Category: Fiber Laser Technology

Development of a compact tunable fiber laser

A team of researchers from the U.S. developed a compact laser system that enables a tunable fiber laser over a wide range. The fiber laser is made from commercial-off-the-shelf components and is designed to emit terahertz radiation by spinning the energy levels of molecules in nitrous oxide (laughing gas).

The tunable fiber lasers provide new data information from the novel computational techniques. This gas laser technology was regarded as old for a long time; therefore, researchers thought that the laser systems were big, low-power, and non-tunable, which is why terahertz sources are considered to be potential.

Compact size and efficiency

Modern tunable fiber lasers have a compact size, can be tuned, and offer more efficiency parameters. Additionally, it is possible to put this fiber laser system in one’s backpack or vehicle for wireless communications or high-resolution imaging. The design of the tunable fiber laser is based on the research done in the 1980s, according to which a gas laser system allows emitting terahertz laser beam waves; the fiber laser is smaller than conventional laser devices, and at a pressure far higher than the theoretical models of the time suggested.

Vibrational states and laser performance

Manufacturers of those fiber laser models did not pay attention to several vibrational states, “assuming that only a handful of vibrations were what ultimately mattered in producing a terahertz wave”. According to the previous models, if a cavity is tiny, molecules vibrating in response to an incoming infrared laser system will collide more often and produce their energy rather than building it up further to spin and emit terahertz waves.

Tracking molecular states

The new fiber laser model enables us to track thousands of relevant vibrational and rotational states among millions of groups of molecules within a single cavity. Then the laser technology performs an analysis of how those molecules respond to the incoming infrared laser beam, depending on their position and direction within the cavity. The researchers succeeded in discovering that the inclusion of all these other vibrational states in tunable fiber lasers (previously ignored by people) leads to the appearance of a buffer.

Quantum cascade laser as the infrared source

For the new model, a quantum cascade laser system has been chosen as the infrared laser beam source. The opportunity to change the frequency of the input fiber laser by turning a dial may change the frequency of the terahertz coming out. Several gas libraries were looked through by researchers in order to detect those that were known to rotate in a specific way in response to an infrared laser beam, finally deciding on nitrous oxide.

Prospects and gas molecules

The stimulation of the quantum cascade laser system results in the creation of a tunable fiber laser at a much smaller size than previously considered possible. Researchers include other gas molecules, for example, carbon monoxide and ammonia, offering a menu of various terahertz generation options with different frequencies and tuning ranges, paired with a quantum cascade laser system.

A combination of fiber lasers and direct-diode lasers

Fiber lasers are often used in combination with direct-diode laser systems. A fiber laser contains an optical fiber that is an end- or side-pumped, while a direct-diode laser system includes a non-gain optical fiber that is simply filled with light that is produced from numerous laser beam diodes connected to the fiber.

It is possible to apply both fiber lasers and direct diode laser systems for material processing. High-power fiber laser systems include either single-mode or multimode outputs, while direct-diode lasers are always multimode because “the etendue of fiber optics for combining light from many laser beam diodes will be substantially above the single-mode limit”.

Improving brightness and laser output

Manufacturers of laser systems are constantly improving the brightness of laser products; herein, numerous material processing applications require the multimodal laser beam. Additionally, the majority, but not all, direct-diode laser systems emit laser beams in the near-infrared.

High-power output through wavelength multiplexing

The wavelength-multiplexing of the laser stacks and polarization-combining submodules allows achieving high-power laser beams. Thus, it is possible to achieve a power of 6 mm-mrad over a broad range of power levels from 100 W to beyond 1000 W.

Transmission and wavelength range

Moreover, a laser beam can then be transmitted to the workpiece in free space or through optical fibers with a core size of 100 or 200 µm. Finally, the laser technology of wavelength multiplexing enables such laser systems to produce within a wavelength range of 900 to 980 nm.

Laser modules for cutting, welding, and pumping

Material processing application also uses laser modules for the same purposes. To be more precise, basic laser modules can reach a bandwidth of less than 25 nm and an output power of 1.5 kW. The application of laser modules includes cutting and welding, as well as high-energy laser pumping.

Advantages of wavelength-multiplexed laser modules

Nevertheless, the laser technology of wavelength multiplexing increases the power levels of this platform far into the multi-kilowatt range without any variation in laser beam properties. Laser modules can include high-power fiber optic cables and laser processing heads, resulting in higher power and efficiency.

Applications in microelectronics, soldering, and heat treatment

The laser system demonstrates the ideal application in soldering microelectronic parts, where relatively tiny spot sizes varying from 0.2 to 3 mm are set over a fairly long working distance. Also, the fiber laser system offers such benefits as quite short rise- and fall-times (less than 10 µs), it keeps up a uniform power distribution across the laser beam, resulting in a perfect solution for multiple heat treatment applications.

Current challenges in conventional laser systems

Lasers are universal tools that nowadays find numerous applications, from entertaining our cats to encryption and coding communications. Conventional laser systems can be energy-intensive; the majority of them are made employing toxic materials, for instance, arsenic and gallium. Thus, it is necessary to find new materials and technologies to make fiber lasers more sustainable.

