Typical CWDM Optical Elements and Features

CWDM VS DWDM differ noticeably in the spacing between adjacent wavelengths. DWDM packs many channels into a small usable spectrum, spacing them 1 to 2 nm apart; DWDM systems support a high channel count, but also require expensive cooling equipment and independent lasers and modulators to ensure that adjacent channels do not interfere. CWDM systems, on the other hand, use 10 to 25 nm spacing, with 1300 or 850 nm lasers that drift less than 0.1 nm/c. This low drift eliminates the need for cooling equipment, which, in turn, reduces the total system cost. As a result, CWDM systems support less total bandwidth than DWDM systems, but with 8 to 16 channels, each operating between 155 Mbps and 3.125 Gbps to over 100 Gbps. Typical systems support eight wavelengths, data rates up to 2.5 Gbps per wavelength, and distances up to 50 km.

CWDM uses lasers with a wide channel CWDM wavelength spacing. In contrast, DWDM, which is widely used in long-haul networks and some metro core networks (particularly those with large diameters), uses lasers with much narrower wavelength spacing, typically 0.8 or 0.4 nm. The wide channel spacing of CWDM means a lower system cost can be achieved. This lower equipment cost is the result of a lower optical CWDM mux/demux cost (due to wider tolerance on the wavelength stability and bandwidth).

CWDM represents significant costs savings-from 25% to 50% at the component level over DWDM, both for equipment OEMs and service provides. CWDM products cost about 3500 dollars per wavelength. Traditional CWDM only scale to about eight wavelengths, but for metro access applications, this may be adaquare. Also, mux demux manufacturer china have found ways to combine CWDM with its regular DWDM blades that allow the systems to scale up to 20 wavelengths. CWDM system architecture can benefit the metro access market because it takes advantage of the inherent natural properties of the optical devices and eliminates the need to artificially control the component characteristics.

8 channels, 1RU Rack Mount, Duplex, CWDM Mux  Demux

The typical CWDM optical elements are as follows:

CWDM Uncooled Coaxial Lasers: Distributed-feedback multiquantum well (DFB/MQW) lasers are often used in CWDM systems. These lasers typically come in eight wavelengths and feature a 13 nm bandwidth. Wavelength drift is typically only 5 nm under normal office conditions (say, with a 50℃ total temperature delta), making temperature compensation unnecessary. For additional cost savings, the lasers do not require external gratings or other filters to achieve CWDM operation. They are available with or without an integral isolator.

CWDM Transmitters/Receives: OC-48 CWDM transmitters typically use an uncooled DFB laser diode and are pigtailed devices in a standard 24-pin DIP package. Six to eight channels are supported (six channels: 1510 to 1610 nm; two additional channels are located at 1470 and at 1490 nm.) The OC-48 receiver typically uses an APD photodetector, has a built-in DC-DC converter, and employs a PLL for clock recovery. Transmission distances of up to 50 km are achievable with these modules.

CWDM Multiplexers/Demultiplexer: These come in 4 or 8 channel module, just 4 channel CWDM Multiplexer or 8 channel CWDM Multiplexer, typically use thin -film filters optimized for CWDM applications, with filtering bands matched t other CWDM wavelengths. Filters need to feature low insertion loss and high isolation between adjacent channels.

CWDM Optical ADD/Drop Modules (OADMS): These are available in various configurations with one, two, or four add and drop channels using the same thin-film filters as the CWDM mux and demux modules.

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The Advantage of CWDM in Metropolitan Area Network

Because of the rapid development of data services, the speed of network convergence is accelerating, MAN is becoming a focus of network construction, market competition pressure makes the telecom operators more sensitive to the cost of network. Aimed at the demand of the market, low-cost MAN CWDM products arises at the moment.

With full spectrum CWDM league (FCA) vigorously promote of CWDM Technology and ITU-T for the standardization of CWDM, it makes CWDM technology equipment manufacturers and operators be the focus of attention. The ITU-T 15th team through CWDM wavelength grid of standard G.694.2, and become a milestone in the history of the development of CWDM technology. The 15th team also puts forward the definition of CWDM system interface right app draft standard. Shanghai bell and other companies in China in the standardization of CWDM technology also has made certain contribution, relevant domestic standards are also under discussion.

