Magnetically tunable ultralow threshold optical bistability by exciting LRSPR in InAs/graphene layers at the terahertz region.

With the experimental corroboration employing a transfer matrix method, an analytical observation of optical bistability using long-range surface plasmon resonance (LRSPR) through the external magnetic field is presented for a very low threshold value. The proposed analytical method has been verified with the reported experimental data provided by Liu et al. [Curr. Appl. Phys.29, 66 (2021)1567-173910.1016/j.cap.2021.06.003]. Now theoretical analysis is further extended in the proposed multilayered structure comprising an InAs layer sandwiched between two graphene layers, whose electromagnetic response at 2 THz can be regulated by employing a magnetic field and may tune the optical bistability without modifying the geometry or the characteristics of the structure. The observed threshold intensity for the switch-up is 6.6615×104 W/c m 2 at 0.001 T; thus, this analytical approach is able to achieve 2 orders lower threshold for magnetically tunable upswitching of the optical bistable process. This suggested magnetically adjustable optical bistable arrangement gives a possibility for the comprehension of optical logic gates, optic memory, opto-transistors, and switches at a low switching threshold due to extraordinary features of the composite layers due to local field amplification of the graphene layer.

Wave-theory-based analysis of a fiber optic bio-sensor illuminated by radially polarized Bessel-Gauss beam: an approach for early diagnosis of breast cancer with a high-resolution wavelength-interrogation technique.

With the establishment of validity using authoritative experimental results, an analytical investigation of an SPR-based fiber optic sensor, employing a wave-theory-based technique for determining breast cancer by shining a radially polarized Bessel-Gauss (RPBG) beam, is proposed. First, by using a radially polarized Gaussian (RPG) beam, the observed sensitivity is 9404.61 dB/RIU, where the acquired results are in good concurrence with the experimental data reported by Yan et al. [Chin. Opt. Lett.7, 909 (2009)COLHBT1671-7694]. Thus, the proposed theory has been validated with the reported experimental data. This theoretical analysis is further extended by utilizing an RPBG beam, where the observed sensitivity is 21,699.26 dB/RIU and 5846 nm/RIU, with a resolution of 4.61×10-7, which is 2.5 times superior to the reported results to date. By using an RPBG beam, the proposed method, to our best knowledge, is the first to achieve much higher sensitivity in the area of fiber optic breast cancer detection. The higher sensitivity achieved at lower concentrations of an HER2 biomarker has led to the idea of early diagnosis of breast cancer by optically assessing it at its earlier stage using a high-resolution wavelength-interrogation technique.

Highly sensitive surface-plasmon-resonance- based fiber optic breast cancer detection by shining a Bessel-Gauss beam: a wave-theory-based approach.

With experimental validation, an analytical exploration of a surface-plasmon-resonance- and evanescent-wave-based fiber optic biosensor, using Bessel-Gauss beams for early detection of breast cancer, is proposed and designed here. The observed sensitivity is 0.58 nm/ng/mL and 11,928.25 dB/RIU with a resolution of 8.38×10-7, which is 10 times better than the reported ray-theory-based articles reported to date using a Gaussian beam. To analyze more effectively the higher-order modes and to achieve more similarity between the analytical and experimental solutions, the wave-theory-based approach is adopted here. With this approach, for the first time to our knowledge using a Bessel-Gauss beam, higher sensitivity is achieved for fiber optic breast cancer detection. The enhanced sensitivity at lower concentrations of the Human Epidermal Growth Factor Receptor 2 biomarker has conceptualized the idea of early detection of breast cancer by optically quantifying the earlier stage of cancer.

Tunable low-threshold bistable Goos-Hänchen shift and Imbert-Fedorov shift using long-range graphene surface plasmons within the terahertz region.

