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Highly nonlinear gain media that are optically pumped by rare-earth doped sources have become a promising approach for the fabrication of all-fiber mid-infrared laser sources. This article focuses on the recent progresses of highly nonlinear chalcogenide microwires as practical gain media for far-detuned wavelength conversion towards the mid-infrared. [ABSTRACT FROM AUTHOR]

We have studied the effect of duty cycle variation in the Fibonacci optical superlattice (FOS) structure by analysing the second harmonic generation (SHG) spectrum. Unlike periodic quasi-phase matching (QPM) device, the variation in duty cycle changes the SHG spectrum asymmetrically. The higher intensity and other multiple peaks in the spectrum change asymmetrically when the duty ratio varies away from 0.5. As a result, the SHG spectrum of lower and higher duty ratios from the ideal FOS device generates multiple dissimilar peaks as it was observed from entirely different QPM devices. However, the main phase matching peak shows symmetric nature, irrespective of the duty cycle variation like the periodic one. Further, we have analysed the correlation spectrum to prove the asymmetric nature of the FOS SHG spectrum. Although FOS device exhibits asymmetric spectral nature in duty cycle variation, it shows the same optical interaction regardless of the pump direction. [ABSTRACT FROM AUTHOR]

Interferometric interrogation technique realized for conventional fiber Bragg grating (FBG) sensors is historically known to offer the highest sensitivity measurements, however, it has not been yet explored for π -phase-shifted FBG ( π FBG) sensors. This, we believe, is due to the complex nature of the reflection/transmission spectrum of a π FBG, which cannot be directly used for interferometric interrogation purpose. Therefore, we propose here an innovative as well as simple concept towards this direction, wherein, the transmission spectrum of a π FBG sensor is optically filtered using a specially designed fiber grating. The resulting filtered spectrum retains the entire characteristics of a π FBG sensor and hence the filtered spectrum can be interrogated with interferometric principles. Furthermore, due to the extremely narrow transmission notch of a π FBG sensor, a fiber interferometer can be realized with significantly longer path difference. This leads to substantially enhanced detection limit as compared to sensors based on a regular FBG of similar length. Theoretical analysis demonstrates that high resolution weak dynamic strain measurement down to 4 p ε ∕ H z is easily achievable. Preliminary experimental results are also presented as proof-of-concept of the proposed interrogation principle. [ABSTRACT FROM AUTHOR]

Broadband wavelength conversion based on degenerate four-wave mixing is theoretically investigated in a hydrogenated amorphous silicon (a-Si:H) waveguide with silicon nitride inter-cladding layer (a-Si:HN). We have found that enhancement of the non-linear effect of a-Si:H waveguide nitride intermediate layer facilitates broadband wavelength conversion. Conversion bandwidth of 490 nm and conversion efficiency of 11.4 dB were achieved in a numerical simulation of a 4 mm-long a-Si:HN waveguide under 1.55 μm continuous wave pumping. This broadband continuous-wave wavelength converter has potential applications in photonic networks, a type of readily manufactured low-cost highly integrated optical circuits. [ABSTRACT FROM PUBLISHER]

An essential factor of the particle number is exploited for the phosphor excitation in phosphor-converted white LEDs. The particle number can clearly reveal the dependence of the light output flux and the correlated color temperature upon the conventional parameters, thickness, and concentration of the phosphors in a simpler way. In addition, we also find that there might exist an optimal particle number for the maximal luminous light output. An empirical function is then proposed for successfully modeling the relation between the output light and the particle number.

We theoretically analyze the phase noise transfer issue between the pump and the wavelength-converted idler for a nondegenerate four-wave mixing (FWM) scheme, as well as study the vector theory in nonlinear semiconductor optical amplifiers (SOAs), in order to design a polarization-insensitive wavelength conversion system employing dual co-polarized pumps. A tunable sampled grating distributed Bragg reflector (SG-DBR) pump laser has been utilized to enable fast wavelength conversion in the sub-microsecond timescale. By using the detailed characterization of the SGDBR laser, we discuss the phase noise performance of the SGDBR laser. Finally, we present a reconfigurable SOA-based all-optical wavelength converter using the fast switching SGDBR tunable laser as one of the pump sources and experimentally study the wavelength conversion of the single polarization quadrature phase shift keying (QPSK) and polarization multiplexed (Pol-Mux) QPSK signals at 12.5-Gbaud. A wide tuning range (>10 nm) and less than 50 ns and 160 ns reconfiguration time have been achieved for the wavelength conversion system for QPSK and PM-QPSK signals, respectively. The performance under the switching environment after the required reconfiguration time is the same as the static case when the wavelengths are fixed. [ABSTRACT FROM AUTHOR]

