Tag Archives: OADM

ABCs of Optical Switch

Optical networking technology has solved the problem of increasing demand for higher transfer data rates and larger bandwidths. In optical network, optical fibre is the fundamental medium of transmission. However, switching, signaling and processing functions are accomplished electronically. So optical switches are naturally developed. Optical switches are widely used for optical protection, test systems (as shown in the following figure), and remotely reconfigurable add-drop multiplexers, etc.


Figure 1. Switch for FS.COM transceiver compatibility test

Two Types of Optical Switches

An optical switch is simply a switch which accepts a photonic signal at one of its ports and send it out through another port based on the routing decision made. There are two kinds of optical switches, including O-E-O (optical–electrical–optical) and the O-O-O (optical–optical–optical) also called all optical switch. OEO switch requires the analogue light signal first converted to a digital form to be processed and routed before being converted back to an analogue light signal. While OOO switching is done purely through photonic means.

oeo and ooo

Advantages of Optical Switches

Compared with electrical switches, optical switches have many advantages.

On one hand, optical switches can save floor space and power consumption significantly. They can save up to 92 percent space and 96 percent power. If translating power savings into cost, it means 3 kw can be reduced for each rack. This can save the carrier from expensive diesel power generators, rectifiers and batteries, the monthly maintenance costs for these devices and the purchasing and maintenance of cooling equipment for these devices.

On the other hand, optical switches are a lot more scalable and faster than electric switches, as all-optical switches are protocol and bit rate independent. Because of the scalability and flexibility all-optical switches have, so transfer rates will not be affected bit rate limitations of switching equipment.

Problems of Optical Switches

Despite those advantages, optical switches still have some problems.

Current optical switching technology can’t realize the technology that photonic signals can be as stored as easily as electrical signals. It is possible to store them using fibre delay lines, as light take a certain time to travel through lengths fibre (200,000 km per second in silica). That means a 10000 bit frame traveling at 10G b/s requires 200m of fibre. This is both expensive and impractical. And once a signal is put through a delay line, it cannot be processed until it comes back out. A solution to this is through adding switches within the lines, but that needs more costs.

The other problem with all – optical switching is that it cannot process header information of packets, especially at such high speed which the signals travel at. The maximum speed electronic routers currently can operate is at 10 Gb/s while optical signals can travel up to 40/100G or even higher. Thus, the routers will not be able to process the signals as fast as the transmission.

Applications of Optical Switches

Optical switches are widely applied in the network.

First, optical switches are used in high speed network which requires very high switching speeds and also requires very large switches to handle the amount of traffic. So switches are likely used within optical cross-connects (OXC). OXC are similar to electronic routers which forward data using switches. An OXC may contain a whole series of optical switches.

Second, optical switches are used for switching protection. If a fibre fails, the switch allows the signal to be rerouted to another fibre before the problem occurs. But this will take milliseconds including detecting the failure, informing the network and switching. Normally this operation requires a 1×2 switch but with complicated cross-connects hundreds may be required.

Third, optical switches can be also used for external modulators, OADM (optical add-drop multiplexers), network monitors and fibre optic component testing.


As the demand for video and audio increasing the challenge of data capabilities and high bandwidth of networks, optical network is absolutely the most cost-effective solution. Optical switches can provide the customers with significant power, space and cost savings. Today, the optical switch market is dominated by several companies, such as Cisco, HP, Arista, Juniper. In early days, original optical transceivers were required to be plugged into these switches. Later, to save the cost, third-party optical transceivers were produced. If you need optical transceivers compliant with these switches, please visit FS.COM.

Multiplex Your Fiber By Using CWDM Or DWDM

Using a WDM(Wavelength Division Multiplexing) for expanding the capacity of the fiber to carry multiple client interfaces is a highly advisable way as the physical fiber optic cabling is not cheap. As WDM widely used you must not unfamiliar with it, it is a technology that combines several streams of data/storage/video or voice protocols on the same physical fiber-optic cable, by using several wavelengths (frequencies) of light with each frequency carrying a different type of data.

