Rewriteable photonic chip uses phase change materials
Researchers in the US have developed photonic integrated circuits (PICs) with rapid prototyping and reprogramming using phase change materials (PCM).
The direct-write and rewritable photonic chip technology developed at the University of Washington in Seattle use a low-loss phase-change material (PCM) thin film that allows a complete end-to-end PIC to be directly laser-written in one step without additional fabrication processes, and any part of the circuit can be erased and rewritten, enabling rapid design modification.
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The team has used the technique for an optical interconnect fabric for reconfigurable networking, a photonic crossbar array for optical computing and a tunable optical filter for optical signal processing.
Combining the programmability of the direct laser writing technique with PCM unlocks opportunities for programmable photonic networking, computing and signal processing. It also provides rapid prototyping and testing in a convenient and cost-efficient manner and eliminates the need for nanofabrication facilities.
The photonic chips are created by using PCM’s marked refractive index contrast between the two nonvolatile phases, amorphous and crystalline, which are reversibly switchable using optical pulses from a commercial using a commercial Heidelberg DWL 66+ laser writing system operating at 405nm and 27.5mW.
The photonic circuit is written on a standard oxidized silicon substrate, which is coated with a 200-nm-thick SiO2 layer covering a 30nm layer of Sb2Se3 on a 330nm Si3N4 film. The SiO2 capping layer protects and prevents oxidation of the Sb2Se3 layer.
A waveguide is created in the Sb2Se3 film by using the crystalline phase (cSb2Se3) as the high-index core and the amorphous phase (aSb2Se3) as the cladding. This binary phase configuration enables the confinement of the fundamental transverse electric (TE0) optical mode within a cSb2Se3 waveguide, assisted by the underlayer of Si3N4.
A series of rectangular aSb2Se3 structures created by the laser had varying widths ranging from 1 μm to 200 nm and the minimum achievable feature size is 300 nm, significantly smaller than other systems.
The team used the technique to build waveguides, gratings, ring resonators, couplers, crossings, and interferometers to build a photonic chip.
The direct-write photonic chips are also rewritable, allowing convenient erasure and recreation of the circuits either partially or entirely, thereby completely changing their functionality to suit very different applications.
Local erasure is achieved by scanning the laser beam at a lower speed (0.1 mm2/min) with a reduced laser power of 15 mW, inducing a phase transition from amorphous Sb2Se3 back to crystalline Sb2Se3 in desired areas, enabling modifications and corrections to the PIC design. Alternatively, global erasure can be accomplished by heating the whole substrate to above 180°C, promoting a complete phase transition across the entire PCM film.
www.science.org/doi/10.1126/sciadv.adk1361
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