Planar sub-wavelength gratings (SWG) can provide coupling and decoupling of femtosecond laser pulses to and from planar photonic waveguides with a thickness of several hundreds nm. Simple coupling by focusing at a waveguide edge of planar waveguide shows low efficiency because of strong diffraction effects caused by small thickness of waveguide layer. Using SWG method of coupling one can place many samples on one substrate independent of substrate edge closeness. Up to 40% coupling efficiency in experiment with CW-laser was previously demonstrated [1]. To couple femtosecond laser pulses with wavelength of 1.55 microns to planar silicon waveguide, a gold metal grating with a period of approximately 630 nm is needed. 1st diffraction maximum will go along waveguide and will couple with waveguide mode, so coupling will occur. There are several methods of sub-wavelength diffraction gratings fabrication. Using this method one can fabricate a free-form pattern with high resolution of several nm. However, a maximum size of a pattern available for FIB is limited by approximately 104 μm2 and it takes long time to produce a whole pattern. The second method is electronic beam lithography. Both methods, FIB and e-beam lithography is highly complicated, expensive and time-consumable. In this paper the laser interference lithography (LIL) is proposed for subwavelength coupling gratings fabrication. This method allows to fabricate large grating patterns (of several sm2) with full process time of several hours and exposure time of several minutes. This method bases on a UV-laser source and optical scheme with Lloyd’s interferometer [2,3]. Laser beam goes through optical scheme with beam expander and spatial filter. Then two different parts of beam (reflected from interferometer’s mirror and direct) exposure the same area of a photoresist film and produce an interference pattern. After that one need to use developer and remove unexposed photoresist to obtain mask for etching or lift-off process with desirable pattern. Experimental setup consists of 355 nm Nd:YAG pulsed laser source with 10 Hz repetition rate, a beam expander and a spatial filter. This system expands beam to diameter of 3 cm, and filtered beam goes to a Lloyd interferometer with 500 μm-thick photoresist film and produce interference light intensity pattern on photoresist layer. Fig. 1 shows optical microscope image of an obtained photoresist grating. Dark lines show exposured photoresist, light lines is clean glass substrate after developing and rinsing process. Period of the structure is approximately 1600 nm. Using such pattern as a mask one can etch underlying material and produce a nanostructure. A series of samples with a period from 860 to 1600 nm is obtained to calibrate dependency of the period on incident angle. Quality of mask is controlled by scanning electron microscope and optical microscope techniques.