University of Twente Department of Electrical Engineering Telecommunication Engineering Group Simulation of a ring resonator-based optical beamformer system for phased array receive antennas by Martin Tijmes Master thesis Executed from July 2008 to April 2009 Supervisor: prof.dr.ir.ing. F.B.J. Leferink Advisors: dr.ir. A. Meijerink dr.ir. C.G.H. Roeloffzen dr.ir. M.J. Bentum M. Burla, MSc Summary This thesis describes the development of a simulator tool that can be used in the field of RF photonics. The development has been performed on the basis of a broadband, continuously tunable ring resonator-based optical beamformer system for phased array receive antennas. The application that is considered in this thesis is airborne satellite reception of digital television. An extensive description of the satellite receiver system is given, in which all the input-output relations of the individual components in the system are considered. It is shown that LabVIEW provides a good simulation environment for the application that is considered, which enables the specification of a suitable signal representation for both the electrical and optical domain. The simulator tool employs a fixed sample rate to circumvent the necessity for the laborious operations of up and downsampling. Based on the discrete-time representation that is introduced, the models are imple- mented in LabVIEW. The simulation model comprises a dynamical implementation of the optical beamforming network (OBFN), such that beamforming can be performed for any number of antenna elements (AEs). The settings that are required for the delay elements in the OBFN are automatically generated, based on the time delay difference between individual AEs. The satellite signals and sky noise are modeled as well, to be able to use a realistic context to test the system and do performance evaluations. Themodelsoftheindividualcomponentshavebeentestedtomatchtheirtheoretical responses. It is recommended to verify a full system simulation with theory, and later on compare with measurements. Thescalabilityofthemodelhasbeeninvestigatedbydeterminingthecomputational complexity relations of the most critical blocks. It was shown that a simulation with more than 2,000 AEs, is likely to be performed within ten minutes. The developed simulator tool appears suitable for applications in RF photonics in general, and can be used in continued work on optical beamforming. The performance of the beamformer is highly dependent on the calculated ring settings for the OBFN. Therefore, the simulated OBFNs are limited insofar that the required settings must be able to be determined. Several recommendations are given to illustrate the usability of the simulator tool, and remarks are given on the extendability and increment of efficiency. iii Contents Summary iii List of abbreviations ix 1 Introduction 1 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Optical beamforming for phased array antennas . . . . . . . . . . . . . 2 1.2.1 Phased array receive antenna . . . . . . . . . . . . . . . . . . . 3 1.2.2 Optical beamformer . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2.3 Previous work on optical beamforming . . . . . . . . . . . . . . 4 1.3 The benefits of simulation . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.4 Assignment goal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.5 Report outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 System overview 9 2.1 Satellite signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 Phased array antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3 Low-noise block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.4 E/O conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.4.1 Laser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.4.2 Mach-Zehnder modulator (MZM) . . . . . . . . . . . . . . . . . 13 2.5 Optical beamforming network . . . . . . . . . . . . . . . . . . . . . . . 15 2.5.1 Optical ring resonators . . . . . . . . . . . . . . . . . . . . . . . 15 2.5.2 Network structure . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.6 Optical sideband filter . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.7 O/E conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.8 Receiver front-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3 Simulation environment and signal representation 23 3.1 Choice of the simulation software environment . . . . . . . . . . . . . . 23 v vi Contents 3.1.1 General requirements . . . . . . . . . . . . . . . . . . . . . . . . 23 3.1.2 General purpose versus dedicated software . . . . . . . . . . . . 25 3.2 Signal representation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.2.1 Continuous-time bandpass representation . . . . . . . . . . . . . 27 3.2.2 Discrete-time representation . . . . . . . . . . . . . . . . . . . . 28 3.2.3 Sampling rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 4 Modeling the optical system components 35 4.1 Optical ring resonators . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 4.1.1 Modeling components . . . . . . . . . . . . . . . . . . . . . . . 36 4.1.2 Simulation model and results . . . . . . . . . . . . . . . . . . . 38 4.2 Optical beamforming network . . . . . . . . . . . . . . . . . . . . . . . 39 4.2.1 Modeling components . . . . . . . . . . . . . . . . . . . . . . . 39 4.2.2 Simulation model and results . . . . . . . . . . . . . . . . . . . 40 4.3 Optical sideband filter . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.3.1 Modeling components . . . . . . . . . . . . . . . . . . . . . . . 42 4.3.2 Simulation model and results . . . . . . . . . . . . . . . . . . . 