Fiber Install & Activation Conventional
What is in a coherent detection system that enables the optical detector to respond to changes in a light wave's frequency and phase?
A local laser, acting as a local oscillator, provides a frequency and phase reference for the photodetector, which enables it to provide photocurrent that is proportional to the light wave's intensity, frequency, and phase.
Optical transport network (OTN)
All high-speed (100 Gbps) systems use this system, along with advanced modulation formats, forward error correction, and coherent detection.
What is a positive-intrinsic-negative (PIN) diode?
An optical detector with current flow that is linear to the intensity of light photons, with one electron/hole pair created for every absorbed photon until saturation.
An optical fiber consists of what three parts?
An optical fiber is made up of three parts: (1) the core, which transports the majority of the optical signal; (2) the cladding, which surrounds the core; and (3) the protective coating around the cladding.
Where would you expect Fresnel reflections to occur in a fiber-optic network?
At connections and mechanical splices where the signal source is entering or exiting the cable.
This diode requires a higher voltage power supply and more complex circuitry, which results in higher operating costs.
Avalanche photodiode
with this diode, the amplification process introduces noise into the electrical output of an optical detector.
Avalanche photodiode
Which of the following is true about fiber-optic cable? Choose all that apply.
Because the optical fiber is made of dielectric material, the cable does not carry electrical current, radiate energy, or produce heat or sparks. A 3/4-inch round fiber-optic cable can be manufactured with up to 864 optical fibers, which weigh approximately 130 pounds per kilometer. Fiber-optic cable is affected less by moisture and thermal conditions than is copper. (2 attempts remaining) Submit
These lasers are mainly sensitive to temperature variations and require greater thermal control, which is provided by additional circuitry.
Distributed feedback (DFB)
What type of optical amplifier is most common, and used exclusively at 1,550 nm?
Erbium-doped fiber amplifiers (EDFA), which operate at 1,550 nm, are the most common type of optical amplifier.
Chromatic dispersion occurs because each wavelength travels through an optical fiber at slightly different velocities, and signals using those wavelengths will arrive at the receive point at different times.
Fabry-Perot (F-P)
Besides protection, what else must the coating on an optical fiber do?
Function over a wide temperature range; be compatible with cable gels; adhere to the glass cladding over the lifetime of the cable; and be mechanically strippable for splicing operations.
Which optical splitter package is similar in appearance and size to a standard fusion splice protector?
Fused biconical taper (FBT).
What do diameter differences between spliced fibers look like on an optical time domain reflectometer (OTDR)?
Gain in one direction and high loss in the opposite direction.
Which architecture and topology today provide video, voice, and data services to thousands of customers?
HFC architectures and redundant optical ring topologies.
during (Indirect modulation), optical power is constant, and the choice of optical source can be made independent of the source's ability to vary light intensity in proportion to the electrical modulation signal.
Indirect modulation
What is the current standardized outside diameter (OD) of the cladding of single-mode fiber?
It is 125 μm, with an accuracy of ±1 μm.
What configuration of fibers is used to save space in fiber-optic cable?
Optical fiber can be grouped in ribbons of four to 24 fibers to save space in fiber-optic cable.
What advantages does packaging optical fibers in a ribbon provide?
Packaging multiple optical fibers together in a ribbon means smaller diameter cables, higher fiber count cables, and lower splice and installation costs.
What are the two parts that an STS-1 frame is divided into?
The STS-1 frame is divided into the transport overhead and the synchronous payload envelope (SPE).
Describe the four main sections of a fiber-optic node.
The four main sections of the optical fiber node are: the optical receiver, the RF amplifier module, the reverse optical transmitter, and the DC power supply.
What does the 20 nm wavelength spacing, specified in the ITU G.694.2 standard, allow?
allows for wavelength variation around the nominal wavelength, which can result when using uncooled distributed feedback (DFB) lasers.
The encoder portion of the ( data encoder/modulator) codes analog signals for conversion into digitial signals and the modulator portion transforms the digital signal into the appropriate modulation format.
data encoder/modulator
What type of modulation scheme is required in order for direct detection to be used?
detection is responsive only to the intensity and variations in intensity of the light waves, thus, intensity modulation with direct detection (IM/DD) is the fully descriptive name for this detection scheme.
current changes that occur during (direct modulation) causes a slight change on the instantaneous wavelength of the generated light from the optical source, called chirp, which is a major limitation.
direct modulation
during the process of converting an electrical signal to an optical signal, the (electrical interface) provides one or a combination of any electrical protocols to the data encoder/modulator
electrical interface
What two types of dispersion make up chromatic dispersion?
material dispersion and waveguide dispersion
has extended reach and is used with digital laser sources in oceanic networks where the optical fiber lengths are well over 1,000 km.
negative dispersion fiber
Which of the following are factors that contribute to an optical receiver's sensitivity? Choose all that apply.
noise, Linear response, back reflections
was developed to overcome the shortcomings of dispersion-shifted fiber when transporting multiplexed light waves.
non-zero dispersion-shifted fiber
is used in networks where the optical fiber lengths are less than 1,000 km.
positive dispersion fiber
What functions does the detector in an optical receiver perform?
wrong-Conversion of an optical carrier to an electrical signal, and modulation of the demodulated optical carrier. Conversion of an optical carrier to an electrical signal, and demodulation of the modulated optical carrier.
