Computers

Fiber Types & Modes of Transmission

In fiber optics, the term "mode" refers to a stable propagation state of light down the fiber. Fibers can have any number of stable propagation states (modes), giving rise to two basic types of optical fibers, multimode and singlemode. Multimode obviously refers to a fiber that has many modes of propagation, while a singlemode, by design, only has one. Whether a particular fiber is multimode or singlemode depends on the fiber geometry, core/clad refractive indices, and the wavelength of operation. Multimode fibers can be further broken down into two subcategories, step-index and graded-index. Each type has distinctive advantages and disadvantages, which will be discussed below in more detail.

Step-Index Multimode Fiber This was the first fiber type to find practical application, and continues to be in wide use today. A step-index multimode fiber allows the light to travel at many different angles within the fiber, thereby allowing many modes of propagation. The term "step" refers to the step function the refractive index takes at the core/clad interface.

The advantages of a step-index multimode fiber are related to the relatively large core area and high numerical apertures. Both of these properties allow light to be easily coupled into the fiber. In turn, this allows the use of inexpensive termination techniques, low cost diodes, and high power handling capability. These fibers are therefore widely used in high power laser delivery applications (medical procedures, material processing), industrial process control links (factory automation), short distance data communications, and fiber sensors.

A disadvantage to step-index multimode is bandwidth. Referring to the figure, the path the light takes down a step-index multimode fiber will be longer or shorter depending on the angle of propagation. This difference in path length causes the pulse of light to spread out during its journey down the fiber. This is known as modal dispersion (see Dispersion section). As one pulse spreads, it eventually interferes with the neighboring pulses, distorting the transmission signal. The longer the fiber length, the more severe this pulse spreading will become. However, this is only a problem in applications that require a coherent signal, as in communications links. Power delivery or sensor systems do not require coherent transmission and many data communication or industrial process control links are relatively short distances (less than 2km), allowing the widespread use of step-index multimode fiber.

There is a wide selection of step-index multimode fiber available. Sizes vary from ~50 to >2000µm core diameters. Their construction can be silica or plastic cladding using silica, plastic, or liquid as a core. There are also applications with no core called hollow waveguides. The silica constructions allow lower attenuation, greater spectral range, higher power handling capability, and greater environmental range. Plastic fibers offer lower cost and greater flexibility, but are limited in transmission and environmental properties. Hollow waveguides are used principally in the IR.

Polymicro offers a wide selection of step-index, multimode fibers, particularly for laser power delivery and stringent or harsh environmental conditions. Please refer to our data sheets.

Graded-Index Multimode Fiber As the name implies, the refractive index of this fiber gradually decreases from the core out through the cladding, as opposed to the abrupt step change of step-index. Instead of taking a zigzag path down the fiber, the gradual change in refractive index directs the light in a sinusoidal path as previously illustrated. Since the light travels faster in a material of lower refractive index, the light traveling on the outer reaches of the graded region moves more quickly, thereby reducing the amount of pulse spreading. The result is a dramatic >25-fold increase in bandwidth over step-index multimode fibers.

Graded-index is actually a compromise between step-index multimode and singlemode fibers, trading off bandwidth for ease of termination and light launch. The graded profile and smaller core increases bandwidth over step-index multimode, but the core sizes are still large enough for convenient termination and use of lower cost diodes. In more recent years, the components and techniques for terminating singlemode has improved dramatically, so graded-index has seen a decline in market share. However, graded-index remains a popular standard for use in medium distance (2-15km) data communication links.

The most common core sizes for graded-index multimode fibers are 50, 62.5, and 100mm. These sizes have become industry standards. The construction is always silica core/silica clad based, with dopants (typically Ge, B, P, and F) used to adjust the refractive index in the graded profile. This fiber is used almost exclusively for medium distance data communication (local area networks), although it is sometimes used for fiber sensor systems. The smaller core area makes this fiber less useful for power delivery applications, however new special, larger core designs specifically for high power applications are available.

