A Multi-Format, Multi-Wavelength Erbium-Doped Fiber Ring Laser Using a Tunable Delay Line Interferometer  
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range, making them highly adaptable for various applications in fields such as spectroscopy, optical coherence tomography, and telecommunications [27; 28]. Multi-wavelength lasers can emit multiple wavelengths of light, either simultaneously or sequentially, finding applications in areas such as wavelength-division multiplexing (WDM) in telecommunications, optical spectroscopy, and medical diagnostics [29]. The gain medium housed within the fiber laser's resonance cavity is essential for amplifying light and generating laser output through population inversion and stimulated emission. Commonly used gain mediums include erbium-doped fiber amplifiers (EDFAs) [8], semiconductor optical amplifiers (SOAs) [30], reflective semiconductor optical amplifiers (RSOAs) [31], Raman amplifiers [32], and fiber optic Brillouin amplifiers [33]. EDFAs use erbium-ion-doped optical fiber to provide a high gain of up to 20-30 dB with a low noise factor. They are suitable for long-distance communication, with a main amplification area aimed at the C-band (1530-1565 nm) and L-band (1565-1625 nm). SOAs use a semiconductor as the gain medium and can amplify a wide range of wavelengths. Still, they have a high noise figure, are sensitive to polarization, and may introduce nonlinear effects. RSOAs are similar to SOAs but have a reflective end, making them suitable for bidirectional communication and remote amplification. Raman amplifiers enhance light signals using the Raman scattering effect and can be used with various types of optical fibers and wavelengths, making them suitable for WDM (wavelength-division multiplexing) systems. Raman amplification can be distributed along the fiber to reduce noise and enhance signal quality over long distances. However, it is important to note that Raman amplifiers can be costly, structurally complex, and may introduce non-linear effects. Brillouin amplifiers are capable of providing gain levels of up to 30-40 dB at pump powers typically below 100 mW. However, they are only suitable for applications requiring narrow frequency amplification, are sensitive to temperature, and are complex to implement. In recent years, there has been significant research into multi-wavelength laser devices that are constructed using the optical fiber ring architecture as the resonant cavity [34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50]. These devices have garnered considerable interest due to their more complex production techniques compared to single-wavelength lasers. They offer a wide range of practical applications, including optical communications, optical fiber sensing, optical signal processing, microwave photonics, high-resolution spectroscopy, wavelength-division multiplexing, time-division multiplexing, and mode division multiplexing systems [29; 34]. One of the most preferred options for these devices is the use of erbium-doped fiber (EDF) as the gain medium, primarily because of its high gain and low noise properties [35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50]. Utilizing EDFAs with high pump conversion efficiency presents a challenge since an increase in temperature results in the deterioration of the homogeneous broadening effect [61]. This, in turn, leads to intense competition between different modes and makes it difficult to generate stable multi-wavelength lasers at room temperature. Researchers have made efforts to address this issue by cooling the EDFA using liquid nitrogen [62; 63], and various alternatives have been explored, including the implementation of fiber Bragg grating systems [35; 36; 37], polarization hole burning [38], and interferometer filters [39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50].