Nonimaging optics
Examples of modern implementations of nonimaging optical designs include automotive headlamps, LCD backlights, illuminated instrument panel displays, fiber optic illumination devices, LED lights, projection display systems and luminaires.
Modern portable and wearable optical devices, and systems of small sizes and low weights may require nanotechnology.
This issue may be addressed by nonimaging metaoptics, which uses metalenses and metamirrors to deal with the optimal transfer of light energy.
[7] Collecting luminescent radiation in photon upconversion devices[8][9] with the compound parabolic concentrator being to-date the most promising geometrical optics collector.
[10] Some of the design methods for nonimaging optics are also finding application in imaging devices, for example some with ultra-high numerical aperture.
Nonimaging optics have been demonstrated to concentrate sunlight to 84,000 times the ambient intensity of sunlight, exceeding the flux found at the surface of the Sun, and approaching the theoretical (2nd law of thermodynamics) limit of heating objects to the temperature of the Sun's surface.
[16] The simplest way to design nonimaging optics is called "the method of strings",[17] based on the edge ray principle.
These were developed primarily to solve the design problems related to solid state automobile headlamps and complex illumination systems.
The 3D SMS design method (U.S. patent 7,460,985) was developed in 2003 by a team of optical scientists at Light Prescriptions Innovators.
The flow-line (or Winston-Welford) design method typically leads to optics which guide the light confining it between two reflective surfaces.
However, a ray r3 at an angle β>θ to the vertical (coming from a point outside the infinite source) bounces around inside the CPC until it is rejected by it.
[1] A variation are the multichannel or stepped flow-line optics in which light is split into several "channels" and then recombined again into a single output.
Choosing now the optical path length S22 between S2 and R2 we have one condition that allows us to calculate point B1 on the bottom surface of the lens.
Choosing now the optical path length S11 between R1 and S1 we have one condition that allows us to calculate point T1 on the top surface of the lens.
Now, refracting at T1 a ray r3 coming from S2 we can calculate a new point B3 and corresponding normal on the bottom surface using the same optical path length S22 between S2 and R2.
Refracting at B3 a ray r4 coming from R1 we can calculate a new point T3 and corresponding normal on the top surface using the same optical path length S11 between R1 and S1.
A ray from S1 refracted at T0 defines a point and normal B2 on the bottom surface, by using constant optical path length S11 between S1 and R1.
Now a ray from R2 refracted at B2 defines a new point and normal T2 on the top surface, by using constant optical path length S22 between S2 and R2.
Figure "SMS skinning" on the left illustrates the process used to fill the gaps between points, completely defining both optical surfaces.
Now a ray r2 coming from S2 and refracted at T01 defines a new point and normal on the bottom surface, by applying the same constant optical path length S22 between S2 and R2.
A ray r1 coming from w1 is refracted at T0 and, with the optical path length S14, a new point B2 and its normal is obtained on the bottom surface.
Now ray r2 coming from w3 is refracted at B2 and, with the optical path length S 23, a new point T2 and its normal is obtained on the top surface.
It allows the design of optics with variable refractive index, and therefore solves some nonimaging problems that are not solvable using other methods.
However, manufacturing of variable refractive index optics is still not possible and this method, although potentially powerful, did not yet find a practical application.
In some applications it is important to achieve a given irradiance (or illuminance) pattern on a target, while allowing for movements or inhomogeneities of the source.
On the left this figure shows a lens L1 L2 capturing sunlight incident at an angle α to the optical axis and concentrating it onto a receiver L3 L4.
The situation in the middle of the figure shows a nonimaging lens L1 L2 is designed in such a way that sunlight (here considered as a set of parallel rays) incident at an angle θ to the optical axis will be concentrated to point L3.
Intermediate rays incident on the first lens at an angle θ will be redirected to points between R1 and R2, fully illuminating the receiver.
Intermediate rays incident on the first lens at an angle α<θ will be redirected to points between R1 and R2, also fully illuminating the receiver.
[2][24] The development started in the mid-1960s at three different locations by V. K. Baranov (USSR) with the study of the focons (focusing cones)[25][26] Martin Ploke (Germany),[27] and Roland Winston (United States),[28] and led to the independent origin of the first nonimaging concentrators,[1] later applied to solar energy concentration.