The potential of GaAs-based photonic crystals for fast all-optical switching in the telecom spectral range is exploited by controlling the surface recombination and, thereby, the carrier relaxation dynamics. The structure is entirely coated with a layer of aluminium oxide using atomic layer deposition. This results in a carrier lifetime of about 10 ps, as determined by spectrally resolved pump-probe measurements. We show that the nonlinear response of the resonator is optimized when it is excited with a few-picoseconds pulse. This dynamics is perfectly captured by our model accounting for the carrier diffusion with an impulse response function. Moreover, the suppression of photo-induced oxidation is revealed to be crucial to demonstrate all-optical operation at GHz rates with average coupled pump power of 0.5 mW (hence 100 fJ/bit). The switching window is 12 ps wide (1/e), as resolved by homodyne pump-probe measurements. The devices respond to a sequence of closely spaced pump pulses demonstrating a gating window close to 10 ps, with a contrast as high as 7 dB. [ABSTRACT FROM AUTHOR]

Fiber Mach–Zehnder interferometers (F-MZI) are widely used for fiber Bragg grating (FBG) sensor interrogation purpose due to their advantages in terms of wide bandwidth, high resolution, and tunable sensitivity. They are appropriate for dynamic strain measurement applications in the areas of vibration analysis, hydrophones, and acoustic emission studies. The interferometer converts the Bragg wavelength shift of an FBG sensor into a corresponding phase shift which is finally recorded as intensity variations at the output. Power fluctuations of the light source as well as disturbances in the light guiding path and/or dependence of light source intensity on wavelength introduce fictitious output intensity variations resulting into significant measurement errors. We propose and experimentally demonstrate a dual-channel F-MZI approach that eliminates the light intensity disturbance noise. Furthermore, the proposed method also improves the demodulated signal quality by a factor of $\sim 3$ dB. [ABSTRACT FROM PUBLISHER]

We theoretically analyze the phase noise transfer issue between the pump and the wavelength-converted idler for a nondegenerate four-wave mixing (FWM) scheme, as well as study the vector theory in nonlinear semiconductor optical amplifiers (SOAs), in order to design a polarization-insensitive wavelength conversion system employing dual co-polarized pumps. A tunable sampled grating distributed Bragg reflector (SG-DBR) pump laser has been utilized to enable fast wavelength conversion in the sub-microsecond timescale. By using the detailed characterization of the SGDBR laser, we discuss the phase noise performance of the SGDBR laser. Finally, we present a reconfigurable SOA-based all-optical wavelength converter using the fast switching SGDBR tunable laser as one of the pump sources and experimentally study the wavelength conversion of the single polarization quadrature phase shift keying (QPSK) and polarization multiplexed (Pol-Mux) QPSK signals at 12.5-Gbaud. A wide tuning range (>10 nm) and less than 50 ns and 160 ns reconfiguration time have been achieved for the wavelength conversion system for QPSK and PM-QPSK signals, respectively. The performance under the switching environment after the required reconfiguration time is the same as the static case when the wavelengths are fixed.

We report on a two-dimensional nonlinear photonic quasicrystal constructed by the generalized dual-grid method. One collinear optical parametric generation, cascading two noncollinear frequency doubling processes are realized for multiple second-order cascaded nonlinearities. Optical properties including wave propagating and temperature detuning characteristics were studied theoretically using the coupled nonlinear wave equations. The scheme has potential application in fields such as quantum optics and spectroscopy. [ABSTRACT FROM AUTHOR]

We propose a slot-width switching (SWS) silicon–organic hybrid waveguide for broadband and efficient wavelength conversion. By switching the slot width of different lengths, the quasi-phase-matching can be obtained. Compared with width-modulated silicon-on-insulator (SOI) waveguide, the non-linear absorption can be ignored in slot waveguide which is filled with p-toluene sulphonate. Consequently, the conversion efficiency at a particular signal wavelength is improved, and the 3-dB conversion bandwidth is also extended. The numerical simulation results indicate that, for a continuous-wave pump at 1550 nm, a conversion bandwidth of 570 nm and a peak conversion efficiency of 11.32 dB can be realized in a 7.5-mm-long SWS waveguide, which is better than that of width-modulated SOI waveguide. [ABSTRACT FROM AUTHOR]

