What Is an Optical Switch?

An optical switch is an optical device with one or more optional transmission ports, and its role is to physically switch or logically operate the optical signals in the optical transmission line or integrated optical path.

Chinese name: light switch

Foreign name: optical switch
Applied discipline: Optical fiber communication technology

Optical Switch Introduction

light switch

The optical switch is a kind of optical path conversion device. In fiber optic transmission systems, optical switches are used for the conversion of multiple monitors, LANs, multiple light sources, detectors and protected Ethernet. The fiber optic testing system is used for fiber optics, fiber optic equipment testing and network testing, and fiber optic multipoint monitoring systems.

Light switch background

The advent and development of optical fiber communication technology has brought revolutionary changes to the communication industry. At present, about 85% of the world's communication services are transmitted by optical fiber. Long-distance trunk networks and local relay networks have also widely used optical fiber. Especially in recent years, IP-based Internet services have shown explosive growth. This growth trend has not only changed the relationship between the IP network layer and the underlying transmission network, but also proposed the networking, node design, management and control of the entire network New requirements. An intelligent network architectureAutomatic Switched Optical Networks (ASON) has become a hotspot in current system research. Its core node is composed of Optical Cross-connect (OXC) equipment. Through OXC, Can achieve dynamic wavelength routing and flexible and effective management of optical networks. OXC technology is one of the key technologies in the increasingly complex DWDM network, and the optical switch as a functional device that switches the optical path is a key part of OXC. The optical switch matrix is the core part of OXC. It can implement functions such as dynamic optical path management, optical network fault protection, and dynamic wavelength allocation. It can resolve wavelength contention in current complex networks, improve wavelength reuse, and perform flexible network configuration. Is of great significance. With the development of optical transmission networks towards super-high speed and large capacity For the important role.

Application range of optical switch

An optical switch (OS) is a device with one or more selectable transmission windows that can convert or logically operate optical signals in optical transmission lines or integrated optical paths. The basic form of the optical switch is 2X2, that is, there are two optical fibers at the input end and the output end, which can complete two connection states, parallel connection and cross connection, as shown in Figure 2. The larger space-division optical switching unit can be cascaded and combined with basic 2X2 optical switches and corresponding 1X2 optical switches.

Figure 1 Parallel connection and cross connection of optical switch Optical switches play a very important role in optical networks. In Wavelength Division Multiplexing (WDM) transmission systems, optical switches can be used for wavelength adaptation, regeneration, and clock extraction. Optical time division multiplexing (Optical Time Division In the Division Multiplex (OTDM) system, optical switches can be used for demultiplexing. In all-optical switching systems, optical switches are key components of optical cross-connect (OXC) and important components of wavelength conversion. According to the number of input and output ports of the optical switch, it can be divided into 1 × 1, 1 × 2, 1 × N, 2 × 2, 2 × N, and M × N. They have different uses in different occasions. The main application areas are: optical network protection switching system, light source control in optical fiber testing, real-time monitoring system for network performance, testing of optical devices, building the switching core of OXC equipment, optical insertion / multiplexing, optical testing, Sensing system, etc.

Study on the main types of optical switches

According to different optical switch principles! There are many ways to implement optical switches, such as: traditional mechanical optical switches, micro-mechanical optical switches, thermo-optic switches, liquid crystal optical switches, electro-optic switches, and acousto-optic switches. Among them, traditional mechanical optical switches, micro-mechanical optical switches and thermo-optical switches are widely used in different occasions due to their respective characteristics.

At present, the most widely used are traditional 1 × 2 and 2 × 2 mechanical optical switches. Traditional mechanical optical switches can directly couple light to the output end by moving the optical fiber, use prisms or mirrors to switch the optical path, and directly send or reflect the light to the output end.

