1550nm External Modulated Optical Transmitter

1550nm External Modulated Optical Transmitter

Short Description:

The external modulated transmitter is specially developed for the CATV signal that satisfies HFC network, and the long-distance transmission of cable phone and cable data.This optical transmitter is a 1550nm DFB laser. The external modulated transmitter can be managed by console or WEB managed, easily mornitor and configure. Working principle It has 7 functi…
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    Description

    The external modulated transmitter is specially developed for the CATV signal that satisfies HFC network, and the long-distance transmission of cable phone and cable data.This optical transmitter is a 1550nm DFB laser. The external modulated transmitter can be managed by console or WEB managed, easily mornitor and configure.

    Working principle

    It has 7 function modules: RF control, DFB laser, optical modulator, SBS control, CSO control, communication/display control and power supply.

    Automatic gain control circuit (AGC) or manual gain control circuit (MGC) amplifies the RF signal. AGC or MGC control makes the optical modulator maintain a suitable input level. Use the detected RF root-meansquare(RMS)-total power to calculate the optical modulation index(OMI).

    In general we recommend using the AGC function, and special users can use the MGC function to adjust the CNR/CSO/CTB performance indexes.

    The core of transmitter is the optical modulator. The 1550nm signal input the optical modulator, make the laser intensity changed follow the external RF signal voltage, and then generate the AM optical signal.

    Stimulated Brillouin Scattering (SBS) occurs, when the optical input power is greater than a certain threshold value. SBS generate the lower frequency backscattered light which will attenuate the transmission light and return to the laser while destroying its performance. Causing optical power fluctuation, generates large noise, and seriously deteriorates the system carrier to noise ratio (CNR). To improve the SBS threshold, this optical transmitter adopts SBS control technology which is independent researched and developed by ourselves. The threshold value can be set up to 19dBm.

    The optical modulator has a two-way optical signal output. Parts of that signal are routed to an InGaAs photodiode. This detection of the optical signal has two functions:

    1) Detect whether the laser is normal working. Once the output optical power is 2dB lower than standard power, alarm will be set off.

    2) Detect CSO distortion to optimize the bias point of the optical modulator. For working normal the detector circuit needs at least two carrier signal inputs with an interval of 24MHz. There is a CSO initialization program in the boot process. If the CSO install failed, the RF indicator will flash red, see details in 6.2 Troubleshooting.

     

    Block Diagram

    optical-transmitter_block_diagram

    Technique Parameters
    Optical Parameters

    ItemUnit           Value
    Optical Wavelengthnm1545~1560 (or specified by the user)
    Side-mode Suppression ratiodB>30
    Relative Intensity NoisedB/Hz<-160
    Wavelength Adjustment RangeGHz+/-50GHz
    Optical PowerdBm2*5, 2*7, 2*8, 2*9, 2*10
    SBS Threshold ValuedBm+13~+19 (Continuously adjustable)
    Laser LinewidthMHz0.3

    Technical Specification

    ItemUnitTechnical Parameters
    RF rangeMHz47~1003
    RF flatness dB+/-0.75
    RF return lossdB >16
    RF input impedanceΩ75
    RF input connector type  F type
    Rated input leveldBμV80
    Input level rangedBμV78~96 (AGC mode, modulating signal)
    AGC control rangedB+3~-3
    MGC adjustable rangedB0~15
    Optical connectorSC/APC, FC/APC
    Operating temperature°C-5~45
    Storage temperature°C-30~+70
    Power Source SpecificationV90~265VAC
    36~72VDC
    ConsumptionW≤60
    Dimensionmm483(L) × 455(W) × 44(H)
    Total Weightkg5.5

    Panel Interface and Menu System Description

    Front Panel

    1Power indicator2AGC indicator3RF modulation degree indicator
    4Laser indicator5LCD6ESC key
    7UP key8DOWN key9Enter key
    10RF input port (or on the rear panel, optional)11-20dB RF input test port

    Rear Panel

    1Ground stud2Power module3Fan
    4RF input port (or on the front panel, optional)5RS232 interface6LAN interface
    7Optical output interface A (or on the front panel, optional)8Optical output interface B (or on the front panel, optional)

    Power Module
    220V Power Module

    1Mounting screws2220V power outlet3Fuse
    4Power switch  

    48V Power Module

    1Mounting screws2+ Positive terminal block3– Negative terminal block

    WEB Network Management

    Open the IE browser, type the IP address and enter the interface as follows:

     

     

    Specification
    Application
    • High-performance long-distance transmission
    • High-power distribution network
    • Redundancy loop architecture
    • FTTx network
    • RFOG application
    • DWDM network
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