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The emergence of optical communications has opened up new perspectives for high‐capacity data transmission and signal processing, to meet the demand of the increasing data traffic. Despite significant progress in multi‐dimensional multiplexing for capacity scaling in fiber–optic communications or photonic networks‐on‐chip, achieving high‐capacity data transmission and signal processing in an entire fiber–chip–fiber system remains a great challenge. This challenge is attributed to the lack of effective multi‐dimensional coupling between fiber and chip. Here, the 3D (de)multiplexing SiO2 chip inscribed by femtosecond laser direct writing is proposed to achieve the multi‐dimensional coupling between the few‐mode fiber (FMF) transmission link and the silicon processing network. Combined with the 2D silicon chip fabricated by a standard lithography process, a multi‐dimensional fiber–chip–fiber communication system designed to transmit and process the hybrid wavelength‐, mode‐ and polarization‐division multiplexing signals in FMF is constructed. The silicon chip integrates Mach–Zehnder interferometer (MZI) switches and arrayed‐waveguide gratings (AWGs) to serve as a reconfigurable optical add/drop multiplexer (ROADM). As a proof‐of‐concept demonstration, a 96‐channel FMF–chip–FMF communication system with a data transmission capacity of 4.032 Tbit s−1, achieving a bit‐error ratio (BER) of less than 3.8 × 10−3, is successfully implemented. [ABSTRACT FROM AUTHOR]

The optimization of swimming training scheme is of great significance to improve the training efficiency and competitive performance of swimmers. However, the traditional swimming training programs often lack of personalized and scientific, can not meet the characteristics and needs of different athletes. The aim of this paper is to realize the automatic recognition of motion trajectory through optical processing technology, so as to improve the swimming training scheme. The optical processing technology of remote sensing image is used to collect video images during swimming training, and the optical processing algorithm is used to extract the trajectory information of swimmers in the images. Then image processing and pattern recognition technology are used to identify and analyze the trajectory, so as to obtain accurate trajectory data. Finally, based on the analysis results, the swimming training scheme is optimized and personalized training suggestions are provided. Through the experiment and result analysis, the effectiveness of optical processing in the optimization of swimming training scheme is verified. Through the automatic identification and analysis of the movement trajectory, the swimmer's skill and ability level can be more accurately understood, thus providing a scientific basis for the formulation and adjustment of training programs. The optical processing can also monitor and record the swimmers' trajectory changes in real time, providing real-time feedback and guidance for coaches to further improve the training effect. [ABSTRACT FROM AUTHOR]

Silicon carbide (Sic) materials find wide-ranging applications in advanced optical systems within the aerospace, astronomical observation, and high-intensity laser fields. The silicon-modified Sic used in this study was created by depositing an amorphous silicon film on the surface of a Sic substrate using electron beam evaporation. Such hard and brittle materials often yield smooth surfaces when subjected to plastic removal. To address the issue of the removal depth of the surface plastic domain for silicon-modified Sic, we propose a method to calculate the indentation depth based on the critical load for the transition from plastic to brittle removal. We conducted a series of nanoindentation and nanoscratching experiments. The critical depth formula was validated through mechanical parameters such as hardness, elastic modulus, and fracture toughness, and the theoretical critical depth of the modified silicon layer was calculated to be 2.71 μm. The research results indicate that the critical load for obtaining the plastic-to-brittle transition point during the nanoindentation experiment is 886 mN, at which point the depth of plastic removal is 2.95 μm, closely matching the theoretical value. The measurements taken with an atomic force microscope near the critical load reveal a scratch depth of 3.12 μm, with a relative error of less than 5% when compared to the calculated value. This study establishes a solid foundation for achieving high-quality surface processing. [ABSTRACT FROM AUTHOR]

