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Phase-matched wavelength conversion is achieved in difference frequency generation (DFG) in a structure of gallium arsenide (GaAs) with periodic arrays of nanoholes. Linear properties (refractive indices) of the structure are determined from the S-parameters of the structure. Finite difference time domain (FDTD) simulation is used to calculate the S-parameters. The longest wavelength achieved is 16.2229 μm and the shortest is 3.2961 μm. The results of the FDTD simulation are compared with results obtained from the effective medium theory by using the Maxwell Garnett model. The comparison shows excellent agreement.

Lithium niobate on insulator (LNOI), by taking advantage of versatile properties of lithium niobate (LN) and a large refractive index contrast, provides an ideal on-chip platform for studying a broad range of optical effects as well as developing various superior photonic devices. It is a game-changer technology for traditional LN-based applications. Especially, with recent advances in the fabrication of high-quality micro-/nano-structures and devices on the LNOI platform, LN-based integrated photonics has been propelled to new heights. In this review, we summarize the latest research advances in lithium niobate thin film (LNTF), with a special focus on nonlinear wave mixing and their photonics applications. Different types of second- and third-order nonlinear processes in LNOI micro- and nano-structures are reviewed, including nonlinear frequency conversion, frequency comb generation and supercontinuum generation. Furthermore, perspectives for photonic integrated circuits (PICs) on the LNOI platform in nonlinear optics regime are predicted.

The lack of anisotropic properties in GaAs prevents the use of birefringence as a phase matching technique in three-wave mixing with GaAs as a nonlinear medium. When metallic nanowires are embedded in GaAs, the composite structure is characterized as a metamaterial with anisotropic properties, if the separation distance between the nanowires is less than the wavelengths of the mixed waves. The effective permittivity is used to investigate this metamaterial structure with its anisotropic properties theoretically in terms of phase matching for difference frequency generation. The resultant difference frequencies, which are in the mid-infrared region, are broadly tunable from 2.8 to 11 μm. This tuning is performed by varying the pump and the signal wavelengths in the range between 1 to 2 μm. The losses of the structure due to absorption are included using the transfer matrix method.

Phase-matched wavelength conversion is achieved in difference frequency generation (DFG) in a structure of gallium arsenide (GaAs) with periodic arrays of nanoholes. Linear properties (refractive indices) of the structure are determined from the S-parameters of the structure. Finite difference time domain (FDTD) simulation is used to calculate the S-parameters. The longest wavelength achieved is 16.2229 μm and the shortest is 3.2961 μm. The results of the FDTD simulation are compared with results obtained from the effective medium theory by using the Maxwell Garnett model. The comparison shows excellent agreement. [ABSTRACT FROM AUTHOR]

A tunable and reconfigurable optical aggregation system is experimentally demonstrated. Optical Nyquist pulses are generated on multiple channels using a microresonator-based Kerr optical frequency comb and insertion of uniform lines by an intensity modulator. Data are modulated on optically generated Nyquist pulses and aggregated through nonlinear wave mixing in a periodically poled lithium niobate (PPLN) waveguide. Two quadrature-phase-shift-keying (QPSK) channels are aggregated to a single 16-quadrature amplitude modulation (16-QAM) channel of Nyquist pulses. To demonstrate the system tunability, we perform aggregation over different baud rates and different modulation formats. The reconfigurability of the system is demonstrated by aggregating two binary-phase-shift-keying (BPSK) channels into a QPSK or a 2-level amplitude-shift keying and a 2-level phase-shift keying (2-ASK/2-PSK) channel by tuning the relative phase and amplitude of the inputs. Furthermore, three BPSK channels are aggregated into one 4-ASK/2-PSK channel. The quality of the aggregated channel is investigated using two different approaches for wave mixing in the PPLN waveguide. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate tunable de-aggregation of two data carrying optical channels using nonlinear wave mixing. For each channel, the signal and its conjugate are coherently added and subtracted in order to map the constellation points onto real and imaginary axes, respectively. Each of two 10 and 15 Gbaud optical channels with a format of 16-quadrature amplitude modulation (16-QAM) are de-aggregated into two 4-level pulse amplitude modulation (4-PAM) signals. We use the same technique to de-aggregate quadrature phase shift keying (QPSK) signals into two binary phase shift keying (BPSK) signals at baud rates of 10 and 15 Gbaud for both channels. System performance is evaluated in terms of the optical signal-to-noise ratio (OSNR), and penalty of ∼ 0.7 dB is observed at bit error rate (BER) of 10−3. [ABSTRACT FROM AUTHOR]