Discovery of a new high-efficiency fiber laser

A group of researchers from the U.S. has discovered a new phenomenon that leads to the creation of a fiber laser system with over 40% efficiency, which is nearly ten times higher than other similar laser systems. The new laser is made from a glass ring on a silicon wafer with only a monolayer coating of siloxane molecules anchored to the surface.

Advantages of the new laser system

Compared to previous versions, this laser system offers improved power consumption, and it is made from more sustainable materials. The operating principle of the surface laser system is based on an extension of the Raman effect that allows understanding how the interaction of light with a material can lead to molecular vibrations resulting in laser beam light emission.

Moreover, this type of laser system has one unique characteristic: the emitted wavelength is determined by the material’s vibrational frequency, but not by its electronic transitions. It is easy to adjust the emitted laser beam light by changing the incident light.

Applications of Raman-based fiber lasers

The laser systems based on Raman technology have numerous applications, such as military communications, microscopy and imaging, the medical area for ablation therapy, a minimally invasive procedure to destroy abnormal tissue such as tumors. The main purpose is to produce a fiber laser system where all of the incident laser beam light will be changed into emitted light.

Challenges in solid-state Raman lasers

In a usual solid-state Raman laser system, the molecules interact with each other, resulting in a performance reduction. That is why a new approach is required to be developed to overcome this challenge. The researchers confirm that if traditional laser systems are regarded as the old energy-inefficient light bulbs, new laser technology will make new laser systems as energy-efficient as LED light bulbs – a brighter result requiring lower energy input.

Improved efficiency via molecular surface constraint

Finally, the efficiency of motion movement is increasing, as well as the ability to act as a laser system by constraining the motion. The molecules are set on the surface of an integrated photonic glass ring that limits an initial laser beam light source. The laser beam light inside the ring excites the surface-constrained molecules, providing an efficiency of nearly 10 times higher, despite there being less material.

New fiber laser technology for nonlinear effects

A novel fiber laser technique for generating second-order nonlinear effects in materials that typically cannot accommodate them could lead to new possibilities for creating these effects for optical computing, fast data processors, and bioimaging. A team of researchers from Georgia demonstrates a technique, based on a red fiber laser, to produce the nonlinear effects.

Laser system setup and experimental design

For the laser system, they develop an array of small plasmonic gold triangles on the surface of a centrosymmetric titanium dioxide or TiO2 slab in the laboratory. Then the gold structure is illuminated with a pulse of laser beam light. The laser beam operates like an optical switch; it breaks the crystal symmetry of the material.

Electron excitation and frequency doubling.

The laser beam pulse causes the electron excitation when it is fired at the array of gold triangles on the TiO2 slab; the excitation doubles the frequency of the laser beam from a second laser system as it reflects from the amorphous TiO2 slab. The fiber laser system has already been tested and demonstrated the blue laser beam that “shows the frequency-doubled light and the green beam that controls the hot-electron migration”.

Operating principle of the fiber laser system

The operating principle of the laser system is based on the optical switch that causes the excitation of high-energy electrons inside the gold triangles; therefore, some electrons go to the titanium dioxide from the triangles’ tips. “Since the migration of electrons to the TiO2 slab primarily happens at the tips of [the] triangles, the electron migration is spatially an asymmetric process, fleetingly breaking the titanium dioxide crystal symmetry optically.”

Symmetry-breaking and material applications

The red laser beam pulse leads to an instant induced symmetry-breaking effect. It is possible to break optically the crystalline symmetry of conventionally linear materials, for example, amorphous titanium dioxide; the fiber laser system allows making a range of optical materials wider. These materials can then be employed in numerous micro- and nanotechnology applications such as high-speed optical data processors.

Control and stability of nonlinear effects

A stable, continuous-wave laser system enables to production of the nonlinear effect to last for as long as the fiber laser is turned on. It is possible to control the number of migrated electrons through the intensity of the red laser beam. More electrons appear inside the gold triangles when the intensity of the optical switch rises, and more electrons are put into the TiO2 slab.

The fiber laser system still requires future improvements, but now it already offers numerous opportunities in the field of nonlinear nanophotonics, as well as plays a crucial role in the field of quantum electron tunneling.

Advantages of fiber laser weapons

Military weapons based on fiber laser technology are considered to be agile; they have virtually infinite ammunition, enabling them to take down different targets. Nonetheless, as fiber technology transforms, so do modern military actions also change, requiring advanced fiber laser weapons for everyday defense. Drones present a prominent security threat to military objects all around the world. Fiber laser weapons are regarded as a low-cost, powerful solution for militaries. The fiber laser technology offers such advantages as high precision, incredible flexibility, reusability, and it also allows minimizing collateral damage because the laser system weapons take out just the required target.

Operating principle of fiber laser weapons

The operating principle of modern fiber laser weapons is based on decades of research. These laser systems operate on batteries utilizing a technology called a spectral beam combined fiber laser. This tiny, powerful laser beam system applies artificial intelligence algorithms to stream fiber lasers into one larger laser beam.

