Fig. 1. Schematic view of the spectrometer assembly. (a) Monochromatic diffuse light enters spectrometer from the top. The light is collimated by the CNT collimator, separated by wavelength by the LVF and ultimately collected by the photodetector array. (b) Complete spectrometer compared in size to a quarter. A 3D printed holder contains the LVF and collimator and is sealed with a plastic window. The photodiode array is attached to a flexible substrate. Full spectrometer is compared to the size of a quarter. (c) CAD illistration of the collimator, LVF, and photodiode array. This exploded view shows the components without the 3D printed holder.

Fig. 2. Monochromated light exits the monochromator and is diffused first by a reflective diffuser and second, by an engineered diffuser that is immediately above the spectrometer. Data are collected with and without the collimator. (a) Modeled intensity distribution from the LVF-photodiode combination with 100μm pore with 5μm sidewalls and varying heights in μm. (b) Schematic of the experimental setup. (c) Spectrum of light taken by the spectrometer from monochromatic diffuse light with center wavelength at 1300 nm and an FWHM of 2 nm with a CNT-M collimator (orange dots) and without one (blue dots). The model in A is fit in amplitude and baseline which shows good agreement with the experimental results (solid line). (d) Diffuse light shone into the spectrometer at different wavelengths (dots), and the spectral response is plotted. At 1300 nm, the FWHM is about 13 nm, matching the expected resolution of the LVF (lines).

Fig. 3. Spectrum measured on the wrist with both a grating-based SWIR spectrometer and our miniaturized spectrometer. The integration time was varied to get the same A/D counts on both devices. The flame integrated from 5500 ms while the miniaturized spectrometer integrated from 30 ms.

Fig. 4. A pulse measured on the wrist. (a) Photo of the spectrometer used on the wrist. (b) The spectrometer was placed directly over the artery with the LEDs placed on the tendon side of the arm. (c) A series of spectra are collected at 10 ms intervals, and the pixel corresponding to 1050 nm is plotted in time, yielding a pulsatile waveform. The 1050 nm peak is chosen to illustrate the pulse due to its large pulsatile amplitude.