Wavefront shaping assisted design of spectral splitters and solar concentrators

Abstract

Spectral splitters, as well as solar concentrators, are commonly designed and optimized using numerical methods. Here, we present an experimental method to spectrally split and concentrate broadband light (420-875 nm) via wavefront shaping. We manage to spatially control white light using a phase-only spatial light modulator. As a result, we are able to split and concentrate three frequency bands, namely red (560-875 nm), green (425-620 nm), and blue (420-535 nm), to two target spots with a total enhancement factor of 715%. Despite the significant overlap between the color channels, we obtain spectral splitting ratios as 52%, 57%, and 66% for red, green, and blue channels, respectively. We show that a higher number of adjustable superpixels ensures higher spectral splitting and concentration. We provide the methods to convert an optimized phase pattern into a diffractive optical element that can be fabricated at large scale and low cost. The experimental method that we introduce, for the first time, enables the optimization and design of SpliCons, which is [Formula: see text] times faster compared to the computational methods.

Figure 1

(a) The experimental setup that is used to emulate spectral splitters and concentrators: SpliCons using an SLM. Broadband light coming from the source coupled to the fiber (F) passes through condenser lens (C) ($\text{f}=160\text{mm}$) and linear polarizer (P) positioned on the way before SLM. A plano-convex lens (L) ($\text{f}=300\text{mm}$) is placed to transfer the image from the SLM surface onto the camera. (b) Image before optimization of the wavefront. (c) Spectrally split and concentrated light. (d) Phase pattern on the SLM that concentrates and spectrally splits light. The images (b) and (c) are raw images obtained from the CCD camera.

Figure 2

(a) An example of physical DOE having seven-step height levels. (b) An example of programmable DOE having seven refractive indices.

Figure 3

The all-in-one single-channel intensity profile (a) before, (b) after wavefront shaping. Differential intensity changes for all-in-one single-channel, blue, green, and red channels are shown separately in panels (c), (d), (e), and (f), respectively.

Figure 4

The enhancement factor of intensity for each channel as a function of (a) number of superpixels and (b) number of major iterations. The spectral splitting ratio for each channel as a function of (c) number of superpixels (d) number of major iterations. The error bars are smaller than the symbol size in all panels.