ECE230 Lab 3 - Lab 3 - fiber optic PDF

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Lab 3 - fiber optic ...

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ECE 230 Lab #3

I affirm that I have not given or received any unauthorized help on this assignment, and that all work is my own. Fiber Optics Transmission Lines Abstract Global communications relies greatly on Fiber Optics due to their large bandwidth, extremely low attenuation and resistance to any external and environmental damage (such as rain, dust and even thunder in some cases). This experiment studies attenuation in single-mode and multi-mode optical fibers. Singlemode cables have a small core that allow only one mode to propagate, therefore lowering loss over large distances. Multi-mode cables allow for multiple rays to propagate at the same time, still, they are not optimal for transmission in long distances. It can be hypothesized that longer wavelengths, lower attenuations, and single-mode fiber optic cables will have lower power loss in comparison to multi-mode cables, indistinctly of the lengths. Results show lower insertion loss in single-mode fiber at 31m and 61m cable lengths. Lower loss is observed with both cable types when longer wavelength was used at the light source. Inconsistent results raised at the 32m cable, which could be adjudicated by wrong connections being made between the meter and light source during experimentation. Introduction In recent times, Fiber Optics cables have risen to be one of the most used and efficient modes of communication. It offers many advantages over other forms of transmission lines due to their capacity to carry higher frequencies, which increases the ability for a TEM line to carry more information in short pulses. Such pulses are created by using LEDs that can rapidly turn on and off. The use of light to carry information forms the basis of how fiber optics cables function. Light guides, made of thin glass fibers are used to transmit signals over long distances and such method is free from disruption by any natural elements like dust, rain, etc. Fiber optic cables are known for their low attenuation, which makes them preferable to other alternatives, and splicing being one of it’s few disadvantages. Modes entering the cable (Figure 1) at different angles can cause a signal to “smear” at the output. One way to increase bandwidth in a fiber optic cable is to reduce the diameter, which reduces the number of modes. A single-mode fiber only has a diameter of 9𝜇𝑚 with thick cladding while a multimode fiber has a diameter of 62.5𝜇𝑚 with thinner cladding. Cladding in a cable is made of low-refractive material to keep light signal within the fiber. Bandwidths are measured in MHz per km. Insertion loss was measured using reference power value shown in equation 1 - where P0 is initial power at the detector and PM0 is initial power at the source monitoring equipment.

Figure 1: Schematic diagram of Fiber Optics Cable Signal traveling has a general path that begins by the input signal being modulated light in the optical transmitter (optical transmitters typically operate at 850nm for short distance and 1300 or 1550nm for long distance). Then, the light signal travels through the cables and eventually is then demodulated at the optical receiver through high gain amplifiers. Several stages in the amplifier help reconstruct the original signal. A hypothesis can be presented, based on the previous background information, that a single-mode fiber will show lower attenuation (power-loss) compared to a multimode cable. We can also infer that longer wavelengths lead to lower attenuation in fiber optics cables. Procedure This lab tests insertion loss in Single-Mode and Multi-Mode fiber optics cables. To measure power loss in various lengths of the given cables, the FLUKE Networks SimpliFiber Pro Fiber test kits is utilized, which includes an optical power meter and a multi-mode light source. A 1m reference cable was attached to the meter for reference measurements. Insertion loss measurements were taken relative to the reference value (specific to cable type and wavelength of test signal) at 31m, 32m, and 61m ( taking in account the reference 1m cable). One end of the cable was attached to the meter and the other to the reference cable. The reference cable remained attached to the light source for all insertion loss measurements. All cable connections were made using corresponding SC-SC. Reference values and insertion loss values are summarized in the Results section. Results Table 1: Reference measurements for Multi-mode optical fiber cable (orange) 850 nm

-20.85 dB

1300 nm

- 20.54 dB

Table 2: Power loss in Multi-mode optical fiber cable (orange)

Length

850 nm

1300 nm

31 m (1 short + 1 long)

0.11 dB

0.08 dB

32 m (2 short + 1 long)

