Sudheesh K Rajput

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• PHD
• Project researcher at Kyoto Institute of Technology

The existing non-interferometric phase imaging methods are unable to retrieve quantitative phase up to microsecond temporal resolution due to the lack of a suitable parallel recording strategy. Therefore, we propose an ultra-high-speed non-interferometric method for phase and multi-plane imaging using partially coherent light sources. The method us...

In recent years, the security of audio data has become paramount in terms of personal information, national security, and forensic evidence. However, most reported systems use digital algorithms and lack their implementation in the optical domain, which can provide better security due to the use of physical keys and high speed. In addition, recentl...

Most optical information processors deal with text or image data, and it is very difficult to deal experimentally with acoustic data. Therefore, optical advances that deal with acoustic data are highly desirable in this area. In particular, the development of a voice or acoustic-signal authentication technique using optical correlation can open a n...

The authors review recent progress in parallel phase-shifting digital holography for high-speed imaging of dynamic and transparent object. A movie of acoustic field and selective images of sound wave propagations at different frequencies were demonstrated.

We propose imaging of axially asymmetric and dynamic 3D temperature distribution of air around a heat source. Method is based on simultaneous reconstruction of phase information from various viewpoints using angular-multiplexing in parallel-phase-shifting digital holography.

We propose an iterative phase estimation from two diffraction images recorded by space division multiplexing. Two intensity images can be captured by polarization camera after separating object intensity of two planes in different polarization directions.

The authors review recent advances in high-speed imaging of dynamic object with parallel phase-shifting digital holography. 3-D imaging of temperature of the air surrounding a heated object was demonstrated as an example of the advances.

We experimentally compared the air temperatures measured by non-contact imaging technique using parallel phase-shifting digital holography with those measured with a thermocouple. This study revealed that the technique has a faster thermal response than thermocouples.

Frame rate of digital light-in-flight recording by holography is estimated from the incident angle of light pulse to the image sensor and the number of sub-holograms in the whole hologram recorded with a single-shot pulse.

Images obtained by parallel two-step phase-shifting digital holography that does not require recording of intensity of reference wave vary according to the pixel-extraction direction. We evaluated the quality of obtained images depending on the variation.

We propose a method for imaging of sound propagating in gas flow. We recorded a sound and gas flow simultaneously and separated the images of sound from phase images disturbed by gas flow.

Digital holographic microscopy (DHM) is a powerful label-free imaging tool that provides three-dimensional (3D) quantitative information of a specimen. In this work, the evaluation of morphological and quantitative parameters of human red blood cells (RBCs) by a new single-shot common-path off-axis digital holographic microscopic system is demonstr...

We propose a simultaneous imaging technique of both sound propagations and spatial distribution of acoustic frequencies. We experimentally demonstrated the proposed technique for the acoustic waves of frequencies 39,500 and 40,500 Hz, which have close sound pressure. The sounds were recorded at the framerate of 100,000 fps by parallel phase-shiftin...

We propose a method for improving the sensitivity in measurement of sound pressure with parallel phase-shifting digital holography by time-frequency filtering. We succeeded in measuring of acoustic wave at 97.75 dB sound pressure level.

We proposed an optical method for imaging of a motion picture of sounds for selected frequency. We recorded three sounds of frequencies 39.5, 40.0, and 40.5 kHz with the frame rate of 100,000 fps by parallel phase-shifting digital holography and succeeded in imaging the sound for selected frequency.

Multimodal optical microscopy combines different optical and physiological principles working together to obtain rich perspectives from a single biological event. In this paper, the recent advances in multimodal microscopy systems based on off-axis digital holography and transport-of-intensity equation are reviewed. Both methods used the common-pat...

Integrated multimodal cross-sectional or volumetric imaging techniques give us fruitful information to understand the behavior or status of target objects such as biological samples. Most of the reported systems for this purpose are either time consuming due to scanning or use of additional reference beams such as in interferometry. Therefore, fast...

Sound is an important invisible physical phenomenon that needs to be explained in several physical and biological processes, along with visual phenomena. For this purpose, multiparameter digital holography (DH) has been proposed to visualize both features simultaneously due to the phase and amplitude reconstruction properties of DH. In this paper,...

The sound wave has been recorded and visualized by optical means such as digital holography (DH), where light wave carries the sound information. However, in DH, an additional reference beam is required, which can create problems in the applications where long-distance propagations are required for sound field studies. In this work, we present a ne...

