MUX and DEMUX
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The basic idea of a Mux device is to integrate multiple signals into a bundle, and this bundle of signals is transmitted and processed in the model as a whole. Paired with Mux is Demux, which separates the signals from each other so that each signal can be processed separately.
Chinese full name: multiplexing and demultiplexing
Full English name: MUX and DEMUX
Abbreviation: multiplexing and demuxification
In order to obtain higher transmission speeds, optical modules generally have several ways:
1. The rate of a single channel is increased, including increasing the bandwidth of the device and using advanced modulation formats;
2. Multi-channel transmission, increase the number of channels of optical fiber, such as SR4, SR8, PSM4, DR4 belong to this category;
3. WDM multiplexing, multiplexing multiple wavelengths into one optical fiber for transmission, such as LR4, CWDM4, FR4, LR8, etc.
In WDM optical modules (e.g CWDM4 optical module), Mux/DeMux is one of the core devices. In traditional optical modules, AWG or TFF (thin film filter) schemes are generally used. In CWDM4 optical modules for silicon photonics technology, silicon-photonics integrated EDG or cascaded MZI is usually used at the origin, and polarization-insensitive DeMux is used at the receiving end, such as AWG based on PLC technology.
1 For space optics solutions, it generally refers to the use of Mux and DeMux composed of thin-film filters to assemble laser chips or detector chips in the same metal components. The metal component here is the encapsulation shell, mainly Box and TO-CAN.
2 AWG-based Mux/DeMux
Another commonly used in optical modules Mux/DeMux is based on PLC technology to make AWG, at the transmitting end, different wavelengths of light are coupled to the input of the AWG waveguide through the lens, and 4 wavelengths of light are coupled into one optical fiber through AWG, and at the receiving end, the output end of AWG is usually polished to a 45° angle bevel. When the multi-wavelength optical signal enters the AWG, it is demultiplexed into 4 channels of light and coupled to the detector by refracting 90° at an oblique angle at the output.
3 EDG-based Mux/DeMux
Based on EDG's Mux/DeMux typically appear in silicon photonics, and EDG can be integrated on the same chip as other silicon photonics devices. Silicon waveguides are usually polarization-dependent, and Mux and Demux based on silicon photonics technology are also polarization-related.
4 Mux/DeMux based on cascaded MZI
Cascade Mach-Zehnder type Mux/DeMux has the advantages of small insertion loss and wide flat top of the spectrum. The structure of cascaded MZI-type Mux/DeMux adopts a directional coupler with a specific splitting ratio and a delay line of a specific length to make a cascaded MZI, and the light of different wavelengths is output at a specific port through the interference of multiple MZIs to realize the multiplexing and demultiplexing of wavelengths.
Overall, based on space optics Mux/DeMux performance is better (insertion loss, PDL, temperature drift), but the device is more expensive and the optical coupling is complex; Mux/DeMux based on waveguide optics has the advantages of high integration, low cost and simple packaging process, but there is still a certain gap between performance and TFF Mux/DeMux of space optics. These types of Mux/DeMux are used in actual products.
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