High Speed Homodyne Detector for Gaussian-Modulated Coherent-State Quantum Key Distribution
by
Yuemeng Chi
A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Graduate Department of Electrical and Computer Engineering University of Toronto
Copyright © 2009 by Yuemeng Chi Abstract
High Speed Homodyne Detector for Gaussian-Modulated Coherent-State Quantum Key
Distribution
Yuemeng Chi
Master of Applied Science
Graduate Department of Electrical and Computer Engineering
University of Toronto
2009
We developed a high speed homodyne detector in the telecommunication wavelength re- gion for a Gaussian-modulated coherent-state quantum key distribution experiment. We are able to achieve a 100 MHz bandwidth, ultra-low electronic noise and pulse-resolved homodyne detector. The bandwidth of this homodyne detector has reached the same order of magnitude of the best homodyne detectors reported. By overcoming photodiode response functions mismatch, choosing proper laser sources, ensuring the homodyne de- tector linearity and stabilizing the homodyne detection system, we demonstrate that the homodyne detector has a 10 dB shot-noise-to-electronic-noise ratio in the time domain at a local oscillator of 5.4 108 photons/pulse at a laser repetition rate of 10 MHz. With this homodyne detector, we expect to increase our GMCS QKD experiment speed by 100 times, which will improve the key generation rate by 1-2 orders of magnitude.
ii Dedication
First and foremost I owe my deepest gratitude to my supervisors, Professor Hoi-
Kwong Lo and Professor Li Qian, who have supported me thoughout my research with their patience and knowledge. I attribute my master work to their encouragement and effort. Without their support, this thesis would not have been completed. It is an honor for me to work with them during my last two years’ study. One simply could not wish for a better or friendlier supervisor.
I am also deeply appreciate the help and advice received from Doctor Bing Qi, who essentially teaches me everything in an optical and electrical lab. I am grateful to Doctor
Bing Qi for his knowledge and many useful discussions that motivated me.
Special thanks are extended to Professor J. Stewart Aitchison, Professor Lacra Pavel, and Professor Joyce Poon for their time, advice, and willingness to serve on the commit- tee.
I would like to show my gratitude to Professor Alex Lvovsky at University of Calgray for generously providing the homodyne detector electronic design and printed circuit board layout. I also thank Professor SunHyun Youn and Nitin Jain for their kind help in building the homodyne detector circuit and sharing a lot of construction experience.
I would also extend my thanks to Liang Tian, who has helped a lot in tuning the homodyne detector circuit. I also would like to acknowledge Professor Namdar Saniei and Doctor Wen Zhu for helpful discussions. It is a pleasure to thank a friendly and cheerful group of fellow students, Viacheslav Burenkov, Wei Cui, Chi-Hang Fred Fung,
Junbo Han, Wolfram Helwig, Kenny Ho, Dongpeng Kang, Xiongfeng Ma, Jason Ng,
Wing-Chau Ng, Chris Sapiano, Peyman Sarrafi, Gigi Wong, Fei Ye, Jiawen Zhang, Lijun
Zhang, and Eric Zhu for their support and friendship. I also thank 3GMetalWorx Inc. for providing a professional shielding metal box for the homodyne detector circuit.
Furthermore, I would like to thank Ms. Diane Silva and Ms. Linda Liu for their efficient and professional administrative work.
iii Finally and most importantly, this thesis would not have been possible without the endless love and support from my family. This thesis is dedicated to my husband and my parents.
iv Contents
1 Introduction 1
1.1 Background...... 1
1.2 Motivation:highspeedhomodynedetector...... 6
1.3 Objective ...... 7
1.4 Organization...... 8
2 Review of GMCS QKD and Homodyne Detection 9
2.1 Gaussian-modulated coherent-state quantum key distribution ...... 9
2.1.1 Protocol...... 9
2.1.2 Stateoftheart...... 12
2.2 Homodynedetection...... 14
2.2.1 Introduction...... 14
2.2.2 Stateoftheart...... 19
2.3 Summary ...... 21
3 GMCS QKD over 20 km Fiber 22
3.1 Experimentalsetup...... 22
3.2 Securekeyrateformula...... 24
3.3 Results...... 27
3.4 Discussions...... 33
3.5 Summary ...... 35
v 4 High Speed Homodyne Detector 37
4.1 RequirementofahomodynedetectorinGMCSQKD...... 37
4.2 Highspeedhomodynedetectordesign...... 38
4.2.1 Homodynedetectoropticalsetupinfiber...... 38
4.2.2 Homodynedetectorelectricalcircuit...... 39
4.3 Challenges...... 40
4.3.1 Lowelectronicnoise...... 41
4.3.2 Differentphotodioderesponsefunctions...... 42
4.3.3 Linearity...... 45
4.3.4 Lasersource...... 47
4.3.5 Optical stability ...... 52
4.4 Summary ...... 54
5 Performance of the Homodyne Detector 55
5.1 Experimentalplan...... 56
5.2 MeasurementwithCWlight...... 56
5.2.1 Experimentalsetup...... 57
5.2.2 Noisemeasurementinthetimedomain...... 58
5.2.3 Noisemeasurementinthefrequencydomain...... 60
5.3 Measurementwithpulsedlight...... 62
5.3.1 Pulsedlasersource...... 62
5.3.2 Noisemeasurementinthetimedomain...... 63
5.3.3 Noisemeasurementinthefrequencydomain...... 73
5.4 Conclusionsanddiscussions...... 77
6 Conclusion and Future Work 81
6.1 Significance and contribution ...... 81
6.2 Futurework...... 83
vi List of Tables
1.1 Secure key rate (bit) per pulse for GMCS [1], decoy state [2] and DPS
[3] protocols over 5-km telecommunication fiber. Secure key rates for de-
coy state and DPS protocols are simulation results based on experimental
conditions...... 5
3.1 Parameters used in the key rate simulation , from Ref. [1]. The length of
thefiberis5km...... 31
3.2 20-km GMCS QKD parameters and results (e: experimental result; c:
calculatedresult)...... 33
3.3 Secure key rate in our GMCS QKD experiment and in Ref. [4] over 20-km
fiber.rep.:repetition...... 33
4.1 SpecificationsofFGA04InGaAsphotodiode(typicalvalues)...... 39
4.2 Specifications of the two lasers used in photodiode linearity test ...... 49
5.1 Parameters in the key rate simulation (given in Ref. [1]). Here we assume