Design and simulation of a coherent transmitter based on a photonic integrated circuit for inter and intra satellite communications

Abstract

Nowadays satellites handle an enormous amount of information. On one hand, each satellite contains numerous instruments that interchange information inside them. On the other hand, satellites communicate with the ground control and between each other, especially in satellite systems. Therefore, being able to manage high bit rates is becoming a necessary feature in any satellite. However, satellites are costly. Launching one kilogram into space can be priced at 25k euros. Therefore, the size and weight of every component in a satellite are crucial. Optical communications systems are a suitable solution for inter and intra satellite communications. These systems are based on transmitters and receivers fabricated using semiconductor materials. These photonic devices, especially semiconductor lasers, show advantages that fit on the satellite requirements, such as electrical pumping, high efficiency, compactness, radiation hardness and low cost. In the last years, semiconductor lasers have shown another advantage, the integration of different optical components such as lasers, modulators, photodiodes, amplifiers, etc. in the same chip. If the number of these components is high, these devices are called photonic integrated circuits, in analogy to electronic integrated circuits. The objective of this work is to design a coherent transmitter based on a photonic integrated circuit containing a multi-section laser and an IQ modulator that can be used as a transmitter for intra and inter satellite optical communications. The design is validated through numerical simulations and the final design will be fabricated by means of an open access foundry. Regarding the multi-section laser, a four-section distributed Bragg re ector laser has been chosen as the most appropriate to be integrated in the photonic integrated circuit. It is designed with the main objective of being a tunable single-mode emitter. The parameter dependence on each of the four sections of the laser is analyzed and thoroughly characterized in terms of power and wavelength tuning. With respect to the IQ modulator, a first step involves the analysis of electro-optical-phase-modulators. After that, the design and characterization of different Mach-Zehnder modulators is done. Finally, two versions of the IQ modulator are designed, for high (up to 10 GHz) and low (up to 250 MHz) frequency RF signals and several parameters such as attenuation and the induced phase shifts are thoroughly analyzed. Finally, both modules are integrated into the coherent transmitter and the layout of the different versions of the chip are designed. The layout contains all the different material layers as well as the electrical routing and optical outputs. The layout is the final design result which is sent to the foundry for fabrication.