What are Laser Diodes?

A laser diode (semiconductor laser) is an electronic component that generates laser light by converting electric current into light using a semiconductor p-n junction. As a light source with excellent directivity and rectilinear propagation that enables easy control of energy, laser diodes are used in a wide range of fields, including optical communications, medicine, sensing, data storage, and entertainment. Their basic principle is to utilize the light generated by recombination of electrons and holes. There are a numerous products available with different wavelengths and output characteristics. This article describes the basic principle, structure, materials, types, and applications of laser diodes.

What Are Laser Diodes?

Laser diodes are also called semiconductor lasers. The term “laser” is an acronym for “Light Amplification by Stimulated Emission of Radiation”, which describes their basic principle of operation. Light in nature and light from LEDs, even if their wavelengths are constant, do not have aligned waveforms or phases. In contrast, laser light is “coherent” light generated by amplifying only one specific wavelength. A coherent light source has phase and waveform aligned; this property and interference can be used to reduce a focal point to an extremely small size (several micrometers or so), which enables a variety of applications such as optical switching and optical modulation.

History and Development

The history of lasers began in 1917, when Albert Einstein first theorized the phenomenon of “stimulated emission”, which is the cornerstone of all laser technology. Thereafter, in 1953 John von Neumann of Germany described the concept of a semiconductor laser in an unpublished paper. And, in 1957 Gordon Gould of the U.S. suggested that stimulated emission could be used to amplify light, and coined the term “LASER” (Light Amplification by Stimulated Emission of Radiation) to designate the process. Thus, laser research was advanced by various scientists, and in 1962 coherent light emission from a gallium arsenide (GaAs) semiconductor laser using a homojunction structure was verified. That same year, oscillation of visible light was also achieved. However, for the semiconductor lasers of this era, continuous oscillation at normal temperatures was a problem, but in the 1970’s, with the discovery of the double heterostructure, continuous oscillation at room temperature became possible.　Since the 1970’s, semiconductor lasers have evolved rapidly, and have come to be used widely in diverse fields.

Principle of Laser Diode Light Emission

A laser diode is a semiconductor device that generates laser light at a specific wavelength. It basically comprises a p-n junction that is formed by a junction of p-type and n-type semiconductors, an active layer that emits light, and mirror surfaces that are coated to reflect the light. To summarize the principle of laser diode light emission, electrons and holes recombine when an electric current flows, and during this process, emitted photons are amplified in the active layer and reflected in the resonator to become laser light. In this article, we first explain the basic structure and light emission principle of “glowing semiconductors” which are common to laser diodes and LEDs.

Basic Structure and Materials of Diodes

A semiconductor is a substance that has electrical properties intermediate between those of a conductor and an insulator (nonconductor) of electricity. Conductors are metallic materials such as iron and gold, while insulators are materials such as rubber and glass. Semiconductors can control electric current by conducting or not conducting electricity. They can also convert energy between light and electricity, depending on how they are used.

Diode elements are mainly made of silicon (Si), the most representative semiconductor material. Silicon is abundant in nature as silica rock (stone composed mainly of silicon dioxide, SiO2) and in other forms. Because it is easy to process, silicon is used in many semiconductor products.

Silicon (Si) is originally an insulator and has almost no free electrons as carriers. Thus, impurities are added to the silicon to increase the carrier concentration in silicon, raising its electrical conductivity for use. Semiconductors in which carriers are increased by adding impurities are called impurity semiconductors. Carriers consist of free electrons and free holes. Semiconductors with increased free electron carriers are called “n-type semiconductors” and those with increased free hole carriers are called “p-type semiconductors”.

※p-type semiconductor (+: positive): hole-rich semiconductor
 n-type semiconductor (–: negative): electron-rich semiconductor

The diode element has a p-n junction structure in which a p-type semiconductor and an n-type semiconductor are joined together. The electrode on the p-type semiconductor is called the anode and the electrode on the n-type semiconductor is called the cathode, and current flows from anode to cathode.

Principle of Diode Light Emission

When a forward voltage is applied to a p-n junction element, holes (positive) and electrons (negative) move toward the p-n junction, and recombine. The extra energy generated in this process is converted into light, which is emitted. This phenomenon is called light emission by recombination.

