Photonics Systems - Introduction

Sergiusz Patela, Dr Sc

Room I/48, Th. 13:00-16:20, Fri. 9:20-10:50

Copying and processing permitted for non- www.patela.net commercial purposes, on condition that proper reference to the source is given. © Sergiusz Patela, 2001-6 Fiber-optic-transmission milestones

1854 - Demonstration of optical waveguide principle in water jets (J. Tyndal) 1960 - Laser (ruby, T. Maiman) 1972 - 4 dB/km multimode fiber 1982 - Single mode fiber reported 1991 - SONET telecommunications standards created 1995 - DWDM deployment began 1998 - > 1 Tb/s in one fiber 2000 - L-band system introduced (1570-1610nm) 40 Gb/s transmission in one channel.

Light detector Light source „noise” (receiver) (transmitter)

Electrical output signal

Electrical input signal Lightguide with splices connectors and couplers

Light wave: electromagnetic wave (signal carrier) characterized by intensity, phase (coherence level), wavelength (frequency), polarization and propagation direction.

Physical phenomena and effects that explain how waveguide works: • Light wave frequency Light = electromagnetic wave of frequency 3x1014Hz, (almost million GHz).

• Total internal reflection effect and extremely low glass attenuation Fibers can guide light at long distances without regeneration

• Wave nature of light and fiber modes Many waveguide parameters and construction details can be explained only if one takes into account that light is a wave guided by a structure of very low cross-section.

Core Cladding Cover

Total internal reflection at the border core-cladding

Fiber diameter: 10 to 50 µm at 1 m distance creates 10 000 reflections.

For the reflection coefficient of 99% after 1 m the signal will be attenuated by 0.9910 000 = 10-44

1. Mode structure (SM, MM) 2. Material (silica, plastic, …) 3. Geometry: planar and fiber waveguides 4. Refractive index distribution (step, gradient index)

Multimode step index fiber

Cladding

Core

Multimode graded index fiber

Cladding

Core

Single mode (step index)

Cladding

Core

© Sergiusz Patela, 2001-6 Photonics Systems - Introduction 8/23 Lightwave spectrum Wavelength (µm) Wavelength (nm) 1014 6 13 1625 - 1650 10 10 1012 × 4 Far L : 1570-1620 4 10 1011 10 C : 1525-1560 6×103 Middle 10 109 S : 1450-1510 1: 1550 1.5×103 Radio waves 108 2: 1300 Near 7 770 10 3: 850 IR 106 Red 5 622 Microwaves 10 Fiber optics 104 587 Orange 103 telecomm bands Yellow 102 Fiber optics 577 Infrared 10 windows Green 1 492 Visible 10-1 Blue Ultraviolet 10-2 455 10-3 X-rays 10-4 390 10-5 Violet 10-6 Gamma rays -7 300 UV 10 Note: 1625 - 1650 band 10-8 Near -9 is used to continuously 250 10 monitor the integrity of 10-10 -11 the fiber without Far 10 200 Cosmic rays 10-12 interfering with the 10-13 signals at 1550 or 1310 10 10-14

[dB/km] 50 30

5 I window II window 3

Attenuation 1 III transmission window 0.5 0.3

0.1 0.6 0.8 1.0 1.2 1.4 1.6 1.8 [µm] wavelength Spectral attenuation of silica glass fiber

1. High information capacity of a single fiber 2. Low loss = repeaterless transmission at long distances 3. Total immunity for EMI (electro magnetic interference) 4. Low weight 5. Small dimensions (diameter) 6. High work safety (low risk of fire, explosion, ignition) 7. Transmission safety (data taping almost impossible). 8. Relatively low cost (getting lower). 9. High reliability 10 Simplicity of installation.

1. Gigabit Ethernet, 2. vertical-cavity surface-emitting lasers (VCSELs), 3. 100Base-SX, 4. small-form-factor (SFF) connectors, 5. quick-cure adhesives, 6. mechanical connectors, 7. centralized cabling, 8. reduced cost of ferrules, 9. reduced cable costs, 10. preterminated cables Eric R. Pearson, Lightwave Magazine, Ten Reasons Fiber is Becoming More Cost-Effective in the Horizontal

Comparison of 50 m fiber waveguide and copper links (Cat. 5 UTP).

Category 5 UTP Fiber

Socket $5.35 $5.70

Patch panel $5.06 $5.19

Connectors Not needed $18.24

Cabel (50 m) $41.58 $43.56

Installation cost $71.25 $66.75

Total $123.24 $139.44

Light Emitting Diode (LED) A semiconductor junction device that emits incoherent optical radiation when biased in the forward direction

Laser Acronym for Light Amplification by Stimulated Emission of Radiation. A device that produces a coherent beam of optical radiation by stimulating electronic, ionic, or molecular transitions to higher energy levels so that when they return to lower energy levels they emit energy Laser Diode (LD, Synonyms - injection laser diode, semiconductor laser ) A laser that uses a forward biased semiconductor junction as the active medium

Light Emitting Diode (LED) Surface Light Emitting Diode (SLED) Edge Light Emitting Diode (ELED) Resonance Cavity Enhanced (RCE) LED Laser FP (Fabry-Perot) DFB (Distributed Feed-Back) DBR (Distributed Bragg Reflectors) VCSEL (Vertical Cavity Surface Emitting Lasers)

Both LED’s and LD’s emitting wavelengths are set by material selection: AlGaAs: 780-860 nm, InGaAsP: 1300, 1550 nm. LED parameters type material wave- fiber coupled power spectral width bandwidth length - fiber type (FWHM) 3 dB nm µW nm MHz SLED AlGaAs 860 95 - 62.5/125 50 50 60 - 50/125 2.5 - 9/125 ELED InGaAsP 1300 20 - 9/125 60 350 ELED InGaAsP 1550 8 - 9/125

Fiber optics LD are available in pigtailed versions and with standard fiber optic receptacles

LD type wave- laser fiber coup- fiber type length power led power nm mW mW FP 1310 5 1 9/125 FP 1310 5 2 62.5/125 FP 1550 5 1 9/125 DFB 1550 5 1 9/125

Definition A device that is responsive to the presence or absence of a stimulus

Stimulus Detector Output

In an optical communications receiver is a device that converts the received optical signal to another form. Note: Currently, this is conversion is from optical to electrical power, however optical-to-optical techniques are under development

For fiber optic applications detectors are available in standardized packages, • pigtailed or

• combined with standard receptacles

ST SC FC

Detector wavelength responsivity dark current type (high respons. range) material nm A/W nA InGaAs 1300 (1000-1700) 0.75 0.1 Si 850 (400-1100) 0.45 1 Ge 1300 (800-1500) 0.65 350

detectors are available as pin or APD structures

Standard and SFF connectors (~ 1dB)

Fiber splicing (~0.1dB) electric arc

Fusion splicing fiber fiber

index matching gel Mechanical splice fiber fiber

alignment sleeve

G. P. Agrawal, Fiber-optic communications systems, John Willey & Sons 1992

Creating fiber optic networks is an adventure not comparable to any other technical task today . Designer have to select everything - hardware type, „standards“, topology and protocols.

On the other hand, properly designed and build networks can be in use even after 20 years - they can be used and evaluated by our children.