A waveguide is the basic wire of integrated photonics, a channel that confines light (or spin waves, or microwaves) by refractive-index or material contrast, and the current research frontier is no longer whether it works but which material platform, loss figure and crosstalk pitch you can get out of a foundry.
Summary
A waveguide is a structure that confines an electromagnetic wave to a cross-section much smaller than free-space propagation would allow and carries it along a defined path. In photonic integrated circuits (PICs) this is usually a high-index core (silicon, silicon nitride, lithium niobate, lithium tantalate) patterned on a lower-index cladding, either as a fully etched strip or as a rib sitting on a residual slab. Everything else on a PIC, modulators, splitters, resonators, delay lines, detectors, is built by locally perturbing a waveguide or by coupling two of them together. The same physics is being reused outside optics: spin-wave waveguides written directly into yttrium iron garnet carry magnons for on-chip microwave processing, and dielectric waveguides feeding movable “pinching” antennas are being proposed as a base-station radio architecture.
Evidence base
Open questions
Does slab-engineered crosstalk cancellation survive real fabrication tolerance, temperature and wavelength ranges across a full reticle, or is the demonstrated zero-crosstalk condition too narrow to become a design rule?
Can the PLACE isotropic-etch route to low-loss 1.2 cm PPLN be run at wafer scale and with the yield a foundry needs, or does it stay a laboratory process?
How far below dB/cm can visible-band lithium tantalate loss be pushed while keeping the 5 dBm power stability advantage over lithium niobate, and does that advantage hold at higher powers?
What pump power and waveguide length does the cavity-less comb architecture actually require to beat a microresonator on total system efficiency, given the resonator’s inherently lower threshold?
Assessment drafted 2026-08-31 from up to 18 KB sources using the technology-scorecard framework; scores are a draft read pending review.
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Frontier questions
Does slab-engineered crosstalk cancellation survive real fabrication tolerance, temperature and wavelength ranges across a full reticle, or is the demonstrated zero-crosstalk condition too narrow to become a design rule 2026 05 28 universal zero crosstalk photonic integration via slab engin?
Can the PLACE isotropic-etch route to low-loss 1.2 cm PPLN be run at wafer scale and with the yield a foundry needs, or does it stay a laboratory process 2026 05 28 isotropic fabrication of centimeter scale low propagation lo?
How far below dB/cm can visible-band lithium tantalate loss be pushed while keeping the 5 dBm power stability advantage over lithium niobate, and does that advantage hold at higher powers 2026 05 14 robust and active visible light integrated photonics on thin?
What pump power and waveguide length does the cavity-less comb architecture actually require to beat a microresonator on total system efficiency, given the resonator's inherently lower threshold 2026 05 28 a cavity less architecture for high power integrated frequen?