The movement of carriers at this time is explained using energy band diagrams for a p-n junction. The left figure below shows the p-n junction with no bias voltage applied, and the right figure shows the p-n junction with a forward bias voltage applied. When a forward voltage is applied, the height of the energy barrier at the p-n junction is lowered, and electrons, which are the majority carriers in the n-type region, move across the energy barrier to the p-type region and recombine with holes, which are the majority carriers in the p-type region, as shown in the figure on the right. The excess energy is emitted as light. On the other hand, holes in the p-type region move to the n-type region and recombine with electrons, which are the majority carriers in the n-type region, and the excess energy is emitted as light in the same way.

As shown in the figures above, there is a difference in energy levels between the conduction band and the valence band, and this energy difference is called the band gap. The transition of electrons from the conduction band to the valence band across the band gap is called an electron transition. In other words, when an electron transitions from the high-energy conduction band to the low-energy valence band and recombines with a hole, the energy corresponding to the band gap is emitted as a photon (light). This is how semiconductors emit light.

Laser Diode Materials, Wavelengths, and Emission Colors

Laser diodes are devices that use semiconductor materials to generate light. The performance and characteristics of laser diodes vary greatly depending on the material chosen. Typical diodes use silicon, but laser diodes use compound semiconductors, and therefore have high luminous efficiency. The choice of material for a laser diode directly affects its wavelength, luminous efficiency, operating temperature, and many other characteristics.

Below, the role of the compound semiconductors used in laser diodes and their characteristics will be discussed in detail.

Role of Compound Semiconductors

While ordinary diodes are made of silicon (Si), laser diodes are made of a class of materials called compound semiconductors. Silicon (Si) is not suitable as a material for light-emitting elements such as laser diodes and LEDs because it hardly emits light due to its low emission transition probability (probability of electric current changing into light).
Semiconductors that emit light such as laser diodes and LEDs are called “direct transition semiconductors,” while semiconductors that do not emit light are called “indirect transition semiconductors”. In semiconductors, electrons transition from the high-energy conduction band to the low-energy valence band. There are two types of such electron transitions, “direct transitions” and “indirect transitions,” depending on the semiconductor material.
The figure below shows indirect and direct transitions. The vertical axis represents energy and the horizontal axis indicates the wavenumber k.

A) Light-emitting semiconductors: “direct transition semiconductors”

A semiconductor in which the lowest level of the conduction band and the top of the valence band are at the same wavenumber k (the spatial oscillation state of the electron wave) is called a “direct transition semiconductor.” When electrons transition between the conduction and valence bands, the wavenumber k does not change. In other words, an electron that has been excited to the conduction band emits the energy difference, the bandgap Eg, in the form of a photon (light) to transition to the valence band, where it recombines with a hole. Accordingly, direct transition semiconductors can generate light with high efficiency and are used as materials for laser diodes and LEDs.
Direct transition semiconductors include GaAs/AlGaAs, GaAlP/InGaAlP, and GaN/InGaN. These semiconductors made of multiple elements are called compound semiconductors. In particular, III-V compound semiconductors, in which Group III and Group V elements are combined, are widely used in light-emitting laser diodes and LEDs.

B) Non-light-emitting semiconductors: “indirect transition semiconductors”

A semiconductor in which the wavenumber k differs between the lowest level of the conduction band and the top of the valence band is called an “indirect transition semiconductor”. When an electron transitions between the conduction band and the valence band, the wavenumber k changes. This change is caused by the emission and absorption of phonons (quanta of lattice vibrations), the energy of which is released as heat. The absorption of photons (light) and the absorption and emission of phonons must occur simultaneously. Indirect transition semiconductors cannot be used as light emitting elements because of their low luminous efficiency due to the low probability of transitions involving the emission of photons (emission transition probability). Indirect transition semiconductors include Si and Ge.

Wavelength Range and Adjustment Methods

The compound semiconductors that are the materials used in laser diodes and LEDs emit light at various wavelengths, such as in the infrared, visible (e.g., red, green), and ultraviolet regions, depending on their composition and constituent ratio. The basic emission wavelength is determined by the energy of the band gap when carriers (electrons and holes in an excited state) recombine in the semiconductor that serves as the active layer.
The relationship between band gap energy (Eg) and wavelength (λ) is expressed by the equation: Eg=hν=hc/λ (h: Planck’s constant, ν: vibration frequency of light, c: speed of light).
From the equation, it can be seen that the band gap energy (Eg) is inversely proportional to the wavelength (λ). In other words, the larger the band gap energy, the shorter the light wavelength λ.

