Light modulating device and electronic apparatus using the same
A light modulating device for modulating incident light in a given wavelength band is provided. The light modulating device may include: a first semiconductor layer; an active layer provided on the first semiconductor layer and having a multiple quantum well structure and a refractive index that is variable according to an electric field applied thereto, and a second semiconductor layer provided on the active layer and including a grating pattern in which a plurality of gratings extending in a first direction are repeatedly arranged in a second direction perpendicular to the first direction. The light modulating device may have high modulation efficiency owing to guided mode resonance by the grating pattern.
1. A light modulating device for modulating incident light in a given wavelength band, the light modulating device comprising:
a first semiconductor layer;
an active layer provided on the first semiconductor layer, the active layer having a multiple quantum well structure and a refractive index that is variable according to an electric field applied thereto; and
a second semiconductor layer provided on the active layer, the second semiconductor layer comprising a grating pattern in which a plurality of gratings extending in a first direction are repeatedly arranged in a second direction perpendicular to the first direction,
wherein the first semiconductor layer comprises a plurality of protruding elements extending in a third direction that is perpendicular to the first direction and the second direction and on which the active layer and the second semiconductor layer are provided, the plurality of protruding elements corresponding to the grating pattern, and
wherein, in the third direction, a thickness of each of the plurality of protruding elements is greater than a thickness of the active layer and a thickness of the second semiconductor layer.
2. The light modulating device of claim 1 , wherein the grating pattern of the second semiconductor layer forms a localized guided mode in the second direction for the incident light in the given wavelength band.
3. The light modulating device of claim 1 , wherein the grating pattern of the second semiconductor layer has a height and a pitch which are less than a center wavelength of the given wavelength band.
4. The light modulating device of claim 1 , wherein the grating pattern of the second semiconductor layer has a height and a pitch which are less than half of a center wavelength of the given wavelength band.
5. The light modulating device of claim 1 , wherein the active layer has an absorption coefficient that is less than 200 cm −1 for light of a resonance wavelength at which a reflectance by the grating pattern exhibits a peak value.
6. The light modulating device of claim 1 , wherein the second semiconductor layer has a first width in the first direction and a second width in the second direction, and
a ratio of the second width to the first width is at least 10.
7. The light modulating device of claim 1 , wherein each of the first semiconductor layer, the active layer, and the second semiconductor layer comprises a Group III-V compound semiconductor.
8. The light modulating device of claim 1 , wherein the active layer has the multiple quantum well structure based on InGaAsP/InP, GaAs/InGaAs, or GaN/AlGaN.
9. The light modulating device of claim 1 , wherein the first semiconductor layer is doped with an N-type dopant, and the second semiconductor layer is doped with a P-type dopant.
10. The light modulating device of claim 1 , wherein the plurality of protruding elements, the active layer and the second semiconductor layer have a structure divided into a plurality of modulation elements that are individually controllable.
11. The light modulating device of claim 10 , wherein the plurality of modulation elements are arranged with a first pitch in the first direction.
12. The light modulating device of claim 11 , wherein the first pitch is less than a center wavelength of the given wavelength band.
13. The light modulating device of claim 10 , wherein the plurality of modulation elements are arranged with a first pitch A 1 in the first direction and with a second pitch A 2 in the second direction.
14. The light modulating device of claim 13 , wherein a ratio A 2 /A 1 of the second pitch A 2 to the first pitch A 1 is about 2.5 or more.
15. The light modulating device of claim 1 , wherein the plurality of protruding elements has a height of 20 nm or more.
16. The light modulating device of claim 1 , wherein spacing between the plurality of protruding elements is within a range of 50 nm to 500 nm.
17. A beam steering device comprising:
the light modulating device of claim 10 ; and
a processor configured to control voltages respectively applied to the plurality of modulation elements such that the light modulating device deflects the incident light at a deflection angle within a given angle range.
18. The beam steering device of claim 17 , wherein the processor is further configured to time-sequentially vary the voltages such that a predetermined area is scanned while the deflection angle is time-sequentially varied within the given angle range.
19. An electronic apparatus comprising:
a light source;
the beam steering device of claim 18 that scans an object by adjusting a direction of light which is incident from the light source; and
a photodetector configured to receive light from the object,
wherein the processor is further configured to control the beam steering device and process an optical signal received from the photodetector.
20. A light modulating device comprising:
a plurality of modulation elements that are spaced apart from each other at a regular interval, in a first direction,
wherein each of the plurality of modulation elements comprises:
a first semiconductor layer having a grating pattern and doped with a first type of dopant;
a second semiconductor layer doped with a second type of dopant; and
a quantum well layer that has a multiple quantum well structure and a refractive index that is variable according to a voltage applied thereto, the quantum well layer being provided between the first semiconductor layer and the second semiconductor layer in a second direction that is perpendicular to the first direction, and
at least one voltage source configured to individually apply a voltage signal between the first semiconductor layer and the second semiconductor layer of each of the plurality of modulation elements,
wherein the second semiconductor layer comprises a plurality of protruding elements extending in the second direction and on which the quantum well layer and the first semiconductor layer are provided, the plurality of protruding elements corresponding to the grating pattern, and
wherein, in the second direction, a thickness of each of the plurality of protruding elements is greater than a thickness of the quantum well layer and a thickness of the first semiconductor layer.