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Dispersion Compensating Fiber 


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Dispersion Compensating Fiber 

Single Mode Fiber Cross Section
Click to Enlarge

Single Mode Fiber
Cross Section
Compatible Connector Supplies
FC/APC Connector30126K1
FC/PC Connector30126D1
Stripping ToolT06S13
Cleaving ToolS90R
FC/APC Connectorization KitCK05
FC/PC Connectorization KitCK03

Features

  • Dispersion Compensating Fiber for Telecom Wavelengths (1500 - 1625 nm)
    • DCF3 is for General Telecom Dispersion Compensation (Negative Dispersion and Low Positive Dispersion Slope)
    • DCF38 is Designed to Compensate Corning SMF-28e+ Fiber
  • Outer Jacket Available upon Request
  • Shipped from Stock with No Minimum Order

Thorlabs offers dispersion compensating optical fiber for custom solutions across a broad spectral range in the telecom region. DCF3 fiber is a non-zero dispersion-shifted fiber (NZ-DSF) with negative dispersion and low positive dispersion slope that is optimal for medium distances and wide band WDM systems. Optical dispersion across the entire C-band enables effective dispersion compensation and suppresses nonlinear impairments. DCF38 has dispersion designed specifically to match and compensate Corning SMF-28e+ or Vascade L1000 fiber. Please see the Dispersion Tutorial tab for more detailed information about dispersion compensating fibers.

Connectorization

Dispersion compensating fibers are fully compatible with typical connectors and termination tools. Loss is slightly higher than typical SM fibers at around 1 dB. Lower losses can be achieved by splicing. Various compatible connectors and tools are summarized in the table to the upper right.

Custom Fiber Patch Cables   Optical Fiber Manufacturing

Splicing

Splicers and tooling designed for Ø125 µm fiber can be used with this fiber. To achieve an optimized fuse, the program should use a shorter fusion time than with conventional SM fibers. This is due to excess diffusion of the core dopants, which alters the guiding properties of the fiber in the splice region. Alteriatively, DCF3 can be used as a bridge between DCF38 and SMF-28 to reduce splice losses. For more information, see "New Technique for Reducing the Splice Loss to Dispersion Compensating Fiber", Edvold B., Gruner-Nielsen, L., Optical Communication, 2, 245-248 (September 19, 1996).

Item #DCF3DCF38
DescriptionNegative Dispersion, NZ-DSF fiber with low, positive dispersion slopeHigh dispersion fiber with negative slope. Designed to be paired with Corning SMF-28e+ or Vascade L1000 Fiber
Dispersion Specifications
Dispersion [ps/(nm*km)]-4.30 to -1.60-49.00 to -30.00
Dispersion Slope [ps/(nm2*km)]0.043 to 0.065-0.155 to -0.075
Effective Area (µm2)4827
Polarization Mode Dispersion (ps/√km)≤0.05≤0.05
Index of Refraction1.470 at 1310 nm
1.469 at 1550 nm
1.476 at 1310 nm
1.474 at 1550 nm
General Specifications
Nominal Mode Field Diameter
@ 1550 nm (µm)
8.1 ± 0.46.01 ± 0.29
Numerical Aperture @ 1550 nm0.140.14
Cladding Diameter (µm)125.0 ± 1.0125.0 ± 1.0
Coating Diameter (µm)250 ± 5250 ± 5
Cutoff Wavelength (nm)≤1500≤1520
Attenuation @ 1550 nm (dB/km)≤0.220≤0.265
Attenuation Slope from 1530 - 1565 nm [dB/(nm*km)]-0.00034 to -0.00010-0.00040 to -0.00011
Standard SM Fiber Dispersion Diagram
Waveguide dispersion offsets chromatic dispersion to produce zero dispersion at 1.31 µm in step-index SM fiber (Click to Enlarge).

Dispersion in Optical Fiber

Chromatic dispersion is a property of optical fiber where different wavelengths of light propogate at different velocities. Chromatic dispersion is a function of wavelength, and is the sum of two components: material and waveguide dispersion. Material dispersion arises from the change in a material's refractive index with wavelength, which changes the propogation velocity of light as a function of wavelength.

Waveguide dispersion is a separate effect, arising from the geometry of the fiber optic waveguide. Waveguide properties are a function of wavelength; consequently, changing the wavelength affects how light is guided in a single-mode fiber. For example, decreasing the wavelength will increase the relative waveguide dimensions, causing a change in the distribution of light in the cladding and core. In general:

Dispersionchromatic(λ) = Dispersionmaterial(λ) + Dispersionwaveguide(λ)

Since material and waveguide dispersion are wavelength dependent, the dispersion is a function of wavelength. The dispersion slope can be positive or negative.

Dispersion-Shifted Fiber Dispersion Diagram
A fiber designed with more waveguide dispersion shifts the zero-dispersion wavelength to 1.55 µm (Click to Enlarge).

Dispersion-Shifted Fiber

In standard step-index single-mode fiber, the sum of the material and waveguide dispersion is zero near 1310 nm, which is called the zero-disperion wavelength. By varying the fiber's waveguide structure, the waveguide dispersion can be shifted up or down, thus changing the zero-dispersion point. Fiber in which the zero-dispersion wavelength has been changed is called zero dispersion-shifted fiber.

An initial strategy was to alter the waveguide structure to shift the zero-dispersion point to the signal wavelength of 1550 nm, creating zero-dispersion shifted fiber (see the diagram to the right). Unfortunately, fixing the dispersion problem is not so simple. When multiple optical channels pass through the same fiber at wavelengths where dispersion is very close to zero, they suffer from a type of crosstalk called four-wave mixing. The degradation is so severe that zero dispersion-shifted fiber cannot be used for dense-WDM systems. To avoid four-wave mixing, the zero-dispersion wavelength is moved outside the transmission band. So-called nonzero dispersion-shifted fibers have a dispersion that is low, but nonzero in the 1550 nm band (typically 0.1 to 6 ps/nm*km). Although dispersion is minimized, it is still present.