1.13 dB

0.37 dB

61 m (1 short + 2 long)

1.19 dB

0.22 dB

Table 3: Reference measurements for Single-mode optical fiber cable 1310 nm

-7.72 dB

1550 nm

- 7.62 dB

Table 4: Power loss in Single-mode optical fiber cable Length

1310 nm

1550 nm

31 m (1 short + 1 long)

0.06 dB

0.51 dB

32 m (2 short + 1 long)

10.71 dB

0.51 dB

61 m (1 short + 2 long)

0.83 dB

0.74 dB

Discussion A reference cable and observing reference power value were attached to get the initial measurements and account for connection losses. Insertion losses are also relative measurements that show difference between input power and the power transmitted through it. SC-SC were used to connect cables and manipulate the total length. The value was saved on FLUKE Pro-optical power meter and all corresponding values recorded in distinct table (1, 2, 3 and 4) Single-mode optical fibers typically have a core of < 10𝜇𝑚 and allow one mode of light to travel, which allows a larger bandwidth and lower power loss. Consequently, they are generally made and used for long distance communications. Multi-mode cables have a larger core and allow for multiple modes to be guided at the same time, making it less-costly than single-mode fibers, however, due to eventually resulting in strong attenuation, they are used for short distances. Some factors that limit optical transmission distance are the type of cable, light source, frequency and connections between cables. The distance an EM wave can propagate without significant power loss can be approximated by skin depth. Skip depth is the point in the material where current density is roughly 37% of the value at the surface, 𝐽0 and is dependent on the physical properties of the cable (Equation 2).

When comparing single and multi-mode cable loss around 1300nm range, the single-mode cable had lower attenuation compared to the multimode cable at the lengths 31m 𝑎𝑛𝑑 61m. At the 32m, power loss was higher at the single-mode cable. In Table 4, when comparing the 1310nm and 1500nm wavelengths

when using a Single-mode cable, we can observe a disagreement to the assumption that longer waves have lower attenuation. These results are against the norm of lower attenuation in single-mode cables due to their smaller core. An important factor to consider is the quality of the reference cable, which the power-loss reference values are dependent on. For such reasons, we can deem possible that the inconsistent value was obtained due to using a second reference cable to create a 32m long cable without knowing its reference value/quality. Other factors of attenuation alteration may be the connections between cables, excessive bending or coupling of LED source onto the cable. Despite these exceptions, the general results show lower insertion loss at longer wavelengths, which is consistent with the hypothesis established previously. Additionally, we can compare the standard specification for single mode cables to the results of this experiment. The specifications for single-mode cable state an attenuation of 0.35dB/km at 1310nm. It can be calculated that the maximum communication distance is ~2.86𝑘𝑚 without any rectifiers along the line. The specifications for a 62.5𝜇𝑚 cable states an attenuation of 0.6 dB/km at 1300nm therefore skin depth distance is ~1.67𝑘𝑚 without severe single loss. Once again, the values demonstrate that single- mode optical fibers are more ideal for long distance communication, and confirm our viable calculations. Conclusion The results are consistent with the knowledge that single-mode fibers have lower attenuation than multimode fibers. Other literature agrees that single-mode optical cables are ideal for long distance communication and usually propagate at 1300nm and 1550nm wavelengths. Error in which higher attenuation was observed in single-mode fiber may be due to the unknown quality of the second reference cable used to create a 32 m cable.

Citations Draka Single-Mode Fiber, Specification Sheet, Link: hhtps://www.prysmiangroup.com/sites/default/files/business_markets/markets/downloads/data sheets/SMF---Single-Mode-Optical-Fiber-SSMF.pdf Fernandez-Canque, Hernando Lautaro and ProQuest (Firm). 2017;2016;. Analog Electronics Applications: Fundamentals of Design and Analysis. Boca Ratón, FL: CRC Press. Lab 3 Manual, PDF File, Lab3_ECE230_Fall2020.pdf OFS Optics, Choosing between Single Mode vs Multimode Fibers, https://www.ofsoptics.com/single-vs-multimode-fiber/...