1550nm External Modulated Optical Transmitter - Baudcom

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 net…
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    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


    Technique Parameters
    Optical Parameters

    Item Unit            Value
    Optical Wavelength nm 1545~1560 (or specified by the user)
    Side-mode Suppression ratio dB >30
    Relative Intensity Noise dB/Hz <-160
    Wavelength Adjustment Range GHz +/-50GHz
    Optical Power dBm 2*5, 2*7, 2*8, 2*9, 2*10
    SBS Threshold Value dBm +13~+19 (Continuously adjustable)
    Laser Linewidth MHz 0.3

    Technical Specification

    Item Unit Technical Parameters
    RF range MHz 47~1003
    RF flatness  dB +/-0.75
    RF return loss dB  >16
    RF input impedance Ω 75
    RF input connector type   F type
    Rated input level dBμV 80
    Input level range dBμV 78~96 (AGC mode, modulating signal)
    AGC control range dB +3~-3
    MGC adjustable range dB 0~15
    Optical connector SC/APC, FC/APC
    Operating temperature °C -5~45
    Storage temperature °C -30~+70
    Power Source Specification V 90~265VAC
    Consumption W ≤60
    Dimension mm 483(L) × 455(W) × 44(H)
    Total Weight kg 5.5

    Panel Interface and Menu System Description

    Front Panel

    1 Power indicator 2 AGC indicator 3 RF modulation degree indicator
    4 Laser indicator 5 LCD 6 ESC key
    7 UP key 8 DOWN key 9 Enter key
    10 RF input port (or on the rear panel, optional) 11 -20dB RF input test port

    Rear Panel

    1 Ground stud 2 Power module 3 Fan
    4 RF input port (or on the front panel, optional) 5 RS232 interface 6 LAN interface
    7 Optical output interface A (or on the front panel, optional) 8 Optical output interface B (or on the front panel, optional)

    Power Module
    220V Power Module

    1 Mounting screws 2 220V power outlet 3 Fuse
    4 Power switch    

    48V Power Module

    1 Mounting screws 2 + Positive terminal block 3 – Negative terminal block

    WEB Network Management

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



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