Comprehensive Fiber Optic Transmissions and Installation Study Guide

Fiber Optic Types and Physical Properties

  • Common Multi-Mode Fiber (MMF) Types:

    • 50/125 μm50/125\,\mu m
    • 62.5/125 μm62.5/125\,\mu m

  • Single Mode (SM) Fiber Characteristics:

    • Jacket Color: Yellow signifies single mode.
    • Low-cost Light Sources: Typically use Fabry-Perot lasers.
    • Core/Cladding Ratio: The transcript identifies Single Mode as 90/12590/125 (Note: standard single-mode is typically 9/1259/125, but 90/12590/125 is the provided value).
    • Dispersion: Single-mode fiber has minimal or no amount of modal dispersion.
    • Lowest Attenuation: The wavelength of 1550 nm1550\,nm provides the lowest loss for single-mode fiber.
    • Termination: Most single-mode fibers are terminated using factory-fabricated pigtails.

  • Multi-Mode Fiber (MMF) Classifications:

    • OM1: Designed for 62.5/125 μm62.5/125\,\mu m fiber.
    • OM5: This type has the highest bandwidth among multi-mode fibers.
    • Laser Optimized MMF: 50/125 μm50/125\,\mu m laser-optimized fiber is contained in an Aqua-colored jacket.
    • Graded Index vs. Step Index: Graded index multi-mode fiber is advantageous because it reduces modal dispersion.

  • Physical Components and Geometry:

    • Cladding: This is the layer surrounding the core (referred to as position "B" in diagnostic figures).
    • Buffer Diameter: Most indoor tight-buffered cables have a buffer diameter of 900 μm900\,\mu m applied directly to the outer layer.
    • Fiber Geometry: This is categorized as an "Intrinsic" tolerance.
    • Color Coding (TIA-598): The sequence includes 12 colors. Specific colors missing in sequences provided include:
      • 1: Blue
      • 2: Orange
      • 6: White
      • 11: Rose

Physics of Light and Signal Transmission

  • Transmission Spectrum: Fiber optic transmission takes place in the infrared portion of the electromagnetic spectrum.

  • Refraction: This term describes the bending of a light wave caused by a change in speed when passing from one transparent medium to another.

  • Wave Properties and Speed:

    • Different wavelengths of light travel at different speeds through the glass.
    • Mode Definition: A "mode" in an optical fiber is defined as a light path.
    • Mode Density: As the wavelength decreases, the number of modes in a fiber increases.

  • Power Levels and Ratios:

    • Decibel (dB): Used to express the ratio between power in and power out.
    • dBm: When using power levels, values below 1 mW1\,mW (milliwatt) are expressed as negative values.
    • Reflectance: The ratio of reflected power to incident power, expressed in decibels (dBdB).
    • Optical Return Loss: A ratio expressed in dBdB used to define the power of the outgoing signal compared to the power of the reflected signal.

  • Fresnel Reflection:

    • Definition: An air gap produced when a connector plug is not fully inserted into the mating sleeve.
    • Impact: This phenomenon disrupts the operation of the laser in a transmitter.

Cable Design and Installation Standards

  • Cable Types and Construction:

    • Indoor/Outdoor Idle Fiber: Bend-insensitive fiber is ideal for indoor installations.
    • Ribbon Cable: Specifically used with MPO/MTPMPO/MTP array connectors.
    • Distribution Cable: An indoor, tight-buffered, non-breakout style cable.
    • Hybrid Cable: A cable defined by the NEC that contains both single-mode and multi-mode fibers within the same jacket.
    • Loose-Tube Cables: These utilize gels, tapes, or powders to prevent water intrusion.
    • Fan-Out Kits: Kits used to transition 250-micron fibers from loose-tube cables into 900-micron protective tubes.

