In the 5G era, the demand for optical cables is the most prominent problem encountered in the deployment of 5G fronthaul networks. The demand for 5G fronthaul bearer solutions is growing rapidly. In order to reduce the consumption of optical fiber resources, passive wavelength division schemes have been widely used.
Wavelength division multiplexing (WDM), including CWDM (coarse wavelength division multiplexing) and DWDM (dense wavelength division multiplexing), etc. Refers to the coupling of multiple signals of different wavelengths on a single fiber for simultaneous transmission. It has multiplexers and demultiplexers. The multiplexer (MUX) combines multiple signal wavelengths in one optical fiber at the transmitting end; the demultiplexer (DEMUX) transmits multiple wavelengths in one optical fiber at the receiving end. The signals of each wavelength are separated. The main purpose of wavelength division multiplexing is to increase the available bandwidth of optical fibers, which can be expanded through WDM without the need to lay more optical fibers. Therefore, it is widely adopted by telecommunications companies.
What is the difference between CWDM and DWDM?
Tje wavelength intervals of CWDM and DWDM is different
CWDM: Wavelength interval ≥ 20nm, usually 8 bands from 1260~1620nm, 20nm interval;
DWDM: Wavelength interval <10nm, usually 1528~1560nm band, wavelength interval is 200GHz (1.6nm), 100GHz (0.8nm) or 50GHz (0.4nm),
The Modulated lasers of CWDM and DWDM are different
Under normal circumstances, CWDM modulated lasers use uncooled lasers, while DWDM uses refrigerated lasers. Cooled lasers use temperature tuning, and uncooled lasers use electronic tuning.
What are the advantages of CWDM vs DWDM?
Compared with DWDM, the biggest advantage of the CWDM system is its low cost. The cost of the device is mainly reflected in filters and lasers. The wide wavelength interval of 20nm makes CWDM have low requirements on the technical indicators of the laser. The structure of the optical multiplexer/demultiplexer is simplified, so the cost is lower.
DWDM is suitable for long-distance transmission. Compared with CWDM, DWDM with tighter wavelength spacing can carry 8 to 160 wavelengths on an optical fiber, which is more suitable for long-distance transmission. With the help of EDFA (Erbium doped fiber amplifier), DWDM system can work within thousands of kilometers.
What is CCWDM?
After knowing what is CWDM and DWDM, let us understand a mini version of CWDM-CCWDM. What is the difference between it and CWDM?
CCWDM is called a compact coarse wavelength division multiplexer, which is a mini version of CWDM. It is based on the wavelength division multiplexing technology of TFF (thin film filter) and works in the same way as CWDM. The difference is that adjacent channels of CCWDM use parallel beams to cascade in free space instead of optical fibers. Without the optical fiber used for cascading, the size of the CCWDM package box is 10 times smaller than the standard CWDM package.
What is the difference between CWDM and CCWDM?
The CWDM system uses a low-cost, non-cooling distributed feedback (DFB) laser, while the CCWDM's collimator and filter are welded on a common substrate, and the cascade structure of the two is different.
A three-port filter used for a specific wavelength of CWDM. Its wavelength channel is composed of two lenses and a TFF matched to the specific wavelength. The reflection port of each filter is connected to the common port of the next filter, and the filters are connected by optical fiber connectors, which is a CWDM multiplexer.
The principle of CCWDM is to use the input lens to focus the optical signal with wavelength λ1, λ2...λn on the input fiber to the first filter; the optical signal with wavelength λ1 passes through the first filter and is coupled to the first output lens In the first output fiber, the optical signal with a wavelength of λ1 is separated; the remaining optical signals are reflected by the first glass slide to the next slide for optical signal separation; and so on, until all the signals are separated. The coupling between the wavelength channels is realized in the form of straight rays that follow the "Zigzag" route.
