Integrated photonic beamformer employing continuously tunable ring resonator-based delays in CMOS-compatible LPCVD waveguide technology C. G. H. Roeloffzen*a, A. Meijerinka, L. Zhuanga, D. A. I. Marpaunga, R. G. Heidemanb, A. Leinseb, M. Hoekmanb, W. van Ettena. aUniversity of Twente, Faculty of Electrical Engineering, Mathematics and Computer Science, Telecommunication Engineering Group, P.O. Box 217, 7500 AE Enschede, The Netherlands bLioniX B.V., P.O. Box 456, 7500 AH Enschede, The Netherlands

System overview & requirements; Contents 1. Introduction; System overview & requirements; Optical beamformer - Ring resonator-based delays; - OBFN structure; - Chip fabrication; - OBFN control block; - E/O & O/E conversion; - System performance. Conclusions MWP » MWP in PAAs » SMART » Conclusions » Questions

1. Introduction: What is beamforming Smart Antenna systems: Switched beam: finite number of fixed predefined patterns Adaptive array: Infinite number of (real time) adjustable patterns MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Introduction: Smart antenna Smart Antenna systems: Using a variety of new signal-processing algorithms, the adaptive system takes advantage of its ability to effectively locate and track various types of signals to dynamically minimize interference and maximize intended signal reception. Beamforming: spatial filtering MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Beamforming: Uniform line array s(t) x0(t) d x1(t)  x2(t) xM(t)  (M-1) MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Beamforminh: Delay-sum When T=, the channels are all time aligned wm are beamformer weights Gain in direction  is wm. Less in other directions due to incoherent addition. Timed array (t-[M-1]T) x w0 (t-[M-2]T) x + w1 (t) x wM-1 MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Beamforming: Similar to FIR filter br Let T=0 (broadside) Represent signal delay across array as a delay line Sample: x[n]=x0 (nT) Looks like an FIR filter! x[n]*w[n] Design w with FIR methods x (t-) w0 x + y(t) w1 (t-) x wM-1 MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Beamforming: Narrowband Narrowband assumption: Let s(t) be bandpass with BW << c / (M-1)d Hz. This means the phase difference between upper and lower band edges for propagation across the entire array is small, e.g. < /10 radian. Most communication signals fit this model. If signal is not narrowband, bandpass filter it and build a new beamformer for each subband. Sample the array x[n]=x(nT), We can now eliminate time delays and use complex weights, w= [w0, …, wM-1] , to both steer (phase align) and weight (control beam shape) MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Beamforming: Narrowband phased array x0[n] x w0 x1[n] x + w1 xM-1[n] x wM-1 m = amplitude weight for sensor m, f0 = bandpass center frequency, Hz, 0 = direction of max response MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Beamforming: FFT implementation Suppose you want to for many beams at once, in different directions. If beam k steered to k , has strongest signal, we assume sources is in that direction. MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Beamforming: FFT implementation many beams at once x0[n] Amplitude Taper (multiply by ) FFT y0[n] x1[n] y1[n] xM-1[n] y(M-1)[n] MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Beamforming: Examples Electronic Digital Optical MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Examples: Electronic beamforming SiGe H. Hashemi, IEEE Communications magazine, Sept 2008 MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Examples: Electronic beamforming CMOS MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Examples: Electronic beamforming MMIC (CMOS & SiGe) + very small chip + TTD & phase shifters Switched delay + Large bandwidth + low power consumption - Large coupling between channels MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Examples: Digital beamforming MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Examples: Digital beamforming Frequency domain beamforming Narrowband decomposition MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Examples: Digital beamforming +Easy implementation of time delays Multiple data converters required Large sampling rate Large number of bits (large dynamic range) Large power consumption MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Examples: Optical beamforming +Easy MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Int: aose Smart MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Introduction: aim and purpose Development of a novel Ku-band antenna for airborne reception of satellite signals , using a broadband conformal phased array Purpose: Live weather reports; High-speed Internet access; Live television through Digital Video Broadcasting via satellite (DVB-s) MWP » MWP in PAAs » SMART » Conclusions » Questions »

1. Introduction: specific targets Conformal phased array structure definition; Broadband stacked patch antenna elements; Broadband integrated optical beamformer based on optical ring resonators in CMOS-compatible waveguide technology; Experimental demonstrator. MWP » MWP in PAAs » SMART » Conclusions » Questions »

