Nonlinear optics is a part of optics, dealing with various kinds of optical nonlinearities e.g. in nonlinear crystal materials (including both dielectrics and semiconductors) or in optical fibers and other waveguide devices. Nonlinear effects with light are those where e.g. twice the optical input intensities does not simply result in twice the output intensities. In nonlinear optics, the superposition principle no longer holds.
Nonlinear optics is the study of how intense light interacts with matter. At high powers, however, the material properties can change more rapidly. This leads to nonlinear effects including self-focusing, solitons and high-harmonic generation.
Research into all-optical processing dates back to the 1980s when the so-called “electronic bottleneck”, the limited speed of electronics, was seen as the major barrier that would limit the information capacity of fiber-optic networks. In this “first era” of optical signal processing the main idea was to use the ultra-fast third order nonlinearity of Kerr-like materials to create fast switches so that an interleaved signal could be de-multiplexed efficiently to different output ports of a device.
A canonical optical switch consisted of a nonlinear Michelson interferometer in which a third order nonlinear element existed in only one of the arms. This type of nonlinear optical switch, therefore, relied on a nonlinear phase shift caused by the real part of the third order nonlinearity.
The advent of WDM significantly changed the emphasis of the research into all-optical signal processing away from switching devices. For example, the challenge in a WDM network was not, at least until recently, to de-multiplex signals at speeds beyond the limits of electronics, but to transfer data from one to another wavelength or to multi-cast data on many channels simultaneously. Conventionally such processes used direct detection and electronic modulation of a wavelength shifted laser or multiple lasers but this can become power-hungry and complex as channel counts rise.
Applications of NLO
Nonlinear optics is a key enabling technology of our modern society, such as in imaging and high-speed data communication. Nonlinear optics is a growing field with applications in laser manufacturing, nanostructure creation, sensor design, optoelectronics, biophotonics, and quantum optics, among other fields. Nonlinear optical materials are essential building elements in a wide range of sectors, including scientific research, industrial production, and military applications.
Nonlinear optics has become the foundation of several different frontier research programs and widely utilized optical systems, including laser manufacturing, optical imaging, information processing and communications, and nanoscale lithography, after many years of progress. Advances in this field have the potential to benefit a wide range of disciplines.
For applications, a field of particular importance is nonlinear frequency conversion, dealing with the generation of new optical frequencies in nonlinear processes. Another wide area is concerned with the effects of optical nonlinearities in various situations, e.g. for the propagation of intense ultrashort pulses in optical fibers, in supercontinuum generation, or for optical signal processing. In other cases, optical nonlinearities are utilized for measurement processes – for example, in autocorrelators and in devices for frequency-resolved optical gating in the context of ultrashort pulse characterization.
Nonlinear fiber optics partly deals with nonlinear frequency conversion (e.g., with supercontinuum generation and fiber-optical parametric oscillators), but also with other uses of fiber nonlinearities – for example, with nonlinear amplification and signal processing.
Nonlinear interactions are also very important for many experiments in quantum optics.
A large number of researchers are working in the area of nonlinear optics, which is the study of all effects that can be described as multi-photon interactions in various materials systems, including cases where the frequency of one or more photons tends to zero. Examples are two photons of the same frequency combining to create one at twice the frequency—known as second harmonic generation—or three photons combining to produce a fourth one—which could potentially lead to things like optical transistors.”
Nonlinear Photonics technology
Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typically observed only at very high light intensities (when the electric field of the light is >108 V/m and thus comparable to the atomic electric field of ~1011 V/m) such as those provided by lasers.
An alternative and potentially better solution is to use nonlinear optics to directly convert light at one wavelength to another using nonlinear mixing processes. The most common material of choice has been periodically-poled lithium niobate (PPLN) for which there are several well-established routes for waveguide fabrication. PPLN based all-optical processors have proven be highly capable in applications such as wavelength conversion; dispersion compensation via phase conjugation; digital signal processing including header recognition, time-slot interchange, etc.
Very many materials and device structures have been considered for third order nonlinear optics although only a few of these have actually been used in demonstrations of optical signal processing. One of the most successful has been silica-based highly nonlinear optical fiber (HLNF) that has been used for parametric signal processing for more than two decades. Several alternative media with much larger material nonlinearity have emerged including bismuth oxide glass; crystalline and amorphous silicon; silicon nitride; AlGaAs; chalcogenide glasses; and high-index doped silica-based glasses.
But the traditional devices suffer from relatively small nonlinear optical coefficients of conventional optical materials. Researchers have discovered that monolayer molybdenum disulfide, a unique two-dimensional (2-D) layered material similar to graphene, has an extremely large nonlinear optical response, which can efficiently convert low-energy photons into coherent high-energy photons.
One of the most commonly used frequency-mixing processes is frequency doubling, or second-harmonic generation. With this technique, the 1064 nm output from Nd:YAG lasers or the 800 nm output from Ti:sapphire lasers can be converted to visible light, with wavelengths of 532 nm (green) or 400 nm (violet) respectively.
