Fabricating lifted Haar transform image compression optical chip based on femtosecond laser

In this paper, a lifted Haar transform (LHT) image compression optical chip has been researched to achieve rapid image compression. The chip comprises 32 same image compression optical circuits, and each circuit contains a 2×2 multimode interference (MMI) coupler and a π/2 delay line phase shifter as the key components. The chip uses highly borosilicate glass as the substrate, Su8 negative photoresist as the core layer, and air as the cladding layer. Its horizontal and longitudinal dimensions are 8 011 µm×10 000 µm. Simulation results present that the designed optical circuit has a coupling ratio ( CR ) of 0: 100 and an insertion loss ( IL ) of 0.001 548 dB. Then the chip is fabricated by femtosecond laser and testing results illustrate that the chip has a CR of 6: 94 and an IL of 0.518 dB. So, the prepared chip possesses good image compression performance.