Optical bandpass filter
View Patent ↗A tunable resonant tunneling gap for resonant tunneling across the tunneling gap. By adjusting the width of the tunneling gap and adjusting an angle of incidence of light onto the tunneling gap, a pass-band shape and center wavelength may be tuned. The tunneling gap may be an air gap between lenses coated with matching Bragg reflectors. The air gap may be adjusted for example using piezo actuators connecting between the lenses. The angle of incidence may be adjusted for example by rotating the lenses, and thus the tunneling gap, relative to an incident beam of light.
1 . A method for tuning a resonant tunneling optical filter operating in a frustrated total internal reflection regime, the method comprising:
providing a resonant tunneling optical filter comprising two hemi-cylindrical or hemi-spherical coupling prisms each having a flat surface coated with a uniform thin film stack specified to enable admittance-matched resonant tunnelling of a selected linear polarization state and wavelength of incident light while reflecting an orthogonal linear polarization of incident light over a wavelength range of interest, the coupling prims having their coated surfaces separated by a tunneling gap of adjustable width and having gap interfaces subject to total internal reflection, the resonant tunneling being mediated by surface states at the interfaces of the tunneling gap;
adjusting an angle of incidence of light onto the resonant tunneling optical filter to cause a variation in resonant energy and frequency of the surface states;
adjusting a width of the tunneling gap of the resonant tunneling optical filter to cause a variation in mutual coupling between the surface states; and
the angle of incidence and the width of the tunneling gap being adjusted in combination wherein the angle of incidence is selected to provide a desired center wavelength and the tunneling gap is selected to provide a desired shape of a passband of the resonant tunneling optical filter.
2 . The method of claim 1 in which the desired shape is a flat top shape.
3 . The method of claim 1 in which the angle of incidence is adjusted by rotating the resonant tunneling optical filter relative to a collimated light source.
4 . A resonant tunneling optical filter operating in a frustrated total internal reflection regime and comprising two hemi-cylindrical or hemi-spherical lenses as input/output coupling prisms, each lens having a respective flat face facing the flat face of the other lens, in which the respective flat faces are each coated with respective thin film stacks, the flat faces being separated in use by an air gap with interfaces subject to total internal reflection, the thin film stacks arranged to provide resonant tunneling across the air gap, the resonant tunneling being mediated by surface states at the interfaces of the air gap, and the air gap being adjustable in thickness, in which adjusting the thickness of the air gap causes a variation in mutual coupling between the surface states, and a center wavelength and shape of a resonant tunneling passband being adjustable by combined adjustments of the air gap thickness and the angular orientation of the air gap relative to a collimated light beam inside the coupling prisms;
wherein adjusting the angular orientation of the air gap relative to the collimated light beam causes a variation in resonant energy and frequency of the surface states.
5 . The resonant tunneling optical filter of claim 4 in which the thin film stacks are spatially uniform.
6 . The resonant tunneling optical filter of claim 4 in which the thin film stacks are substantially identical.
7 . The resonant tunneling optical filter of claim 4 in which the thin film stacks are configured for admittance matching to TE-polarized light.
8 . The resonant tunneling optical filter of claim 4 in which the thin film stacks are configured for admittance matching to TM-polarized light.
9 . The resonant tunneling optical filter of claim 4 mounted on a stage for rotation around an axis.
10 . The resonant tunneling optical filter of claim 4 in which the lenses are arranged to provide focusing and/or collimation to a beam of light directed towards the resonant tunneling optical filter.
11 . An optical assembly comprising the resonant tunneling optical filter of claim 4 in combination with additional optics arranged to direct collimated light to the resonant tunneling optical filter.
12 . The optical assembly of claim 11 in which the additional optics comprise supplementary lenses.
13 . An imaging system comprising a resonant tunneling optical filter as claimed in claim 4 wherein the resonant tunneling optical filter comprises hemi-spherical lenses and an input lens arranged to direct rays of an incoming image to enter the hemi-spherical lenses and to be substantially collimated within the hemi-spherical lenses.
14 . The imaging system of claim 13 further comprising an output lens arranged to form an image from light received from the resonant tunneling optical filter.