2. To my beloved parents,
for their support and help
during the past eight years!

3. Abstract
Biosensors are applied for the detection of biological analytes. Thereby, "Label-Free" and "Label"
systems are distinguished. A major advantage of label-free systems is the possible detection of
analytes without marking them with additional molecules, so-called labels or markers. This cir-
cumstance eliminates the labelling step from the procedure and hence saves time and money. Both
factors are nowadays very important, especially in drug development.
In this master thesis, integrated in a larger CTI-funded project, designs and simulations of a next-
generation label-free biosensors based on planar waveguides are made.
After an introduction into the theoretical fundamentals, the existing wavelength interrogated opti-
cal sensor (WIOS) based on coupling gratings is modelled and simulated. The obtained results are
compared with an already used software and with experimentally data.
The most important part of the master thesis is the modelling and simulation of passive sensors
based on Bragg gratings. It is presented in chapter 5. Two dierent designs are elaborated. The
rst design consists of a single Bragg grating (DFB), the second design is composed of two Bragg
gratings and a resonator (DBR). The designs and simulations are done for the operating wave-
lengths 850nm and 1550nm in both, TETM polarisation. Possible parameter deviations due to
production tolerances are investigated. The designs are then validated using a gure of merit. For
this comparison, sensor performance and the possible parameter deviations are considered. Based
on the results, three designs are recommended for production at Optics Balzers. The last part of
this chapter gives an overview of the process operation for the production of such designs, including
the required masks. Finally, the whole sensor system with a possible coupling structure and a taper
is presented.
The nal chapter deals with active sensors. These sensors are able to produce light used for the
sensing on their own. Based on a given waveguide channel amplier, two possible structures (again
DFB and DBR) are discussed. Having shown the results, a theoretical discussion and argumenta-
tion concerning the capability of such active sensors is made. A summary and outlook conclude
this master thesis.
B.Sc.(FHO) Mirjad Keka Master Thesis 2012/2013 Optical Systems Engineering

4. Contents
Author's Declaration iii
Abstract v
List of Abbreviations vii
List of Symbols ix
1 Introduction 1
1.1 Integration of this Master Thesis in an Industrial Project . . . . . . . . . . . . . . 3
1.2 The Goal of this Master Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Sensing Principle 5
2.1 Planar Waveguide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Sensor Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 In- and Outcoupling Gratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Readout Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Theoretical Fundamentals 9
3.1 Basics of Electromagnetic Wave Theory for Planar Waveguides . . . . . . . . . . . 9
3.1.1 TE and TM Polarisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.2 Maxwell's Equations for Planar Waveguides . . . . . . . . . . . . . . . . . . 10
3.2 Formation of Guided Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3 Plane-Wave Propagation in Planar Waveguides . . . . . . . . . . . . . . . . . . . . 14
3.3.1 Normalised Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.4 Grating Coupler Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.5 Evanescent Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.6 Bragg Gratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.7 Basic Principle of Lasers and Resonators . . . . . . . . . . . . . . . . . . . . . . . . 23
3.7.1 Introduction to Lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.7.2 Functional Principle of a Laser . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.7.3 Basic Structure of a Laser . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.7.4 The Optical Resonator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.7.5 Energy-Level Transitions of Neodymium and Erbium . . . . . . . . . . . . . 27
3.8 Basic Principle of Distributed Feedback and Distributed Bragg Reector Lasers . . 28
3.8.1 Spectral Linewidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.8.2 Coupling Coecients and Dierent DFB Structures . . . . . . . . . . . . . 29
B.Sc.(FHO) Mirjad Keka Master Thesis 2012/2013 Optical Systems Engineering

5. Contents
4 Existing Label-Free WIOS Chip 31
4.1 Dierent Modelling Congurations for Label-Free Biosensors . . . . . . . . . . . . . 31
4.2 Detailed Description of the WIOS Chip . . . . . . . . . . . . . . . . . . . . . . . . 31
4.3 Comparison Between two Software-Tools . . . . . . . . . . . . . . . . . . . . . . . . 32
4.4 Comparison Between Simulation and Experiment . . . . . . . . . . . . . . . . . . . 35
4.4.1 Measurement Setup for the Verication of the WIOS Chips . . . . . . . . . 35
4.4.2 Results of the Comparison Between Simulation Results and Experiment . . 36
4.5 Chapter Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
5 Passive Label-Free Biosensors 39
5.1 Replication of an Existing Biosensor Utilising an Optical Grated-Waveguide Cavity 39
5.1.1 Simulation Results for the Replicated Biosensor . . . . . . . . . . . . . . . . 40
5.1.2 Investigation of the Various Design Parameters . . . . . . . . . . . . . . . . 41
5.2 Excursus: Impact of SNR and FWHM on Wavelength Shift Calculation . . . . . . 44
5.3 Design and Simulation of a Passive Biosensor Based on a DFB Structure . . . . . . 46
5.3.1 Simulation Results for an Operational Wavelength of 850 nm . . . . . . . . 46
5.3.2 Simulation Results for an Operational Wavelength of 1550 nm . . . . . . . . 49
5.4 Design and Simulation of a Passive Biosensor Based on a DBR Structure . . . . . . 52
5.4.1 Simulation Results for an Operational Wavelength of 850 nm . . . . . . . . 53
5.4.2 Simulation Results for an Operational Wavelength of 1550 nm . . . . . . . . 55
5.5 Comparison of the Various Sensor Designs . . . . . . . . . . . . . . . . . . . . . . . 57
5.6 Light Coupling into the Waveguide . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.7 Design Recommendations for the Production of the Sensors at Optics Balzers . . . 61
5.7.1 Process Operation for the Production of the Sensors at Optics Balzers . . . 62
5.8 Chapter Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
6 Active Label-Free Biosensors 67
6.1 Replication of an Existing Waveguide Channel Amplier . . . . . . . . . . . . . . . 67
6.2 Design and Simulation of an Active Biosensor Based on a DFB Structure . . . . . . 69
6.3 Design and Simulation of an Active Biosensor Based on a DBR Structure . . . . . 70
6.4 Theoretical Discussion and Argumentation Concerning Active Label-Free Biosensors 71
6.5 Chapter Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
7 Conclusions and Future Work 77
7.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
7.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
8 Acknowledgement 79
Bibliography 81
List of Figures 83
List of Tables 87
xiv