What would life be like without lasers? Part C - Using Lasers to Burn and Read CDs and DVDs

CDs and DVDs are everywhere these days. Whether they are used to hold music, data or computer software, they have become the standard medium for distributing large quantities of information in a reliable package. Compact discs are now easy and cheap to produce. If you have a computer and CD-R drive, you can create your own CDs, including any information you want.

The Disc
A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch (1.2 mm) thick. Most of a CD consists of a piece of clear polycarbonate plastic, shaped like a disc. During manufacture, this plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic. A cross section of a complete CD looks like this: The Spiral
A CD has a single spiral track of data, circling from the inside of the disc to the outside. What the picture on the right does not even begin to impress upon you is how incredibly small the data track is -- it is approximately 0.5 microns wide, with 1.6 microns separating one track from the next. (A micron is a millionth of a meter.) And the bumps are even more miniscule...

The Bumps
The elongated bumps that make up the track are each 0.5 microns wide, a minimum of 0.83 microns long and 125 nanometers high. (A nanometer is a billionth of a meter.) Looking through the polycarbonate layer at the bumps, they look something like this:The bumps are arranged in a spiral path, starting at the center of the disc. The CD player spins the disc while the laser assembly moves outward from the center of the CD.

CD Player Components
The CD player has the job of finding and reading the data stored as bumps on the CD. Considering how small the bumps are, the CD player is an exceptionally precise piece of equipment. The drive consists of three fundamental components:

• A drive motor spins the disc.
• A laser and a lens system focus in on and read the bumps.
• A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track.

You will often read about "pits" on a CD instead of bumps. They appear as pits on the aluminum side, but on the side the laser reads from, they are bumps.

The incredibly small dimensions of the bumps make the spiral track on a CD extremely long. If you could lift the data track off a CD and stretch it out into a straight line, it would be 0.5 microns wide and almost 3.5 miles (5 km) long! To read something this small you need an incredibly precise disc-reading mechanism. The key element in this mechanism is the pinpoint beam of a laser.

The fundamental job of the CD player is to focus the laser on the track of bumps. The laser beam passes through the polycarbonate layer, reflects off the aluminum layer and hits an opto-electronic device that detects changes in light. The bumps reflect light differently than the "lands" (the rest of the aluminum layer), and the opto-electronic sensor detects that change in reflectivity. The electronics in the drive interpret the changes in reflectivity in order to read the bits that make up the bytes.

The hardest part is keeping the laser beam centered on the data track. This centering is the job of the tracking system. The tracking system, as it plays the CD, has to continually move the laser outward. As the laser moves outward from the center of the disc, the bumps move past the laser faster. Therefore, as the laser moves outward, the spindle motor must slow the speed of the CD. That way, the bumps travel past the laser at a constant speed, and the data comes off the disc at a constant rate.

CDs store music and other files in digital form -- that is, the information on the disc is represented by a series of 1s and 0s. In conventional CDs, these 1s and 0s are represented by millions of tiny bumps and flat areas on the disc's reflective surface.

To read this information, the CD player passes a laser beam over the track. When the laser passes over a flat area in the track, the beam is reflected directly to an optical sensor on the laser assembly. The CD player interprets this as a 1. When the beam passes over a bump, the light is bounced away from the optical sensor. The CD player recognizes this as a 0.

The advent of CD burners marked a huge cultural shift. The technology made it feasible for the average person to gather songs and make their own CDs. Today, writable CD drives (CD burners) are standard equipment in new PCs, and more and more audio enthusiasts are adding separate CD burners to their stereo systems.

CD burners darken microscopic areas of CD-R discs to record a digital pattern of reflective and non-reflective areas that can be read by a standard CD player. Since the data must be accurately encoded on such a small scale, the burning system must be extremely precise.

In addition to the standard read laser, a CD burner has a write laser. The write laser is more powerful than the read laser, so it interacts with the disc differently: It alters the surface instead of just bouncing light off it. Read lasers are not intense enough to darken the dye material, so simply playing a CD-R in a CD drive will not destroy any encoded information.

Questions or comments? E-mail us!

