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Optical Fiber Communications And
Cr-doped fiber amplifier
ASSOC. PROF. CHUNNIEN LIU
NATIONAL CHUNG-HSING UNIV. 1
Home work Reports (A4, total 2 pages, submit as MS-word file, not pdf.) Question 1 (A4, 1 page) Please explain the optical fiber communication system.
Question 2 (A4, 1 page) Please tell me the several advantages of optical fiber communications. And how to add the communicated speed.
Deadline: 2020.6.15 TTI-students to Prof. Yoshimura NCHU-students to Prof. Lin
Introduction Visible light:
Electromagnetic wave(wavelength: 0.38-0.76μm)
Color Wavelength Frequency Photon energy
Violet 380–450 nm 680–790 THz 2.95–3.10 eV
Blue 450–485 nm 620–680 THz 2.64–2.75 eV
Cyan 485–500 nm 600–620 THz 2.48–2.52 eV
Green 500–565 nm 530–600 THz 2.25–2.34 eV
Yellow 565–590 nm 510–530 THz 2.10–2.17 eV
Orange 590–625 nm 480–510 THz 2.00–2.10 eV
Red 625–740 nm 405–480 THz 1.65–2.00 eV
Introduction A communication system is a collection of individual communications networks, transmission systems, relay stations, tributary stations, and data terminal equipment (DTE) usually capable of interconnection and interoperation to form an integrated whole. The components of a communications system serve a common purpose, are technically compatible, use common procedures, respond to controls, and operate in union.
-1854 John Tyndall
Tyndall knew light was trapped temporarily inside the stream of water, but he couldn’t explain why. Today, using a combination of mathematics and science, the explanation is very straightforward. Tyndall’s 1870 experiment demonstrated the principle known as “total internal reflection.” Simply stated: Total internal reflection is a special optical condition in which optical rays cannot escape the material in which they are traveling.
-1966 Charles K. Kao(1933-2018)
In 1965 Kao with Hockham concluded that the fundamental limitation for glass light attenuation is below 20 dB/km (decibels per kilometer, is a measure of the attenuation of a signal over a distance), which is a key threshold value for optical communications. However, at the time of this determination, optical fibres commonly exhibited light loss as high as 1,000 dB/km and even more. This conclusion opened the intense race to find low-loss materials and suitable fibres for reaching such criteria.
Introduction Year 1980 1985 1990 1996 2002
Generation First Second Third Fourth Fifth
Type Graded-index fibers Single-mode fibers Single-mode lasers Optical amplifiers Raman amplification
Bit rate 45 Mb/s 100 Mb/s
To 1.7 Gb/s
10 Gb/s 10 Tb/s 40 Gb/s
to 160 Gb/s
Repeater spacing 10 km 50 km 100 km 10,000 km
24,000 km to
Operating wavelength 0.8 um 1.3 um 1.55 um
1.45 um to
1.53 um to
4th or 5th Mobile Networks (4G/5G) Triple Play Service (Communications)
• The speed of mobile network between 4G (1~50 Mbit/s) and 5G (1~10 Gbit/s) shows an improvement of 100 times.
• Until now, the fiber network (1~50 Gbit/s) is widely used and needs to be upgrade. • The new-generation of 400 Gbit/s and 1 Tbit/s communication system have been discussed at 2019 OFC.
Fiber to the x (FTTx)
Optical Fiber Structure
Glass optical fibers are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses as well as crystalline materials like sapphire, are used for longer-wavelength infrared or other specialized applications. Silica and fluoride glasses usually have refractive indices of about 1.5, but some materials such as the chalcogenides can have indices as high as 3. Typically the index difference between core and cladding is less than one percent. An optical fiber consists of three basic concentric elements: the core, the cladding, and the outer coating.
Optical Fiber Characteristic
1. Silica exhibits fairly good optical transmission over a wide range of wavelengths. In the near-infrared (near IR) portion of the spectrum, particularly around 1.5 µm, silica can have extremely low absorption and scattering losses of the order of 0.2 dB/km. Such remarkably low losses are possible only because ultra-pure silicon is available.
2. they permit transmission over longer distances and at higher bandwidths (data transfer rates) than electrical cables.
3. No electromagnetic interference. 4. Inexhaustible materials(SiO2)
Optical Fiber Attenuation of an optical fiber as a function of the wavelength.