Increasing the speed of operation in all optical signal processing is very important. For reaching this goal one needs high speed optical devices. Optical half adders are one of the important building blocks required in optical processing. In this paper an optical half adder was proposed by combining nonlinear photonic crystal ring resonators with optical waveguides. Finite difference time domain method wase used for simulating the final structure. The simulation results confirmed that the rise time for the proposed structure is about 1 ps. [ABSTRACT FROM AUTHOR]

ABSTRACTUsing a continuous laser to soften glass locally is a novel way of selective glass forming. Due to gaussian distribution of laser power density, a temperature gradient will be generated on glass treated with localized irradiation by laser, which brings about the coexistence of a glass state and a viscoelastic state. This situation creates a bulge on the surface of the softened area. Based on this phenomenon, we propose a measurement approach and a calculation model for the softening zone width of glass irradiated locally by laser and verify the calculation model through simulations and experiments. The maximum temperature deviation of the proposed temperature field prediction model is 4.7°C, while the minimum deviation is 0.53°C; making the deviation between the calculation model of the softening zone width and the experimental measurement result less than 0.319%.

Using a continuous laser to soften glass locally is a novel way of selective glass forming. Due to gaussian distribution of laser power density, a temperature gradient will be generated on glass treated with localized irradiation by laser, which brings about the coexistence of a glass state and a viscoelastic state. This situation creates a bulge on the surface of the softened area. Based on this phenomenon, we propose a measurement approach and a calculation model for the softening zone width of glass irradiated locally by laser and verify the calculation model through simulations and experiments. The maximum temperature deviation of the proposed temperature field prediction model is 4.7°C, while the minimum deviation is 0.53°C; making the deviation between the calculation model of the softening zone width and the experimental measurement result less than 0.319%. [ABSTRACT FROM AUTHOR]

The continuous digitization of healthcare services makes them more targeted by security attackers that attempt to steal the patients' confidential records and hijack their healthcare rights. Consequently, many existing approaches were proposed to protect healthcare data and services. However, these current solutions lack efficiency, as indicated by the high number of security breaches in healthcare systems. Therefore, this research was motivated to introduce a more efficient algorithm that achieves several essential security requirements such as authentication, confidentiality, and integrity while preserving high resistance against a comprehensive set of different security threats. This proposed algorithm is a hybrid optical-based that utilizes effective hashing, steganography, and encryption techniques for the secure transmission of color or grayscale medical images, even over insecure channels. The input medical image is initially decomposed into three color components (red, green, and blue). Then, each one of these color components is forwarded to multiple sequential security stages. At the first security stage, the Discrete Wavelet Transform (DWT)-based compressive sensing technique is employed to compress the color components of the plaintext medical image to obtain the compressed image components. After that, the sigmoid function-based quantization process is applied to the compressed image components to generate the digital quantized image components. The digital pixels of these components will then be encrypted using Rubik's cube-based encryption algorithm to obtain the final ciphertext medical image. In parallel, to ensure the authentication and integrity of the transmitted medical image, the image phase component is extracted using the optical Double Random Phase Encoding (DRPE) technique. Then, it is quantized before concatenation with a secret key and forwarded to the SHA-256 hashing algorithm to generate the HMAC digest (Hash-based Message Authentication Code value). The HMAC digest is then embedded using Least Significant Bit (LSB)-based steganography within the final encrypted color medical image to increase its secrecy. The proposed algorithm was extensively evaluated using different quality and security assessment metrics to validate its robustness and efficiency against various channel noise and attacks. The obtained outcomes prove the higher performance of the proposed algorithm for secure medical image communication than other recent and related security algorithms in terms of all tested computational and security parameters. In addition, the obtained results confirm that the optical-based security techniques have superior efficiency & robustness and low complexity compared to the related traditional digital-based security techniques. [ABSTRACT FROM AUTHOR]

