A Prism-Grating Component for 5G Communication
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Publish time:
2025-10-24
A Prism-Grating Component for 5G Communication
Introduction
5G, the fifth generation of mobile communication technology, defines three major application scenarios: Enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (uRLLC), and Massive Machine-Type Communications (mMTC), ultimately aiming to achieve the Internet of Everything (IoE). The peak theoretical transmission speed of 5G can reach tens of Gb per second, which is hundreds of times faster than 4G networks [1]. The 5G era requires approximately 4-5 times the number of base stations needed for 4G, with a bandwidth that is 10 times greater. The dense networking of 5G base stations necessitates the extensive use of optical fibers and cables, placing greater demands and higher standards on optical networks. Long-distance communication relies on optical fibers, where greater communication capacity requires larger bandwidth capacity for optical fiber communication. One method to increase the bandwidth capacity of fiber optic communication is to employ Wavelength Division Multipplexing (WDM).
Wavelength Division Multiplexing (WDM) is a technology that enables the simultaneous transmission of two or multiple optical signals at different wavelengths over a single optical fiber [2]. Specifically, at the transmitting end, optical carrier signals (each carrying information) at different wavelengths are combined by a multiplexer (also referred to as a combiner) and coupled into the same fiber for transmission. At the receiving end, a demultiplexer separates these wavelength-division multiplexed carriers, which are then processed by an optical receiver to recover the original signals.
The primary types of WDM multiplexers include fused biconical taper, dielectric film, grating, and planar configurations. Moreover, the Reconfigurable Optical Add-Drop Multiplexer (ROADM, Figure 1), based on Wavelength Selective Switch (WSS, Figure 2) technology, serves as a critical component in WDM optical networks.
Figure 1 Reconfigurable Optical Add-Drop Multiplexer，ROADM
Figure 2 Wavelength Selective Switch ,WSS [ Public domain via the Internet ]
For grating-based wavelength division multiplexers, the spectral resolution of the grating largely determines the bandwidth capacity of fiber optic communications. The formula for the spectral resolution capability of a grating is:
P = jN
where j is the diffraction order and N is the total number of grating lines within a defined area. To a significant extent, the spectral resolution of the grating is determined by N[4]. By increasing the line density (grating period density), the spectral resolution can be enhanced. However, for planar transmission gratings, when the period width is less than half the wavelength of the incident light, no diffraction occurs. Consequently, the line density of planar gratings cannot be excessively high, generally not exceeding 1200 lines/mm, which imposes certain limitations.
Prism-Grating Design Scheme
To address the conflict between the high bandwidth capacity requirements of 5G communications and the limitations imposed by the line density of planar gratings, this paper implements a high-line-density prism-grating structure. This design aims to increase the bandwidth capacity of fiber optic communications while meeting the demands for high spectral resolution. A physical image of the component is shown in Figure 3.
Figure 3. Schematic Diagram and Actual Device Photo of the Prism-grating Structure
The optical path diagram after light interaction with the aforementioned prism grating is shown in Figure 4. :
Figure 4. Optical Path Diagram of the Prism-Grating
Through theoretical simulation and design, the line density of this prism-grating exceeds 1600 lines/mm, approximately 1.5 times that of conventional planar gratings. This enhancement improves the spectral resolution of the grating, thereby increasing the communication bandwidth capacity of the Wavelength Division Multiplexer (WDM). The basic design parameters are listed in Table 1.
Component | Refractive index | Critical angle θA |
|
Prism | 1.444 | 86° |
|
Component | Refractive index | Thickness |
|
Adhesive | 1.541 | 20 μm |
|
Component C | Thickness | Depth | Line density |
Gold layer | 200 nm | 230 nm | 1620 line/mm |
Table 1. Parameters of the Prism-Grating
Under this design scheme, the relationship between the diffraction efficiency of the prism-grating and the grating depth is shown in Figure 5. The diffraction efficiency approaches 100% when the grating depth is between 0.22 μm and 0.25 μm.
Figure 5. Relationship between Diffraction Efficiency and Grating Trench Depth
The relationship between the diffraction efficiency and the incident light wavelength under this design is shown in Figure 6. Within the communication band of 1.50 μm to 1.58 μm, the theoretical diffraction efficiency is greater than 98%.
Figure 6. Relationship between Diffraction Efficiency and Incident Light Wavelength
Prism-Grating Fabrication Process
The fabrication of this prism-grating employs two key process technologies: manufacturing the grating master using high-precision lithography machine exposure technology (as shown in Figure 7), and replicating the prism-grating based on a lift-off process. With this fabrication process, the achieved line density period accuracy is ±0.1 line/mm, and the grating line verticality is ±0.1°. Compared to related products from foreign companies, this process can reduce costs by approximately 50%.
Figure 7. High-Precision Lithography Machine
Conclusion
The prism-grating introduced in this paper achieves a theoretical diffraction efficiency of over 98%, a line density period accuracy of ±0.1 line/mm, and a grating line verticality of ±0.1°. Compared to conventional planar gratings, its spectral resolution is increased by about 1.5 times. Furthermore, it features a simple manufacturing process and high cost-effectiveness, making it a preferred component for grating-based Wavelength Division Multiplexers.
Reference
[1] Editorial Department of Secrecy Science and Technology. Overview of 5G Mobile Communication[J]. Secrecy Science and Technology.
[2] HU Xian-zhi, LIU Yi. Introduction to Optical Fiber Communication[M]. People's Posts and Telecommunications Press.
[3] SONG Jun. Technology Feature: Wavelength Selective Switch (WSS)[R]. Shenzhen University, Optical Fiber Online Editorial Department.
[4] PALMER, Christopher. Diffraction Grating Handbook(6th ed.)[M]. Newport Corporation.
[5] JI Wei-ling. Application Status and Development Prospects of Wavelength Division Multiplexing Technology[J]. Nanjing University of Posts and Telecommunications.
[6] GONG Chun-yang. Research on Key Technologies of Micro-Nano Grating Etching Based on Holographic Lithography[D]. Changchun University of Science and Technology.
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