Board Edge Mount Active Optical Connector

By: Jocelyn Lauzon, Tomasz Oleszczak, Saïd El Kharraz from Reflex Photonics
Eric Hickey, Sean Langelier from Amphenol Aerospace

Reflex Photonics has developed compact 40G full duplex (4+4) 10 Gbps/lane optical fiber transceivers for harsh environment applications such as Aerospace and Defense.
These products were made to be embedded on printed-circuit boards in close proximity to high speed electronics in high performance embedded computing systems to optimize their performance. Going one step further, the industry was asking for these transceivers to be integrated in board edge connectors to free-up more space on the board and avoid optical fiber handling. This implied important challenges for bi-planar position tolerancing between the electrical interface on a horizontal board and the optical interface based on a multi-fiber MT ferrule, in an orthogonal plane.

The final configuration of the active optical connector is called the LightCONEX.

LightCONEX® is developed in partnership with Amphenol Aerospace

Reflex Photonics LightABLE optical transceivers

LighABLE embedded transceiver

Reflex Photonics Inc. has developed compact 12.5 Gbps/lanes optical fiber transceivers for harsh environment applications such as Aerospace and Defense.
The LightABLE™ product series offers chip size transceivers with the following features:

  • Performance: 10Gbps/ch from −40 ºC to 100 °C
  • Sensitivity: better than −12 dBm for BER 10−12
  • Multimode OM3 fiber
  • 850 nm wavelength
  • Standard MT parallel fiber connector
  • Embedded, board mount, close proximity to FPGA/switch chip

Reflex Photonics LightCONEX optical transceivers

LightCONEX blind mate optical interconnect for VPX embedded computing systems

VPX blind mate active optical plug-in to backplane connector for embedded communication. Reference VITA 66 standards; interface under discussion VITA 67.3.

OpenVPX is the architecture framework that defines system level VPX interoperability for multi-vendor, multi-module, integrated system environments.

Define interfaces between plug-in modules and chassis for harsh environment applications.

LightCONEX description

The design was made to respect VITA 66.0 optical interconnect on VPX base standard. The tolerances on the position of the electrical pins in the horizontal plane are ±50 µm. The lateral / longitudinal RMS tolerances on the optical connector, in the orthogonal plane,  prior to connection, are ±100 µm and the angular tolerance is ±0.47º. These tolerances include the ±50 µm tolerances of the electrical pins in the orthogonal plane.
In order to limit the additive position tolerance over 2 orthogonal planes, alignment pins are used for the horizontal plane, through the LightCONEX housing, the same housing that supports both the electrical and optical interfaces. In the orthogonal plane, where the optical connection is made, the precision of the alignment is ensured by the combination of 3 guides. The VPX pin on the backplane and interface of the plug -in module offers a preliminary gross alignment. A guide tab on the backplane insert and guiding shroud sitting on top of the MT ferrule interface provides a more precise alignment, that is then completed by the MT ferrule dowel pins on the MT ferrule interface, ensuring 12 fiber array to 12 fiber array physical contact with optical transmission losses less than 0.3dB for all channels for 50 µm core diameter OM3 fibers transmitting 850 nm optical signals. The vertical precision tolerance on the position of the optical fibers in the ferrule is initially ±200 µm, prior to connection, including tilt angle. The optical connector interface can resist a mated force (between the plug-in module and backplane) of 7.8 N (1.75 lb) for the MT ferrule and a total tensile force of 28.25 N (30 g/contact). 

Bi-planar position tolerancing

Bi-planar position tolerancing
  • Electrical pins in the horizontal plane: ±50 mm
  • Lateral/longitudinal RMS tolerances on optical connector in orthogonal plane: ± 100 mm, ± 0.47°
  • Vertical tolerance on optical fibers (including tilt): ±200 mm
  • Alignment pins on cLGA socket, through housing

Optical connection alignment precision

Optical connection alignment precision is ensured by the combination of 3 guides:

Optical connection alignment precision is ensured by the combination of 3 guides:

  1. VPX key guide pin
  2. Guiding shroud
  3. MT ferrule alignment pins

The transceiver is screwed-in, through the host PCB, into the optical transceiver housing, through an LGA (land grid array) electrical socket. Amphenol’s cLGA socket offers potential multiple connection /disconnection cycles while maintaining a low -profile needed to ensure high-density rack-mountability for these board-edge active connectors.