Dispersion-Compensating Fiber Dispersion Diagram
Only total dispersion is shown in this graph. (Click to Enlarge)

Dispersion-Compensating Fiber

Since dispersion is inevitable in optical fibers, dispersion-compensating fibers, such as those sold on this page, can be incorporated into optical systems. The overall dispersion of these fibers is opposite in sign and much larger in magnitude than that of standard fiber, so they can be used to cancel out or compensate the dispersion of a standard single-mode fiber, such as a nonzero dispersion-shifted fiber. A negative dispersion slope enables effective cancellation of dispersion over a larger wavelength range, since the dispersion slope of standard fiber is usually positive. Generally, a short length of dispersion-compensating fiber is spliced into a longer length of standard fiber to compensate for dispersion, as in the example below.

Dispersion Compensation Schematic

Dispersion Management

Dispersion can cause various penalties in signal transmission in optical communications systems. Thus, dispersion management is a very important part of designing a fiber optic transmission system. The following table, provided by ITU* standards, which gives the maximum distances for different transmission bit rates and fiber types at around 1550 nm as limited by dispersion.

Bit rate per channel (Gbps)SDHSONETSSMFNZ-DSF
2.5 GbpsSTM-16 OC-48640 km4400 km
10 GbpsSTM-64 OC-19250-100 km300-500 km
40 GbpsSTM-256OC-7685 km20-30 km

*ITU: International Telecommunication Union
SDH: Syhcnronous Digital Hierarchy
SONET: Sychronous Optical Network
SSMF: Standard Single Mode Fiber

NZ-DSF: Non-Zero Dispersion Shifter Fiber
STM: SDH Level and Frame Format
OC: SONET Optical Carrier Level


There are different techniques to reduce the impact of chromatic dispersion, among them fiber with small dispersion, using fiber with negative dispersion, or dispersion compensating optics. Chromatic dispersion may or may not need to be compensated for in an optical system. Total fiber system dispersion can be estimated by:

CDtotal = CDfi + CDDCM + CDother

Where:
CDfi = total fiber chromatic dispersion
CDDCM = total chromatic dispersion of dispersion compensating systems
CDother = total chromatic dispersion due to other components

A dispersion limit, CDlimit, is provided by ITU standards providing the maximum allowable accumulated chromatic dispersion. In general, the relation CDlimit ≥ CDtotal  should be true. When CDlimit= CDtotal , a 1 dB decrease in signal strength as a function of bit rate will be present.

Bit Rate per Channel (Gbps)SDHSONETTotal Allowable Dispersion Coefficient at 1550 nm for a Given Link with SSMF (CDlimit)
2.5 GbpsSTM-16 OC-4812000 to 16000 ps/nm
10 GbpsSTM-64 OC-192800 to 1000 ps/nm
40 GbpsSTM-256OC-76860 to 100 ps/nm

Dispersion Compensating Planning Example

Transmitted Power: 4 dBm
Signal: 10 Gbps
CDlimit: ±1000 ps/nm
Length: 100 km
Fiber: Single Mode with Dispersion: 18.0 ps/(nm x km) at λ = 1550 nm

First, is dispersion compensation necessary? CDfi = Dispersion x Length = 18.00 ps/(nm x km) x 100 km = 1800 ps/nm. The dispersion limit for this system is CDlimit = ±1000 ps/nm, and so we need dispersion compensation. For this example, we need CDlimit - CDDCM ≥ CDfi.

To reach the positive limit:
CDDCM ≤ 1000 ps/nm - 1800 ps/nm = -800 ps/nm
To reach the negative limit:
CDDCM ≥ -1000 ps/nm - 1800 ps/nm = -2800 ps/nm

Thus, we need -2800 ps/nm ≤ CDDCM ≤ -800 ps/nm. Our DCF38 fiber has dispersion -38.0 ps/(nm x km), so we can use two 13.2 km segments for a total CDDCM of: CDDCM = 2 x 13.2 km x -38.0 ps/ (nm x km) = -1003.2 ps/nm.

Our total dispersion is then CDtot = -1003.2 ps/nm + 1800 ps/nm = 796.8 ps/nm, which is below the dispersion compensation limit.

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Posted Comments:
Poster: mchen
Posted Date: 2014-01-28 17:16:05.367
What are the dispersion and the loss of DCF38 at 2 micron? Do you have DCF designed for 2 micron? Thanks a lot, Mike
Poster: tcohen
Posted Date: 2012-06-20 09:32:00.0
Response from Tim at Thorlabs: The cutoff wavelengths for these fibers are =1500nm and =1520nm. Below this, many modes will propagate and there will be much more dispersion. I would like to talk to you about the length of fiber needed and the dispersion requirements for your system so that we can see what solution would be best for your application. I will contact you directly to get more information.
Poster: tttang
Posted Date: 2012-06-17 03:52:52.0
Do you have low-dispersion optical fiber for Ti:sapphire fs laser (800nm)? or would you be able to provide some information of these dispersion compensating fiber at 800nm? Thank you very much. -Tom.
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DCF3 Support Documentation
DCF3 Customer Inspired! Non-Zero Dispersion Compensating Fiber, Dispersion: -3.0 ps/nm*km
$5.02
Per Meter
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DCF38 Support Documentation
DCF38 Customer Inspired! Dispersion Compensating Fiber for SMF-28e+, Dispersion: -38 ps/nm*km
$6.10
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