## 1 Introduction  
Continuous-wave (CW) lasers in the visible wavelength have drawn increased interest over the past decades for applications in fundamental research, industry, and light displays. For example, orange lasers with wavelengths close to 600 nm assume a critical part in a plethora of present-day applications, for example, photodynamic treatment [1], flow cytometry [2], spectroscopy [3], astronomy [4], optogenetics and neuroscience [5], and laser projection shows [6]. Until now, there are no traditional diode lasers emitting in the near 600 nm because of an absence of appropriate direct band gap materials [7]. Despite noteworthy progress towards achieving the shortest wavelength in the orange range at 599 nm using direct emission by GalnP material, the approach is restricted in wavelength adjustability [8]. Therefore, the development of smaller and more efficient solid-state lasers with the utilization of a nonlinear effect is an attractive path for overcoming this restriction. Likewise, sum frequency generation (SFG), in particular, is a potential approach to generating orange light with periodically inverted structures [9]. The quasi-phase-matching (QPM) method utilizing periodically poled lithium niobate (PPLN) is very appealing for actualizing broadband SFG due to its several advantages [10]. Meanwhile, various CW light sources near the 600 nm wavelength region have already been illustrated using several approaches, for instance, use of resonant cavities in SFG [11; 12], frequency doubling in Raman-shifted 1064 nm lasers [13], tunable output in Cr: Forsterite material [14], avalanche upconversion in Pr, Yb:BaY\({}_{2}\)F\({}_{8}\)[15], and in quantum-well InGaP/InAlGaP semiconductor lasers [16]. Unfortunately, the input wavelength acceptance bandwidth in single-period structures is very restricted and also constrained in tunability. Nevertheless, non-uniform structures have been created, which are commonly more appropriate for wide-band wavelength converters since they give numerous spatial vectors contrasted to single-period structures. Until now, the different ways of dealing with executing QPM range from single-period structures to Fibonacci optical superlattice [17], non-uniform [18], linearly chirped [19], apodized and un-apodized [20; 21], and multi-sectioned [22]. A widely-tunable source within the 770 nm wavelength region has additionally been implemented based on chirped periodically poled lithium niobate with a phase matching bandwidth as extensive as 50 nm [23]. This advancement has prompted the use of a single crystal for the generation of several wavelengths in the visible range that are very reasonable for entertainment applications. For instance, a tunable orange laser in the range of 601 nm to 604 nm in quasi-periodically poled lithium tantalate (LT) superlattice has been implemented [24]. Additionally, more than 1 W optical parametric oscillator (OPO) tunable from 605 to 616 nm based on MgO:PPLN was implemented recently [25]. OPOs, emitting in the visible wavelength range, have also been utilized for high resolution Doppler-free spectroscopy, albeit, such OPOs are excessively bulky [26]. It would be more attractive to extend the QPM capabilities of the non-uniform poled structures, with fixed grating parameters, and, thus, further broaden the fundamental wavelength acceptance bandwidth. One of the more promising simple approaches to add reconfigurable abilities to step-chirped structures is by utilization of varying temperature distribution along the length of the crystal. The inhomogeneity of temperature distribution as a result of the thermal differences set at MgO:PPLN crystal facets, actuates a wave vector mismatch in each step (with a different uniform period) resulting from non-uniform distribution of refractive index along the crystal length, i.e., different wavelength regions can be reconfigured.