In this work, it is demonstrated numerically that an asymmetric Moiré fiber grating operated in reflection can provide the required spectral response to implement an all-optical fractional differentiator. In our case, the accumulated phase shift is not associated with a point phase shift, as when working with fiber Bragg gratings and long-period gratings with punctual defects, but is distributed all over the grating. The proposed device is supported by numerical simulations, and a dimensionless deviation factor is calculated to make quantitative analysis feasible. The performance of the proposed device is analyzed using numerical simulations by computing the fractional time derivatives of the complex field of an arbitrary transform-limited Gaussian pulse. A comparison with the performance given by theoretical differentiation is also presented. [ABSTRACT FROM AUTHOR]

Silicon carbide (Sic) materials find wide-ranging applications in advanced optical systems within the aerospace, astronomical observation, and high-intensity laser fields. The silicon-modified Sic used in this study was created by depositing an amorphous silicon film on the surface of a Sic substrate using electron beam evaporation. Such hard and brittle materials often yield smooth surfaces when subjected to plastic removal. To address the issue of the removal depth of the surface plastic domain for silicon-modified Sic, we propose a method to calculate the indentation depth based on the critical load for the transition from plastic to brittle removal. We conducted a series of nanoindentation and nanoscratching experiments. The critical depth formula was validated through mechanical parameters such as hardness, elastic modulus, and fracture toughness, and the theoretical critical depth of the modified silicon layer was calculated to be 2.71 μm. The research results indicate that the critical load for obtaining the plastic-to-brittle transition point during the nanoindentation experiment is 886 mN, at which point the depth of plastic removal is 2.95 μm, closely matching the theoretical value. The measurements taken with an atomic force microscope near the critical load reveal a scratch depth of 3.12 μm, with a relative error of less than 5% when compared to the calculated value. This study establishes a solid foundation for achieving high-quality surface processing.

We propose a new design of an electro-optic full adder by using coupled Si microring resonators for highly dense integration. The device size is significantly reduced by using doubly coupled microring resonators as a power divider. A newly designed crossing waveguide is included in the device. Our design reduces the optical waveguide footprint to approximately 60 μm × 100 μm per bit. Numerical analysis of the full adder operation shows the effectiveness and feasibility of our proposed electro-optic full adder.

In this work, it is demonstrated numerically that an asymmetric Moiré fiber grating operated in reflection can provide the required spectral response to implement an all-optical fractional differentiator. In our case, the accumulated phase shift is not associated with a point phase shift, as when working with fiber Bragg gratings and long-period gratings with punctual defects, but is distributed all over the grating. The proposed device is supported by numerical simulations, and a dimensionless deviation factor is calculated to make quantitative analysis feasible. The performance of the proposed device is analyzed using numerical simulations by computing the fractional time derivatives of the complex field of an arbitrary transform-limited Gaussian pulse. A comparison with the performance given by theoretical differentiation is also presented.

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This study investigated the the gas jet forming process for optical aspherical mirror blanks. The trend of the influence of the gas jet parameters on the surface shape of the mirror blanks was inferred by analysing the variation in the morphology of the gas jet stream. Based on the theoretical analysis, the inference was verified by numerical simulation. The experimental results were compared with the simulation predictions, and it was found that the average prediction deviation for the diameter was 1.07 mm, while the average prediction deviation for the principal curvature was 0.03665 mm−1, which is challenging to correct in simulation. Therefore, we developed a dimensionless prediction model of the surface curvature and surface diameter of the mirror blanks by considering the jet parameters using experimental data. The model’s average prediction error for the surface diameter of the formed surface was 0.3192 mm, and the average prediction error of the principal curvature for the formed surface was 0.00269 mm−1.

