Lecturer: Ivan Kassamakov, Docent Assistants: Risto Montonen and Anton Nolvi, Doctoral

Lecturer: Ivan Kassamakov, Docent Assistants: Risto Montonen and Anton Nolvi, Doctoral students Course webpage: Course webpage: http://electronics.physics.helsinki.fi/teaching/optics-2016-2/

Personal information Ivan Kassamakov e-mail: ivan.kassamakov@helsinki.fi office: PHYSICUM - PHY C 318 (9:00-19:00) Risto Montonen e-mail: risto.montonen@helsinki.fi office: PHYSICUM - PHY A 312 Anton Nolvi e-mail: anton.nolvi@helsinki.finolvi@helsinki office: PHYSICUM - PHY C 317

Schedule: Lectures: Tuesdays: 10:15 12:00, 19.01.2016 03.05.2016, Lecture Room: PHYSICUM - PHY D116 SH; Exercises: Tuesdays: 12:15 14:00, 19.01.2012 03.05.2016, Lecture Room: PHYSICUM - PHY D116 SH; Demonstrations: Demonstrations: Electronics Laboratory: PHYSICUM - PHY C 312-316.

Lectures Lecture # Week # Place - Lecture Room Date Starting time Ending time 01 OPTIIKKA : LUENTO 3 PHYSICUM - PHY D116 SH 19.1.2016 10:15 12:00 02 OPTIIKKA : LUENTO 4 PHYSICUM - PHY D116 SH 26.1.2016 10:15 12:00 03 OPTIIKKA : LUENTO 5 PHYSICUM - PHY D116 SH 02.2.2016 10:15 12:00 04 OPTIIKKA : LUENTO 6 PHYSICUM - PHY D116 SH 09.2.2016 10:15 12:00 05 OPTIIKKA : LUENTO 7 PHYSICUM - PHY D116 SH 16.2.2016 10:15 12:00 06 OPTIIKKA : LUENTO 8 PHYSICUM - PHY D116 SH 23.2.2016 10:15 12:00 07 OPTIIKKA : LUENTO 9 PHYSICUM - PHY D116 SH 01.3.2016 10:15 12:00 08 OPTIIKKA : LUENTO 11 PHYSICUM - PHY D116 SH 15.3.2016 10:15 12:00 09 OPTIIKKA : LUENTO 12 PHYSICUM - PHY D116 SH 22.3.2016 10:15 12:00 10 OPTIIKKA : LUENTO 14 PHYSICUM - PHY D116 SH 05.4.2016 10:15 12:00 11 OPTIIKKA : LUENTO 15 PHYSICUM - PHY D116 SH 12.4.2016 10:15 12:00 12 OPTIIKKA : LUENTO 16 PHYSICUM - PHY D116 SH 19.4.2016 10:15 12:00 13 OPTIIKKA : LUENTO 17 PHYSICUM - PHY D116 SH 26.4.2016 10:15 12:00 14 OPTIIKKA : LUENTO 18 PHYSICUM - PHY D116 SH 03.5.2016 10:15 12:00

Exercises Exercises # Week # Place - Lecture Room Date Starting time Ending time 01 OPTIIKKA : LUENTO 3 PHYSICUM - PHY D116 SH 19.1.2016 14:15 16:00 02 OPTIIKKA : LUENTO 4 PHYSICUM - PHY D116 SH 26.1.2016 14:15 16:00 03 OPTIIKKA : LUENTO 5 PHYSICUM - PHY D116 SH 02.2.2016 14:15 16:00 04 OPTIIKKA : LUENTO 6 PHYSICUM - PHY D116 SH 09.2.2016 14:15 16:00 05 OPTIIKKA : LUENTO 7 PHYSICUM - PHY D116 SH 16.2.2016 14:15 16:00 06 OPTIIKKA : LUENTO 8 PHYSICUM - PHY D116 SH 23.2.2016 14:15 16:00 07 OPTIIKKA : LUENTO 9 PHYSICUM - PHY D116 SH 01.3.2016 14:15 16:00 08 OPTIIKKA : LUENTO 11 PHYSICUM - PHY D116 SH 15.3.2016 14:15 16:00 09 OPTIIKKA : LUENTO 12 PHYSICUM - PHY D116 SH 22.3.2016 14:15 16:00 10 OPTIIKKA : LUENTO 14 PHYSICUM - PHY D116 SH 05.4.2016 14:15 16:00 11 OPTIIKKA : LUENTO 15 PHYSICUM - PHY D116 SH 12.4.2016 14:15 16:00 12 OPTIIKKA : LUENTO 16 PHYSICUM - PHY D116 SH 19.4.2016 14:15 16:00 13 OPTIIKKA : LUENTO 17 PHYSICUM - PHY D116 SH 26.4.2016 14:15 16:00 14 OPTIIKKA : LUENTO 18 PHYSICUM - PHY D116 SH 03.5.2016 14:15 16:00

Total Internal Reflection

Numerical Aperture (NA) NA: A dimensionless number that characterizes the range of angles over which the system can accept or emit light noutside n air ; c air NA n outside sin c n 2 1 n 2 2 E l If 1 62 d 1 52 fi d th NA 0 56 B l l ti th i Example: If n 1 = 1.62 and n 2 =1.52 we find the NA =0.56. By calculating the arc sine (sin -1 ) of 0.56 we determine THE CRITICAL ANGLE = 34º and the ACCEPTANCE ANGLE = 68º.

