Variable Optical Attenuators

Posted on July 8, 2014 by admin

An optical attenuator is an electronic device commonly used to decrease the level of power of an optical signal in a fiber optic communication system. In fiber optics, attenuation is also called transmission loss. It is the reduction in light signal intensity with respect to the distance traveled by the signal in a transmission medium. Attenuation is an important element to limit the transmission of a digital signal traveling in large distances. An optical attenuator reduces this optical signal as it travels along a free space or an optical fiber.

Optical fiber attenuators may employ several principles when used in fiber optic communications. One common principle is the gap loss principle. Attenuators using this principle are sensitive to the modal distribution ahead of the attenuator. Thus, they should be utilized at or near the transmitting end. If not, the attenuators could establish less loss than intended. This problem is avoided by attenuators that use absorptive or reflective principles.

There are three basic types of optical attenuator: the fixed attenuator, step-wise attenuator and the continuously variable attenuator. Fixed attenuators reduce light signals by specific amount with negligible or no reflection. Because signal reflection is not an issue, fixed attenuators are known for more accurate data transmission. Important elements associated with fixed attenuators include the flatness over a specified frequency, range, voltage standing wave ratio (VSWR), amount of attenuation, average and peak power-handling capability, performance over a specific temperature, size and height. Fixed attenuators are also often used to enhance interstage matching in an electronic circuit. Thorlab’s fixed attenuators are available from 5 dB to 25 dB. Mini-Circuits’ fixed attenuators are packaged in rugged plug-in and connector models. They are available in both 50- and 76-ohm models ranging from 1to 40 dB spanning DC to 1500 MHz.

In variable optical attenuators (VOA), resistors are replaced with solid state devices such as the metal semiconductor field effect transistor (MESFETs) and PIN diodes. VOA attenuates light signal or beam in a controlled manner, thus producing an output optical beam with different attenuated intensity. The attenuator adjusts the power ratio between the light beam coming from the device and the light beam entering the device over a changeable rate. VOA is usually used in fiber optic communication systems to regulate optical power levels in order to prevent damages in optical receivers which may be due to irregular or fluctuating power levels. The price of commercial VOA varies depending on the manufacturing technology used. Some of manufacturers of VOA are Timbercon and Arcoptix.

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A brief description of theSingle Mode Visible Wavelength Couplers

Posted on July 4, 2014 by admin

On-page content and optimization by itself is no longer enough. Unfortunately, link popularity has become a dominant factor in deciding who ranks the highest within the major search engines, especially within Google. If a competitor of yours is both optimized for the same target search terms and has a higher quantity and/or higher quality of back links, they are going to outrank you: period. Even if your website is perfectly optimized for an extremely niche search term and no other site in the world even mentions your exact phrase, you may still have trouble finding your website if you do not have at least a few back links to “validate” your website.

If it came down to a contest between on-page optimization efforts against link building efforts, links would win hands down. You may find it shocking to hear a President of an optimization firm saying such a thing, but its true. I would challenge anyone to outrank a website that has a massive number of quality back links by using on-page optimization efforts alone with zero link building efforts. Whereas, you can easily outrank a website that is extremely well optimized by focusing heavily on link building efforts. An interesting example is Apple.com. One of the most important elements of optimization is to place the target key phrase within the meta title tag. However, search for the word “computers” on Google and you will find Apple.com on the first page of results. Apple does not even mention the word computers in their meta title tag. How is this possible when there are literally millions of competing websites that are aggressively trying to show up for this term by applying various optimization efforts? The answer is that Apple.com has a superior volume of back links (over 70,000 in Google alone). And a large percentage of these links include the word computers within the anchor text (i.e. Apple Computers, Mac Computers, etc.).

Does this mean Optimization is dead?

The answer of course, is no. Search engines still love websites that have tons of fresh and relevant content. It is the basis of what search engine results are all about. Copywriting fees are worth every penny when it comes to adding well written descriptions of your products and services onto your website. Professional optimization companies still flourish because of the success they bring to their clients through increased rankings and traffic. For optimum results, you need both optimization and links to succeed today.

It’s not just the quantity of incoming links, but the quality and relevance of the websites from which they come, as well as what words are used within the visible text portion of the hyperlinks, i.e. “anchor text.” Reciprocated links have less value than they use to and can potentially hurt your rankings if you are exchanging with too many unrelated websites, i.e. bad neighborhoods. One-way links are the best links.