Compound semiconductors for laser diodes and LEDs are manufactured by epitaxial growth of thin-film crystals with p-n junctions on a substrate semiconductor material. In order to stack good-quality thin-film crystals, the lattice constants of the semiconductor substrate and each crystal layer should match. So when selecting materials, the lattice constants must be considered in addition to the band gap energy.

The figure above shows the relationship between lattice constants and band gap energy (= wavelength) for III-V compound semiconductors. Materials with large band gap energies tend to have small lattice constants, while materials with small band gap energies tend to have large lattice constants. It also shows that, in principle, III-V compound semiconductors can be used at a wide range of wavelengths in the UV, visible, and infrared regions. For example, we can see that if a GaInP p-n junction is grown on a GaAs substrate, the lattice constants are well matched, and an emission wavelength of about 650 nm can be obtained.

Relation Between Emission Color and Wavelength

Laser diode (semiconductor laser) light, with its high monochromaticity, generates light which has nearly a single wavelength, as opposed to light issuing from an LED, which has a broad range of wavelengths. There are lasers operating at various wavelengths; of the light emitted, that at wavelengths that can be seen with the human eye is called “visible light”. Representative wavelengths are as follows.

Materials and Emission Colors

The following are some of the main materials used in laser diodes (semiconductor lasers).

• ・Gallium Arsenide (GaAs) : The most widely used laser diode material, capable of covering a wide range of wavelengths
  High performance can be achieved due to advances in the development of semiconductor manufacturing technology.
• ・Gallium Nitride (GaN) : Well known for highly efficient blue-light LEDs and high-output UV LEDs
• ・Indium Phosphorus (InP) : Used in high-speed communication applications and in near-infrared laser diodes

Manufacturing processes for laser diodes typically use techniques called chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). By using these techniques, extremely fine layers can be grown, enabling the manufacture of high-precision semiconductor lasers. In addition, the emission wavelength and output power of the laser diode can be controlled through the selection of semiconductor materials and precise adjustment of the manufacturing process.

Principle of Laser Diode Oscillation

We have discussed the structure and materials of the “light-emitting semiconductors” that are common to laser diodes and LEDs. So what is the difference between laser diodes and LEDs?　The term “laser” is an acronym for “Light Amplification by Stimulated Emission of Radiation”. As the name implies, the basic requirement for lasers is to use stimulated emission to extract amplified light; this is what differentiates them from LEDs.
From here, we will explain the principle of laser diode oscillation: the “stimulated emission” and “amplification” of light.

Amplification of Light by Stimulated Emission

As mentioned earlier, semiconductors emit energy as light when electrons transition from the conduction band to the valence band and recombine with holes. There are two types of light emission: spontaneous emission and stimulated emission.

In spontaneous emission, electrons in the conduction band recombine with holes in the valence band, each time without interaction, to emit light, and each recombination is completed with the emission of one photon. As mentioned earlier, the wavelength of the light is determined by the magnitude of the band gap energy at which the semiconductor carriers recombine. In actual recombination, however, electrons with energies different in magnitude from the band gap energy recombine with holes in the valence band, so the spontaneously emitted light has a random polarization and phase.

In contrast, in “stimulated emission,” when light λ1 corresponding to the band gap energy Eg between the conduction band and the valence band passes through, electrons in the conduction band are stimulated by the interaction with the light and transition to the ground state of the valence band. At this time, light (photons) with the same energy (wavelength) and phase as the light λ1 is emitted. At first a single photon becomes two, and these two photons further stimulate electrons in the conduction band to become four, and so on. As the stimulated emission increases, intense light with the same wavelength and phase is extracted. This is how stimulated emission of laser light occurs.