References:

Brain, Marshall. "How CDs Work." 01 April 2000. HowStuffWorks.com. <http://electronics.howstuffworks.com/cd.htm> 02 November 2009.

Harris, Tom. "How CD Burners Work." 01 August 2001. HowStuffWorks.com. <http://computer.howstuffworks.com/cd-burner.htm> 02 November 2009.

What would life be like without lasers? Part B - Lasers and Fiber Optics in High-Speed Internet & Smart Phones

The Internet, fax machines, smart phones, and other mobile devices are a way of life in modern society. All these technologies rely on lasers and fiber optics.

The properties of laser beams that allow them to be excellent carriers of high-data-rate signals (like high-speed Internet) are: 1) they are extremely high-frequency (0.3 GHz) carriers; and, 2) they have the coherence properties of radio or microwave radiation. These properties allow laser beams to carry many concurrent high-frequency signals.

Laser beams travel through the air in straight lines except when they are bent by lenses or prisms or reflected by mirrors. Optical fibers permit the transmission, or “piping,” of laser beams in flexible cables that can be wrapped around corners or laid on the ocean floor. An optical fiber is a fine glass or plastic strand that carries light internally along its length. Fiber-optic cables, which consist of bundles of optical fibers, are used to transmit laser beams in high-data-rate (high-bandwidth) optical communication. Optical fibers prevent the laser signals from being blocked or scattered by clouds or other particles in the atmosphere or by electromagnetic interference. This means that laser beams can travel over long distances without significant distortion or attenuation.

Fiber-optic cables can support Internet systems with up to 3 trillion bits per second at transfer rates as high as 111 gigabits per second (Gb/s), although 10 or 40 Gb/s is typical. The fibers used in long-distance telecommunication applications are always glass because glass causes only minimal attenuation. Both multi-mode and single-mode fibers are used, with multi-mode fiber used mostly for short distances (up to 600 yards) and single-mode fiber used for longer distances.

The process of communicating using fiber optics involves five basic steps: Creating the optical signal by modulating the laser output beam, relaying the modulated laser signal along the fiber, ensuring that the signal does not become too distorted or weak, receiving the optical signal, and converting the signal into an electrical signal.

Optical fibers are widely used to transmit telephone signals, Internet communication, and cable television signals. Due to much lower attenuation and interference, optical fiber has significant advantages over electrical transmission in long-distance and high-demand applications. Because of these advantages, optical fibers have largely replaced copper wire in core communication networks in the developed world. For example, many landline cell tower connections are made over optical fiber.

As one of the most talked about technological breakthroughs of the last few decades, laser/fiber-optic Internet carries a big name and responsibility in today’s world. Through the use of lasers and fiber optics, the computer and the Internet have evolved into realities that not too long ago were considered purely imaginary. Computers that used to take up entire rooms can now fit in a person’s back pocket. The Internet, which was created to help secure U.S. military networks, has now united the world with information.

With lasers and fiber optics, the frustrating days of slow Internet connections are forever in the past. Some people argue that wireless Internet is still faster than fiber-optic Internet, but that is not true. Laser/fiber-optic Internet is nearly a million times faster than wireless. A fiber-optic Internet cable can carry up to around three trillion bits per second. At that rate, the Library of Congress could be downloaded to your computer within a minute, compared to about eighty years for a dial-up connection (Fiberoptics VP).

The first transatlantic fiber-optic cable was installed in 1988, using glass fibers so transparent that repeaters (to regenerate and recondition the signal) were needed only about every 40 miles. In 1997, the Fiber Optics Link Around the World (FLAG) became the longest single-cable network in the world, providing infrastructure for the next-generation Internet. The 17,500-mile cable begins in England and runs through the Strait of Gibraltar to Palermo, Sicily, before crossing the Mediterranean to Egypt. It then goes to Dubai and UAR before crossing the Indian Ocean, Bay of Bengal, and Andaman Sea, through Thailand, and across the China Sea to Hong Kong and Japan (National Academy of Engineering).

Transistors get a lot of attention in the digital world, but the backstage heroes are lasers. Red lasers brought us compact discs and cheap long-distance communication. Blue lasers, which cram even more data into a small spot, became a hit around 1999 and have made possible Blu-ray DVDs (Elizabeth Corcoran, Forbes Magazine, June 08, 2009).

