Optical Switch
Optical switches are widely used in optical industry for various applications based on switching time and quantity of no. ports required. There are many applications of optical switch such as provisioning of the optical paths, protection switching, high speed packet switched networks and modulators. The same has been explained below in detail.
Provisioning of optical paths
In this application, optical switches are being used to re-configure wavelength cross-connects to provide support for new light paths. This requires advanced software techniques. This application avoids the need of manual fiber patch panel in use since days. As mentioned in the table here switches with switching time in milliseconds can be used but it should be large enough with more no. of ports.
Protection switching
This application is targeted in the failure instance of optical fiber cable. When any fault occurs on primary fiber cable which is carrying the traffic, the optical switches help move the traffic over the secondary fiber cable. This requires switching period to be larger probably in milliseconds. The switching time covers time to detect the fault, indicate failure to all the network elements and time to transfer the entire load to the backup secondary fiber optic cable.
Packet switched networks
Packet switching requires very fast switches as they need to operate packet by packet basis. This application requires switching time to be less than the packet size duration. At 10Gbps, typically Ethernet packet of size 60 to 1500 bytes need about 48 to 1200 ns respectively. Hence switching time should be very less in the order of neon seconds for this application. These switches require lesser no. of ports.
Modulators
They are also used as external modulators which makes the light on and off with respect to laser source. Here switches need to operate in the fraction of bit duration and hence requires switching time in the order of pico-sec.
Following table summarizes switching time and number of ports required for optical switch for the above mentioned applications.
| Application | Switching Time | Number of ports |
|---|---|---|
| Light path provisioning | 1 to 10 ms | greater than 1000 |
| Protection Switching | 1 to 10 ms | 2 to 1000 |
| Packet Switching | 1 ns | greater than 100 |
| external modulation | 10 pico-sec | 1 |
Optical switch parameters
• Number of Ports
• Switching time
• Insertion loss, should be as minimum as possible
• Extinction ratio, ratio of output power in switch's on state to the output power in off state.
• Crosstalk, referred as ratio of the power at output from desired input with the sum of power from all the other inputs
• Low Polarization dependent loss (PDL)
• Reliability in MTBF or other parameters
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