Fig. 1. The 3D view (a) and the top view (b) of the present ultra-high-resolution on-chip spectrometer. Schematic configurations of the ultra-high-Q resonator (c) and the wideband resonator (d). (e) The principle of the spectrum retrieved process.

Fig. 2. (a) Microscope images of the fabricated ultrahigh-resolution spectrometer. Zoom-in views of the grating coupler (b), the wideband resonator (c), the Euler bend (d), and the heater on ultra-high-Q resonator (e).

Fig. 3. (a) Measured spectrum response of the fabricated 10-channel wideband resonators. (b) Measured spectral responses at the through/drop ports of the ultrahigh-Q resonator; Inset: the resonance peak. (c) The spectral response of the ultrahigh-Q resonator when applying different heating power. (d) The resonance wavelength as the heating power P_h increases. (e) The calibrated wavelength-power map. As an example, the arrow indicates the peak wavelength λ_i dropped by the i-th cascaded wideband resonator when the heating power P_h is 30 mW.

Fig. 4. Retrieved spectrum for a given spectrum with a single peak when using the present on-chip spectrometer as well as a commercial OSA with a resolution of 0.02 nm. (a) The peak wavelength is 1546.61 nm locating at channel C₁. (b) The peak wavelength is 1549.45 nm locating at channel C₄. (c) The peak wavelength is 1552.67 nm locating at channel C₇.

Fig. 5. Normalized retrieved spectrum with double peak input at channel C₇. (a) (1552.627, 1552.632) nm, (b) (1552.024, 1552.624) nm, (c) (1552.643, 1552.646) nm.

Fig. 6. Measured results for the spectrum generated from a commercial fiber Bragg filter.