the housing
• Unlimited mating cycles — the external cable connector can be connected and disconnected without any optical degradation
• Stainless Steel AISI 316 standard — corrosion-resistant; other thread sizes and housing materials available on request
• Minimum form factor — compact bulkhead footprint minimises penetration area on the pressure housing face

Technical Specifications

Typical Applications

• AUV and ROV pressure housing single-fibre optical feedthroughs for internal electronics to external sensor connections
• Subsea instrument housing fibre optic data and video penetrations
• Junction box single-fibre optical port for inter-node data links
• Oceanographic instrument chassis fibre penetration for high-speed data telemetry
• Cabled observatory node chassis single-fibre optical I/O ports
• Offshore sensor housing optical penetrations for condition monitoring systems

Why Expanded Beam — The Advantage Over Physical Contact Fibre Connectors

1. Tolerates Contamination — No Precision Polishing Required Subsea

Expanded beam technology enlarges the light beam to approximately 1.5 mm in diameter before it crosses the air gap between the two lenses. At this diameter, a dust particle or water droplet on the lens face occupies only a tiny fraction of the beam cross-section, causing negligible signal loss. Physical contact connectors focus light through a 9 µm core (single-mode) — a single dust particle can completely obstruct the beam and cause catastrophic signal loss. In subsea environments where cleaning is difficult or impossible, expanded beam is the only reliable choice.

2. Unlimited Mating Cycles — No Wear Mechanism

Physical contact connectors degrade with every mating cycle as the polished ferrule faces abrade against each other. Expanded beam connectors mate lens-to-lens across an air gap — there is no physical contact between the optical surfaces, no abrasion, and no degradation of optical performance over time. Unlimited mating cycles are qualified without any change in insertion loss.

3. Field Re-terminable — No Specialist Polishing Equipment Required

The spherical ball lens design allows the connector to be re-terminated in the field using a simple termination kit. The lens can be cleaned with a cotton swab in seconds. Physical contact connectors require precision polishing machines and inspection microscopes to achieve an acceptable end-face geometry — impractical on a vessel deck or at a shoreside deployment site.

4. Multiple Housing Materials for Any Environment

Available in Nickel Aluminium Bronze C63000, Stainless Steel AISI 316, and Titanium Grade 2 — allowing system designers to optimise for corrosion resistance, weight, or cost depending on mission profile and deployment duration.

5. Mixed Single-Mode and Multi-Mode in One Connector

Both single-mode and multi-mode fibres can be accommodated within the same connector body, enabling a single connector to serve mixed data (single-mode, long-distance) and video (multi-mode, short-distance) circuits simultaneously — reducing connector count and penetration points on the pressure housing.

Installation, Cleaning, and Maintenance Guidelines

Lens Cleaning Procedure

• Inspect the ball lens face under a 400× inspection microscope before every mating cycle — even minor contamination visible at this magnification should be removed before connecting.
• Clean the lens face with a lint-free cotton swab dampened with isopropyl alcohol (IPA, 99%+ purity). Allow to dry completely before mating — residual IPA causes temporary elevated insertion loss.
• Do not use dry swabs — they generate static charge that attracts particles back to the lens surface.
• Never touch the lens surface with bare fingers — skin oils cause persistent contamination that requires repeated cleaning cycles.

Mating Procedure

• Verify lens faces are clean and free of contamination on both connectors before mating.
• Align the connector keying features before applying axial force — do not rotate the connector during insertion if it is a push-pull (CCP) type.
• For threaded types (BCR/FCR), engage threads carefully and tighten to the specified torque — do not overtighten as this can distort the housing and affect optical alignment.
• Verify optical continuity with an optical power meter after mating — acceptable insertion loss should be within the connector's specified range.

Storage and Protection

• Always install protective dust caps on unmated connector faces during storage, transit, and any period when the connector is not in use.
• Store connectors in a clean, dry environment — the ball lens is robust, but contamination accumulation over extended storage will require cleaning before use.
• For long-term seabed deployment with one connector face unmated, use a pressure-rated protective cap rated to the full deployment depth.