Optical Wavelength Conversion Unit. STM-64 Transmitting Optical Wavelength Conversion Unit with FEC Function, страница 5

TWC adopts O/E/O mode, and the block diagram of its function is shown in     Figure 3-4.

Figure 3-4 Principle block diagram of TWC board

In the diagram, O/E conversion part converts STM-16 optical signals into electrical signals through the photoelectric detector, recovers the signals and extracts the clock after amplitude-limited amplification and then sends out SDH digital signals and clock signals. The jitter suppression part, after processing the SDH signals, filters out the jitters generated during signal regeneration by making use of the phase-locked clock, then multiplexes into SDH digital signals, thus enabling the system to possess very good jitter suppression ability. B1 detection circuit performs B1 error code counting of TWC board input signals, thus monitoring the performance of the accessed SDH equipment. The function of E/O part is to convert the electrical signals into optical signals with specific wavelengths. It is composed of driver, modulator and laser. The driver accomplishes amplification and shaping of the digital electrical signals, the laser transmits the laser carrier of specific wavelengths, while the modulator modulates the digital electrical signals to the optical carrier.

2. Functions

The optical transmitting module used on TWC board is a high performance module with the wavelengths in compliance with ITU-T G.692 recommendations and with excellent dispersion tolerance.

n  Line code pattern: in compliance with ITU-T G.707 recommendation, being scrambling NRZ code.

n  TWC board has the regeneration function, with performance indexes such as input jitter tolerance and jitter transfer characteristics up to the standards specified by ITU-T.

n  TWC board provides the monitoring on regeneration section B1 byte, ( B1 error code report, B1 over threshold, B1 deterioration), and through the monitoring on B1 byte, faults on the line can be located.

n  The output optical wavelengths completely comply with the standards ITU-T G.692 recommendation, the nominal central frequency is 192.1~195.2THz and central frequency offset is ≤10GHz (during the service life) .

n  The minimum extinction ratio of transmitting optical signals is ≥10dB; eye pattern complies with ITU-T G.957 recommendation; the max. –20dB bandwidth is 0.2 nm; and the min. Side-mode suppression ratio is 35dB.

n  The minimum. Receiving sensitivity of the optical receiver: -25 dBm ( APD receiving module) or –18 dBm ( PIN receiving module) ( under the condition of bit error rate BER=1.0E-12)

n  Overload optical power of the optical receiver: -9dBm (APD receiving module) or 0dBm (PIN receiving module)

n  The following monitoring functions are available: laser bias current monitoring, laser cooling current monitoring, transmitting optical power monitoring and receiving optical power monitoring, etc. Especially the monitoring of the receiving optical power makes the fault locating more convenient.

n  Automatic laser shutdown function (ALS) is also available. When no light is received, the optical transmitting module will be automatically shut down.

3. Application

n  TWC optical input port receives STM-16 signals in compliance with ITU-T G.957 recommendation and the optical transmitting port sends STM-16 signals in compliance with ITU-T G.692 recommendation to optical multiplexing board for multiplexing.

n  TWC can be inserted in 1~13 board position of OptiX BWS 320G subrack.

n  The optical connector on TWC board handle bar is of SC type.

4. Common alarm performance

TWC board is mainly composed of the optical transmitting module and optical receiving module, so its alarms mainly reflect the working status of these two modules. Alarms of TWC board are shown in Table 3-3.

Table 3-3 List of TWC board alarms