Freeform direct-write and rewritable photonic integrated circuits in phase-change thin films

Abstract

Photonic integrated circuits (PICs) with rapid prototyping and reprogramming capabilities promise revolutionary impacts on a plethora of photonic technologies. We report direct-write and rewritable photonic circuits on a low-loss phase-change material (PCM) thin film. Complete end-to-end PICs are directly laser-written in one step without additional fabrication processes, and any part of the circuit can be erased and rewritten, facilitating rapid design modification. We demonstrate the versatility of this technique for diverse applications, including an optical interconnect fabric for reconfigurable networking, a photonic crossbar array for optical computing, and a tunable optical filter for optical signal processing. By combining the programmability of the direct laser writing technique with PCM, our technique unlocks opportunities for programmable photonic networking, computing, and signal processing. Moreover, the rewritable photonic circuits enable rapid prototyping and testing in a convenient and cost-efficient manner, eliminate the need for nanofabrication facilities, and thus promote the proliferation of photonics research and education to a broader community.

Rewritable Photonic Integrated Circuit Canvas Based on Low-Loss Phase Change Material and Nanosecond Pulsed Lasers

“…In this work, we demonstrated low-loss, laser-written waveguides in a nonvolatile PCM platform using inexpensive benchtop components (setup cost < $22,000) that in total are 50X less expensive than the mask writing laser used in other works. 13,28 We also demonstrate the first rewritable PIC platform using the wide band gap PCM Sb 2 S 3 , which can enable PICs operating in the near-visible spectrum range (∼800 nm). Our platform exhibits a high patterning resolution of 300 nm with reversible and arbitrary patterning capability.…”

“…One approach is to reduce the scattering loss due to the domain boundary scattering of polycrystalline Sb 2 S 3 , which can be mitigated by engineering the pulsed laser conditions to reduce the loss. For example, one can guide the crystal growth direction by laser writing crystallization instead of hot plate to reduce the boundary . Alternatively, since our PCM laser writing platform is PCM transferrable, another approach is to use other low-loss PCMs such as Sb 2 Se 3 , which provides a much better mode confinement with lower loss (See Supplement Section S8 for further comparison between Sb 2 S 3 and Sb 2 Se 3 ).…”

“…The waveguides or arbitrary photonic structures can be written and erased between the grating coupler pairs. These predefined grating couplers could be removed since the gratings can be made out of the PCM itself, 13 but the coupling efficiency in our case remains inferior to an etched grating. The optical response of the laser-written devices was then measured via a vertical fiber coupling setup.…”

“…For example, one can guide the crystal growth direction by laser writing crystallization instead of hot plate to reduce the boundary. 13 Looking forward, the experimentally demonstrated rewritable PIC canvas represents a new direction for PIC development. Fabricating and testing photonic structures no longer requires weeks of work by highly trained students/ technicians, specialized environments, or million-dollar equipment.…”

“…One practical way to amorphize the PCMs is through short optical pulses, 11 while crystallization can be achieved by annealing PCMs on a hot plate 12 or longer optical pulses. 13 Laser-written PCM metasurfaces or metalenses have been demonstrated using femtosecond 14−17 or nanosecond laser pulses, 18 but optical loss is not critical in these applications since the light only interacts with PCMs over a short distance (<100 nm). In contrast, loss becomes paramount for PICs due to the much longer millimeter or even centimeter propagation length.…”