Advances in Widely Tunable Lasers Richard Schatz Laboratory of Photonics Royal Institute of Technology

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1 Advances in Widely Tunable Lasers Richard Schatz Laboratory of Photonics Royal Institute of Technology Tunability of common semiconductor lasers Widely tunable laser types Syntune MGY laser: tuning principle & performance Tunable modulation and wavelength conversion The tunable transmitter of tomorrow 1 Why tunability? Inventory reduction, sparing purposes (cost premium around 20% compared to DFB) Spectroscopy Measurement equipment Tomorrow: Wavelength routing? 2 1

2 Common Semiconductor Laser Types FP Fabry- Perot + very simple - multimode DBR B DFB Distributed Bragg Reflector Distributed Feed- Back + single mode + electric tunability ~ 10 nm - two waveguide materials - two contacts + simple - thermal tunability ~4 nm - inherently double mode PS-DFB Phase- Shifted Distributed Feed- Back VCSEL Vertical Cavity Surface Emitting Laser Tunability limited by Δλ Δn Γ < 1 10 λ n g 2 + single mode - thermal tunability ~4 nm - more complicated than DFB - needs antireflection coating + on wafer testing: low cost - thermal tunability~2 nm -low power - difficult transverse single mode - difficult >1.2 μm 3 DFB array Widely Tunable Lasers NTT (8 DFB) Fujitsu (8 DFB) Furukawa (12 DFB) Santur (MEMS-switch 12 DFB) + DFB technology + stable λ - coupler loss - chip size - powe consumption External cavity laser Tunable mirror or filter Iolon, Nec, Pirelli, Fujitsu, Intel + tuning range + spectral properties - size - tuning speed - modulation speed Monolithic DBR laser with sampled grating SG-DBR DS-DBR JDSU (Agility) Bookham Syntune + monolitic (incl. SOA & modulator) + size + tuning speed + power consumption + control - electrically induced - phase noise MGY-laser Jens Buus and Edmond J. Murphy, Tunable Lasers in Optical Networks,Journal of Lightwave Technology, Vol. 24, Issue 1, pp

Modulated Grating Y-branch Laser fabricated by Syntune Wide tuning by additive Vernier effect using two slightly different multi-peak reflectors Upper Lower Upper reflector MMI Lower

3 Modulated Grating Y-branch Laser fabricated by Syntune Wide tuning by additive Vernier effect using two slightly different multi-peak reflectors Upper Lower Upper reflector MMI Lower reflector Common phase Gain Front facet 5 40 nm tunability with high side mode suppression ratio and output power SMSR > 40 db Output power > 10 dbm Power variation < 1.5 db without compensation 6 3

4 Direct Modulation vs Modulator I bias +ΔI + I bias + - V bias +ΔV + Simpler + Higher Output Power + Inherently Linear Modulation (Radio over fiber applications) + Lower Chirp + Higher Extinction Ratio + Higher Modulation Bandwidth 7 Syntune S4500 C-band tunable 10 Gb/s transmitter Monolithically integrated MGY+SOA+MZM Full C-band tuning (89 channels at 50 GHz spacing) <100 ns switching time >40dB SMSR <±2.5 GHz wavelength drift over life >4dBm output power <2dB dispersion penalty (-800 to +800 ps/nm), <3.5 V driving voltage >11dB extinction ratio 8 4

Directly Modulated MGY-laser using chirp managed transmission Chirp adjusted so that a zero cause a π phaseshift, 101 becomes 10-1 dispersion tolerant External filter utilizes the chirp to enhance

5 Directly Modulated MGY-laser using chirp managed transmission Chirp adjusted so that a zero cause a π phaseshift, 101 becomes 10-1 dispersion tolerant External filter utilizes the chirp to enhance extinction ratio Matsui et al.,widely Tunable Modulated Grating Y-branch Chirped Managed Laser postdeadline ECOC Gb/s over 200 km standard fiber using direct modulation and chirp managed transmission 18 GHz bandwidth dt Error free 10 Gbit/s transmission over 200 km mw output power at all wavelengths db Extinction ratio Matsui et al.,widely Tunable Modulated Grating Y-branch Chirped Managed Laser postdeadline ECOC

6 Tunable wavelength conversion ( to ) at 10 Gb/s with MGY-laser integrated with SOA SOA IFR Gain MMI Right reflector Common phase Left reflector Utilising cross-gain modulation in SOA Conversion efficiency 20-70% Collaboration with University of Ghent Chacinski et al. OFC Recent Advances in Widely Tunable Lasers Richard Schatz Tunability of common semiconductor lasers Widely tunable laser types Syntune MGY laser: tuning principle & performance Tunable modulation and wavelength conversion The tunable transmitter of tomorrow 12 6

