An Injection Laser Diode (ILD) or a Laser Diode (LD) or a Diode Laser is a semiconductor that is much similar to that of an LED (Light Emitting Diode) where a diode siphoned legitimately with electrical current can lead to a lasing condition at the junction of a diode. Laser diodes can convert electrical energy directly into light. Initiated by a potential difference, the doped P-N transition offers joining of the electron with a hole (positive space). As the electron gets dropped to a low energy level from a high energy level, radiations are emitted in the form of photons. This is an example of spontaneous emission. Whenever the procedure is continued, stimulated emission can be generated.

The type of material used as semiconductors helps in determining the emitted beam's wavelength. Laser diodes that we use today range from ultraviolet to infrared spectrum. Laser diodes are the most well-known type of lasers created, with a wide scope of utilization that incorporates barcode readers, CD / DVD / Blu-ray disc recording/reading, optic communications, laser pointers, laser printing, light beam illumination, and laser scanning. Laser diodes can be utilized for general illumination with the help of phosphor (found in white LEDs).

Theory of Operation

A laser diode is electrically referred to as a PIN diode. The laser diode comes with the active region in the intrinsic (I) region, and the holes, as well as the electrons, are pushed into that region from the P and the N regions respectively. One of the very first studies on diode laser was carried out on simple P-N diodes. Today all lasers utilize the Double Hetero Structure implementation. Here the photons and the carriers are restricted so as to expand their odds for recombination and generation of light. In contrast to the regular diode, the main aim of a laser diode is to join up all the carriers in the intrinsic region and generate light. Therefore, laser diodes are created utilizing Direct Band Gap semiconductors. The epitaxial structure of a laser diode is formed by utilizing the technique of crystal growth, generally initiating from the N-doped layer and building up the intrinsic doped active layer, succeeded by the P-doped cladding, and a contact layer. Most often, the active layer comes with quantum wells that offer higher efficiency and lower threshold current.

Applications

• Medical uses – In the field of medical science, especially that of dentistry have discovered several uses of diode lasers. It's small size and cheap cost along with user-friendliness make it very much alluring to clinicians for minor delicate tissue strategies.

• Telecommunications, Spectrometry, and scanning – Laser diodes are used much widely in telecommunication as easily coupled and modulated light sources for carrying out fiber optics communication. It has also found its use in barcode readers. Visible lasers (generally red and green) are also very much popular as laser pointers.

This was all we have regarding laser diodes. Hope you enjoyed going through it. Brands that manufacture them are Finisar, OSRAM and TT Electronics. Make sure to follow them using the links as provided.

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A photodiode is referred to that semiconductor equipment that transforms light into an electric current. The electric current is formed when photons get absorbed in photodiodes. This electrical equipment may consist of built-in lenses, optical filters, with small and large surface areas. One of the commonly and traditionally used solar cells known as electric solar power is an example of a large area photodiode.

Photodiodes are much similar to regularly used semiconductor diodes but they might be either uncovered or covered with an optical fiber connection or window to enable light to come and hit some of the sensitive device’s parts. To uplift the response of speed, several diodes intended for use as a photodiode utilizes a PIN junction in place of a P-N junction. A photodiode is designed basically to work in reverse bias.

Principle of Operation

As said earlier, a photodiode is a PIN structure or a P-N junction. Whenever a photon containing enough energy hits the diode, it forms an electron-hole pair. This process is called the photoelectric effect. If the assimilation happens in the depletion region of the junction, or one dispersion length away from it, these electron and holes are cleared from the junction by the electric field generated inside the depletion region. Thus the electrons go towards the cathode while the holes move toward the anode, producing a photocurrent. The net amount of current passing through the photodiode is equal to the sum of the dark current (current formed in the absence of light) and the photocurrent. Thus to get a maximum value of the device’s sensitivity, the dark current should be minimized.

Materials

The materials that can be utilized to create a photodiode is the basic to characterize its properties because only photons that are having enough energy to excite electrons across the bandgap of the material will generate notable photocurrents.