Optical Resonator

In order for laser oscillation to occur, the gain of the amplification effect of this stimulated emission must be made sufficient large. To achieve this, a laser diode has two reflecting surfaces (mirrors) facing each other, between which light is repeatedly reflected back and forth. This structure with parallel reflecting surfaces on both sides of the optical amplifying medium is called a Fabry-Perot resonator, and in particular, the interior of the resonator is called a cavity. In nearly all lasers, and not only semiconductor-based laser diodes, this resonator plays an important role in laser oscillation.
However, simply reflecting light back and forth in the cavity does not allow the light to be extracted from the laser diode. To get light out of a reflecting surface, it is necessary to reduce the reflectance of one reflecting surface, that is, some of the light must be reflected and some transmitted. It is important to optimize the reflectance (or transmittance) of the reflecting surfaces in order to efficiently extract light from the laser diode. When light is sufficiently amplified to a certain level of intensity by traveling back and forth in the cavity, the light penetrates the reflecting surface with reduced reflectance. This is the principle of laser oscillation.
Generally, laser diodes have a structure in which a cleaved surface of a semiconductor is used as a reflecting surface and light is emitted from the cleaved surface. A laser diode with this structure is called an edge-emitting laser (EEL).

Structure of Laser Diodes (Light Confinement, Carrier Control)

In order to realize practical laser diodes with high luminous efficiency, various structures have been studied. Confinement of light and carriers is particularly important for efficient light extraction from laser diodes.
First, we will explain the basic principle of light confinement, i.e., optical waveguides.

Optical Waveguides

Light has the property of being confined to areas with a high refractive index. In optical waveguides, the part where light propagates is called the “core” and the surrounding area is called the “cladding”. The refractive index n2 of the core is higher than that of the cladding n1, and the difference in refractive index confines light to the core. Light is guided while repeatedly undergoing total reflection at the interface between the core and the cladding.

One example of use of this optical waveguide action is optical fibers. An optical fiber consists of a “core” that is the light transmitting part, a “cladding” around the core, and a surface coating. The cladding is made of a material with a lower refractive index than the core, so that light is confined to the core and propagates in a zigzag manner through the core. This property of light is also used in the structure of laser diode elements.

Double Heterostructure

Semiconductors used in LEDs and laser diodes have a double heterojunction structure in order to efficiently extract light energy (increase luminous efficiency). Generally, a junction of crystals made of different materials is called a heterojunction, and a double heterojunction means that it has two of these heterojunctions. In a double heterojunction, a semiconductor layer called the “active layer” is sandwiched between n-type and p-type semiconductors called the “cladding layers. The “active layer,” which is the center of the light emission, has a smaller band gap energy, while the “cladding layers” have larger band gap energies than the active layer.

The double heterostructure plays two roles: confining light and confining carriers.

• ・Light confinement:By using a layer with a high refractive index as the active layer and layers with low refractive indexes as the cladding layers, light is confined within the active layer in the middle, as in an optical fiber.
• ・Carrier confinement:Carriers (electrons and holes) are also confined within the active layer. This function is explained in the energy diagram of a double heterojunction.

The left figure above shows a double heterojunction with no bias voltage applied. Although electrons are abundant in the n-type cladding layer, there is an energy barrier between the active layer and the n-type cladding layer, and also between the active layer and the p-type cladding layer due to the band gap difference. Therefore, electrons cannot enter the active layer and remain in the n-type cladding layer. In contrast, holes can enter the active layer because there is no energy barrier between the active layer and the p-type cladding layer.
The figure on the right shows the structure with a forward voltage applied. The energy barrier for electrons in the n-type cladding layer is eliminated and electrons can move to the active layer. However, the energy barrier between the active layer and the P-type cladding layer due to the difference in band gap remains, so the electrons are held back and remain in the active layer. The holes from the p-type cladding layer stay in the active layer as well. Emission occurs when electrons from the n-type cladding layer and holes from the p-type cladding layer recombine in the active layer. Due to this structure, carriers (electrons and holes) are confined in the active layer and their density becomes very high, resulting in high probability of recombination. This effect is called the carrier confinement effect. This effect makes it possible to produce semiconductors with high luminous efficiency.

