Hung Kai Chen, Christopher Chase*, and Michael Huang
Bandwidth10 LTD, 1218 Seventh St., Suite A, Berkeley, CA, USA
- 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.
- 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.
- 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