This supplementary material describes a monolithic thin-film lithium niobate (LN) broadband spectrometer with one nanometre resolution. The device uses scattering waveguides (EFSs) to achieve high spectral resolution. The internal efficiency of the device is maximized by optimizing the scattering efficiency of EFSs, which is calculated using the formula η = 2κL·exp(-κL), where κ is the linear attenuation factor and L is the sampling region length. The optimal efficiency is achieved when κL = 1, corresponding to a scattering efficiency of 1.2% per wire. The nanowires are designed to be 50 nm wide, which is 1/8 of the standing wave period at 1550 nm. Finite-difference time-domain (FDTD) simulations were used to optimize the design parameters, and the results showed a scattering efficiency of 1.1% per wire. Fabrication of the EFSs on LNOI waveguides confirmed the design, with a measured internal efficiency of 52% for 89 nanowires. The device efficiency is limited by fabrication imperfections and material differences. The device also addresses DC drift effects, which can cause chirp in the interferogram. This is mitigated by sweeping the modulation voltage and using a known frequency laser to calculate the average periodicity. The spectrometer was tested with a broadband super-luminescent diode (SLED), demonstrating its ability to resolve the source spectrum with a FWHM of 47.9 nm. The bandwidth of the device is limited by the single-mode condition of the waveguides, which operate from around 1200 nm to over 2000 nm. However, the device's lower wavelength limit is constrained by the responsivity of InGaAs pixels, and the upper limit is around 1700 nm. The device supports single-mode operation at wavelengths above 1250 nm, but multi-mode operation at 1064 nm leads to mode-mixing, which complicates the reconstruction of the interferogram. Simulations confirmed that the waveguide supports up to the third order TE mode at 1064 nm, which overlaps with the fundamental mode. The device's performance is consistent across the measurable bandwidth, although it overestimates the FWHM by an order of magnitude.This supplementary material describes a monolithic thin-film lithium niobate (LN) broadband spectrometer with one nanometre resolution. The device uses scattering waveguides (EFSs) to achieve high spectral resolution. The internal efficiency of the device is maximized by optimizing the scattering efficiency of EFSs, which is calculated using the formula η = 2κL·exp(-κL), where κ is the linear attenuation factor and L is the sampling region length. The optimal efficiency is achieved when κL = 1, corresponding to a scattering efficiency of 1.2% per wire. The nanowires are designed to be 50 nm wide, which is 1/8 of the standing wave period at 1550 nm. Finite-difference time-domain (FDTD) simulations were used to optimize the design parameters, and the results showed a scattering efficiency of 1.1% per wire. Fabrication of the EFSs on LNOI waveguides confirmed the design, with a measured internal efficiency of 52% for 89 nanowires. The device efficiency is limited by fabrication imperfections and material differences. The device also addresses DC drift effects, which can cause chirp in the interferogram. This is mitigated by sweeping the modulation voltage and using a known frequency laser to calculate the average periodicity. The spectrometer was tested with a broadband super-luminescent diode (SLED), demonstrating its ability to resolve the source spectrum with a FWHM of 47.9 nm. The bandwidth of the device is limited by the single-mode condition of the waveguides, which operate from around 1200 nm to over 2000 nm. However, the device's lower wavelength limit is constrained by the responsivity of InGaAs pixels, and the upper limit is around 1700 nm. The device supports single-mode operation at wavelengths above 1250 nm, but multi-mode operation at 1064 nm leads to mode-mixing, which complicates the reconstruction of the interferogram. Simulations confirmed that the waveguide supports up to the third order TE mode at 1064 nm, which overlaps with the fundamental mode. The device's performance is consistent across the measurable bandwidth, although it overestimates the FWHM by an order of magnitude.