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Han JL, Li MQ, Wu RB et al. High fiber-to-fiber net gain in erbium-doped thin film lithium niobate waveguide amplifier as an external gain chip. Opto-Electron Sci 4, 250004 (2025). doi: 10.29026/oes.2025.250004
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High fiber-to-fiber net gain in erbium-doped thin film lithium niobate waveguide amplifier as an external gain chip
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Abstract
Miniaturized erbium-doped waveguide amplifiers attracted great interests in recent decades due to their high gain-efficiency and function-scalability in the telecom C-band. In this work, an erbium-doped thin film lithium niobate waveguide amplifier achieving >10 dB off-chip (fiber-to-fiber) net gain and >20 mW fiber-output amplified power is demonstrated, thanks to the low-propagation-loss waveguides and robust waveguide edge-couplers prepared by the photolithography assisted chemomechanical etching technique. Systematic investigation on the fabricated waveguide amplifiers reveals remarkable optical gain around the peak wavelength of1532 nm as well as the low fiber-coupling loss of −1.2 dB/facet. A fiber Bragg-grating based waveguide laser is further demonstrated using the fabricated waveguide amplifier as the external gain chip, which generates >2 mW off-chip power continuous-wave lasing around the gain peak at1532 nm. The unambiguous demonstration of fiber-to-fiber net gain of the erbium-doped thinfilm lithium niobate (TFLN) waveguide amplifier as well as its external gain chip application will benefit diverse fields demanding scalable gain elements with high-speed tunability. -
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References
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Supplementary information for High fiber-to-fiber net gain in erbium-doped thin film lithium niobate waveguide amplifier as an external gain chip 
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Han JL, Li MQ, Wu RB et al. High fiber-to-fiber net gain in erbium-doped thin film lithium niobate waveguide amplifier as an external gain chip. Opto-Electron Sci 4, 250004 (2025). doi: 10.29026/oes.2025.250004
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Figure 1.
Design and modal evolution of the SSC-integrated EDWA chip. (a) the schematic of the SSC-integrated EDWA chip. (b) The simulated modal evolution in the SSC region with the insets (i–v) showing the cross-section modal distribution at different propagation positions (dashed lines). The bottom inset shows the fluorescence microscope image of the SSC region. (c) The measured SSC-output mode profile. (d) The measured UHNA7 output mode profile.
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Figure 2.
Gain characterization of the EDWA chip. (a) The experimental schematic. (b) The Er3+ energy-level diagram. (c) The photoluminescence spectrum from the TFLN-waveguide. (d) The fiber-to-fiber net gain curves measured at two different signal wavelengths. (e) The fiber-to-fiber transmission loss curves measured at four different signal wavelengths. (f) The spectra of the input signal and the output signal with/without pump measured at −14 dBm input power. (g) The input and output signal spectra measured at 10 dBm input power. The insets in (f) and (g) show the enlarged spectra around the signal wavelength.
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Figure 3.
Gain saturation of the ASE from the EDWA chip. (a) Forward ASE spectra evolution with pump powers. (b) Backward ASE spectra evolution with pump powers. (c) The normalized ASE spectra at low (unsaturated) and high (saturated) pump powers. (d) The spectral linewidths of the ASE-peak at
1532 nm vs pump powers. The insets in (a) and (b) show the ASE power saturation at three different wavelengths. -
Figure 4.
External laser generation using the EDWA chip. (a) The experimental schematic. (b) The reflection spectra of the FBGs with two different rates. (c) The generated laser powers vs coupled pump powers, with the laser spectra evolution around the pump threshold shown in the inset. (d) The laser spectrum at the maximum output power of 2.1 mW with the enlarged laser spectral profile shown in the inset. (e) The generated laser spectra with the FBG output couplers of different reflection rates.
