Edwin Jan Klein - Universiteit Twente

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Chapter 6 6.1 Introduction About half of the work that is described in this thesis was carried out within the NAIS project. This project, which was previously described in Chapter 1.4.1, aimed to create an integrated optic WDM-Transceiver for application PON-Networks. As was already shown in Figure 1.5 this transceiver is a highly integrated, highly complex component that combines many functions, such as modulators, filters and switches on a single chip. A simple implementation of this device, able to receive and send data on four different channels (using a total of 8 channels), in which all functions have been implemented using microring resonators is given in Figure 6.1 [135] The main features on the chip are a λ-filter and modulator section used for outgoing (upstream) communication and a section with a channel selector comprised of several wavelength selective switches that can select a single channel from incoming (downstream) communication. The section for upstream communication uses an array comprised of four MRs to filter out distinct wavelengths from a broadband light source. One or several of these wavelengths are then modulated to create the upstream signal. For the downstream signal a point of concern is the fact that the polarization state of this signal is not known. This is no problem when the microring resonators used, have polarization independent behavior. However, it is difficult to make polarization independent microring resonators in silicon nitride, the material of choice for this device. The channel selector is therefore implemented using polarization diversity (also see Chapter 8) where the TE and TM polarization of the signal are operated on individually. To this end the polarizations are first separated after which the TM signal is converted to TE. The two TE polarized signals are then operated on by two identical switch matrices as shown in the figure. Figure 6.1. Implementation of the NAIS 4-channel WDM-Transceiver for use in PON Networks that is exclusively comprised of microring resonators. The separation of the TE and TM polarization with a resonator is fairly straightforward since it only requires a resonator that cannot go in resonance for the TM polarization, for instance by ensuring very high cavity losses for the TM polarization. Making a polarization converter based on a microring resonator is more complicated, however, but can be achieved by using a microring resonator that has sloped resonator sidewalls [136-138]. Because of the polarization diversity approach the resonators only have to be optimized for the TE polarization, making the overall 130
131 Microring-resonator building blocks design simpler and easier to fabricate. In fact, in the implementation that is shown most resonators, except those used for modulation and polarization conversion, can then be implemented using the same type of resonator. This resonator is the basic “resonator building block” used in most devices described in this thesis. In Section 6.2 the design of this resonator is presented, followed by the characterization of a number of different resonators in Section 6.3. In this section the thermal tuning of these resonators is also investigated. In Section 6.4 the design and characterization of a wavelength selective switch are discussed. This switch is one of the realized sub-components of the NAIS transceiver, where it is used in the channel selector. The basic principle behind the switch, which is based on the overlap of the resonance wavelengths of two cascaded resonators, is also found in the λ-router which is presented in the next chapter. As such the switch can also be seen as a building block because the same considerations that go into the design of a single switch also largely apply to the switch matrix used in the router. 6.2 A vertically coupled microring resonator based building block The basic microring resonator building block referred to in the introduction consists of a vertically coupled microring resonator that is made tunable using a thin-film metal heater. The ring and port waveguides of this resonator are made in Si3N4 embedded in SiO2. As stated in Chapter 5.1 these materials were chosen for their high index contrast of ≈0.55, their low optical loss and high material stability. a) Figure 6.2. Isometric rendering a) and a realized version b) of a vertically coupled MR building block that has side-coupled port waveguides. The marker next to the resonator is used to check the vertical alignment of the resonator. a) b) Figure 6.3. Isometric rendering a) and a realized version b) of a vertically coupled tunable MR building block that is cross-coupled to the port waveguides. The marker next to the resonator measures the vertical as well as the horizontal alignment of the resonator. b)
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DENSELY INTEGRATED MICRORING- RESON
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DENSELY INTEGRATED MICRORING- RESON
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To my parents…
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esonators is limited by the spacing
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iv Samenvatting Dit proefschrift be
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schakelaar “aan” is, dan is de
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3.6.2 Overlap loss reduction.......
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Chapter 1 Introduction The devices
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1.2 Broadband to the home 3 Introdu
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1.3 Bringing Fiber to the Home 5 In
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Figure 1.5. The technological scope
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9 Introduction these basic paramete
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Chapter 2 2.1 Introduction Integrat
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Chapter 2 light Icav2 in the cavity
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Chapter 2 ∆ = ⎛ β r − β g
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Chapter 2 2.3.3 Combined model The
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Chapter 2 FC 4µ 1µ 2 ⋅ χr = 2
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Chapter 2 P Through /P In (dB) 0 -1
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Chapter 2 The figure shows that it
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Chapter 2 In − jϕr1 2 Figure 2.1
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Chapter 2 differences between the f
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Chapter 2 M = ⋅ FSR = N ⋅ FSR F
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Chapter 2 the heat will therefore f
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Chapter 2 index. Although this can
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Chapter 2 resonators for instance h
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Chapter 2 a rather complex MEMS bas
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Chapter 3 3.1 Introduction The most
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Chapter 3 3.2.1 Drop port on-resona
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Chapter 3 3.2.3 Filter bandwidth In
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Chapter 3 (resulting in a higher ba
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Chapter 3 Figure 3.11. Residual cha
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Chapter 3 3.3 Geometrical design ch
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Chapter 3 resonator and the port wa
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Chapter 3 Another important fact wh
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Chapter 3 The flowchart of the desi
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Chapter 3 While the resonator in th
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Chapter 3 3.6.1 Port waveguide and
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Chapter 3 overlap losses are only 0
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Chapter 3 3.7 Component design cons
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Chapter 3 By maximizing the power t
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Chapter 3 important, due to the fac
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Chapter 4 4.1 Introduction As was s
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Chapter 4 4.2.1 Transient response
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Chapter 4 Under the condition that
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Chapter 4 Figure 4.4. Screenshot of
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Chapter 4 The equations required to
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Densely integrated devices for WDM-
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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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