During the last few Search Engine Strategies conferences, I could not help but notice an increasing number of link-related workshops, including a class dedicated to purchasing text links. Matt Cutts, official spokesman and software engineer for Google shared how he personally believes that buying links is like a politician buying votes and that incoming links should only grow naturally. He shared that the best way to receive incoming text links was to offer something truly helpful and/or unique and interesting to the public and that this would generate free unsolicited, incoming links without even asking. He offered some extreme examples of very creative websites, which caused a national media stir. Within minutes frustrated attendees spoke up about how the search engines started this whole thing by giving too much criteria to links in the first place, and that buying links on other sites (be it through banners or text links) has been a conventional form of advertising well before Google even existed.

Some commented that if Google was considering penalization for sites that buy or sell links, they should start with Yahoo, since Yahoo earns a good portion of their income from selling paid text links (i.e. $299/year directory listings). Interesting enough, Google actually recommends on their website that you submit to directories such as Yahoo.

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Single Mode Visible Wavelength Couplers

Posted on July 3, 2014 by admin

It is easy to blame weight gain on to a slow metabolism and the exercise environment for the last 40 odd years has allowed much of this to occur. Although many people exercise they are most often are doing things that do not contribute to the strong lean and slim body they desire.

For years the idea that low intensity, long duration, single mode, so called ‘fat burning’ models of exercise have existed which we now know do not give us the true health and fat loss results that we expect.

We have previously been mainly focused on simply ‘burning off’ calories while we are exercising yet we really need to be performing the type of exercise that tells our body to grow, to build new metabolically active tissue that has us running at a higher metabolic rate all day and all night long.

This means we can ‘teach’ our body to be a more efficient fat burning machine as we now have the knowledge and understanding or how exercise impacts on our hormones and metabolism. But for this to be truly effect the exercise that we do has to be intense enough cause mechanical and metabolic muscle failure to stimulate the hormones that cause a ripple affect that lasts long after the exercise session has ended.

Long duration activities do not do this and when we stop doing them our metabolic rate goes back to our old slowed level and does not burn as much fuel as it could be if we changed our exercise regime.

Proper strength training exercise that directly targets the muscles offers exactly what we need to boost our metabolism for maximum health benefits or fat loss. Strength training offers short duration, high intensity exercise that can give us as much as three times the results in half the time of old fashioned low intensity activities.

You are really training for the metabolic effect that offers a real body transformation and strength training is perfect for people frustrated by cook-book exercise prescriptions that are so ineffective and time consuming. This knowledge is going to be of great help to gyms and healthcare providers in the future to combat the massive growing epidemic of overweight people that now number two thirds of the population.

Strength training exercise is so effective in making the changes to the metabolism right down at cellular level where it really matters only a little is needed. Just 2-3 sessions each week done with enough intensity (degree of effort) used will give a huge boost to the metabolism.

Imagine just boosting the rate your body burns fuel by as little as 5 percent and it is possible to increase the ‘burn’ up to 15 percent. This is where you will get long-term fat loss from as your body chews up that stored energy for fuel for the muscles to use.

If you are not already get yourself started on a strength training program and use it as your number one exercise regime doing it first and foremost each week. You will be delighted when you finally start to see visible and measurable results. Give it some time and slowly you will have your slim trim body returned to you for good.

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850nm Fiber Optic In-line Polarizer

Posted on July 2, 2014 by admin

A fibre optic cable tester is a hand-held troubleshooting device that sends red light from a semiconductor laser (635nm) down a fiber to check for faults such as cracked fibers or defective splices.

The visible red light travels along the fibre core until it reaches a fault, where it leaks out of the fiber. Light leaking through the fault can be seen through plastic coatings and jackets under suitable illumination. Infrared light in the signal leaks out at the same point, but your eyes cannot see it. The tester emits Class II red laser beam, making the light escaping from the damaged fiber easily visible from a distance.

Attenuation of glass fibres is much higher at 630 to 670nm wavelengths of red light than in the 1300 to 1650nm transmission window, but the red light can still travel up to 5km through standard fibers. Note that the fibers must be exposed to use fiber optic cable tester effectively. If the red light leaks out inside a thick cable wrapped in black plastic, you can’t see it.

This technique is particularly valuable in equipment bays and other places inside buildings where fibres are exposed.

