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Broadband tunable narrow-linewidth laser based on scattering-enhanced fiber covering E-S-C-L bands

Minzhi Xu, Zechun Geng, Da Wei, Yujia Li, Juntao He, Chaoze Zhang, Wei Du, Lei Gao, Leilei Shi, Ligang Huang, Jindong Wang, Tao Zhu

TL;DR

The paper tackles the challenge of achieving broadband tunability without sacrificing linewidth in semiconductor lasers. It introduces a hybrid cavity architecture that uses polarization‑multiplexed parallel SOAs and a scattering‑enhanced feedback fiber, together with a wideband blazed‑grating tunable filter, to realize continuous tuning from $1337.47$ nm to $1631.39$ nm. The key contributions include a physics‑based model of distributed Rayleigh feedback, the experimental demonstration of a $293.92$ nm tuning range with linewidths of $1.54$–$2.61$ kHz, and sub‑millisecond switching times across the tuning band. This work offers a robust, high‑purity broadband laser suitable for dense wavelength division multiplexing, high‑resolution spectroscopy, and related photonic systems.

Abstract

This work demonstrates a broadband tunable narrow-linewidth laser based on scattering-enhanced fiber, covering the E-S-C-L wavelength bands from 1337.47 nm to 1631.39 nm, with a total tuning span of 293.92 nm. The laser employs two semiconductor optical amplifiers (SOAs) centered at 1420 nm and 1550 nm, which are connected into a single ring resonator via polarization multiplexing. Wavelength selection and tunability is realized using an ultra-broadband tunable filter based on a blazed grating. To suppress side longitude modes, an 18-meter-long femtosecond-laser-empowered random scattering fiber is utilized inside the cavity as a feedback medium, yielding an output linewidths between 1.54 kHz and 2.61 kHz. Benefited from the fast response of the galvanometer mirror and short relaxation time of SOAs, wavelength switching time is less than 1 ms under different tuning channels among the wavelength range of near 300 nm. The stable single-longitude-mode operation is maintained across the entire tuning range. The exceptionally broad tuning range and high spectral purity of the laser endow it with significant application potentials across a wide range of fields.

Broadband tunable narrow-linewidth laser based on scattering-enhanced fiber covering E-S-C-L bands

TL;DR

The paper tackles the challenge of achieving broadband tunability without sacrificing linewidth in semiconductor lasers. It introduces a hybrid cavity architecture that uses polarization‑multiplexed parallel SOAs and a scattering‑enhanced feedback fiber, together with a wideband blazed‑grating tunable filter, to realize continuous tuning from nm to nm. The key contributions include a physics‑based model of distributed Rayleigh feedback, the experimental demonstration of a nm tuning range with linewidths of – kHz, and sub‑millisecond switching times across the tuning band. This work offers a robust, high‑purity broadband laser suitable for dense wavelength division multiplexing, high‑resolution spectroscopy, and related photonic systems.

Abstract

This work demonstrates a broadband tunable narrow-linewidth laser based on scattering-enhanced fiber, covering the E-S-C-L wavelength bands from 1337.47 nm to 1631.39 nm, with a total tuning span of 293.92 nm. The laser employs two semiconductor optical amplifiers (SOAs) centered at 1420 nm and 1550 nm, which are connected into a single ring resonator via polarization multiplexing. Wavelength selection and tunability is realized using an ultra-broadband tunable filter based on a blazed grating. To suppress side longitude modes, an 18-meter-long femtosecond-laser-empowered random scattering fiber is utilized inside the cavity as a feedback medium, yielding an output linewidths between 1.54 kHz and 2.61 kHz. Benefited from the fast response of the galvanometer mirror and short relaxation time of SOAs, wavelength switching time is less than 1 ms under different tuning channels among the wavelength range of near 300 nm. The stable single-longitude-mode operation is maintained across the entire tuning range. The exceptionally broad tuning range and high spectral purity of the laser endow it with significant application potentials across a wide range of fields.
Paper Structure (5 sections, 4 equations, 5 figures)

This paper contains 5 sections, 4 equations, 5 figures.

Table of Contents

  1. Introduction
  2. PHYSICS PRINCIPLES AND METHODS
  3. EXPERIMENTAL SETUP AND TUNING PERFORMANCE
  4. TIME‑FREQUENCY CHARACTERIZATION AND DISCUSSION
  5. CONCLUSION

Figures (5)

  • Figure 1: Comparative experiment between polarization beam splitting (PBS) and optical coupler (OC). (a) Experimental setup for insertion loss comparison between PBS and OC, BLS, broadband light source; OSA, optical spectrum analyzer. (b) Insertion loss of PBS versus OC. (c) Experimental setup for output laser spectrum comparison between PBS and OC. (d) Output spectra of PBS and OC.
  • Figure 2: Experimental setup and schematic diagram. (a) Experimental setup: SOA$_{1}$ and SOA$_{2}$, semiconductor optical amplifier; PBS$_{1}$ and PBS$_{2}$, polarization beam splitter; CPC, compact polarization controller; PC$_{1}$ and PC$_{2}$, polarization controller; CIR$_{1}$ and CIR$_{2}$, circulator; FC, fiber collimator; GM, galvanometer mirror; BG, blazed grating; ISO, isolator; OC, optical coupler; SEF, scattering-enhanced fiber; FOR, fiber optic reflector. (b) Backward optical signal measurement via scattering-enhanced fiber. (c) scattering-enhanced fiber image. (d) Laser wavelength tuning schematic. (e) Characterization of mode evolution via SOA current tuning.
  • Figure 3: Characterization of the tunable filter and laser. (a) Designed structure of the tunable optical filter. (b) Tunable reflection spectra of the optical filter. (c) Statistical analysis of optical filter insertion loss and 3 dB bandwidth at different wavelengths tuning. (d) Spontaneous emission spectra of SOA$_{1}$ and SOA$_{2}$. (e) Optical spectra of the tunable laser. (f) Precisely tuned laser spectra.
  • Figure 4: Analyzing and evaluating the dynamic behavior and process of wavelength switching. (a) Integrated spectral profiles during wavelength switching. (b) Concatenated laser intensity signals representing wavelength switching. (c) Eye diagram of temporal evolution for switching from $\lambda_{1}$ to $\lambda_{2}$. (d) Eye diagram of temporal evolution for switching from $\lambda_{2}$ to $\lambda_{1}$. (e) Statistics of switching interval durations.
  • Figure 5: Characterization of tunable laser frequency characteristics. (a) Laser linewidths at different wavelengths tuning. (b) Concatenated laser linewidths across wavelengths. (c) Frequency noise at different wavelengths tuning. (d) Performance comparison with the state of the art and previous research.