Frequently Asked Questions About Gain Chip, SLDs And SOAs

Optical devices, optoelectronic devices and semiconductor optical devices are used to control and generate light as well as manipulate light for different applications. Such devices are used in many different industries like military, health, medicine and telecommunications. They have also transformed communication on an entirely different scale as optical devices are the reason television exists.

Though they are cutting-edge technologies, they are quite difficult to make sense of. To make sure they are easier to understand here are some FAQs about such devices.

Gain Chips

Gain chips are optical devices for communication. They are semiconductor optical elements or devices that are utilized as the optical gain medium of external cavity laser diodes. They are also used as a TLS (Tunable Light Source), which can change the wavelength of the oscillation by using filters like wavelength or frequency selection. An example of such filters would be diffraction grating.

A gain chip is a key element in the development of lasers like tunable diode lasers or high-stability external cavity diode lasers. Gain chips resemble laser diode chips, but they also include a dense anti-reflective coating on one or both sides, which significantly decreases or eliminates self-lacing.


Q-1: Is the active layer structure of the gain chip and BOA the same?

Answer: The difference lies in the waveguide structure as the active layer structure is essentially the same. Gain chips employ a bent waveguide structure, whereas BOAs employs an angled waveguide structure.

Q-2: What is the exit angle of optical output?

Answer: The exit angle of optical output is approximately 20 degrees.

Q-3: How high is the wall-plug efficiency?

Answer: Wall-plug efficiency is also called radiance efficiency or power conversion efficiency. It measures the efficiency with which electrical power is converted to optical power. It is calculated from the current–optical output along with external cavity resonance. The wall-plug efficiency is generally known to be as high as 15%.

Q-4: Is there a way to prevent mode hopping at wavelength sweeping?

Answer: This can be achieved by adjusting the optical length of the gain chip as well as changing the chip temperature and current.

Superluminescent Diode [SLD]

Learn more about gain chip, superluminescent diode, and semiconductor optical amplifier with these frequently asked questions. Get answers to common questions about these technologies & understand their benefits & features.

SLDs are edge-emitting semiconductor and optoelectronic devices that effuse broadband optical radiation or broadband light which is based on superluminescence. They are also called Superluminescent Light Emitting Diodes (SLEDs).

In construction, they resemble laser diodes. They consist of an electrically driven p–n junction as well as an optical waveguide. Though, they deliberately do not have any optical feedback by reflections. This is done to ensure that no laser action can happen.

Superluminescent diodes combine the low coherence of standard LEDs with the high-power output and brightness of typical laser diodes. The emission optical bandwidth generally varies from 5 to 750 nm of broadband emission.


Q-1: How do SLDs work?

Answer: SLDs are based on an electrically driven p–n junction which becomes optically active when it is biased in a forward direction. It then emits amplified spontaneous emissions across a wide range of wavelengths. When an electrical current crosses the active area from the p-section to the n-section and causes spontaneous recombination of positive and negative electrical carriers, light is generated. This is then amplified as it travels through the length of the SLD.

Q-2: What are some current and voltage requirements of SLDs?

Answer: For functioning, superluminescent diodes typically need a little voltage and current. Hundreds of milliAmps are needed for the low-current variants that are on the market, and less than 5 V is needed for emission. High-current variants may need up to 1 A of current while maintaining the same voltage requirements.

Q-3: How to use SLD safely?

Answer: Firstly, when working with SLDs, maintain at the least, the same protective measures used for laser diodes. Secondly, make use of only specialized laser diode temperature and current controllers or controllers specifically made to be used on superluminescent diodes. Furthermore, Make sure to protect the SLD from optical feedback as this can affect the performance of low-to-medium-power SLDs and can damage high-power SLDs. 

Lastly, when activating your SLD module, always begin at a low optical power level. If the output power clearly differs from the specification data, don’t raise the SLD power; instead, investigate the cause of the disparity before proceeding.

Q-4: What is the luminescence difference between LDs, SLDs, and LEDs? 

Answer: LDs, SLDs, and LEDs are all types of light sources, but they have different properties and applications. The main difference in luminescence between these three is the spectral width and coherence of the light they emit.

Semiconductor Optical Amplifiers [SOA]

An SOA is a semiconductor element used to amplify light. In other words, SOAs are used to enhance and amplify optical signals. They are versatile devices/elements as they are known to be quite useful as key parts of optical networks.

Semiconductor optical amplifiers can be thought of as laser diode that has both ends covered in a non-reflecting coating. They are used as signal amplifiers and can be used in telecommunication to mitigate the loss of signals. As they work on a gain medium, they help in gaining the signal that has been lost and ensure the full delivery of a signal. A semiconductor optical amplifier operates on the same fundamental principles as a semiconductor laser, but without feedback.


Q-1: What are the limitations of semiconductor optical amplifiers?

Answer: Along with the general limitation of being able to operate only at a specific wavelength or range of wavelength, SOAs have lower gain, produce more noise, are dependent on polarization and have high non-linearity.

Q-2: What are the types of SOAs?

Answer: There are two types of semiconductor optical amplifiers, namely; Fabry-Perot amplifiers (FPA) & Non-resonant traveling-wave amplifiers (TWA).

Q-3: What are some critical performance parameters of optical amplifiers?

Answer: Some important performance parameters of semiconductor optical amplifiers are bandwidth, tunability, wavelength, output power, temperature coefficient, size, cost, efficiency, gain, internal noise, stability, complexity, sensitivity to component variations and drift. The importance of each parameter is dependent on uses and situations.