The Application of Optical Passive Components in WDM System

Based on the DWDM technology, the all-optical network make full use of fiber optic cables which have huge transmission capacity, it must be the next-generation high reliability, fast speed information network technology. Fiber optic attenuators are widely and important optical passive components, especially in the all-optical network.

Optical attenuator is applied into WDM system upstream and downstream node channel, power balance, EDFA gain flatness, optical communication lines, system evaluation, research and adjustments, correction and so on. It is in accordance with customers’ requirements by absorbing or reflecting off part of the optical power and then reduce the signal power as expectation. It’s position in the optical fiber network just shown in the figure.


Warm Tips:  TX – Transmitter                    RX – Receiver

                     WL – Wavelength Locker       MOD – Modem

                      FM –  Filtration Module       OXC – Optical Cross Connect

                      OADM – Optical Add Drop Multiplexer

In the WDM system, EDFA is a necessary component, it is quite important for achieving all-optical network communication. However, because of the limitation of gaining window ports for EDFA, it makes different wavelengths have different gain multiplier, it leaded to energy imbalance between the channels of a WDM sytstem. Then it will result in following three problems:

  • Received Energy imbalance will beyond the allowed dynamic range finally.
  • Accumulation of SNR imbalance can cause gain of a certain wavelength of BER, it may lower than the required BER (bit error rate).
  • Because of the shortage of the gain, the minimum signal power of the channel may be lower than the sensitivity of the receiver.

In the DWDM optical network which has multiple contact node, such as MAN, the transmission distances and the volume of the business between the different channels are different, each channel’s transmission must be balanced, including power, BER, signal to noise ratio and so on. The application of variable fibre optic attenuator is the first solution in the system.

Moreover, optical attenuators are also important for optical telecommunication link and the test for the system. Fiber optic cable link and the system need to be examined before laying them, then it can insure some performance parameters of the system or link road, so that it is easy to do some optimization test. So we need to simulate the actual situation, mainly the proper attenuation for the signal, then we will find out the actual situation after the long distance transmission.

Some Structions of CWDM From Fiberstore

We all know that there is a type of WDM called CWDM, which has a 20 nm channel spacing. And the channel spacing is so wide because it is designed for non temperature controlled laser transmitters. The passbands for CWDM typically must be wide and flat with a bandwidth greater than 14 nm. The band multiplexer is a good way to make a CWDM de/multiplexer. The Figure show me that a waveguide a layout for an 8 channel cwdm multiplexer and the measured response. Because the channel spacing is so wide, the AWG grating orders are vary small and having unequal path lengths in the AWL, adds a negligible amount of chromatic dispersion (allowing one to use a “U” shape for the AWL, making it more compact). Thus, the AWGs take on a “W” shape, and the AWL takes on a “U” shape. A highly compact silica waveguide PLC 4 channel CWDM multiplexer made using a completely different technique, a two dimensional reflective hologram.


Transparent CWDM MUX/DEMUX EQUIPMENT is typically passive (not powered). Passive devices cannot generate or repeat optical signals. Additionally, IOAs operate in a small wavelength range that overlaps only three CWDM signals. Some CWDM signals are unaffected by IOAs, so each CWDM span must terminate at a distance determined by the unamplified signals. Therefore, no benefit is realized by amplifying any of the CWDM signals. This means that all optical signals loss introduces by CWDM mux/demux equipment, splices, connectors, and the fiber must be subtracted from the launch power of the colored GBIC/SFP installed in the client.

CWDM can be used by enterprise on leased dark fiber to increase capacity (for example, from 1Gbps to 8 Gbps or 16 Gbps) over metro area distance. One problem with CWDM is that the wavelengths are not compatible with erbium-doped fiber amplifier (EDFA) technology, which amplifies all light signals within their frequency range.


