Laser Diode – Definition, Characteristics, and Applications

Today’s photonics technology relies heavily on LASER diodes. LASER stands for “Light Amplification by Stimulated Emission of Radiation“. A high power laser diode is a PN junction diode that generates laser radiation when current is applied in the forward direction.

The optical and electrical characteristics of semiconductor materials and PN junctions are how these diodes function. In contrast to light-emitting diodes, which release light spontaneously, this diode emits coherent light through stimulated emission.

In contrast to LEDs, LASER emits light more reasonably, but both diodes’ constituent components are the same. Depending on the composition of the active layer, these diodes have wavelengths that range from visible to infrared.

The article covers an outline of the laser diode, its applications, characteristics and advantages and disadvantages.

Definition

It is a semiconductor used to produce high-intensity coherent light using a technique similar to Light Amplification by Stimulated Emission of Radiation (LASER). Coherent light, in this context, refers to light signals produced by the apparatus with the same frequency and phase. Similar to LEDs, this diode operates on the concept of stimulated emission.

Although the waves in sunlight and fluorescent lamps have different wavelengths, they are not in sync. However, these diodes produce a thin laser light beam in which every light signal has the same wavelength and moves in unison.

Because lasers are so intense, they can focus on very small areas. These are employed in various gadgets, including Radar, security systems, laser printers, barcode readers, and FOCs (Fibre optic communications). Usually, Its temperature ranges between 20 to 25 °C.

Did You Know? A single pass of the 10W laser diode may cut 4-5 millimetres of plywood, wood, or acrylic.

 Symbol

The symbol for a laser diode is

Construction

The construction of a laser module includes using different materials such as metal contacts, p-type materials, n-type materials, and intrinsic layers. The input terminals of this device are attached to metal plates inserted into the n-type and p-type layers. These high power laser diodes are also called Homojunction Laser Diodes.

An intrinsic region is employed between the p-type and n-type semiconductors to maximise the capacity of the transition site and allow for more charge carriers to accumulate at the junction.

It improves output power by allowing multiple electrons to interact through holes simultaneously. An optical lens focuses the laser light produced from the elliptical region. Typically, a metal case surrounds the PIN diode’s whole configuration.

Laser Diode: Types

These are available in several varieties, including the following.

Double Heterostructure

In this form of diode, a substance-like Heterostructure is placed between p-type and n-type materials. Given the presence of heterostructure substances, this kind of diode is referred to as a double heterostructure laser diode. Its principal advantage is that the active portion of this diode can be employed for improved optical amplification.

Quantum Well

Another high power laser diode is where the quantum well layer is present at the centre of the device. Quantum energy is mostly utilised to transition electrons and other charge carriers from higher to lower energies, which leads to increased effectiveness.

Separate Confinement Heterostructure

A thin intermediate layer in quantum well laser diodes generates effective light confinement. Two extra layers are added to the initial three layers to balance this within each different laser diode. These layers help to effectively confine the generated light since they have a lower refractive index.

Vertical-Cavity Surface-Emitting

In all the previously stated laser diodes, the optical cavity is positioned perpendicular to the direction of current flow. However, the optical cavity in the vertical cavity surface emitting it is positioned parallel to the direction of current flow. The partially reflecting mirrors are put near the extremities of the optical cavity.

Other Types of Laser Diodes

• Interband Cascade Laser Diode
• External Cavity Diode Laser
• Quantum Cascade Laser Diode
• Distributed Feedback Laser Diode
• Distributed Bragg Reflector Laser Diode
• Vertical External Cavity Surface Emitting Laser Diode (VCSEL)

Advantages

The following are some of the advantages of laser diodes.

• The laser’s operating power is low in comparison to other diodes.
• These diodes are relatively simple to handle.
• One can create a high-efficiency light.
• Power usage is minimal.
• The cost of production and operation is lower.
• Long Durability
• Extremely Reliable

Disadvantages

The following are some of the disadvantages of laser diodes.

• It is costlier when compared to other diodes.
• Laser rays are particularly hazardous to the eyes.
• These are temperature-sensitive; when the temperature rises, it will impact the operation of the diode.
• high power applications are not appropriate.

