Fiber optics interconnect has emerged as the only viable technology to carry the massive amount of information generated by high resolution radars, infra-red cameras and other sensors.
By: Gérald Persaud, VP Business Development and Michel Têtu, Senior Business Development Advisor
Command, control, compute, communicate, intelligence, surveillance, and reconnaissance systems (C4ISR) rely on accurate views of local situations for decisions that are critical to national defense. Fiber optics interconnect has emerged as the only viable technology to carry the massive amount of information generated by high resolution radars, infra-red cameras and other sensors. Fiber optic-interconnect are small, immune to EMI and has superior bandwidth to traditional copper interconnect.
Reflex Photonics optical embedded transceivers are small, rugged, lower power components enabling the transmission and processing of high bandwidth sensor information.
Eyes and ears everywhere
Illustration of the relation between the different elements of C4ISR systems (Command, Control, Compute, Communicate, Intelligence, Surveillance, Reconnaissance).
Intelligence, surveillance, and reconnaissance (ISR) trend is for more information and accurate views of the situations with longer mission times. For example, UAVs with high resolution sensors and high performance embedded computing have become an invaluable tool to defense. They can survey large areas quickly and at much lower cost than manned aircraft.
ISR systems need:
- Higher resolution sensor arrays with high BW fiber optic interfaces
- Enormous signal processing with scalable computers
- Lower SWaP-C
- Rugged and reliable components to survive extreme temperature, vibration, and moisture …
Parallel optics – The embedded leap for C4ISR
Parallel optics provides multiple high bandwidth interconnects in a space ten time smaller than co-axial copper interconnects. With almost unlimited bandwidth it is clear that all future interconnects for embedded systems will use parallel optics.
Reflex Photonics supplies chip size rugged parallel optics transceivers to operate in harsh military environments. These embedded parallel optical modules are qualified to MIL-STD-883E for severe environmental conditions.
- SMT construction provides high resistance to shock and vibration via low CG and solder attach
- SMT support heat sinking to host board to reduce height and weight
- MT connector enables pick-and-place part
- MT connector simplifies manufacturability (no pigtail)
- Low-mass cable and retainer tolerates high shock and vibration
- High temp materials/simple structure = reliable performance in harsh environments
High temperature materials and simple structure equals reliable performance in harsh environments.
System performance - BER
System performance of an optical link is determined by the quality of the signal generated by the TX, lane impairments (fiber optics cable and interconnects) and the sensitivity of the receiver over a bandwidth range. Rugged transceivers must operate over wide temperatures (at least -40 ºC to 85 ºC) which makes it challenging to maintain low bit error rates (BER) at the high operating speed. For example, the laser response slows with temperature making it difficult to maintain an open eye at speed beyond 6 Gbps. At high temperatures the laser output power declines and causes a decrease in signal to noise ratio. As well, the response time decreases which can cause a high level of ringing. The TX eye diagram is a useful method to assess the quality of the signal generated over temperature. Open eyes correlates to low BER as the receiver is given more bit time to accurately discriminate a high signal from a low signal.
The eye diagram in figure below shows the LightABLE transmitting 10 Gbps at -40 ºC. It uses the 802.3ab Ethernet mask to show there is a huge bit time margin for the receiver to accurately detect a high from a low. This is why Reflex Photonics transceivers can deliver BER better than 10-15.
- Laser response slows significantly below -30 ºC causing eye to close at 10G
- The closing eye has a significant impact on BER
- IEEE802.3ab specifies a BER of 10-12 - high performance systems expect 10-15
Rugged optics requirements
Reflex Photonics LightABLE embedded transceivers offer small SWaP-C, operation over industrial temperature range (-40 °C to 85 °C), a bit error rate (BER) as low as 10-15, survivability to storage temperature from - 57 °C to 125 °C. The LightABLE can be surface mounted using leaded or RoHS reflow processes or it can be plugged into a board with a Meg-Array socket. Mounting the LightABLE close to the electrical driver delivers the best signal integrity and lowest power operation. The optical fiber interface is a standard MT ferrule directly attached to the module for compatibility with standard connectors and cables.
- -40 ºC to 85 ºC or wider
- Considerations: BER at 10G – due to laser response over temperature
- -57 ºC to 125 ºC
- Considerations: Reliability – mechanical stress, laser alignment
Shock and vibration
- MIL-STD-810xx – aircraft, land vehicles, gun shock
- Socket with low wipe contact is a concern
- Mechanical attach strength – SMT vs socket
- SMT offers low height without bulky heat sinks for tightly stacked blades
- Embedded optics typically consumes 100 mW/10G lane
- Weight is typically 5 g
- Seal to avoid moisture from obstructing optics
- For example, rapid decompression condenses air moisture
Bit error rate (BER)
- IEEE802.3ab for 10G Ethernet is specified as 10-12
- High performance systems expect 10-15 to avoid power hungry FEC, CDR, or equalizers.
- Higher the BW, lower the expected BER!
- Link budget is the loss that can be tolerated between the transmitter and the receiver for a certain BER
- Main sources of loss are connector return loss and mode dispersion for multimode fiber
- TX output should be derated based on mask margin – jitter power penalty
- Scalable BW – up to 28G
- Signal integrity – BER of 10-15
- Low loss – 0.003 dB/m (OM3 @10G)
- Reach – 300 m (OM3 @10G)
- Small – 125 µm diameter fiber
- Light weight – <1.5 g/m (OM3)
- High I/O density – 48 fibers in MT connector
- Lower power – 100 mW/10Gbps
- -40 ºC to 85 ºC operation @ 10 Gbps
- MIL-STD-810xx Shock and vibration
- Moisture resistant
- EMI and nuclear radiation immune