Tunable Lasers
Max Robinson, MBA1
Issue date: 11/12/01 Section: Technology
One of the nice things about living on campus is being able to plug my computer into Stanford’s really fast network. Once you get used to having connection speeds like this, it is hard to go back to something slower. As more people come to realize the joys of having a high speed, or broadband Internet connection, the amount of data flowing over the Internet will grow even faster, and most of this data will be sent over fiber optic networks for the majority of the distance it travels. (For those who really want to take advantage of your high-speed connection, I recommend checking out www.BMWfilms.com).
A fiber optic connection is just a thin strand of glass until it is “lit” by a laser, and at the origin of every piece of data that travels down that fiber, there is a laser blinking off and on billions of times a second. Over a strand of fiber optic cable thinner than a human hair, several different wavelengths of light can be transmitted without interfering with each other. Physicists and engineers developed Dense Wavelength Division Multiplexing (DWDM) to take advantage of this characteristic by separating signals into several different wavelengths of light. Each wavelength needs to have a laser transmitting at that wavelength to send the bits of data that make up the e-mails, music, video, and other information that travels over a network.
Most lasers that are in networks now are set to transmit at only one wavelength. Tunable lasers, however, can be switched to transmit over a spectrum of wavelengths, and are the key to a faster, fatter Internet. Currently, the most popular use of tunable lasers is as easy replacement parts, though.
Lasers are expensive components, and if a company needed to keep a spare laser for each wavelength, that would be a significant inventory of spare parts (a spare laser for each of 128 different wavelengths commonly used). A tunable laser, though, could take the place of several spare parts. When one laser goes bad, you simply replace it with a tunable laser and set it to the desired wavelength. Most tunable lasers can not be tuned over the full range of wavelengths used, but if you can replace 128 spare lasers with only four tunable spare lasers, you can save a good bit in spare parts.
The real advantage of tunable lasers will be realized once they can be placed into a network and actually controlled to change wavelengths as network traffic demands. If you are trying to watch the latest car chase scene by Ang Lee, and that Internet path happens to be on a crowded wavelength, the tunable laser will be able to ease the traffic congestion by switching to a different wavelength that has less traffic. Combining tunable lasers with optical switches will allow the Internet to grow much faster without having to dig trenches to lay more lines.
Different Flavors
Tunable lasers are generally one of two different types: EEL’s or VCSEL’s. Edge Emitting Lasers (EEL’s) are formed out of semiconductor material with the active-channel, or the laser area, oriented horizontally. Several EEL’s can be produced on a single wafer of material, but they must be cut and separated before they can be tested or used. The other type of laser commonly used in fiber optics is the Vertical Cavity Surface Emitting Laser (VCSEL), or “vixel”. Unlike edge-emitters, VCSEL’s are grown so that the laser channel is vertical, and the beam comes out of the top surface of the laser. Like edge-emitters, numerous lasers can be made on a single wafer, but they can be more easily tested, since the wafer does not have to be cut before the emitting surface of the laser is exposed.
In general, the edge-emitters tend to have a higher maximum output, but the light is emitted in an elliptical shape, which must be directed into a round fiber. Lenses can be used to focus the light or reshape it into a circular shape, though. VCSEL’s tend to be cheaper and easier to make, but they are not usually able to achieve the same power as EEL’s. Also, since the laser can be grown in a circular shape, the light is emitted in a more circular shape, and is more easily coupled to a fiber.
These lasers are attached into housings that are anywhere from the size of a pencil eraser, to the size of a piece of candy (like a Jolly Rancher or Starburst). A common package for edge emitting lasers is a 14-pin “butterfly” package, with a fiber optic plug coming out of one end. The packages typically incorporate the laser, the fiber optic cable, and lenses and circuits to control the laser output.
Laser Manufacturers
Each individual laser is about the size of a grain of salt. These tiny lasers require very precise tolerances in assembling the components inside the housing packages. Many companies still perform this process manually, with operators using manual bonding equipment to place and attach each laser and all of the other components inside the package. Often, these components are difficult to test in upstream manufacturing processes, and so a lot of work goes into producing each laser package before it is tested. Many companies are moving to automate this process, but they are still working the bugs out of their processes.
Inventories of lasers are pretty high right now, and most analysts don’t expect this market to start picking up until the first or second quarters of next year. At that point, the companies that have developed automated processes will be able to respond more quickly and rapidly to the upswing in the market. Last year, this market was estimated to be roughly $100 million, and it is expected to grow to over $1.5 billion in the next two to three years.
The companies involved in this market include several big name companies, such as Nortel, Lucent and their optoelectronics spin-off Agere, Marconi, JDS Uniphase, and ADC Telecommunications to name a few. There are also several small start-up companies that entered this field in the past couple of years, many of which are still privately held. These include companies like Blue Sky Research, Iolon, Ignis Optics, Agility Communications, NTT Electronics and many others. Each company has their own “special sauce” methods of packaging the lasers, as well as making the lasers give out higher power, switch faster, or be tunable over a wider range of wavelengths.
