The essential components of a laser are an external energy source, a gain or amplifier medium, and a resonator. When a medium, for example an Nd:YAG crystal is arranged so between two mirrors that photons always trigger an “induced emission”, this is called an optical resonator. Semiconductor lasers are solid-state lasers based on semiconductor gain media, where optical amplification is usually achieved by stimulated emission at an interband transition under conditions of a high carrier density in the conduction band.
Most semiconductor lasers are laser diodes, which are pumped with an electrical current in a region where an n-doped and a p-doped semiconductor material meet. However, there are also optically pumped semiconductor lasers, where carriers are generated by absorbed pump light, and quantum cascade lasers, where intraband transitions are utilized.
Semiconductor lasers make powerful, precise beams of light (like ordinary lasers), but they’re about the same size as simple LEDs. Semiconductor lasers are advanced and efficient as compared to the conventional lasers as they use active semiconductor materials for light amplification. These lasers are small in size, require less power and are much more efficient than conventional lasers, which make them the smarter choice in the manufacturing of laser-based system. Moreover, semiconductor lasers cost less than conventional lasers. In telecommunication industry, semiconductor lasers are mostly used in fiber optic cables to enable fast and efficient communication.
Semiconductor laser technology
A semiconductor laser is a specially fabricated pn junction device (both the p and n regions are highly doped) which emits coherent light when it is forward biased. p region is rich in “holes” or, in other words, slightly lacking electrons, the tiny negatively charged particles inside atoms and and n-type has slightly too many electrons. Electrons are injected into the diode, they combine with holes, and some of their excess energy is converted into photons, which interact with more incoming electrons, helping to produce more photons—and so on in a kind of self-perpetuating process called resonance. This repeated conversion of incoming electrons into outgoing photons is analogous to the process of stimulated emission that occurs in a conventional, gas-based laser.
In a conventional laser, a concentrated light beam is produced by “pumping” the light emitted from atoms repeatedly between two mirrors. In a laser diode, an equivalent process happens when the photons bounce back and forth in the microscopic junction (roughly one micrometer wide) between the slices of p-type and n-type semiconductor, which is technically known as a Fabry-Perot resonant cavity (a kind of interferometer). The amplified laser light eventually emerges from the polished end of the gap in a beam parallel to the junction.
It is made from Gallium Arsenide (GaAs) which operated at low temperature and emits light in near IR region. Now the semiconductor laser are also made to emit light almost in the spectrum from UV to IR using different semiconductor materials. They are of very small size (0.1 mm long) as simple LEDs, efficient, portable and operate at low power. These are widely used in Optical fibre communications, in CD players, CD-ROM Drives, optical reading, laser printing etc.
While the most common semiconductor lasers are operating in the near-infrared spectral region, some others generate red light (e.g. in GaInP-based laser pointers) or blue or violet light (with gallium nitrides). For mid-infrared emission, there are e.g. lead selenide (PbSe) lasers (lead salt lasers) and quantum cascade lasers.
Stacked laser diodes
Early laser diodes could fire out only a single, relatively puny beam, but ingenious electronics engineers soon found ways to make them considerably more powerful. Since the 1990s, one common approach has been to mount a number of laser diodes on top of one another (like an apartment building) and then focus their individual beams into a single output beam using a collimator and/or lens. This kind of arrangement is variously called a semiconductor laser stack, stacked laser diode, or just a diode stack. Apart from making more power than a single laser diode, a stack opens up the possibility of generating multiple different wavelengths at the same time (because each laser in the stack can make a different one). Instead of a single P-N junction, there are multiple ones, and the laser light beams emerge from the active layers in between them; typically, there’s also at least one tunnel junction between the stacked layers. A single pair of terminals (sometimes called Ohmic contacts) feeds electrical power to the entire stack.
Types of Semiconductor Lasers
There is a great variety of different semiconductor lasers, spanning wide parameter regions and many different application areas:
- Small edge-emitting laser diodes generate a few milliwatts (or up to 0.5 W) of output power in a beam with high beam quality. They are used e.g. in laser pointers, in CD players, and for optical fiber communications.
- External cavity diode lasers contain a laser diode as the gain medium of a longer laser cavity. They are often wavelength-tunable and exhibit a small emission linewidth.
- Both monolithic and external-cavity low-power levels can also be mode-locked for ultrashort pulse generation.
- Broad area laser diodes generate up to a few watts of output power, but with significantly poorer beam quality.
- High-power diode bars contain an array of broad-area emitters, generating tens of watts with poor beam quality.
- High-power stacked diode bars can generate extremely high powers of hundreds or thousands of watts.
- Surface-emitting lasers (VCSELs) emit the laser radiation in a direction perpendicular to the wafer, delivering a few milliwatts with high beam quality.
- Optically pumped surface-emitting external-cavity semiconductor lasers (VECSELs) are capable of generating multi-watt output powers with excellent beam quality, even in mode-locked operation. Electrically pumped photonic crystal surface-emitting lasers promise to reach similar performance.
- Quantum cascade lasers operate on intraband transitions (rather than interband transitions) and usually emit in the mid-infrared region, sometimes in the terahertz region. They are used e.g. for trace gas analysis.
Typical Characteristics and Applications
Some typical aspects of semiconductor lasers are:
- Electrical pumping with moderate voltages and high efficiency is possible particularly for high-power diode lasers, and allows their use e.g. as pump sources for highly efficient solid-state lasers (→ diode-pumped lasers) and even as direct diode lasers.
