## 1 Introduction  
[PERSON] first demonstrated the unusual electromagnetic properties such as negative permittivity or permeability of complex materials [1], which is known as metamaterials (MMs) [2]. The characteristics of MMs depend on its physical structure, not its chemical composition, which makes it suitable for use in various applications such as absorbers [3], filters [4], antennae [5], imaging [6], invisible clocks [7], sensors [8], polarization converters [9], and lenses [10]. [PERSON] first introduced the metamaterial perfect absorber (MPA) [11],which has opened a new research area due to its extensive use in different applications such as energy harvesting [12], solar cells [13], photodetectors [14], and thermal emitters. [15]. Researchers are currently conducting extensive research on the MPA design for application in the infrared, THz, and microwave frequencies, and they are achieving low-loss devices through structural optimization [16; 17]. In addition, solar energy harvesting using the MPA of total visible light has drawn research attention [18; 19; 20]. Appropriate electric and magnetic resonance engineering can achieve uniform absorption properties. Most researchers have shown different types of MPA structures with limited absorption properties such as limited frequency and low absorption level. Only a few studies have been found on the full visible optical wavelength region. The visible wavelength range is 380-750 nm, which corresponds to a frequency spectrum of 400-790 THz. Polarization-insensitive properties are essential for absorber design because of the unique absorption rate at different polarization incident angles [8; 21]. Moreover, a broad level of incident angle stability is required for efficient absorption rate [22].  
In [23], a Cu, Si\({}_{3}\)N\({}_{4}\), and Si material-based four-layer optical wavelength absorber was designed for 400-700 nm, where the lowest absorption was about 80% with a peak absorption level of 97%. In [24], an absorption above 83% was found in the visible optical wavelength region from 370 to 880 nm, and the peak absorption value reached 92% by using Au and SiO\({}_{2}\) materials. In [25], a small-size Ag and SiO\({}_{2}\)-based absorber was presented for 300-700 nm, where the absorption bandwidth and absorption level were decreased, but the peak absorption value was increased to 98%. In addition, the polarization insensitivity was not found in [23; 24; 25] and the oblique incident angle stability was also not presented. In [22], a three-layered (tungsten-silicon dioxide-tungsten) metamaterial optical region absorber was presented, where an absorption bandwidth above 91.24% was achieved from 389.34 to 697.19 nm with a peak absorption of 99.99%. The polarization insensitivity and 60\({}^{\circ}\) incident angle stability were found at absorption levels up to 70%. In [26], an Au and Si-based absorber was proposed with increased incident angle stability up to 65\({}^{\circ}\). However, the absorption level decreased to 80%. A Ni and Si-based absorber was proposed for an absorption level above 90% at wavelengths from 400 to 700 nm [27]. After analyzing the previous research, it is clear that an MMA that is polarization-insensitive and has oblique incident angle stability with a high-absorption-level MMA for the entire wavelength (380-750 nm) is highly desirable for visible optical metamaterial absorber applications.  
This paper presents a three-layer MMA of ultra-wide absorption bandwidth from 380 to 750 nm for visible optical wavelengths. The polarization conversion ratio (PCR) value was analyzed to verify the proposed design as an absorber. Absorption properties at different polarization angles and oblique incident angles were analyzed for both TE and TM modes, which showed unique absorption properties for both modes. The proposed MMA achieved an absorption above 92.2% at the operating wavelength with an average and peak absorption of 97.2% and 99.99%, respectively.