Why are laser diodes most effective when coupled to singlemode fiber?
Its high coupled power, directionality, and speed.
How is a fusion splicer set up?
Make a number of test splices to set up the fusion splicer and to verify the instrument's settings and calibration for both the environment and the type of fiber to be spliced.
What are the primary causes of intrinsic loss in single-mode fiber?
Material absorption and Rayleigh scattering.
Chromatic dispersion is a combination of which two dispersions?
Material and waveguide dispersion.
What is the typical optical input level requirement for a digital return receiver?
Minimum optical input levels for a return digital receiver are in the -20 dBm range.
Ethernet
Most IP transmissions occur using this standard.
What do most mechanical splices use to minimize reflectance?
Most mechanical splices use fixed V-groove alignment methods and index matching fluids or gels to minimize reflectance.
What amplitude should quadrature amplitude modulation (QAM) be adjusted to in an optical transmitter?
Most optical transmitter manufacturers specify that QAM carriers should be 6 to 10 dB below the analog video carriers.
Which type of optical fiber is limited by both attenuation and modal dispersion and is used extensively in private LANs and CCTV security applications?
Multimode fibers all have higher attenuation and are bandwidth-limited due to the effects of modal dispersion.
What must be done at the splice closure if the fiber-optic cable has metallic armor or strength members?
National and local electric codes mandate that cable armor and metallic cable strength members must be bonded together in the splice closure in order to form a continuous electrical path from cable to cable, bonding all cables to an approved ground.
What are the factors that contribute to an optical receiver's sensitivity?
Noise, responsivity, response time, linear response, back reflection, and optical detector material.
What does the amplification process in an avalanche photodiode (APD) introduce into the electrical output of an optical detector?
Noise.
What happens if the optical signal exceeds the maximum specified input power into a photodetector?
Nonlinear operation resulting in distortion, data errors, and signal loss.
Polarization mode dispersion
Occurs when data rates reach 10 Gbps and higher and one of the modes begins to propagate slower than the other.
What are the primary reasons that optical fibers have wavelength-specific attenuation?
Optical fibers have wavelength-specific attenuation due primarily to material absorption and Rayleigh scattering.
What are the general categories of optical splice applications?
Optical splice applications can generally be categorized as: in-line splices, branch splices, splitters, mid-entry splices, pigtails, restoration splices, and splices for acceptance testing.
Which component of a digital optical network is used to receive digital modulation light waves and convert them to an electrical signal?
Optical transponder.
How is optimal sensitivity in an optical receiver obtained?
Optimal sensitivity in an optical receiver is obtained by minimizing the noise from signal-independent thermal noise and signal-dependent shot noise.
This diode is the most common type of photodiode used in optical receivers, because it is relatively inexpensive and can be operated from a standard power supply.
Positive-intrinsic-negative (PIN) diode
With this diode, the current flow is linear to the intensity of light photons, as one electron/hole pair is created for every absorbed photon until saturation.
Positive-intrinsic-negative (PIN) diode
How many splice points do preterminated panels require?
Preterminated panels save an enormous amount of time and effort in completing the installation of inside fiber-optic cable and require only one splice point.
What are the benefits of restricting the optical transmission to a single mode?
Restricting the optical transmission to a single mode greatly increases the fiber's signal capacity, lowers its signal attenuation, and decreases manufacturing costs.
mechanical splices
Splice losses of less than 0.1 dB are routinely achieved with mechanical splices which are used on modern, tight-tolerance single-mode fibers (SMF).
What does the CMTS do?
The CMTS provides connectivity between a cable modem located at the customer premises and the Internet.
What are the three categories of WDM that are defined by the ITU?
The ITU defines three categories of WDM: wide wavelength division multiplexing (WWDM), coarse wavelength division multiplexing (CWDM), and dense wavelength division multiplexing (DWDM).
What type of single-mode fiber is intended for fiber-to-the-home (FTTH) installations?
The ITU-T G.657 bend-insensitive fiber (BIF).
Which standards organization is considered to be the creator of the world's most recognized communications standards, known as recommendations?