Optical Confinement and Carrier Control

A basic laser diode element has a double hetero structure, but there are several types. First, a laser called a broad-area laser (full-surface electrode type laser) has electrodes attached to the entire surfaces of the p-type and n-type regions. In this structure, current flows over a wide area and laser light is emitted from a wide area of the active layer, resulting in a very large current flow, and consequently such devices are not suitable for practical use. Therefore, stripe lasers have been devised in which current is injected into only a portion of the active layer. Among these, inner stripe lasers, in which a layer with a lower refractive index than the active layer is embedded around the active layer, have become the mainstream. Similarly to the principle of optical fibers, light confinement occurs in the active layer. Since lasers with this structure have stable oscillation modes and are highly practical, most laser diodes currently use this structure.

In other words, in the active layer of a laser diode element, light is confined not only vertically by the double heterojunction but also horizontally by the embedded stripes. This structure has enabled practical application of laser diodes with high luminous efficiency.
Stacked laser diodes, in which multiple active layers are stacked to further increase luminous efficiency, are also now in practical use, and product lineups are expanding. As a result, laser diodes are used in a wide range of applications, from earlier uses in CD/DVD pickups and photosensitive applications in laser printers and MFPs (Multi-Function Printers) to the current applications as light sources in optical sensors, for which demand is growing. In recent years, development of laser diodes with high output power of as much as hundreds of watts has been underway, and it is expected that these laser diodes will be used as light sources for LiDAR devices that will be necessary for automated driving.

How Laser Diodes Differ from LEDs and Natural Light

Laser diodes (semiconductor lasers) and LEDs are both light sources that use semiconductor elements, and the mechanisms by which they generate light are similar. A difference between them is whether or not “stimulated emission” occurs. Whereas LEDs emit the generated light without modification (spontaneous emission), light generation by a semiconductor laser is due to what is called “stimulated emission”. A resonance structure causes light generated by the device itself to travel back and forth within an active layer while being amplified, and the resulting oscillation produces even more intense light with the phase aligned. Compared with LED light and natural light, the light thus emitted by a laser has the following features.

• 1. High directivity and highly rectilinear propagation
  LED light and natural light comprise random wavelengths, phases, and directions, so that light is easily dispersed in all directions. On the other hand, laser light has high directivity, with divergence only within an extremely small angle. This is because the mechanism of semiconductor laser light emission generates light with the same wavelength and phase, concentrated in the same direction, so that there is almost no broadening of the beam even at a considerable distance from the light source; moreover, the light remains intense as it propagates rectilinearly in one direction. Such features are one reason why laser diodes have been adopted in so many different applications.

  

• 2. Highly monochromatic
  The light emitted by a laser diode is highly monochromatic, with a very narrow wavelength distribution; because of this feature, there is little splitting-up or spreading even when such light passes through a prism. This is because laser light has the same wavelength and phase, and is concentrated in the same direction. As a result, laser diodes can efficiently produce light at specific wavelengths, resulting in brilliant and color-reproducible light. The figure below shows that laser light is more focused at specific wavelengths compared to LEDs.

  

  In contrast, natural light such as sunlight is a mixture of colors at various wavelengths, and when such light passes through a prism, it is split up into light of seven different colors. LED light also has wavelengths over a broad range, and as the wavelengths diverge, the light intensity declines.

  

Due to this high monochromaticity, laser light is well-suited for use in optical measurements, laser therapy, and other applications where light of a specific wavelength is required.

• 3. Excellent coherence, high energy density
  Because laser light has excellent coherence, multiple such light beams can be made to interfere to become more intense. This is because the laser light has a single wavelength, and the light at this wavelength is “coherent”, that is, has the same phase. Light beams from several of such laser diodes are in phase, so that when the beams overlap, they are amplified.
  On the other hand, light from LEDs and natural light have multiple wavelengths, the wavelengths and phases of such light are different, so that when they overlap there is no interference resulting in amplification. Moreover, because laser light is precisely aligned in direction and phase, it can be highly concentrated, so that light energy can easily be intensified in a single direction. If for example sunlight were concentrated using a lens, the energy of the concentrated light could cause paper to burn; but laser light, with its more highly concentrated energy, can reach such high energy densities as to cause even metals to melt.

  

Laser Diode Types

Types of Lasers

Lasers are used in a wide ranging of fields, among them medicine, industry, and communications, and are classified according to the material used as the laser medium.
In addition to the laser diodes introduced in this article, there are also the following types.

