All-optical switch introduction

The all-optical switch is the main element in the optical communication network. As the key to realize all optical network, it has a low pumping power, high switch efficiency, fast response time characteristics, so much attention in recent years has been paid.

From the late 1980s to the present, many research groups have conducted in-depth research of all kinds of all-optical switch. All-optical switch is a very important technology, it can be applied to the field of optical communications, optical computers, optical information processing and optical data processing. Optical switch as the key components of a new generation of all-optical network, mainly used to achieve light level routing, wavelength selection, optical add-drop multiplexing and optical cross-connect and self-healing protection. Therefore, the response speed optical switch, crosstalk, insertion loss performance will directly affect the quality of optical communication. The optical networking implementation depends on the light switches, optical filter, a new generation amplifier, dense wavelength division multiplexing technology devices and technological progress.

Optical switches applications in all-optical networks in addition should have a fast response speed, low insertion loss, low channel crosstalk and polarization insensitive, should also have integration and scalability and low-cost, low-power, good thermal stability and other characteristics. All-optical switch is expected to reflect its huge potential in the following applications.

(1) The calculation speed of computer depends on the increased speed of the switching elements and chip size reduction, in which regard has encountered a bottleneck. The development of optical computer is a possible way out. Optical computers may be fast photonic switching chip and chip the outside optical interconnects constitutes. Accordingly, the optical switch is the key to the development of optical computers.

(2) Electronic communication is gradually optical fiber communication replaced in order to meet the growing demand for communication capacity. Dense Wavelength Division Multiplexing technology, optical fiber communication signal transmission to achieve all optical signal exchange also rely on electronics, limiting the improvement of optical communication rate. Therefore, all-optical communication is the key to all-optical switch.

(3) Fiber optic communication systems in the long-haul network, metropolitan area network, the access network between the optical switch required by the optical cross-connects to complete; optical switch network between users rely on the OADM. The optical cross-connect and add-drop multiplexer is constituted by an optical switch array Thus, the optical switch is the basis for all-optical switching.

From the 1970s began to study the optical bistability has more than 30 years of history. However, the study of all-optical switching is also faced with many practical problems, mainly due to three reasons.

(1) All-optical switch is based on the third-order nonlinear effect. The desired optical power of switch is too high, which often takes more than the light intensity of the signal light more than five orders of magnitude. Not like the low-power electronic switch, it can’t achieve low-power light control.

(2) Due to the strong input light caused by the strong thermal effect, particularly in the dielectric absorption peak at a wavelength switching device, the heat absorption so that the device is very unstable and difficult to achieve a cascading operation of the device.

(3) The laser beam propagation in the medium microns, the power density is not high, but the nonlinear effect limited distance required to produce nonlinear power is too difficult to compress to the transverse dimension of the beam.

Therefore, reducing the switching power is the study of all-optical switch is an important task. Subject the light through the fiber waveguide or a planar integrated optical waveguide having a wavelength order of magnitude transverse dimension, can obtain a higher light power density and a longer interaction length, thereby greatly improving the efficiency of generating nonlinear optical effects, and may lower optical power to achieve all-optical switch. Waveguide-type optical switch become the main object of study. Silicon waveguides (including optical fiber) in the communication band absorption is small, but non-linear too weak, the accumulation of available ring cavity nonlinear.

Source: FiberStore

A new type of Optical Switch using a quantum dot

An optical switch developed at the Joint Quantum Institute (JQI) spurs the mark integration of photonics and electronics.

What, isn’t electronics adequate? Well, nothing travels faster than light, as well as in your time and effort to hurry in the processing andtransmission of knowledge, the combined use of photons along with electrons is desirable for developing a workable opto-electronic protocol. The JQI switch can steer a beam of light from one direction toanother in only 120 picoseconds, requiring hardly any power, no more than 90 atto joules. At the wavelength used, in the near infrared,this amounts to about 140 photons. This is actually the setup of a waveguide made from a photonic crystal, a great device put into the fiber optic transmission area.

A quantum dot is placed inside a tiny zone free from holes. Light is distributed into and from the waveguide via endcaps. If properly timed, a pump laser pulse allows probe pulse to exit the side. When the probe and pump beams are not aligned, the probe beam will exit the farend of the waveguide. The center piece of most electronic gear is the transistor, a solid-state component where a gate signal is used to a nearby tiny conducting pathway, thus switching on and off the passage of the information signal.