Singlemode Fiber In singlemode fiber the core size is reduced to the point (5-10mm diameter) where only one mode, the primary mode, can be guided. This mode essentially travels straight through the fiber and thus is not subject to the pulse spreading seen in multimode fiber due to different path lengths. The net effect is a substantial increase in bandwidth since all the light is traveling at the same speed for the same distance. In addition, using the primary mode and higher operational wavelengths (1310 and 1550nm) results in very low attenuation. For these reasons, singlemode is the fiber of choice for long distance data and voice communication.

Singlemode does experience some distortion of the signal, but this is due primarily to chromatic dispersion, which is variation in light speed due to the pulse not being purely monochromatic. This type of dispersion is very small when compared to the modal dispersion experienced in multimode fibers.

Singlemode fiber typically consists of a silica core/silica clad construction with a step-index refractive index profile. The core and/or clad is doped to obtain the index difference between the core and clad. The core size, being very small, is more difficult and costly to terminate versus the multimode fibers, but for long distance systems this cost is acceptable. In contrast, the small core size does not allow a great deal of power input, and therefore this fiber is generally not suitable for power delivery and many sensor applications.

Because each VLAN need to be on an a separate subnet, we normally need a level 3 device to lift the packages from one subnet to the other.

The simplest way of doing that is to hook up a router to the switsh, and use a so called "router on a stick"configuration. However, this is seldom done i a production environment today.

For example, a telephone directory in the U.S. usually is accessed by the last name of the person or business looked for. However, it can also be accessed by the telephone number ( which used to be called a "reverse directory" ) or the address of the party. In Thailand, the telephone directory is alphabetized by the FIRST name of the party listed.

A fully relational database for a telephone directory would allow access by any of these plus others (e.g. siblings/partners/children/... of the party, etc. )

The amount a computer repair technician can earn depends on where in the world the person is employed, and how the employment is organized, as well as the abilities of the technician.

Here are a variety of answers and opinions from many WikiAnswer contributors:

1. In my opinion, you would be lucky to be earning £13,000 a year after years of experience and a degree. There is no money in this business and it is constant hassle and stress.

2. My dad is a computer repair technician making over $62,000 a year with 12 years of experience on top of that he is a Realtor, business broker, teacher, and an accountant also owning his own small business for computers at PCCIA.

3. In my opinion, if one is only making $13,000 a year then perhaps that person is not very skillful at computer repair. In my opinion, you can make $50,000 a year but you start making usually $30,000 a year. If you charge prices for service around $100 per fix, $150 to a virus clean, and so on and so forth.

4. In my opinion, the people in my town (it is a small town) make about $80-90 an hour... they make about $208,000 a year. And that's with just the degree, so you could be 21 and make the same amount of money as that.

5. In my opinion, one person simply cannot make $208,000 a year fixing computers.

6. In my opinion, how much you earn would be determine greatly by your location, and where you are working at I started at $28,000 a year with no experience and a two years degree (most job offer that I've received was lower) Friends of mine started at computer repair shops making much less (but gaining more experience). With experience, you can expect (depending on how much and what degrees you have) $35,000- $45,000 a year.

7. I've been in this field for years. I've worked for multiple companies in many different capacities. I worked for Gateway Computers via a third party call center that they had outsourced in 2000 and my starting rate was USD 7.50 and I ended three years later at the same rate of pay with MANY more responsibilities. The company lost the contract however and we moved to supporting home electronics manufactured by Samsung. The pay was the same, but the satisfaction was just not there.

8. I moved into a specialty field as an on-site technician for a company that manufactured computerized bingo systems making $27,000 salary with paid travel and ended four years later at $38,000 but again the work was not satisfying and the hours were terrible. I walked away from that and took a job as a depot tech in a small computer store just down the hill from a Best Buy.

