Basic Knowledge about Optical Switch

Introduction of Optical Switch

Optical switch is an optical device that enables signals to be selectively switched from one circuit to another in optical fibers or integrated optical circuits (IOCs). It is widely used in optical switching, configuration optical add/drop multiplexer(OADM), optical fiber ring protection and optical cross and connection system. It could be divided four types, opto-mechanical optical switch, MEMS optical switch, solid-state fiber optical switch and rackmount & benchtop optical switch. Optical switch is one of the main factors to affect the optical performance of the fiber network. It plays a very important role in the optical network.

optical switch types

Functionality of Optical Switch

The functionality of an optical switch can be described as an optical connection. A connection is the association between two ports on a switch and is indicated as a pair of port identifiers (i, j), where i and j are two ports among which the connection is established. An optical signal could be applied to one of the connected ports. However, the nature of the signal emerging at the other port depends on the optical switch. A connection can be in the on state or the off state. A connection is said to be in the on state if an optical signal applied to one port emerges at the other port with essentially zero loss in optical energy. A connection is said to be in the off state if essentially zero optical energy emerges at the other port.

Connections established in optical switches can be unidirectional or bidirectional. A unidirectional connection only allows optical signal transmission in one direction between the connected ports. A bidirectional connection allows optical signal transmission in both directions over the connection. Connections in passive and transparent optical switches are bidirectional. The same as, if a connection (i, j) is set up, optical transmission is possible from i to j and from j to i.

A passive optical switch does not have optical gain elements, but an active optical switch has optical gain elements. An all-optical switch is a transparent optical switch in which the actuating signal is also optical. Thus an optical signal is used to switch the path another optical signal takes through the optical switch.

Key Features of Optical Switch
  • Compact design
  • Short switching time
  • Low cross talk, Low Insertion Loss
  • Wide operating wavelength Range
  • Highly Stability & Reliability
  • Epoxy-free on optical path
  • Single mode or Multimode optional
Applications of Optical Switch
  • Wavelength selective switches
  • R&D in laboratory
  • Fiber sensor
  • Channel blocking
  • Optical channel monitoring in optical networks
  • Module and System Integration
  • Metropolitan Area Network
  • Network protection and restoration
  • Instrumentation, testing, and measurement

Optical switching technology is driven by the need to provide flexibility in optical network connectivity. With this article, we have learned the basic knowledge of optical switch and known that it is widely used in passive optical network.  In fact, there are more other passive optical components used in passive optical work, such as optical circulator, optical attenuator, and fiber collimator and so on. We will learn one by one in this blog. In addition, if you have any requirements of passive optical components, we welcome you to visit Fiberstore, as it  is a professional supplier in this field.

Application of Optical Add-Drop Multiplexer

What’s the Optical Add-drop Multiplexer?

The optical add-drop multiplexers (OADM) are used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a single mode fiber (SMF). This is a type of optical node, which is generally used for the construction of optical telecommunications networks. An OADM may be considered to be a specific type of cross connect cabinet.

A traditional OADM consists of three stages: an optical demultiplexer, and optical multiplexers, and between them a method of reconfiguring the paths between the optical demultiplexer, the optical multiplexer and a set of ports for adding and dropping signals. The optical demultiplexer separates wavelengths in an input fiber onto ports. The reconfiguration can be achieved by a fiber patch panel or by optical switches which direct the wavelengths to the optical multiplexer or to drop ports. The optical multiplexer multiplexes the wavelength channels that are to continue on from demultiplexer ports with those from the add ports, onto a single output fiber.

Principles of OADM technology

General OADM node can use four port model (Figure 1) to represent, includes three basic functions: Drop required wavelength signal, Add rumored signal to other wavelengths pass through unaffected. OADM specific network process is as follows: WDM signal coming from the line contains mangy wavelength signals into OADM’s “MainInput” side, according to business required, from many wavelength signals to selectively retrieved from the end (Drop) output desired wavelength signal, relative to the end from the Add the wavelength of the input signal to be transmitted. While the other has nothing to do with the local wavelength channels directly through the OADM, and rumored signals multiplexed together, the line output from the OADM (Main Output) Output.

OADM node technical classification

Optical drop multiplexer network technologies can be divided into two types, fixed optical drop multiplexer (Fixed OADM, FOADM) and reconfigurable optical drop multiplexer (Reconfigurable OADM, ROADM).

Fixed Optical Drop Multiplexer (FOADM)

FOADM to filter as the main component, and its function is fixed to join or retrieve certain light wavelengths. General common FOADM can be divided into three types, namely Thin Film Filter type (TFF type), Fiber Bragg Grating (FBG type) and integrated planar Arrayed Waveguide Gratings (AWG type).

TFF FOADM

Thin Film Filter (TFF FOADM)

TFF FOADM using thin film between the filtering effect of the different refractive index.

Fiber Bragg Grating (FBG FOADM)

FBG FOADM use of fiber Bragg grating filtering effect, with two circulator can become FOADM.

Arrayed Waveguide Gratings (AWG FOADM)

AWG FOADM gererally used in semiconductor fabrication processes, the integration of different refractive index material is formed on a flat substrate in a planar waveguide, when different wavelength light source is incident through the couping after the import side, due to take a different path length, while the different phase delay caused by different wavelengths and thus produce certain wavelengths in the export side to form a constructive or destructive interference, making waves in the export side, the different wavelengths will follow the design on a different channel to reach, and thus achieve FOADM function.

Reconfigurable Optical Add/Drop Multiplexer (ROADM)

ROADM can always be adjusted with the distribution network to add and drop wavelength, which reconstruct the network resource allocation, the flexibility to meet the requires of modern urban network, so a flexible ROADM features, plus optical switch substantial advantage, making the current fastest growing ROADM based optical switches based ROADM (switch based OADM). ROADM mainly be the optical switch, multiplexer and demultiplexer composed, Switch-based OADM, mainly divided into Wavelength independent switch array and wavelength selection switch.

Wavelength independent switch array

Type 1: Wavelength independent switch array

Wavelength selective switch

Type 2: Wavelength selective switch

All kinds of optical drop multiplexer performance comparison

optical drop multiplexer performance

OADM network applications

WDM ROADM optical fiber suitable for different network environments

OADM network applications

OADM in the metropolitan network development tendency

1. Arbitrary choice must be retrieved, adding wavelength, the wavelength can take advantage of the limited resources, the node can be retrieved with the need to do to join the adjustment of the signal wavelength, and has a remote control functions. This can provide dynamic reconfiguration of optical communications network capable ROADM will be connected to the backbone network critical devices. And FOADM is used for wavelength demand network access will be smaller parts to reduce costs. Furthermore, ROADM use to all kinds of Tunable Laser, unable Filter, or wavelength selective optical switches and other components.

2. Must be able to convert incompatible wavelength suitable for the backbone network will be transmitted wavelengths. Therefore, OADM be combined with wavelength conversioin Transponder or other functional components.

3. Must be able to compensate for the node to make acquisistion, adding such action energy loss. Therefore, OADM optical amplifiers must be combined with functional components.

4. Wavelength signals related specifications, such as: the signal to noise ratio (S/N), the energy balance between the signal wavelength, etc., are required to meet network requirements. Therefore must be combined OADM variable optical attenuators (VOA), dispersion compensation module (DCM) and other components.