The measurement of distance plays an integral part in many aspects of modern societies. In this paper an integrated mode-locked laser on a chip is used for distance measurement based on mode-resolved interferometry. The emission from the on-chip source with a repetition rate of 2.5 GHz and a spectral bandwidth of 3 nm is coupled into a Michelson interferometer. The interferometer output is recorded as a spectral interferogram, which is captured in a single camera image. The images are analyzed using Hilbert transform to extract the distance. The distance derived shows a deviation of 6 \mum from the reference, for a distance up to 25 mm. We also demonstrate interferometry with repetition frequency sweep which can also be used with the source. Performance is expected to be better in the near future with the rapid developments in the field of on-chip laser sources which are demonstrating larger spectral widths and coherence lengths.

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Spectroscopy is a powerful tool to investigate the physical properties of complex systems. The interaction of light with matter allows to get insights into the structure of it. Chapter 1 is dedicated to introduce this topic and to show the developments of the technologies that paved the way to its success. Special focus is given to the techniques that are used in this work. This includes monolithically integrated tunable laser sources, as well as integrated mode locked lasers. In Chapter 2 we guide through the design process of single mode laser source using the generic approach and exploiting the availabilty of multi-project wafers. The design of a Fabry-Perot laser along with its benefits, drawbacks and the underlying physical concepts will be demonstrated. This requires theoretical background in solid state physics; the necessary basics are given in the text. Chapter 3 makes use of this background and expand the design to ring lasers. Chapter 3 also illustrates characterisation techniques for such laser sources. The presented device is investigated regarding its capabilities for gas spectroscopy. To reach different absorption lines that enable spectroscopy for different gas species, the laser design has been adapted for longerwavelengths. In Chapter 4we will showthat despite the reduced performance due to the lower technological status, gas spectroscopy can still be feasible with such devices. Besides the spectroscopical applications photonic integrated circuits can find use in the field of distance metrology. A setup verified the feasibility of a modelocked laser in combination with a VIPA spectrometer to obtain metrological data with a single camera image, which is demonstrated in Chapter 5. This chapter also concludes the investigation of monolithically integrated laser sources. In addition to on-chip lasers, this work investigates fiber-based frequency comb lasers. With a much lower repetition frequency in comparison to integrated pulsed lasers, the corresponding mode-spacing in the frequency domain sets different requirements of the spectrometer. On the other hand the denser and yet wider spectral coverage allows for spectroscopy over a wider range of absorption lines. Chapter 6 is dedicated to introduce frequency comb lasers and the virtually imaged phased-array (VIPA) spectrometer. The combination of both is used to determine the temperature of CO2 by looking at its absorption behaviour. Similar measurements have been executed in ambient air and are summarised in Chapter 7. Due to the low concentration of CO2 in ambient air, this required a very long path length. In Chapter 8 we demonstrate an optimised setup to increase the stability of the method introduced in Chapter 6. The improved setup is more stable with respect to ambient fluctuations and is portable, which allows measurements outside of laboratory conditions. The final chapter, Chapter 9, summarises the results of all the presented experiments and discusses the impact it can have on future devices making use the presented methods.@en

In this paper a generic monolithic photonic integration technology platform and tunable laser devices for gas sensing applications at 2 μm will be presented. The basic set of long wavelength optical functions which is fundamental for a generic photonic integration approach is realized using planar, but-joint, active-passive integration on indium phosphide substrate with active components based on strained InGaAs quantum wells. Using this limited set of basic building blocks a novel geometry, widely tunable laser source was designed and fabricated within the first long wavelength multiproject wafer run. The fabricated laser operates around 2027 nm, covers a record tuning range of 31 nm and is successfully employed in absorption measurements of carbon dioxide. These results demonstrate a fully functional long wavelength photonic integrated circuit that operates at these wavelengths. Moreover, the process steps and material system used for the long wavelength technology are almost identical to the ones which are used in the technology process at 1.5μm which makes it straightforward and hassle-free to transfer to the photonic foundries with existing fabrication lines. The changes from the 1550 nm technology and the trade-offs made in the building block design and layer stack will be discussed.

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We present a widely tunable extended cavity ring laser operating at 2 μm that is monolithically integrated on an indium phosphide substrate. The photonic integrated circuit is designed and fabricated within a multiproject wafer run using a generic integration technology platform. The laser features an intracavity tuning mechanism based on nested asymmetric Mach-Zehnder interferometers with voltage controlled electro-refractive modulators. The laser operates in a single-mode regime and is tunable over the recorded wavelength range of 31 nm, spanning from 2011 to 2042 nm. Its capability for high-resolution scanning is demonstrated in a single-line spectroscopy experiment using a carbon dioxide reference cell.@en

In this work we present a design of an external optical cavity based on Fabry-Perot etalons applied to a 100 MHz Er-doped fiber optical frequency comb working at 1560 nm to increase its repetition frequency. A Fabry-Perot cavity is constructed based on a transportable cage system with two silver mirrors in plano-concave geometry including the mode-matching lenses, fiber coupled collimation package and detection unit. The system enables full 3D angle mirror tilting and x-y off axis movement as well as distance between the mirrors. We demonstrate the increase of repetition frequency by direct measurement of the beat frequency and spectrally by using the virtually imaged phased array images.@en

Progress on the development of a long wavelength (∼2 μm) generic monolithic photonic integration technology on indium phosphide substrate and a novel concept of a tunable laser realized as a photonic integrated circuit using such technology are presented. Insights into the development of active and passive waveguide structures which are used to define a limited set of on-chip functionalities in the form of building blocks will be given. A novel tunable laser was proposed and designed using such predefined set of basic building blocks. The laser geometry features an intra-cavity wavelength tuning mechanism based on asymmetric Mach-Zehnder interferometers in a nested configuration. The photonic integrated circuit chip was fabricated within the first long wavelength multi-project wafer run. The experimental evaluations of the fabricated device show a record tuning range of 31 nm around 2027 nm and successful measurements of a 0.86 GHz wide absorption line of carbon dioxide. These results provide a demonstration of a fully functional photonic integrated circuit operating at wavelengths that are much longer than those in the typical telecommunication windows as well as the use of indium phosphide based generic photonic integration technologies for gas sensing applications.@en

Monolithic integration of four widely tunable extended cavity lasers suitable for gas detection is presented. Each laser features a precise, grid-less tuning mechanism with a low-linewidth, single-mode output over a wide wavelength range of 74nm.@en