  • NEC (National Electrical Code) Definitions:

    • Nonconductive Cable: A factory assembly of one or more optical fibers with an overall covering containing no electrically conductive materials.
    • OFNP: Stands for Optical Fiber Nonconductive Plenum.
    • Riser Rated: Defined as a cable for vertical runs from floor to floor that is not low-smoke rated.

  • Installation Requirements:

    • Cable Length (Indoor): Unrated indoor cables should not exceed 50 ft50\,ft from the point of entrance.
    • Minimum Bend Radius: After installation, the minimum bend radius is 10×10 \times the cable diameter.
    • Conduit Fill Ratio: The maximum cross-sectional area fill ratio for a conduit with one cable is 53%53\%.
    • Grounding: If a cable has metallic members, the NEC requires bonding to ground at termination points.
    • Cable Slack: Slack is included in the fiber plant to facilitate moves, adds, and changes.
    • Sequential Markings: Markings on the cable used to determine the length of the run.

Connectors and Splicing Technology

  • Connector Standards:

    • MPO/MTP: An array connector used for high-density applications.
    • LC: A Small Form Factor (SFFSFF) connector requiring special adapters and cleaning materials.
    • SC: A standard connector type frequently used in building networks.
    • Mating Sleeves: Bulkhead mount adapters used to align the ferrules of two connectors.

  • Polishing and End-Phases:

    • APC (Angled Physical Contact): The end-face type that provides the lowest reflection.
    • Ferrule Bonding: During assembly, the ferrule is typically bonded to the cladding of the fiber.
    • Inspection: Connectors must be cleaned prior to mating. Minor defects are only allowed on the outer cladding when inspecting the end-phase.

  • Splicing and Losses:

    • Maximum Insertion Loss (Splice): Specified as 0.3 dB0.3\,dB by the TIA standard.
    • Maximum Insertion Loss (Mated Pair): Specified as 0.75 dB0.75\,dB by ANSI for commercial buildings.
    • Quality Factors: Cleanliness is the most critical factor for a good quality splice. For a proper cleave, the blade must be held perpendicular to the fiber.
    • Fiber Mismatch: This often occurs during automated or "splice-on" termination types.

Testing Procedures and Evaluation Tiers

  • Testing Tiers:

    • Tier 1: Requires optical loss testing and polarity verification.
    • Tier 2: Requires OTDROTDR testing.

  • Testing Equipment:

    • VISP (Video Inspecting Scope Probe): A safer tool for inspecting the end-phase of a fiber.
    • VFL (Visual Fault Locator): A non-intrusive device used to verify active traffic or troubleshoot in the 630−670 nm630-670\,nm range.
    • Attenuator: A passive device used to reduce the power level of an optical signal (contrasted with a repeater).
    • OTDR (Optical Time Domain Reflectometer): Used to test fiber spans, calculate loss per kilometer (dB/kmdB/km), and measure the total distance of the span.
    • Optical Power Meter: Used for acceptance testing, measuring and recording values in dB/kmdB/km.

  • Light Sources for Testing:

    • LED: Used to test multi-mode enterprise networks.
    • VCSEL (Vertical Cavity Surface Emitting Laser): Ideal wavelengths are typically below 850 nm850\,nm.
    • Mandrel Wrap: Used to reduce the number of high-order modes when testing multi-mode fibers.

Safety Requirements and Workplace Standards

  • Regulatory Agencies:

    • OSHA: The government agency that enforces safety rules in the workplace.
    • NEC/CEC: These codes apply mainly to public and private premises installations.

  • Laser Safety:

    • Infrared Hazards: Infrared lasers can be dangerous because they are invisible to the unaided eye.
    • Class 1: Refers to the lowest optical power level and fewest associated hazards.

  • Best Practices:

    • Waste Disposal: The best way to dispose of waste fiber is in a covered container clearly marked for fiber optic waste.
    • Chemical Safety: Safety Data Sheets (SDSSDS) or Material Safety Data Sheets (MSDSMSDS) must be available whenever chemicals are used.
    • Macro-bending: Improper bending of optical fiber may cause macro-bending losses.