Extreme ultraviolet lithography objective lenses require surface figure accuracy of approximately sub-nanometer root mean square (RMS). As the key equipment for sub-nanometer accuracy figuring, the dynamic and static performance of ion beam figuring (IBF) machine tools are critical. However, the related research is not sufficient and comprehensive. To this end, a general model of dynamic and static performance requirements on three-axis IBF machine tools was established. The requirements on dynamic and static performance under different figuring process for different surface shape were comprehensively analyzed. Analysis results revealed that the three-axis IBF machine tools require typical motion accuracy better than 100 μm and certain dynamic performance for achieving sub-nanometer accuracy. According to the theoretical and simulation results, a process optimization based on analysis of dynamic and static performance requirements of IBF machine tools for sub-nanometer figuring is proposed. To verify the proposed method, a Φ90 mm mirror with 2.594 nm RMS was figured to 0.251 nm RMS by optimizing the processing parameters to ensure that the IBF machine tool with measured performance (positioning error of 52.74 μm, 53.04 μm, 37.71 μm, and maximum acceleration of 1.0 m/s2, 1.3 m/s2, and 1.5 m/s2 for axes x, y, and z, respectively) meets the performance requirements. The proposed method can promote the application of three-axis IBF machine tools in sub-nanometer accuracy figuring.

We propose and numerically validate an all‐optical scheme to generate a train of optical pulses. Modulation of a continuous wave with a periodic binary temporal phase pattern followed by a spectral phase shaping enables us to obtain ultrashort pulse trains. An ideal step phase profile as well as a profile arisen from a bandwidth‐limited device is investigated. Analytical guidelines describing pulse train formation and their characteristics are provided. Pulses with a duration of a few picoseconds at a repetition rate of 10 GHz can be expected for realistic experimental conditions. [ABSTRACT FROM AUTHOR]

1D organic micro/nanostructures (OMNSs) based on π‐conjugated molecules are considered to be suitable candidates as photonic units due to their unique photophysical advantages over traditional ones in low‐temperature solution‐processed approach, tunable emission color, the built‐in cavity for optical confinement, and so forth. These inherent characteristics of OMNSs make them have broad application prospects in photonics devices, such as nanolasers, optical waveguides, and optical logical gates. In this review, the recent processes of OMNSs in terms of light generation, light confinement, and propagation are introduced, separately. Some representative works of OMNSs are discussed in the direction of optical modulation and processing. However, huge challenges still remain before the OMNSs are actually used as components of optical circuits in the photonics chips. The summary and the expectations are presented for the future development of 1D organic micro/nanostructures photonics. [ABSTRACT FROM AUTHOR]

Since Gerchberg-Saxton algorithm was developed, it has been applied in various fields, e.g., optical display and optical tweezers. In this paper, three-dimensional (3D) Gerchberg-Saxton optical correlation is proposed. A 2D image is divided into particle-like points placed in 3D space, which are simultaneously encoded into the cascaded phase masks by using a modified Gerchberg-Saxton algorithm. The extracted phase masks can be flexibly compressed, and the decoded images can be verified via optical correlation. It is also illustrated that high security and high flexibility can be achieved by using the proposed 3D Gerchberg-Saxton correlation method. The proposed 3D Gerchberg-Saxton algorithm can provide a new and significant insight on optical correlation.

Diffraction optical elements (DOE) are important elements of systems for images displaying and processing. The DOE materials with both positive and negative birefringence enhance performances and functionality of such systems. We have calculated diffraction of rays passing through (OAGSM) by using our original Exedeep software. At the first time the diffraction parameters for both transmitted and reflected TE‐ and TM‐waves are calculated for materials with both positive and negative optical anisotropy. The simulation results are to be used to create DOE for visible, IR and THz range. [ABSTRACT FROM AUTHOR]

Modulation format conversion is useful when the signal is transmitted through networks employing different modulation formats. It is also expected to increase the spectral efficiency and reduce power consumption in network nodes by applying all-optical signal processing to the modulation format conversion. In this paper, we propose an all-optical modulation format conversion system between on-off keying, quadrature phase-shift keying, and 8-ary quadrature amplitude modulation using optical nonlinear effects in semiconductor optical amplifier and optical threshold device. We also evaluate the conversion performances of the system by numerical simulation in terms of optical signal-to-noise ratio, optical signal power, and accumulated chromatic dispersion. [ABSTRACT FROM AUTHOR]