Fiber Communication System
O E S C L U
OH- ion absorption
OH- ion free
Low Loss Fiber Spectrum O
E S C L U
300-nm Cr-Doped Fiber Amplifier
• Recently, Cr-doped fibers (CDFs) have demonstrated broadband emissions in the whole 1200-1600 nm range. It is interesting to develop a single fiber amplifier to cover the bandwidth of 1300-1600 nm in low-loss transmission.
• The bandwidth of Cr-doped fiber amplifier (CDFA) is 4.3 times than the commercial EDFA.
Er doped fiber (EDFA)
Cr doped fiber (CDFA)
C band (1530~1565nm: 35nm)
L band (1570~1605nm: 35nm)
Total : 70nm
( 300 nm )
Fabrication of Multi-mode Cr-Doped Fiber (MMCDF)
} MMCDF fabrication a. Bulk Cr:YAG crystal diameter from 500 µm was reduced
to 70 µm. Then, the crystal rod was put in a silica tube.
b. The LHPG system fabricated a double-clad MMCDF of 14 µm core diameter and length of 6.7 cm.
Core: 14 µm Inner Cladding: 95 µm
Outer Cladding: 320 µm
LHPG growth chamber
Laser heated pedestal growth (LHPG)
S.M. Yeh, et. al., J. Lightw. Technol., 2009. 14
Gain Measurement of MMCDF •Single pump
S.M. Yeh, et. al., J. Lightw. Technol, 2009. 15
Gain Performance of MMCDF
0 1 2 3 Pump power (W)
MMCDF of core diameter of 14 µm and length of 6.7 cm
Gross gain = 2.8 dB 1. The gross gain of Cr-doped fiber amplifier (CDFA) is defined as:
G (dB) = 10log [(Ps+p -Pp)/Ps] 2. The insertion loss in dB unit is defined as:
IL (dB) = 10log (Pout / Pin) where the Pin and Pout are the input and output signal power at the facet of CDFA, respectively.
Insertion loss = 1.6 dB
3. The net gain of CDFAs is defined as: Gn(dB) = Gg(dB) – IL(dB)
Net gain = 2.8 dB – 1.6 dB = 1.2 dB
This is the first demonstration of a net gain in a broadband Cr-doped fiber amplifier (CDFA).
S.M. Yeh, et. al., J. Lightw. Technol, 2009.
S.M. Yeh, et. al., J. Lightw. Technol, 2009. 16
40 Gbit/s Single Channel Communication System
• Four test conditions for eye diagram and bit error rate (BER) : (a) back-to-back (BTB), (b) CDFA without Pumping, (c) CDFA with 4.0 W Pumping, and (d) CDFA with 8.0 W Pumping.
• All the eye diagrams and BER performance showed successful. This result further verified that no pattern dependence was observed in CDFAs. 17
Structure of 300-nm CDFA in FTTH System
40 Gbit/s and 1550 nm signal: Power penalty was 0.4 dB with CDFA and 1.6 dB after 10 km.
40 Gbit/s and 1310 nm signal: Power penalty was 0 dB with CDFA and 0.7 dB after 10 km.
Mode Reduction of CDF (I)
S.M. Yeh, et. al., J. Lightw. Technol, 2009.
Lower Threshold of Few-mode/Single-mode
• Lower threshold pumping power
• Reduce the heat effect by pumping
• Increase the gain efficiency
M. J. F. Digonnet et.al., Appl. Opt., 1985.
Mode Reduction of CDF (II)
Core diameter：14 µm
Few-mode or single-mode:
• Reduce the core diameter.
• Reduce core/clad index difference.
Cr:YAG index：1.82 @1064 nm SiO2/Silica index：1.45 @1064 nm Numerical aperture (NA)：1.1
Fabrication of Few Mode CDF (FMCDF)
The few-mode Cr-doped fiber (FMCDF) was fabricated by LHPG system with multi- core reduction process. The FMCDF exhibited a core diameter of 2 µm and V-number of 3.77 to provide a few-mode characteristics.
Mode Characteristics of FMCDF
Gain Performance of FMCDF
Gross gain = 2.4 dB
FMCDF of core diameter of 2 µm and length of 4 cm
A gross gain of 2.4 dB at 1400-nm wavelength was obtained at 0.2 W pump power. Compared with the MMCDF of gross gain of 2.8 dB at 3 W pump power, the pumping efficiency of gross gain for the FMCDF showed an improvement of 10 times.