Parallel Optical All Pass Filter Equalisers and Implementation

Parallel Optical All Pass Filter Equalisers and Implementation by Wisit Loedhammacakra Supervision team Dr Wai Pang Ng Prof R. Cryan Prof. Z. Ghassemlooy Northumbria Communication Research Laboratories (NCRL) Northumbria University 13 th June 2007

Overview • Long-haul communication systems • Problem Statement • Chromatic Dispersion • Parallel Optical All Pass Filter Equaliser • Conclusion

Long-haul Communication System 1 Ideal Communication Systems • Audio • Video Tx Rx • Data Ideal communication system: Attenuation and dispersion limit • Unlimited transmission bit rate (B) BL product (as a benchmark for • Unlimited transmission distance (L) system’s performance) Ø Quality of digital communication systems can be monitored from bit error rate (BER) of system. Ø Error-free detection, BER less than 10 e-9 (Single error in one billion transmitted bits)

Long-haul Communication System 2 Evolution of Long-haul communication systems x x x Source: Agrawal

Long-haul Communication System 3 Optical Communication systems Generation Year Operation wavelength Attenuation 1 st 1970 s 0. 8 μm 1 d. B/km 45 M 10 km MMF 2 nd 1980 s 1. 3 μm 0. 5 d. B/km 100 M 50 km MMF 3 rd 1990 1. 55 μm 0. 2 d. B/km 2. 5 G 70 km SMF 4 th 1996 1. 55 μm 0. 2 d. B/km 2. 5 G 100 km SMF EDFA WDM SMF CD compensation 5 th 1999 1. 55 μm 0. 2 d. B/km Bit rate Repeat bit/s length 10 G 100 km Fibre type Special system Electronic repeater

Problem Statement Single Mode Fibre (SMF) ? Attenuation Dispersion • 1. 31 μm chromatic dispersion (CD) is zero, but high attenuation is 0. 5 d. B/km. • 1. 55 μm has high CD of 17 ps/nm-km while attenuation is the lowest (0. 2 d. B/km).

Chromatic Dispersion 1 Fibre Transmitted pulse 3 bits pattern of dispersed pulse Dispersed pulse 3 bits pattern of restored pulse

Chromatic Dispersion 2 Core of fibre

Chromatic Dispersion 3 Output Pulses of Different Lengths of SMF

Summed signal Chromatic Dispersion 4 Chromatic Dispersion Effect Transmitted pulse Summed signal Dispersed pulse at 111 km

Chromatic Dispersion 5 The Bit Rate-length Product • Doubling the bit rate (B) would reduce the repeater-less length (L) of optical communication systems by a factor of 4. • CD is the main limiting factor for repeater-less length.

Chromatic Dispersion 6 Dispersion Compensation Techniques DSF DCF FBG MZI OPC OAPF Dispersion shifted fibre Dispersion compensating fibre Fibre Bragg grating Mach-Zehnder interferometer Optical phase conjugation Optical all pass filter Optical Bandwidth Wide Narrow Wide Insertion Loss Accept High Accept Installation Difficult Accept Difficult Dispersion No Rippled No Ripple Temperature Stable Unstable Stable Dispersion Tunable No No Possible Cost High Accept

Parallel optical all pass filter equaliser (p-OAPF)

p-OAPF Equaliser 1 Compensated System by Using OAPF (a) (b) (c)

p-OAPF Equaliser 2 OAPF is Implemented With IIR Structure

p-OAPF Equaliser 3 Compensated System by Using p-OAPF

CD limits 10 Gb/s system at 30 km Conclusion Adjust the phase of the optical pulse back to the phase of transmitted optical pulse p-OAPF Be implemented in optical domain by using IIR structure and optical components Capable of extending the length to 90 km in 10 Gb/s systems

