## 2 Fundamentals of PICs  
Integrated photonics is a field that emphasizes the development and application of photonic devices united onto a single platform, often referred to as a PIC [26]. These devices manipulate light (photons) instead of electrical signals (electrons), leveraging the exceptional properties of light for a variety of applications. The fundamental components of integrated photonics include WGs, modulators, detectors, and light sources, each playing a critical role in the functionality of PICs. WGs are the backbone of any photonic integrated circuit. They confine and direct light within the chip, much like electrical wires guide electricity [27; 28]. The design of WGs involves controlling the index contrast between the core and the cladding materials, ensuring efficient light propagation with minimal losses [29]. Materials commonly used for WGs include Si, Si\({}_{3}\)N\({}_{4}\), and indium phosphide (InP), each offering different advantages such as compatibility with existing semiconductor manufacturing processes, low propagation losses, or efficient light emission and detection capabilities [30; 31]. Optical modulators are essential for encoding information into a light wave [32]. They function by varying the intensity, phase, or polarization of the light passing through them [33]. In integrated photonics, modulators often exploit the electro-optic (EO) or thermo-optic (TO) effects [34]. The EO effect, observed in materials like LN and Si, allows for rapid modulation of the refractive index with an applied electric field [13]. TO modulators, on the other hand, change the refractive index through temperature variations, though they tend to be slower and consume more power [35]. Advanced modulators are continuously being developed to balance speed, efficiency, and integration compatibility [36; 37]. Detectors in integrated photonics convert optical signals back into electrical signals. They are crucial for applications where data need to be read out or further processed electronically [38]. Photodetectors (PDs) in PICs are typically made from materials with high optical absorption coefficients, such as germanium (Ge) integrated on Si, or III-V compounds like indium gallium arsenide (InGaAs) [15]. These materials are chosen based on their sensitivity to specific wavelengths and their ability to integrate seamlessly with other photonic components on the same chip [39]. Figure 1: The aspects of integrated photonics discussed in this paper. The development of on-chip infrared cameras represents a significant advancement in imaging technology, integrating infrared sensing capabilities directly onto semiconductor chips [40]. This innovation leverages microelectromechanical systems (MEMS) and advanced fabrication techniques to create compact, low-power, and cost-effective infrared sensors [41; 42]. By embedding infrared detection directly on the chip, these cameras offer enhanced performance, higher resolution, and faster response times. This breakthrough is poised to impact various fields, including consumer electronics, healthcare, security, and automotive industries, enabling applications like night vision, thermal imaging, and non-invasive medical diagnostics [43; 44]. Light sources, including lasers and light-emitting diodes (LEDs), are pivotal in integrated photonics. Integrating efficient, coherent light sources onto photonic chips has been a significant challenge due to the material incompatibilities and the thermal management issues involved. Hybrid integration techniques, where III-V semiconductor lasers are bonded onto Si chips, have become a popular approach [45; 46; 47]. Alternatively, on-chip generation of light through Si photonics has made progress with technologies like Si Raman lasers and Si-based light-emitting diodes [48]. The study conducted by [PERSON] et al. demonstrated that transformation optics techniques enable the design and integration of functional components made from planar gradient index materials into photonic circuits [49].