Energy distribution and environmental resistance

The energy in the laser system weapons spreads by mirrors and lenses, which enable adjustments based on weather or atmospheric conditions. Additionally, the fiber laser weapons are not exposed to gravity or wind resistance. Militaries “can take out engines, instantly burn tires, sink a boat or bring down drones in a fraction of a second” with weapons based on fiber laser technology due to significantly focused energy laser beams.

Efficiency and logistical advantages

Additionally, it is unnecessary to launch a new projectile; when adjusting aim, simply repositioning the fiber laser suffices. The benefits of laser weapon systems as a munitions solution include that troops do not carry large quantities of ammunition, but instead only one weapon system. There is no need to transport hazardous munitions where mishaps may occur since the intense energy of laser beam weapons comes directly from generators or batteries.

Cost-effectiveness and mobility

Therefore, the lightweight of dangerous munitions also simply implies less cargo, resulting in less equipment and more stealthy troop movements. Standard missiles also have a high cost, while fiber laser weapons have almost infinitely renewable power, which is why the cost of the fiber laser system is offset by not needing to permanently buy munitions.

All the mentioned benefits of laser system weapons do not mean full replacement of conventional munitions; they only complement them. Nowadays, there are fully functioning fiber laser systems ready for field testing, and some capabilities have already been demonstrated.

Topological fiber lasers: a breakthrough

A team of researchers from Singapore designed the first electrically driven topological laser system. This fiber laser efficiently overcomes manufacturing imperfections due to the application of topologically protected photonic modes. In the 1980s, the researchers discovered that electrons flowing in certain materials had “topological” qualities; therefore, installed in fiber laser systems, they allowed electrons to flow around corners or defects without scattering or leaking.

This topological technique has been recently applied to photons by a team of researchers from Singapore. They used a quantum cascade fiber laser on advanced semiconductor wafers developed by the team. The team exploited a design that included a valley photonic crystal to reach topological states on a laser beam platform.

Design of the compact fiber laser system

The design of the compact fiber laser system contains “hexagonal holes arranged in a triangular lattice, etched into a semiconductor wafer. Within the microstructure, the topological states of light circulate within a triangular loop with a 1.2-mm circumference. The loop acts as an optical resonator to accumulate the light energy required to form a laser beam.” The laser beam travels in this loop and navigates the sharp angles of the triangle because of certain characteristics of topological states, whereas normal lightwaves are disrupted by the sharp angles, preventing them from circulating smoothly.

Electrically pumped THz quantum cascade fiber lasers

The quantum cascade fiber laser allows emitting a laser beam at terahertz (THz) frequencies. Although previous demonstrations needed an external laser beam source for optical pumping, now the developed fiber laser is based on an electrically pumped THz quantum cascade technology that uses topologically protected valley edge states; thus, the application includes the valley degree of freedom in photonic crystals. Electrically driven semiconductor laser systems are considered to be the most standard type of laser technology device at present and have a wide range of applications, from barcode readers to laser ranging sensors for autonomous vehicles.

The manufacture of fiber laser systems has numerous challenges, and modern laser module designs may not work well if any imperfections are introduced into the structure of the laser during manufacturing. The innovative topological laser system addresses the issue and may lead to more effective production using current laser technologies.

Recently, researchers from Massachusetts have developed a novel fiber laser system that has a compact size and is able to emit light with a high level of spectral purity. The fiber laser’s light remains unchanged in environmental conditions. The researchers confirm that the novel laser system will be useful for future scientific applications that include:

• clock improvement for Global Positioning Systems or GPS;
• determination of space gravitational waves;
• quantum computing.

Advantages of the fiber laser system

The fiber laser system has a lot of advantages, such as small size, the ability to emit exceptionally pure light, and unresponsiveness to the environment. Also, laser technology allows creating an environmentally stable, narrow, portable linewidth laser due to the fiber used for the laser module. A laser system is developed to emit purely in one wavelength, but there are still environmental influences that cause noise, changing the light frequency. The researchers using a novel technique have developed an optical fiber laser with a spectral linewidth narrower than ever achieved by a fiber or semiconductor laser.

Principle of operation

The main goal of the development is the replacement of ultra-low expansion (ULE) cavity lasers with a compact one that isn’t sensitive to environmental noise. The principle of laser module operation includes the use of a short loop of optical fiber configured as a ring resonator.

Performance and applications

Since fiber laser systems are portable and solid, and also have immunity to environmental changes, the researchers made the combination of fiber laser advantages with the nonlinear optical effect to develop a laser with a linewidth of just 20 hertz, compared to other laser systems, whose linewidths range from 1000 to 10,000 hertz, and semiconductor lasers’ linewidth is around 1 million hertz.
The development of laser systems can be used for the creation of a new generation of optical atomic clocks used for GPS-enabled devices. These clocks will provide a more accurate pinpoint of the arrival time of the signal and improve the location accuracy of today’s GPS systems.
This device will be quite useful for interferometers like the ones used by the Laser Interferometer Gravitational-wave Observatory or LIGO, to detect gravitational waves coming from colliding black holes or collapsing stars.