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Non-Linear Optical Materials and Applications

Nonlinear optical (NLO) materials have long been known to interact with light, to produce a nonlinear response. Nonlinear optical materials use nonlinear dependence of the refraction index on the applied electric field to produce other frequencies. This results in either harmonic generation or frequency shifting. The development of the field was enhanced in parallel with the introduction of lasers, because laser beams possess the energy density necessary to produce nonlinear effects.

 

NLO phenomena have been observed at wavelengths from deep infrared to extreme UV, and even used to generate THz radiation. Optical nonlinearities are exhibited by crystals, amorphous materials, polymers, liquid crystals, semiconductors, organics, liquids, gases and plasmas. The composition of these materials, generally falls into one of two classes, either inorganic or organic. Inorganic NLO materials such as lithium niobate (LiNbO3 ) or potassium dihydrogen phosphate (KH2PO4 ) are known to exhibit second harmonic generation (SHG) effect.

Lithium niobate powders have attracted a great deal of attention due to their potential applications mainly because of its unique electro-optic, acousto-optic, and nonlinear optical properties. Over the last 40 years, lasers using inorganic materials have been employed as optical materials and consequently these materials have dominated optical technology.

 

During the 1990’s, p-electron organic materials were identified as promising candidates for nonlinear optical
applications. However, more recent studies of NLO materials have focused on the use of organic materials
with π-electron conjugated systems. Such materials offer the advantages of larger optical nonlinearity and faster optical response. Other driving forces behind the recent development of organic NLO’s include higher bandwidth, lower driving voltage, more flexible device design, and potentially lower processing cost. For chromophores to be of utility for nonlinear optical applications, they must be assembled into a noncentrosymmetric lattice.

 

Optical Switch Forms Inroad for All-Optical Signal Processing

An optical switch developed by Caltech researchers harnesses the property of optical nonlinearity and aims to enable ultrafast all-optical signal processing and computing. Although optical nonlinear functions enable applications in integrated photonics, including all-optical information processing and photonic neural networks, most nanophotonic platforms demonstrate weak native nonlinearity. This barrier necessitates large driving energies, high-Q cavities, or integration with other materials with stronger nonlinearity, the researchers said.

The on/off property of switches is the foundation of logic gates and binary computation and is the purpose for which transistors were designed. Achieving the same feat with light has proven difficult. Unlike electrons in transistors, which can strongly affect each other’s flow and thereby cause “switching,” photons usually do not easily interact with one another, the researchers said.

The team led by Alireza Marandi, assistant professor of electrical engineering and applied physics at Caltech, developed its switch using lithium niobate. Because of the way that atoms are arranged within the crystalline material, the optical signals that it produces as outputs are not proportional to the input signals.

Recent advancements in nanofabrication techniques enabled the team to create lithium niobate-based integrated photonic devices that allow for the confinement of light in a very small space. The smaller the space, the greater the intensity of light — though the power remains the same. As a result, the pulses of light carrying information through such an optical system could provide a stronger nonlinear response than would be possible otherwise.

The team also decreased the duration of light pulses and used a specific design to keep the pulses short as they propagate through the device, resulting in each pulse having higher peak power. This tactic confined the light temporarily.

The team then combined the two tactics to substantially increase the strength of nonlinearity for a given pulse energy, which means the photons now affect one another much more strongly.

The net result was a nonlinear splitter in which the light pulses are routed to two different outputs based on their energies, which enabled switching to occur in less than 50 fs.

By comparison, state-of-the-art electronic switches take tens of picoseconds.

 

Military Applications

Early applications of NLO included second harmonic generation, Q-switching and mode-locking, all of which extended the applications of lasers. Fiber optic communications early showed the deleterious impact of NLO in glass. With narrow-line lasers, ultra-fine resolution spectroscopy became possible. Today we see a plethora of promising future applications for NLO, including quantum optics, quantum computing, ultra-cold atoms, plasma physics and particle accelerators, to name a few, with many more to come.

