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NASA’s ESD is a small form-factor electromagnetic signal detector fabricated on a photonic crystal substrate (e.g., silicon-on-insulator wafer, III-V platform). It integrates a (1) miniature on-chip antenna (e.g., microstrip antenna) aligned to the desired operational frequency, (2) 2-D photonic crystal, and (3) electro-optic polymer (located on the photonic crystal). At the heart of the detector is the 2D photonic crystal. Using an array of carefully sized pores or “nano-cavities,” a waveguide is formed that governs the crystal’s optical transmission properties. An electro-optic polymer (a material that shifts its refractive index in response to external electric fields) is used to coat the photonic crystal. The combination of the 2D photonic crystal and EO polymer make up the resonator. A compact antenna with separate active feed and ground regions is placed near the photonic crystal, creating a gap through which the electromagnetic signal couples to the photonic crystal structure. Under normal conditions (no external signal), the EO polymer’s refractive index remains unchanged, producing a stable resonant notch in the device’s optical transmission. When the antenna intercepts an electromagnetic wave, the resulting electric field modifies the EO polymer’s refractive index, causing a measurable shift in the resonator’s optical output. By monitoring this shift, a photodetector can accurately determine the presence and magnitude of the incoming electromagnetic wave. NASA’s low SWaP-C, high precision ESD can be adapted for use in a variety of systems including remote sensing instruments (e.g., radiometers, spectrometers), transceivers for 5G communications networks, and other electromagnetic signal detection applications. The invention is available for patent licensing.