Waveguide amplifiers have always been significant key components for optical communication. Unfortunately, the low concentration of rare earth ions doped in the host material and the inadequate optimization of the waveguide structure have been the common bottleneck limitations. Here, a novel material, NaYF₄/NaLuF₄: 20% Yb³⁺, 2% Er³⁺ nanoparticle-Polymeric Methyl Methacrylate covalent-linking nanocomposite, was synthesized. The concentrations of Er³⁺ and Yb³⁺ doping increased an order of magnitude. Under a 980 nm laser excitation, highly efficient emission at 1.53 μm was obtained. The characteristic parameters of the single mode waveguide were carefully designed and optimized by using a finite difference method. A formulized iteration method is presented for solving the rate equations and the propagation equations of the EYCDWA, and both the steady state behavior and the gain were numerically simulated. The optimal Er³⁺ and Yb³⁺ concentrations are 2.8 × 10²⁶ m⁻³ and 2.8 × 10²⁷ m⁻³, and the optimal waveguide length is 1.3 cm. Both theoretical and experimental results indicated that, for an input signal power of 0.1 mW and a pump power of 400 mW, a net gain of 15.1 dB at 1530 nm is demonstrated. This result is the highest gain ever reported in polymer-based waveguide amplifiers doped with inorganic Er³⁺-Yb³⁺ codoped nanocrystals.

Temporal cavity soliton generation in fiber cavities or microresonators has achieved great breakthroughs and found significant applications in many fields. Despite recent advances in soliton frequency comb generation via external driving or pump light, it remains challenging to identify a versatile approach for driving the cavity coherently, tuning the mode spacing of soliton frequency combs largely, and achieving long-term operation. Here, instead of using external pump light to drive the cavity coherently, intra-cavity pumping is proposed to drive a Kerr-nonlinear optical cavity for generating temporal solitons and soliton frequency combs. By introducing the Brillouin gain into the cavity, the generated intra-cavity Brillouin lasers are used as the pump light to drive the cavity coherently for generating temporal solitons. In contrast to previous works, the soliton pulses form spontaneously via intra-cavity pumping without the need for fine-tuning the external pump light (to match the cavity resonance), which enables the generation of soliton frequency combs via cascaded four-wave mixing between multiple wavelength intra-cavity Brillouin lasers. Furthermore, by varying the frequency separation of multiple wavelength intra-cavity Brillouin lasers, the soliton pulses with a pulse width of hundreds of femtoseconds and a repetition rate of gigahertz (GHz) to terahertz (THz) are achieved via intra-cavity pumping, corresponding to the generation of soliton frequency combs with step tunable mode spacing from GHz to THz.

A U-shaped double-side polished plastic optical fiber (POF) is demonstrated as a liquid refractive index (RI) sensor. The refractive index of glycerinum solutions is identified by the intensity detection on the bending and evanescent wave loss change. Heat treatment and mechanical polishing are adopted to form the symmetrical side-polished POF probe. The processing parameters are experimentally optimized on the power transmittance. The sensitivity of 1541%/RIU (Refractive Index Unit) can be obtained with a resolution of 5.35 × 10⁻⁴ in the scope of 1.33–1.39. The favorable temperature characteristic is proved to offer stable RI sensing from 20 to 50 °C. This simple POF sensor has potentials in low-cost visible light intensity RI detection.

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A solution-processable erbium-ytterbium codoped complex is synthesized. The absorption and photoluminescence spectra of the complex are observed. The full width at half maximum of the emission spectrum is 80 nm around 1530 nm. A structure of embedded waveguide with the complex as core layer is designed. With an input signal power of 0.3 mW, an optical gain of 5.2 dB at a wavelength of 1550 nm is obtained in a 15-mm-long waveguide when the cladding layer is SU-8. When the cladding layer is polymethyl methacrylate, an optical gain of 6.5 dB is obtained in a 12-mm-long waveguide with an input signal power of 1 mW.