The International Telecommunication Union (ITU).
What are the four hierarchical layers of which the SONET signal is comprised?
The SONET signal is comprised of the photonic, section, line, and path hierarchical layers.
The phenomenon, total internal reflection, is what enables an optical fiber to guide light. What characteristic of optical fiber causes total internal reflection?
The difference in refractive indexes, between cladding and core, causes light to be reflected off the cladding and back into the core along the optical fiber.
What is a drawback of using Fabry-Perot (F-P) lasers in high-speed data (HSD) networks?
The emission of a number of discrete wavelengths or side modes.
What is the purpose of the ferrule in an optical connector?
The ferrule provides precise alignment and centering of the optical fiber within the connector.
Microbends
The intrinsic type of this loss is caused by minute deviations in the fiber core, as measured from the center of the fiber.
Name and describe the two key standards used for DWDM.
The key standards for DWDM transmission include: (1) ITU-T G.692, which defines digital systems, components, and optical interfaces for multi-channel systems with optical amplifiers; and (2) Telcordia-GR-1312-Core, which addresses generic requirements for optical amplifiers and proprietary DWDM systems.
What is one advantage and one disadvantage of single-mode fiber with a large mode field diameter (MFD)?
The larger the MFD, the easier it is to splice and connectorize the fiber, although it becomes more sensitive to bending losses.
What is a characteristic of light in a laser beam?
The laser beam consists of a limited range of wavelengths (monochromatic), with all light waves in phase (coherent light).
What are the main elements of an optical transmitter?
The main elements of an optical transmitter consist of an electrical interface, a data encoder/modulator, a laser, and an optical interface.
What are the most common products that transfer contamination?
The most common products that transfer contamination are the airborne contaminants, cable moisture repellent gels (used inside the buffer tubes), and the coating residue left from the removal of the 250 µm coatings from the 125 µm fiber.
What is most important when installing fiber-optic cable in the aerial plant?
The most important concerns with aerial fiber-optic cable installation are span length, cable tension, and cable sag.
What element in an optical receiver detects light waves and converts that energy into an electrical current and also acts as an optical demodulator?
The optical detector, also known as a photodiode, converts light waves to a flow of electrical current, and since the photocurrent is proportional to the light waves' intensity, the photodetector is also a demodulator.
What are two critical factors for a successful fiber-optic cable installation?
The pulling tension and the cable bend radius are the two critical factors for a successful fiber-optic cable installation.
What is the dominant method used for storing fiber-optic cable slack in aerial installations?
The snowshoe, which was designed for fiber-optic cable applications, is the dominant method for storing slack in aerial installations.
What does the spectral width of a laser or light emitting diode (LED) define?
The spectral width or bandwidth of a laser or LED defines the width of an optical emission at intersecting points of a line drawn across the emission's signature profile, 3 dB (or 50%) down from the emission's peak amplitude.
What is 8-VSB?
The term 8-VSB stands for eight-level vestigial sideband modulation. It is the modulation method used for broadcast channels in the ATSC digital television standard, and the modulation that is used primarily in North America.
The frame structure of a synchronous transport signal (STS) is divided into two parts. What are they?
The transport overhead, which contains the section and line layers, and the synchronous payload envelope, which contains the path overhead and the payload data.
What is the basic function of a true optical patch panel?
The true optical patch panel provides cross-connection between different optical sources and destinations, and is also the first link between the transmission equipment and the outside network.
What does the use of the mid-entry splice provide when used extensively in metropolitan area networks (MAN)?
The use of the mid-entry splice is intended to minimize the number of splices at drop-off points in MANs.
What characteristic of fiber-optic cable enhances the security of signals being transported in the network?
There is no EMI or RFI radiation, or other detectable energy, radiating from the cable, so the transport of signal through fiber-optic cable is very secure.
Synchronous optical network (SONET) and the synchronous digital hierarchy (SDH)
These standards were proposed in the late 1980s and have become a global standard for data transmission over fiber.
Macrobends
This loss shows up when the fiber bend radius decreases.
Wide wavelength division multiplexing (WWDM)
This multiplexing process does not need to use expensive or sophisticated lasers and optical detectors.
Coarse wavelength division multiplexing (CWDM)
This system has wide channel spacings, to allow lower-cost lasers and filters to be used.
What installation tactic should be used to reduce the pulling tension on long lengths of fiber-optic cable?
To reduce the pulling tension on long lengths of fiber-optic cable, the installation should begin near the middle of the cable span. Pull the cable to the designated destination in one direction, then remove the cable from the reel and lay it in a figure-eight pattern on the ground, and pull the cable in the other direction.
Why was the zero-dispersion point in single-mode fiber moved to 1,550 nm?