Optical pulse processor meets the urgent demand for high-speed, ultra wideband devices, which can avoid electrical confinements in various fields, e.g., alloptical communication, optical computing technology, coherent control and microwave fields. To date, great efforts have been made particularly in on-chip programmable pulse processing. Here, we experimentally demonstrate a programmable pulse processor employing 16-cascaded Mach-Zehnder interferometer coupled microring resonator (MZI-MRR) structure based on silicon-oninsulator wafer. With micro-heaters loaded to the device, both amplitude and frequency tunings can be realized in each MZI-MRR unit. Thanks to its reconfigurability and integration ability, the pulse processor has exhibited versatile functions. First, it can serve as a fractional differentiator whose tuning range is 0.51–2.23 with deviation no more than 7%. Second, the device can be tuned into a programmable optical filter whose bandwidth varies from 0.15 to 0.97 nm. The optical filter is also shape tunable. Especially, 15-channel wavelength selective switches are generated. [ABSTRACT FROM AUTHOR]

An advanced optical structure such as a synthetic hologram (also called a computer-generated hologram) is designed for sub-terahertz radiation. The detailed design process is carried out using the ping-pong method, which is based on the modified iterative Gerchberg–Saxton algorithm. The novelty lies in designing and manufacturing a single hologram structure creating two different images at two distances. The hologram area is small in relation to the wavelength used (the largest hologram dimension is equivalent to around 57 wavelengths). Thus, it consists of a small amount of coded information, but despite this fact, the reconstruction is successful. Moreover, one of the reconstructed images is larger than the hologram area. Good accordance between numerical simulations and experimental evaluation was obtained. [ABSTRACT FROM AUTHOR]

Chemical mechanical polishing (CMP) is the key application process in the fabrication of large optical flats to achieve global planarity and smooth surface. The large-diameter pad is a significant part and plays a vital role in CMP. To improve the polishing quality and efficiency, high-profile accuracy of the pad, conditioned by a diamond conditioner, is necessary. However, the conventional conditioning method (CCM) has been unable to satisfy the machining requirements for optical flats, and it is a challenge to improve the conditioning accuracy of the large-diameter polyurethane pad. In this study, we propose an advanced conditioning method (ACM) using the idea of subaperture conditioning, which reduces the size of the conditioner and adds the traverse movement to control the removal of different regions. Based on the conditioning density distribution model, the effect of conditioner diameter and process parameters on the pad planarity is investigated. The conditioning accuracy of the pad and polishing quality of the optical flats obtained with ACM are compared with those of a CCM. Experimental results showed that ACM can create the surface shape of the pad more uniformly than CCM. Furthermore, the polishing accuracy of the large optical flats of ACM exceeds that of CCM. [ABSTRACT FROM AUTHOR]

Single-pixel imaging has emerged over recent years as a novel imaging technique, which has significant application prospects. In this paper, we propose and experimentally demonstrate a scheme that can achieve single-pixel non-imaging object recognition by acquiring the Fourier spectrum. In an experiment, a four-step phase-shifting sinusoid illumination light is used to irradiate the object image, the value of the light intensity is measured with a single-pixel detection unit, and the Fourier coefficients of the object image are obtained by a differential measurement. The Fourier coefficients are first cast into binary numbers to obtain the hash value. We propose a new method of perceptual hashing algorithm, which is combined with a discrete Fourier transform to calculate the hash value. The hash distance is obtained by calculating the difference of the hash value between the object image and the contrast images. By setting an appropriate threshold, the object image can be quickly and accurately recognized. The proposed scheme realizes single-pixel non-imaging perceptual hashing object recognition by using fewer measurements. Our result might open a new path for realizing object recognition with non-imaging. [ABSTRACT FROM AUTHOR]

