Comparison Between CWDM & DWDM Technology

For a better signal transmission in fiber-optic communication, different kinds of technologies are applied to the industry. Wavelength-division multiplexing (WDM) is one of the commonly used technologies which multiplexes a number of optical carrier signals onto a single optic fiber by using different wavelengths of laser light. That is to say, WDM enables two or more than two wavelength signals to transmit through different optical channels in the same optical fiber at the same time.

In the WDM system, there are two types of divisions - CWDM (coarse wavelength division multiplexing) and DWDM (dense wavelength division multiplexing). They are both using multiple wavelengths of laser light for signal transmission on a single fiber. However, from the aspects of channel spacing, transmission reach, modulation laser and cost, CWDM and DWDM still have a lot of differences. This article will focus on these distinctions and hope you can have a general understanding about CWDM and DWDM technology.

Channel Spacing

As their names suggest, the words “coarse” and “dense” reveal the difference in channel spacing. CWDM has a wider spacing than DWDM. It is able to transport up to 16 wavelengths with a channel spacing of 20 nm in the spectrum grid from 1270 nm to 1610 nm. But DWDM can carry 40, 80 or up to 160 wavelengths with a narrower spacing of 0.8 nm, 0.4 nm or 0.2 nm from the wavelengths of 1525 nm to 1565 nm (C band) or 1570 nm to 1610 nm (L band). It is no doubt that DWDM has a higher performance for transmitting a greater number of multiple wavelengths on a single fiber.

Transmission Reach

Since the wavelengths are highly integrated in the fiber during light transmission, DWDM is able to reach a longer distance than CWDM. The amplified wavelengths provide DWDM with the ability of suffering less interference over long-haul cables. Unlike DWDM system, CWDM is unable to travel unlimited distance. The maximum reach of CWDM is about 160 kilometers but an amplified DWDM system can go much further as the signal strength is boosted periodically throughout the run.

Modulation Laser

CWDM system uses the uncooled laser while DWDM system uses the cooling laser. Laser cooling refers to a number of techniques in which atomic and molecular samples are cooled down to near absolute zero through the interaction with one or more laser fields. Cooling laser adopts temperature tuning which ensures better performance, higher safety and longer life span of DWDM system. But it also consumes more power than the electronic tuning uncooled laser used by CWDM system.

Cost

Because the range of temperature distribution is nonuniform in a very wide wavelength, so the temperature tuning is very difficult to realize, thus using the cooling laser technique increases the cost of DWDM system. Typically, DWDM equipment is four or five times more expensive than CWDM equipment.

Conclusion

CWDM and DWDM are both coming from the WDM technology that is capable of conveying multiple wavelengths in a single fiber. But with different characteristics, people should think twice before choosing the CWDM or DWDM system. CWDM usually costs less but its performance is far behind DWDM. Both your requirements and budget need to be taken into consideration. Moreover, the WDM products including CWDM mux/demux module, DWDM mux/demux module and optical splitter are highly welcome in the market.

Article source: http://www.fiber-optic-cable-sale.com/comparison-between-cwdm-dwdm-technology.html.

Reasons for Choosing Optic Fiber Over Copper Cable

 Nowadays, facilities like studios and control rooms are being upgraded to support the 4G or even 5G networks. This calls for fiber-based infrastructures to support the higher data rates. Optic fiber can provide substantial advantages of high performance over longer distances, virtually unlimited bandwidth, reduced sensitivity to electrical interference, lower cost and design of greater space and lighter weight. These benefits make optic fiber much better than the average copper cable. Followings are some specifically explanatory reasons for choosing optic fiber over copper cable.

 Firstly, the virtually unlimited bandwidth of optical fiber is better than the bandwidth limit of copper coaxial cable (coax). With a relatively low attenuation, the unlimited bandwidth is able to produce some rather surprising increases in capacity and range. Here’s an example, some fiber optic product combinations can reach the link length of more than 100km while a copper cable can only handle 3G for up to 75m. It can also carry multiple signals and a wide range of signal formats in a single cable. Moreover, the virtually unlimited bandwidth makes it possible for optic fibers to transmit bidirectional wavelengths with one in the forward direction and another in the reverse direction. 