cLGA socket or connector

cLGA socket or connector

Exploded view of the board assembly

Exploded view of the board assembly

Environmental Qualification Tests

The environmental qualification effort that is planned for this new product includes 1000 thermal cycling form -40 to 85°C as per MIL -STD-883 method 1010, vibration tests as per MIL -STD-883 method 2007, live vibration tests as per MIL -STD-1344 method 2005, mechanical shock tests as per MIL -STD-883 method 2002 and MIL -STD-1344 method 2004, thermal shock tests as per MIL -STD-883 method 1011, damp heat tests as per MIL -STD-202 method 103, salt fog as per MIL -STD-1344 method 1001, sand & dust as per MIL -STD-810 method 510, insertion/extraction force as per MIL -STD-1344 method 2013 and 500 mate/unmate cycles as per MIL -M-28787.

 

Performance test setup

Performance Test Setup. TX

Transmit setup

Performance Test Setup. RX

Receive setup

Results of design verifications tests

Rack-mount integrations were completed in order to confirm the volume manufacturing compatible assembly procedure and the required mechanical tolerance accuracy of the connector through blind mating. Moreover, through design verification tests on the transceiver module, we confirmed the excellent performance of these active optical connectors for operating temperature ranges of at least −40 ºC to 85 °C, at 10 Gbps per lane, giving bit error rates better than 10−12 for sensitivities of at least −12 dBm, when all 4+4 lanes are active simultaneously at 10 Gbps. Prototypes have been submitted to 1000 temperature cycles from −40 ºC to 85 °C and no significant degradation of their performances were observed after completion of these tests.

Results of design verifications tests at −40ºC

LightCONEX eye digram at −40 ºC

Results of design verifications tests at room temperature

LightCONEX eye digram at room temperature

Results of design verifications tests at 85ºC

LightCONEX eye digram at 85 ºC

Results of Environmental Qualification Tests

Vibration: based on MIL-STD-883, Method 2007.3; 20 Hz to 2000 Hz, 20 g, 16 min par axis: PASS
Thermal shock: MIL-STD-883, Method 1011.9, 20 cycles, 0 ºC to 100 °C, 10 min dwell time, 5 s transient time: PASS
Temperature cycling: MIL-STD-883, Method 1010.8; 1000 cycles −40 ºC to 85 °C, ramp > 10 °C/min, 5 minutes dwell time: PASS

Upcoming Environmental Qualification Tests

Damp heat: MIL-STD-202, Method 103B; 85% humidity, 85°C, 500 h
Cold storage: MIL-STD-810, Method 502.5; −57 °C, 168 h
Temperature cycling: MIL-STD-883, Method 1010.8, 100 cycles, −57 ºC to 100 °C, ramp > 10 °C/min, 5 minutes dwell time .
Mechanical shock: MIL-STD-883, Method 2002.4; 500 g, 0. 5 ms pulse, 5 repetitions, 6 directions.

VITA 46 Environmental Qualification Tests

Live Vibration: MIL-STD-1344, Method 2005, Test Condition V, Letter D; 1.5 h per axis, 0.1G2/Hz (see solid curve below)
Live Vibration and Temperature Cycling: Same as above, plus −40 ºC to 100 °C cycling with 30 min dwells and 15 min ramps
Mechanical Shock: MIL-STD-1344, Method 2004, Test Condition A; 50 g in perpendicular axis, 80 g in other axes, 11 ms, half sine, 3 repetition, 6 directions
Humidity/Temperature Cycling: MIL-STD-1344, Method 1002, Type III; 85 to 95% humidity, with 28 ºC to 71 °C temperature cycles over 24 h, 10 cycles for a total of 240 h
Salt Fog: MIL-STD-1344, Method 1001, Test C; 35 °C, 0.5 to 3 ml of NaCl solution per hour for each 80 cm2 area for a total of 500 h
Sand and Dust: MIL-STD-810, Method 510.4, Procedure I; Blowing dust particle size < 150 mm, velocity 1750 ft/min; Blowing sand particle size > 150 mm but < 850mm, velocity 5700 ft/min
Durability with Misalignment: MIL-M-28787, 500 mate/unmate cycles with an initial misalignment of 2 mm