In this paper we present a data multiplexing method for simultaneous storage in a single package composed by several optical fields of tridimensional (3D) objects, and their individual cross-talk free retrieval. Optical field data are extracted from off axis Fourier holograms, and then sampled by multiplying them with random binary masks. The resulting sampled optical fields can be used to reconstruct the original objects. Sampling causes a loss of quality that can be controlled by the number of white pixels in the binary masks and by applying a padding procedure on the optical field data. This process can be performed using a different binary mask for each optical field, and then added to form a multiplexed package. With the adequate choice of sampling and padding, we can achieve a volume reduction in the multiplexed package over the addition of all individual optical fields. Moreover, the package can be multiplied by a binary mask to select a specific optical field, and after the reconstruction procedure, the corresponding 3D object is recovered without any cross-talk. We demonstrate the effectiveness of our proposal for data compression with a comparison with discrete cosine transform filtering. Experimental results confirm the validity of our proposal. [ABSTRACT FROM AUTHOR]

An advanced optical structure such as a synthetic hologram (also called a computer-generated hologram) is designed for sub-terahertz radiation. The detailed design process is carried out using the ping-pong method, which is based on the modified iterative Gerchberg⁻Saxton algorithm. The novelty lies in designing and manufacturing a single hologram structure creating two different images at two distances. The hologram area is small in relation to the wavelength used (the largest hologram dimension is equivalent to around 57 wavelengths). Thus, it consists of a small amount of coded information, but despite this fact, the reconstruction is successful. Moreover, one of the reconstructed images is larger than the hologram area. Good accordance between numerical simulations and experimental evaluation was obtained.

The nonlinear propagation characteristics of multiwavelength optical signals in silicon waveguides are investigated for all-optical regeneration. Our experiment and simulation show that the multiwavelength regenerators based on silicon waveguides can be developed with a clock-pump scheme by properly setting the signal and pump power levels, ensuring that the Q-factor degradation induced by the Kerr nonlinear cross talk of the input signals is <1.0 dB and the clock-pump power is no more than the saturated input level related to the nonlinear loss. A three-wavelength regeneration experiment based on the clock-pump four-wave-mixing scheme was demonstrated in the silicon nanowire waveguide, and both the extinction ratio and Q-factor are improved by >3.0 dB for 12.5 Gbit∕s on–off keying signals. The feasibility of an eight-wavelength regeneration with the clock pump is also verified by simulation. [ABSTRACT FROM AUTHOR]

Conversion between multilevel modulation formats is one of the key functions for flexible networking aimed at high spectral efficiency in optical fiber transmission. The authors previously proposed an all-optical conversion system from quadrature phase shift keying signal to simultaneous two binary phase shift keying (BPSK) signals by using four-wave mixing and interference. Since the converted BPSK signals are spatially separated, there is an issue that they cannot be transmitted at the same time through a single fiber core when redirected to the same destination. In this paper, therefore, we consider to solve the issue by converting to a symbol rate doubled single BPSK signal using a pulse width compression technique. Numerical simulation reveals that the location of the pulse width compressor affects the system performances evaluated by bit error rate and constellation diagram. [ABSTRACT FROM PUBLISHER]

All-optical arbitrary-order temporal differentiators are demonstrated with phase-modulated fiber Bragg gratings (PM-FBGs) in transmission for the first time. The transmissive PM-FBGs are designed by employing a novel two-step nonlinear optimization method, which consists of unconstrained nonlinear optimization method step and constrained nonlinear optimization method step. Specifically, the first unconstrained nonlinear step is used to get appropriate parameters as input to the second step, while the second constrained nonlinear step is employed to generate more accurate result based on the output of the first step. The proposed method does not impose much restriction on the initial input parameters and also improves the result accuracy compared with previous one-step nonlinear optimization method. Examples of 0.5th-order, first-order, and second-order differentiators are designed and numerically simulated. The numerical results show that the designed PM-FBG differentiators are very accurate with a bandwidth up to 500 GHz. Moreover, the proposed method can be applied in designing arbitrary-order differentiators with the differentiation order n > 0. [ABSTRACT FROM PUBLISHER]

