Real-Time Coherent ONU Based on Fully Analogue Processing of OOK

SignalsF. Bottoni

Internal Workshop 20Scuola Superiore Sant’Anna, Pisa

January 29th, 2015

Next Generation PON requirements

1. Required capacity: any next generation ONU should support at least 1 Gb/s! (40 Gb/S DS and 10 Gb/s US)

2. ODN reuse: next generation-PONs should be able to reuse deployed optical power splitters within legacy TDM-PONs (Loss Budget 35÷40 dB)!

3. Coexistence: NG-PONs shoud operate in the available spectrum not already used by legacy PONs!

• Coherent WDM-PONs (included in the initial discussions for the standardization on NG-PON2) are interesting schemes to fulfill 1,2,3 but do require low cost devices/architectures

• COCONUT Project is aiming at demonstrating optical coherent technologies suitable for UDWDM-PONs

Real-Time Coherent ONU Based on Fully Analogue Processing of OOK Signals

Real-Time Coherent ONU Based on Fully Analogue Processing of OOK Signals

Technique Drawbacks

DSP and phase modulation format (PDM-QPSK [1], DQPSK [2])

Receiver complexity

Heterodyne detection and analogue processing [3]

heterodyne detection has some problems with Ultra-Dense (6.25 GHz) spacing

Self-Homodyne receivers in Reflective-PONs [4]

reflective architectures are not compatible with power-split ODN

Proposed architecture: homodyne detection (phase diversity) + ASK modulation

No ADC’s and DSP are needed to demodulate the signal

[1] Lavery, D. et al., "Digital Coherent Receivers for Long-Reach Optical Access Networks," Lightwave Technology, Journal of , Feb.15, 2013[2] Smolorz, S. et al. "Demonstration of a coherent UDWDM-PON with real-time processing," OFC/NFOEC, vol., no., pp.1,3, 6-10 March 2011[3] N. Satoshi et al. "Coherent WDM-PON using directly modulated local laser for simple heterodyne transceiver," ECOC 2005, vol.3, pp.449-450, 2005[4] Cho, K.Y.et al., "10-Gb/s, 80-km reach RSOA-based WDM PON employing QPSK signal and self-homodyne receiver," OFC/NFOEC 4-8 March 2012

Coherent receiver schemes for PON

Real-Time Coherent ONU Based on Fully Analogue Processing of OOK Signals

→ ProposalPhase diversity (relaxed requirements in terms of frequency locking and laser linewidths) homodyne receiver by using 3x3 optical coupler and DFB as LO

→ Key PointUse of commercially available and low cost electronics (squaring circuits, adder etc.)

Power split

Feeder Fiber

OLT

DFB externally (or directly) modulated at 1.25 Gb/s

DFB MZM

Setup/Architecture

C-ONU

LO

3x3

X2

X2

X2

Real-Time Coherent ONU Based on Fully Analogue Processing of OOK Signals

2

3

4

56789

10

-50-48-46-44-42-40-38-36-34

58km SMF

b2b

-log(

BE

R)

Power (dBm)

FEC limit

→ Measured sensitivity is around -47 dBm

→ BER performance (i.e. sensitivity -47 dBm) in line with the results obtained using offline digital processing

Results: BER performance

2

3

4

56789

10

-50-48-46-44-42-40-38-36-34

Digital RX

Analog RX

-log(

BE

R)

Power (dBm)

FEC limit

Real-Time Coherent ONU Based on Fully Analogue Processing of OOK Signals

→ negligible penalty (0.5 dB at BER = 10-10) is observed with the longest sequence (PRBS 231 -1)

→ Curves at v=1 GHz slightly better than at lower detuning: second harmonic filtered out at higher detuning + DC blocks after the PDs

2

3

4

56789

10

-50-48-46-44-42-40-38-36-34

PRBS 27 - 1

PRBS 231 - 1

-log(

BE

R)

Power (dBm)

FEC limit

Results: BER performance

2

3

4

56789

10

-50-48-46-44-42-40-38-36-34

= 300 MHz = 700 MHz = 1 GHz

-log(

BE

R)

Power (dBm)

FEC limit300 MHz

700 MHz

1 GHz

200 ps/div

Real-Time Coherent ONU Based on Fully Analogue Processing of OOK Signals

→ Real time implementation of a ASK coherent receiver

→ Results (sensitivity -47 dBm) indicate that a coherent ONU receiver based on devices commonly available (3x3 coupler, common DFB as LO and analogue devices for demodulation) and analogue processing is feasible

→ Under investigation

→ Real-time polarization independent and UDWDM operation

→ 2.5 Gb/s transmission

Conclusions

email: f.bottoni@sssup.it email: f.bottoni@sssup.it

thank you!thank you!