Live Vibration: MIL-STD-1344, Method 2005, Test Condition V

Conclusion

  • Introduction of the LightCONEX: a new board edge mount active optical connectors
  • A novel VPX blind mate active optical plug-in to backplane connector for embedded communication systems
  • The plug-in printed-circuit board interface integrates a low-profile, rugged, 4+4 channels fiber optic transceiver (or 12TX, or 12RX) operating at 10 Gbps per lane, over a temperature range from −40 ºC to 85 °C
  • Future perspective: 28Gbps per lane and 12+12 transceivers

Rugged Optical Transceivers for Embedded Computing Systems

The objective of this white paper is to show how important and critical optical interconnect is becoming in the development of high-performance embedded systems.
By: Gérald Persaud, VP Business Development and Michel Têtu, Senior Business Development Advisor

Embedded Systems Market to Reach $133B by 2020*

Eyes and ears everywhere

For military and aerospace applications, C4ISR (Command, Control, Compute, Communicate, Intelligence, Surveillance, Reconnaissance) is invaluable for almost instantaneous high-end decision making. 

*: MarketsandMarkets

Command, Control, Compute, Communicate, Intelligence, Surveillance, Reconnaissance

Intelligence, Surveillance, and Reconnaissance Process

The Intelligence, Surveillance and Reconnaissance process (ISR) requires the collection and processing of signals generated by a large amount of sensors of various types like active electronically scanned array (AESA) radars, high resolution cameras, sonars and so on. Analog signals are digitized and transmitted to a high performance embedded computing unit (HPEC) for data fusion and processing through high bit-rate fiber-optic links. Through deep learning algorithms, actions to be taken are identified and communicated to decisional centers. 

ISR Technology Trends

HPEC are made of multiple high-speed microprocessors, memory and storage set on electronic boards usually interconnected through copper backplane circuitry.
However with the data rate of these interconnects reaching over 10 Gbps, optical interconnects begin to be the preferred choice due to their high bandwidth, high density I/O, low loss, low weight, and immunity against EMI.

  • Sensors: higher resolution cameras and radars
  • Processor: multicore, low power GPGPU, GPP, FPGA
  • Storage: solid state, small, rugged, reliable (RAID)
  • Sensor fusion: correlate information from sensors
  • Computing: Virtualization, parallel processing 
  • Small SWaP: more capability for SFF (3U VPX)
  • All digital: multi-purposed, software defined functionality
  • Intelligent: learning machines
  • Data rich: real-time and historical data
  • Secure: hack-resistant communications
  • Reliable: no single point failure
  • Small: more payload for other systems
  • Scalable: simple upgrades, long life
  • Multi-purposed: target ID, weather, communications.
Computerized Command, Control, Communications, Intelligence, Surveillance

Illustration of the relation between the different elements of C4ISR systems (Command, Control, Compute, Communicate, Intelligence, Surveillance, Reconnaissance).

Applications of optical interconnect in some high-performance systems

Space Fence Radar: Toward all-digital AESA radar

Learn more on the Space Fence project 

US Air Force Space Surveillance Network

Active electronically scanned array (AESA) radar
  • Detect, track, catalog satellites and debris on earth orbits
Transmitter array
  • S-Band (2 GHz to 4 GHz)
  • 36 000 independent radiating elements
  • Can generate thousands of radar beams
Receiver array
  • Separate from transmitter array
  • 86 000 independent receiving elements
  • DBF and frequency multiplexing allow for thousands of received beams
Space fence US Air force Space Surveillance Network

ISR technology trends: BAE ARGUS IS system

Learn more on the BAE ARGUS system

  • Four high-resolution visible light cameras
  • Uses 368 CCD COTS 5 Mp cameras
  • 4×48 fiber optical ribbon cables
  • 16×SNAP 12 @ 3 Gbps offering 600 Gbps total I/O throughput

Optical interconnect is used on ARGUS IS system

  • High BW, low latency
  • Small SWaP
  • High density
  • Defines system performance
Optical interconnect in BAE Argus IS
Autonomous Real-Time Ground Ubiquitous Surveillance Imaging System (ARGUS-IS)

Electrical vs optical interconnect power consumption

This diagram shows a rough evaluation of electrical power consumption for the connection of a sensor to an embedded computer system. Here we only consider the front-end of each system. Optic interconnect need 2 to 3 times less power than an electrical connection.

