Lightweight BiDi Fiber Optic Links with SGMII & Smart Spool Management

The Heavy Cost of High-Altitude Tethered Operations  

Tethered drones (multirotor TUAVs) have revolutionized persistent surveillance by replacing onboard batteries with a ground-supplied power cable. However, to achieve robust command and control at high altitudes, these drones rely on optical fiber for a “fly-by-fiber” link. While fiber offers superior bandwidth, zero RF interference, and absolute data security, it introduces a critical physical liability: weight. 

Conventional fiber systems require two separate strands (one for transmitting, one for receiving). In a tethered drone ascending to operational altitudes (100m+), this duplex fiber doubles the tether’s mass. That extra weight acts as a downward force, reducing flight time, limiting payload capacity, and increasing mechanical stress on rotors. In short: heavy fiber jeopardizes drone integrity. 

BiDi (Single-Fiber Bidirectional) Technology 

Our innovation leverages BiDi (Bidirectional) optics. BiDi transceivers use wavelength division multiplexing (WDM) to transmit and receive data simultaneously on a single fiber strand. 

By replacing two fibers with one, BiDi slashes the tether’s linear weight density in half. 

Why BiDi?  

• Lightweight & Intact Drones: A single, lighter fiber reduces tether drag and gravitational load, keeping the drone stable and structurally intact during high-altitude operations. 

• Preserved Performance: Achieves full duplex communication (same bandwidth as two fibers) without adding a second strand. 

• Security & Interference: Maintains all advantages of a fly-by-fiber link (zero EMI/RFI, tapping-proof data). 

With BiDi, your tethered drone no longer carries dead weight. It ascends faster, longer, carries more sensor payload, and operates with greater mechanical reliability. 

SGMII SFP: The Adaptable, Low-Power Serial Bridge 

While optical transceivers handle the fiber link itself, a robust electrical interface is still required between the drone flight controller/payload processor and the optical module. That’s where the SGMII SFP combination comes in. SGMII (Serial Gigabit Media Independent Interface) paired with the SFP (Small Form‑factor Pluggable) form factor delivers a compact, low‑power, high‑speed serial bridge tailored for tethered UAV applications. 

What does SGMII SFP bring to tethered drones & ground systems?  

• High‑speed serial connectivity: Enables full gigabit data transfer between drone, tether, and ground station for HD video + telemetry. 

• Low power consumption: Critical for drones: less heat, longer flight time, smaller power supplies. 

• Protocol & distance flexibility: Works for both short intra‑drone links (PCBs) and long tether runs (100m+). 

• Interoperability: Bridges switches, routers, servers, and embedded processors seamlessly. 

• Real‑time deterministic behavior: Essential for automation and control systems (flight stability, live payload commands). 

The key advantage is speed translation. Many drone processors operate at 100 Mbps or 1 Gbps Ethernet, while ground‑side switches often have only 10 Gbps or 25 Gbps capable ports. The SGMII SFP handles this mismatch by converting the lower-speed serial signals from the drone side to a format compatible with higher-speed switch ports on the ground, and vice versa—all without requiring a separate external PHY or media converter. 

Additionally, SGMII’s low pin count and minimal power draw (often under 1 watt) align perfectly with weight‑ and energy‑sensitive UAV designs. And because it uses the SFP form factor, you can swap or upgrade the optical interface (single‑mode, multi‑mode, or other variants) without redesigning the main board—giving you a future‑proof, field‑serviceable solution. 

Fiber Optic Spools: Managing the Tether Without Signal Loss 

A lightweight fiber is only useful if it can be deployed, retrieved, and stored without damage. Fiber optic spools solve the mechanical half of the tether paradox. A fiber optic spool is a cylinder‑shaped device used to store, manage, and deploy fiber optic cables properly. Spools prevent tangling, kinking, and excessive bending—all of which degrade signal quality or break the fiber. In tethered drone operations, the spool sits on the ground (or a moving vehicle) and pays out or retracts the single‑strand BiDi tether as the drone ascends or descends.  

Several spool types are well-suited for drone operations. An empty spool allows you to re-spool a custom-length BiDi tether to match your exact mission requirements. A preloaded spool comes ready-to-fly with single-fiber BiDi cable already installed, saving preparation time in the field. A bi-directional spool enables both controlled unwinding and retraction, making it ideal for vertical takeoff and landing where the tether must pay out and reel back in smoothly. Finally, a portable spool is designed for field-deployable systems, such as mobile ground stations that need to move while the drone is airborne. 

Key Components of a Drone‑Ready Fiber Spool 

• Core Spool Body: Maintains the required bend radius (prevents micro‑bends and signal loss). 

• Flanges: Keep the tether from spilling off the spool during rapid ascent/descent. 

• Cable Guides: Ensure even winding to avoid overlapping or snagging. 

•  Material: Lightweight reinforced plastics or metals for field durability. 

Benefits of Using a Fiber Spool in Your Tethered Drone System:

First, a fiber spool preserves signal integrity by preventing kinks and excessive bending, which maintains BiDi’s full data quality. Second, it enhances durability by protecting the single fiber from abrasion, crush, and repeated winding cycles. Third, spools offer scalability, allowing you to easily swap spools for different tether lengths such as 50 meters, 100 meters, or 200 meters and beyond. Finally, spools enable thorough testing and calibration by providing controlled fiber payout for pre-flight optical loss checks. 

Don’t let heavy duplex fiber, power‑hungry interfaces, or tangled cables ground your potential. Use BiDi to cut weight, SGMII SFP to save power and ensure interoperability, and fiber spools to manage the tether with integrity.