• Solid-state lasers：These lasers use a solid-state material (excluding semiconductors) as the laser medium; representative examples include ruby lasers and YAG lasers. The world’s first laser to undergo oscillation was a ruby laser. YAG lasers with a wavelength of 1064 nm use crystals as the medium, and are widely employed in industrial applications such as metal processing. Even though semiconductors are solids, when used as a laser medium the resulting lasers have quite different characteristics, and so such devices are generally are classified separately as laser diodes.
• Liquid lasers：These lasers use a liquid as the laser medium, and are broadly divided into three types–organic dye lasers, organic chelate compound lasers, and inorganic lasers–according to the characteristics of the medium used. Of these, organic dye lasers are representative; as the medium, they use an organic dye obtained by dissolving dye molecules in an organic solvent. These so-called “tunable wavelength lasers” enable continuous selection of the emission wavelength, including visible light, through the dye molecules dissolved in the organic solvent. They are often used in scientific fields such as spectroscopic measurement and analysis.
• Gas lasers：Gas lasers use a gas as the laser medium. Compared with other lasers, the laser medium is homogeneous as losses are low, and consequently one feature of these devices is the ability to obtain large laser outputs.
  One such representative gas laser, the carbon dioxide gas laser (CO2 laser), is widely used in industrial applications due to its high output, making it suitable for processing and welding various materials. It is also used in medical applications as a laser scalpel.

Types of Laser Diodes (Semiconductor Lasers)

Laser diodes can be categorized according to the direction in which light is emitted.

• Edge Emitting Laser (EEL):
  This laser uses a cleaved surface of a semiconductor as a reflecting mirror, in a structure that emits light from the cleaved surface.
• Surface Emitting Laser (SEL):
  In this laser structure, light is emitted in the perpendicular direction from a surface of the semiconductor substrate.
• Vertical Cavity Surface Emitting Laser (VCSEL):
  Light is caused to resonate in the direction perpendicular to a face of the semiconductor substrate, and is emitted in the direction perpendicular to the face.
  This structure has a number of features, including a small threshold current, rapid modulation at small currents, and minimal temperature characteristics, so that it is commonly used in optical communication and sensor fields.

types of laser diodes are used in various applications according to their respective characteristics.

Packages Used for Laser Diodes

Current laser diodes widely employ CAN packages, which have a cylindrical metal body and a light output window in a tip part. They generally have the following characteristics.

• 1.External dimensions：Packages with diameters from 3.8 mm to 5.6 mm can be used; heights are from 2.5 mm to 6 mm or so.
  The industry-standard size is 5.6 mm dia. CAN type.
  For quad-beam LDs and some communication systems, the larger 9.0 mm dia. size is used.
  In the optical disc field, where cost is emphasized, frames made of resins are also adopted.
• 2.Body materials：In general, metals such as brass, stainless steel, and aluminum are used.
  Light output window: A narrow window is provided in the tip; light is output from this window.
  Windows are normally formed from silicon or glass; diameters range from 100 µm to 500 µm.
  For cost-sensitive applications, there are also products without cover glass.
• 3.Pinout：The CAN package is normally provided with either two or three pins.
  When there are two pins, the device is a laser diode or a PIN photodiode; if there are three pins, one is used for temperature sensing.

In recent years, surface mount package devices and bare chip shipments have been made available. Laser diode applications seem set for further expansion.

Lifetime of Laser Diodes

The average lifetime of laser diodes depends on the operating environment (temperature of use, static electricity, power supply noise, and so on), but when turned on continuously under typical conditions (case temperature 25°C), is said to be around 10,000 hours. When the operating temperature during use is high, the lifetime is shorter, and electrostatic discharge (ESD) can cause failures. In addition, surges and noise occurring in the supplied power can culminate in destruction of a laser device.
In order to use a laser diode over a long period, it is effective to take such measures as dissipating heat using a heat sink, adequately preventing static electricity and surges, using noise filters and the like, and holding the output down to the minimum required level.
Laser output light, with its high power density, can impart harm to the human body if used incorrectly even when emission amounts are small, and thus is extremely dangerous. Hence laser light must be used after having taken thorough safety precautions.

