THz Near-Field Imaging Sensor Using Integrated Substrateless Silicon Interferometer

Terahertz (THz) time-domain spectroscopy (TDS) technology has greatly advanced various THz applications ranging from fundamental science to industrial non-destructive imaging. However, traditional THz- TDS systems rely on complex setups with femtosecond pulse lasers and bulky free-space optical components, hindering their miniaturization. A more practical approach introduces THz frequency domain imaging using semiconductor laser diodes, which replace femtosecond laser and facilitate integration into photonic integrated circuit (PIC) chips. Despite its promise, addressing real-world imaging applications remains challenging due to the need for free-space optics, which also negatively impact resolution due to the diffraction limit. To overcome this limitation, this study explores the use of silicon (Si) microphotonics, focusing on an integrated Y -junction that operates as an interferometer. The Y -junction essentially replaces all free-space components, paving the way towards compact, monolithically integrated all-silicon structures that span just ~ 1 cm, We demonstrate near-field imaging at 325 GHz employing the Y-junction. The experiments achieve a 500-µm spatial resolution and a 100-µm depth resolution, showcasing potential for handheld THz near-field imaging sensors.