The computer store I was in managed to compete with BB and a few other local stores for around 3 years and I loved my job. It was the only time I felt as if I were accomplishing anything and actually helping people. Our pricing schedule was fair and we tried our best to offer top notch service. I was eventually promoted to senior technician and was given the responsibility of on-site tech and I made $24,000 a year starting out and ended with around $28,000 when the shop owner closed the location because he felt we weren't making enough money. Although I enjoyed my job, I could barely pay my bills.

I managed to get back into the electronic gaming industry at around $38,000 a year plus travel and commissions, but the work isn't as fulfilling to me as the time I spent at the computer shop. My current job has its ups and downs, for example, I'm a salaried employee, but there are weeks that I may work 11 hours total. I'm still paid and I enjoy my freedom. I wouldn't do it otherwise. However, there are also weeks where I've worked nearly 80 hours just to get a project completed. It pays the bills though and I get to travel to some nice places.

Oh, I also freelance in my spare time but it's never amounted to a livable income and I'd love to know how the father of the poster above has managed to make so much. I'd gladly give up my job if I could make a steady income instead of $1000 one week and none the next.

As an added bonus: My ex-wife worked as a GeekSquad agent and still does. She has been with GeekSquad for around six years and worked with me as a tech for Gateway before that. She started at around $8/hr and when we split around two or three years ago she was topped out at $9.50 but they only gave her around 20 hours a week. In my opinion, it's not worth it for the stress.

Hopefully, the answer to your question is in there somewhere. Honestly, I'd say that if you were contemplating a career as a repair tech, consider a manager of a fast food chain location instead, unless it's just your raison d'être.

9. I wanted to add my 2 cents to this, as "computer repair technician'' is very vague and is assuming you wish to repair PCs. In my opinion, there isn't any money in this line of work in the UK, and you *could* make more money working on a line in a factory.

However, IT is incredibly diverse, and if you were to become highly accredited (no, I don't mean get a degree, complete and utter waste of time) in a popular platform - say, VMWare - you could very quickly earn salaries of 40, 50, 60k or upwards.

I'm now an architect, but as a system admin I was earning in the region of 45k plus car, benefits etc. I've now gone into pre-sales and am earning in the region of 70k plus benefits.

I'll just reiterate about the qualifications; a degree is mostly, entirely, non-essential. You would be far, far better off studying a platform off your own back, or working in an environment as a junior where you can get access to enterprise-class systems. From there you can decide, do you want to become a server guy, OS guy, storage guy, networking guy etc. Following on from that, take the necessary courses/certifications to become proficient. From there, you will earn the money.

If you get a degree, most likely you'll be stuck in a low paying job unless you leverage your degree and add to it with experience.

10. In my opinion, there is money in IT. I started out on 52,000 a year with no experience and just finished a 6-month course in IT. No degree just a certificate.

Companies are getting desperate for IT staff now and they are willing to pay whatever it takes to get ahead of the competition. Technology is the way of the future and IT technicians will be a big part of that. There are so many different areas to explore in IT. Not just repairing a computer.

I have seen numerous jobs advertised in a number of places offering 130,000 + per year as a server administrator or network engineer. And that's just the start of it. You could certainly earn more if you are smart about it and have a passion for IT. There are more and more devices and new technology coming out each and every year. Someone needs to show people how to use it, fix it, support the person using it or even run an entire company with it. I have only been in IT for one year but i can tell you that if you are passionate about IT then you can go a long way.

I study and work in Australia. There are so many opportunities in IT at the moment and there won't be a shortage any time soon. Whether that is in Australia or around the world. And don't just stick to one thing. Explore all possibilities and learn as much as you can. Try to be an all rounder. That way employers will see you are good in every area of IT and not just one. Besides just sticking to one main area is a little boring for my liking. I would like to be proficient in most areas if not all.

There is no reason why you can't get a good paying IT job. You might have to travel a little but what is the harm in that. Get out in the world of technology and see what it has to offer you.