Materials that are used popularly to make photodiodes are:-

• Silicon – Range of electromagnetic spectrum wavelength is from 190nm to 1100nm.
• Germanium - Range of electromagnetic spectrum wavelength is from 400nm to 1700nm.
• Indium gallium arsenide - Range of electromagnetic spectrum wavelength is from 800nm to 2600nm.
• Lead (II) sulfide - Range of electromagnetic spectrum wavelength is from <1000nm to 3500nm.
• Mercury cadmium telluride - Range of electromagnetic spectrum wavelength is from 400nm to 14000nm.

The noise generated by silicon-based photodiodes is less as compared with the germanium-based photodiodes. The reason behind this is that they have greater bandgaps.

Comparison with Photomultipliers

A photomultiplier is a device that can generate an electrical signal from the incident photons.

Advantages of photodiodes over photomultipliers:

• Low noise.
• Light in weight and compact.
• It has a longer lifetime.
• High voltage is not needed.
• Quantum efficiency is high.

Disadvantages of photodiodes over photomultipliers:

• The area is small.
• Response time is slower.
• Overall sensitivity is much low.

This was all we have regarding photodiodes. Hope you enjoyed going through it. Brands that manufacture them are Osram, First Sensor, and Vishay. Make sure to follow them using the links as provided.

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LED is a light-producing semiconductor which discharges light when electric current moves through it. The electrons present in the semiconductor get attached with electron holes and release photons (energy). The shade of the light is dictated by the vitality required for electrons to overcome the bandgap of the semiconductor. White light can be generated by a film of a light-emitting phosphor on the device.

The earliest LEDs, which was developed in around 1962, used to emit infrared lights of low intensity. Infrared LEDs have found its use mostly in remote control circuits which can be found in equipment linked with consumer electronics. Modern LEDs come with ultraviolet, infrared and visible wavelengths with the high light output.

LEDs have several advantages over an incandescent light. They are:

• Long Lifetime
• Small Size
• Fast switching
• Improved physical robustness

LEDs have found its use in automotive headlamps, traffic signals, plant growing light, aviation light, medical devices, lighted wallpaper, camera flashes, plant growing light, and advertising.

In contrast with a laser, the light that is released from an LED is neither highly monochromatic nor spectrally coherent. Still, its spectrum is adequately narrow that it can be recognized by the human eye as a saturated color.

High Power LEDs

High Power LEDs are referred to as those LEDs that have higher brightness as well as power and is much costly as compared to that of small LEDs. The most common rating of an LED is 20mA. Any LED that has a higher rating than this can be said to be a high power LED. Generally, the power rating is 10w, 8w, 5w, 3w, 1w, 0.5w, 0.25w and so on. The brightness of small power LEDs is in mcd while that of the high power LEDs is calculated in lm. Presently, high power LEDs are utilized in flashlights, automobile lights, lighting fixtures, etc. 

High Power LEDs can be categorized into 3 types:

• The first type is classified according to the rating power. It can be 100W, 90W……10W, 5W, 1W, 0.5W.
• The second type is the way it is packed. It includes simulated superflux epoxy package, large dimension epoxy package, MCPCB package, power SMD package, TO package, MCPCB integration package, etc.
• The third type is according to the extent of luminous decay. It includes non-low as well as low luminous decay High Power LEDs.

High power LEDs are vitality productive structure which generates adequate lumen yields perfect for mainstream lighting applications. High Power LEDs provides one of the best solid-state light source allowing the user to find out some of the creative ideas related to lighting. The high power LEDs come in both O’Ring as well as Star configurations. Both of this configuration provides the best possible color temperature as well as color rendering capabilities. With an ostensibly related shading temperature of 3200K, nearest to the customary indoor light source, it is especially fit to architects and light planners.

This was all we have regarding High Power LEDs – White. Hope you liked going through it. Brands that manufacture them are Cree, Lumileds, and OSRAM. Make sure to check them out using the links as provided.

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