Fig. 1. Structure schematic of the miniaturized spectrometer. Three major parts including FTS chip, triplet lens, and linear CCD form the miniaturized spectrometer. In the FTS chip, the green box indicates the MZI array, and the yellow boxes indicate the Y-junction splitter and combiner. The two arms of each MZI have the same rotation angle but different radii as R₁ and R₂, leading to the OPD (optical path difference). The OPD in each MZI changes across the array along with the variation of the rotation angle.

Fig. 2. Relation between the retrieved spectrum peak and the effective refractive index change.

Fig. 3. (a) Photograph of our quartz-based FTS chip next to a quarter. (b) Micrograph of adjacent splitters in two MZIs; waveguides between them are accompanying waveguides used to improve fabrication, and no light transmits in them.

Fig. 4. Normalized 2-D color scaling graph based on the transformation matrix T resulting from the entire measured transmission spectra of all the 51 MZIs from 460 nm to 510 nm.

Fig. 5. Original and retrieved normalized spectra of the light emitted by a 532 nm laser.

Fig. 6. Spot diagrams when (a) the object height is 0 mm and the aperture angle is 7 deg at wavelengths of 0.48 μm, 0.55 μm, and 0.78 μm; (b) the object height is 0.5 mm and the aperture angle is 7 deg at wavelengths of 0.48 μm, 0.55 μm, and 0.78 μm. The unit of the scaleplate is μm.

Fig. 7. Photograph of the mounted miniature spectrometer with the FTS chip, triplet lens, linear CCD, and a controlling electric circuit board.

Fig. 8. CCD readout when 532 nm lasing light illuminates the input plane of the FTS chip. When no light enters the sensing element, the CCD readout is around 2640. The smaller the readout number is, the larger the optical power is. The red number in the figure marks the related MZI in the chip.

Fig. 9. Original and retrieved spectra of 532 nm lasing light.

Table 1. Performance Comparison between Our Miniature Spectrometer and Hamamatsu C12666MA