11. In my opinion, there is no longer money in computers. I worked on the first computers, which were Z100 and Z150. The Z100 sported an 8086 processor, maybe 8k of memory and two 51/4" floppy drives. The dos OS lived on a floppy. The Z150 was really hot with a 10-megabyte hard drive, which really speed up the DOS command prompt. I was working in field support and traveling half of the time, I was making $50K and that was nice back in 1988. Once the technology advanced and continued advancing dropping the price of a system way down, things started getting tough in the marketplace for employment. A computer w/ 40 - 60 megs storage and 4 megs of memory were selling for $2500 - $3000 in 1995. Today's phones are light years ahead of those old desktops! The shuttle program shot spacecraft into outer space running on a 286 and DOS! As more and more people understood the workings of the mysterious computer, this brought the technical skill value down to a dime a dozen. 300 applications for a single job, major competition for less and less pay. This is when I decided to Jump Ship Fast! Therefore, in my opinion, there is no money in computer repair or integration. Tech Support pays a bit more, but there are idiots out there, and dealing with them daily becomes like the mail, it does not stop! Ever! This is how the term "going postal" came to us. A tech support rep last at most 2 years, then what? Okay, I'm done!

12. In my opinion, here are some averages from year to year: 1-4 years: $20,000 - $50,000, 5-9 years: $22,000 - $51,000, 10-19 years: $23,000 - $58,000, 20 years or more: $31,000 - $74,000. The pay differs in accordance with where you live, how much you are needed, if you have a degree and for whom you work.

13. I just graduated from college with my associates degree in IT and I'm making $18.00/hour as an entry level field service tech. Plus I freelance on the side, and make anywhere from $20 to $35 per hour. I have several friends in the IT field that are currently earning 6 figure incomes. I cannot imagine only making 13K a year as a tech! Someone must be extremely lazy or stupid if they are only making that much! The money is definitely out there in IT!

14.It's the whipping boy of the PC industry, depending on the area of the country don't expect much. Even with certifications and degrees you will probably be lucky to start @ $11 p/h in the Midwest. Your best bet, keep studying and get your networking admin certifications as well. I finally got sick of companies expecting me to fly like an eagle, while paying me like a hummingbird and started freelancing. Far better opportunities are to be had by freelancing. True horror story follows while contracting through Unisys I was requested to make a service call to repair a 2u server with a bad drive controller. Round trip 1800 miles B.T.W. "flat rate pay" no mileage, no travel expenses, and to top it off it took 2 days because the IT admin on site didn't know how to rebuild the freaking array. Literally after factoring in hours, and out of pocket expenses lost money on that gig. Lesson learned, if your going to be a tech in the Midwest be prepared to go it alone and freelance. I charge $45 for basic services and $70 + parts cost on other repairs. This translates to $140 an hour if you repair 2 laptops an hour "easy enough". Far better than being a whipping boy for some repair shop

15.For us , in Madagascar, the computer repair technician earn is around 20$, it is not good for us. Sad!!!

16. It also depend upon their abilities in India. In India those who are having high knowledge about it earns more. So having knowledge of each and every part of computer is very important.

17. My experience with computers dates back to 1982. I started working with computers on the Boroughs B29/XE500. It was actually a server from which you could run 25 dumb terminals. It was really cool and had a 50MB hard drive. Then came the Zenith 100s, 150s, etc. I have been completely out of the computer business for about 5 years now. However, when I was in the business as a computer technician, I charged a fee of $50.00 per hour...flat rate. Before starting out on my own I tried unsuccessfully to get a job at several well established computer repair companies in the area but they just didn't have the workload to justify another technician. Come to find out they were charging $100+ per hour and some jobs, such as virus removal, software installation, hard drive installation, etc., were set at exorbitant flat rate fees.

To make a long story shorter, within 2 years some of those businesses started folding because I did a better job cheaper. The owner/manager of one company that turned me down for a job earlier actually applied for a job with my company...I turned him down naturally even though I had all the business I could handle and was forced to turn clientele away. My last year, I cleared OVER $10K per month. If you are good at it, treat your clientele well, and don't try to get rich quick, your income is only limited by the number of hours in the day.