University of Bristol - Explore Bristol Research. Peer reviewed version. Link to published version (if available): /LEOSST.2009.

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1 Khawaja, BAM., & Cryan, MJ. (2009). A hybrid mode locked laser as millimetre wave modulated data source for radio-over-fiber systems. In IEEE/LEOS Summer Topical Meeting, 2009 (LEOSST '09), Newport Beach, CA (pp ). Institute of Electrical and Electronics Engineers (IEEE). DOI: /LEOSST Peer reviewed version Link to published version (if available): /LEOSST Link to publication record in Explore Bristol Research PDF-document University of Bristol - Explore Bristol Research General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available:

2 A Hybrid Mode Locked Laser As Millimetre Wave Modulated Data Source For Radio-Over-Fibre Systems Bilal A. Khawaja and Martin J. Cryan Photonics Research Group Department of Electronic and Electrical Engineering University of Bristol, Bristol, BS8 1UB, UK. Contact:

3 Outline Radio-over-Fibre (RoF) Systems and 60GHz RoF System Mode-Locked Lasers (MLL) and Hybrid Mode Locking Comparison of Injection Locked (IL) MLL with IL-Oscillator and Phase shifting Wireless Injection Locking BPSK data transmission Conclusion and Future Work

4 Radio-over-Fibre (RoF) Systems Optical fibres low loss compared to RF cables at higher frequencies Long RoF links Application in phased array antenna systems Millimetre wave signals can be transmitted to many thousands of antennas RoF technique incorporating MLL allows phase shifting to be performed remotely from the array Future proof : fibre can handle very high frequencies and data rates

5 60GHz Communication systems Large unlicensed band ~9GHz bandwidth Up to 4Gbps wireless data transmission (WiHD) [1] Monolithic integration of antennas Reduced chip size - 60GHz Tx and Rx modules recently shown [2] (10mm x 10mm) Very high free space loss at 60GHz and high attenuation due to atmospheric oxygen Good frequency re-use simplifies system design [1] WirelessHD 1.0, 4Gbps Radio Standard Completed ( WirelessHD organisation is a Promoter of 60GHz band [2] A millimetre wave technology company ( - Vubiq, Inc. 65 Enterprise, Aliso Viejo, CA 92656, US

6 60GHz Radio-over-Fibre Systems 60GHz RoF systems Advantages [1-2] Steerable Beams Overcomes problem of delivering 4Gbps data to remote site No need to generate 60GHz at remote site 40GHz MLLs have been used: mm-wave phase shifters mm-wave data source Central Base Station In-building Fibre Based System MLL+ integrated antenna arrays beam steering (high speed internet access systems) [1] IEEE J. Light. Tech., 25 (11), pp. 1-6, 2007 [2] IEEE Microwave Photon. Tech. Digest 2000, pp

7 60GHz Antenna Systems Conventional 60GHz Antenna System Remote End 60GHz Local Oscillator Central Base Station ~ m Co-axial Cable Mixer Amplifier 4GB/s Baseband Data from Base Station MLL based 60GHz Antenna System Remote End S.A MLL Amplifier Laptops generating 60Ghz signals Mixer >1Km Gain Section Central P.D Base Station 4 GB/s Baseband Data to Base Station 60GHz Local Oscillator Optical Fibre Signal Direction

8 Mode-Locked Lasers as Millimetre wave sources Fabry-Perot (FP) lasers Short saturable absorber (SA) section Reverse biasing SA - Synchronize longitudinal modes Pulses repetition frequency (cavity round trip time) Device ~1mm long mm-wave frequencies S.A MLL supplied by Heinrich- Hertz-Institute (HHI), Berlin Gain 1080m Different mode exhibiting random Phase relationship [1] Light Out Modes locked together in Phase [1] [1] Mode Locking of Novel Semiconductor Lasers, PhD. Thesis by Craig.A Williamson Dec 2003, University of Essex, UK. pp

9 S21 (db) Hybrid Mode-Locking Setup and Results Port 1 VNA Port Hybrid injection locking around 40GHz -60 Power Supply S.A. Gain Bias (I g ) P.D P-1 and P-2 are phase locked Frequency (GHz) Single Mode Fibre Lens S 21 link gain of I g = 110mA and V sa = -1.1V [1] [1] B. Khawaja and M. Cryan, A Millimetre Wave Phase Shifter Using a 40GHz Hybrid Mode Locked Laser, IEEE International Conf. on Emerging tech. (ICET), Pakistan, Oct 2008

10 S21 (db) S21 Phase (Degrees) Millimetre Wave Phase Shift using Vector Network Analyser (VNA) Flat Plateau in S 21 locking range S 21 phase measurement - VNA allows observation of phase response We observe classical injection locked (IL) oscillator phase response given by: ( ) Sin 1 L MHz Vsa - 1.5V Vsa - 1.5V (Phase) 172 o Frequency (GHz) +0.6dBm RF Input to S.A [1] Where ω 0 = output signal, ω 1 = Injected signal and Δω L = locking range of oscillator [1] B. Khawaja and M. Cryan, Study of Millimeter Wave Phase Shift In 40GHz Hybrid Mode Locked Lasers, IEEE Microwave and Wireless Comp Lett., 19 (3), pp. 182, (2009)

