Presentation is loading. Please wait.

Presentation is loading. Please wait.

Penn-Ohio Chapter Training September 20, 2012. Harmonic Confidential Introduction Review of optical components and their impact on system performance.

Similar presentations


Presentation on theme: "Penn-Ohio Chapter Training September 20, 2012. Harmonic Confidential Introduction Review of optical components and their impact on system performance."— Presentation transcript:

1 Penn-Ohio Chapter Training September 20, 2012

2 Harmonic Confidential Introduction Review of optical components and their impact on system performance Direct fed 1310 TX Long haul 1550 TX 1550nm Broadcast / narrowcast Full band TX (O-band, C-band, EM, EAM) Summary

3 Harmonic Confidential O/T O/R RFin RFout Splices Connectors Transmitter fiber splice/connector Optical amplifier Receiver

4 Harmonic Confidential O/T O/R RFin RFout Splices Connectors Transmitter fiber splice/connector Optical amplifier Receiver Performance is going to depend on: RF drive level, launched power, laser RIN, number of channels, reflection parameters, EDFA noise figure, EDFA input power, received power, receiver quantum efficiency, receiver Thermal noise, Input performance, receiver output power, optical modulation index, number of wavelength in the system, flatness of the filters, transmitter linearization quality, splice quantity, SBS parameters, laser chirp, type of fiber, connector cleanliness, ……

5 Harmonic Confidential Transmitter (PWL) Receiver

6 Harmonic Confidential Attenuation − 1310 nm: < 0.35 dB/km − Minimum loss near 1550 nm: < 0.22 dB/km − Standard design 1550 nm: 0.25 dB/km Dispersion − Dispersion: Traveling speed of a lightwave in a medium varies with wavelength − Dispersion parameter for SMF-28 fiber Zero near 1310 nm nm

7 Harmonic Confidential Attenuation (dB/km) Wavelength, nm

8 Harmonic Confidential Wavelength, nm Dispersion [ps/(nm* km)] Standard Dispersion Shift Dispersion Flat

9 Harmonic Confidential Linewidth RIN noise Wavelength Center wavelength (nm) Power (dBm or mW) (0dBm=1mW, 10dBm=10mW, 20dBm=100mW) Linewidth (typical MHz) RIN noise (typical 155dB/Hz) Chirp (MHz/mA)

10 Harmonic Confidential Uncooled DFB − No temperature control  Wavelength varies with temperature − Cheaper − Used for non-WDM application or CWDM application Cooled DFB − Uses a TEC to keep the temperature constant. − Wavelength stays constant with outside temperature − Used for DWDM − More expensive.

11 Harmonic Confidential Directly modulated Externally modulated Laser RF Pre-distortion Bias circuit Optical Output RF Input Laser Modulator RF Pre-distortion Bias circuit Optical Output RF Input

12 Harmonic Confidential curve is non linear Wavelength depends on current  chirp

13 Harmonic Confidential Time Optical Level (Power) Transmitter DC output power, P 0 Modulation index per single channel, m single ch. =P PPP0PPP0 (m single ch.  100 %, otherwise clipping)

14 Harmonic Confidential For a multichannel system, the RF carriers are uncorrelated and the effective modulation index is the root mean square (rms) sum of the indexes of each channels. Composite OMI= N 1/2 x (OMI/ch) where N is the total channel number, m single is the modulation index of a single channel. Total RMS modulation should be limited to 25-30%. Example: for 80a, OMI per channel= 3.5%

15 Harmonic Confidential Pin RIN limited (flat) Shot noise Limited (1dB/dB) Thermal noise Limited (2dB/dB) The higher the received power the better the CNR Not applicable to direct-mod 1550nm FS trransmitters

16 Harmonic Confidential OMI Performance CNR increases 1dB per dB CSO degrades 1dB per dB CTB degrades 2dB per dB The higher the OMI the better the CNR but the worst the distortion

17 Harmonic Confidential OMI Performance CNR has an optimum point CSO degrades 1dB per dB CTB degrades 2dB per dB

18 Harmonic Confidential I Current Chirp + dispersion creates distortion - No full band directly modulated system at 1550nm only at 1310nm - Externally modulated system at 1550nm for analog

19 Harmonic Confidential Initial setup − Verify RF input is the correct level. − RF input should be flat. − Note: Factory Settings (Harmonic) 80 unmodulated carriers 45 to 550 MHz. Above 550 is 450 MHz digital -6db down from analog. RF input level is 15dbmv. If the channel load is different adjust RF input accordingly. − Run Auto Setup (Harmonic) − Fine Tune the transmitter by manually adjusting the internal RF pad. Periodically − Verify RF input is flat and the correct level. − Verify delta between the analog and digital channels. − If the transmitter is in MGC and the channel load has changed re- optimize the RF input to the laser.

