10 Gbps Tunable VCSEL-based SFP+ with Integrated G.METRO Functionality for Fronthaul Access Networks

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Hung Kai Chen, Christopher Chase*, and Michael Huang
Bandwidth10 LTD, 1218 Seventh St., Suite A, Berkeley, CA, USA
Email: cchase@bandwidth10.com

Introduction
Motivation

  • Low cost, 10 Gbps, tunable, 1550 nm transceiver for DWDM PON front haul access networks driven by C-RAN architectures
  • Tunablility needed for lower in the field installation and maintenance costs
  • Conventional wavelength lockers are too costly for the access market.

Innovations

  • High contrast grating (HCG) as a MEMS-actuatable mirror for a low cost directly-modulated tunable VCSEL-based transceiver
  • Using the AWG and other components alreadypresent in the system, the laser wavelength can be locked without any integrated locker using draft ITU-T G.METRO approach.
  • Low speed optical signaling integrated in the transceiver can change channel, wavelength lock laser, and provide other system level functions without any additional hardware.

 

VCSEL-Based SFP+

  • Designed for cost-sensitive, DWDM market applications
  • SFP+ form factor with tunable VCSELTOSA and APD receiver at up to 10 Gbpsover 10+ km of fiber with no compensation.
  • 16+ channelson a 100 GHz DWDM grid inthe C or L band

  • ＜1.5 W power consumption
  • Operates over commercialtemperature range
  • Industrial temperature range upto 3 Gbps
  • Industrial temperature at 10Gbps in development
  • 50+ dB SMSR for all channels
  • Power ~+1~-1 dBm across the tuning range

  • Consistent ER achievedacross the tuning range of 5±0.1 dB
  • Bit error rate of 4 channels across the tuning range was measured at 10.3 Gbps
  • with PRBS 231-1, back-to-back and after 10 km of SMF-28

  • Power penalty is ~ 2.7dB for 10 km of fiber at 10 Gbps for all channels.
  • Received power at 10 Gbps at a BER of 10-3 Back-to-back was -29.2dBm
  • Longer links can be realized using DCM
  • Allows for 22+ dB link budgets at 10 Gbps
  • Bit error rate after fiber transmission for 4 channels
  • This transceiver is a promising option for DWDM front haul access networks where low cost wavelength-locker-free transceivers are needed.

Transceiver Design with Integrated Low Speed Overlay

  • Transceiver follows draft ITU-T G.METRO specifications
  • Control signal is sent from the head end side of the link to the tail end of the link, controlling tail end receiver.
  • Control signal is a low duty cycle (~7-9%) signal at ~50 kbps, not interfering with the high speed payload
  • Tail end can send a pilot tone back to the head end, which can be used to ascertain the channel of the tail end transceiver with a tap on all of the signals and external signal processing on the head end side.
  • The transmitted low speed control signal is inserted by the MCU through low speed control of laser bias current, external to the high speed driver
  • Received low speed signal is detected and decoded by MCU after low speed/high speed filter split.
  • G.METRO commands and wavelength tuning data can be communicated through I2C interface
  • Implementation of tail end sending DDMI and other control information in progress

Wavelength Tuning and Stabilization by G.METRO

  • We use a system level feedback loop and components already in the networks such as the AWG to achieve wavelength stabilization in a DWDM system
  • This results in significantly lower overall system costs compared to having a wavelength locker in every transceiver.
  • Our SFP+ can act as the tail end unit in the system. HEE is under development
  • The TEE SFP+ can be remote controlled by the head-end equipment to change channels, fine tune the wavelength, and reset.
  • The same commands are also supported over I2C so the host can alternatively be used instead of low speed overlay, depending on the system-level approach

  • The system scans the transceiver wavelength until the power drop at the AWG’s band edges is seen, determining the edges of the AWG filter.
  • Afterwards, the wavelength is centered in the middle of the two band edges.
  • Channel can be repeatedly locked within ±15 pm using this technique.

Finding AWG center and locking wavelength

 

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