We report efficient frequency downconversion of a continuous-wave low-power Raman laser using intracavity difference frequency mixing in a periodically poled lithium niobate (PPLN)-adopted optical parametric oscillator (OPO). The Raman laser was obtained using a 1060-nm fiber laser and 137-m passive fiber. Its central wavelength was fixed at 1111 nm with the power ranging from 320 mW to 5.984 W. The 1060- and 1111-nm pump beams were incident into the OPO at the same time. The high-power 1060-nm pump beam built parametric oscillation first, and the difference frequency generation (DFG) occurred between the low-power Raman laser and intracavity signal laser. The PPLN temperature was properly controlled at 45°C to ensure both the OPO and DFG processes synchronously satisfy phase matching conditions. Benefiting from intracavity high signal power, the Raman laser was successfully converted to the 3560-nm midinfrared radiation under every investigated pump power level. The maximum 3560-nm idler power reached 1.026 W, indicating a 17.4% pump-to-idler slope efficiency and about 15% optical-to-optical conversion efficiency. The comparative experiments also verified that the phase matching conditions were satisfied maximally at 45°C. [ABSTRACT FROM AUTHOR]

Highlights • The CPMI was built to measure the optimal phase-matching angle of KDP crystal. • The measurement accuracy of CPMI is rather high which is 10 μrad. • Working posture adjustment system and temperature control system are applied to CPMI. Abstract An instrument has been developed to measure the optimal phase-matching angle of large-aperture potassium dihydrogen phosphate (KDP) crystal. KDP crystal in the frequency converter is applied to generate a third harmonic generation, which is important to achieve inertial confinement fusion (ICF). To achieve high harmonic conversion efficiency, the tuning angle of KDP crystal should be optimal when the frequency converter is working online in ICF facilities. The optimal tuning angle of KDP crystal must be measured off-line before KDP crystal is mounted in the facility. The Crystal Phase-matching angle Metrology Instrument (CPMI) can measure the optimal phase-matching angle and harmonic conversion efficiency of KDP crystal off-line. The CPMI is housed in ISO 5 clean room and several methods are taken to keep the temperature stable. The automatic alignment system is built in the CPMI which makes the measurement convenient and fast. The working posture adjustment system is applied to measure the optimal phase-matching angle when KDP crystal is in the working posture. The integration control system is assisted to measure the phase-matching angle automatically, which can increase the work efficiency immensely. Some experiments are done to test the measuring accuracy. The experiments indicate that the measuring error does not exceed 10 μrad and the repeated accuracy does not exceed 3 μrad. The CPMI can replace on-line measuring of the optimal phase-matching angle, which is economical and time-saving. [ABSTRACT FROM AUTHOR]

Abstract This paper describes the use of a wave mixing technique to monitor thermal aging of adhesive joints. This newly developed technique measures the acoustic nonlinearity parameter of the adhesive in the joint. One of the significant features of this technique is that it requires only one-side access to the adhesive joint being measured, which significantly increases the technique's utility in field applications. To demonstrate the effectiveness of the new technique, measurements are conducted on adhesively joined samples that are thermally aged under different heating conditions, i.e., different temperature profiles and aging times. The results show that the measured acoustic nonlinearity parameter of the adhesive is very sensitive to thermal aging. On the other hand, linear reflection from the adhesive layer remains almost a constant among all the aging conditions investigated in this study. It is therefore concluded that the acoustic nonlinearity parameter is a much more sensitive measure of thermal aging of adhesive joints. [ABSTRACT FROM AUTHOR]

Abstract We analyze, through numerical simulations, a method for generating unidirectional flux in colloidal systems using non-degenerate two-wave mixing. The approach uses a bidirectional PZT modulation and a laser grating amplitude modulation to suppress the reversal of the grating velocity with each cycle of the PZT. The dependence of the particle flux on modulation frequency is determined through numerical solution of the differential equations and the suppression of sedimentation in an extended colloidal system is analyzed. [ABSTRACT FROM AUTHOR]

