Scientists have found an approach to decode the info “jumbled up” by light taking a trip through a scattering medium like ground glass, with potential applications in optical computing and machine knowing. The group showed that the optical input-output reaction of a nonlinear scattering medium can be represented by a third-order tensor, providing a brand-new approach to optical file encryption and logic gates.
Decoding the optical reaction of nonlinear scattering media: A leap towards highly scalable physical operators.
Is it possible to see through a scattering medium such as ground glass? Traditionally, this would be considered difficult. When light travel through an opaque substance, the information carried within the light ends up being “jumbled up”, nearly as if undergoes complex file encryption.
Recently, a remarkable clinical breakthrough by Professor Choi Wonshiks group from the IBS Center for Molecular Spectroscopy and Dynamics (IBS CMSD) has actually unveiled a technique to utilize this phenomenon in the fields of optical computing and device knowing.
Considering that 2010, several previous studies have attempted to harness info lost due to spreading media, such as biological tissues, utilizing mathematics. This has been generally done by utilizing optical operators such as linear scattering matrices, which can be used to identify the input-output relationships of photons as they go through scattering.
This subject has been of primary research interest for Professor Chois team from the IBS CMSD, which published many works that integrate both hardware and software-based adaptive optics for tissue imaging. A few of their work was shown in new types of microscopic lens that can translucent scattering medium with high opacity, such as mouse skulls, as well as perform deep 3D imaging of tissues.
The nonlinear scattering medium, as shown in (a), displays scattering and nonlinear modulation through nonlinear nanoparticles, making its action difficult to characterize utilizing standard direct matrices. To determine the nonlinear reaction, a nonlinear second-harmonic interference system, as shown in (b), was developed. Credit: Institute for Basic Science
Nevertheless, things end up being far more intricate when nonlinearity gets in the equation. If a scattering medium creates nonlinear signals, it can no longer be represented merely by a direct matrix, as the principle of superposition is broken. Furthermore, measuring the nonlinear input-output attributes becomes an overwhelming obstacle, setting a demanding phase for research study.
Unwinding the Mystery of Nonlinear Scattering Media
This time, Professor Chois team has actually achieved yet another scientific development. They became the first to find that the optical input-output reaction of a nonlinear scattering medium can be specified by a third-order tensor, instead of a linear matrix.
Third-order tensor is a mathematical things used to represent relationships between 3 sets of data. In basic terms, it is a range of numbers arranged in a three-dimensional structure. Tensors are generalizations of scalars (0th-order tensors), vectors (1st-order tensors), and matrices (2nd-order tensors) and are commonly used in different fields of mathematics, physics, and engineering to explain physical amounts and their relationships.
The info of light that is spread and modulated by the nonlinear scattering medium arbitrarily alters, making it challenging to reconstruct the initial information, as revealed in the right picture of (a). This can be described as optical file encryption. However, by knowing the input-output action attributes, it is possible to reconstruct the original information from the random output speckle, as revealed in (b). This procedure can be considered as decrypting the encrypted info. With only linear reaction attributes that do not include cross-terms, it was not possible to correctly reconstruct the details, as displayed in (c). Credit: Institute for Basic Science
To demonstrate this, the group made use of a medium consisted of barium titanate nanoparticles, which create nonlinear 2nd harmonic generation (SHG) signals due to the intrinsic noncentrosymmetric residential or commercial properties of barium titanate. These SHG signals emerge as a square of the input electric field through the second harmonic process, triggering cross-terms when several input channels are triggered all at once, interrupting the linear superposition concept. The researchers designed and experimentally verified a novel theoretical structure including these cross-terms in a third-order tensor.
To show this, the researchers determined cross-terms by separating the difference between the output electrical fields produced when 2 input channels were triggered concurrently, and when each channel was activated individually. This demanded an additional 1,176 measurements set by the possible combinations of 2 independent input channels, even with simply 49 input channels.
” The effort needed to discover cross-terms from weak nonlinear signals was significant,” noted Dr. Moon Jungho, the research studys lead author.
Real-World Applications Unleashed
The tensor stemmed from the nonlinear scattering medium has a higher rank than matrices of direct scattering media, hinting at its prospective as a scalable physical operator. The group showed this through the real-world execution of nonlinear optical file encryption and all-optical reasoning gates.
Initially, the group successfully demonstrated that nonlinear scattering media can be used for the optical encryption procedure. When specific image information is inputted into the media, the output 2nd harmonic wave signals are shown as random patterns, similar to a series of encryption processes.
( a) A nonlinear optical logic circuit was carried out utilizing the digital phase-conjugation approach with a nonlinear scattering medium. By using the phase-conjugate field of the cross-term (c), it is possible to produce an AND gate (b) that focuses light only when both input channels are active at the very same time. Considering that all nonlinear input-output reactions are taped, it is likewise possible to execute a multi-channel AND gate as displayed in (d). Credit: Institute for Basic Science
Conversely, by carrying out an inverse operation of the third-order tensor representation of the second harmonic wave, the original input information can be obtained through a decryption procedure. Making use of the inverted operation of the tensor input-output reaction, they deciphered initial signals from randomly encoded SHG signals, which uses improved security over standard optical encryption that utilizes linear scattering media.
Additionally, the integration of digital phase conjugation enabled the scientists to showcase all-optical AND reasoning gates that trigger just when 2 specific input channels are all at once triggered. This method offers possible benefits over silicon-based logic, including decreased energy intake and light-speed parallel processing capabilities.
This research study is expected to open up brand-new frontiers in the worlds of optical computing and device knowing. “In the burgeoning field of all-optical device learning, nonlinear optical layers are essential in improving model performance. We are currently examining how our research might be integrated into this field,” specified Professor Choi.
Reference: “Measuring the spreading tensor of a disordered nonlinear medium” by Jungho Moon, Ye-Chan Cho, Sungsam Kang, Mooseok Jang and Wonshik Choi, 31 July 2023, Nature Physics.DOI: 10.1038/ s41567-023-02163-8.
The research study was moneyed by the Institute for Basic Science.
The nonlinear scattering medium, as shown in (a), exhibits scattering and nonlinear modulation through nonlinear nanoparticles, making its reaction difficult to identify using standard direct matrices. To determine the nonlinear response, a nonlinear second-harmonic interference system, as revealed in (b), was established. If a scattering medium generates nonlinear signals, it can no longer be represented just by a direct matrix, as the concept of superposition is violated. The information of light that is scattered and regulated by the nonlinear scattering medium randomly alters, making it difficult to rebuild the initial details, as revealed in the ideal image of (a).( a) A nonlinear optical reasoning circuit was carried out utilizing the digital phase-conjugation method with a nonlinear scattering medium.