- A wide range of wavelengths are accessible with different devices, covering much of the visible, near-infrared and mid-infrared spectral region. Some devices also allow for wavelength tuning.
Small laser diodes allow fast switching and modulation of the optical power, allowing their use e.g. in transmitters of fiber-optic links.
- Such characteristics have made semiconductor lasers the technologically most important type of lasers. Their applications are extremely widespread, including areas as diverse as optical data transmission, optical data storage, metrology, laser spectroscopy, laser material processing, pumping solid-state lasers (→ diode-pumped lasers), and various kinds of medical treatments.
Because of their compact size and lightweight and ruggedness, semiconductor lasers are ideal for military and aerospace applications. Used directly or as pumps for other lasers, semiconductor lasers are used in a wide variety of applications including both the transmission optical energy to a target and receiving a portion of it back in order to measure various physical properties of the target in a remote fashion.
Defense lasers that transmit energy to the target are common at both low and high power levels. On the low power end (<500mW), direct diode lasers are used for free-space communications for line of sight transmission. At slightly higher power, direct diode lasers are used to initiate ordinances. For even higher powers and long wavelengths, diode lasers can be used directly or to pump solid state lasers which disable incoming heat seeking missiles. At the highest power levels of 50-100kW, high energy solid state lasers for missile defense are being developed. These lasers use >100kW of diode pump light per laser and are expected to be deployed by land, sea, and air in the years to come.
Another class of defense laser is those which are used to extract information from a target. At the low power end, for example, range finding lasers enable the user measure distance and illuminators enable the user to view unprecedented levels of detail. At higher power, remote sensing and LIDAR lasers allow the user to detect bio-chemical agents, clear air turbulence and other atmospheric conditions.This new class of direct diode rangefinders and compact LIDAR systems is based on QPC’s proprietary high efficiency material design around the Eyesafe wavelength of 1550nm and unique high power single mode laser designs exceeding 1W CW.
A new class of non-lethal laser weapons use high brightness green light to warn targets at a distance that is far enough to allow escalation of force and even suppress a potential threat while decreasing the risk for potential collateral damage. QPC’s visible laser product line, based on integrated diode wavelength stabilization technology, allows integration of compact and efficient green lasers on various platforms from rifles to airborne and ground vehicles.
Semiconductor Laser Market
The Global Semiconductor Lasers Market size is estimated to be USD 7.12 billion in 2019 and is predicted to reach USD 14.53 billion by 2030 with a CAGR of 6.7% from 2020-2030.
The increasing adoption of fiber optic lasers in the telecommunication industry and the rising preference of semiconductor lasers as compared to other light sources are driving the semiconductor lasers market globally. Also, the increasing use of 3D printing in the architectural and healthcare sector is likely to augment the demand and popularity of semiconductor lasers.
Furthermore, factors such as compact size, low cost, and long life are expected to contribute to the growth semiconductors lasers during the forecast period. However, low packing tolerance, delicate design and low reliability are expected to inhibit the growth of semiconductor lasers market in the near future. On the other hand, increase in research and development activities coupled with increased demand of data storage is expected to create lucrative opportunities in the market over the forecast period.
There is a rapid increase in the use of semiconductor lasers for different applications. The semiconductor laser is vital in the healthcare sector due to their extensive use for cosmetic procedures, medical diagnosis, and therapies. On the basis of application, the Global Semiconductor Laser market has been segmented into: Optical Storage & Display, Telecom & Communication, Industrial Applications, and Medical Application
Moreover, they are ideal for military and defense applications due to their compact size, lightweight, and ruggedness. In the defense sector, the new high brightness semiconductor laser technology is permitting diode lasers to be used directly in applications where DPSS lasers were the only solution. i.e., target designation, countermeasures, and potentially even high energy lasers. Semiconductor diode lasers are offering advantages over other light sources for applications in dentistry, dermatology and other applications.
In addition, the launch of 3D printers has further increased the demand in this market as this technology is widely used in healthcare to produce fabricated prosthetic limbs and various other life-sciences applications. With the increase in sales of smarpthone, technologies like OLED and VCEL in the smartphone segment are also propelling the growth of semiconductor laser market. Also, the growth in the semiconductor industry may fuel the growth of the market.
On the basis of product type, the Global Semiconductor Laser market has been segmented into:
- Blue Laser
- Red Laser
- Infrared Laser
North America held the lion share of the market and is anticipated to continue holding the major market share throughout the forecast period. The initiatives taken by the U.S. Federal Government, in association with the International Electrotechnical Commission (IEC), endorses and encourages the usage of 3D printers particularly in the healthcare sector with specific mandatory directives, which is expected to drive the market in North America.
Asia-Pacific is also anticipated to register the highest growth rate over the forecast period, due to the high manufacturing and industrialization in the region. Also, government initiatives and investments in Asia-Pacific are promoting the growth of numerous sectors. The exponential growth in the communication industry in countries, such as Japan, China, South Korea, and India, is anticipated to drive the laser market in the region, during the forecast period. Moreover, countries like China, Taiwan, Korea, Japan are the house of smartphone manufacturers such as Apple, Oneplus, Vivo. Samsung, among others which makes semiconductor manufacturer around these regions to produce semiconductor laser to cater to smartphone manufacturers.
Key vendors operating in this market space include Sony, Nichia, Ushio, Osram, TOPTICA Photonics, Egismos Technology, Arima Lasers, Ondax, Panasonic, Sharp, ROHM, Hamamatsu, Newport Corp, Finisar, Mitsubishi Electric, Huaguang Photoelectric and QSI