 

Most NLO materials used for military and intelligence purposes are optical crystals. In these crystals, the electric field associated with light can interact with the crystal’s internal structure – also known as its lattice – in non-linear (unexpected) ways. This nonlinear response usually only occurs under very intense irradiation, like that from a laser, and can be used to achieve frequency-converting processes that can shift the laser’s wavelength into the spectral range needed for a particular use or application. For efficient frequency conversion, a crystal must:

  • Be non-centrosymmetric (have a non-zero nonlinearity)
  • Have a nonlinear d-coefficient large enough to generate tunable wavelengths over a broad range
  • Be highly transparent at the required input and output wavelengths
  • Be able to match different phases

 

Because NLO materials are in great demand worldwide, growing these crystals in a material growth laboratory is a critical way to help meet the need. For EW systems developers and U.S. Department of Defense (DoD) partners, in particular, growing non-linear crystals internally may be the smartest – or only – way to assure consistent and readily available materials when they are needed most.

 

Shifting a laser light’s wavelength and frequency makes it possible to operationalize unused EMS wavelengths in contested areas, preventing adversaries from using those wavelengths while crippling their communications, targeting, and signal detection capabilities. It also allows more lasers to operate in the infrared (IR) portion of the EMS, which means more opportunities to use laser-guided targeting systems, laser-based aircraft and ground vehicle countermeasures systems, EO/IR sensors, laser weapons sights, precision range finders, vehicle protection systems (VPS), and more.

 

Non-Linear Optical (NLO) materials are at the core of many optical electronic warfare (EW) systems and other next-generation defense technologies because they can be used to shift the wavelength and frequency of laser light, enabling operation in parts of the electromagnetic spectrum (EMS) that would normally be inaccessible.

 

Global Non-Linear Optical Materials and Applications Market

Nonlinear Optical Materials Market was valued at around USD 4124.68 million in 2021 & estimated to reach USD 7785.54636 by 2028

 

By the product type, the Non-Linear Optical Materials and Applications market is primarily split into: Lithium-Niobate, Potassium Titanyl Phosphate, ß-Barium Borate, Lithium Triborate.

 

As per application side, the global non-linear optical materials market can be categorized into Electronics, Automotive and Aerospace. Nonlinear optical (NLO) materials are widely used by electronics industry and automotive technology. In addition, the assembly technology described here can be used for other nonlinear crystal types. As well as for space applications, this method can be used for solid-state lasers in medical technology or materials processing. Parts of the research described here were carried out on behalf of the Federal Ministry for Economic Affairs and Energy within the framework of the R&D project. They have grant numbers 50EE1235 and 50EP1301. The work is part of a joint project between DLR RfM and CNES within the scope of the German-French MERLIN satellite project.

 

In terms of region, the global non-linear optical materials market is divided into key regions such as North America, Europe, Asia-Pacific, and Rest of the World (RoW). North America accounted for the largest market share in the global non-linear optical materials market. Europe held the second largest market share in the total non-linear optical materials market. This regional market is anticipated to report steady rise in the near future, thanks to the significant rise in the automotive industry. Asia Pacific is expected to be the fastest growing region owing to rapidly growing industrialization and urbanization in India and China. In Asia Pacific, China holds the most prominent market for non-linear optical material due to the ongoing industrialization in this country, which has led to a robust growth in the Aerospace industry in China. Overall, the Asia Pacific non-linear optical materials market is expected to experience a considerable rise in the near future.

 

The industry is consolidated in nature with the presence of giant global players. This had resulted in increased competition between the manufacturers and the distributors. Key companies in the industry include CASIX, Inc, Cleveland Crystals, Inc, Coherent, Inc, Conoptics, Inc, Cristal Laser SA, Crystal Technology, Inc, Deltronic Crystal Industries, EKSMA OPTICS, Fujian Castech Crystals, Inrad Inc, JDS Uniphase Corporation and Laser Optics. The prominent market players maintain the competitive edge in the global market by spending more on research and development activities to bring innovative solutions for diversified industries. The leading players in the non-linear optical materials Market are striving to bring down the prices further and bring in new innovative formulations into the market.

 

 

Key players/manufacturers include: CASIX, Cleveland Crystals, Coherent Conoptics, Cristal Laser, Crystal Technology, Deltronic Crystal Industries, EKSMA OPTICS, Fujian Castech Crystals, Inrad, JDS Uniphase Corporation, Laser Optics, LINOS Photonics, Northrop Grumman SYNOPTICS, Nova Phase, Quantum Technology, Raicol Crystals, Saint-Gobain Crystals, and Vloc

 

References and Resources also include:

https://www.baesystems.com/en-us/definition/what-are-non-linear-optical-materials

https://www.photonics.com/Articles/Optical_Switch_Forms_Inroad_for_All-Optical/a68234

About Rajesh Uppal

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