Control of resonance mode using a fine-structured grating: toward a high resolving power filter.

A band-stop filter with high resolving power is designed for mid-infrared spectroscopic sensing and imaging applications. By utilizing a truncated grating consisting of multiple gold nanowires in each unit cell of the periodic structure, compression of the stop bandwidth and improvement of the resonance extinction are realized simultaneously. It shows only a single stop band at ∼4.474  μm with 15 dB extinction and >80% background transmission over a wide spectral range. The obtained narrow linewidth (∼1.45  nm) enables a spectral resolving power higher than 3000. Flexible control of the filtering performance is investigated by adjusting the variety of geometrical parameters. Moreover, the structure may have potential applications in refractive index sensing.