This tutorial highlights challenges and opportunities in achieving efficient flexible optical networks. Optical signal processing may potentially increase network flexibility because of its functions’ transparency, tunability, and reconfigurability. We review recent advances in high-speed optical signal processing techniques that might enable flexible networks. Various optical approaches that enable key functions are discussed, including format conversion, increases in spectral efficiency, and phase-sensitive operations. We also discuss the potential utilization of basic enabling technologies, such as optical frequency combs and optical nonlinear devices. [ABSTRACT FROM AUTHOR]

We analyze and simulate numerically a bidirectional intracavity field of a ring laser with a χ (2) nonlinear crystal for sum frequency generation placed within the cavity. Injecting in the nonlinear crystal from one side a beam with a large CW component and a small-amplitude modulation, and from the other side a time-continuous bias beam, we demonstrate numerically that it is possible to reproduce the time-varying portion of the injected light in the circulating modes. This effectively subtracts the CW pedestal from the signal beam. At the same time, the wavelength of the detected light is converted to one that may be more suitable for efficient photo-detection. Our analysis includes rate equations that model two external counter-propagating beams injected in the ring laser cavity and mixed in the nonlinear crystal with the ring laser modes with which they co-propagate. [ABSTRACT FROM AUTHOR]

We experimentally study non-degenerate two-wave mixing with a harmonically varying frequency shift in dark ruby and colloidal media and compare the results to theoretical models for the detailed process in these two very different physical systems. Excellent agreement is found for both the radiative decay in ruby as well as the particle diffusion driven relaxation of nano-particle colloidal media. The results show that there is a universal asymmetry in the oscillating energy exchange waveform which arises from symmetry-broken grating dynamics of the in-phase and out-of-phase gratings. [ABSTRACT FROM AUTHOR]

The achievement of wideband high-gain optical parametric amplification has not been shown in micrometer-scale cavities. In this paper we have computationally investigated the optical parametric amplification process in a few micrometer-long dispersive microresonator. By performing a gain medium resonance frequency dependent analysis of optical parametric amplification, we have found that it is possible to achieve a wideband high-gain optical amplification in a dispersive microresonator. In order to account for the effects of dispersion (modeled by the polarization damping coefficient) and the resonance frequency of the gain medium on optical parametric amplification, we have solved the wave equation in parallel with the nonlinear equation of electron cloud motion, using the finite difference time domain method. Then we have determined the resonance frequency values that yield an enhanced or a resonant case of optical parametric amplification, via gain factor optimization. It was observed that if the microresonator is more dispersive (has a lower polarization damping coefficient), then there are more resonance frequencies that yield an optical gain resonance. At these gain resonances, a very wideband, high-gain optical amplification seems possible in the micron scale, which, to our knowledge, has not been previously reported in the context of nonlinear wave mixing theory.

Adaptive holographic interferometry is a promising method for high-sensitivity phase-modulation measurements in the presence of slow perturbations from the environment. This technique is based on the use of a nonlinear recombining medium. We report the realization of an adaptive holographic interferometer relying on an optically addressed liquid crystal spatial light modulator operating at 1.55 μm. The beam-coupling process that occurs in a GaAs-liquid crystal device, allows obtaining a phase-modulation sensitivity of 200 μrad/sqrt (Hz) at 1 kHz. The interferometer behaves as an optical high-pass filter, with a cutoff frequency of approximately 10 Hz, thus, filtering slow-phase disturbances, such as due to temperature variations or low-frequency fluctuations, and keeping the detection linear without the need of heterodyne or active stabilization. Moreover, owing to the basic principle of holography, this technique can be used with complex wave fronts such as the speckled field reflected by a highly scattering surface or the optical field at the output of a multimode optical fiber. We demonstrate both theoretically and experimentally that using a multimode optical fiber as a sensing element, rather than a single-mode fiber, allows improving the interferometer phase sensitivity. Finally, we present a phase-optical time domain reflectometry (OTDR) optical fiber sensor using the adaptive holographic interferometer. [ABSTRACT FROM AUTHOR]