11 Millimetre wave Phase Shifter using MLL and Planar Antennas Future 60GHz RoF systems MLLs + antennas integration low frequencies [1] Hybrid MLL driven by a planar antenna connected to the S.A section has been presented [2] Towards the full monolithic integration of MLLs and antennas Important part of future low cost mm-wave WLAN systems (beam steering capabilities) [1] V. Sittakul and M. Cryan, IEEE J. Light. Tech, 25 (11), pp. 3358, (2007) [2] B. Khawaja, I. Djordjevic, and M. Cryan, A Millimeter Wave Phase Shifter Using A Wireless Hybrid Mode Locked Laser, OFC 2009, San Diego, California, USA, OSA Technical Digest (CD), paper OTuM5

12 S21 (db) S21 Normalised Phase (Degrees) MLL and Antennas Measurement Setup and Results Network Analyzer (Agilent E8364A) Port - 1 Port - 2 Horn Antenna 26.6dB Patch Antenna G L ~21 db Power Supply Bias Tee S.A Gain Bias (I g ) MLL injection 10cm wireless range PD mm-wave Amps Distance d Co-axial cable loss = 40GHz mm-wave Amps Single Mode Fibre Lens mm-wave amps used to overcome path loss 1m SMF Wireless Injection Locking Setup using Horn and Patch Antennas ~ +14dBm estimated power to S.A section o Vsa V Vsa - 1.2V Vsa V Vsa - 1.2V (Phase) Vsa V (Phase) Frequency (GHz)

13 BPSK Data Transmission Pattern Generator 40GHz Wiltron Sweeper Infiniium Oscilloscope Quality Factor Q = PBRS NRZ Data Up-Conversion IF 40GHz RF CW output = +6dBm Coaxial cable Loss = 40GHz + 30dB LPF IF Down-Conversion 20ns 200mV (a) RF LO G L ~ 24dB Mixer db RF Splitter LO RF dB Mixer dB Quality Factor Q = 5 SA RoF Link 40GHz MLL 1m SM Fibre Lens 50GHz U 2 T PD 20ns 200mV (b) Power Supply Setup Configuration for NRZ-BPSK Data Transmission using MLL - RoF Link Down converted BPSK data eye patterns after MLL-RoF Link for the data rates of (a) 24MB/s and (b) 26MB/s

14 BPSK Wireless Data Transmission Coaxial cable loss = 40GHz PBRS NRZ Data Up-Conversion Pattern Generator IF 40GHz Wiltron Sweeper 40GHz RF CW output = +6dBm Coaxial cable Loss = 40GHz Infiniium Oscilloscope + 30dB LPF IF Down-Conversion Quality Factor Q = 7 RF LO + 25dB Mixer dB RF Splitter LO RF dB Mixer dB 20ns 500mV (a) Quality Factor Q = 7 3 cm G L ~ 19.5dB SA RoF Link 40GHz MLL 1m SM Fibre Lens 50GHz U 2 T PD Power Supply Setup Configuration for NRZ-BPSK Wireless Data Transmission using Horn to Patch Antenna and MLL-RoF Link 20ns 500mV (b) Down converted BPSK data eye patterns after MLL-RoF Link for the data rates of (a) 18MB/s and (b) 20MB/s

15 Conclusion and Future Work Shown the characteristic of Injection locked MLL as compare to classical IL-Oscillator Shown hybrid Mode Locking of 40GHz MLL using a wireless connection to the S.A section using planar antenna Shown first wireless data transmission over MLL Radio-overfibre link Stepping stone to full monolithic integration of MLLs with antennas Dramatic reduction of costs in RoF systems Possible application of MLLs in low cost wireless LAN smart antenna systems Acknowledgements To: Bristol University Alumni Foundation for partial travel funding. National University of Science and Technology (NUST), Pakistan for PhD. funding. Department of Electronic and Electrical Engineering, University of Bristol, UK for funding.

16 Return Loss (db) Millimetre Wave Patch Antennas 4.3mm RT/Duroid substrate K-connector end plate 2.34mm Glass bead to feed-line transition Feed-line 1.59 mm Design Brass mounting fixture ADS Momentum Antennas Design Simulated Measured Patch Antenna - 1 Measured Patch Antenna Frequency (GHz) RT / Duroid high frequency glass microfibre substrate due to low loss r = 2.33 and Thickness = 0.254mm Patch Dimensions 2.34mm x 1.59mm

17 Mode-Locked Laser Device Mounting Configuration S.A MLL Device Used for Measurement Gain Light Out 1080m Fibre Lense Gain S.A 50Ω line K-Connector Picture of the MLL Setup Gold Plated Ceramic block Gold bond wires 8mm DC probe MLL Device Mounting Configuration Brass Mounting fixture

18 40GHz Amplifier Mounting Hittite (HMC-ALH369) mm-wave GaAs low noise amplifier Tx-line connection for Drain Bias (V dd ) Configuration 100F By-Pass Capacitor RF-Out Txline BWs K connector with end plate Brass mounting fixture RF-IN Tx-line and BW 40GHz Amplifier chip