 Applications

These are used in every major area of electronics, including:

• Consumer Electronics: Some common examples of the application of laser diodes include CD/DVD players, barcode readers, laser printers, fibre optic communication etc.
• Medical Equipment: These are used for non-invasive cataract surgery, the removal of cancerous cells, and other medical procedures.
• Autonomous Vehicles: LIDAR systems used for autonomous driving are made using laser diode technology.
• Scientific Instruments: Lasers are employed in scientific instruments like rangefinders, spectrometric instruments, and remote contactless measurement equipment.
• Industrial Applications: These include the precision cutting of materials using high-intensity laser beams generated by laser diodes. In 3D printing, they are also utilised to soften the substance.

Characteristics

L-I Characteristics

• The light energy rises with rising laser current, but it is temperature-dependent.
• Likewise, the chart demonstrates that the laser energy rises after a specific threshold laser current. The laser current threshold value increases significantly with temperature.
• In a nutshell, the threshold value of the laser current during which light energy is emitted increases with the temperature. Given that there is no light energy beyond this threshold, it must be driven up to the laser current threshold value.
• The laser current threshold value must be identified to ensure a reliable operation. 

V-I Characteristics

The initial power voltage of it is typically 1.5 V. Additionally; the operating temperature impacts the forward voltage.

The accompanying diagram illustrates how voltage affects the current in a diode.

In the characteristics mentioned above, the horizontal line defines the current, while the vertical line defines the optical power of the produced light. Therefore, based on these characteristics, it is clear that after the power reaches the threshold voltage, it will progressively grow for a slight increase in the current. This diode’s ability to generate power depends on the device’s and the environment’s temperature.

Features

The features of the laser light produced by these are as follows:

Coherence: Coherence is a crucial laser characteristic that results from stimulated emission. Essentially, it indicates that the transmitted light waves‘ wavelengths are in phase. Since they are produced through spontaneous photon emission, common light sources like LEDs do not possess the quality of coherence.

Monochromaticity: This diode emits monochromatic light, which has a single wavelength. The light produced will have a single colour if it has waves with a single wavelength.

Brightness: The light’s brightness is calculated mainly using the metric power per unit surface area per unit solid angle. Due to continual reflections, this diode emits a bright, high power light. The technology can therefore generate brilliant light.

Directionality: The light emitted by a laser diode does not display significant divergence because laser light is intensely focused. In a laser diode, the released photons experience multiple reflections through the mirror, causing directionality. The light is skipped as it deviates from its axis. As a result, just a light beam that has been greatly concentrated is produced.

Interesting Details: A tunable diode laser is a light source to illuminate the measurement region. A photodiode evaluates the transmitted light. The detection of absorption signals is typically improved by using laser light with a modified wavelength. Thus, a tunable laser diode is one whose operating wavelength can be changed precisely. Even though all laser gain media allow minor shifts in output wavelength, only a few kinds of lasers enable continuous tuning over a sizable wavelength range.

Conclusion

The focus of this article is a general outline of laser diode behaviour. Major electronic industries like consumer electronics, healthcare, autonomous vehicles, science, industrial applications, etc. employ them. The wavelength range of laser diodes is 810–1064 nm.

Frequently Asked Questions

1. What is the purpose of a pulsed laser diode?

Ans. The purpose of a pulsed laser diode driver is to deliver a repeating sequence of current pulses at a predetermined output level over user-defined time intervals. It is a voltage-controlled constant current source. The output to the laser is specified in units of time and amplitude.

2. What do laser diodes mean?

Ans. It is also described as an injection laser or a diode laser, is a type of semiconductor that releases multiple radiations (in which the wavelengths are all at the same phase and frequency) in the infrared or visible spectrum when current flows through it. 

3. How many different kinds of laser diodes exist?

Ans. Different kinds of laser diodes include: MLM, referred to as a Fabry-Perot laser. SLM is referred to as a Single longitudinal mode laser. 

4. What function does a laser serve?

Ans. Fibre-optic communication, DVDs, CDs, and CD-ROMs have all been made possible due to their significance in science, business, and entertainment. Without lasers, there wouldn’t be accurate commercial aeroplane navigation procedures, certain life-saving cancer therapies, or grocery bar code readers.