Optical Inverter Research Articles

All-optically untangling light propagation through multimode fibers

When light propagates through a complex medium, such as a multimode optical fiber (MMF), the spatial information it carries is scrambled. In this work we experimentally demonstrate an all-optical strategy to unscramble this light again. We first create a digital model capturing the way light has been scattered, and then use this model to inverse-design and build a complementary optical system–which we call an optical inverter–that reverses this scattering process. Our implementation of this concept is based on multi-plane light conversion, and can also be understood as a physical matrix pre-conditioner, or a linear diffractive optical neural network. We present three design strategies allowing different aspects of device performance to be prioritized. We experimentally demonstrate a prototype optical inverter capable of simultaneously unscrambling up to 30 spatial modes that have propagated through a 1 m long MMF, and show how this promises near instantaneous incoherent imaging, without the need for any beam scanning or computational processing. We also demonstrate the reconfigurable nature of this prototype, allowing it to adapt and deliver a new optical transformation if the MMF it is matched to changes configuration. Our work represents a step towards a new way to see through scattering media. Beyond imaging, this concept may also have applications to the fields of optical communications, optical computing and quantum photonics.

How to Build the “Optical Inverse” of a Multimode Fibre

When light propagates through multimode optical fibres (MMFs), the spatial information it carries is scrambled. Wavefront shaping reverses this scrambling, typically one spatial mode at a time—enabling deployment of MMFs as ultrathin microendoscopes. Here, we go beyond sequential wavefront shaping by showing how to simultaneously unscramble all spatial modes emerging from an MMF in parallel. We introduce a passive multiple-scattering element—crafted through the process of inverse design—that is complementary to an MMF and undoes its optical effects. This “optical inverter” makes possible single-shot widefield imaging and super-resolution imaging through MMFs. Our design consists of a cascade of diffractive elements, and can be understood from the perspective of both multi-plane light conversion, and as a physically inspired diffractive neural network. This physical architecture outperforms state-of-the-art electronic neural networks tasked with unscrambling light, as it preserves the phase and coherence information of optical signals flowing through it. We show, in numerical simulations, how to efficiently sort and tune the relative phase of up to ~ 400 step-index fibre modes, reforming incoherent images of scenes at arbitrary distances from the fibre facet. Our optical inverter can dynamically adapt to see through experimentally realistic flexible fibres—made possible by moulding optical memory effects into its design. The scheme is based on current fabrication technology so could be realised in the near future. Beyond imaging, these concepts open up a range of new avenues for optical multiplexing, communications, and computation in the realms of classical and quantum photonics.

Research on preparation technology of optical fiber image inverters with large aperture

The optical fiber image inverters are the key components which applied in low-light level night vision device, and the optical fiber image inverters with large aperture can achieve the detection of wide field of view, large view and further visual range. However, the existing twisting operation process cannot produce the qualified products. The twisting operation process with rotation differential velocity combined with double internal furnace heating design was adopted, and finally the large-aperture optical fiber image inverters with required performance indexes were prepared. The test results show that the angle concentration amount in twisting region is decreased to 5.98 °/mm, which significantly improves the edge resolution of the large-aperture optical fiber image inverters.

Pupil inversion Mach-Zehnder interferometry for diffraction-limited optical astronomical imaging

We present theoretical and laboratory experimental results on a robust interferometric device based on pupil inversion, or 180° rotational shearing interferometry. The image of an astronomical object degraded by the atmosphere turbulence can be restored (ideally up to the diffraction limit) by a numerical post-processing of the interferogram. Unlike previous Michelson configurations that return half of the light to the sky, the Mach-Zehnder interferometer has no fundamental losses when both outputs are used. The interferogram is formed by two overlapped images of the telescope pupil, but one of them is spatially inverted, and out of phase by π/2 only in its half. This optical operation is achieved in a robust way by inserting a refractive optical image inverter and a binary phase plate in one of the arms of the interferometer. In this way, the system has no polarization dependence or moving parts since the plate allows the object to be retrieved numerically from just one interferogram (single exposition) or a few independent interferograms. For that, several algorithms are proposed. Likewise, we include a laboratory proof-of-concept in which a diffraction-limited image is obtained in spite of presence of aberrations and photon noise.

