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We propose a nanogap-enhanced phase-change waveguide with silicon PIN heaters. Thanks to the enhanced light-matter interaction in the nanogap, the proposed structure exhibits strong attenuation (Δα = ∼35 dB/µm) and optical phase (Δneff = ∼1.2) modulation atλ = 1550 nm when achieving complete phase transitions. We further investigate two active optical devices based on the proposed waveguide, including an electro-absorption modulator and a 1 × 2 directional-coupler optical switch. Finite-difference time-domain simulation of the proposed modulator shows a high extinction ratio of ∼17 dB at 1550 nm with an active segment of volume only ∼0.004λ3. By exploiting a directional coupler design, we present a 1 × 2 optical switch with an insertion loss of < 4 dB and a compact coupling length of ∼ 15 µm while maintaining small crosstalk less than −7.2 dB over an optical bandwidth of 50 nm. Thermal analysis shows that a 10 V pulse of 30 ns (1×1 modulator) and 55 ns (1×2 switch) in duration is required to raise the GST temperature of the phase-change waveguide above the melting temperature to induce the amorphization; however, the complete crystallization occurs by applying a 5 V pulse of 180 ns (1×1 modulator) and a 6 V pulse of 200 ns (1×2 switch), respectively.
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Trident edge coupler on thin-film lithium niobate for optimized coupling of octave-separated wavelengths for nonlinear applications
We introduce a trident edge coupler design optimized for the simultaneous coupling of two widely separated wavelengths (2 µm and 1 µm) between a lensed fiber and a 600-nm-thick X-cut lithium-niobate-on-insulator (LNOI) waveguide. These wavelengths are commonly encountered in nonlinear wave mixing applications, representing either the fundamental and second harmonics in second harmonic generation (SHG) processes or the leading and trailing edges of an octave-spanning spectrum generated through broadband nonlinear processes such as frequency comb or supercontinuum generation. Achieving efficient coupling between fibers and strongly confined waveguides in integrated platforms, such as LNOI, can be challenging due to the significant difference in spot sizes between the two wavelengths. Our trident edge coupler offers coupling losses below 1.4 dB for the 2 µm and 1 µm spots simultaneously, showcasing an average transmission enhancement of around 10% compared to the baseline of a single linear taper. Furthermore, it enables a reduction of transmission at 1.5 µm, a typical pump wavelength, with an attenuation of transmission over 10 dB compared to those at the 2 µm and 1 µm wavelengths.
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- Award ID(s):
- 2323752
- PAR ID:
- 10523697
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Continuum
- Volume:
- 3
- Issue:
- 7
- ISSN:
- 2770-0208
- Format(s):
- Medium: X Size: Article No. 1116
- Size(s):
- Article No. 1116
- Sponsoring Org:
- National Science Foundation
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