Sound field imaging techniques have been found very useful for acoustic designs. Building on this idea, innovative techniques are needed and presented in this paper, where we report on developed imaging of the sound field radiated from speakers by parallel phase-shifting digital holography. We adopted an ultrasonic wave radiated from a speaker for...

The demand for single-shot and common-path holographic systems has become increasingly important in recent years, as such systems offer various advantages compared to their counterparts. Single-shot holographic systems, for example, reduce computational complexity as only a single hologram with the object information required to process, making the...

In this paper, we propose an optical multimodal biometric encryption technique which uses digital holography (DH) for multiple biometric recording and successive optical encryption methods, by means of keys generated from biometric data. Physiological biometrics, such as fingerprints or iris scans, along with behavioral biometrics such as voice, ar...

We present fluorescence imaging of plant cells based on transport of intensity equation and Fresnel propagation. At first, the phase distribution is obtained from the recorded three- defocus fluorescence intensity images and then from phase and corresponding intensity defocus image, the focus images of plant cell sample can be retrieved at various...

We propose a nonscanning three-dimensional (3-D) fluorescence imaging technique using the transport of intensity equation (TIE) and free-space Fresnel propagation. In this imaging technique, a phase distribution corresponding to defocused fluorescence images with a point-light-source-like shape is retrieved by a TIE-based phase retrieval algorithm....

Optical voice encryption based on digital holography (DH), which uses the double random phase encoding (DRPE) in the Fourier transform domain, has been proposed [Opt. Lett. 42, 4619 (2017)OPLEDP0146-959210.1364/OL.42.004619]. In the present work, we propose optical voice encryption in other optical domains such as fractional Fourier, Fresnel, and g...

In this Letter, a concept of new multi-parameter imaging that can acquire visual and audio data of dynamic object phenomena simultaneously by a holographic technique is proposed. Temporal intensity distributions give us visual information of the dynamic events. The temporal profile of the phase distribution can give different information of the dyn...

We present the characteristics of indirect frequency measurement system based on off-axis digital holography (DH) for vibrating objects, which works on phase change characteristics of a medium where sound wave propagates. The sound field measurement method using off-axis DH already proposed by the author’s group is applied to the measurement of vib...

Water-related diseases affect societies in all parts of the world. Online sensors are considered a solution to the problems associated with laboratory testing in potable water. One of the most active research areas of such online sensors has been within optics. Digital holographic microscopy (DHM) has the potential to rival state-of-the-art techniq...

We propose an optical voice encryption scheme based on digital holography (DH). An off-axis DH is employed to acquire voice information by obtaining phase retardation occurring in the object wave due to sound wave propagation. The acquired hologram, including voice information, is encrypted using optical image encryption. The DH reconstruction and...

In this paper electronic origin of negative dielectric permeability in metals is discussed.

We propose a novel optical asymmetric cryptosystem combining the photon counting imaging with phase-truncated Fresnel transform, which can be used for complete information retrieval and authentication verification. The proposed combination overcomes the weakness of photon counting-based double random phase-encoding scheme. For retrieval of original...

We propose a novel security scheme based on the double random phase fractional domain encoding (DRPE) and modified Gerchberg-Saxton (G-S) phase retrieval algorithm for securing two images simultaneously. Any one of the images to be encrypted is converted into a phase-only image using modified G-S algorithm and this function is used as a key for enc...

We propose an image encryption system based on phase mask multiplexing and photon counting imaging (PCI) technique for multiple image authentications and digital hologram security. Multiple images to be authenticated are converted into phase-only images using a phase-retrieval algorithm in fractional Fourier transform domain. The multiple phase-onl...

We propose a new scheme for simultaneous encryption of gray-scale and color images based on DRPE and modified Gerchberg-Saxton phase retrieval algorithm. The simulation results prove the effectiveness and security strength of scheme.

We propose an optical image security scheme based on polarized light encoding and the photon counting technique. An input image is encoded using the concept of polarized light, which is parameterized using Stokes–Mueller formalism. The encoded image is further encrypted by applying the photon counting imaging technique to obtain a photon limited im...

