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Institutional Subscription. Free Shipping Free global shipping No minimum order. Preface Chapter 1 Concentrators and Their Uses 1. Powered by. You are connected as. Connect with:. Use your name:. For nonplanar receivers, the reflector shape required to create an ideal concentrator is not parabolic. The convention is to use CPC-type.
An example of a CPC-type concentrator for a tubular receiver is shown in Fig. Part of the reflector is an involute and the remainder reflects rays from the extreme input angle to the tangent of the receiver. The design of CPC-type concentrators for nonplanar sources has been described. Designs with gaps between reflector and receiver— and with prisms attached to the receiver, have also been described. CPC-type geometries are also used in laser pump cavities.
Circles are drawn to identify the parabola vertex and the edges of the CPC input and output apertures. Arrays of CPCs or CPC-like structures have also been applied to the liquid crystal displays,, illumination,89 and solar collection. A CEC is shown in Fig. Hottel strings can be used to compute the etendue of the collected radiation see Sec. The CHC concentrates the flux. Arrangements where the CHC is just a cone are possible. Edge of source is imaged onto edge of output aperture. Edge of virtual source is imaged onto the edge of the output port.
If the virtual source is located at the output aperture of the concentrator, then an ideal concentrator in both 2D and 3D can be created see Fig.
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Generically, this is a hyperboloid of revolution and is commonly called a trumpet. Such a device is called a dielectric compound parabolic concentrator DCPC. In this immersed exit port case, the standard CPC construction can still be used, but the exit port area is now n times smaller in 2D and n2 smaller in 3D. To avoid excessively long systems, other optical surfaces are typically added. Often, a CPC-type concentrator is combined with a primary element such as a condensing lens or a parabolic reflector.
There are also designs where the optical surface of the primary and the optical surface of the concentrator are designed together, which often blurs the distinction between primary and concentrator.
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There are numerous examples of lenses combined with a nonimaging device in the literature. One approach is to place a lens with the finite-size aperture shown in Fig. Such a combination typically produces a shorter package length than a CPC-type concentrator. Both the lens curvature and the CHC reflector can be optimized to minimize the effects of aberrations, or the combination can be adjusted so that the CHC turns into a cone.
When TIR is used to implement the mirrors, the mirror reflection losses can be eliminated, with the drawback that the package size grows slightly. A design procedure for a lens mirror combination with maximum concentration was presented by Ning, who coined the term dielectric total internal reflecting concentrator DTIRC and showed significant package improvements over the DCPC. Eichhorn describes the use of CPC, CEC, and CHC devices in conventional optical systems, and uses explicit forms for the six coefficients of a generalized quadric surface.
There have been numerous investigations of systems that have a parabolic primary and a nonimaging secondary. Asymmetric concentrators have also been investigated. Winston showed that an off-axis parabolic system can improve collection by tilting the input port of a secondary concentrator relative to the parabolic axis.
Other asymmetric designs have been investigated. Ries also investigated a complementary Cassegrain used for concentration. Simultaneous Multiple Surfaces. Minano and coworkers have investigated a number of concentrator geometries where the edge of the source does not touch the edge of a reflector. The procedure has been called simultaneous multiple surfaces SMS and builds on the multisurface aspheric lens procedure described by Schultz.
The I surface is typically used for refraction the first time the ray intersects the surface and TIR for the second ray intersection.
The I surface is sometimes mirrored over portions of the surface if reflection is desired but the angles do not satisfy the TIR condition. SMS can be used to design all reflecting configurations. Restricted Exit Angle Concentrators with Lenses If the angular distribution of the flux is constant across an aperture and the centroid of the distribution is normal to the aperture, then the distribution is called telecentric.
Many optical systems require the transfer of flux from one location to another. If the desired distribution of flux at the second location is also telecentric, then the system is called doubly telecentric.
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An afocal imaging system can be modified to provide a doubly telecentric imaging system when used with finite conjugates. In nonimaging systems, flux must often be transferred from one aperture to another and the angular distribution at the second aperture must be constant across the aperture.
However, the point-by-point mapping is not required in nonimaging systems. A single lens can provide this transfer of radiation, as shown in Fig. This type of lens is a collimator and is similar to a Fourier transform lens; it has been called a beam transformer. The receiver is immersed in both cases.
In the RXI case, the central portion of the refractive surface is mirrored. The aberrations introduced by a lens can limit the etendue preservation of the aggregate flux collected by the lens. The increase in etendue tends to become more severe as range of angles collected by the lens increases. A picture is shown in Fig. FIGURE 19 Condenser to provide an angle to area transformation and produce a distribution that is symmetric about the optical axis at both input and output planes.
In general, the transition can be made sharper by increasing the cone length; however, there may be multiple local minima for a specific situation.
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Edmonds uses a prism where hot spots that may occur are defocused after propagating through the prism. Two nonimaging concentrators have also been investigated for use in fiber-optic coupling. One of the standard design methods for concentrators has been to design a system using a meridional slice and then simply rotate the design about the optical axis. In some cases, such as the CPC used with a disk receiver, this may only introduce a small loss; however, there are cases where the losses are large. The standard CPC-type concentrator for use with a circular receiver90, is an example where this loss is large.
To assess the loss, compare the 2D and 3D cases. The rays refract at the input port, total internally reflect TIR at the sidewalls, and then refract at the output port. The 2D case provides maximum concentration. The dilution is quite large. Feuermann provides a more detailed investigation of this type of 2D-to-3D etendue mismatch. Ries93 shows how skew preservation in a rotationally symmetric system can limit system performance even though the etendue of the source and receiver may be the same. The etendues of the disk, sphere, and cylinder are all the same.
A second example where a cylinder is coupled to a disk is shown in Fig. This figure highlights losses and dilution. For skew values where the skewness distribution for the receiver is greater than the source, dilution occurs. Where the source is greater than the receiver, losses occur. If the size of the disk is reduced, then the dilution will also decrease, but the losses increase. If the disk is made bigger, then the losses decrease, but the dilution increases. Skew ray analysis of inhomogeneous sources and targets has also been considered. One way of avoiding the skew ray limit in a system with a rotationally symmetric source and a rotationally symmetric receiver is to avoid the use of rotationally symmetric optics to couple the flux from source to target.
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A device called a star concentrator has been devised and shown to improve the concentration. The star concentrator derives its name from the fact that the cross section of the concentrator looks like a star with numerous lobes. The star concentrator is designed using a global optimization procedure. Performance of the star concentrator, assuming a reflectivity of 1, provides performance that exceeds the performance possible using a rotationally symmetric system. The star concentrator approach has also been investigated for the case of coupling from a cylindrical source to a rectangular aperture.
The problem of coupling flux from a rotationally symmetric source to a spectrometer slit motivated some earlier efforts to overcome the skewness limit. The dissection can be done while preserving the NA of the input e. Benesch calls this system an optical image transformer and it is similar in function to Bowen's image slicer.
The etendue for all three cases is constant. Laser arrays can also use dissectors to improve performance. The image dissector breaks an input square beam into four smaller square regions that are placed side by side at the output.
The lens array breaks the input beam into four rectangles that are superimposed at the output. Both systems use field lenses at the output.