A Comprehensive Overview of Fiber Optic Technology

• According to the function

  According to the function or mode of transmission, there are two main types of optical fiber. The mode is basically the path through which the light beam travels. The following are two types of an optical fiber according to function or mode of transmission.

  • Single-Mode Fiber Optic Cables: As the name suggests, the single-mode fiber optic cable has only one mode of transmission. It generally has only one optical strand via which the light beam travels. Single-mode optical fiber typically features a relatively narrow core diameter of size 8.3 to 10 microns. The speed of transmission in this type of optical fiber is over 1310nm to 1550nm. There are further 2 categories of single-mode fiber, detailed as follows.
    • OS1: OS1 is a type of single-mode fiber optic cable that features 8-9µ core diameter but the attenuation in this type of cable is high. Therefore, over the distance, the light signal starts dispersing or losing its strength due to high attenuation. This cable is generally used in internal and short distance fiber optic networking.
    • OS2: OS2 is another type of single-mode fiber optic cable that features the same diameter as OS1 but has lower attenuation. Due to this, the signal strength in this type of fiber remains consistent from the transmitter to the receiver. Therefore, this OS2 single-mode fiber optics is used for outdoor and underground signal transmission.

    Note: Here, in OS1 and OS2, OS stands for optical single-mode.

    Single-mode fiber optic cables are used for telephone and Internet applications.

  • Multi-Mode Fiber Optic Cables: A multi-mode fiber optic cable features a core that is 10 times larger as compared to a single-mode fiber optic cable. This type of fiber optic cable enables multi-mode transmission through the core. This means the light waves can travel in several different paths through the core only. Multimode fiber optic cables are used for short-distance data transmission like the interconnection of two different networking devices. Multi-mode fiber optics are further categorized based on different criteria, namely fiber characteristics and core diameter.
    • Fiber characteristics: Refractive index is a characteristic of optical fiber that impacts the path of transmission. Due to the low refractive index of cladding, the light rays reflect back to the core. This defines two different types of multi-mode fibers based on fiber characteristics.
      • Multi-Mode Graded Index Fiber:  Graded index optical fiber features graded refractive index. In this fiber, the refractive index diminishes gradually from the core to the cladding. This way, the core possesses the highest refractive index causing light waves to return back to the core in case of path change. Due to this phenomenon, the light waves generate a semi-elliptical wave path inside the fiber. This reduces the dispersion of light and attenuation as well.
      • Multi-Mode Step Index Fiber: This type of fiber has a large core diameter of about 100 microns. Due to this, there is a fluctuation in the refractive index at multiple points inside the core. Therefore, the light waves that form digital pulsation can travel straight inside the core but others travel in a zigzag manner. This causes dispersion and change in the speed of different light waves. Due to the high dispersion, all light waves reach at receiving point at different times. This may cause loss or absence of data at specific times. However, for short-distance applications like endoscopy, this type of fiber optic cable is suitable.
      • Core Diameter and Feature Bandwidth: The following are types of multi-mode fiber optic cables depending on core diameter and bandwidth. The types, core diameters, and featured bandwidths are listed in the table below.
        

        Type of Optical Fiber	Core Diameter (µm)	Feature/Bandwidth
        OM1	62.5	Higher bandwidth FDDI-Grade Cables
        OM2	50	High control over light propagation
        OM3	50	Optimized for lasers
        OM4	50	Higher bandwidth and longer reach as compared to other types.

        Note: Here, in OM1 and OM2, OM stands for optical multi-mode.

• Number of Fiber Strands

  Depending on the number of strands, the capability of a fiber optic cable differs, therefore the following are the types based on the number of strands.

  • Simplex Fiber Optics Cables: Simplex fiber optics cables enable data transmission in a single direction.
  • Duplex Fiber Optics Cables: Duplex fiber optic cables are 2-strands that provide bi-directional communication. In this case, a transmitter and a receiver are interchangeable. In full-duplex mode, the cable allows bi-directional transmission simultaneously. However, in half-duplex mode, the bi-directional transmission is possible but at different time span.