Laser Diode Applications

• 1. Optical discs (CDs, DVDs, Blu-ray Discs)
  Laser diodes are used in optical pickups (devices for playing and recording data) for digital recording media called optical discs, such as CDs, DVDs, and BDs. Laser light can be used to read out (play) data such as music and videos, and write (record) such information.
  A laser beam is used to detect the presence of slight depressions and protrusions and convert these into electrical signals such as sound or video. For CDs, infrared lasers are mainly used; in the case of DVDs, red-light lasers are used. The shorter the wavelength, the smaller the region into which the laser light can be constrained, so that a larger amount of information can be recorded and played back. Consequently, blue laser light is used in the pickups for Blu-ray discs and next-generation DVDs.

  

• 2. Laser printers, MFPs （Multi-Function Printers）, etc.
  Laser diodes, with their excellent light concentrating ability, are used for sensitization in laser printers and multi-function printers. By irradiating a photosensitive drum, a signal is transferred to paper. Laser printers offer fast printing speeds with little degradation of the printed media, and so are widely used in offices and other places where large-volume printing is necessary.
• 3. Optical communications
  Infrared lasers with wavelengths of 1300 nm and up are used. Because power losses are small and enormous amounts of information can be converted into optical signals and transmitted long distances, they are used as light sources in optical fiber communications. Such lasers are also used for optical data transmission in wireless communication systems where fast communication speeds are required. Device precision is advancing, aiming at uses in the communication field where faster transmission over longer distances is increasingly in demand.
• 4. Laser microscopes
  Laser microscopes irradiate a sample with laser light and detect the reflected light to enable observation. By using laser light with wavelengths shorter than visible light, observation at higher resolution is made possible.
• 5. Pointers, markers
  Laser light, which is highly rectilinear, is also utilized by laser pointers. It is also well-suited for use as markers to mark vertical and horizontal intervals on walls and ceilings; such markers are used at construction sites and elsewhere when installing equipment or performing construction operations.
• 6. Optical distance measurement, 3D sensors
  Because laser diodes (semiconductor lasers) have high rectilinearity and precision, they are also used for optical measurement. LiDAR (Light Detection and Ranging), which uses laser light to measure the shape of an object and its distance, is employed in the automated driving support systems of automobiles and in aerial surveying, and is also installed in smartphones and AR headsets. In addition, applications are being found in such various fields as velocity measurement and gravitational wave detection.
• 7. Smoke and dust sensors
  Laser diodes (semiconductor lasers) are used as light sources for sensors. Light from a laser collides with smoke or with fine dust particles in the air and is scattered, indicating the presence of smoke or dust.
• 8. Laser therapy
  In medical fields, laser diodes are used in diagnosis and therapy of disorders, surgery and irradiation therapy by utilizing photodynamic reactions. Hereafter further applications are anticipated in, for example, skin therapy, eye surgery, dental treatments, and endoscopic procedures.
• 9. Material processing
  Laser diodes (semiconductor lasers) can generate high-output light, and so are used as light sources to process such materials as metals, plastics, and ceramics. Laser processing is capable of fast and highly precise machining, and is well-suited to such applications as cutting and boring holes in hard-to-machine materials.
• 10. Entertainment
  Laser diodes (semiconductor lasers) are also used in entertainment fields, including live performances, concerts, and projection mapping. The characteristics of laser light can be exploited to create fantastic presentations.

Methods of Purchase

ROHM supplies semiconductor products to customers around the world; these products include laser diodes.

Our products can be purchased from the following online distributors.

• ・Digikey（https://www.digikey.com/）
• ・MOUSER（https://www.mouser.com/）
• ・Farnell（https://www.farnell.com/）
• ・Chip1Stop（https://www.chip1stop.com/）
• ・CoreStaff（https://www.zaikostore.com/zaikostore/）

In addition to ROHM products, these distributors handle laser diode (semiconductor laser) products from other manufacturers.
Product prices, inventory, delivery times and the like can be compared to select the best semiconductor laser.

Download datasheets from ROHM

The following laser diodes are introduced on the ROHM website.

• ・High-output semiconductor lasers
• ・Infrared semiconductor lasers
• ・VCSEL
• ・Red semiconductor lasers
• ・Multibeam semiconductor lasers