Compact nano-void spectrometer based on a stable engineered scattering system

Abstract

Random scattering of light in disordered media can be used for highly sensitive speckle-based wavemeters and spectrometers. However, the multiple scattering events that fold long optical paths within a compact space also make such devices exceedingly sensitive to vibrations and small disturbances to the disordered media. Here, we show how scattering can be engineered so that it can be used for a compact computational spectrometer that is largely insensitive to environmental factors. We designed and fabricated a three-dimensional pseudo-random nano-void pattern with 62% scattering efficiency. The controlled amount of multiple scattering ensured a sufficiently long optical path for the target resolution of 100 pm, with optimal long-term stability. The 200-μm-thick scattering silica substrate was integrated in a compact assembly with a low-cost camera sensor. The target resolution was achieved for full spectrum measurements while single wavelengths could be determined with 50 pm resolution. Such tailored scattering systems can improve the trade-off among cost, size, stability, and spectral resolution in computational spectrometers.

Low-cost fiber Bragg grating interrogation with a femtosecond laser written scattering chip

“…Using multiple planes increases scattering efficiency by facilitating multiple backwards and forward light passes (circa 60% of incident light was scattered). 11 Each plane measures 1 × 1 mm with 1000 × 1000 voids (average lateral void separation 1 µm). To enhance randomization of the wavefront, the position of each void was randomized in either the horizontal x or vertical y directions by adding an offset in range ±0.4 µm, alternating direction for each layer.…”

“…19 For a long-term reconstruction, the chip-based device would be superior, since its high temporal stability was already demonstrated. 8,9 To quantify the devices' performance, the strain values were reconstructed using the highest correlation value for the given strain reference (column-wise) from their correlation matrices as shown in Figure 4. For each test, the applied strain was increased linearly from 0 to 850 µϵ over the time span shown.…”

“…The core principle of our approach utilizes a scattering medium as a spatial-spectral converter which generates unique and highly deterministic speckle patterns for different wavelengths. [8][9][10] Since applied strain will shift the FBG signal wavelength, this results in different speckle patterns. This in turn allows the system to directly reconstruct the strain values from the speckles, without needing to infer the spectral information.…”

Magnetic field sensing using laser written birefringent scattering medium

“…Full details of the scattering medium design and fabrication are presented in our previous work. 5 3. METHODS…”

“…3 To solve this challenge, our team developed a 3D silica scattering chip (Figure 1) for generating the speckles with high intrinsic stability (>7 days). 5 The scattering chip-based system benefits from no moving parts, low cost, straightforward manufacturing and applicability over a wide wavelength regime (as long as the sensor can detect the scattered light). Due to local stress-induced birefringence within the chip, the resulting speckles are also polarization dependent.…”