We present an optical model that was developed for the purpose of simulation and optimization of luminescent down-shifting layers based on phosphor particles. The model combines three-dimensional ray tracing with a novel effective scattering approach based on the Mie scattering theory. Verification of the model with experimental results shows that the model accurately takes various layer parameters into account, such as the layer thickness, the phosphor volume concentration, and the phosphor particle size distribution. Finally, using the verified model, we investigate the concept of luminescent down-shifting in organic solar cells and discuss the optimal layer parameters. Preliminary simulation results show that in the case of the studied solar cell, an improvement in the short-circuit current density of more than 6 % can be obtained. [ABSTRACT FROM AUTHOR]

We report on a two-dimensional nonlinear photonic quasicrystal (2DNPQC) constructed by the generalized dual-grid method. It can simultaneously phase match three nonlinear frequency conversions. Optical properties of the 2DNPQC are investigated and a set of red-yellow-green laser are realized. The wave propagating and temperature detuning characteristics were studied theoretically. The scheme has potential application in fields such as quantum optics. [ABSTRACT FROM AUTHOR]

White light LEDs are playing a more and more important role in display in various structures. Here, a new modeling algorithm is proposed for use in phosphor-converted white light-emitting diodes (pcW-LEDs); the algorithm can be used to accurately simulate color appearances, potentially enabling optical designers to remove yellowish/bluish spots in LED lighting. The proposed modeling method was applied to simulate a pcW-LED without an encapsulation lens, and subsequently, a pcW-LED with a hemispherical lens. Both simulations accurately predicted the blue and yellow light distribution. The model was further verified by applying a total internal reflector lens to the pcW-LED. In the midfield region, the blue and yellow light distribution exhibited large variations as the observation distance changed; this varying light pattern for both the blue and yellow lights can be accurately predicted using the proposed model. The developed optical model should facilitate designing a pcW-LED that features high-quality illumination and increased color uniformity. [ABSTRACT FROM AUTHOR]

A new scheme for a flexible modulation and bit rate independent, polarization-insensitive optical wavelength converter (WC) based on four-wave mixing in a highly nonlinear fiber is demonstrated and characterized for different modulation formats and data rates. Its robustness is demonstrated in a data transmission experiment in which the WC is incorporated at the mid-point of a transmission line based on installed fiber. In addition, an optical feedback system designed to prevent slow polarization drift of the pumps, and consequently, to ensure the long-term stability of the system is implemented and characterized. The WC is tested with the feedback system in place enabling turn-key operation. [ABSTRACT FROM PUBLISHER]

In the paper, an optical design for a standard light source is proposed and demonstrated to perform high stability, high angular CCT (correlated color temperature) uniformity, and adjustable light pattern from a Lambertian-like pattern to a narrow light pattern with a full-width at half-maximum (FWHM) angle of 60 °. The optical module contains a color-mixing cylinder, a diffuser, and an absorbed cylinder. The simulation well predicts the corresponding measurements and the angular CCT deviation can be kept a certain low level, which is much lower than a general phosphor converted white LED. In addition, we apply a pcW-LED of CREE XML as the light source to the optical module to show the general adoptability of the optical module. The measurement shows that the similar behavior, with adjustable light pattern from 120 ° to 60 °. In addition, the angular correlated color temperature deviation (ACCTD) is always kept an extremely low level. [ABSTRACT FROM PUBLISHER]

The AlGaAs material platform has been intensively used to develop nonlinear photonic devices on-a-chip, thanks to its superior nonlinear optical properties. We propose a new AlGaAs waveguide geometry, called half-core etched, which represents a compromise between two previously studied geometries, namely the nanowire and strip-loaded waveguides, combining their best qualities. We performed tunable four-wave mixing (FWM) experiments in all three of these geometries in the telecommunications C-band (wavelengths around 1550 nm), with a pulsed pump beam and a continuous-wave (CW) signal beam. The maximum FWM peak efficiencies achieved in the nanowire, strip-loaded and half-core geometries were about − 5 dB , − 8 dB and − 9 dB , respectively. These values are among the highest reported in AlGaAs waveguides. The signal-to-idler conversion ranges were also remarkable: 161 nm for the strip-loaded and half-core waveguides and 152 nm for the nanowire. Based on our findings, we conclude that the half-core geometry is an alternative approach to the nanowire geometry, which has been earlier deemed the most efficient geometry, to perform wavelength conversion in the spectral region above the half-bandgap. Moreover, we show that the half-core geometry exhibits fewer issues associated with multiphoton absorption than the nanowire geometry. [ABSTRACT FROM AUTHOR]

