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Blog posts : "General"

Measuring Coherent System OSNR using integral method

For coherent signals with wide optical spectrum, the traditional scanning method using an OSA or inband polarization method (EXFO) cannot correctly measure system OSNR. Therefore, use the integral method to measure OSNR of coherent signals.

Perform the following operations to measure OSNR using t…

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Method to Resolve the Adjacent-Channel Interference in 100G Transmission.

In a non-coherent WDM system, each optical channel on the line side uses only one binary channel to carry service information. The service transmission rate on each optical channel is called bit rate while the binary channel rate is called baud rate. In this sense, the baud rate was equal to the bit…

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Basics of Coherent System.

What Is Coherent Communication?

Definition of coherent light

A coherent light consists of two light waves that:

1) Have the same oscillation direction.

2) Have the same oscillation frequency.

3) Have the same phase or maintain a constant phase relationship with each other. Two coheren…

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Why heterodyne detection technique is used in Coherent technology receivers rather homodyne?

As we know that either homodyne or heterodyne detection can be used to convert the received optical signal into an electrical form. In the case of homodyne detection, the optical signal is demodulated directly to the baseband. Although simple in concept, homodyne detection is difficult to implement …

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Basic understanding on Tap ratio for Splitter/Coupler

Fiber splitters/couplers divide optical power from one common port to two or more split ports and combine all optical power from the split ports to one common port (1 × N coupler). They operate across the entire band or bands such as C, L, or O bands. The three port 1 × 2 tap is a splitter commonly…

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Why it is Good to have ORL >30dB for general fiber links?

Optical return loss (ORL) is the logarithmic ratio of the launch (incident) power divided by the total reflected power seen at the launch point. The total reflected power is the total accumulated reflected optical power measured at the launch caused by fiber Rayleigh scattering and Fresnel reflectio…

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A keynote on BER (Bit Error Rate)

Bit error rate, BER is a key parameter that is used in assessing systems that transmit digital data from one location to another.

BER can be affected by a number of factors. By manipulating the variables that can be controlled it is possible to optimise a system to provide the performance levels th…

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Q and dBQ : A Walkthrough

Q is the quality of a communication signal and is related to BER. A lower BER gives a higher Q and thus a higher Q gives better performance. Q is primarily used for translating relatively large BER differences into manageable values.

Pre-FEC signal fail and Pre-FEC signal degrade thresholds are pro…

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A short note on DRA (Distributed Raman amplification)

A Raman amplifier is a well-known amplifier configura­tion. This amplifier uses conventional fiber (rather doped fibers), which may be co-or counter-pumped to provide amplification over a wavelength range which is a function of the pump wavelength. The Raman amplifier relies upon forward or backward…

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Why Red Band is preferred over Blue in DWDM?

The ITU approved DWDM band extends from 1528.77 nm to 1563.86 nm, and divides into the red band and the blue band.

The red band encompasses the longer wavelengths of 1546.12 nm and higher.

The blue band wavelengths fall below 1546.12 nm.

This division has a practical value because useful…

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ODUkT_TT and ODUkT/ODUk_A TCM modes

ODU Server and their respective possible clients


Definition of OTN Frame Payload Type(PT) 20 & 21?

  As defined in G.709 an ODUk container consist of an OPUk (Optical Payload Unit) plus a specific ODUk Overhead (OH).    OPUk OH information is added to the OPUk information payload to create anOPUk.  It includes information to support the adaptation of client signals.Within the OPUk overhead there …

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ODUflex properties versus concatenation properties

What is the soak time period to detect LOS on a port?

To detect a failure that occurs at the source (e.g., laser failure) or the transmission facility (e.g., fiber cut), all incoming SONET signals are monitored for loss of physical-layer signal (optical or electrical). The detection of an LOS defect must take place within a reasonably short period of t…

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Why No Auto-Negotiation for Fiber Optic Media?

Auto-Negotiation for fiber optic media segments turned out to be sufficiently difficult to achieve that most Ethernet fiber optic segments do not support Auto-Negotiation. During the development of the Auto-Negotiation standard, attempts were made to de‐ velop a system of Auto-Negotiation signaling …

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The Ethernet Frame:A walkthrough

The Ethernet Frame

The organization of the Ethernet frame is central to the operation of the system. The Ethernet standard determines both the structure of a frame and when a station is allowed to send a frame. The frame was first defined in the original Ethernet DEC-Intel-Xerox (DIX) standard, a…

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PAUSE Frames:An Overview

PAUSE frames are mechanism used in  Ethernet flow control that allows an interface or switch port to send a signal requesting a short pause in frame transmission.

The PAUSE system of flow control on full-duplex link segments, originally defined in 802.3x, uses MAC control frames to carry the PAUSE…

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40/100 Gigabit Ethernet Technology Overview


For more than 30 years, Ethernet has evolved to meet the growing demands of packet‐switched networks. It has become the unifying technology enabling communications via the Internet and other networks using Internet Protocol (IP). Due to its proven low cost, known reliability, and simpl…

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Glimpse of Carrier Ethernet-I

Carrier Ethernet: A Formal Definition

The MEF (Metro Ethernet Forum)  has defined Carrier Ethernet as the “ubiquitous, standardized, Carrier-class service defined by five attributes that distinguish Carrier Ethernet from the familiar LAN based Ethernet.” As depicted in Figure , these five attri…

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20 Blog Posts