Single Mode Fiber Coupling Sensitivities and Tolerancing Dec
Single Mode Fiber Coupling Sensitivities and Tolerancing Dec. 5, 2006 Lori Moore 1
Overview • Basic Definitions • Misalignments – – Lateral Angular Longitudinal Mode mismatch • Example Tolerancing Problem – Coupling between two single mode fibers in air • Figure of Merit – Coupling Efficiency – Why • Starting point for more complex systems • Non-linear tolerancing problem Dec. 5, 2006 Lori Moore 2
Single Mode Fiber Definitions Variables used • ωo = mode field radius (1/e 2) • n 0 = index outside of fiber • λ = wavelength Dec. 5, 2006 Lori Moore λ (um) ω0 (um) 1. 55 5. 25 1. 3 4. 65 1. 06 3. 1 0. 86 2. 5 0. 63 1. 85 3
Loss Due to Lateral Misalignment Dec. 5, 2006 Lori Moore 4
Loss Due to Lateral Misalignment λ = 1. 3 μm ω0 = 4. 65 μm Dec. 5, 2006 Lori Moore 5
Loss Due to Angular Misalignment Dec. 5, 2006 Lori Moore 6
Loss Due to Angular Misalignment λ = 1. 3 μm ω0 = 4. 65 μm Dec. 5, 2006 Lori Moore 7
Loss Due to Longitudinal Misalignment Dec. 5, 2006 Lori Moore 8
Loss Due to Longitudinal Misalignment λ = 1. 3 μm ω0 = 4. 65 μm n 0 = 1 Dec. 5, 2006 Lori Moore 9
Loss Due to Mode Mismatch Dec. 5, 2006 Lori Moore 10
Loss Due to Mode Mismatch λ = 1. 3 μm ω0 = 4. 65 μm n 0 = 1 Dec. 5, 2006 Lori Moore 11
Example Tolerancing Problem • Goal – Loss < 0. 46 d. B (10%) • Other constrains – Fiber to Fiber coupling – Wavelength = 1. 3 μm – Mode field radius = 4. 65 μm (1/e 2) – Gap material is air (n = 1) Dec. 5, 2006 Lori Moore 12
Perturbation Analysis Can’t Assume Linearity Dec. 5, 2006 Lori Moore 13
One Possible Solution Dec. 5, 2006 Lori Moore 14
Closing Remarks and References • Other issues to consider – – Dirt on fiber Burning the fiber with too much power Humidity Wavelength • References – OFR catalogue • http: //www. ofr. com/misc/OFR_2001_Fiber. pdf – Further Reading • For gaussian beam propagation – Lasers, A. E. Siegman (1986) especially Chapter 17 and 20 Dec. 5, 2006 Lori Moore 15
Conversion from Decibels to Transmission Percent Calculating Loss in d. B (Ld. B) Dec. 5, 2006 Calculating Loss in % (L%) Lori Moore 16
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