Gordon Snyder, Director of the NSF/ATE ICT Center, says, “The entire landline infrastructure is being replaced with fiber.” More valuable comments about this from Gordon can be found at the following blogspots:
http://ictcenter.blogspot.com/2009/09/why-verizon-is-sunsetting-public.html
http://ictcenter.blogspot.com/2009/09/verizon-no-longer-concerned-with-tele.html

Questions or comments? Post your comments here or e-mail me!

What if there were no lasers today?

When you hear the word, “laser” what are you reminded of? Luke Skywalker? Star Wars? High-tech wars between spacecraft?

Well, those concepts make good movies and TV shows, but they don’t make very good sense - in a practical way. In the last 40+ years, we have created a wide range of lasers (some whose output you can’t even see) and we’ve learned how to control them and use them to make our life better and to do things we’ve never been able to do with any other device - incredible breakthroughs in medicine, communications, manufacturing, entertainment and lots more. Unless we happen to be involved in the development of some application of the laser we probably don’t even know they are being used - right before our eyes!

Lasers now come in a variety of configurations and output wavelengths (colors), in continuous and pulsed beams, and at high and low power levels. We can often find a “laser solution” to a particular problem by selecting a laser with an output that suits our needs best. The unique properties of lasers that make them useful are:

• Monochromatic - Most lasers emit a beam of light at a very pure color (or wavelength). This means that the beam will be selectively transmitted, absorbed or reflected when other beams of light are not affected the same way.


• Collimated - A laser ray can be made to remain a very narrow beam that will travel long distances without spreading out much. A laser beam can be sent all the way to the moon and spread so little that it still makes a powerful spot when it hits something.


• A powerful Source of Heat that can be directed and pin pointed to an exact spot where it may melt or vaporize the target material, and yet leave the surrounding material unaffected.
  
• Coherent - Because laser light is much better organized than ordinary light, lasers have the same “information-carrying” properties that radio waves have, except the laser is working at much, much higher frequencies. This allows huge amounts of information, and many, many channels to be sent over a laser beam. Sometimes the laser beam is sent in the air; and sometimes it is “piped” in tiny plastic or glass strands called “fiber optics”.

So what are some common uses of lasers that we use every day? Here are a few:

Supermarket Checkout Systems
A low-power laser beam is scanned across the “bar codes” that are attached to products we buy. When we check out at a superstore, we just place the product with its bar code face down on the window of the scanner, the laser beam sweeps across the bar code and the reflected laser beam is read as a code that identifies the product. This uses the collimated and monochromatic characteristics of the laser.

LASIK Eye Surgery
LASIK (laser-assisted in situ keratomileusis) is a surgical procedure that uses a laser to correct nearsightedness, farsightedness, and/or astigmatism. In LASIK, a thin flap in the cornea is created using a femtosecond laser. The surgeon folds back the flap, and then removes some corneal tissue underneath using an excimer laser. The flap is then laid back in place, covering the area where the corneal tissue was removed. With nearsighted people, the goal of LASIK is to flatten the too-steep cornea; with farsighted people, a steeper cornea is desired. LASIK can also correct astigmatism by smoothing an irregular cornea into a more normal shape. This application uses the collimated, monochromatic and heat properties of the laser. (Unfortunately, laser pioneers are too old to be considered good candidates for LASIK.)

Laser Printers & Copiers
The physical phenomenon at work in a laser printer is static electricity, the same energy that makes clothes in the dryer stick together. A laser printer uses this phenomenon as a sort of "temporary glue" to hold toner on a photoconductive drum. The laser "writes" the print information on a photoconductive revolving drum, which then transfers it to a sheet of paper. This uses the collimated and heat properties of the laser. The information is then sealed to the paper with heat from a fuser, producing a very high-resolution copy.
(From www.howstuffworks.com/laserprinter.htm )

There are more laser applications to talk about (internet, displays, entertainment, pointers, and defense/homeland security equipment); but, those will have to wait until there’s another blog posting.

