World wide Optical Networking Knowledge Center

 Introduction:   In modern communication systems, information is digitized, coded to logic levels “1” and “0” and often further encoded into complex modulation schemes such as Pulse Amplitude Modulation (PAM) or Quadrature Amplitude Modulation (QAM). Integrity of the information at the received end can be critical, so it is essential that any errors can be avoided, and if not, repaired.   When major errors occur in the transmitted data, such as where significant parts of the data is missing, or the frame looks very different from what is expected, Equipment Management Systems can determine a problem and manage it accordingly. But, minor errors, where only a small number of bits in the frame are corrupt, the data looks the same to the system and errors are therefore not so easily spotted. One single error can be enough to cause the meaning of the message to be drastically altered, but the system has no way of knowing it.     The diagram shows th...

In telecommunication Bit rate and baud rate are two important terms. Bit rate and baud rate play important role when we talk about Serial protocol  UART or modulation schemes like BPSK or QPSK   etc., Bit rate is the transmission of number of bits per second. It determines the number of bits traveled per second. Baud rate is defined as the number of signal units(also called as elements) per second. It determines how many times the state of a signal is changing.  For example baud rate is 9600 means 9600 signal level changes are happening within a second.It can determine how much bandwidth is required to send the signal. Relation between Bit rate(r), Baud rate(R), the number of bit per baud(n) Bit rate(r) = R x n Baud rate(R)= r/n

  The Optical Internetworking Forum (OIF) who created the 400ZR standard. 400ZR is targeted towards edge and relatively short reach, up to 120km DCI applications. Around the same time, the OpenROADM Multi-Source Agreement (MSA) also defined a specification for a 400G DWDM pluggable. Their specification focused on what service provider networks would need, such as long optical reach (>120km), advanced forward error correction (known as oFEC) and selectable data rates (100G, 200G, 300G, or 400G). Though the additional capabilities were achievable, it would require more power than the 15W specified for ZR. Therefore, OpenROADM’s specification became known as ZR+. Ultimately, between the two organizations and the various optics manufacturers, they agreed to take the best of the OIF and OpenROADM standards, combine them and call it OpenZR+. By combing the features of each in the same form factor, it leaves us with one highly versatile coherent DWDM optic, as illustrated...

 What is Cohorent Optical Device?   One of the most significant innovations in DWDM system development was the introduction of coherent optical technology . Coherent optical devices utilize advanced optics and digital signal processors (DSP) to transmit and receive complex light wave modulations, enabling high-speed data transmission. Coherent modulation continues to be the driving force behind high speed optical devices, including 400G and beyond.    

  CWDM A CWDM system commonly supports eight wavelengths per fiber and is designed for short-range communications, using wide-range frequencies with wavelengths spread far apart.  Since CWDM is based on 20-nm channel spacing from 1470 to 1610 nm, it’s typically deployed on fiber spans up to 80km or less because optical amplifiers cannot be used with large spacing channels. This wide spacing of channels allows the use of moderately priced optics. However, the capacity of the links as well as the distance supported are less with CWDM than with DWDM. Generally, CWDM is used for lower cost, lower capacity (sub-10G) and shorter distance applications where cost is an important factor. More recently, the prices for both CWDM and DWDM components have become reasonably comparable. CWDM wavelengths are currently capable of transporting up to 10 Gigabit Ethernet and 16G Fiber Channel, and it is quite unlikely for this capacity to further increase in the future.   DWDM ...

  What is CDR (Clock and Data Recovery) in Optical modules?   The full name of CDR is clock and data recovery, which can be simply understood as after the optical signal is converted into an electrical signal, the receiver performs electrical domain shaping and clock recovery.    CDR has two main functions 1. The first is to provide clock signal for each circuit of receiver;  2. The second is to judge the received signal, which is convenient for data signal recovery and subsequent processing.   Because when the optical signal is transmitted to a certain distance, it is usually long-distance transmission, and its waveform will appear a certain degree of distortion. The signals received by the receiver are pulse signals of different lengths. At this time, at the receiver, we can not get the data we need. Therefore, signal regeneration is needed at this time. Signal regeneration functions include re amplification, re shaping and re timin...

  Introduction:     DWDM is a technology that combines large number of independent information carrying wavelengths onto the same fiber and thereby increases the transmission capacity of fiber. The “spectral bands” where the optical fiber and the transmission equipment can operate more efficiently are specified by ITU - T as O, E, S, C, L and U bands (from 1260 nm to 1675 nm). While setting up the transmission link, there is a need to ensure that the signal can be retrieved intelligibly at the receiving end. This can be done preferably by using optical amplifiers that serve as the key component of a DWDM system. When the signal is amplified by the optical amplifier (OA), like EDFA, its optical signal to noise ratio (OSNR) is reduced, and this is the primary reason to have limited number of OAs in a network. One of the mitigation is to use RAMAN amplifier but it also has some intrinsic noise, though it is less than that of EDFA . The OSNR values that matter the most are ...