Electrical vs optical interconnect power consumption

Summary of Embedded Optics Benefits

LighABLE embedded transceiver

Reflex Photonics chip size rugged parallel optic transceivers meet the requirements for harsh environment applications. 

Performance

  • Proven: Thousands used in aerospace and defense applications
  • Scalable BW: 28 Gbps+
  • Receiver sensitivity: –12 dBm
  • Low bit error rates: 10−15
  • Low loss: 0.003 dB/m (OM3 @850 nm)
  • Reach: 300 m (OM3 @10G)
480G full duplex I/O card

480G full duplex I/O. FPGA processors, server cards, and cellular systems.

 

Small SWaP-C

  • Chip size optical transceivers
  • Less than 5 mm high
  • Light weight electronics and glass fiber
  • I/O density: 48 fibers in MT connector
  • Low power consumption: 1.2 W for 12 lanes @10 Gbps
Optic fiber offer much better I/O density that copper interconnect.

Micro-coaxial connectors compared to optical MT ferrule connector

 

Rugged

  • Complies with Telcordia GR-468-CORE and MIL-STD-883E standards for severe environmental conditions.
  • Operating temperature: −40 °C to 85 °C operation @ 10 Gbps
  • Storage temperature: − 57 °C to 125 °C
  • Moisture and thermal shock resistant
  • EMI and EMP immune
Optic fiber are immune to electro magnetic interferences.

Harsh environment

 

VPX optical interconnect standards

ANSI/VITA Standard

  • ANSI/VITA 66.0: Optical Interconnect On VPX
  • ANSI/VITA 66.1: Full Size MT Variant
  • ANSI/VITA 66.2: ARINC 801 Variant
  • ANSI/VITA 66.3: Mini-Expended Beam Variant
  • ANSI/VITA 66.4: Half Size MT Variant
VITA 66.X standard
VITA 66.X standard

Image courtesy of TE Connectivity

VITA 66.4 backplane
VITA 66.4 standard

Image courtesy of ELMA

Under consideration

VITA 65: Open VPX
VITA 67.3C: VPX: Coaxial & Optical Interconnect,
VITA 76: High Performance Cable Standard
VITA 78: Space VPX Systems
VITA 78.1: Space VPX Lite
VITA 74 VNX: Small Form Factor VPX

VITA 67.3C standard
VITA 67.3C standard

Image courtesy of TE Connectivity

LightCONEX blind mate optical interconnect

For a higher level of integration, Reflex Photonics in collaboration with Amphenol Aerospace, developed optical blind mate connectors where the optical transceiver is directly embedded in the plug-in module connector  following ANSI/VITA VPX technology.

  • Supports 2 level maintenance
  • Integrates optical transceiver into plug-in module connector
  • Less board space needed for optical interface
  • Fits VITA 66.4 backplane aperture for upgrades
  • No need for fiber optic handling
VPX board with VITA 46 and LightCONEX plug-in connectors.

VPX board with VITA 46 and LightCONEX plug-in connectors.

VPX backplane with LightCONEX blind mate optic

ELMA 3U VPX backplane with VITA 46 and LightCONEX connectors.

VPX backplane with LightCONEX blind mate optic

Close-up of the LightCONEX plug-in module connector.

VPX backplane with LightCONEX blind mate optic

Close-up of the LightCONEX backplane connector.

VPX optical solutions with Reflex Photonics embedded optics

Amphenol VPX media converter

  • 6U VPX media converter
  • Converts backplane high-speed signal to front optical and electrical Ethernet I/O
  • 32 × 10G BASE SR in a VITA 66.1 connector
  • 4 × 10G BASE-T and 8 × 1G BASE-T
Amphenol VPX media converter. Converts backplane high-speed signal to front optical and electrical Ethernet I/O

Interface Concept Optical FMC Board

  • Transceiver board (12TX + 12RX)
  • 120 Gbps full duplex
  • Supports front panel Optical Interface
  • Interfaces with 3U VPX FPGA boards
 New generation Optical FMC cards use LightABLE LH SR12 embedded optical transceivers.

Meritec Active Optical Module

  • Extends electrical reach to 100 m @10Gbps
  • Converts electrical to optical signals
  • Size 17 VITA 76 electrical connector
  • 12-lane MT optical in a size 11 shell
Meritec Active Optical Module.  Converts electrical to optical signals Size 17 VITA 76 electrical connector 12-lane MT optical in a size 11 shell.

