## 1 Introduction  
The field of photonics has become an indispensable component of modern-day communication technology. The developments and demands from the telecommunication industry has driven a major boost in photonic technology and vice-versa in the last 35 years. Both fundamental and applied sciences have benefited from and contributed to the age of photonics. The platform of guided light in fibers and waveguides has opened the gates to next-generation instrumentation in astronomy. At the same time, the spin-offs from astrophotonics are extensively being adapted in other streams of science and technology.  
The field of astrophotonics revolves around collecting astronomical light into guided channels, manipulating the transport and reconfiguration of the light, and filtering/dispersing/combining the guided light. A combination of one or more of these functionalities has led to a wide spectrum of astrophotonic instruments. They serve the purpose of leading new astronomical investigations or making the current investigations more efficient and cost-effective. Some of these scientific frontiers are: Detailed kinematic studies of galaxies [1], observing faint sources in the early universe [2], discovering and characterizing exoplanets and their atmospheres [3], and studying the first galaxies in the universe [4]. Following these pursuits requires large telescopes and innovative ways to manipulate the light to extract the most information from a limited number of photons.  
The next two decades will mark the age of thirty-meter scale telescopes [5; 6]. However, the volume, mass, and cost of conventional optical instruments grow as \(D^{2}\)-\(D^{3}\) (where \(D\) is the diameter of the telescope), creating new challenges for instrumentation [7]. At the same time, there is an explosion in the number of large astronomical surveys discovering a multitude of new transients, exoplanets, and galaxies. This necessitates development of new instruments for large telescopes that are compact and cost-effective while providing the flexibility to address the challenge of high-throughput characterization for these large surveys.  
Photonic technologies provide a promising platform for building next-generation instruments that are flexible (in terms of light manipulation), compact (volumes of a few tens of cubic centimetres) and lightweight (a few hundreds of grams), thanks to manipulation of guided light [8; 9]. In addition, they are cost-effective, due to the advantages of mass-fabrication. Therefore, the astronomical community has pursued this direction very positively and built a wide variety of instruments from the near-ultraviolet (NUV) [10] to mid-infrared (MIR) wavebands [11]. As an example of the growth of astrophotonics, Figure 1 shows the number of citations of papers related to astrophotonic spectrographs. However, the current technical know-how is still far from complete or ideal, leaving many challenges that will likely be addressed in the near future.  
In this paper, we focus on the recent developments in the field of astrophotonic spectrographs. To paint a complete picture, in Sections 2 and 3, respectively, we briefly discuss the steps to channel the light from the telescope to the spectrograph and condition it. Photonic dispersion concepts, and their implementation and challenges are described in Section 4. In Section 5, we discuss new developments in calibration and detection that are particularly of interest to astrophotonic spectrographs. Lastly, in Section 6, we summarize and discuss the impact of photonic spectrographs in the near future in astronomy as well as other applications.