Edwin Jan Klein - Universiteit Twente

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Chapter 2 M = ⋅ FSR = N ⋅ FSR FSR (2.36) 1 2 Tot where M and N are integers and have no common divisor. Using (2.36) it can be shown that if, for instance, one ring has a FSR of 4.5 nm and the other has a FSR of 4 nm, their combined FSR is 36 nm, nearly the width of the ITU C-band. The through and drop responses of this particular arrangement are shown in Figure 2.18a for a Vernier filter comprised of two resonators placed in serial cascade as depicted in Figure 2.18b. The responses were obtained for R1=45 µm, R2=50 µm, κ1,2,3,4=0.4 and αdB=1 dB/cm. Power (dB) 0 -10 -20 -30 -40 -50 P Drop PThrough 1530 1540 1550 1560 Wavelength (nm) Figure 2.18a. Through and drop response of a Vernier serial cascade resonator. 30 Figure 2.18b. Vernier serial cascade resonator. The drop response clearly shows that the maximum dropped power through the filter occurs only once in the 40 nm range shown, at λ=1550 nm. A potentially negative side effect of the Vernier filter, the “side lobes”, occurs in the response at those frequencies where there is still some overlap between the responses of the individual resonators. In the shown drop response the power dropped by highest side lobe is still -11 dB, enough to cause interference in most applications. By carefully choosing the radius and finesse of the comprising resonators, however, these effects may be limited. In addition cleanup filters can be added to improve the spectrum [68, 69]. Another potential problem of the Vernier cascade resonator can be seen in the through response. Because the two resonators in the filter are essentially separated from each other the first resonator will simply drop all frequencies for which it is in resonance. This poses a problem in devices where many (Vernier) filters are placed along the same waveguide because power that is dropped but not used by filters on this waveguide is essentially lost for successive filters. A second (or higher) order Vernier filter, as shown in Figure 2.19b can then offer a solution. In the responses of this filter, obtained for R1=45 µm, R2=50 µm, κ1,3=0.4, κ2=0.086 and αdB=1 dB/cm, the through response now only shows a clear dip at λ=1550 nm whereas only minor notches are seen at other wavelengths.
Power (dB) 0 -10 -20 -30 -40 -50 -60 PDrop P Through 1530 1540 1550 1560 Wavelength (nm) Figure 2.19a. Through and drop response of a second order Vernier resonator. 2.8 Resonator tuning 31 The Micro-Resonator Figure 2.19b. Second order Vernier resonator. In addition to the use of optical resonators in a passive filters such as those described in the previous paragraphs it is also possible to actively vary some of the parameters of the micro-resonator, thereby altering its response. This process of “tuning” can be used to compensate for errors in fabrication but is more commonly used to add some form of active functionality. In the case of the micro-resonator two main types of tuning can be distinguished. The first type alters the resonator in such a way that its resonant wavelength is shifted but does not alter the shape of its response. The second type does not shift the response of the resonator but rather changes the shape of the filter response. 2.8.1 Wavelength tuning methods The resonant wavelength of a resonator can be shifted (tuned) by changing the optical roundtrip path length of the resonator. The most straightforward way to change the optical path length is to change the index in one or all of the materials of the resonator waveguide. This will change the effective index which, in turn, will alter the roundtrip phase of the light in the resonator and therefore the wavelength for which it achieves maximum resonance. A few of the effects that can change the optical index of a waveguide are: Thermo-optic: The thermo-optic effect uses heat to change the refractive index of the waveguide materials [70-76]. The thermo-optic effect in materials is relatively large when compared to other effects. Certain materials, such for instance polymers or silicon, can have a very high thermo-optic coefficient (TOC) in the order of 10 -4 °C -1 (∆n/∆T). Other materials such Si3N4 and SiO2, used to fabricate many of the devices in the following chapters, have a lower TOC in the order of 10 -5 °C -1 . Generally the thermo-optic effect is easy to use because it only requires the addition of a heating element to an already existing device. Since this element is commonly implemented using a thin-film metal resistor [73] it has to be placed at some distance from the waveguide in order to avoid optical losses. When the heater is switched on
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Chapter 4 using an approach based o
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Chapter 4 4.5.1 Architecture The Au
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Chapter 4 4.5.2 Simulation method A
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Chapter 4 Figure 4.9. A Primitive w
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Chapter 4 Listing 4.3. Pseudo code
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Chapter 4 Listing 4.4. Pseudo code
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Chapter 4 simulated output spectra
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Chapter 4 Figure 4.21. The reflecto
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Chapter 4 P Drop /P In (dB) 0 -10 -
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Chapter 4 Figure 4.27a. OADM with r
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Chapter 4 will propagate through th
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Chapter 4 As demonstrated by these
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Chapter 4 What is more interesting
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Chapter 4 method it does allow time
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Chapter 4 complex than the interact
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Chapter 5 5.1 Introduction The mate
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Chapter 5 wafer is used (step 1). T
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Chapter 5 range of 0.9 to 1.1 µm.
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Chapter 5 The process flow with the
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Chapter 5 5.3.3 Mask layout The big
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Chapter 5 5.4. Fabrication and mask
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Chapter 5 1. Definition of the vert
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Chapter 5 5.4.2 Fabrication The fab
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Chapter 5 Figure 5.21. Process flow
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Chapter 5 removed using lift-off of
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Chapter 6 6.1 Introduction About ha
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Chapter 6 In early, comparatively s
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Chapter 6 that the TEOS has a very
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Chapter 6 The most important aspect
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Chapter 6 6.2.3 Chromium heater des
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Chapter 6 Therefore, even if the si
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Chapter 6 Next, the heater was heat
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Chapter 6 6.3 Characterization of s
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Chapter 6 polarization maintaining
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Chapter 6 the resonators in this gr
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Chapter 6 Although the fitted coupl
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Chapter 6 a cladding thickness of 3
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Chapter 6 6.4 A wavelength selectiv
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Chapter 6 A possible explanation fo
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Chapter 7 Densely integrated device
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Densely integrated devices for WDM-
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7.2.2 Spectral measurements Densely
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Power Densely integrated devices fo
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7.3.4 Characterization Densely inte
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Figure 7.31a. Eye pattern of the re
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Chapter 8 8.1 Introduction In most
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Chapter 8 amount of power will be d
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Chapter 8 Another problem that may
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Chapter 8 halves that are each comp
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Chapter 9 Discussion and Conclusion
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Appendix A. Mason’s rule Several
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Appendix B. Crosstalk Derivation Th
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List of Acronyms ADSL - Asymmetric
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List of Symbols Q - Quality Factor
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Bibliography [1] Dan Schiller, “E
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Regions,” IEEE Photonics Technolo
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[66] B. E. Little, S. T. Chu, J. V.
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[97] H. Haeiwa, T. Naganawa and Y.
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[135] A. Driessen, D. H. Geuzebroek
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[165] T. Barwicz, M. R. Watts, M. A
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Publication List Patents (pending)
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R. Dekker, L.T.H.Hilderink, M.B.J.
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Networks (BB Photonics),” Interna
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Dankwoord/Acknowledgements Zo, dit
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Edwin Jan Klein - Universiteit Twente

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