In conclusion

Reflex Photonics rugged parallel optic transceivers meet the requirements for harsh environment applications and offer:

High performance with less SWaP-C

Operation under industrial temperature range (-40°C to 85°C) with BER as low as 10−15 delivering 10 Gbps/ch and –12 dBm sensitivity. Less than 5 mm high. Low power consumption 100 mW/ch.

Proven

Thousands used in aerospace and defense applications.

 

Rugged

Fully qualified following Telcordia GR-468-CORE and MIL-STD-883E standards for severe environmental conditions. 

Reliable

Successful 2500 h Accelerated Life Testing @ 100 °C.
Storage temperature from −57 °C to 125 °C.

Winning edge for design engineers

Parallel Optics: The Next Leap for Embedded System

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

C4ISR applications

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

Command, Control, Compute, Communicate, Intelligence, Surveillance, Reconnaissance
Computerized Command, Control, Communications, Intelligence, Surveillance

Illustration of the relation between the different elements of C4ISR systems (Command, Control, Compute, Communicate, Intelligence, Surveillance, Reconnaissance).

ISR trend

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 …
UAVs with high resolution sensors and high performance embedded computing have become an invaluable tool to defense. These drones can survey large areas quickly and at much lower cost than manned aircraft.
Phased array radar require massive amount of interconnect bandwidth

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. 

Surface mount

  • 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

Optical Connector

  • MT connector enables pick-and-place part
  • MT connector simplifies manufacturability (no pigtail)

Cable

  • 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.

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.

System performance -BER
10G Challenge. The closing eye has a significant impact on BER

10G Challenge

  • 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.

Operating temperature

  • -40 ºC to 85 ºC or wider
  • Considerations: BER at 10G – due to laser response over temperature

Storage temperature

  • -57 ºC to 125 ºC
  • Considerations: Reliability – mechanical stress, laser alignment

Shock and vibration

  • MIL-STD-810xx – aircraft, land vehicles, gun shock
  • Considerations:
    • Socket with low wipe contact is a concern
    • Mechanical attach strength – SMT vs socket

SWaP-C

  • 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

Moisture

  • 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

  • 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

Performance

  • Scalable BW – up to 28G
  • Signal integrity – BER of 10-15
  • Low loss – 0.003 dB/m (OM3 @10G)
  • Reach – 300 m (OM3 @10G)
480G full duplex I/O card

SWaP-C

  • 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
Optic fiber offer much better I/O density that copper interconnect.

Rugged

  • -40 ºC to 85 ºC operation @ 10 Gbps
  • MIL-STD-810xx Shock and vibration
  • Moisture resistant
  • EMI and nuclear radiation immune
Optic fiber are immune to electro magnetic interferences.

Reliability of Connectorized 10 Gbps/Lane Optical Fiber Transceivers

These products passed extensive qualification tests to demonstrate their robustness; including 1000 temperature cycles, damp heat, vibration, mechanical shock and thermal shock.
By: Jocelyn Lauzon, Tomasz Oleszczak, David Rolston, Robert Varano, Saïd El Kharraz, Naeem Safdari

Introduction

Reflex Photonics Inc. has developed compact 4+4 12.5 Gbps/lanes optical fiber transceivers for harsh environment applications such as Aerospace and Defense (see Fig. 1a). The LightABLE™ product series offers chip size transceivers that can operate from -40°C to 100 °C with a reach of more than 100 m on OM3 fibers with bit error rates (BER) as low as 10-15.
These products passed extensive qualification tests to demonstrate their robustness; including 1000 temperature cycles, damp heat, vibration, mechanical shock and thermal shock [1, 2]. What remained to be tested was their live reliability, through a 12-fiber ribbon cable pigtail mated to the LightABLE™ product through the proprietary MicroClip MT ferrule design (see Fig. 1b).

LightABLE rugged embedded transceivers

Fig. 1. a) LightABLE optical fiber transceivers

MicroClip MT ferrule

Fig. 1b) MicroClip MT ferrule mating between a LightABLE and a 12-fiber ribbon cable.