20 Harmonic Confidential

21 Externally modulated. Transmitter Rx EDFA Optical Amplifier Optical Receiver

22 Harmonic Confidential Directly modulated Externally modulated Laser RF Pre-distortion Bias circuit Optical Output RF Input Laser Modulator RF Pre-distortion Bias circuit Optical Output RF Input

23 Harmonic Confidential Non-linear effect in fiber that limits the amount of light that can be launched into fiber to about 7dBm per 20MHz BW) Special technique are used to limit the effect of SBS in externally modulated system allow launch of 17dBm with one wavelength Beating between incoming & reflected laser beams introduce additional CSO & CTB distortions P in P out P refl P trans Acoustic wave light

24 Harmonic Confidential Initial setup − Verify RF input level of 18 dBmV (Harmonic) − RF input should be flat. − Turn Switch to Factory Settings in AGC (Harmonic) − Note: Factory settings -RF input 18dBmv -MGC- 80 NTSC Channels - Set pilot pads accordingly. -Check for SBS and adjust accordingly. SBS Adjustment (Harmonic) -Under Transmitter adjustments -Select Dual tone for links less than 85km. Select Single tone for links longer than 85 km. In single tone max optical launch power is 14dBm. Adjust SBS 1 or SBS2 as necessary.

25 Harmonic Confidential

26 Headend 1550-nm BC Tx 1 2 N Hub Nodes Optical filter BC NC Important parameters - Channel loading - link noise - Optical Rx power - Optical delta - Drive levels

27 Harmonic Confidential Good performance (>51 dB CNR) using fewer fibers Good fiber reach (50 km or more) Now possible to use O-Hubs instead of buildings Some limitations starting to become apparent − Older narrowcast transmitters limited to 8 QAMs − Newer transmitters support up to 50 QAMs CNR BC alone CNR BC+NC NC number of QAM BER QAM − Must decrease BC/NC optical delta − Dual receivers offer advantage

28 Harmonic Confidential 1- Setup the BC transmitter at the right level (not overdriven) 2- Setup the optical delta between BC and NC. -10 for 64 QAM and -6 for 256 QAM. 3 -Adjust RF pad on NC TX to have the proper level for the QAM NC compared to the BC. (1)(2) (3)

29 Harmonic Confidential

30

31 Headend 1550-nm BC Tx 1 2 Hub Nodes Optical Filter BC NC + RF filter + RF combiner Removes the NC noise on the BC Removes the BC beat term below the NC (if BC Tx is overdriven) Optical delta is not so important anymore Level of NC QAMs are adjusted in the node

32 Harmonic Confidential

33 WDM Full Spectrum Transmitters O-Band (1260nm – 1360nm) is older technology limited by Raman Crosstalk. Large wavelength separation causes a problem … trade off between number of wavelengths and launched power Two competing technologies at C-Band ( nm) Low chirp laser sources such as external modulation or electro- absorbtion modulator (EAM) Widely available laser sources using newest predistortion technology to control dispersion FS Transmitters offer segmentation options never before possible and have advantages over BC/NC architectures

34 Harmonic Confidential Broadcast-Narrowcast vs. Full Spectrum

35 Harmonic Confidential Direct Fed Nodes with Full Spectrum 1550nm TX

36 Harmonic Confidential Full Spectrum Performance Considerations Is it time to re-think our node input levels ?? Traditionally, we have targeted 0 dBm or higher Modeling shows that levels of -5 to +3 dBm offers flat MER performance with mostly QAM loading RIN limited (flat) Operating region, traditional Operating region, DWDM 1550 nm

37 Harmonic Confidential The overall CNR of a fiber optic communication system from all the noise sources: mModulation Index Per Channel r Detector Responsivity [A / W], 1310nm: 0.85, 1550nm: 1.0 P r Detected Average Optical Power [W] BNoise Equivalent Bandwidth, Video BW For TV system [Hz] qElectron Charge [Coulomb], 1.6 * I th Receiver Thermal Noise [A/Hz 0.5 ] RINRelative Intensity Noise [Hz -1 ] From Various Sources. Signal Relative Intensity Of Light Shot NoiseThermal Noise CNR of Optical Link

38 Harmonic Confidential Laser RIN - Typically Small Contribution EDFA Noise - Small or large depending on optical input power (per wavelength) into the EDFA and number of EDFAs in the link. Fiber Noise - Depends on the technology and fiber length. Large contribution with long fibers with SPL; small contribution with HLT and PWL. CIN (Intermodulation Noise) - Depends on QAM load, fiber length, technology,.. Four Wave Mixing (FWM) - Depends on number of optical channels, wavelength separation between channels, optical power into fiber,… IF link noise is dominated by RIN noise, then… CNR doesn’t improve much with increased received power RIN noise behaves like this: 1dB increase of optical received power translates into 2dB increase in RF carrier level and 2dB increase in noise power translating into RIN generated CNR independent of received power RIN Sources Raising the node optical levels may actually decrease the CNR/MER because you have increased the RIN as a result of increased power in the fiber

39 Harmonic Confidential Full Spectrum Performance Considerations Is it time to re-think our node input levels ?? Traditionally, we have targeted 0 dBm or higher Modeling shows that levels of -5 to –3 dBm offers optimum performance What should the performance target be for MER ?? Today, operators strive for dB MER Studies suggest that with all QAM networks, dB MER offers great performance and plenty of margin Some say that BER is a better performance indicator

40 Harmonic Confidential


Download ppt "Penn-Ohio Chapter Training September 20, 2012. Harmonic Confidential Introduction Review of optical components and their impact on system performance."

Similar presentations


Ads by Google