 Secondly, the cost of fiber is not that expensive as it was before. In general, fiber cable is more expensive than copper cable in the short run, but it may be less expensive in the long run. The typical published price in the US for a single core PVC jacketed single-mode fiber is even cheaper than broadcast quality coax cable, suitable for HD-SDI, thus it is not a dream to make the cost of other optic fibers less than the cost of copper cable in the future. When transmitting the different signal types of digital systems, for instance, two video signals with four channels of audio, this benefit is required to make the digital systems affordable for people. In a word, bandwidth costs money, and fiber offers a way to minimize these costs. 

 Thirdly, the design of size and weight of the optic fiber is better than the copper cable. For example, a 2.9mm single core fiber weighs about 9 grams per meter, but a 1694A coax is about 61 grams per meter which is over six and a half times heavier than optic fiber. This kind of advantage is especially benefit for production trucks or OB vans which can solve the tight space and weight problems.

 From the discussion above, we may have a general understanding of why we should choose optic fiber rather than copper cable. In addition, there are also some ways for easier fiber transition. 

 One is the using of Small Form-factor Pluggable (SFP) fiber optic transceiver. SFP fiber modules are small, hot-pluggable devices used to provide fiber connectivity to 3G/HD/SD devices. The single-mode SFP fiber optic transceiver helps devices to be used over long range without degrading signal quality. The most important benefit is that SFP simplifies the migration to fiber. 

 Another method is the utilizing of CWDM fiber. It is ideally used to meet the demand of carrying multiple and different signals across long distances, either building-to-building or truck-to-truck. The CWDM MUX unit can combine at most 18 different wavelengths into a single optical fiber, and it is the same for CWDM DEMUX in reverse. Signal types are irrelevant to these units, thus different signals like AES, MADI, DVB-ASI, 3G/HD/SD-SDI or Ethernet can travel on the same fiber link. 

 To sum up, the benefits of choosing optic fiber are more than choosing copper cable. Because fiber cable costs less than it was once, becomes physically smaller, and weighs less. Also, compared to one copper coax, a single fiber is available to carry 18 full 3G signals, and a fiber signal path can be 500 to 1000 times longer than that of copper coax. From a system design, installation and maintenance perspective, the application of SFP fiber and CWDM fiber also helps a simpler proposition for optic fiber cable. Hence, optic fiber is highly recommended to be used in all broadcast facilities, as well as at pay TV operator networks. Optic fiber is a better choice for everyone.

CWDM SFP

CWDM SFP is a kind of single mode transceiver used for Gigabit Ethernet and fiber channel applications. It is made up of three parts: a uncooled laser transmitter, a PIN photodiode integrated with a trans-impedance preamplifier and a MCU control unit. The wavelengths of CWDM SFP are between 1470nm and 1610nm distinguished by different colors. Most commonly used CWDM SFP transceivers include CWDM SFP 1470, CWDM SFP 1490, CWDM SFP 1510, CWDM SFP 1530, CWDM SFP 1550, CWDM SFP 1570, CWDM SFP 1590, CWDM SFP 1610. CWDM SFP can support the high performance of 1.25Gbps data rate and 80km distance of signal transmission.

CWDM

Coarse Wavelength-Division Multiplexing (CWDM) is an economical technique to save fiber resources through transmitting multiple wavelengths on one optic fiber. Especially, CWDM has the benefit of low cost becuase of its uncooled modulating lazer which only consumes 0.5w power. The cost of CWDM system only takes up 30% of the DWDM expense. Thus, CWDM is suitable for the application in short distance, high bandwidth and areas with dense access points. However, the disadvantage of CWDM is that its supportable wavelengths are limited, usually for five or six different optic wavelengths between 1270nm and 1610nm with a 20nm interval.