Questions or comments? Post your comments here or e-mail me!

Technical Challenges During the Emergence of the Laser - 1960’s

Q-Switched Ruby Laser with "Rat’s Nest" Calorimeter - 1962
Click here to view the image above in a larger format.

In the late 1950’s and early 1960’s, scientists accomplished the extraordinary feats of predicting, discovering and making the first lasers operational. Throughout the 1960s, scientists continued to lead in discovering new solid, gas and liquid materials that could be used as the active medium in lasers, providing new output wavelengths, higher energy and/or pulsed power outputs and greater efficiencies.

By 1961, electrical and mechanical engineers also joined laser R&D staffs in the development and refinement of laser systems and related equipment. We were faced with technical challenges for which we were not prepared in our education and/or prior experience. Some of the challenges we faced were:

• Engineers and physicists did not usually work together or even speak the same technical language. We learned to work in teams and to develop mutual respect for each other - because we needed each other’s unique experience and expertise.
• There were no textbooks and few journal articles about lasers; we had to learn about them as we worked on them. We were discovering new phenomena and revising existing theories.
• In the 1960’s, most engineers’ knowledge of optics was limited to what they learned in a few weeks of study in sophomore physics. Many of us had to learn more depth in geometrical optics from a book by Jenkins & White; wave (or physical) optics from a book by Strong.
• Light was traditionally measured in photometric units (lumens, foot candles, angstroms etc). We had to transition to radiometric units (joules, watts, nanometers etc).
• Safety aspects of laser beams was neither known nor respected. Laser safety became an R&D field of its own. Laser safety goggles had not been invented.
• There was no instrument used to measure the energy in an optical pulse (i.e. output of a pulsed laser.) Robert M. Baker, a Fellow Electronics Engineer at the Westinghouse Defense Center, devised and tested a “rats nest” calorimeter, composed of tens of meters of coated, fine copper wire, tangled and placed in a small beaker. The pulsed laser beam was directed into the “rats nest”; the change in electrical resistance, due to the heat rise in the copper, was measured; the temperature rise in the wire was calculated and related to the laser pulse energy absorbed by the “rats nest”.
• The physics of “negative absorption” or “optical gain” could only be understood through an understanding of modern physics and quantum mechanics. Some of us had “lightly” learned these fields in graduate studies; others had to struggle through these topics in other ways.
• Operation of solid lasers, like ruby, required fluent knowledge and facility in cryogenics and high voltage power supplies and capacitor banks. Most engineers had to learn these practices “on the job”.
• As new applications of lasers were proposed in fields such as defense, materials processing, medical therapeutics, communications, remote sensing and others, engineers were required to devise, revise and adapt equipment to accommodate laser and optical components, devices and systems.
• We learned, by mistakes, that a high power, pulsed ruby laser cannot be focused with an achromat lens without destroying the cement that joins the components of the lens together. Achromat lenses were not needed for monochromatic laser light.
• We also learned that most anti-reflective coatings, needed on gas laser tubes and the ends of solid laser rods, were also vulnerable to damage by the laser radiation. We solved this problem by positioning the end of the laser rods and the windows at Brewster’s angle to minimize reflections; thereby eliminating the need for AR coatings.

This list is far from comprehensive, but it’s what first came to mind and it’s long enough for this blog posting. Perhaps you were also working on lasers in the 1960’s. I would invite you to comment on other challenges that you faced.

Visit http://www.laserfest.org/ to learn more about the 50th anniversary celebration of the laser!

Celebrating 50 years of the Laser in 2010

A little more than 48 years ago, when I was a fledgling young electrical engineer at the Westinghouse Defense Center in Baltimore, I had a fortunate occasion that transformed my career into one of the most exciting experiences I could expect in my life. I was developing and testing some electronic timing/counting circuits for airborne radar systems; I was bored to death and wondering why I had dragged my young wife up to Baltimore from Texas to live in this “foreign land”, away from friends, relatives and Mexican food.