Practically, frequency doubling is carried out by placing a nonlinear medium in a laser beam. While there are many types of nonlinear media, the most common media are crystals. Commonly used crystals are BBO (β-barium borate), KDP (potassium dihydrogen phosphate), KTP (potassium titanyl phosphate), and lithium niobate. These crystals have the necessary properties of being strongly birefringent (necessary to obtain phase matching), having a specific crystal symmetry, being transparent for both the impinging laser light and the frequency-doubled wavelength, and having high damage thresholds, which makes them resistant against the high-intensity laser light.
Optical phase conjugation
It is possible, using nonlinear optical processes, to exactly reverse the propagation direction and phase variation of a beam of light. The reversed beam is called a conjugate beam, and thus the technique is known as optical phase conjugation(also called time reversal, wavefront reversal and retroreflection).
Materials for optical phase conjugating are important for correcting laser beam aberrations to near diffraction-limited beam quality, for combining a laser array into a single coherent beam and for imaging through atmospheric turbulence.
Transceivers and switches utilizing NLM materials are capable of operating at much higher rates per channel and wavelength than existing technologies. Instead of 5G, think 8G. This enables higher bandwidth, smaller components, and lower power consumption, which in turn allows for a higher density of photonic hardware components within a datacenter. As a result, with NLM technology, a smaller footprint can be achieved with less space in data centers, meeting stricter cabling space requirements and HVAC needs. These capabilities are critical for post-400G networking technologies.
Quantum Nonlinear Optics
Quantum nonlinear optics provides a means to generate and manipulate light at the quantum level, with applications in enhanced sensing and metrology, and in quantum information processing and networking.
Quantum Nonlinear Optics is an effort focused on fabricating devices that can enable breakthroughs in integrated photonics in the coming years. Stanford LINQS Laboratory for Integrated Nano-Quantum Systems, is focussing on interactions between photons in nonlinear media. They can be especially strong in materials like lithium niobate (LiNbO3, LN), where just three photons can interact with each other through the second-order nonlinearity χ(2).
Phased array 5G and satellite antennas
Phased arrays incorporating NLM materials offer the potential for very high-speed beam steering for application in 5G wireless and custom optical communication systems. NLM materials can be used in slots tens of nanometers wide, enabling small yet highly functional antennas, and in arrays in the thousands. Such implementations have the potential to revolutionize communication.
NLM-enabled ground-based satellite antennas provide support to companies seeking to provide worldwide internet access. Additionally, NLM materials enable a variety of other antennas, including unique direct RF-to-optical antennas and low-cost, on-chip antennas for Internet of Things (IoT) applications.
Optical interconnects and backplanes
NLM-enabled optical interconnects are sufficiently small in size and power-efficient to enable moving data between CPUs, GPUs, and memory, as well as between modules within a chip. This enables manufacturers to achieve significant speed and energy breakthroughs. High-performance computing (HPC) manufacturers can deploy optical backplanes for faster connections using less power within a smaller form factor.
Optical processing in machine learning
Arrays of nanophotonic or plasmonic modulators utilizing NLM materials can be assembled to perform high-speed neural net functions. Utilizing NLM materials enables a greater density of components within the chips, enabling larger data arrays, faster bandwidths, a smaller device footprint, and very low energy consumption in this high-demand and high-growth application.
A natural fit for photonic innovation, lidar sensing measures distances by illuminating the target with laser light and measuring the reflection with a sensor, outputting digital 3D representations based on laser return times and wavelengths. Materials from NLM enable compact and rapidly steerable solid-state lidar devices that have terrestrial, airborne, and mobile applications, such as surveying, geology, and self-driving cars.
The quantum computing market explosion will only be enhanced with photonics. NLM materials can survive the demanding cryogenic temperatures required for quantum computing applications and can facilitate optical data transfer and photonic qbits. As they’re easy to use, NLM materials also increase the manufacturability and performance of quantum devices.
Military uses of nonlinear optical materials range from laser beamsteering and control of beam quality to eye-protection and guided-wave photonic devices and components. Materials for optical phase conjugating are important for correcting laser beam aberrations to near diffraction-limited beam quality, for combining a laser array into a single coherent beam and for imaging through atmospheric turbulence. Materials for eye-safe optical sources and electro-optic sensor and eye protection are also important for battlefield applications.
Materials for other military applications include guided-wave modulators and switches for photonics, optical correlators for automatic target recognition, 2-D spatial light modulators for high-speed parallel processors and metrology of surface motion and strain or air turbulence near an aerofoil surface. Nonlinear optical (NLO) techniques are also finding new applications in the generation and control of microwaves and millimeter waves.
Global Non-Linear Optical Materials and Applications Market
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.
In 2020, the global Non-Linear Optical Materials and Applications market size was USD million and it is expected to reach USD million by the end of 2027, with a CAGR of % between 2021 and 2027. 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