2. System overview & requirements 8x8 8x1 gain 40x40 optical beam width Antenna array RF front-end beamformer to receiver(s) with amplitude tapering scan angle Frequency range: 10.7 – 12.75 GHz (Ku band) Polarization: 2 linear (H/V) Scan angle: -60 to +60 degrees Gain: > 32 dB Selectivity: << 2 degrees No. elements: ~1600 Element spacing: ~/2 (~1.5 cm, or ~50 ps) Maximum delay: ~2 ns Delay compensation by phase shifters?  beam squint at outer frequencies!  (Broadband) time delay compensation required ! 1  Continuous delay tuning required ! MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: overview plane position & angle antenna viewing angle feedback loop control block Antenna elements RF front-end OBFN chip E/O O/E to receiver(s) ? ? ? tunable broadband delays & amplitude weights. MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: ORR-based delays Single ring resonator:  Phase T : Round trip time;  : Power coupling coefficient;  : Additional phase.  f  Group delay Periodic transfer function; Flat magnitude response. Phase transition around resonance frequency; Bell-shaped group delay response; Trade-off: delay vs. bandwidth  f MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: ORR-based delays Cascaded ring resonators: ripple bandwidth  Group delay Rippled group delay response; Enhanced bandwidth; Trade-off: delay vs. bandwidth vs. delay ripple vs. no. rings;  f Or in other words: for given delay ripple requirements: Required no. rings is roughly proportional to product of required optical bandwidth and maximum delay MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: 8x1 OBFN 8x1 Optical beam forming network (OBFN) combining network with tunable combiners (for amplitude tapering) 8 inputs with tunable delays 1 output 12 rings 7 combiners  31 tuning elements MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: chip fabrication Fabrication process of TriPleX Technology MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: chip fabrication TriPleXTM results Group birefringence (Bg) Channel attenuation (dB/cm) Polarization dependent loss (PDL, in dB) Insertion loss (IL) without spot size converter (dB) ≤ 1×10-4 ≤ 0.10 0.12 1 1.4 2 1.1×10-1 0.12 0.20 1 8.0 2,3 1: chip length 3 cm 2: here, small core fibers were used (MFD of 3.5 µm) 3: minimal bend radius ~400 µm MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: 8x1 OBFN chip Single-chip 8x1 OBFN realized in CMOS-compatible optical waveguide technology TriPleX Technology 1 cm 4.85 cm x 0.95 cm Heater bondpad MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: OBFN control block beam angle delays + amplitudes ARM7 microprocessor chip parameters (is and is) DA conversion & amplification heater voltages MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: OBFN measurements OBFN Measurement results L. Zhuang et al., IEEE Photonics Technology Letters, vol. 19, no. 15, Aug. 2007 1 ns ~ 30 cm delay distance in vacuum MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion E/O and O/E conversions? low optical bandwidth; high linearity; low noise RF front-end LNA photo-diode DM laser OBFN chirp! TIA electrical » optical optical » electrical MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion E/O and O/E conversions? low optical bandwidth; high linearity; low noise RF front-end LNA photo-diode CW laser mod. OBFN beat noise! TIA electrical » optical optical » electrical MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion E/O and O/E conversions? low optical bandwidth; high linearity; low noise RF front-end LNA photo-diode mod. OBFN CW laser TIA electrical » optical optical » electrical MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion spectrum frequency 2 x 12.75 = 25.5 GHz 12.75 GHz RF front-end 10.7 GHz LNA photo-diode mod. OBFN CW laser TIA electrical » optical optical » electrical MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion spectrum frequency 2 x 2.15 = 4.3 GHz 2150 MHz RF front-end 950 MHz LNB LNA photo-diode mod. OBFN CW laser TIA electrical » optical optical » electrical MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion spectrum frequency single-sideband modulation with suppressed carrier (SSB-SC) Implementation of optical SSB modulation? Optical heterodyning; Phase shift method; Filter-based method. RF front-end 1.2 GHz LNB photo-diode Balanced optical detection: cancels individual intensity terms; mixing term remains; reduces laser intensity noise; enhances dynamic range. SSB-SC mod. filter OBFN CW laser filter TIA electrical » optical optical » electrical MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion spectrum frequency single-sideband modulation with suppressed carrier (SSB-SC) Filter requirements: Broad pass band and stop band (1.2 GHz); 1.9 GHz guard band; High stop band suppression; Low pass band ripple and dispersion; Low loss; Compact; Same technology as OBFN. RF front-end 1.2 GHz LNB mod. OBFN CW laser filter TIA electrical » optical 1 chip ! optical » electrical MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion Optical sideband filter chip in the same technology as the OBFN 5 mm MZI + Ring MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion Measured filter response 3 GHz Bandwidth—Suppression Tradeoff 14 GHz 20 GHz 25 dB FSR 40 GHz MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion Spectrum measurement of modulated optical signal Optical heterodyning technique:  f f1  f f1 f2  f  f MZM OSBF SA fiber coupler RF  f f1 – f2  f  f f2 MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion Spectrum measurement of modulated optical signal Measured filter response, and measured spectrum of modulated optical signal, with and without sideband-filtering MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion RF phase response measurements RF output RF input 1-2 GHz Measured RF phase response of one beamformer channel, for different delay values. MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: E/O and O/E conversion Signal combination measurements RF input 0-1 GHz CH 1 CH 2 Output CH 3 CH 4 Measured output RF power of beamformer with intensity modulation and direct detection, for - 1 channel, - 2 combined channels, - 4 combined channels MWP » MWP in PAAs » SMART » Conclusions » Questions »

3. Optical beamformer: Conclusions A novel squint-free, continuously tunable beamformer mechanism for a phased array antenna system has been described and partly demonstrated. It is based on filter-based optical SSB-SC modulation, and ORR-based OBFN, and balanced coherent detection. This scheme minimizes the bandwidth requirements on OBFN and enhances the dynamic range. Different measurements on optical beamformer chip successfully verify the feasibility of the proposed system. MWP » MWP in PAAs » SMART » Conclusions » Questions »