ENE623/EIE 696 Optical Networks Lecture 1

Historical Development of Optical Communications  1790 – Claude Chappe invented ‘optical telegraph’.  1880 – Graham Bell invented ‘photophone’.  1930 – Heinrich Lamm presented unclad-fibers, but it showed poor performance.  1954 – van Heel and Kapany reported about the 1 st clad- fibers by covering a bare fiber with a transparent of lower refractive index.

Historical Development of Optical Communications  1960 – Maimen demonstrated the 1 st laser for communications.  1966 – Kuo and Hockham introduced fiber communications with low attenuation (< 20 dB/km).  1970 – Maurer, Keck, and Schultz made a single-mode fused silica fiber (very pure with high melting point and a low refractive index) for 633 nm wavelength of HeNe laser.  1977 – Fibers used at 850 nm from GaAlAs laser.

Historical Development of Optical Communications  1980’s – A 2 nd generation of optical communication at 1300 nm with 0.5 dB/km for fiber attenuation.  1990’s – A 3 rd generation operates at 1550 nm with fiber loss of 0.2 dB/km with EDFA serving as an optical amplifier. Signals also could be sent via WDM.

Preview on Fiber Optic Communication  Basic schematic diagram

Preview on Fiber Optic Communication  The advantages of optical fiber communication over electrical based system are  Low attenuation  High bandwidth  Immune to electro-magnetic interference  Short circuiting, Earthing, and Fire Free  Low in weight and volume  Data security

Preview on Fiber Optic Communication  The transmission passbands for installed fibers today are 0.85, 1.3, and 1.55 μ m (near-infrared).  Wavelength of 1.6+ μ m can be seen in some applications.  There are more than 25,000 GHz of capacity in each of the three wavelength bands.

Preview on Fiber Optic Communication  Digital transmission – The sampling theorem says that an analog signal can be accurately transmitted if sampling rate is twice the highest frequency contained in that signal.  Let R be the required transmission rate. R can be expressed by where m = number of bits/sample f s = sampling frequency = 2(  f)

Preview on Fiber Optic Communication Message TypeUsed bandwidth(B) Voice (telephone)4 kHz Music -- AM10 kHz Music -- FM200 kHz TV (Video + Audio)6 MHz

Preview on Fiber Optic Communication Number of Voice channels Transmission Designation Signaling DesignationData Rate kb/s 24T1DS Mb/s 48 (2-T1 systems)T1CDS-1C3.152 Mb/s 96 (4-T1 systems)T2DS Mb/s 672 (7-T2 systems)T3DS Mb/s 1344 (2-T3 systems)T3CDS-3C Mb/s 4032 (6-T3 systems)T4DS Mb/s

Example 1  A telephone system has m = 8 bits/sample. Find R.  Sol n

Preview on Fiber Optic Communication  A transmission standard developed for optical communication is called SONET (Synchronous Optical NETwork). Transmission (electrical) Designation (optical) SDH systemData Rate(Mb/s) STS-1OC STS-3cOC-3STM STS-12OC-12STM STS-24OC-24STM-81, STS-48OC-48STM-162, STS-96OC-96STM-324, STS-192OC-192STM-649, STS-768OC - 768STM-12839,813.12

Preview on Fiber Optic Communication BandDescriptorRange(nm) O-bandOriginal E-bandExtended S-bandShort wavelength C-bandConventional1530 – 1565 L-bandLong wavelength U-bandUltra-long wavelength

Installations  Optical fiber installations:  on poles  in ducts  undersea

Fiber Attenuation History

Preview on Fiber Optic Networks  Fiber-To-The-Home (FTTH) 2.5 Gbps  Mid 90’s 10 Gbps  y2k 40 Gbps and beyond  state of art

Preview on Fiber Optic Networks  Now a number of channels per fiber is more than 128.  This was increased from 32 channels/fiber in  The link attenuation is less than 0.2 dB/km at 1.55 μ m wavelength.  BER can be achieved at with a help of Er-doped fiber amplifier (EDFA).

Optical Fiber Source: ARC Electronics

Fibers Source: Optical Fiber Communications, G.Keiser, McGraw Hill.

Connectors Source: ARC Electronics

Optical communication systems  Multiplexing refers to transmission of multiple channels over one fiber.  Channels can be data, voice, video, and so on.  We may classify the communication systems into 3 classes as:  Point-to-point link  Multipoint link  Network

Example 2  A cable consists of 100 fibers. Each fiber can carry signals of 5 Gbps. If audio message encoded with 8 bits/sample is being sent, how many conversations can be sent via one cable?  Sol n

Example 3  By using the same cable as previous example, how many TV channels could be sent via a cable.  Sol n

Generations of Fiber Usage  Bandwidth and error rate improved (fatter links), but propagation delay not changed (same length). Source: Fiber Optic Network Paul E. Green, Prentice Hall.

Generations of Fiber Usage  First generation: no fiber (copper link)  2 nd generation:  Fiber used for point-to-point link only.  Multiplexing & switching carried out electronically.  3 rd generation:  Fiber used for multiplexing and switching as well as point-to- point transmission.

Generations of Fiber Usage  Copper links  Copper links are more vulnerable to outside influence since moving electrons influence each other.  It is also affected by electromagnetic wave (EM wave).  Fiber links  Moving photons of light in a fiber do not interact with other moving photons.  EM wave has no effect on a fiber as well.

Fiber Bandwidth  We all know that  where λ = free-space wavelength ν = optical frequency c = speed of light at free-space

Fiber Bandwidth  At = 1.5 µm, the attenuation is about 0.2 dB/km, and there is a window about  = 200 nm wide between wavelengths having double that number of dB per kilometer.  The useful bandwidth is about 25,000 GHz.

Fiber Bandwidth  This can applied to = 1.3 µm and 0.85 µm as well.  For 0.85 µm, this band is not defined by an attenuation standpoint, but by the range which GaAs components can be easily made.

Fiber Bandwidth λ (nm) ν (x10 14 Hz) Δ ν (x10 13 Hz) Δν / ν

Multiplexing  Space Division Multiplexing  Frequency Division Multiplexing  Time Division Multiplexing  Wavelength Division Multiplexing

Wavelength-Division Multiplexing  For example, 16 channel WDM using 1,300 nm or 1,550 nm with 100 GHz channel spacing.  Therefore, bandwidth = 16 x 100 = 1,600 GHz.  LAN = Local Area Network (< 2 km)  MAN = Metropolitan Area Network ( < 100 km)  WAN = Wide Area Network (unlimited)