## 1 Introduction  
In comparison to the available configurations for distributed fiber sensing, those that are Brillouin scattering-based appear to offer somewhat superior spatial resolution with a long sensor reach [1]. However, despite several such appealing advantages, they have captured (and are expected to capture) only a marginal share of the total commercial distributed fiber sensor market [2]. While application requirements certainly lead one's choosing the most appropriate sensor type, relative cost, without doubt, is a recognized disadvantage for Brillouin-based systems [3]. Hence, in response came the development of new system architectures, including Brillouin optical correlation domain reflectometry (BOCDR) [4; 5]. Nevertheless, the mundane commonality among nearly all Brillouin-based systems, whether for reasons of cost, convenience, or ubiquity, is the use of standard (i.e., telecommunications) single mode fiber as the key sensing element.  
There are a wide variety of very good reviews that focus on, or include a discussion of, Brillouin-based distributed sensing systems for numerous applications [1; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. Most of these focus on the system architecture. However, as discussed here, there is an emerging body of work focusing on fiber design as a path towards system simplification and improvement. A subset of these even focus on novel materials, for example to realize fibers with custom thermo-mechanical response. The purpose of this paper is to offer a brief review of some of these novel fiber configurations, with a focus on the importance of the enabling material in these approaches. While Brillouin scattering has been studied in micro-structured fiber [16; 17; 18; 19; 20], and non-silicate systems, including phosphate [21], tellurite [22], ZBLAN [23], and chalcogenide (As\({}_{2}\)Se\({}_{3}\)[24; 25] and As\({}_{2}\)S\({}_{3}\)[25]) glasses, this review will focus on solid singly- or multiply-clad, circular-geometry fibers in silicate glass systems. Such configurations offer the best compatibility with conventional components and fiber fabrication processes.  
Ultimately, it is the hope of the authors that this brief review will serve to (at least partly) reinforce the importance of, and need for, fiber and material design in distributed sensor systems, generally. This paper is written from the perspective of fiber makers and designers, and therefore new system-level analyses (such as sensitivity, sensor configurations, etc.) are not considered. Rather, without prejudice toward any one approach, and with apologies to those not described herein, a wide variety of fiber technologies are described with the hopes of inspiring novel thinking with regard to distributed sensor systems based on Brillouin scattering. That said, the remainder of this paper is arranged as follows. The next section focuses on the waveguide properties of the optical fiber, both acoustic and optical, and, from that, other basic features, such as the Brillouin gain spectrum, are formulated. After that, a discussion of materials, both more and less common, is provided, with some focus on the fiber thermo-mechanical response. This, then, leads into a discussion of tailored fiber configurations and concomitant sensing approaches, with some focus on discriminative sensing. Finally, the paper concludes with a few closing remarks and future perspectives.