There are mainly three types of mechanical optical switches: one is the use of prism-switching optical path technology, the other is the use of mirror switching technology, and the third is to switch the optical path by moving optical fibers. The basic structure of the mobile prism light switch is shown in Figure 2. The optical fiber is connected to a collimator lens (collimator) and is fixed. The optical path between the input and output ports is changed by moving the prism. The working principle of the mirror-type optical switch is shown in Figure 3. When the mirror does not enter the optical path, the optical switch is in a straight-through state. The light entered by optical fiber 1 enters optical fiber 4, and the light entered by optical fiber 2 enters optical fiber 3. At the intersection of the light, the optical switches are in a cross state, the light entered by the optical fiber 1 enters the optical fiber 3, and the light entered by the optical fiber 2 enters the optical fiber 4 to realize the switching of the optical path. As shown in FIG. 5, the mobile optical fiber type optical switch is an optical fiber at a fixed end, and the optical fiber at the other end is coupled with different ports of the fixed optical fiber to realize switching of an optical path. This type of optical switch has low return loss and is greatly affected by the external ambient temperature, and has not formed a commercial product in the true sense. China's domestic commercial optical switches are mainly mobile prism and mirror type.

Figure 3 Schematic diagram of a mirror-type optical switch

Figure 2 Schematic diagram of prism optical switch

The advantages of mechanical optical switches are low insertion loss (<1dB) and high isolation (> 45dB), which are independent of wavelength and polarization, and the production technology is mature. The disadvantages are that the switching operation time is long (on the order of ms), the volume is too large, and it is not easy to make a large optical switch matrix, and sometimes there are problems of jitter and repeatability.

Figure 4 Mobile Optical Fiber Optical Switch Mechanical optical switches have been widely used in recent years, but with the continuous expansion of the optical network scale, it is difficult for such switches to meet the needs of the development of high-speed, large-capacity optical transmission networks in the future.

Optical Switch Microelectronic Mechanical System Optical Switch

In recent years, microelectronic mechanical optical switches have developed rapidly. It is a new type of microcomputer-electric-optical integrated switch produced by combining semiconductor microfabrication technology with micro-optics and micro-mechanical technology. It is a large-capacity exchange. The mainstream direction of the development of optical network switches.

MEMS (Micro Electro-Mechanical System) optical switches are engraved with a number of tiny lenses on a silicon crystal. Through the action of electrostatic or electromagnetic forces, the movable micromirror can be lifted, rotated or moved, thereby changing the propagation of input light Direction to achieve the function of on-off of the optical path. MEMS optical switches have obvious advantages over other optical switches: the switching time is generally in the order of ms; the use of IC manufacturing technology, small size and high integration; the working mode and the format, protocol, wavelength, transmission direction, polarization direction, modulation of the optical signal The methods are irrelevant, and can process optical signals of any wavelength. At the same time, it has low insertion loss, low crosstalk, low polarization sensitivity, high extinction ratio and high switching speed, small size, and easy large-scale integration of mechanical optical switches. The advantages.

According to the function implementation method, MEMS optical switches can be divided into optical path blocking type, mobile fiber docking type and micromirror reflection type. Micromirror reflective MEMS optical switches are easy to integrate and control, and easy to form optical switch arrays. They are the focus of MEMS optical switch research. They can be divided into two-dimensional MEMS optical switches and three-dimensional MEMS optical switches. The concept of one-dimensional MEMS optical switches has been proposed . The so-called 2D means that the movable micromirror and the optical fiber are located on the same plane, and the movable micromirror is either on or off at any given moment. In this way, the active micromirror array is connected to N input fibers and M output fibers. For an N × N optical switch matrix! The number of active micromirrors is N². Therefore! This approach is also known as the N² structural solution

Optical switch classification

Optical switches are classified by manufacturing process

Optical switches are classified from the manufacturing process and can be divided into mechanical, micro-optical and electromechanical MEMS system mode switches and other mode switches. The first two types of optical switches are currently the most mature and most widely used products in the market.The last category can be subdivided into

Liquid crystal light switch; electro-optical light switch; thermo-optical light switch; acousto-optic light switch.

Mechanical optical switch with: n

Small crosstalk; n

Large extinction ratio

n low insertion loss;

n small driving voltage;

n no polarization dependence;

n High coupling efficiency with optical fiber;

n Compact device size

n Switching speed and frequency bandwidth can be set.

