Fiber Amplifiers

Deeper Dive into Fiber Amplifiers

What is the Difference Between Lasers and Amplifiers?

In both a laser and an optical amplifier, energy (the excitation source) is pumped into a gain material until more molecules or atoms are in an excited energy state than the ground state, as shown in the figure below. Once this condition, population inversion, is satisfied, the gain medium is now cable of supporting stimulated emission, which allows photons with energy equal to the energy level gap to be amplified. While a detailed analysis of how stimulated emission works, is beyond the scope of this blog post, a simplified explanation is that the incident photon “knocks” the atom or molecule down to a lower level causing an identical photon to be emitted by the medium following the laws of conservation of energy and momentum.

The difference between lasers and amplifiers comes in when we look at the origin of the incident photon. In a laser, the resonator “catches” a spontaneously emitted photon. It then redirects it back into the gain medium repeatedly until the laser gain threshold is reached, initiating the lasing process. In an optical amplifier, though, there is no resonator. Instead, the photons come from an outside source known as a seed laser, which is then amplified via stimulated emission as it passes through the length of the amplifier. As a result, you can now take a lower power laser with your desired properties (linewidth, pulse width, beam profile, etc.) and increase its power without affecting its overall performance.

Laser Sources for LIDAR Applications

As we covered extensively in “Single Frequency Fiber Lasers for Doppler Lidar,” if you want to measure both the speed at which an object is moving and its location, there is no better option than frequency modulated (FM) lidar. For this signal processing methodology to work, you need to maintain precise control over the laser frequency. While a wide variety of single-frequency lasers have been used in Doppler lidar research, the industry as a whole has adopted single-frequency fiber lasers as the ideal light source. Here at RPMC Lasers, we offer a wide assortment of 1-micron and 1.5-micron fiber lasers and amplifiers from BKtel, which are ideal for FM lidar, especially applications in the automotive (selfdriving cars) and wind farm (windspeed monitoring) industries. All of the lasers produced by BKtel are compliant with all Telcordia requirements and are beyond rugged with operating temperatures ranging
from -40oC to +65oC.

Read the full article here.

Automotive LIDAR

It is essential to point out that LFM is not the only possible FM LIDAR waveform.  Lidar systems have also been known to employ non-linear frequency modulation, sparse frequency modulation, Costas matrix encoding, and even pseudo-random phase noise.  Regardless of the which FM LIDAR waveform is utilized they all have one thing in common, they require an extremely narrow linewidth laser source.  This arises from the fact that you cannot precisely modulate the frequency of the laser light if the laser’s frequency is drifting over time.  While there have been some cases where single frequency diode and diode-pumped solid-state (DPSS) lasers have been used for LIDAR, the community as a whole has settled on the single-frequency fiber lasers as the ideal light source.

Advantages of Fiber Lasers for LIDAR Applications

As discussed in our previous white paper, fiber lasers have several advantages over traditional DPSS lasers all of which derive from the geometry of the fiber optic itself, namely the innate ability to have an extremely long single-mode optical cavity.   This geometry allows for the production of either high-pulse energy, single-mode q-switched lasers, or extremely narrow band lasers with near-perfectly single-frequency output.  Commercially available erbium (Er) doped fiber lasers lase at approximately 1550 nm, which corresponds to the peak absorption band of water making them “eye-safe” which is critical for the deployment of many LIDAR systems.    Lastly, these devices are ideal for incorporation with Er-doped fiber amplifiers (EDFAs), which were initially designed for long haul telecommunications, to boost the signal strength for long-range applications.

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What is Laser Amplifier Noise?

In principle laser amplifier noise is no different than the amplifier noise induced in an audio system, and just as in a home stereo system the quality of the amplifier will have a tremendous effect on the quality of output signal.  Therefore, in this post we will attempt to answer the question what is laser amplifier noise, and perhaps more importantly how amplifier noise can affect the overall performance of your system.

As we discussed in our previous post on the subject, there are surprisingly few differences between amplifiers and lasers.  The only real difference is that unlike a laser, an amplifier does not have a resonator.  This means that in a laser amplifier there is no means of “catching” a spontaneously emitted photon and redirecting it back into the gain medium to start the stimulated emission process.  Instead, an amplifier relies on the input laser beam to trigger stimulated emission, making all of the emitted photons identical to those of the incoming laser beam.  This simplified explanation ignores the fact that there are still spontaneous emissions going on in the amplifier, which degrades the signal to noise ratio (SNR).

Read the full article here.

How Can We Help?

RPMC Lasers is your Fiber Amplifier Supplier. Our technical staff has over 100 years of combined knowledge, a vast understanding of the laser industry, and hands-on technical experience, enabling them to find the best laser for their clients, whether a standard or custom configuration. 

With over 25 years experience matching the right laser source to your application, and our wide range of industry-leading fiber amplifier options, the team at RPMC is prepared and eager to help you find the right solution!

If you have any questions, or if you would like some assistance please Contact Us here. Furthermore, you can email us at info@rpmclasers.com to talk to a knowledgeable Product Manager.

Alternatively, use the filters on this page to assist in narrowing down the selection of fiber amplifiers for sale. Finally, head to our Knowledge Center with our Lasers 101 page and Blogs, Whitepapers, and FAQ pages for further, in-depth reading.

Finally, check out our Limited Supply – In Stock – Buy Now page: This page contains an ever-changing assortment of various types of new lasers at marked-down/discount prices.