As the the growth of the market demand and the standardization of CWDM technology rapidly, many communication equipment manufacturers such as Nortel, Ciena, Huawei, alcatel Shanghai bell (asb), fire network developed related products and gain a wide range of applications in the market.

CWDM system is a low cost WDM transmission technology towards MAN access layer. In principle, CWDM is using optical multiplexer to different wavelengths of light to reuse the signals to single fiber optic transmission, at the link of the receiving end, with the aid of photolysis of multiplex fiber mixed signal is decomposed into different wavelength signal, connected to the corresponding receiving equipment. And the main difference with DWDM is that: compared with the 0.2nm to 1.2 nm wavelength spacing in DWDM system, CWDM Wavelength Spacing is wider, wavelength spacing of 20 nm industry accepted standards. Each wavelength of band cover the single-mode fiber system of O, E, S, C, L band and so on.

fiber loss

Because of CWDM system has wide wavelength spacing and low demand to technical parameters of laser. Since wavelength spacing up to 20 nm, the system maximum wavelength shift can reach -6.5℃~+6.5 ℃, the emission wavelength of laser precision can be up to +/- 3nm, and the working temperature range (-5℃~70℃), wavelength drift caused by temperature change is still in the allowable range, laser without temperature control mechanism, so the structure of the laser greatly simplified, yield improvement.

In addition, the larger wavelength spacing means recovery device/solution of multiplexer structure is greatly simplified. CWDM system, for example, the CWDM Filter layer coating layer can be reduced to 50, and DWDM system of 100 GHZ filter film coating layer number is about 150, resulting in increased yield, cost reduction, and the filter supplier has greatly increased competition. CWDM filter cost less than the cost of DWDM filter about more than 50%, and with the increase of automation production technology, it will be further reduction.

Still CWDM positioning the short distance transmission in metropolitan area network (within 80 km), and channel rate is generally not more than 2.5 Gbps, so there is no need for light amplification, dispersion, nonlinear and other considerations in the transmission lines, then you can make the system is simplified.

By means of some of these, by expanding wavelength spacing and simplifying equipment, the cost of optical channel made the CWDM system unit can be reduced to 1/2 or even 1/5 of the DWDM system, it has strong advantages in the metropolitan area network access layer.

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The development direction of future of the optical attenuator

In the optical communication system, and in many occasions there need to reduce the power of the optical signal, for example, the optical power of the optical receiver is very sensitive to overloading, the input power must be controlled within the input range of the receiver to prevent saturation. Another example, optical amplifier in front of the balance between different channel input power can prevent one or some channels of the input power is too big, cause the optical amplifier gain saturation, etc. The main role of the user in accordance with the requirements of the optical signal is expected to be attenuated, the application area is absorbed or reflected by the system losses and various experiments fall out PHR, evaluation system.

Optical attenuator can be divided into fixed and variable optical attenuator attenuators, fixed attenuators can also be subdivided into a pigtail style fixed attenuators, attenuator converter, conversion formula fixed attenuator, optical attenuator fixed conversion formula, depending on the type of the interface, there may be FC, SC, ST Attenuator, FC-SC, FC-ST, SC-ST Attenuator. Inverter-type fixed attenuator can be divided into SC-FC, ST-FC, SC-ST, FC, ST, SC Attenuator.

With the development of optical communication technology, The performance of optical attenuator are: low insertion loss, high return loss, resolution, linearity and repeatability, the amount of attenuation adjustable range, attenuation of high precision, small volume during the environmental good performance. Among them, resolution linearity depends on the decay resistance of components and adopted reading display mode and mechanical adjustment mechanism to adjust the structure and mechanical methods used also depends on repeatability.

Optical attenuator insertion loss mainly from transmission accuracy and coupling fiber collimator technology insertion loss and attenuation unit, which focuses on technology fiber collimator production, if the fiber and self-focusing lens and two Coupling very good, you can make the spaces between the fiber collimator optical attenuator insertion loss is greatly reduced.

Amount of attenuation and insertion loss of the optical attenuator is an important technical indicator. Indicator optical attenuation amount of the fixed attenuator insertion loss is actually, in addition to the variable attenuation amount of the optical attenuator, there is a separate insertion loss indicator. Quality variable attenuator insertion loss 1.0dB less. The common variable fiber optical attenuator of the indicators can be used less than 0.3 dB.