Performance assessment of a new infrared phototransistor based on JL-TFET structure: Numerical study and circuit level investigation

This work aims to investigate the performance of a new Junctionless (JL) Ge-gate Tunneling-FET phototransistor for Infrared sensing applications. The electrical and optical performances of the considered sensor are numerically analyzed, where both switching and optoelectronic properties are reported. In this context, we address the influence of the Ge-gate doping level and high-k gate dielectric on the variation of optical Figures-of-Merit (FoMs) parameters such as responsivity, ION/IOFF ratio and optical commutation speed. Interestingly, it was revealed that the proposed design provides promising pathways for enhancing the phototransistor FoMs as compared to the conventional FET-based sensors. In the second stage of our investigation, we provide a performance assessment of the proposed phototransistor by analyzing its switching capabilities as compared to the conventional design, where the device is implemented in an optical inverter circuit. The obtained results indicate the superior optoelectronic performance offered by the proposed design in comparison with the conventional devices in terms of optical commutation speed and optoelectronic gain. Therefore, this contribution can provide new insights concerning the benefit of adopting JL-TFET design for future high-performance and ultra-low power deep submicron CMOS optoelectronic applications.

All-optical switching and limiting properties of a Ru (II) Schiff-base complex for nonlinear optical applications

A salen-based ruthenium (Ru) (II) complex was synthesized for possible use in nonlinear optical device applications. The Ru complex was doped in a polymer matrix to fabricate films using a low-cost spin-coating technique. The third-order nonlinear optical parameters of the complex were investigated by Z-scan and degenerate four-wave mixing techniques. The study reveals two-order enhancement of third-order optical susceptibility χ(3) and exhibits superior limiting capability due to a reverse saturable absorption process. All-optical switching action for the films indicates that the sample can function as an optical inverter or a NOT gate. Hence, the Ru (II) Schiff-base complex materializes as a possible candidate for use in nonlinear optical devices.

Realization of all‐optical logic gates using injection locking in a distributed feedback laser diode

ABSTRACTIn this article, we experimentally demonstrate an all‐optical inverter and NOR logic working at 10 Gbit/s using injection locking technique in a Distributed Feedback laser diode. The proposed optical inverter operate at 10 Gb/s with very good extinction ratio of around 15 dB with a power penalty of only 2 dB at BER of 10−9. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:940–944, 2016

Photonic-crystal-based all-optical NOT logic gate.

In the present paper, we have utilized the concept of photonic crystals for the implementation of an optical NOT gate inverter. The designed structure has a hexagonal arrangement of silicon rods in air substrate. The logic function is based on the phenomenon of the existence of the photonic bandgap and resulting guided modes in defect photonic crystal waveguides. We have plotted the transmission, extinction ratio, and tolerance analysis graphs for the structure, and it has been observed that the maximum output is obtained for a telecom wavelength of 1.554μm. Dispersion curves are obtained using the plane wave expansion method, and the transmission is simulated using the finite element method. The proposed structure is applicable for photonic integrated circuits due to its simple structure and clear operating principle.

All optical nonlinear and switching characteristics of a novel ruthenium complex

Third-order nonlinear optical properties of a novel ruthenium complex (2-thioxo-1,3-dithiole-4,5-dithiolato) triphenylarsenic Ru(III), have been investigated by employing Z-scan and DFWM techniques. The compound shows self-defocusing effect. Its nonlinear refractive index, third-order nonlinear optical susceptibility and the second-order hyperpolarizability are seen to be of the order of 10−9, 10−10 and 10−30esu respectively. The nonlinear absorption coefficient is of the order of 10−9m/W. This material exhibits good optical power limiting capability which is seen to occur due to reverse saturable absorption. Experiments on all-optical switching action indicate that the sample can function as an optical inverter or a NOT gate.