We propose a novel optical information encryption and authentication scheme that uses asymmetric keys generated by the phase-truncation approach and the phase-retrieval algorithm. Multiple images bonded with random phase masks are Fourier transformed, and obtained spectra are amplitude- and phase-truncated. The phase-truncated spectra are encoded i...

We propose a novel nonlinear image-encryption scheme based on a Gerchberg–Saxton (G-S) phase-retrieval algorithm in the Fresnel transform domain. The decryption process can be performed using conventional double random phase encoding (DRPE) architecture. The encryption is realized by applying G-S phase-retrieval algorithm twice, which generates two...

We propose an image encryption scheme based on the double phase encoding in fractional Fourier transform domain for securing two gray-scale images. For encryption, an image to be encrypted is converted into a phase-only image using modified Gerchberg-Saxton algorithm, which serves as a fractional Fourier domain key for encrypting another image empl...

In this paper, we show that amplitude- and phase-truncation-based optical asymmetric cryptosystem is vulnerable to known-plaintext attack. The decryption keys are generated with the help of modified Gerchberg-Saxton phase retrieval algorithm from known-plaintext and ciphertext. With the help of the generated keys, the encrypted image, which is encr...

It is believed that asymmetric cryptosystem based on phase-truncated Fourier transform has immunity against knownplaintext attack. However, generation of two asymmetric keys is possible, if plaintext-ciphertext pair is known. In this paper, we show that amplitude- and phase-truncation-based asymmetric cryptosystem is vulnerable to known-plaintext a...

We propose an asymmetric image encryption and decryption scheme based on phase-truncated Fourier transform and polarization encoding. An image bonded with a random phase mask is Fourier transformed and the obtained spectrum is amplitude- and phase-truncated. The phase-truncated value is encrypted using the polarized light in which two independent o...

We propose a novel multiple image encryption based on fractional Fourier transform (FRT) and known-plaintext attack with modified Gerchberg-Saxton (G-S) phase retrieval algorithm. Multiple images to be encrypted are encoded into corresponding phase-only masks (POMs) using modified G-S algorithm. These POMs are multiplexed into a single POM, which m...

Most of the reported optical techniques of encryption in literature belong to the category of symmetric cryptosystems, in which the keys used for encryption are identical to the decryption keys. In an environment of network security, a symmetric cryptosystem would suffer from problems in key distribution, management, and delivery. In this paper, we...

In this paper, an image encryption scheme based on polarized light encoding and a phase-truncation approach in the Fresnel transform domain is proposed. The phase-truncated data obtained by an asymmetric cryptosystem is encrypted and decrypted by using the concept of the Stokes–Mueller formalism. Image encryption based on polarization of light usin...

In this paper, we propose a scheme for information security under the basic double random phase encoding framework but with enhanced complexity and immunity against the known-plaintext attack. Modified Gerchberg–Saxton algorithm is used to convert a primary image into a phase-only mask (POM). The POM is used as a Fresnel domain key for encrypting a...

Collision is a phenomenon in which two distinct inputs produce an identical output, so if an attacker finds the encryption keys in such a way that when it is applied to an encrypted image, it produces an arbitrary image instead of original one. We propose collision in an asymmetric cryptosystem based on a phase-truncated Fresnel transform. For encr...

We propose an image encryption and authentication verification scheme based on fractional nonconventional joint transform correlator architecture. For image encryption, an input image bonded with a random phase mask (RPM) and a separate key phase mask (another RPM) are fractional Fourier transformed independently. The obtained spectra are multiplex...

A single channel asymmetric color image encryption scheme is proposed that uses an amplitude- and phase- truncation approach with interference of polarized wavefronts. Instead of commonly used random phase masks, wavelength-dependent structured phase masks (SPM) are used in the fractional Fourier transform domain for image encoding. The primary col...

We propose an image encryption technique based on the interference principle and phase-truncation approach in the fractional Fourier domain. The proposed scheme offers multiple levels of security with asymmetric keys and is free from the silhouette problem. Multiple input images bonded with random phase masks are independently fractional Fourier tr...

We propose collision in asymmetric cryptosystem based on phase-truncated Fresnel transform. An arbitrary image can be generated from ciphertext or watermark embedded in a host image with the help of phase retrieval algorithm. Computer simulation results support the idea of the proposed collision.

We present a color image encryption and decryption scheme using polarization encoding. The proposed method offers flexibility in the encryption key design. The effectiveness of the scheme is studied with numerical simulation results.