Shining a flashlight beam down a multimode fiber can serve the same function, and has long been used to trace fiber continuity as well. However, the flashlight couples little light into a single mode fiber.

Whether installing or troubleshooting, the fiber optic cable tester is an essential tool that quickly and easily locates problem areas in fiber cables. By pinpointing the exact location of fiber damage, technicians can diagnose, troubleshoot, and fix the problem effectively. The cable tester is also used for conducting continuity tests and performing fibre identification.

The Continuous/Flash control button lets operators choose between continuous or flashing illumination.

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Single Mode Visible Wavelength Couplers

Posted on July 1, 2014 by admin

As the technology of laser marking has advanced, new markets have evolved to take advantage of increasingly faster marking speeds as well as greater marking precision and imaging capabilities. Continuing developments in laser-cavity design, beam-steering and focusing optics, and computer hardware and software are expanding the role of the systems.

Steering the beam

Of the available marking technologies, beam-steered laser marking systems provide users with the greatest amount of image flexibility in a fast, permanent, noncontact marking process. As manufacturing processes become more automated and after-sale tracking more prevalent, laser markers are frequently the only method available to produce individually unique, permanent images at high speed.

Beam-steered laser marking systems usually incorporate either a CO2 or Nd:YAG laser. The CO2 laser emits a continuous-wave output in the far-infrared (10.6-um wavelength) while the Nd:YAG laser emits in the near-infrared (1.06 um) in either a CW or pulsed mode (1 to 50 kHz). The Nd:YAG laser is also unique in its ability to produce very short, high-peak-power pulses when operated in the pulsed mode. For example, a typical 60-W-average-power Nd:YAG laser can produce peak powers on the order of 90 kW at 1-kHz pulse rate.

The delivery optics consist of either a simple focusing lens assembly or a combination fixed upcollimator and flat-field lens assembly. In either instance, the laser beam is directed across the work surface by mirrors mounted on two high-speed, computer-controlled galvanometers.

The simple focusing assembly offers the advantages of low cost and fewer optical components and is routinely used with CO2 lasers. The flat field lens design, though more expensive, maintains the focal point of the marking beam on a flat plane for more consistent image characteristics throughout the marking field. The flat-field lens also produces higher power density on the work surface than the simple focusing assembly due to the shorter effective focal length. The flat-field lens design is always preferred for high-accuracy and high-image-quality applications and is usually incorporated with Nd:YAG lasers.

Both designs provide the user with a selection of lenses that establish both the diameter of the marking field and the marking-line width. Longer-focal-length lenses provide larger working areas, but the line width is also enlarged, thus reducing the power density on the work surface. The user must compensate by either increasing the laser output power and/or decreasing the marking speed which usually consists of two lenses and may be placed anywhere in the beam path before the focusing lens. A beam expander often is used instead of extending the beam path approximately 10 more feet, in which the beam expands through its inherent tendency to diverge as it exits the resonator cavity. A spatial filter inserted within the beam expander produces the best mode quality in close-coupled systems, by passing the beam through a small aperture.

The last optical element that a laser beam encounters is the focusing lens. With CO2 lasers, this lens is usually made from one of several materials: Zinc selenide (ZnSe), gallium arsenide (GaAs) or germanium (Ge). ZnSe, a dense, yellow material that is transparent to visible wavelengths, is by far the most common of these materials, and it allows a low-power, HeNe laser beam through for alignment purposes. This is a great advantage over GaAs or Ge which are opaque to light from the visible portion of the spectrum.

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850nm Fiber Optic In-line Polarizer

Posted on June 27, 2014 by admin

FC fiber optic attenuators are very popular in telecommunication networks. They are used to reduce optical light intensity for optimal operating condition or to equalize optical power across light wavelengths in a WDM (Wavelength Division Multiplexing) fiber system.

FC optical attenuators come in several types for a variety of applications.

:: Male to Female Doped Fiber Plug Type FC Fixed Attenuator

This type of attenuators are also called build out types. They contain doped fiber suitable for both 1310nm and 1550nm operation. Fixed attenuation values are available in 1dB increments from 1 to 20dB.

The build out FC attenuators are installed between an mating sleeve and a connector (plug). Because they are based on doped fiber, this type of attenuators have exceptional optical performance and reliability.

:: Female to Female Absorption Filter Adapter Type FC Fixed Attenuator

This type of attenuators are also called bulkhead type. They incorporate absorption filters in the centers of the adapter housings. In use, the filters are interposed between the end-faces of mating plugs.