To take advantage of the low intrinsic absorption and lower attenuation at 1,550 nm in single-mode fiber.
True or False Due to the tight tolerances of single-mode fibers (SMF), it is easier and faster to splice factory-built pigtails to the fibers than to install connectors.
True
What is more accurate, technically correct, and critical to use when defining the optical transport region of a single-mode fiber?
When defining the optical transport region of a single-mode fiber, MFD is more accurate, technically correct, and critical to use than the core diameter.
Give three examples of mechanical defects that a technician should visually inspect the splice for while visible on the splicer screen.
While the splice is visible on the splicer's display screen, visually inspect the splice for mechanical defects such as hairline fractures, bulging, or necking, which could indicate a mechanically weak splice and may result in future splice failure.
What are three specific safety disciplines when working with optical fibers?
Working with optical fibers requires specific safety disciplines, including the proper use of tools, safety eyewear, and the proper handling of chemicals.
What factors must be considered when designing high-speed optical circuits?
data rate, bandwidth requirements, and the dynamic range of the optical link.
the modulation signal is applied to the (light source) which could be either a light emitting diode or laser diode.
light source
What is the wavelength of a 150 MHz carrier wave? Use the speed of light measured in meters per second to finish this equation: 300 x 106 divided by 150 x 106.
2 meters.
What is a major benefit of using a scalable node?
A major benefit of a scalable node is that it offers a wide variety of configuration options, which allows for future network upgrades.
Refractive index
A measure of how much the speed of light is changed when traveling through a material as compared to traveling through a vacuum.
What device is used in digital networks at intervals to regenerate the transported signal in order to reduce or eliminate data errors?
A repeater is a device inserted at intervals in a digital network to regenerate the transported signal in order to reduce or eliminate data errors.
How many virtual tributaries (VT) of 1.728 Mbps may be byte interleaved into a single STS-1?
A single STS-1 may contain up to 28 VTs (4 × 1.728 Mbps = 6.912 Mbps, 6.912 Mbps × 7 VT-G = 48.384 Mbps); path, section, and line overhead are added to form an STS-1 (51.84 Mbps) data rate.
Dense wavelength division multiplexing (DWDM)
Can use different frequency spacings, depending on the number of optical channels required.
Chromatic dispersion
Caused by a combination of material and waveguide dispersion.
Modal dispersion
Caused by different modes arriving at different times, and is what limits the use of multimode fiber
What variations of the star topology are used in PONs?
Centralized split, distributed star, and home-run are variations of the star topology used in PONs.
Chromatic dispersion is a combination of which two types of dispersion in single-mode fiber?
Chromatic dispersion is a combination of material dispersion and waveguide dispersion in single-mode fiber.
What type of optical detection can improve the sensitivity of an optical receiver by as much as 20 dB?
Coherent detection can improve the sensitivity of the optical receiver by as much as 20 dB.
Radio frequency over glass (RFoG)
Defines fiber-to-the-x (FTTx) networks that are optimized for compatibility with a hybrid fiber/coax (HFC) plant that uses existing set-top boxes (STB) and DOCSIS modems.
mechanical splices
Despite higher attenuation losses, mechanical splices preferred for some splice applications due to their simplicity.
Which type of optical detection involves a photodiode that converts the light waves to an electrical signal that varies in proportion to intensity changes in the light waves?
Direct
What are the two methods used to modulate an optical carrier?
Direct modulation and indirect modulation (also called external modulation) are the two types of methods used to modulate an optical carrier.
Wavelength division multiplexing (WDM)
During this multiplexing process, the optical output from multiple lasers operating at different wavelengths is combined and transported over a single, common optical fiber.
Dense wavelength division multiplexing (DWDM)
During this multiplexing process, the wavelength spacing is typically specified by gigahertz (GHz) instead of wavelengths.
Coarse wavelength division multiplexing (CWDM) applications were expanded to include use in what band, where a large OH absorption loss occurred with older single-mode fibers?
E band
Why are Erbium-doped fiber amplifiers (EDFA) frequently used in optical networks that contain multiple splitters and couplers?
EDFAs are used to compensate for splitting and combining losses in optical networks that contain multiple splitters and couplers.
One of the drawbacks of this laser is the emission of a number of discrete wavelengths or side modes.
Fabry-Perot (F-P)
How might WWDM be used in a passive optical network (PON) application?
In a PON application, the 1,550 nm and 1,490 nm wavelengths could be used to transport television and HSD signals throughout the network, and the 1,310 nm wavelengths could be used to transport HSD signals from the connected premises to the headend.
(Indirect modulation) virtually eliminates chirp, and provides isolation from back reflections for improved relative intensity noise performance
Indirect modulation