LightCONEX™ blind mate optical interconnect for VPX embedded computing systems integrates a LightABLE optical transceiver into the plug-in module 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