A Wavelength Converter Integrated with a Discretely Tunable Laser ...

6 1. Introduction
(wavelength blocking), resulting a reduced capacity of the network.
On the other hand, if wavelength conversion is employed in nodes A and B, then wavelengths
can be assigned locally within each subnetwork. This greatly facilitates network management,
prevents wavelength blocking and provides full scalability of the network. A schematic of a
wavelength converting cross connect (WXC) is shown in Fig. 1.5. In the WXC, the WDM
channels of the inputs are first demultiplexed and then space switched. Next each channel can
be wavelength converted and, finally, the wavelengths are multiplexed again in their respective
WDM outputs.
1.4 Thesis overview
This thesis describes and analyzes the realization of photonic integrated circuits (PICs), containing
all-optical wavelength converters, and a converter integrated with a widely, discretely
tunable laser. An overview of wavelength converter types and their performance is given in
Chapter 2. The chapter also motivates the choice of the Mach-Zehnder interferometer type
converter that is used in this thesis. The converter chip was fabricated in a newly developed
layer stack, in which active and passive regions have been monolithically integrated. Chapter 3
describes the measurement of test structures in the new stack, along with some basic theory.
Trade-offs that are involved in the integration process are discussed in Chapter 4, and the fabrication
of the circuits is described in Chapter 5. The last three chapters deal with the design
and measurements of the circuits. First, the realization of a discretely tunable laser with absolute
wavelength control is discussed in Chapter 6. Next, the realization of a Mach-Zehnder
interferometric wavelength converter is described in Chapter 7. Finally, Chapter 8 presents the
integration of the converter and the widely tunable laser. The first device of this type reported
to the best of our knowledge [2].