Packaged DFB-laser integrated with Trawelling- Wave

Distance 1/(Bitrate) 2 10 Gbit/s: 65 km 40 Gbit/s: 4 km 100

7 Packaged DFB-laser integrated with Trawelling- Wave Electroabsorption Modulator for 100 GbE 100 Gb/s NRZ PRBS dbm average power 4.3 db extinction ratio 13 Fiber Dispersion Dispersive fiber Distance 1/(Bitrate) 2 10 Gbit/s: 65 km 40 Gbit/s: 4 km 100 Gbit/s: 650 m! The solution? Adaptive dispersion compensation needed but still difficult to reach e.g. 65 km with 100 Gbit/s! 14 7

8 Radio Evolution vs Photonic Evolution 1887 Spark gap Transmitter On-Off keying 1903 First arc transmitter with continuos radio waves FSK keying 1906 First radio broadcast of voice and music AM modulation 1914 First coherent radio transmitter AM modulation FM stereo Broad- casting 1918 Superhetero- dyne receiver 1961 SSB modul- ation 1933 FM modul- ation. Subcarrier FM modulation First pulsed 1970 First CW 1970 First low loss 1975 First DFB Research on semiconductor semiconductor optical fiber singlemode coherent laser laser laser optical receivers 1987 First Erbiumdoped Fiber Amplifier Today fiber-optic systems for telecom still utilize simple on-off keying and direct detection (Morse code and crystal receiver) 15 Radio systems today are the future for photonics GSM WiFi GPS DVBS ADSL DVBT UMTS (3G) GMSK Gaussian Minimum Shift Keying OFDM or CCK Orthogonal frequency-division multiplexing CDMA Code Division Multiple Access QPSK Quadrature phase shift keying DMT Discrete multitone OFDM with QAM W-CDMA Next generation optical transmission systems will be advanced digital radio systems at optical frequencies 16 8

.. Higher spectral efficiency ( lower modulation

fiber dispersion More wavelength channels per fiber

bandwidth demands of electronics and photonics 17

16-QAM 1bit/symbol 1bit/symbol 2bits/symbol

9 Use more advanced modulation formats! DQPSK, QPSK, QAM, OFDM, SCM, SSB... Higher spectral efficiency ( lower modulation bandwidth for same bitrate) Better tolerance to fiber dispersion More wavelength channels per fiber (or higher bitrate for same channel grid) Lower bandwidth demands of electronics and photonics 17 Different carrier modulation formats OOK PSK QPSK 16-QAM 1bit/symbol 1bit/symbol 2bits/symbol 4bits/symbol Polarization multiplex yields another doubling of capacity within same WDM channel 18 9

10 Optical QPSK system with Polarization Multiplex (one channel in a WDM system) Complex integrated optical transmitters & receivers will be needed for low cost! 19 Subcarrier modulation 1-20 subcarriers, RF-generated Multicarrier modulation formats Optical Carrier OFDM Orthogonal Frequency Division Multiplex subcarriers, digitally generated. Carriers orthogonal over bitslot 200 THz±k. 10 GHz CDMA Code Division Multiple Access Carriers consist of orthogonal digital code sequencies instead of sinuses 200 THz±k. 10 MHz 20 10

Optical Subcarrier System for 100GbE Compare with ADSL modem for high speed data over telephone line High demands on linearity of modulator and detector Integrated optical

5 1550 1550.5 1551 λ Signal on fiber with IP data in baseband and DVBT on subcarrier IP data Other signal, e.g., DVBT Mixer Subcarrier @ GHz FBG Upper sideband filtered out and directly detected with low speed PIN detector λ B Other signal, e.

11 Optical Subcarrier System for 100GbE Compare with ADSL modem for high speed data over telephone line High demands on linearity of modulator and detector Integrated optical components needed for low cost km Transmission of 12.5 Gbit/s Baseband and DVBT on 45 GHz Subcarrier IP data Tunable Laser M-Z Modulator λ Signal on fiber with IP data in baseband and DVBT on subcarrier IP data Other signal, e.g., DVBT Mixer GHz FBG Upper sideband filtered out and directly detected with low speed PIN detector λ B Other signal, e.g., DVBT FBG Dispersion tolerant since only one sideband is used Residual lower sideband is filtered away by receiver filter 22 11

12 Final conclusions Monolithic 10 Gbit/s widely tunable lasers are today integrated with modulators and manufactured at high volumes and low price Monolithic devices offers fast tuning <100 ns over 40 nm. Can be modulated with integrated modulator, direct modulation or optically for direct wavelength conversion. Selling point today compared to DFB is the inventory reduction. Deployment today enables wavelength routing in the future. Future tunable lasers will be integrated with modulators for spectrally efficient modulation formats 23 12

Chapter 1 Introduction

Chapter 1 Introduction 1-1 Preface Telecommunication lasers have evolved substantially since the introduction of the early AlGaAs-based semiconductor lasers in the late 1970s suitable for transmitting