Spectral separation limits of interlaced photonic processors

Determine whether an interlaced-structure photonic processor can spectrally separate more than three wavelengths, and characterize how far apart or how close the target wavelengths may be while still permitting spectral separation using a single current configuration.

Background

The paper experimentally demonstrates spectral demultiplexing and multiplexing at three wavelengths with a six-channel broadband universal photonic processor based on an interlaced architecture. The authors note that universal operation at each wavelength independently does not guarantee that multiple wavelength-specific transformations can be realized simultaneously with one shared heater-current configuration.

The authors explicitly identify unresolved spectral-capability questions concerning both the number of wavelengths that can be separated and the allowable spectral spacing between them. Although the measured wavelength sweeps suggest an average characteristic peak width of approximately 15 nm, the broader limits of multiwavelength operation remain unresolved and are identified as requiring further experimental and theoretical investigation.

References

Although a more detailed study of the spectral capabilities of the interferometer architecture in question, i.e., the interlaced structure, is outside the scope of this work, we would like to draw attention to some open questions. For example, the question may naturally arise whether optical signals can be spectrally separated for more than three wavelengths on such a photonic processor. On the other hand, using a chip for spectral separation of three wavelengths, it is reasonable to ask: how spectrally far apart can the wavelengths of the target signals be, and conversely, how close can the wavelengths of the target signals be located? A partial answer to the latter question can be suggested using experimentally measured wavelength sweeps shown in Fig. \ref{fig:multi}, as it can be seen from these graphs that the average characteristic peak width (from maximum to zero) is around 15 nanometers. This gives us a physical insight that the minimum allowable wavelength resolution for our device is 15 nm. Nevertheless, these and other questions show that the study of optical interferometers with an interlaced structure requires ongoing research, both experimental and theoretical.

— Universal Broadband Linear Optical Transformations by an Interlaced Structured Integrated Photonic Processor  (2609.08552 - Kondratyev et al., 8 Sep 2026) in Discussion and conclusion