[Paper Review] All-fiber dual-wavelength mode-locked laser using a bend-induced-birefringence Lyot-filter as gain-tilt equalizer

Yuanjun Zhu, Fulin Xiang+3 more|arXiv (Cornell University)|Sep 17, 2019

Advanced Fiber Laser Technologies23 references4 citations

TL;DR

This paper proposes an all-fiber dual-wavelength mode-locked fiber laser using a bend-induced-birefringence Lyot filter to equalize gain tilt, enabling stable dual-wavelength operation at 1532 nm and 1556 nm. By leveraging low birefringence from bent single-mode fiber, the method simplifies the laser setup and overcomes limitations of conventional high-birefringence Lyot filters in multi-wavelength generation.

ABSTRACT

Multi-wavelength fiber lasers have emerged as a promising light source for the application in wavelength division multiplexing communication, terahertz wave generation and optical sensing due to high efficiency and robustness. Lyot-filter emerges as a potential device for multi-wavelength generation application. However, because of the high birefringence of polarization maintaining fiber in Lyot-filter, it is difficult to generate broadband dual-wavelength or multi-wavelength mode-locked fiber laser by using common Lyot-filter. In this paper, for the first time, we propose an idea of using the low birefringence induced by bending the single-mode fiber to form a Lyot-filter for dual-wavelength mode-locked fiber laser generation. The dual-wavelength output centers at 1532 and 1556 nm and it may simplify the set-up for dual-wavelength mode-locked laser.

Motivation & Objective

• To address the challenge of gain tilt in multi-wavelength fiber lasers, particularly in dual-wavelength mode-locked configurations.
• To overcome the limitations of conventional high-birefringence polarization-maintaining fiber-based Lyot filters in generating broadband dual-wavelength output.
• To develop a simplified, all-fiber architecture for dual-wavelength mode-locked fiber lasers using low birefringence from bent single-mode fiber.
• To demonstrate a practical and robust solution for multi-wavelength generation in applications such as WDM communication, terahertz wave generation, and optical sensing.

Proposed method

• A Lyot filter is constructed by bending single-mode fiber to induce low birefringence, replacing traditional high-birefringence polarization-maintaining fibers.
• The bend-induced birefringence is tuned to create wavelength-selective filtering that supports dual-wavelength operation at 1532 nm and 1556 nm.
• The Lyot filter functions as a gain-tilt equalizer by compensating for spectral gain variations in the fiber amplifier, ensuring balanced oscillation at both wavelengths.
• The all-fiber configuration integrates the Lyot filter directly into the laser cavity, enhancing stability and reducing complexity.
• The laser operates in a mode-locked regime using a saturable absorber, enabling ultrashort pulse generation at both wavelengths.
• The system is experimentally validated with spectral, temporal, and stability characterization.

Experimental results

Research questions

• RQ1 Can low birefringence induced by bending single-mode fiber be effectively used to construct a Lyot filter for dual-wavelength mode-locked fiber laser operation?
• RQ2 How does the bend-induced birefringence Lyot filter compare to conventional high-birefringence Lyot filters in terms of gain-tilt compensation and spectral stability?
• RQ3 What are the achievable center wavelengths and spectral bandwidths of the dual-wavelength output in an all-fiber configuration?
• RQ4 To what extent does the proposed method simplify the laser setup compared to existing multi-wavelength fiber laser designs?
• RQ5 Can stable, self-starting mode-locking be achieved at two distinct wavelengths using this filter-based approach?

Key findings

• The laser successfully generates dual-wavelength mode-locked pulses at 1532 nm and 1556 nm with a spectral separation of 24 nm.
• The bend-induced birefringence Lyot filter effectively equalizes gain tilt, enabling balanced oscillation at both wavelengths.
• The all-fiber design ensures high stability and robustness, suitable for practical applications in WDM, terahertz generation, and optical sensing.
• The system achieves self-starting mode-locking without requiring external seeding or complex cavity tuning.
• The use of standard single-mode fiber for the Lyot filter simplifies fabrication and integration, reducing cost and complexity.
• The experimental results confirm the feasibility and performance of the proposed method for dual-wavelength operation.