Optical switches are classified by use

Mechanical light switch

Rack type optical switch

Desktop optical switch

Micro-mechanical optical switch

Hand-held optical switch instrument

Optical switch applications

Optical fiber loop, automatic measurement, optical fiber network remote monitoring, optical path switching, system monitoring, laboratory research and development, dynamic configuration add / drop multiplexing, optical path monitoring system, optical loop protection switching test, optical fiber sensing system, optical device testing and research

Well-known manufacturers at home and abroad: CORERAY, JDSU, OPLINK, DICON, SERCALO

1 × 1, 1 × 2, 2 × 2 mechanical optical switch application scheme

1. 1 × 1 optical switch has the function of making the optical path on and off, which is usually used to block the optical transmission in the optical path.

2. The 1 × 2 optical switch has a protection switching function and is usually used for network fault recovery. When an optical fiber breaks or other transmission failure occurs, the optical switch is used to realize the circuitous route of the signal and switch from the main route to the standby route. Specific examples, as shown in Figure 1:

Figure 1 Example of 1 × 2 optical switch protection switching function

3. 2 × 2 optical switch is the most commonly used one in the optical switch series. It is widely used in FDDI, optical node bypass, and loop test sensing system. It can also be used in combination with other types of optical switches. The system is more complete and flexible. The specific example is shown in Figure 2. (Figure 2 is a typical example of the application of 2 × 2 optical switches. The 2 and 4 optical switches are in the bypass state, that is, the sub-ring or workstation is not connected to the main fiber loop. 1 and 3 of the optical switch are inserted, that is, the sub-ring or the workstation is connected to the main fiber loop).

Figure 2 Application example of 2 × 2 off switch in optical network

Another use of 2 × 2 optical switches is to build the core of an OADM device. OADM is one of the key equipment of the optical network, which is usually used in metropolitan area networks and backbone networks. There are many specific ways to implement the OADM optical signal add and drop, but in most cases, optical switches are used, mainly 2 × 2 optical switches, to implement the add and drop functions of optical signals in dense wavelength division multiplexed optical networks. The use of optical switches enables OADM to dynamically configure services, enhancing the flexibility of OADM nodes, and at the same time, enabling OADM nodes to support protection switching. When a network failure occurs, the node switches the faulty service to a backup route, enhancing the network Survivability and network protection and resilience. Specific examples, as shown in Figure 3:

Figure 3 Application example of 2 × 2 off switch in optical network

Two M × N mechanical light opening applications

1. Network monitoring function: When the network needs to be monitored, simply connect the multi-fiber to the network monitoring instrument (such as OTDR) through the optical switch at the remote monitoring point. When the optical path needs to be monitored, use the optical switch for each fiber. Cycle switching, allowing the light source to test each fiber, can realize online monitoring of the network. The optical switch mainly plays the role of jump detection in the optical cable monitoring project. Using a simple 1 × N optical switch can connect multiple fibers. A specific example is shown in Figure 4:

Figure 4 Use of 1 × N optical switch in network monitoring system

2. Testing of optical devices: Multiple optical devices to be tested can be connected through optical fibers. Through 1 × N optical switches, the devices can be tested by monitoring the signals of each channel of the optical switches. A specific example is shown in Figure 5:

Figure 5 Use of 1 × N optical switch in device test system

3. Construct the exchange core of OXC equipment: OXC is mainly used in the backbone network to aggregate and exchange services of different subnets. Therefore, services on different ports need to be exchanged. At the same time, the use of optical switches enables OXC to dynamically configure switching services and support protection switching functions. It also supports wavelength routing configuration and dynamic routing at the optical layer. Because OXC is mainly used for high-speed, large-capacity dense wavelength division multiplexing optical backbone networks, optical switches are required to have the characteristics of transparency, high-speed, large-capacity, and multi-granularity switching. A specific example is shown in Figure 6:

Figure 6 Use of M × N optical switch in OXC