Modes The optical fiber support a set of discrete modes Qualitatively these modes can be thought of as different propagation angle Geometry used for calculation of the modal dispersion i in a multimode optical fiber

A Single-mode, Stepped-index Optical Fiber

Cladding Air cladding Glass cladding stronger smaller acceptance angle

Modes of propagation p cut off external light rays may strike the air/fiber interface and still Acceptance angle :The maximum angle in which g y y propagate down the Fiber with <10 db loss. Numerical Aperture (NA): A dimensionless number that characterizes the range of angles over which the system can accept or emit light NA n outside sin cut off n 2 1 n 2 2

Modes The optical fiber support a set of discrete modes Qualitatively these modes can be thought of as different propagation angle Geometry used for calculation of the modal dispersion in a multimode optical fiber d N n n 2 2 1 2 2 Number of modes

Lecture 2 Fiber Structure

Dispersioni Pulse spreading when propagating through the fibre. Three types of dispersion: Mode-dispersion: Light travelling in different modes undergoes different delays through the fibre. Not present in SM! Material-dispersion (chromatic): Refractive index is function of wavelength Waveguide-dispersion: Propagation of different wavelengths depends on the characteristic of the waveguide, e.g. Index, geometry of core and cladding.

Type of Fiber Modes 2.405

Chromatic dispersion

Pulse spreading Original bits To much spreading results in intersymbol- interference Limits the maximum transmissionrate through the fibre. Difficult to distinguish between bits

Pulse Spreading due to Dispersion Bit 1 Bit 2 Bit 1 Bit 2 Bit 1 Bit 2 Bit 1 Bit 2 Bit 1 Bit 2

Source-to-fiber coupling Coupling Efficiency: NA of light source Dimension of light source NA of fiber Fiber core diameter MM fiber coupling: Overfilled: high order mode in the light source will be loss into cladding area Underfilled: all mode available in the source can propagate along the fiber

Coupling Light into SM Fiber Coupling into the tiny 10 micrometer core is demandingdi Lining up the light-source is a significant part of the production cost Laser is preferred light-source LED has too large beam

Mechanical misalignments

Fiber cleaving

Optical Fiber cross-section 1. A core, having high refractive index. 2. Cladding. 3. Buffer, protective polymer layer. 4. Jacket, protective polymer layer.

Fiber Drawing 1965: Kao and Hockham proposed fibers for broadband communication 1970s: commercial methods of producing low-loss fibers by Corning and AT&T. 1990: single-mode fiber, capacity 622 Mbit/s

Chemical Vapor Deposition (CVD) Chemical Vapor Deposition is chemical reactions which transform gaseous molecules, l called precursor, into a solid material, in the form of thin film or powder, on the surface of a substrate.

Chemical Vapor Deposition (CVD) Diffusion Adsorption Decomposition Vaporization of of i Precursor of i Precursor and Molecules Transport and l Incorporation to of to the Precursor Surface into Molecules Solid l Films into Reactor

Modified Chemical Vapor Deposition (MCVD) 1. The method was developed by Bell Laboratories. 2. The gaseous mixture of reactants is fed at the end of a rotating silica tube. 3. This tube is heated by a traversing oxygen-hydrogen burner. 4. As a result of chemical reactions glass particles, called soot, are formed and deposited d on internal wall of the tube. 5. The soot is then vitrified by the traversing burner to provide a thin glass layer. 6. The process is repeated many times as the cladding layers and core layers are formed. 7. When the deposition is finished, the temperature of the burner is increased to collapse the tube into a solid preform.

Outside Vapor Deposition (OVD) 1. The process was exclusively used by Corning since the 1970s, and the patent of such a technology has expired since July 2000. 2. Halogens and O 2 react in a hot flame to form hot glass soot, which is deposited layer by layer on an aluminium oxide or graphite mandrel. 3. The central mandrel is removed after deposition. 5. In the last step, called sintering, a hollow porous preform is dehydrated and collapsed in controlled atmosphere, (e. g. helium) to form desired preform.

Vapor-phase phase Axial Deposition 1. In VAD method, the preform can be fabricated continuously. 2. Starting chemicals are carried from the bottom into oxygen-hydrogen y g burner flame to produce glass soot which is deposited on the end of a rotating silica rod. 3. A porous preform is then grown in the axial direction. 4. The starting rod is pulled upward and rotated in the same way as that used to grow single crystals. 5. Finally the preform is dehydrated d d and vitrified in ring heaters. 6. This process is preferred for the mass production.

Fiber Drawing 1. The drawing gprocess is integrated with the coating process to avoid contamination of fiber surface. 2. The tip of the perform is heated in a furnace to a molten state. 3. Formed molten gob falls down under the force of gravity while shrinking in diameter into a proper diameter strand. 4 It is controlled contin o sl d ring the 4. It is controlled continuously during the drawing process.

Fiber Drawing 5. Fibre diameter drift cannot exceed 0.1%. 6. The strand is threaded through a series coating applicators immediately after drawing. 7. Liquid prepolymer coatings are cured by thermal or ultraviolet apparatus. 8. Dual coating, soft inner and hard outer, is needed to avoid microbending and protect against impact and crushing forces in either manufacturing process or installation. 9. The fiber with coatings is pulled down and wound on a winding drum. 10. The drawing process must take place in air conditioned room, because air pollution influences fiber attenuation.

Fiber-Optic Cable

Global Undersea Fiber Systems

Microstructure fiber In microstructure fiber, air holes act as the cladding surrounding a glass core. Such fibers have different dispersion properties. Air holes Core Such fiber has many applications, from medical imaging g to optical clocks. Photographs courtesy of Jinendra Ranka, Lucent

Fibre optics cable Optical Fiber Fabrication