43 4.4 Laser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.4.1 Modeling components . . . . . . . . . . . . . . . . . . . . . . . 44 4.4.2 Simulation model and results . . . . . . . . . . . . . . . . . . . 45 4.5 Mach-Zehnder modulator . . . . . . . . . . . . . . . . . . . . . . . . . . 45 4.5.1 Modeling components . . . . . . . . . . . . . . . . . . . . . . . 45 4.5.2 Simulation model and results . . . . . . . . . . . . . . . . . . . 46 4.6 Balanced detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 4.6.1 Modeling components . . . . . . . . . . . . . . . . . . . . . . . 47 4.6.2 Simulation model and results . . . . . . . . . . . . . . . . . . . 48 4.7 Noise in the optical beamformer . . . . . . . . . . . . . . . . . . . . . . 48 4.7.1 Dark current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.7.2 Shot noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.7.3 Thermal noise in the photodiode . . . . . . . . . . . . . . . . . 51 4.7.4 Thermal noise in the transimpedance amplifier (TIA) . . . . . . 52 4.7.5 Thermal noise in the MZM . . . . . . . . . . . . . . . . . . . . . 54 4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 5 Defining a context for the optical beamformer 57 5.1 Signal reception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 5.1.1 Definition of the satellite signal . . . . . . . . . . . . . . . . . . 57 5.1.2 DVB-S reception by the antenna elements . . . . . . . . . . . . 59 5.1.3 Downconversion by the LNBs . . . . . . . . . . . . . . . . . . . 61 Contents vii 5.1.4 Noise generated by the AEs and the LNBs . . . . . . . . . . . . 61 5.1.5 Implementation in LabVIEW . . . . . . . . . . . . . . . . . . . 62 5.2 Noise reception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 5.2.1 Noise picked up by the AEs . . . . . . . . . . . . . . . . . . . . 64 5.2.2 Coherent noise sources . . . . . . . . . . . . . . . . . . . . . . . 65 5.2.3 Sky noise model in LabVIEW . . . . . . . . . . . . . . . . . . . 66 5.2.4 Combining the generation of the satellite signal with sky noise generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 5.3 Decoding a selected channel . . . . . . . . . . . . . . . . . . . . . . . . 69 5.3.1 Implementation in LabVIEW . . . . . . . . . . . . . . . . . . . 70 5.4 System simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 5.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 6 Computational complexity 75 6.1 Determining the complexity of the model . . . . . . . . . . . . . . . . . 75 6.1.1 Specifying the complexity . . . . . . . . . . . . . . . . . . . . . 75 6.1.2 Critical blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 6.1.3 Extrapolation of the complexity relations . . . . . . . . . . . . . 78 6.2 Indication of the required computational time . . . . . . . . . . . . . . 79 6.3 Possible optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.4 Increase in complexity for more advanced models . . . . . . . . . . . . 81 6.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 7 Conclusions and recommendations 85 7.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 7.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 References 93 A OBFN structure 95 A.1 Defining the OBFN structure . . . . . . . . . . . . . . . . . . . . . . . 95 A.2 Retrieving the ORR settings . . . . . . . . . . . . . . . . . . . . . . . . 97 B Power spectral density in the discrete time domain 99 C Simulator documentation 103 C.1 General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 C.2 User interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 C.2.1 Generate message . . . . . . . . . . . . . . . . . . . . . . . . . . 105 C.2.2 QPSK modulation . . . . . . . . . . . . . . . . . . . . . . . . . 105 C.2.3 Signal reception . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 viii Contents C.2.4 Sky noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 C.2.5 MZM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 C.2.6 OBFN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 C.2.7 OSBF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 C.2.8 Balanced detection . . . . . . . . . . . . . . . . . . . . . . . . . 107 C.2.9 Bandpass filter . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 C.2.10 Demodulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 C.3 Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 List of abbreviations AE antenna element BER bit error rate BPF bandpass filter CATV cable TV CMBR cosmic microwave background radiation CMOS complementary metal-oxide-semiconductor CNR carrier-to-noise ratio DC directional coupler DSB double-sideband DSB-SC double-sideband suppressed-carrier DVB digital video broadcasting DVB-S DVB-satellite DVB-S2 DVB-satellite version 2 EMI electromagnetic interference ETSI European Telecommunications Standards Institute FSR free spectral range IF intermediate frequency ISI inter-symbol interference LNA low-noise amplifier LNB low-noise block ix x List of abbreviations LO local oscillator LPF low-pass filter MEMPHIS Merging Electronics and Micro&nano PHotonics in Integrated Systems MPEG Moving Pictures Expert Group MZI Mach-Zehnder interferometer MZM Mach-Zehnder modulator OBFN optical beamforming network OSBF optical sideband filter ORR optical ring resonator PAA phased array antenna PCB printed circuit board PSD power spectral density PSK phase-shift keying QPSK quadrature phase-shift keying RAM random access memory RIN relative intensity noise RF radio-frequency RoF radio-over-fiber SANDRA Seamless Aeronautical Networking through integration of Data links, Radios, and Antennas SMART SMart Antenna systems for Radio Transceivers SNR signal-to-noise ratio SSB single-sideband SSB-SC single-sideband suppressed-carrier RS Reed-Solomon RTT roundtrip time