Bulkhead attenuators utilize a wavelength sensitive neutral density filter to achieve attenuation. They can be inserted easily between jumpers or permanently mounted in a fiber distribution cabinet. This type of FC attenuators can be used for either multimode or single mode applications.

They use a filter to induce attenuation and are wavelength dependent, so you need to choose between 1310nm or 1550nm versions.

:: Applications

FC attenuators are widely used in telecom and data networks, power equalization in DWDM networks, CATV and multimedia applications, testing instruments, Fiber to the Home, and more.

Colin Yao is the sales manager at Fiber Optics For Sale Co. and an expert on optic cabling technologies and products.

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Single Mode Visible Wavelength Couplers

Posted on June 26, 2014 by admin

An optical attenuator is an electronic device commonly used to decrease the level of power of an optical signal in a fiber optic communication system. In fiber optics, attenuation is also called transmission loss. It is the reduction in light signal intensity with respect to the distance traveled by the signal in a transmission medium. Attenuation is an important element to limit the transmission of a digital signal traveling in large distances. An optical attenuator reduces this optical signal as it travels along a free space or an optical fiber.

Optical fiber attenuators may employ several principles when used in fiber optic communications. One common principle is the gap loss principle. Attenuators using this principle are sensitive to the modal distribution ahead of the attenuator. Thus, they should be utilized at or near the transmitting end. If not, the attenuators could establish less loss than intended. This problem is avoided by attenuators that use absorptive or reflective principles.

There are three basic types of optical attenuator: the fixed attenuator, step-wise attenuator and the continuously variable attenuator. Fixed attenuators reduce light signals by specific amount with negligible or no reflection. Because signal reflection is not an issue, fixed attenuators are known for more accurate data transmission. Important elements associated with fixed attenuators include the flatness over a specified frequency, range, voltage standing wave ratio (VSWR), amount of attenuation, average and peak power-handling capability, performance over a specific temperature, size and height. Fixed attenuators are also often used to enhance interstage matching in an electronic circuit. Thorlab’s fixed attenuators are available from 5 dB to 25 dB. Mini-Circuits’ fixed attenuators are packaged in rugged plug-in and connector models. They are available in both 50- and 76-ohm models ranging from 1to 40 dB spanning DC to 1500 MHz.

In variable optical attenuators (VOA), resistors are replaced with solid state devices such as the metal semiconductor field effect transistor (MESFETs) and PIN diodes. VOA attenuates light signal or beam in a controlled manner, thus producing an output optical beam with different attenuated intensity. The attenuator adjusts the power ratio between the light beam coming from the device and the light beam entering the device over a changeable rate. VOA is usually used in fiber optic communication systems to regulate optical power levels in order to prevent damages in optical receivers which may be due to irregular or fluctuating power levels. The price of commercial VOA varies depending on the manufacturing technology used. Some of manufacturers of VOA are Timbercon and Arcoptix.

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PM Fiber Components

Posted on June 19, 2014 by admin

Due to their low cost, high tensile strength, high impact resistance and good chemical resistance, glass fibers are used extensively in commercial composite applications. However, their properties cannot match those of carbon fiber components for high-performance composite applications. They posses a relatively low modulus and have inferior fatigue properties compared to carbon fiber components. The three most common glass fibers used in composites are E-glass, S-2 glass and quartz.

Aramid fibers have a combination of good tensile strength and modulus, light weight, excellent toughness with an outstanding ballistic and impact resistance. However, due to the lack of adhesion to the matrix, they exhibit relatively poor transverse tension, longitudinal compression and interlaminar shear strengths.

Carbon fibre components and graphite fibre components are the most prevalent fiber forms in high performance composite structures. Carbon and graphite fibres can be produced with a wide range of properties; however, they generally exhibit superior tensile and compressive strength, possess high moduli, have excellent fatigue characteristics and do not corrode. Carbon and graphite fibers can be made from rayon, pitch or PAN precursors, although rayon is rarely used because of its low yield and high cost. PAN-based carbon fibers having strengths ranging from 500 to 1,000 ksi and moduli ranging from 30 to 45 msi with elongations of up to 2% are commercially available.

Fibres and Reinforcements: The String That Provides the Strength.

