**Programmable High-Resolution Spectral Processor in C-band Enabled by Low-Cost Compact Light Paths**

#### **Zichen Liu <sup>1</sup> , Chao Li <sup>2</sup> , Jin Tao <sup>3</sup> and Shaohua Yu 3,\***


Received: 2 October 2020; Accepted: 3 December 2020; Published: 7 December 2020

**Abstract:** The flexible photonics spectral processor (PSP) is an indispensable element for elastic optical transmission networks that adopt wavelength division multiplexing (WDM) technology. The resolution and system cost are two vital metrics when developing a PSP. In this paper, a high-resolution 1 × 6 programmable PSP is investigated and experimentally demonstrated by using low-cost compact spatial light paths, which is enabled by a 2 K (1080p) liquid crystal on silicon (LCoS) and two cascaded transmission gratings with a 1000 line/mm resolution. For each wavelength channel, the filtering bandwidth and power attenuation can be manipulated independently. The total insertion loss (IL) for six ports is in the range of 5.9~9.4 dB over the full C-band. The achieved 3-dB bandwidths are able to adjust from 6.2 GHz to 5 THz. Furthermore, multiple system experiments utilizing the proposed PSP, such as flexible spectral shaping and optical frequency comb generation, are carried out to validate the feasibility for the WDM systems.

**Keywords:** programmable; photonics spectral processor (PSP); liquid crystal on silicon (LCoS); high-resolution and low-cost; optical frequency combs (OFC)
