# A High-Performance Thin-Film Sensor in 6G for Remote Sensing of the Sea Surface
## 1 Introduction
The vast ocean is a body of water that is in motion all the time; for example, the sea surface wind field, wave field, current field, tides, and eddies are all simultaneously changing elements in the ocean's dynamic environment [11; 12; 13; 14]. Therefore, the time-domain characteristics of ocean remote sensing are very important. Only by maintaining good dynamics in ocean observation can the change process of ocean elements be reflected in a timely and accurate manner. Because the spectral difference in different ocean elements is very small, only the refinement of the sensor waveband can ensure an accurate reflection of various ocean elements. In summary, it is necessary to select the appropriate waveband of electromagnetic waves to complete the remote sensing detection of marine water bodies in order to meet the spatial resolution of time and to achieve effective sensing detection capabilities and high-efficiency transmission capability [15; 16; 17; 18; 19; 20; 21]. THz technology utilizes the change in the waveform amplitude and phase of the THz pulse through the sample material to reflect the material properties of the sample. The amplitude and phase information are directly related to the absorption coefficient and refractive index of the sample so that the complex refractive index of the material can be directly obtained. This technology has a very high signal-to-noise ratio, high detection accuracy, low photon energy, and high permeability to oil contaminants such as paraffin; it has advantages that other wavelengths of light do not have, and it is, therefore, a very important means of remote sensing detection [22; 23; 24]. At the same time, sixth-generation (6G) technology adopts millimeter-wave and THz technology to optimize spatial communication transmissions, leading to transmission rates for wireless or mobile terminals of up to 11 Gb/s and meeting the requirements of remote sensing technology for fast communication. The integration of 6G remote sensing technology will enable satellite communication to cover the entire expense between heaven and Earth. This will result in the establishment of a comprehensive network that combines ground remote sensing and ocean remote sensing, creating a global broadband network that seamlessly covers near-earth space [25]. Any location within this near-earth space will have access to fast wireless data transmission. Due to the ubiquitous broadband network that spans heaven and Earth, the satellite remote sensing system will be able to transmit commands at any given moment, free from the constraints of geographical limitations. Similarly, the transmission of remote sensing data will not be restricted by specific time windows. With virtually limitless measurement and control resources and receiving capabilities, remote sensing technology will no longer be confined by these resources. As a result, the maximum utilization of remote sensing technology resources will be achieved. The utilization of 6G technology in remote sensing for monitoring marine water quality has gained significant attention in the research community. The effective implementation and adoption of 6G technology heavily rely on the use of functional devices operating in the THz band. However, current THz detectors face several challenges, including limited detection area, suboptimal performance at room temperature, and difficulties in mass production. THz incoherent detectors, also known as direct detectors, can be categorized into thermal detectors and photonic detectors based on their detection principles. Thermal detectors have a relatively simple structure and can detect a wide range of the spectrum, but their sensitivity is not high. On the other hand, photonic detectors receive THz energy and convert the internal electronic state of atoms or molecules in the detector into measurable electrical signals via the photoelectric effect. These signals are then amplified to detect THz waves. Photonic detectors typically employ photoconductive and photovoltaic-type structures.