π-phase-shifted fiber Bragg gratings (πFBG) have been extensively explored by various research groups in the recent past as a high-resolution optical fiber sensor for both static and dynamic strain measurement applications. A phase-shifted FBG exhibits very sharp resonance in its spectral response which offers enhanced dynamic strain measurement capability in comparison to regular FBG sensors. External perturbation induced modulation in the centroid wavelength of the resonance is estimated from the wavelength-shift measurements. The interrogation system that measures the wavelength-shift represents a key element in terms of both cost and performance as it has to determine relatively small shifts in central wavelength of πFBG spectra. This article gives a review of the current state-of-the-art for πFBG sensor interrogation principles with a systematic and complete overview of the available experimental configurations and their working principles. A detailed description of the existing interrogation architectures is provided together with analysis in terms of measurement sensitivity, dynamic range and complexity of the different experimental configurations. The associated advantages and the limitations of different architecture are also touched upon. It is expected that πFBG sensors will be widely applied in practice in near future due to the availability of cost-effective interrogation and multiplexing techniques as well as its low-cost fabrication and high-resolution sensing capability. The present article can be used as a future guideline for differentiating the various interrogation principles of πFBG sensor to be utilized for small amplitude dynamic strain perturbation measurement. [ABSTRACT FROM AUTHOR]

• The proposed unconventional single pump configuration of WE-OPC makes the process more energy efficient. • Realization of WE-OPC has been done through DFG resulting in usage of only two Ti:PPLN waveguides instead of four. • Higher conversion efficiencies of 3.3 dB and 3.49 dB obtained for higher frequency band to lower frequency band and vice versa respectively. • Two identical Ti:PPLN waveguides with the same grating period used for HF to LF band conversion and vice versa. • Laser diode maintains pump power of 100 mW thereby avoiding photorefractive damage associated with Ti:PPLN crystals. An unconventional single pump configuration of Wavelength Exchanged Optical Phase Conjugation (WE-OPC) through Difference Frequency Generation (DFG) employing two identical Ti:PPLN waveguides having same grating period and a single pump source is theoretically analyzed and simulated resulting in higher conversion efficiency of OPC.WE-OPC has been found very effective in extenuating nonlinearity and inflating spectral efficiency in optical transmission systems. The proposed WE-OPC enabled WDM optical transmission system modeled as a wavelength converter has been simulated with 10 channels offering much higher conversion efficiencies of about 3.3 dB and 3.49 dB for higher frequency band to lower frequency band and vice versa respectively. [ABSTRACT FROM AUTHOR]

Tremendous scientific progress has been achieved through the development of nonlinear integrated photonics. Prominent examples are Kerr frequency comb generation in microresonators, and supercontinuum generation and frequency conversion in nonlinear photonic waveguides. A high conversion efficiency is enabling for applications of nonlinear optics, including such broad directions as high‐speed optical signal processing, metrology, and quantum communication and computation. In this work, a gallium‐arsenide‐on‐insulator (GaAs) platform for nonlinear photonics is demonstrated. GaAs has among the highest second‐ and third‐order nonlinear optical coefficients, and the use of a silica cladding results in waveguides with a large refractive index contrast and low propagation loss for expanded designs of nonlinear processes. By harnessing these properties and developing nanofabrication with GaAs, a record normalized second‐harmonic efficiency of 13 000% W−1 cm−2 at a fundamental wavelength of 2 µm is reported. This work paves the way for high performance nonlinear photonic integrated circuits, which not only can transition advanced functionalities outside the lab through fundamentally reduced power consumption and footprint, but also enables future optical sources and detectors. A gallium‐arsenide‐on‐insulator platform for integrated nonlinear photonics is demonstrated on silicon substrate. Waveguides on this platform have high nonlinear coefficients, large index contrasts, and low propagation losses. By harnessing those properties, a second‐harmonic generation with a record‐normalized efficiency of 13 000% W−1 cm−2 is achieved. This work paves the way to high performance nonlinear photonic integrated circuits. [ABSTRACT FROM AUTHOR]