Fiber Optic Switch
is a device with one or more selected transmission windows that can
perform mutual conversion or logical operation on optical signals in
optical transmission lines or integrated optical circuits. The basic
form of optical switch is 2x2, that is, every input port and output
port have two optical fibers, which can complete two connection states,
parallel connection and cross connection. The large space optical switch
unit can be composed of the combination of a basic 2x2 and 1x2 fiber optic switch.
Optical switches play an important role in optical networks. In
Wavelength Division Multiplexing (WDM) transmission systems, optical
switches can be used for wavelength driving, regeneration and clock
extraction. In Optical Time 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 are also important components for wavelength
conversion. The number of input and output ports of the switch can be
divided into 1×1, 1×2, 1×N, 2×2, 2×N, M×N, etc. They have different uses
in different occasions. They can be widely used in protection switching
system of optical network, light source control in optical fiber
testing, real-time monitoring system of network performance, testing of
optical devices, construction of switching core of OXC equipment,
optical add/drop multiplexing, optical testing, optical Sensing systems,
etc.
Main Types of Fiber Optic Switches
At present, the most widely used ones are still 1×2 and 2×2 mechanical optical switches.
Traditional opto-mechanical optic switches can directly couple light to
the output end through moving optical fibers, use prisms and reflectors
to switch light paths, and send or reflect light directly to the output
end.
There are three main types of mechanical optical switches: one uses
prism switching light path technology, the other uses mirror switching
technology, and the third uses moving optical fiber to switch the light
path. The optical fiber is connected to the lens (collimator) that plays
a collimating role and is fixed. The optical path between the input and
port output is changed by moving the prism. When the reflector does not
enter the light path, the optical switch is in a straight-through
state. The light entering from fiber 1 enters fiber 4, and the light
entering from fiber 2 enters fiber 3. When the reflector is at the
intersection of the two light rays, the optical switch is in the
intersection state. , the light entering fiber 1 enters fiber 3, and the
light entering fiber 2 enters fiber 4 to achieve optical path
switching. The mobile optical fiber optical switch is an optical fiber
with fixed ends. The device at the other end of the mobile device is
connected to different ports of the fixed device to realize switching of
optical paths. This type of optical switch has low return loss and is
greatly affected by ambient temperature. There is no real switching
product.
The advantages of mechanical optical switches are low insertion loss
(<1dB), high isolation (>45dB), independent of wavelength and
detour, and mature production technology. Faced with the total switching
action time (ms), the size is relatively large, and it is not
suitable for large-scale foreign optical switch matrices, and sometimes
there are problems of rebound and poor repeatability. Mechanical optical
switches have been widely used in recent years. However, as the scale
of optical networks continues to expand, this type of switch is
difficult to adapt to the future development needs of high-speed and
large-capacity optical transmission networks.
Micro-electro-mechanical System (MEMS) Optical Switches
Microelectronic mechanical optical switches have developed rapidly in
recent years. They are a new type of micro-electro-optical integrated
switch produced by combining semiconductor micro-processing technology
with micro-optical and micro-mechanical technologies. It is a new type
of switch for large-capacity switching optical networks. The mainstream
direction of switch development.
MEMS(Micro Electro-Mechanical System) optical switches are carved
into a number of tiny lenses on a silicon crystal. Through the action of
electrostatic force or electromagnetic force, the movable mirrors can
be raised, lowered, rotated or moved, thereby changing the propagation
direction of the input light to realize the function of optical path
on/off. MEMS optical switches
have obvious advantages over other optical switches. The switching time
is measured in microseconds. MEMS fiber optic switch adopts IC
manufacturing technology, is small in size and highly integrated. The
working method has nothing with the format, protocol, wavelength,
transmission direction, matrix direction, and modulation of the optical
signal. It can process optical signals of any wavelength. Besides, it
has the advantages of low insertion loss, low crosstalk, low
polarization sensitivity, high extinction ratio, high switching speed,
small size, and easy large-scale integration.
According to functions, MEMS optical switches can be divided into
optical path bias type, moving fiber contact type and mirror reflection
type. Mirror reflection type MEMS optical switches are easy to integrate
and control, and can easily form an optical switch array. They are the
focus of MEMS optical switch research. They can be divided into 2D MEMS
optical switches and 3D MEMS optical switches. The concept of 1D MEMS
fiber optic switches is also proposed. The so-called 2D means that the
movable mirror and fiber are located on the same plane, and the mirror
is either on or off at any specified moment. In this mode, the mirror
array is connected to N input fibers and M output fibers. The number of
mirrors required for an N×N matrix optical switch is N². Therefore this
method is also called N² structure scheme.