Polarization encoded optical N-valued inverter

An inverter, in wider sense, may be defined as a transformation of an incoming state into an outgoing state in a logic-based information processing system. In this paper, a simple circuit for inverters two-valued (binary), three-valued (ternary), and four-valued (quaternary) logical systems has been designed. An outline has been given for designing of all possible 27 three-valued inverters. The circuit is designed with the help of a polarization converter and a polarization isolator only. Mathematical analysis of the polarization converters is established with Jones matrix. This circuit will be useful in a future all-optical multivalued logic-based information processing system.

Design and analysis of all-optical inverter using SOA-based Mach–Zehnder interferometer

In this paper an optical Boolean inverter gate has been simulated first time, with SOA-based Mach–Zehnder interferometer (SOA-MZI). The control and continuous clock pulse are properly selected so that SOA is heavily saturated and at the same time the switched out continuous clock pulse are compressed by the control pulse present there. To optimize the gate performance, the output contrast ratio (CR) and extinction ratio (ER) have been taken for the optimization criteria and the result is investigated at different Gb/s. However, the operation is limited by SOAs recovery time.

RF phase shifter using a distributed feedback laser in microwave transport systems

This work experimentally demonstrates the efficacy of a radio-frequency phase shifter using a distributed feedback laser in a microwave transport system. Phase shifts of about 101 degrees are obtained at 8.75 GHz. The proposed phase shifter can amplify microwave signals and thereby improve transmission performance. Additionally, a similar single sideband modulation can be generated by the phase shifter. Experimental results indicate that the proposed phase shifter can be used in future long-distance microwave transport systems and all optical inverters.

Cascadable optical inversion using 1550 nm VCSEL

A novel, cascadable optical inverter is demonstrated up to 2.5 Gbit/s using a commerically available 1550 nm VCSEL. Experimental results show cascadable operation based on positive noise margin transfer characteristics and extinction ratio (ER) regeneration. Errorless performance is measured with sensitivity penalties of 0 and 1.4 dB and output ER exceeding 6 dB at 1 and 2.5 Gbit/s, respectively.

Emitter-Induced Gain Effects on Dual-Emitter Phototransistor as an Electrooptical Switch

In this paper, an investigation of the static/dynamic performance of dual-emitter phototransistors (DEPTs) as an electrooptical switch was made. In the static case, the measured optical gains (the collector photocurrents) of DEPTs operated at a 12.5-muW optical power have been enhanced from 13.7 to 20.2 (88 to 129 muA) due to an emitter-induced gain high (EIGH) from photocurrent modulation. For DEPTs as an electrooptical switch, the EIGH from photocurrent modulation and the emitter-induced gain effect from junction-voltage modulation dominate the dynamic operation. In the case of continuous light input, good bistable-state output characteristics can be realized with an electrical clock signal. When the switch is operated with a 2-V supply voltage and a 10-kOmega load resistance, the stable electrical-logic swing (ELS) is 0.41 V for a 1-V/1-kHz clock signal. Electrical inputs of 5-, 10-, and 50-kHz clock signals are also employed to achieve outputs with increased ELSs of 1.18, 1.19, and 1.3 V, respectively. An optical inverter is realized. When two clock signals, an electrical input and an optical input, are employed, DEPTs are operated as a tristable-state switch.

Cascadable all-optical inverter based on a nonlinear vertical-cavity semiconductor optical amplifier

We report, for the first time to our knowledge, the operation of a cascadable, low-optical-switching-power(~10 microW) small-area (~100 microm(2)) high-speed (80 ps fall time) all-optical inverter. This inverter employs cross-gain modulation, polarization gain anisotropy, and highly nonlinear gain characteristics of an electrically pumped vertical-cavity semiconductor optical amplifier (VCSOA). The measured transfer characteristics of such an optical inverter resemble those of standard electronic metal-oxide semiconductor field-effect transistor-based inverters exhibiting high noise margin and high extinction ratio (~9.3 dB), making VCSOAs an ideal building block for all-optical logic and memory.

