A laser diode, or LD, is an electrically pumped semiconductor laser in which the active laser medium is formed by a p-n junction of a semiconductor diode similar to that found in a light-emitting diode.
The laser diode is the most common type of laser produced with a wide range of uses that include, but are not limited to, fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray Disc reading and recording, laser printing, laser scanning and increasingly directional lighting sources.
A laser diode is electrically a P-i-n diode. The active region of the laser diode is in the intrinsic (I) region, and the carriers, electrons and holes, are pumped into it from the N and P regions respectively.
While initial diode laser research was conducted on simple P-N diodes, all modern lasers use the double-hetero structure implementation, where the carriers and the photons are confined in order to maximize their chances for recombination and light generation.
Unlike a regular diode used in electronics, the goal for a laser diode is that all carriers recombine in the I region, and produce light. Thus, laser diodes are fabricated using direct bandgap semiconductors. The laser diode epitaxial structure is grown using one of the crystal growth techniques, usually starting from an N doped substrate, and growing the I doped active layer, followed by the P doped cladding, and a contact layer. The active layer most often consists of quantum wells,
One of the most commonly used and important laser diode specifications or characteristics is the L/I curve. It plots the drive current supplied against the light output.
This laser diode specification is used to determine the current required to obtain a particular level of light output at a given current. It can also be seen that the light output is also very dependent upon the temperature.
From this characteristic, it can be seen that there is a threshold current below which the laser action does not take place. The laser diode should be operated clear of this point to ensure reliable operation over the full operating temperature range as the threshold current rises with increasing temperature. It is typically found that the laser threshold current rises exponentially with temperature.
Ø Laser Diode Specifications & Characteristics
a summary or overview of laser diode specifications, parameters and characteristics used in defining laser diode performance for datasheets.
In this section
• Laser diode technology
• Laser diode types
• Structure & materials
• Theory & operation
• Specs & characteristics
• Lifetime, failure & reliability
• Other diodes
When using a laser diode it is essential to know its performance characteristics. Accordingly laser diode specifications are required when designing equipment using laser diodes or for maintenance using near equivalents.
Like any electronics components, many of the specifications are relatively generic, but other parameters will tend to be more focussed on the particular component. This is true for laser diode specifications and characteristics.
There are a number of laser diode specifications, or laser diode characteristics that are key to the overall performance and these are outlined.