Flexible conversion between multilevel modulation formats is one of the key processing functions to realize adaptive modulation techniques for flexible networking aimed at high spectral efficiency in optical fiber transmission. The authors have proposed an all-optical format conversion system from binary phase-shift keying (BPSK) to quadrature PSK (QPSK) and its reverse conversion from QPSK to BPSK. The latter had an advantage of wavelength-shift-free conversion from an incident QPSK to simultaneous two BPSK outputs without loss of the transmitting data. However, it was limited only for a single polarization signal. In this paper, we propose a novel method of wavelength-preserved conversion for polarization division multiplexed QPSK signal with arbitrary polarization rotation angle to the $x$-axis on the $x$ –$y$ polarization plane which is orthogonal to the propagation axis. The method is based on the orthogonal dual-pump four-wave-mixing (FWM) in the highly nonlinear fiber with a nonlinear optical loop mirror configuration, which has advantages that it separately outputs the original signal and the phase conjugate signal and has independent FWM efficiency of the signal polarization angle. We show the system performances such as bit-error-rate and optical signal-to-noise ratio penalty evaluated by numerical simulations. [ABSTRACT FROM PUBLISHER]

In this work, we present a method to generate vector beams with a 4f polarization Fourier filtering system that combines a spatial light modulator (SLM) at the input plane and a polarization diffraction grating (PDG) at the output plane. In the Fourier plane, two quarter-wave plates are employed to transform the +1 and −1 diffraction orders onto circular right (RCP) and left (LCP) polarizations, respectively. The PDG at the output plane recombines the two beams producing the colinear superposition of RCP and LCP beams. The application of a random encoding technique to multiplex diffractive elements on the SLM allows the independent encoding of different patterns on the final beam, thus arbitrary vector beams can be generated at the output. Experimental results are included that demonstrate the capability for this approach to encode a variety of polarization vector beams with different topological charges. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the possibility to perform a fractional differentiation of arbitrary order on a given light pulse by propagation through a single long-period grating. A simple analytical expression is obtained also, relating the fractional order of differentiation with the parameters of the long-period grating. A secant hyperbolic like pulse of 23 ps time width with a chirp parameter of −30 was successfully fractionally differentiated to the 0.5th order. The proposal was corroborated experimentally and numerically. The device may find applications in real time phase recovery. [ABSTRACT FROM AUTHOR]

Nonlinear effects are observed in a non-adiabatically tapered optical fibre. The designed structure allows for the introduction of self-phase modulation, which is observed through pulse breaking and spectral broadening, in approximately a centimetre of propagation using a commercial telecom laser. These devices are simple to fabricate and suitable to generate and control a variety of nonlinear effects in practical applications because they do not experience short-term degradation as previously reported approaches. Experimental and theoretical results are obtained, showing a good agreement. [ABSTRACT FROM AUTHOR]

We demonstrate a low-loss, ultrawideband (UWB), programmable radio frequency photonic phase filter utilizing a broadband optical frequency comb, interferometric pulse shaping configuration, and a balanced photodetector for spread spectrum pulse compression. We present UWB linear frequency-chirped pulse compression with bandwidths exceeding 7 GHz. The filter insertion loss for these experiments can be as low as 0.5 dB. In addition, the bandwidth and chirp rate of the phase filter are programmable. To further illustrate the programmability of the proposed filter, we report pulse compression experiments for UWB Costas sequences with bandwidth over 6 GHz. Finally, we perform a spread-spectrum jamming-resistant pulse compression experiment with the chirp filter, where a processing gain of \sim17.3 dB, proportional to the time-bandwidth product of the filter, enables the recovery of a transmitted UWB signal in the presence of jamming. [ABSTRACT FROM PUBLISHER]