Test setup

In order to confirm the fiber mating reliability of this product, two different tests were undertaken: a live vibration test as per MIL-STD-883K, Method 2007.3 [1] and a live fiber pull test as per GR-468-CORE, Section 3.3.1.3.2 [2].
The test configuration is described in Fig. 2. The configuration corresponds to a loopback test, where the signals incident to the 4 transceiver detector lane of the device under test (DUT) generates the signals that drive the 4 transmitter lanes of the same DUT, that are then analyzed for error count. Before reaching the optical detector of the DUT, the 10 Gbps pseudo-random binary sequence (PRBS31) optical signal is attenuated to the sensitivity limit of the detector for a BER of 10-12 in normal room temperature test conditions (no vibration or pull test weight). Thus, if there is a signal degradation of the DUT while it is submitted to vibration or pull test weight, there will be a cumulative effect from the transmitter and receiver sections of the DUT that would impact the error count.
The live vibration test involved 5 different SR4 LightABLE units on TinLead (SN63 material) ball grid arrays (BGA) that were soldered to a printed circuit board. Having optical fiber transceivers that are connectorized rather than fiber pigtailed does allow for these products to be soldered to printed circuit boards using a standard reflow process; but then the reliability of the fiber mating associated to a connectorized configuration has to be confirmed through a process such as what is described here. During the live vibration test, each DUT, soldered to the test board, is fixed on a dynamic shaker bench and excited with single harmonic motion according to the following vibration profile: the vibration frequency is to be varied logarithmically between 20 Hz and 80 Hz and then set at a 20 g peak acceleration condition from 80 Hz to 2000 Hz; for 16 minutes in each of the orientations X, Y and Z. All 3 orientations are tested successively with the same unit (see Fig. 3a).

Live vibration and fiber pull tests configuration.

Fig. 2. Live vibration and fiber pull tests configuration.

The same test conditions were repeated for 3 pluggable DUT, having a MegArray™ electrical interface, instead of the surface mount BGA.
The same configuration was used for the fiber pull tests, for 3 DUT units, with the difference that no dynamic shaker was involved and that a weight was applied directly on the 12-fiber ribbon cable connected to the DUT, about 20 in. from the unit, while it is fixed vertically (see Fig. 3b).

LightABLE being subjected to vibration test

Fig. 3. a) Live vibration test setup for the longitudinal orientation

LightABLE being subjected to live fiber pull test
Live vibration test conditions

Live vibration test conditions

Live vibration test conditions

Vibration spectrum profile

The DUT must display, on all lanes, at all times during the tests, a BER better than 10-12 for the test result to be considered a success.

Results

For all lanes of all DUT submitted to the live vibration tests, either soldered to the test board or plugged, for all 3 orientations, the BER was better than 10-12, with most lanes from most units showing no errors during the tests.
For the live fiber pull tests, we did not measure any error on any lane during the tests, for an applied weight up to 1 kg.
This exceeds by a factor of 2 the limit set by Telcordia GR-468-CORE for the Fiber Integrity Side Pull Test [2].

 

Live vibration test results

Live vibration test results

Live fiber pull test results

Live fiber pull test results

References

[1] MIL-STD-883K, Test Method Standard Microcircuits, US Department of Defense, April 2016.
[2] GR-468-Core, Issue 2, Generic Reliability Assurance Requirements for Optoelectronic Devices Used in Telecommunications, Telcordia, September 2004.

Rugged Optic: New Possibilities for HPEC in Harsh Environment

High input/output interconnects are essential to high performance embedded computing systems (HPEC) and optical technology offering small size and weight and requiring low power consumption is becoming the preferred technology. However for harsh environmental conditions as encountered in defense and aerospace applications rugged optical systems must be devised.
by Michel Têtu, Reflex Photonics Inc.

High Performance Embedded Computing Systems (HPEC)

High performance embedded computing (HPEC) systems are essential to decisional systems where a huge amount of data must be collected and processed in a very short time to guide proper decisions and urgent actions. These systems are generally made of multiple electronic boards interconnected in a box through a backplane circuitry. Most of this circuitry is made of copper wiring but optical interconnects start to be used when high bandwidth high density I/O are requested.

C4ISR Applications

In the defense world, HPEC plays a major role in C4ISR systems (Command, Control, Compute, Communicate, Intelligence, Surveillance, Reconnaissance). For some applications, like active electronically scanned array radar, the information is generated by thousands of sensors. This information is usually in the form of analog signal and has to be digitized before being transmitted to the processing unit. The analog-to-digital conversion has to be high resolution and the communication link to the processing element has to be at high bit rate. (figure 1)
These C4ISR systems are often mounted on mobile platforms and used in harsh environment where extreme storage temperature, wide operating temperature range, high mechanical shocks and vibration are encountered. These operational constraints mandate the use of rugged systems and components. Other important characteristics of these systems are that they must be of small size and weight and consume as little operating power as possible.