An analytical exploration of bistable spatial and angular lateral shifts at terahertz radiation in a multilayered long-range graphene surface plasmon resonant configuration is proposed with a Kerr polymer at a ultra-low threshold of 200W/cm2 for low Fermi energy at 1 ps relaxation time. Here, spatial Goos-Hänchen shift is observed 10 times larger than the previously reported papers. The hysteretic behavior of the spatial and angular Imbert-Fedorov shift by tuning the incident electric field and tunability of the threshold intensities is also realized, which has not been previously reported. The proposed idea explores new avenues in lateral-shift-based optical switches and optical sensors.

Investigation of modal-interference-induced fiber optic refractive index sensor: markedly enhanced sensitivity realized by shining an optical vortex beam.

A highly sensitive multimode-interference-based refractive index sensor is reported here by shining an optical vortex beam. The sensor probe is formed by splicing a length of no-core fiber in between two air-core vortex fibers. The coupling characteristics of various modes inside the sensor and their effect on sensing properties are numerically analyzed. Simulation results show that the sensing scheme proffers a maximum sensing resolution of 7.59×10-6 and 4.18×10-6 RIU for no-core fiber length of 29.40 and 44.60 mm, respectively. Because of its high sensitivity, the study has potential applications in the chemical and biological sensing fields.

Analysis of high-resolution electro-optical beam steering by long-range surface plasmon resonance using a ZnSe prism.

A proposal on high-resolution electro-optical beam steering is conceptualized analytically using a long-range surface plasmon resonance configuration comprising a liquid crystal layer of E44 for 1550 nm wavelength. With the tuning of the refractive index of E44 through variations of applied voltage from 0 to 10 V, an optical beam steering can be attained considering the composite effect of spatial and angular Goos-Hanchen and Imbert-Fedorov shifts. As compared with the existing beam shift processes in µrad by mechanical means, here, the computed angular resolution is 3.40 nrad. The proposed idea finds a new avenue in the field of pulse generation, optical sensor applications, and atomic force microscopy, mitigating existing drawbacks.

Long-range surface plasmon-induced tunable ultralow threshold optical bistability using graphene sheets at terahertz frequency.

A proposal on optical bistability at ultralow switching threshold and lower Fermi-level of graphene around 2 THz is implemented analytically through the proposed long-range surface plasmon resonance configuration by employing local field enhancement effects owing to the excitation of a graphene symmetric mode within graphene sheets. Reported threshold intensity for the optical bistability to date is 1.6 kW/cm2 within the terahertz region and 1.83 MW/cm2 at near-IR range. Whereas the proposed scheme explores the possibility of reducing this threshold down to 143.68 W/cm2, this technique proffers potential applications in nanoillumination, optical memory, and all-optical switching at an ultra-low threshold.

Dispersion compensated optical amplifier in Ti-diffused PPLN ridge waveguide.

Nonlinear optical phase conjugation is known to be an effective technique for dispersion compensation in optical fibers. It requires an optical filter to separate out only the phase conjugated signal at the output to achieve signal pulse re-narrowing by its subsequent propagation through an identical medium. In this paper, a compact design, which integrates the optical phase conjugator and the filter on a single substrate of periodically poled lithium niobate and facilitates the use of a single pump source for both phase conjugation and amplification, is proposed and analyzed using computer simulations.

Simultaneous multi-wavelength oscillation of Nd laser around 1.3 mum: A potential source for coherent terahertz generation.

Simultaneous oscillations of 1318.8nm, 1320.0nm, 1332.6nm, 1335.0nm, 1338.2nm and 1339.0nm in a side, pulsed-diode-laser-array pumped Nd:YAG laser is realized for both free running and Q-switched operation. An average power of 1.1W is obtained for an absorbed pump power of 7.1W with an effective optical slope efficiency of 33%. The difference frequency interactions among these wavelengths may be used to generate radiation in the range 0.13-3.43THz. With the two most intense lines at 1318.8nm and 1338.2nm, it is possible to generate coherent radiation at 3.3THz with numerically estimated peak power of 0.21W in a 1.5mm thick GaSe crystal.