The goal is to produce inexpensive lasers that can be tuned across all channels of a DWDM system, but that can also switch fast and still deliver enough power to be useful over a long distance. So far most tunable lasers can only do two of these functions. The next couple of years will prove to be a very interesting time for this industry.
If you would like to know more about the optoelectronics industry in general, check out www.lightreading.com, or www.redherring.com.
A fiber optic connection is just a thin strand of glass until it is “lit” by a laser, and at the origin of every piece of data that travels down that fiber, there is a laser blinking off and on billions of times a second. Over a strand of fiber optic cable thinner than a human hair, several different wavelengths of light can be transmitted without interfering with each other. Physicists and engineers developed Dense Wavelength Division Multiplexing (DWDM) to take advantage of this characteristic by separating signals into several different wavelengths of light. Each wavelength needs to have a laser transmitting at that wavelength to send the bits of data that make up the e-mails, music, video, and other information that travels over a network.
Most lasers that are in networks now are set to transmit at only one wavelength. Tunable lasers, however, can be switched to transmit over a spectrum of wavelengths, and are the key to a faster, fatter Internet. Currently, the most popular use of tunable lasers is as easy replacement parts, though.
Lasers are expensive components, and if a company needed to keep a spare laser for each wavelength, that would be a significant inventory of spare parts (a spare laser for each of 128 different wavelengths commonly used). A tunable laser, though, could take the place of several spare parts. When one laser goes bad, you simply replace it with a tunable laser and set it to the desired wavelength. Most tunable lasers can not be tuned over the full range of wavelengths used, but if you can replace 128 spare lasers with only four tunable spare lasers, you can save a good bit in spare parts.
The real advantage of tunable lasers will be realized once they can be placed into a network and actually controlled to change wavelengths as network traffic demands. If you are trying to watch the latest car chase scene by Ang Lee, and that Internet path happens to be on a crowded wavelength, the tunable laser will be able to ease the traffic congestion by switching to a different wavelength that has less traffic. Combining tunable lasers with optical switches will allow the Internet to grow much faster without having to dig trenches to lay more lines.
Different Flavors
Tunable lasers are generally one of two different types: EEL’s or VCSEL’s. Edge Emitting Lasers (EEL’s) are formed out of semiconductor material with the active-channel, or the laser area, oriented horizontally. Several EEL’s can be produced on a single wafer of material, but they must be cut and separated before they can be tested or used. The other type of laser commonly used in fiber optics is the Vertical Cavity Surface Emitting Laser (VCSEL), or “vixel”. Unlike edge-emitters, VCSEL’s are grown so that the laser channel is vertical, and the beam comes out of the top surface of the laser. Like edge-emitters, numerous lasers can be made on a single wafer, but they can be more easily tested, since the wafer does not have to be cut before the emitting surface of the laser is exposed.
In general, the edge-emitters tend to have a higher maximum output, but the light is emitted in an elliptical shape, which must be directed into a round fiber. Lenses can be used to focus the light or reshape it into a circular shape, though. VCSEL’s tend to be cheaper and easier to make, but they are not usually able to achieve the same power as EEL’s. Also, since the laser can be grown in a circular shape, the light is emitted in a more circular shape, and is more easily coupled to a fiber.
These lasers are attached into housings that are anywhere from the size of a pencil eraser, to the size of a piece of candy (like a Jolly Rancher or Starburst). A common package for edge emitting lasers is a 14-pin “butterfly” package, with a fiber optic plug coming out of one end. The packages typically incorporate the laser, the fiber optic cable, and lenses and circuits to control the laser output.
Laser Manufacturers
Each individual laser is about the size of a grain of salt. These tiny lasers require very precise tolerances in assembling the components inside the housing packages. Many companies still perform this process manually, with operators using manual bonding equipment to place and attach each laser and all of the other components inside the package. Often, these components are difficult to test in upstream manufacturing processes, and so a lot of work goes into producing each laser package before it is tested. Many companies are moving to automate this process, but they are still working the bugs out of their processes.
Inventories of lasers are pretty high right now, and most analysts don’t expect this market to start picking up until the first or second quarters of next year. At that point, the companies that have developed automated processes will be able to respond more quickly and rapidly to the upswing in the market. Last year, this market was estimated to be roughly $100 million, and it is expected to grow to over $1.5 billion in the next two to three years.
The companies involved in this market include several big name companies, such as Nortel, Lucent and their optoelectronics spin-off Agere, Marconi, JDS Uniphase, and ADC Telecommunications to name a few. There are also several small start-up companies that entered this field in the past couple of years, many of which are still privately held. These include companies like Blue Sky Research, Iolon, Ignis Optics, Agility Communications, NTT Electronics and many others. Each company has their own “special sauce” methods of packaging the lasers, as well as making the lasers give out higher power, switch faster, or be tunable over a wider range of wavelengths.
The goal is to produce inexpensive lasers that can be tuned across all channels of a DWDM system, but that can also switch fast and still deliver enough power to be useful over a long distance. So far most tunable lasers can only do two of these functions. The next couple of years will prove to be a very interesting time for this industry.
If you would like to know more about the optoelectronics industry in general, check out www.lightreading.com, or www.redherring.com.