OPTO-ELECTRONIC TECHNOLOGIES Pierre LECOY, Professor, ECP Elective Course S Lecture 2 : OPTICAL FIBERS Pierre LECOY Manufacturing, connecting Fiberoptic measurements Passive components (splitters, multiplexers ) Active components (modulators, switches ) OPTICAL FIBERS Manufacturing Pierre LECOY Pierre LECOY - Optical fibers4 MAIN OPTICAL FIBER TYPES MaterialPolymereAll silica (core doped with GeO 2 ) TypeMultimode Multimode graded index Standard single-mode Disp. shifted single-mode Diameters core / cladding ( m) 980/100050/12562,5/1259/1257/125 Used wavelengths attenuation Visible 200 dB/km 0,85 m & 1,3 m 3 dB/km 0,9 dB/km 1,3 & 1,55 m 0,5 0,2 dB/km 1,5 to 1,6 m 0,22 dB/km Typical bitrates and distances 10 100 Mbps 100 m 100 Mbps /5 km 1 Gb/s /400 m 100 Mbps 2 km 1 to 10 Gbps 20 50 km n x 10 Gbps milliers de km Practical use Specific problems Very easy temperature Rather easy More difficult connections Global cost Low Rather low Higher (interfaces, connectors) Main applications Lightening, displays, data trans. on very short range high bitrate LANs (Gigabit Ethernet short range) All bitrates LANs Very high bitrate LANs, MANs, FTTH/PONs Very long haul links (using amplifiers and WDM) Pierre LECOY - Optical fibers5 Polystyrene PLASTIC FIBERS Attenuation : strong but quite flat in visible range 01 (dB/km) (m) PMMA Applications lightening, displays.. Applications : low-cost, very short-range links Rather high bitrate (100 Mbps, soon 1 Gbps) ? Pierre LECOY - Optical fibers6 Other materials : Phosphore (P 2 O 5 ) decreases the vitrification temperature Fluor decreases the inner cladding index MANUFACTURING OF SILICA OPTICAL FIBERS 1st step : preform Glass rod, homothetic to the fiber to be manufactured 1 to 2 m long, 2 to 3 cm in diameter manufactured by chemical vapor deposition (CVD) : oxydation SiCl 4 + O 2 SiO 2 + 2Cl 2 GeCl 4 + O 2 GeO 2 + 2Cl 2 2nd step : drawing Transformation into a fiber : 10 to100 km long, 125 m in diameter see : Pierre LECOY - Optical fibers7 MCVD PROCESS Modified Chemical Vapor Deposition Preform manufacturing for all-silica fibers : tube Gas (oxygene + chlorides) Flame vitrification deposit Pierre LECOY - Optical fibers8 MCVD PROCESS Modified Chemical Vapor Deposition Doc. CNET vitrification Preform manufacturing for all-silica fibers : tube Gas (oxygene + chlorides) Flame Deposit of successive layers index profile Pierre LECOY - Optical fibers9 MCVD PROCESS Preform manufacturing for all-silica fibers : Flame Collapsing : To increase the fiber length : Outer dposition One preform 10 to 100 km fiber Pierre LECOY - Optical fibers10 MCVD PROCESS Index profile elaboration in the preform : Graded-index fiber Tube Outer cladding SiO 2 SiO 2 + GeO 2 Depressed inner cladding fiber Si0 2 + F r n(r) allows all index profiles core Inner cladding Standard single-mode fiber more complex process : plasma CDV (PCVD) Higher investments and efficiency Pierre LECOY - Optical fibers11 MCVD manufacturing bench Doc. DRAKA Pierre LECOY - Optical fibers12 DRAWING The preform is transformed into a fiber : Doc. TELCITE Screen-test (mechanical withstand) Furnace Preform Diameter measurement Control Enduction Polymerisation Primary coating Fiber protection (mechanical and chemical) Cladding modes absorption Pierre LECOY - Optical fibers13 OPTICAL FIBER CABLES Doc. ACOME Pierre LECOY - Optical fibers14 SUBMARINE CABLES Polythylene insulator Cooper conductor (repeaters remote feeding) Steel wires Optical Fibers Tube External armouring (protection in shallow water) Pierre LECOY - Optical fibers15 CONNECTING FIBERS 3 types : Connectors Mechanical splice Fused splice Intermediate adaptor Pierre LECOY - Optical fibers16 CONNECTING FIBERS Loses : due to Fresnel reflection du to a bad positionning : excentricity misalignment shift (in contactless connectors) due to parameter misfit minimised by angle- polishing (APC) Pierre LECOY - Optical fibers17 OPTICAL CONNECTORS A lot of different types ! OPTICAL FIBERS Pierre LECOY Measurements Pierre LECOY - Optical fibers19 FIBER MEASUREMENTS Fiber parameters measurements : Multimode fibers : Core/cladding diameters Numerical aperture Single-mode fibers : Mode-field diameter Cutt-off wavelength Done by the fiber manufacturer Done (also) by the fiber user Transmission parameters measurements : attnuation bandwidth (pulse response) chromatic dispersion (measurement of g ) polarization dispersion Pierre LECOY - Optical fibers20 REFLECTOMETRY OTDR, Optical Time Domain Reflectometry Rayleigh scattering reflections splitter Laser transmitter pulse generator receiver Measure, processing, display Light back Set-up connector Fiber or link under test Pierre LECOY - Optical fibers21 REFLECTOMETRY Received power vs time display : ratio 10 ns/m Dynamic range Fiber end reflection 1/2.P r (dBm) t = 2z/v g Input reflection localized attenuation Reflecting defect Noise constant attenuation zone P r (dBm) = P e (dBm) - A (dB) + S (dB) - 2 Slope = (z) Resolution : z = t.v g /2 OPTICAL COMPONENTS AND DEVICES Passive optical components : splitters, multiplexers Pierre LECOY, Professor ECP Pierre LECOY - Optical fibers23 COMPONENTS FOR FIBEROPTIC SYSTEMS Type Technology Optical, passive Optical, active Optical non reciprocal Opto- electronic Verres (fibres assembles ou substrats de verre) Couplers Filters Attenuators Multiplexers Switches (slow) Doped-fiber or guide amplifiers Cristals type LiNbO 3 id. Modulators Switches Isolators Semi-conductors III-V or Silicon id. electro- absorption modulators Semi-conductors amplifiers Sources Detectors Pierre LECOY - Optical fibers24 INTEGRATED OPTICS Interests : integration of optiical waveguides on a single transparent substrate bulk and reproductible realization many optical functions are possible Technologies : on glasses : low losses, only passive functions dielectric cristals (LiNbO 3 ) active optical functions semi-conductors (III-V) opto-electronic et electronic functions But higher losses Unavoidable, for creating complex shapes Losses : radiative (in angles and bends) at guide access Pierre LECOY - Optical fibers25 SPLITTERS X-splitterY -splitter laterally stuck or fused fibers half X-splitter splits the power in 2 parts, equal ot not -3dB agregates signals (coupler) ! Losses are reciprocal -3dB Pierre LECOY - Optical fibers26 SPLITTERS Fiber assembly Glass integrated optics ATI CORNING Edge fused fibers Ralis lENSEA Pierre LECOY - Optical fibers27 STAR COUPLER Twisted and fused fibers technology loss : 10 log n(theoretical) + excess loss PePe P e /n n fibers Use : multipoint networks (star LANs, FTTH/PON ) The same signal on all outputs (e.g. broadcast) Pierre LECOY - Optical fibers28 WAVELENGTH DIVISION MULTIPLEXING Differents types : 2 broad channels (or 2 windows) ; low selectivity Interests : - increases the link capacity (even if already installed) - allows multiterminal networks several narrow channels : DWDM, Dense Wavelength Division Multiplexing CWDM, Coarse Wavelength Division Multiplexing Pierre LECOY - Optical fibers29 WAVELENGTH DIVISION MULTIPLEXER type : 2 access, dichroic filter technology dichroic filter 1 and 2 1, transmitted 2 reflected Between 2 transmission windows allows multiplexing of signals in the same direction, or in opposite direction (full duplex) transmission reflection 1 window 1 window 2 Pierre LECOY - Optical fibers30 WAVELENGTH DIVISION MULTIPLEXERS Using diffraction gratings : diffraction on a blazed surface + interferences Order 2 sin mm =m Order 1 Incident plane wave (common access fiber) Selective access fibers, photodiode arrays Operating by reflection : (transmission is also possible, holographic for example) Applications : (de)multiplexers spectral analysis Pierre LECOY - Optical fibers31 WAVELENGTH DIVISION MULTIPLEXERS type : 2 outputs, coupling technology between two narrow wavelengths Or for splitting two wavelength coms (interleaver) selective coupling between single-mode guides 1 n 1 transmitted coupled Pierre LECOY - Optical fibers32 WAVELENGTH DIVISION MULTIPLEXERS Principle of AWG ( arrayed waveguide) interference effect between guides of different lengths Takes advantage from integrated optics Pierre LECOY - Optical fibers33 optical fiber (or guide) periodically modulated index (period = ) BRAGG GRATINGS Principle of photoinscripted Bragg gratings (FBG, Fiber Bragg Grating) : A single wavelength is reflected : for which a phase matching occures between elementary reflections : = .2n Applications : filters, (de)multiplexers, elongation sensors other vawelengths are transmitted Pierre LECOY - Optical fibers34 ADD-DROP MULTIPLEXER OADM, Optical Add-Drop Multiplexer i drop (signal 1) i add (signal 2) Bragg i circulators allows to extract a signal, and to insert another one at its place, without demultiplexing all channels Pierre LECOY - Optical fibers35 CHROMATIC DISPERSION COMPENSATOR Use of a chirped Bragg grating ref. Fiber Systems Compensator slope in ps/nm Must be equal to D C.L in order to compensate a fiber length L on-demand component OPTICAL COMPONENTS AND DEVICES Active components : modulators, switches Pierre LECOY, Professor ECP Pierre LECOY - Optical fibers37 substrate guides electrodes ACTIVE OPTICAL COMPONENTS Electro-optic effect (Pockels effect) : the refraction index varies linearily under an electric field in an electro-optic crystal (LiNbO 3, lithium niobate ) Field lines e e +V-V Control voltage n increases n decreases Phase modulation n = n 3.r.e/2 r' effective electro- optic coefficient half-wave voltage : V /2 = /n 3 r shifts phase by Pierre LECOY - Optical fibers38 OTDM, experimental 160 Gbps in laboratory DIRECTIONAL ELECTRO-OPTIC COUPLER Principle : schema with 2 electrodes guides electrodes matching coupling -V +V mismatching no coupling Guides Substrate 4 electrodes control // state X state input Applications : fast switching (