LC APC Variable Fiber Optic VOA In-Line Attenuator 0 to 30dB

From the point of view of market demand, while optical attenuator will develope toward miniaturization, serialization, low price direction, on the other hand, because of common type optical attenuator has been quite mature, so optical attenuator research will focus on its high performance aspects in the future. Here, it should be noted that, because of a device are any reflection will cause the frequency drift and line noise sources, which affect the optical communication system, CATV networks, related to the optical communication, and even cause the entire system misuse, destruction of their normal work; while high return loss attenuator attenuator is an important direction of development.

With the continuous development of optical communications, the applications of optical attenuator is also increasing. To ensure error-free high-speed transmission line, the optical power of the respective channel signal reaches a certain value, high-precision optical attenuator return loss is essential. Using attenuated fiber optical attenuator can be a good match with common optical fiber connectors, because Ultra-wideband consistent attenuation can ensure the product is fully compatible with DWDM, CATV and other communication now and future, will be widely used.

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The value-added function of the modulator based on indium phosphide equipment

Indium phosphide (InP) is a binary semiconductor composed of indium and phosphorus. InP is used in high-power and high-frequency electronics because of its superior electron velocity with respect to the more common semiconductors silicon and gallium arsenide. It also has a direct bandgap, making it useful for optoelectronics devices like laser diodes. InP is also used as a substrate for epitaxial indium gallium arsenide based opto-electronic devices.

The Inp material system has a rich history as an integration platform. The complementary functions or features discussed here have been demonstrated either integrated with Inp-based MZMs, or in epitaxial growth structures compatible with Inp-based MZMs.

The main works of the Inp material system is deep helium implantation has been used to creat point defects in zinc doped InP layers to remove carriers from participating in conduction, with minimal impact to the optical waveguide properties. This helium implant process can be used to isolate electrodes and has been shown to remain stable under extensive thermal, electrical, and optical stress conditions.

Evanescently coupled waveguide InGaAs power detectors insensitive to the optical signal wavelength and input power have been monolithically integrated with the Inp-based MZM, as a simple extension of the spot-size converter fabrication process. These detectors are placed on the complementary and/or in-line out put waveguides to provide feedback for transmitter control.

Leuthold and Joyner have proposed a method to actively tune the power splitting ratio in a 2 x 2 MM and the active tuning of the cross/bar MM1 power splitting ratio betwwen 1 and > 1.7 is demonstrated. The tuning is achieved for < 3 mA of applied current to helium implant isolated edge electrodes on a 10.3 micron 2 x 2 MMI and it produces < 0.15 dB optical loss. This split ratio dynamic range, if applied to the 2 x 2 MMI combiner in the zero chirp modulator design presented, produces sufficient optical power imbalance to move between zero chirp and he optimal negative chirp for maxium dispersion limited reach. A current tunable MMI has also been demonstrated using selective zinc diffusion.

An output power variable fiber optic attenuator is a commonly required function in transmitters for pratical optical communication systems. Early fixed wavelength MZM transmitters used integrated electroabsorption pads on the input of the InP-based MZM to provide this variable optical attenuator function. The same processes used to implement the MMI tunable power optical splitter could be used to implementa wavelength independent variable optical attenuator is simple. The 1 x 1 MMI is a rest ricted symmetric interference device in which only even modes are excited. Therefore, by asymmetrically modifying the refractive index along a selected cross section within the MMI waveguide, such that a phase change of π is induced, mode conversion of the even modes into odd modes is realized. The odd modes are rejected at the MMI output waveguide.

FC Type Variable Fiber Optic Attenuator 1 to 30dB Range

Semiconductor optical amplifiers have been integrated prior to MZMs that use InGaAsP/InP MQW cores, and lossless operation has been demonstrated in 10 Gb/s 1MDD and 40 Gbit/s DPSK applications.

Future applications will benefit from exploration of a single Inp chip for dual polarization Cartesian MZMs, through the monolithic intergration of a TE to TM polarization converter and a polarization combining waveguide element. The demonstrated polarization manipulation functions in InP materials have not used waveguide structures compatible with an MZM. THis commercial application will hopefully spur further reasearch in this area.

Welcome to fiberstore to ask much more questions about fiber optical attenuator, we will provide attentive service for anyone. http://www.fiberstore.com/

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