As for the fiber optical amplifier, we have a wide range of it, such as EDFA optical amplifier Booster Amplifier, CATV amplifier, In-line Amplifier, Booster Amplifier, WDM amplifier and so on, want to know more knowledge of it, you can visit into Fiberstore’s tutorial. Related product you can vist Fiberstore’s home page, you must find what you want.

Let me introduce our company, Fiberstore. it designs, manufactures, and sells a broad range of optical communication products, including passive optical network, such as the passive cwdm mux or optical splitter used in the enterprise, access, and metropolitan segments of the market, In particular, Fiberstore products include optical subsystems used in fiber-to-the-premise, or FTTP, deployments which many telecommunication service providers are using to deliver video, voice, and data services.

Optical Amplifiers Applied into the Fiber Optic Networks

As we know, most optical amplifier amplify client light through stimulated emission. An optical amplifier is nothing but a laser without feedback. Optical gain is achieved when the amplifier is pumped optically or electrically to achieved population inversion. Optical amplification depends on:

  • Frequency (or wavelength) of incident signal
  • Local bean intensity

General applications of optical amplifiers are:

  • In-line Amplifier
  • Pre-amplifiers
  • Power Amplifier

The Figure shows basic operation of optical amplifier


The external pump source energy us absorbed by the electrons in the active medium. The electros shifts to the higher energy level producing population inversion. Photos of incoming signal triggers these excited electros to lower level thourhg a stimulated emission peocess, producing amplified opticla signal.


Breif Introduction

The active medium in an optical fiber amplifier consists of a nominally 10 to 30m length of optical fiber that has been lightly doped with a rare-earth element such as Erbium, Ytterbium, Neodymium or Praseodymium. The host fiber material can be either standard silica, a fluoride-based glass or a multicomponent glass.

The operating regions of these devices depends on the host material and the doping elements. Fluorozirconate glasses doped with P or N are used for operation in the 1300-nm window, since newither of these ions can amplify 1300 nm signals when enbedded in the silica glass.

The most popular material for long haul telecommunication application is a silica fiber doped with Erbium, which is known as Erbium-doped fiber amplifier or EDFA. The operation of an EDFA by itself normally is limited to the 1530 to 1560 nm region.


  • Active medium is created by erbium, ytterbium, neodymium, praseodymium
  • DFA can pump device at several different wavelength.
  • Low coupling loss
  • Constant gain.

Today’s Key recommendation product: C-band 40 Channels Booster EDFA for DWDM Networks

Booster EDFA

The DWDM-EDFA-BA-O23 Booster Amplifier is an easy-to-use and cost-efficient device for DWMD fiber optic link amplification which operates at the transmission side of the link. It is designed to amplify aggregated optic input power for reach extension. Using dual-stage pump laser design and internal Gain Flattening Filter (GFF) to compensate the erbium fiber gain variation, it features high input power, low noise, and up to output power:23dBm. Software control is standard via an RS-232 interface for status monitoring and pump current adjustments.


  • Booster Amplifier, carries whole C-Band 1528nm ~ 1561nm of 40 channel on metro DWDM distance extension or single wavelength distance extension application
    100GHz channel spacing
  • input power:-5~+10dBm
  • output power:23dBm
  • Low Noise Figure: Typical 4.5dB
  • High Flatness: Typical 1dB
  • 19” 1RU rack enclosure
  • SC/UPC, SC/APC, FC/UPC, FC/APC, LC/UPC, LC/APC , ST/UPC and ST/APC connectors are available
  • Single or dual 110VAC, 220VAC, 100~240VAC and/or -48VDC power supply
  • Reliable 980nm and 1480nm pump lasers
  • 10 years of operation life
  • 3 years warranty standard
  • Compatible with Telecordia GR-1312-CORE
  • OEM is available

Fiberstore is a quite professional store to sale EDFA amplifier and splitter, we can have a detailed description and product detail pictures, and the most rewarding part is that Fiberstore has a quite reasonable price, such as the aoove product, it just 3683 dollars at such good quality.