Investigation of Transient Response of Erbium-doped Fiber Lasers by Semi-classical Theory

The transient response of all optical gain clamped multi channel erbium doped fiber amplifiers (EDFA's) and optical fiber inverter is studied by a semi-classical model. Using the semi-classical theory, the electric field interacting with mater is considered classical and the medium is quantized according to the equations of motion for density matrix. The rate equations and self consistency equations, which yield amplitude and phase of the electric fields of oscillator and amplifying channels are derived by considering Maxwell's equations and equation of motion of density matrix. The governing equations form a system of coupled partial differential equations. The relaxation oscillation behavior of stabilized multi channels erbium doped fiber amplifier and transient time response of an optical fiber inverter are simulated by the numerical solution of this system. The theoretical findings are in a good agreement with the previous experimental results that are reported.

Modeling of a high‐speed polarization controller based on a vertical‐cavity surface‐emitting laser

AbstractPhotonic networks have gained attention as the next generation optical communication system because their communication processes use wavelength information in the optical region. Generally, because the polarization states of the optical wavelengths propagating in optical fibers are irregular, strong noise is generated because the optical devices constructing the photonic network exhibit a dependence on polarized light. To suppress this noise, polarization control becomes an important technology. In this research, we propose a new polarization controller to bring out the superior features of the surface‐emitting laser and examine its dynamic characteristics. In this paper, we also conduct analysis based on the multimode rate equations that consider high‐order lateral modes and polarization modes, and dynamic analysis of the polarization controller based on analyzing the optical inverter characteristics obtained by the lateral mode switching, which becomes the fundamental principle of the light input and output. Based on the static and dynamic characteristics, we demonstrated the possibility of a high‐speed polarization controller using a surface‐emitting laser structure. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(1): 41– 49, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20258

All-optical inverter based on long-wavelength vertical-cavity surface-emitting laser

An all-optical inverter using transverse mode switching in a 1.5-/spl mu/m vertical-cavity surface-emitting laser (VCSEL) was demonstrated theoretically and experimentally. The fundamental mode in a single-mode VCSEL was strongly suppressed when external light was injected into an LP02 high-order mode, resulting in an on-off ratio of over 20 dB. The polarization dependence of the static optical input--output characteristics of inverter operations was as low as /spl sim/13%. The VCSEL-based optical inverter operated with a 5-Gb/s nonreturn-to-zero (NRZ) input signal. A theoretical result using two-mode rate equations is in good agreement with experimental results.

Reverse saturable absorption in Er+3 doped systems

This work reports on reverse saturable absorption (RSA) from Er3+ doped systems. RSA is characterized by a decrease in the transmitted intensity as the incident intensity increases. This effect is interesting due to its potential application in optical devices such as optical inverters, optical limiters and switches. Particularly, Er doped systems pumped at wavelengths around 830nm may exhibit RSA. In this case, the RSA process is achieved because the resonant excited-state (4I13/2–4S3/2) absorption cross section is larger than the quasiresonant ground state (4I15/2–4I9/2) absorption cross section. We have simulated the transmitted intensity of Er doped samples as a function of laser intensity, laser wavelength and Er concentration. Our results indicate that Er concentration plays an important role in the process. RSA is intensified as cross relaxation between Er ions increases. Moreover, the effect of optical limiting is observed and is dependent on the cross relaxation among Er ions.

Nonlinear optical input–output characteristics of 1.55 μm injection-locked vertical-cavity surface-emitting lasers

The optical input–output characteristics of a 1.55 μm vertical-cavity surface-emitting laser (VCSEL) with external light injection to its fundamental mode were investigated. Appropriate wavelength detuning of external light enables abrupt modal switching in an injection-locked VCSEL. We found that the obtained nonlinear transfer function is strongly dependent on the distance between a VCSEL and an input lensed fiber. As the distance was changed, different optical input–output characteristics were observed, demonstrating that such a VCSEL can be employed in various optical signal-processing schemes, for example as an optical regenerator or an optical inverter.