The analogous process in photonics would be a solid-state component which provides a gate, enabling or disabling the passage of light through a nearby waveguide, or as a router,for switching beams in different directions. Within the JQI experiment, prepared and conducted in the University of Maryland and at the National Institute for Standards and Technology (NIST) by Edo Waks and his colleagues, an all-optical switch has been created utilizing a quantum dot placed in the resonant cavity. The dot, consisting of a nm-sized sandwich of the elements indium and arsenic, is so tiny that electrons moving inside can emit light at only discrete wavelengths, as though the dot were an atom. The quantum dot sits inside a photonic crystal, a material that has been tired of many tiny holes.

The holes preclude the passage of sunshine with the crystal except for a narrow wavelength range. Actually, the dot sits in the small hole-free arcade which acts just like a resonant cavity. When light travels on the nearby waveguide a lot of it gets into the cavity, where it interacts using the quantum dot. And it is this interaction which could transform the waveguide’s transmission properties. Although 140 photons are needed in the waveguide to create switching action,only about 6 photons actually are required to bring about modulationof the quantum dot, thus throwing the switch.

Previous optical switches happen to be able to work only by utilizing bulky nonlinear-crystals and high input power. The JQI switch, by comparison, achieves high-nonlinear interactions using a single quantum dot and very low power input. Switching required only 90 atto joules of power, some five times less than the very best previous reported device made at labs in Japan, which itself used 100 times less power than other all-optical switches. Japan switch, however, has the advantage of operating at room temperature, as the JQI switch needs a temperature close to 40 K.

Continuing our analogy with electronics: light traveling on the waveguide by means of an information-carrying beam could be switched from one direction to another using the presence of asecond pulse, a control beam. To steer the probe beam the side from the device, the slightly detuned pump beam needs toarrive simultaneously with the probe beam, that is on resonance with the dot. The dot lies just off the middle tabs on the waveguide, inside the cavity. The temperature from the quantum dot is tuned to become resonant using the cavity, leading to strong coupling. If the pump beam doesn’t reach the same time as the probe, the probe beam will exit in another direction.

Source: http://www.fiberstore.com/

Brief Introduction to Optical Switch

The advent and development of fiber optic communication technology has brought a revolutionary change to the communications industry. Nowadays in the world, about 85% of communication services via optical fiber transmission, long haul network and local relay network has been widely using fiber optics.

Dense Wavelength Division Multiplexing (DWDM) technology development and maturation has opened up a vast space for the full application of the bandwidth and capacity of optical fiber transmission. With a high rate, large bandwidth obvious advantage, DWDM optical communication network has become the development of communication network trend. Especially in recent years, an IP-based Internet business explosive growth, this growth trend has not only changed the relationship between the IP network layer and the underlying transport network, and the networking of the entire network, the node design, management and control new requirements.

An intelligent network architecture – Automatic Switched Optical Network (ASON) has become a research hotspot of today’s systems. Its core node optical cross-connect (OXC). Constitute dynamic wavelength routing and optical network flexible and effective management can be realized by the OXC equipment. OXC technology is one of the key technologies increasingly complex DWDM network, optical switch for switching the optical path of functional devices, is a key part of the OXC. Optical switch matrix is ​​the core part of the OXC, it can achieve dynamic optical path management, optical network fault protection, wavelength dynamic allocation function, the solution to the current complex network of wavelength contention and improve the wavelength reuse, flexible configuration of the network are There is of great significance.

Optical switch is not only the core device in OXC, but also widely used in the following areas.

(1) Optical network protection switching system, the actual optical transmission system have left spare fibers when working channel transmission interruption or performance degradation to a certain extent, the main signal light switch automatically go to standby fiber system transmission, so that the receiving end received normal signal and feeling less than the network has a fault, the network nodes connected in a ring to further improve the survivability of the network.

(2) Real-time network performance monitoring system, remote fiber test points, 1 × N multi-channel optical switch, a plurality of optical fibers connected to the Optical Time Domain Reflectometer, real-time network monitoring, computer-controlled optical switch switching sequence and time to achieve the detection of all fiber, and test results are returned to the network control center, once found a road problems, can be processed directly in the network management center.

(3) The light switch is also used in optical fiber communication device testing system and metropolitan area networks, the poor access network/multiplexing and switching equipment. The introduction of the light switch in the future all-optical networks more flexible, intelligent, survivability. Optical switching technology has become the key to future optical networking, optical switching technology plays an increasingly important role in the field of communication, automatic control.

In many types of optical switches, MEMS optical switch is considered most likely to become the mainstream of the optical switch device. In this paper, an overview of the basis of the principle characteristics of a variety of optical switch on, the focus of several major MEMS optical switch, and outlined their structure and performance characteristics.