Small SWaP Optical Interconnects

The optical interconnects can be used to carry the information from the sensors site to the computing site, between the computing boards, and between the computing system and the communication system. Optical interconnects are perfectly suited to meet the requirements of small SWaP in harsh environment.
It is well known that the size of lasers and photodetectors is of the order of a millimeter. The wavelength involved is of the order of a micron, so the fiber diameter required to guide the light is less than a millimeter. Made out of silica the weight per meter of a fiber is negligible. The weight of an optical transceiver results is mainly made of the electronic board needed to drive the laser and amplify the current generated by the photodetector, the optical connector, and the mechanical housing.
Because the light is guided through a highly homogeneous material, the signal attenuation resulting from scattering is extremely low (2.3 dB/km). This low fiber attenuation and the high efficiency of signal conversion (from electrical-to-optical of the laser, and from optical-to-electrical of the photodetector) generate very low electrical power requirements in order to drive a transceiver and carry the signal over hundreds of meters.
In addition, the fiber is dielectric so there is no susceptibility to electromagnetic interference (EMI). All of these benefits offer great advantages over copper interconnections.

 

Computerized Command, Control, Communications, Intelligence, Surveillance

Figure 1
Illustration of the relation between the different elements of C4ISR systems (Command, Control, Compute, Communicate, Intelligence, Surveillance, Reconnaissance).

LightABLE embedded transceiver in surface mount and pluggable variants

Figure 2
LightABLE products (transmitter, receiver, or transceivers) can be surface mounted or plugged. They are fully qualified for harsh environment.

Rugged Parallel Optic Transceiver

Reflex Photonics has developed the LightABLE products family to meet the demanding requirements of optical interconnects for HPEC used in harsh environment as encountered in defense and aerospace applications. The LightABLE 40G SR4 is a 4-lane full duplex transceiver operating at 10 Gbps per lane and the LightABLE 120G SR12 is a 12-lane transmitter or receiver operating at 10 Gbps per lane. (figure 2) These embedded parallel optic modules have been fully qualified following the Telcordia GR-468-CORE and MIL-STD- 883E standards and includes severe environmental, mechanical and long-term reliability tests. They offer: small SWaP, operation under 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 optical fiber interface is a standard MT ferrule directly attached to the module for compatibility with standard die mounting processes. The LightABLE products can be surface mounted with regular lead or RoHS reflow process or plugged in close proximity to high-speed electronics and support high temperature reflow process; a unique feature for such products. (figure 3)

LightABLE MicroClip

Figure 3
The MicroClip is a low-profile, low-mass spring loaded MT ferrule.

A proprietary MicroClip MT ferrule has been also devised by Reflex Photonics to connect the LightABLE module to a 12-fiber ribbon cable pigtail. The MicroClip is a low-profile, lowmass spring loaded mechanical assembly that offers a rugged optical connection that is resistant for shock and vibration and is suitable for harsh environment. The MicroClip has proven it can withstand a 1 kg live traffic fiber pull test when mated to its products (40G SR4 and 120G SR12), without any signal performance degradation. This result exceeds by a factor of 2 the requirements of Telecordia GR-468-CORE Fiber Integrity Side Pull Test and confirms the reliability of the Reflex Photonics fiber ribbon interface with the LightABLE and its MicroClip ferrule.
To achieve such performances the LightABLE products are designed with unique features and assembly processes in order to:

  • Maintain laser response over the temperature range;
  • Avoid mechanical stress between parts;
  • Use surface mount technology and low height parts for high resistance to shock and vibration;
  • Use no heat sink or pigtail fiber for pick and place manufacturability;
  • Use sealed enclosure to avoid moisture from obstructing optics.

The future of optical interconnects in HPEC applications

Although there is a large interest for optical interconnects, it is fair to say that we are only at the beginning of their use in the development of high performance embedded computing systems. We see, in open standards organization like VITA, many working groups considering modifications to standardized board-to-backplane connectors in order to include optical interconnects.