• Construction

  According to constructional design, the following types of multi-mode fiber optics cables are found.

  • Loose Tube Fiber Optic Cables: In this type, a plastic buffer tube houses the fiber optic cable. The gel material is filled between the internal diameter or buffer tube and the outer diameter of the cable jacket to prevent water intrusion. The buffer tube is then stranded with a dielectric material to create an anti-buckling structure. These types of cables are suitable for outside and underground applications.
  • Tight-Buffered Fiber Optic Cables: In this type, there is no gap between the buffer tube and the fiber optic strand. Due to the direct contact, this type of cable can be used for plenum connections in the presence of air media or for outside equipment connection.

• Core: Core is the main component of fiber optic cable construction. It is basically the medium via which the light signal is transmitted. This is the main glass-drawn strand of fiber optics that possess an outer diameter of sizes 9µ, 50µ, 62.5µ and 100µ. Since the outer diameter of the core is in microns, it is the smallest yet most important component of fiber optic cable.
• Cladding: Cladding is the casing that acts as shielding or boundary to the photons to travel inside the fiber channel only. It causes refraction and prevents light waves from optical scattering.
• Coating: Coating is a plastic casing that bounds the core and cladding together. It acts as a reinforcing medium to keep the core intact and offers extra protection against optical scattering. The coating is made in thickness between 250 to 900 microns.
• Strengthening Fiber: Strengthening fibers are the components that help protect the core. It protects the fiber optic core from excessive tension during installation and external crashing forces. Strengthening fiber acts exactly as the name suggests, it strengthens the core for appropriate light signal transmission. Generally, Kevlar® is the material used for strengthening fiber.
• Cable Jacket: Cable jacket is the outermost layer of a fiber optic cable. The jacket offers protection against external forces. The cable jackets are color-coded according to the type of cable. Common color-codes of fiber optic cable jackets are black, yellow, and orange.

• The signal transmission phenomenon of fiber optics is a function of total internal reflection.
• Basically, fiber optic transmits data in the form of a photon beam that is a light wave. Reflection and refraction are characteristics of the light wave.
• When the light beam enters the core diameter, it incidents on the core at a small incident angle.
• However, due to the low refractive index of the cladding material, the light beam faces total reflection inside the core. This is called total internal reflection.
• Due to the high incident angle than the critical angle, the phenomenon of total internal reflection repeats periodically causing the light beam to travel in a zigzag manner.
• By following the total internal reflection several times, the light beam reaches the receiving end of the fiber.  

• Fiber optic transmission of telecommunication signals is a full-duplex action. The fiber optic cable is integrated with a transmitter at the input end and a receiver at the output end.
• The transmitter gets the telecommunication audio signal in the form of electric waves.
• The transmitter converts the signal in the form of an optical wave as the transmitter consists of semiconductor LEDs or laser sources.
• The optical conditioned beam is relayed via optical fiber ensuring there is no dispersion, distortion, or diminishing of the signal to avoid data loss.
• As the light wave reaches the receiver, the signal is deconditioned to the electrical signal. However, the receiver catches the signal by using semiconductor photodetectors, and further, the data is converted into an electrical signal by a fiber optic converter.

• Splicing: Fiber optic splicing is a technique in which two fiber optic cables are aligned to transmit data. The centerline of both fiber optic cables is aligned which means the cores are set inline for dispersion-free data transmission.
• Termination by connectors: The fiber optic connectors are plug and play type. They act as a linking intermediate device for two fiber optic cables. Depending on the type of the connector, the fiber optic cables can be screwed, latched, or snapped-in together. The following are a few popular types of fiber optic connectors used today.
  • Plastic Fiber Optic Cable Connector
  • Bionic Connector
  • ST Connector (ST)
  • Standard Connector (SC)
  • Ferrule Core Connector (FC)
  • Lucent Connector (LC)
  • LX-5 Connector
  • MU Connector
  • MPO Connector
  • Enterprise Systems Connection Connector (ESCON)
  • Opti-Jack Connector
  • Fiber Distributed Data Interface Connector (FDDI)
  • LX-5 Connector
  • MT-RJ Connector
  • MT Connector
  • E200 Connector