Two types of WDM architecture available: Coarse Wavelength Division Multiplexing (CWDM) and Dense Wavelength Division Multiplexing (DWDM). CWDM/DWDM multiplexer and demultiplexerand OADM (Optical Add-Drop Multiplexer) are common fit in with Passive. With the use of optical amplifiers and the development of the OTN (Optical Transport Network) layer equipped with FEC (Forward Error Correction), the distance of the fiber optical communication can reach thousands of Kilometers without the need for regeneration sites.

CWDM, each CWDM wavelength typically supports up to 2.5Gbps and can be expanded to 10Gbps support. The CWDM is limited to 16 wavelengths and is typically deployed at networks up to 80Km since optical amplifiers cannot be used due to the large spacing between channels. CWDM uses a wide spectrum and accommodates eight channels. This wide spacing of channels allows for the use of moderately priced optics, but limits capacity. CWDM is typically used for lower-cost, lower-capacity, shorter-distance applications where cost is the paramount decision criteria.

The CWDM Mux/Demux (or CWDM multiplexer/demultiplexer) is often a flexible plug-and-play network solution, which helps insurers and enterprise companies to affordably implement denote point or ring based WDM optical networks. CWDM Mux/demux is perfectly created for transport PDH, SDH / SONET, ETHERNET services over WDM, CWDM and DWDM in optical metro edge and access networks. CWDM Multiplexer Modules can be found in 4, 8 and 16 channel configurations. These modules passively multiplex the optical signal outputs from 4 too much electronic products, send on them someone optical fiber and after that de-multiplex the signals into separate, distinct signals for input into gadgets across the opposite end for your fiber optic link.

Typically CWDM solutions provide 8 wavelengths capability enabling the transport of 8 client interfaces over the same fiber. However, the relatively large separation between the CWDM wavelengths allows expansion of the CWDM network with an additional 44 wavelengths with 100GHz spacing utilizing DWDM technology, thus expanding the existing infrastructure capability and utilizing the same equipment as part of the integrated solution.

DWDM is a technology allowing high throughput capacity over longer distances commonly ranging between 44-88 channels/wavelengths and transferring data rates from 100Mbps up to 100Gbps per wavelength.

DWDM systems pack 16 or more channels into a narrow spectrum window very near the 1550nm local attenuation minimum. Decreasing channel spacing requires the use of more precise and costly optics, but allows for significantly more scalability. Typical DWDM systems provide 1-44 channels of capacity, with some new systems, offering up to 80-160 channels. DWDM is typically used where high capacity is needed over a limited fiber resource or where it is cost prohibitive to deploy more fiber.

The DWDM multiplexer/demultiplexer Modules are made to multiplex multiple DWDM channels into one or two fibers. Based on type CWDM Mux/Demux unit, with optional expansion, can transmit and receive as much as 4, 8, 16 or 32 connections of various standards, data rates or protocols over one single fiber optic link without disturbing one another.

Ultimately, the choice to use CWDM or DWDM is a difficult decision, first we should understand the difference between them clearly.

CWDM scales to 18 distinct channels. While, DWDM scales up to 80 channels (or more), allows vastly more expansion. The main advantage of CWDM is the cost of the optics which is typically 1/3rd of the cost of the equivalent DWDM optic. CWDM products are popular in less precision optics and lower cost, less power consumption, un-cooled lasers with lower maintenance requirements. This difference in economic scale, the limited budget that many customers face, and typical initial requirements not to exceed 8 wavelengths, means that CWDM is a more popular entry point for many customers.

Buying CWDM or DWDM is driven by the number of wavelengths needed and the future growth projections. If you only need a handful of waves and use 1Gbps optics, CWDM is the way to go. If you need dozens of waves, 10Gbps speeds, DWDM is the only option.