Tunable optical metasurfaces based on slot mode resonances

A tunable optical structure cell comprising a first, a second, a third, and a fourth pairs of nanobars, each of the first and the fourth pair including two adjacent parallel nanobars with a first slot therebetween, and each of the second and the third pair including two adjacent parallel nanobars with a second slot therebetween, and

• wherein:
• the nanobars are oriented along a first direction, and positioned adjacent to each other along a second direction;
• the second direction being perpendicular to the first direction;
• the first and the second slots are oriented along the first direction;
• the first and the second slot comprises, each, notches arranged periodically along the first direction;
• the nanobar pairs are positioned adjacent to each other along the second direction such that the second nanobar pair is interposed between the first and the third nanobar pair, and the third nanobar pair is interposed between the second and the fourth nanobar pair;
• the first and the fourth nanobar pairs are structurally replicas of each other, and the second and the third nanobar pairs are structurally replicas of each other;
• within each of the first and the fourth nanobar pairs, one nanobar is configured to receive a first bias voltage and the other nanobar of the same pair is configured to receive a second bias voltage, the second bias voltage being different from the first bias voltage;
• within each of the second and the third nanobar pairs, one nanobar is configured to receive a third bias voltage and the other nanobar of the same pair is configured to receive the first bias voltage, the third bias voltage being different or same from the first bias voltage;
• a bias voltage received by two nanobars that are adjacent but belong to different pairs are the same;
• the tunable optical structure cell is configured to receive an optical signal, thus generating a first slot resonance in correspondence with the first slots, and a second slot resonance in correspondence with the second slots;
• wavelength and quality-factor of the first slot resonance is controlled based on a selection from one or more of a1) a depth along the first or the second direction of each notch of the first slot, b1) a width of each notch of the first slot, c1) a width of the first slot, d1) the period of the notch along the first slot, and a difference of the first and the second bias voltages, and
• independently from the wavelength and the quality-factor of the first slot resonance, a wavelength and quality-factor of the second slot resonance is controlled based on a selection from one or more of a1) a depth along the first or the second direction of each notch of the second slot, b1) a width of each notch of the second slot, c1) a width of the second slot, d1) the period of the notch along the second slot, and a difference of the first and the third bias voltages.

A beam-steering structure cell comprising:

• a pair of blocking nanobars;
• a pair of parallel nanobars with a first slot therebetween;
• the pair interposed between the blocking nanobars of the pair of blocking nanobars;
• a mirror disposed underneath nanobars and blocking nanobars;
• wherein:
• the nanobars and are oriented along a first direction, and positioned adjacent to each other along a second direction;
• the second direction being perpendicular to the first direction;
• the blocking nanobars are oriented along the first direction and positioned along the second direction;
• each first slot is oriented along the first direction;
• each first slot comprises notches arranged periodically along the first direction;
• one nanobar of the pair of nanobars is configured to receive a first bias voltage and the other nanobar of the pair is configured to receive a second bias voltage, the second bias voltage being different from the first bias voltage;
• the beam-steering structure cell is configured to receive an optical signal, thus generating a slot resonance;
• a wavelength and quality-factor of the slot resonance is controlled based on a selection from one or more of a) a depth along the first or the second direction of each notch, b) a width of each notch, c) a width of the slot, d) the period of the notch along the first slot, and a difference of the first and the second bias voltages.

A method of tuning a wavelength and quality-factor of a resonance of an optical structure, the method comprising:

• providing four pairs of nanobars;
• disposing the two nanobars of each pair side to side and in parallel with each other;
• orienting the nanobars along a first direction and arranging the nanobars along a second direction, the second direction being perpendicular to the first direction;
• forming a slot in-between the two bars of each pair of nanobars;
• forming notches along each slot;
• the notches being periodically arranged along the first direction;
• adjusting one or more of a) a depth along the first direction of the notches, b) a depth along the second direction of the notches, c) a width of the nanobars, d) the period of the notch along the slot,
• in correspondence with a desired slot resonance wavelength;
• illuminating the optical structure with an optical signal, thus generating a slot resonance having the desired wavelength in each slot;
• applying a first bias voltage to a first nanobar of a first pair of the four pairs of nanobars;
• applying a second bias voltage to a second nanobar of the first pair of the four pairs of nanobars;
• applying the second bias voltage to a first nanobar of a second pair of the four pairs of nanobars;
• applying a third bias voltage to a second nanobar of the second pair of the four pairs of nanobars;
• applying the third bias voltage to a first nanobar of a third pair of the four pairs of nanobars;
• applying the second bias voltage to a second nanobar the third pair of the four pairs of nanobars;
• applying the second bias voltage to a first nanobar of a fourth pair of the four pairs of nanobars, and
• applying the first bias voltage to a second nanobar of the fourth pair of the four pairs of nanobars.