Category Archives: Fiber Optics

Fiber Optic Deployment Woes

We recently had a customer who reported that one of our products was reporting low RF video output power. This normally is caused by an issue with equipment setup, but everything this customer did was fine. It turned out that … Continue reading

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Laser Slope Efficiency and Curve Fitting

Introduction I have spent much of my summer dealing with issues related to the high temperature characteristics of lasers. These issues have stirred within me an interest in laser slope efficiency . Slope efficiency, also known as SE, is simply … Continue reading

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Laser Tracking Error and Curve Fitting

Introduction I had a request for an example of how the output power of a laser varies with temperature. We call this parameter tracking error. Tracking error varies from part to part and the manufacturers simply put a bound on … Continue reading

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A Little Specification Reading Before Bed

Nothing like reading ITU optical specifications to help you get to sleep after an active day. Since I have been doing some work on dispersion, let's pull up ITU G.695 - Characteristics of Optical Systems. I want to see if the work published in my previous blog posts on dispersion are consistent with what is contained in an industry standard. This will be a fairly brief post, but it will pull together the information from several previous posts. Continue reading

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Optical Fiber Dispersion Formula - Where Did This Come From?

Most Fiber-To-The-Home (FTTH) deployments in North America use SMF-28e fiber from Corning, which is to fiber what Kleenex is to tissue. Unfortunately, I am so familiar with this particularly product that I can recite its specifications from memory. However, there is one aspect of SMF-28e's datasheet that I have never really understood – the chromatic dispersion formula shown in Figure 1. This formula is used to determine the fiber parameter D(λ), which specifies the travel time difference (in picoseconds [ps]) for photons that differ by 1 nm in wavelength over 1 km of fiber. Continue reading

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Some Laser Basics

Introduction I am doing some interesting work with lasers this week. I thought it would be useful to provide some background on how we build and control lasers. We deploy a lot of lasers in outdoor applications, which means that … Continue reading

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The Power of a Simple Magnifying Glass

Introduction My favorite radio program is Science Friday. Last week, their web page included an excellent video where Science Friday's resourceful intern, Flora Lichtman, gave a wonderful explanation behind the use of a lens to concentrate the Sun's power. Her … Continue reading

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Test Time and Estimating Bit Error Rate

Test time is expensive. Since our products need to conform to industry standards for Bit Error Rate (BER), we need to test for BER. It is important that we test long enough to ensure that we meet the requirements, yet not so long as to spend more money than we need to. Continue reading

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Laser Failure Rate Estimate Example

I have spent some time lately talking to people about laser failure characteristics. Most electronic component reliability modeling is done using the exponential probability distribution, which assumes the components have a constant failure rate and there is no wear-out mechanism. It turns out that lasers have a wear-out mechanism, which means the exponential probability distribution is not appropriate. Laser failure rates are usually modeled by a lognormal probability distribution, as are the failure rates of brakes (Figure 1) and incandescent light bulbs. These components have reliabilities that are dominated by wear-out mechanisms that accelerate when damage to a small region grows exponentially. A good example would be a hard spot on a brake pad that becomes hot during braking relative to the rest of the pad. This hard spot tends grow quickly because the heat generated during braking concentrates there. Continue reading

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Magic Number Analysis – Converting Spectral Width to Sigma

Introduction Engineering seems to have a lot of "magic numbers" – numbers used in equations with no explanations of where they come from. I REALLY do not like magic numbers because years from now some other engineer will be staring … Continue reading

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