In some variations, the present invention provides a method for forming a chip-scale photonic frequency channelizer or spectrum analyzer. A low-loss waveguide forms a long delay-line in a first level, from which a large number of filter-taps form narrow channel passbands. Multi-dimensional laser-written waveguides feed a slab waveguide coupler located at a stacked, second level. A chip-scale RF-photonic spectrum analyzer provided by this invention has extremely high resolution, such as a passband width of about 30 MHz over a free spectral range of 12 GHz, while occupying a device footprint of only about 10 cm2 area.