1. Advanced Modulation and Detection Techniques for Single-Mode Optical Fiber Motivations  Optical transmission systems still use relatively unsophisticated communication techniques.  Advanced modulation and detection methods will: Increase transmission capacity Improve tolerance to dispersion, nonlinearity and other transmission impairments  Performance of optical systems is usually evaluated by Monte Carlo simulation, especially in the nonlinear regime.  Accurate analytical techniques aid in system design. Ongoing or Future Projects  Coherent optical detection Optical phase locking of MEMS external-cavity lasers 20 Gb/s QPSK transmission experiments  Impairment compensation techniques Electrical compensation of nonlinear phase noise Electrical equalization of dispersion  Analytical Techniques Error-probability computation in nonlinear transmission systems Effect of laser and nonlinear phase noises on optical QAM EIEI EQEQ Linear Regime EIEI EQEQ Nonlinear Regime Nonlinear Phase Noise with PSK or DPSK Constellation Non-Binary Modulation and Coherent Detection Increase Spectral Efficiency 1 2 3 4 Number of Constellation Points M 2 4 8 16 SNR/bit Required Relative to 2-PAM (dB) -3036912 15 QAM / Coherent PSK / Coherent DPSK / Differentially Coherent PAM / Non-Coherent 1 2 3 4 Relative Spectral Efficiency log 2 ( M ) (b/symbol) Relative Spectral Efficiency log 2 ( M ) (b/symbol) Number of Constellation Points M 2 4 8 16 SNR/bit Required Relative to 2-PAM (dB) -3036912 15 QAM / Coherent PSK / Coherent DPSK / Differentially Coherent PAM / Non-Coherent QAM / Coherent PSK / Coherent DPSK / Differentially Coherent PAM / Non-Coherent MEMS External- Cavity Laser (Iolon,  < 200 kHz) Coherent Detection of QPSK using MEMS External Cavity Lasers E SI E SQ Signal Local Oscillator E LI E LQ Photocurrent iQiQ iIiI f fSfS fSfS … Encoder Bits 90  EIEI EQEQ Elect. LPF iIiI iQiQ Local Oscillator Laser f L = f S f 0 f 0 90  00 Trans. Laser Adaptive Spatial-Domain Signal Processing in Multi-Mode Optical Fiber (with Professors S. Fan, M. A. Horowitz and O. Solgaard) Motivations  Multi-mode fiber is widely installed in local-area networks.  Fiber supports hundreds of propagating modes, which are orthogonal spatial degrees of freedom.  Modes propagate with different group delays, leading to modal dispersion. The bit rate-distance product is limited to well below 10 Gb/s-km in installed fibers.  Adaptive spatial-domain optical signal processing will be used to: Reduce modal dispersion, increasing bit rate-distance product in single-input, single-output (SISO) transmission. Multiplex several information streams in different modes, enabling multi-input, multi-output (MIMO) transmission.  Modal dispersion is analogous to multipath fading in wireless: should it be eliminated or exploited? Ongoing or Future Projects  Experiments Characterization of principal modes in multi-mode fiber SISO and MIMO transmission at 10 Gb/s per channel  Modeling and Analysis Statistical models for mode coupling in multi-mode fiber Information-theoretic capacity of MIMO systems  Adaptive Algorithms Efficient SISO and MIMO algorithms Single-Input, Single-Output (SISO) Transmission Multi-Input, Multi-Output (MIMO) Transmission Simulated Adaptive SISO Transmission 10 Gb/s, 1 km, 64  m step-index fiber 20  20 pixel, binary-phase spatial-light modulator 0510152025 0 0.2 0.4 0.6 0.8 1 Bit Interval (at 10 Gb/s) Impulse response after SLM adaptation Intensity (a.u.) 051015202530 0 0.2 0.4 0.6 0.8 1 Bit Interval (at 10 Gb/s) Intensity (a.u.) Impulse response for initial SLM setting Transmitted field distribution after SLM adaptation Position (  m)  40  20 0 2040  40  20 0 20 40 Position (  m) Transmitted field distribution for initial SLM setting Position (  m)  40  20 0 20 40 Position (  m)  40  20 0 2040 Stanford Optical Communications Group Professor Joseph M. Kahn, Department of Electrical Engineering Office: 372 Packard Lab: 41-A Ginzton Laboratory