Technology

Breakthrough in on-chip spectrometry

LyteChip’s digital Fourier Transform (dFT) spectrometer combines the high resolution and wide spectral range of FTIR spectroscopy with the small footprint and low cost of silicon photonics.

About the Digital Fourier Transform

The target performance for LyteChip’s first prototype is less than 0.1 nm resolution for the near-infrared regime of 1200-1650 nm wavelength, all in a handheld spectrometer device. We plan to improve on and further miniaturize our prototype to achieve equal or better resolution than commercial benchtop spectrometers, for one tenth of the cost.

Figure 1. Block diagram of the on-chip dFT spectrometer photonic circuit design.

The purpose of the dFT spectrometer is to split and combine light to create an on-chip interferometer. As shown in Figure 1, input light from an optical fiber is split into the upper and lower arms of a Mach-Zehnder interferometer with dynamic path lengths, each controlled by a series of switches. The spectrometer sweeps through all switch configurations and path lengths, measuring the relative phase shift between the two arms.

The unique circuit design allows exponential performance scaling with the number of switches. Each pair of switches that are added to the circuit result in a two-fold increase in the spectral channel number increasing spectral resolution. Figure 2 shows the experimental setup and resulting transmission spectra for a design with six switches, resulting in 64 path length permutations. The spectrometer uses an elastic-D1 spectrum reconstruction algorithm to recover an approximation of the input spectrum, with a resolution determined by the number of path length permutations.

LyteChip’s exciting new approach to FTIR spectroscopy is only possible due to recent advances in silicon photonics manufacturing capabilities. As silicon photonics improves in cost and reliability, so too will LyteChip’s technology.

Figure 2. Schematic diagram of the original dFT spectrometer lab characterization setup (left) with transmission spectra (right) for 64 permutations of the on/off switch combinations, which serves as a basis set for spectrum reconstruction.

The result is a powerful and accurate spectrometer on a chip which can achieve twice the spectral resolution compared to the classical Rayleigh limit.

For more information, check out the following
Nature Communications publication

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LyteChip is a fabless silicon photonics company focusing on chip-scale miniaturized spectrometers

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