## 1 Introduction  
Performance-boosting of bandwidth and long-distance coverage are currently the most pressing concerns for end-to-end connection and quality of service in both wired and wireless broadband access [1; 2; 3; 4; 5]. Thus, the goals of transmitting and receiving more data as enhanced Mobile Broadband (eMBB), interconnecting millions of devices at once by means of massive machine type communication (mMTC), and increasing responsiveness by ultra-reliability and low latency communication (URLLC) for fifth-generation (5G) new radio (NR) next-generation communication systems are considerably studied [6; 7; 8; 9; 10; 11; 12; 13]. The radio-over-fiber (RoF) technique, which can generate and deliver millimeter-wave signals in the optical domain, is a good candidate for next-generation communication systems due to the advantages of fiber such as high capacity, low attenuation, lightweight, and being free from electromagnetic noise interference (EMI) [14; 15; 16; 17; 18]. In the RoF transmission system, the desired signal can be optically upconverted to a higher frequency band by means of selecting the specific wavelength. Hence, the multi-wavelength generation technique plays an important role in the RoF system. Conventional multi-wavelength schemes use an array of laser sources, external modulators, and local oscillators. However, adding multiple devices in the central station increases the overall cost of the transmission system. In [19; 20; 21], semiconductor optical amplifiers (SOAs) and erbium-doped fiber amplifiers (EDFAs) are utilized as gain mediums to generate multi-wavelengths. Although EDFA has the characteristics of a flatter gain spectrum, lower polarization-dependent gain, and higher saturation power, it has a strong line broadening and cross-saturation at room temperature. Hence, it is challenging to secure stable multi-wavelength lasing at room temperature usingEDFA. In [22], an SOA-based ring laser using coupled ring cavities is used to generate multi-wavelength. However, its performance is limited by polarization, and it is difficult to control the cavity.  
Optoelectronic oscillators (OEOs) have attracted much attention owing to the characteristics of high-quality factors, extremely low noise, excellent performance even at higher frequencies, and other characteristics that are not achieved with electronic oscillators. Conventional OEO schemes require external modulators [23; 24; 25] and continuous-wave lasers. However, an external modulator causes high insertion loss due to its low modulation efficiency. Therefore, the conventional OEO scheme needs three electrical amplifiers [23].  
In this research, a self-start multi-wavelength laser source is proposed and experimentally demonstrated, achieved by directly modulating a commercially available distributed feedback laser diode (DFB-LD) without any local oscillator. The self-start multi-wavelength laser source is based on a self-starting optoelectronic oscillator [23]. A double-pass filter composed of an optical circulator, tunable delay line interferometer (TDLI), and an optical fiber reflector (OFR) is proposed to enhance the tone-to-noise ratio (TNR). A tunable filter (OTF) is used to choose wavelengths for baseband or wireless signal. A reflective semiconductor optical amplifier (RSOA) modulates data signals and is sent across a 25 km single-mode fiber (SMF). The system performance is verified using clear eye diagrams and error-free signal transmission.