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Blog posts : "General"

What are main advantages and drawbacks of EDFAs?

The main advantages and drawbacks of EDFAs are as follows.


  • Commercially available in C band (1,530 to 1,565 nm) and L band (1,560 to 1,605) and up to  84-nm range at the laboratory stage.
  • Excellent coupling: The amplifier medium is an SM fiber;
  • Insensitivity to light polariz…

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A Lower Order-ODU or LO-ODU is an ODUk, whose OPUk transports a inside mapped client.

An Higher Order-ODU or HO-ODU is an ODUk, whose OPUk transports an inside multiplexed ODUj.

LO-ODU and HO-ODU have the same structure but with different clients.
The LO-ODU is either mapped into the …

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Invalid Data Flag or Suspect Interval in PM(Performance Monitoring) counters.

The ITU standards define a “suspect internal flag” which should indicate if the data contained within a register is ‘suspect’ (conditions defined in Q.822). This is more frequently referred to as the IDF (Invalid Data Flag).

PM is bounded by strict data collection  rules as defined in stand…

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Why does coherent detection introduce pre-FEC bit errors?

Why does coherent detection introduce pre-FEC bit errors?

  • The DSP algorithm at the receive end detects and analyzes the phase and amplitude of a received signal in real time to calculate and compensate the distortion of the signal caused by factors such as CD, PMD, and nonlinearity. Because CD…

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FEC and Latency

Why does FEC introduce latency?

The addition of FEC overhead at the transmit end and FEC decoding at the receive end cause latency in signal transmission.

Relationship between latency and FEC scheme types

  • To improve the correction capability, more powerful and complex FEC codes must be u…

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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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What is Red and Blue and 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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20 Blog Posts