• Bandwidth: Fiber optics offers high bandwidth. It can transmit data with frequency up to 2 x 104 Hz.
• Throughput: Fiber optics offer excellent throughput, as it can transfer up to 100 Gigabits per second in a channel.
• Noise Immunity: Fiber optics cables are immune to external noise and other environmental interruptions. As these cables do not use electric signals for signal transmission, they remain unaffected by EMI.
• EMI/RFI Immunity: Fiber optics are highly immune to electromagnetic and radio frequency interference. This helps in uninterrupted signal transmission via fiber optic cables.
• Negligible Transmission Losses: Owing to noise and EMI/RFI immunity, the data loss in fiber optics is negligible. Transmission loss in fiber optics cable is as less as 0.1 dB/km.
• Size and Scalability: A fiber optic cable is compact- sized as compared to a copper cable. Also due to less data loss during transmission, the fiber-optic network and data transmission speed are scalable from 150 meters to 40000 meters.
• Connector Compatibility: Fiber optics cables are highly compatible with a wide range of connector types, old and new. These cables are compatible with ST, LT, MT-RJ, LC, and many more types of connectors.

• ITU Standards: These standards are established by the International Telecommunication Union. Since telecommunication is one of the most prominent applications of fiber optic technology, these standards are followed by telecommunication resource suppliers. These standards specify fiber optic design characteristics and dispersion curve in order to achieve the highest transmission rates.
  • ITU G.651.1: This standard specifies design and performance specifications for multi-mode graded-index cable for transmission at rate 850nm or 1350nm.
  • ITU G.651.2: This standard addresses the single-mode fiber, its MFD, and ZDW. The fiber has a mode field diameter (MFD) to fit into the zero-dispersion window (ZDW).
  • ITU G.651.3: It gives specifications for dispersion-shifted single-mode fiber to fit into the zero-dispersion window (ZDW).
  • ITU G.651.4: This is a standardization for cut-off-shifted single-mode transmission. It is to allow higher mode transmission at lower transmission loss limits.
  • ITU G.651.5: This standardizes the fabric for non-zero dispersion-shifted highly rated transmission.
  • ITU G.651.6: It states the standards for CWDM/DWDM transmission at high transmission rates.
  • ITU G.651.7: It states the operational characteristics for bending-loss intensive single-mode fiber optic installation.
• IEC Standard 61300-3-35: This is an inspection standard that is set to ensure the general performance level. It inspects the cable for loss, returns loss performance, and connectivity with several types of connectors.

Applications of Fiber Optics

The fiber optics technology is implemented across several industries. The following are a few common applications of fiber optics.

Conclusion:

Owing to its beneficial features and customizable capabilities, fiber optics technology has been widespread over the globe. Due to the signal transmission at the speed of light, this technology has paved its way to several industrial applications for audio, video, and image signal transmission in the form of light waves. The fiber optics are used in computer networking, as well as in the electronics and broadcasting industry for optimizing connections and speed of data transfer. The telephone companies are slowly adopting this technology, which suggests, they will continue to lead the communication industry for several years. To gain more information about fiber optics technology and related products, please visit/contact VERSITRON at https://www.versitron.com.

Disclaimer

The information provided in this white paper is intended solely for general information purposes. The practice of Engineering differs across each project, as it is driven by site-specific circumstances. Thus, any business decision based on the implementation must be taken only after consultation with a qualified and licensed professional who is capable of addressing all relevant factors, challenges, and desired outcomes. The information in these white papers is derived from various verified sources and posted after reasonable care and attention. It is possible that some information may appear incomplete, incorrect, or inapplicable considering your particular condition. In such a condition, VERSITRON does not accept the liability for direct or indirect losses resulting from using, relying, or acting upon the information in this white paper.