My engineering manager approached me just before lunch one day in June 1961, and showed me a copy of the latest issue of Scientific American magazine. He said, “Here, read this article about a helium-neon laser that had been created at Bell Labs. We want to build the second one, and I want to know if you would like to have this assignment.” I read the article, struggled through the quantum mechanics, modern physics and optics, and couldn’t imagine any practical applications for this curious device. But I also couldn’t think of anything else that I wanted to do, so I returned from lunch and responded with “why not”?

We had the HeNe lasing @ 1.153 microns (with a flat mirror Fabry-Perot etalon cavity) before the end of the year. Then we set out to build a ruby laser like Ted Maiman had demonstrated at Hughes. When we got it to operate (with a pulse energy output of about two joules), we focused the beam, with a one-inch focal length lens, on a razor blade, and blew a hole in it. Now we knew the potential application; we had the ultimate weapon to “blow ICBM’s out of the sky” and save the USA from nuclear weapon destruction! The Department of Defense also caught the laser fever; within months, R&D $$ for laser development began to flow like a river. We tried to make more powerful lasers by discovering other materials that would lase (someone even reported that they had made jello to lase.) We built ruby laser oscillator/amplifiers to raise the output power and sent them to military labs for more testing.

I not only shot more razor blades, I shot other, more exotic materials; calculated the volume of material removed and measured the impulse generated by the rapid “blow-off” at the material’s surface. In 1963 Soviet Premier Nikita Khrushchev visited the United Nations, beat his shoe on the podium, and showed a hand ruler that had a small hole in it made from a ruby laser. He declared that the USSR had the ultimate weapon that would allow them to control the world. By that time, I had determined that it might be more effective to “throw the laser at the ICBM” than it would be to try to shoot it out of the sky. Laser weapons’ research continued, and some useful devices have no doubt been developed that have made our military more efficient and our country safer.

But many more unique, useful laser applications have been developed in medicine, surgery, telecommunications, manufacturing, homeland security, lighting, displays and nanotechnology, to name a few. Lasers (today, a part of photonics) is an enabling technology that has provided new solutions to difficult problems, made our country a safer place to live and improved our quality of life. I’m so glad that I am a part of this scientific achievement. I’m an engineer and an educator; I didn’t discover the laser, but I am proud to have been part of its development; I’ve contributed to new applications; and I’ve been working for the last 35 years to build the laser (photonics) technician workforce - a critical element in this exciting and useful field.

Next year, the American Physical Society (APS), along with other sponsors, like OP-TEC, is leading a national celebration to commemorate the 50th year of the laser. This celebration is called LaserFest.

Check out the plans, information, history and opportunities to participate in LaserFest by visiting the APS web site at www.laserfest.org.

For the next several weeks I will be writing about LaserFest and some of my early memories of the emergence of the laser, including some early pioneer colleagues, technologies that had to be created/changed to support laser development, the transition from “laser systems development” to “laser applications development”, and the need/response for laser technicians.

The Photonics College Network Was Launched!

The OP-TEC Photonics College Network (OPCN) was initiated last week, at the HI-TEC Conference in Scottsdale, Arizona. Twenty-three faculty members and administrators were present, representing 18 of the nation’s 29 photonics colleges. Two additional faculty members also attended, representing two other colleges that are planning to start new photonics programs in the near future.

The OPCN met for five hours over two evenings, and accomplished the following:

• In a “networking session”, members exchanged contact information, program descriptions and student recruitment brochures.
• Members asked OP-TEC to create and maintain an OPCN community web site, open only to members, for the purpose of sharing successful strategies and engaging in discussions on issues and problems related to photonics technician education.
• Members agreed to participate in conducting Regional Needs Assessments of photonics technician job opportunities.
• Members agreed to participate in quarterly teleconferences, beginning in September 2009.
• Members requested OP-TEC to develop and conduct monthly webinars on photonics education innovations and technical updates. These 1-hour webinars will be led by OPCN members, OP-TEC center staff and technical experts. Topics will be agreed upon in the next six weeks, and the webinars will begin in the fall of 2009.

OP-TEC announced that matching mini grants would be awarded in 2009-2010, on a competitive basis, for selected OPCN members to initiate proven strategies to increase photonics student enrollment/retention at OPCN colleges.