Pitch-based high-modulus graphite fibers having a modulus between 50 and 145 msi are often used in space structures requiring high rigidity. Two-dimensional woven products are usually offered as 0¡ã, 90¡ã constructions. Weaves are made on a loom by interlacing two orthogonal (mutually perpendicular) sets of yarns (warp and fill). The warp direction is parallel to the length of the roll, while the fill, weft, or woof direction is perpendicular to the length of the roll. Weaves may be classified by the pattern of interlacing including plain weaves, basket weaves, satin weaves, twill weaves, leno and mock leno weaves. Reinforced mats (chopped fibers or swirled fibers) and chopped fibers are also available for parts requiring lower mechanical properties.

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PM Fiber Components

Posted on June 18, 2014 by admin

“When using VOAs in Dense Wavelength Division Multiplexing (DWDM) optical networks, there are two critical performance parameters that must be minimized: wavelength-dependent loss (WDL) and the polarization-dependent loss (PDL). The WDL refers to the variation in attenuation loss over the specified wavelength range. The PDL refers to the variation in attenuation loss over all states of input polarization. In a VOA, WDL and PDL can vary as a function of the attenuation level. WDL and PDL are undesirable because they contribute to increasing differences in optical power between wavelength channels, which in turn increases the need for channel power equalization and increases the cost and complexity of optical networks. Various design approaches have been proposed to reduce WDL in ES-VOA, see for example U.S. Pat. No. 7,295,748.

“In a further development the ES-VOA component is packaged inside a Small Form factor Pluggable (SFP) housing. This product is referred to as SFP VOA. The SFP VOA offers several advantages compared to the stand-alone pigtailed ES-VOA component described above: (1) the SFP VOA is pluggable, the customer can gradually populate SFP VOA slots on the host system board as the system capacity is increased, (2) the SFP VOA pluggability allows for easy replacement, (3) no fiber management is required since the SFP VOA is connectorized, (4) the interface is digital and the attenuation level is set by a firmware instruction from the host board, the customer does not need to design control and drive hardware and does not need to know the specific characteristics of the ES-VOA component.

“However, compared to the stand-alone pigtailed ES-VOA, the SFP VOA suffers from higher WDL and higher PDL. The inventors have investigated the possibility that this may be caused by modal interference between the fundamental mode and co-propagating cladding modes launched in the output fiber..
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Variable Optical Attenuators

Posted on June 17, 2014 by admin

By a News Reporter-Staff News Editor at Journal of Engineering — A patent by the inventors Wang, Zhongjian (Shenzhen, CN); Ayliffe, Michael (Ottawa, CA); Yu, Qinrong (San Jose, CA); Liu, Niki (Shenzhen, CN); Fan, Rongtang (Shenzhen, CN), filed on December 23, 2011, was published online on May 27, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8737778 is assigned to JDS Uniphase Corporation (Milpitas, CA).

The following quote was obtained by the news editors from the background information supplied by the inventors: “Variable Optical Attenuators (VOAs) are common components used in optical communication networks. One common VOA technology is based on an Electro-Static (ES) Micro-Electro-Mechanical (MEMS) chip. The ES-VOA component has an input optical fiber, a lens, a MEMS tilting minor and an output optical fiber. The lens focuses the input light onto the MEMS tilting mirror, and the reflected light is directed towards the output fiber. A voltage is applied to the MEMS chip, the voltage amplitude controls the mirror tilt angle. By varying the voltage and minor tilt angle, the position of the reflected spot on the output fiber is varied. With the output spot aligned to the center of output fiber core, the attenuation is minimum and limited only by the insertion loss (typically .about.0.5 dB). As the output spot of the beam of reflected light is misaligned relative to the output fiber core, the amount of light launched into the output fiber core is reduced (attenuated), and correspondingly more light is launched into the fiber cladding, and a higher level of attenuation is achieved. The maximum attenuation can be 30 dB and higher, mainly limited by the tilt range of the mirror.

“There exist multiple other VOA technologies, each have advantages and disadvantages. Examples include motor-controlled vane attenuator, thermal MEMS-controlled attenuator, Mach-Zehnder attenuators, Electro-Absorption attenuators, liquid-crystal attenuators. The main advantages of the ES-VOA is rapid switching time (<2 ms), compact size (5.56 mm diameter package), low cost, low power dissipation, and high dynamic range (>30 dB). These advantages have made the ES-VOA the most common VOA solution in optical fiber networks applications..
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