Category Archives: optics

Optical Fiber Attenuation Specifications

I needed to estimate the loss on a fiber network today – something that I have done hundreds of times before. However, today was a bit different because I decided to look at how sensitive my results were to my assumptions on when the fiber was deployed. I was a bit surprised to see how much fiber has improved with respect to losses due to contamination by OH molecules, a problem often referred to as the water peak. Continue reading

 
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Computing Lux Level Given A Lamp's Power Spectrum

I have assigned my interns a couple of simple design tasks – one of the tasks involves performing measurements on that amount ambient light that leaks into our enclosures. This task is going to provide data that will drive the design of a simple ambient light sensor for use within our enclosures to tell if the door has been opened. Open door sensors are a notorious source of false alarms. We used to use mechanical/magnetic sensors, but they proved to be unreliable. We are now looking at using ambient light sensors. Continue reading

 
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A Quick Look at Wavelength Crosstalk

I was reviewing an industry standard when I saw Figure 1, which clearly looked wrong – the asymptotes seem like they are in the wrong place. I decided to take a closer look at this figure and see if I could determine what the correct version of this chart would be. Continue reading

 
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Relative Sizes in Photographs Can Be Deceiving

I often see photographs that appear to show objects with different size relationships than we usually see. In Figure 1, for example, we see the Moon as nearly the same size as the sailboat. This happened because the sailboat is some distance from the camera and its angular extent is comparable to that of the Moon. Continue reading

 
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Samsung S5 Field of View

I use a Samsung S5 phone for my daily smart phone work. Recently, I have even started to use its camera/video system for some rough measurement work (examples here and here). This work has made me a bit curious about the how the camera subsystem was designed. In this post, I will document a very rough experiment that I performed over lunch today in which I measured the S5 camera's Field of View (FOV). I will also compute the field of view using some information that Samsung provides. The agreement between the results seem reasonable considering my crude approach. Continue reading

 
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Lighthouse Visual Ranges

Yesterday, I received a question from a reader who was puzzled by a web page written by a flat earther that presented a seemingly rational argument in favor of the flat earth position. In a nutshell, the flat earther's argument says that to see a lighthouse at long distance on spherical Earth would mean that you would have to be able to see around the horizon. Therefore, the Earth must be flat. I may be mischaracterizing their argument, so you may want to visit web sites that go into the details of the flat earth rationale. Of course, I argue that refraction can literally allow you to see "around" the horizon. Continue reading

 
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Designing an LED Backlight

I was reading an application note by Texas Instruments yesterday on how to design an LED backlight for an LCD display (Figure 1). The article was interesting, but it did bother me because it presented a rather involved formula and did not provided any motivation for the formula, a derivation, or even definitions of the parameters used in the formula. Continue reading

 
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Using a Laser To Deliver Multi-Channel, Broadcast Video

Introduction Everyday, I work on delivering fiber-based, video access equipment to service providers. The increased demand for High-Definition Television (HDTV, Figure 1) has increased the need for fiber in the video distribution network. Today, fiber optic cable is often used … Continue reading

 
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Spy Camera Math

Introduction I just listened to a very interesting interview of Philip Pressel, a retired Perkin-Elmer mechanical engineer and satellite surveillance camera designer. The interview was conducted by Vince Houghton of the International Spy Museum. Philip discussed how the recently declassified … Continue reading

 
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Optical Power Budgets and A Quick Dispersion Calculation

For those who are not familiar with dispersion, take a look at Figure 1, which provides a qualitative view of dispersion. The digital data can be view as a stream of optical power pulses, ones being represented by power and zeros represented by near zero power. The pulses of optical power can be viewed as composed of a range of wavelengths (i.e. color). The different colors all move at different speeds along the fiber. This speed difference causes the pulse to spread out as it travels down the fiber. As the pulses spread out, they begin to overlap each other and their power levels reduce. This makes detection less reliable and is one of the fiber impairments that limits the range and data rate of optical fiber. Continue reading

 
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