Papers Publications 1. W. Loedhammacakra, W. P. Ng, and R. A. Cryan, "Investigation of an Optical All Pass Filter for a 10 Gb/s Optical Communication System, " presented at PG-NET 2005 Proceeding, Liverpool John Moores University, UK, pp. 170 -175, 27 -28 June 2005. 2. W. Loedhammacakra, W. P. Ng, and R. A. Cryan, "An Improved Chromatic Dispersion Compensation Technique Employing an Optical All Pass Filter Equaliser in a 10 Gb/s Optical System, " presented at The Tenth High Frequency Postgraduate Student Colloquium, University of Leeds, UK, pp. 105 -108, 5 -6 September 2005. 3. W. Loedhammacakra, W. P. Ng, and R. A. Cryan, "Chromatic Dispersion Compensation Using an Optical All Pass Filter for a 10 Gb/s Optical Communication System at 160 km, " presented at London Communication Symposium 2005, University College London, UK, pp. 255 -258, 8 -9 September 2005. 4. W. Loedhammacakra, W. P. Ng, and R. A. Cryan, “Chromatic Dispersion Compensation Employing Optical All Pass Filter by Using IIR Structure for 10 Gb/s Optical Communication System, ” presented at the IEE Photonics Professional Network Seminar on Optical Fibre Communications and Electronic Signal Processing, The IEE Savoy place, London, UK, pp 17/1 -17/6, 15 December 2005. 5. W. Loedhammacakra, W. P. Ng, R. A. Cryan, and Z. Ghassemlooy, “Investigation of Optical All Pass Filter to Compensate Chromatic Dispersion in a 10 Gb/s Optical Communication System at 160 km, ” CSNDSP 2006, Patras, Greece, pp. 454 – 458, 19 – 21 July 2006. 6. W. P. Ng, W. Loedhammacakra, R. A. Cryan, and Z. Ghassemlooy, “Performance Analysis of the Parallel Optical All-pass Filter Equalizer for Chromatic Dispersion Compensation at 10 Gb/s, ” under-review by Globecom 2007. 7. W. P. Ng, W. Loedhammacakra, R. A. Cryan, and Z. Ghassemlooy, “Characterisation of a Parallel Optical All Pass Filter for Chromatic Dispersion Equalisation in 10 Gb/s System , ” under-review by IET processing on signal processing. Posters 1. Chromatic Dispersion Compensation Technique Employing OAPF in Optical Communication Systems, presented at UK Grad Poster Competitive 2006, Northumbria University, Newcastle, Aril 2006. 2. High Speed Optical Network Need Low Dispersion, presented at Britain’s Early-State Engineers on UK Engineering research and R&D, House of Commons, London, December 2006.

Acknowledgements I would like to thank: Ø My supervision team (Dr. Wai Pang Ng, Prof. R. Cryan and Prof. Z. Ghassemlooy) Ø OCR Group leader (Prof. Z. Ghassemlooy) for all of his support Ø Dr Krishna Busawon and Dr Mark Leach for all of the useful discussions we had Ø My colleague in Room E 405 and E 409 Especially, Hoa, Popoola, Sujan and Ming Feng for discussion and helpful.

Thank you Question & Discussion

Optical All Pass Filter Equaliser 1 Phases of SMF, Rectangular and Dispersed Pulse • The interested bandwidth is between 193. 49 – 193. 51 THz, which phase response of dispersed pulse is same as phase response of SMF.

Optical All Pass Filter Equaliser 2 Phase Response of Ideal Equaliser and OAPF • The phase response of the ideal equaliser is used as the optimisation criterion. • The phase response of OAPF at upper frequency does not equalise properly.

Optical All Pass Filter Equaliser 3 Optical Communication System

Optical All Pass Filter Equaliser 6 Output Pulses • A dispersed pulse was equalised back to 100 ps at FWHM. • The larger pulse width on the right hand side of compensated pulse is not properly compensated and resulted in higher ISI and BER.

Optical All Pass Filter Equaliser 5 Phase response • The compensated phase is close to zero at lower frequency. • At the higher frequency, the phase response is not properly compensated.

Results 1 Compensated Phase Response by p-OAPF

Results 2 Compensated Pulse by p-OAPF