Dr. Fred Seeber, Professor Emeritus at Camden County College, provided a seminar to the OPCN members on Laser Safety, highlighting the recently released ANSI Z136.5 Safe Use of Lasers in Educational Institutions. Copies of the new ANSI Standard were given to each OPCN member in attendance.

The following colleges were represented at the meetings: Bellingham Technical College; Camden County College; Central Carolina Community College; Central New Mexico Community College; College of Lake County; Delaware Technical College; Idaho State University (2-yr program); Indian Hills Community College; Indian River State College; Indiana University of Pennsylvania (2-yr Northpointe Campus); Irvine Valley College/CACT; Ivy Tech Community College; Monroe Community College; Northwest Vista Community College; Pima Community College; Sinclair Community College; Texas State Technical College; TriCounty Technical College; Valencia Community College; and, Wallace State Community College.

Membership in OPCN is available, without charge, to other two-year colleges offering photonics education. If you would like additional information about OPCN, please contact us at op-tec@op-tec.org.

Retraining for Photonics Technicians

Many U.S. employers of photonics technicians are hiring workers that are underprepared for their jobs. Some of these techs are educated/trained in other technical fields; some have only a high school education, or some post secondary education in an unrelated field. A recent study conducted for OP-TEC reveals that employers are hiring 400-600 unprepared photonics techs each year. Employers don’t want to do this, but they’re doing it to survive; they need to fill staffing slots to meet their commitments and our colleges aren’t turning out enough photonics grads.

We need 2200 new photonics techs this year, but our colleges are only producing about 250 completers. OP-TEC is working with our U.S. colleges to start more photonics AAS degree programs and to increase the enrollment and completion rates of existing programs. But it will take years for us to “build our capacity” to have enough completers to fill the annual demand for photonics techs.

In the meantime, employers will continue to “make do” with underprepared workers; and these new or transferred workers will have to “learn on the job”. On the job training (OJT) is important and useful, but it is usually limited to survival training on specific equipment and processes that are peculiar to an employer’s current equipment and work assignments. It rarely includes the basic knowledge and skills that underpin the technology and provide the foundation for survival and/or growth. In the case of photonics, this basic knowledge/skill includes geometric and wave optics, laser operation and output characteristics - and laser safety.

So, what can be done “in the meantime”? If photonics techs need some education and training in this field, and if they are near one of the colleges in our country that offers photonics courses (see a map of these college locations in my May 6 blog posting), then they should investigate the offerings that are available locally. But this option may not be practical for the following reasons:

• There is not a photonics college within commuting distance.
• You may not have the time available to attend the college 2-3 evenings/week.

To address the need of employed photonics techs for education/training in this field, OP-TEC has developed and tested hybrid online courses in optics and photonics that can be offered by any college that has the appropriate faculty and labs to teach them. The course is hybrid because of the way it is delivered. Students can take the classroom part of the course “online” from their homes, workplace or while they are on the road. Videos of the lab activities are also shown online. Periodically, students come to the college to conduct the hands-on lab activities. This can be once every other two weeks or all at the end of the course, depending on the preference of the students and the college. If sufficient students from one employer constitute a course, the labs could be conducted at the employer worksite.

The six modules in the first course cover the following basic topics:

• Nature and Properties of Light
• Optical Handling and Positioning
• Laser Safety
• Geometric Optics
• Wave Optics
• Principles of Lasers

Employers have verified that these topics constitute the “core” of basic photonics. Supplemental math material can also be included for those students who need to brush up on their skills in algebra and trig.

In our nation’s present economic condition, with a high jobless rate, the news about available jobs in photonics sounds like a golden opportunity for some unemployed workers to “get back on the payroll” and enter some rewarding careers. But if you’re unprepared for a job, you’ll probably stay at the entry-level job, with little chance for advancement; you might even get laid off when a more qualified person can be hired. So, if you want to have a successful, rewarding career as a photonics technician, it’s important that you build your knowledge and skills in the basics of photonics technology.

If you’re interested and need to get connected with a photonics college, contact OP-TEC. Or, if you’re an employer looking for a way to upgrade your techs in photonics, we can help you find a college to provide these services. Contact us for more information!