Numerical simulations demonstrate that mid-infrared pulses are arbitrarily shaped during the differential frequency mixing of two femtosecond near-infrared pulses propagating in an engineered quasi-periodic poled medium with optical nonlinearity and group velocity dispersion. Shaped pulses, including linearly chirped pulses and pulse trains, are generated with high conversion efficiencies. [ABSTRACT FROM AUTHOR]

We demonstrate a reconfigurable high-speed optical tapped delay line (TDL), enabling several fundamental real-time signal processing functions such as correlation (for pattern search) and equalization. Weighted taps are created and added using optical multicasting and multiplexing schemes that utilize the nonlinear wave mixings in the periodically poled lithium niobate (PPLN) waveguides. Tunable tap delays are realized using the conversion-dispersion technique. In the demonstrated TDL, the amplitude and phase of tap coefficients can be varied, enabling signal processing on amplitude- and phase-encoded optical signals. We experimentally demonstrate the tunability of the TDL in time, amplitude, and phase. We analyze the TDL's theory of operation and present experimental results on reconfigurable pattern search (correlation) on on-off-keyed and phase-shift-keyed signals at data rates of up to 80 Gb/s, as well as equalization for chromatic dispersion.

Adaptive holographic interferometry is a promising method for high-sensitivity phase modulation measurements in the presence of slow perturbations from the environment. This technique is based on the use of a nonlinear recombining medium. Here, we report the use of an adaptive holographic interferometer based on an optically addressed spatial light modulator. Owing to the physical mechanisms involved, the interferometer adapts to slow phase variations within a range of 5–10 Hz. Moreover, owing to the basic principle of holography, this technique can be used with complex wave fronts such as the speckled field reflected by a highly scattering surface or the optical field at the output of a multimode optical fiber. We demonstrate both theoretically and experimentally, that using a multimode optical fiber as sensing element, rather than a single mode fiber, allows improving the interferometer phase sensitivity. Finally, we present a phase-OTDR optical fiber sensor using the adaptive holographic interferometer. [ABSTRACT FROM PUBLISHER]

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 experimentally demonstrated two enabling architectures for remotely controlled optical quadrature-phase-shift-keying (QPSK) correlators based on both linear and nonlinear elements. The correlator site was located far from the transmitter site and had no access to the local optical power. In the first demonstration, a remote correlator based on a cascade of Mach–Zehnder interferometers (MZIs) was phase-controlled through optical power sent from the transmitter via an optical fiber link. The issue of power loss because of fiber nonlinearities was further addressed by monitoring and managing the backscattered power. In this manner, the power delivered through the link was boosted by ∼ 13 dB. Another ∼ 6 dB gain in the delivered power was obtained by adding a second source of light power. The correlator was shown to be able to identify different target patterns within incoming QPSK signals at different baud rates from 10 to 50 Gbaud. In the second architecture, we experimentally demonstrated a tunable optical correlator for a 10/15-Gbaud QPSK data signal using temperature-controlled nonlinear wave mixing at a remote node. A high-power pump was phase-modulated to overcome the link backscattering effect and was sent along with the signal copies to a remote correlator node through an optical fiber link. The waves generated at the output of the correlator were sent back to the transmitter for the monitoring of the operation. We showed a power boost of more than 3 dB for the correlated signal at a temperature drift of 2 °C. Using remote control and monitoring, improved constellation diagrams with lower error vector magnitudes (EVMs) for a temperature drift range of < 2 °C were 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]

Homodyne detection is of significant interest in optical communications because it detects both the amplitude and phase information of the incoming data channel. One of the challenges in implementing a homodyne receiver is to recover the phase and frequency of the incoming data and to lock these to the local oscillator. We proposed and demonstrated a tunable homodyne detection scheme using two continuous wave pumps to automatically lock a “local” pump laser to an incoming 20-to-40-Gbaud QPSK data signal. Open eyes are obtained for both in-phase and quadrature components of the signal after ∼200-km transmission over single mode fiber (SMF-28) and dispersion compensation fiber without any carrier recovery. The BER performance of the proposed homodyne detection scheme is also performed with and without transmission. [ABSTRACT FROM PUBLISHER]

A novel sensing technique is developed that makes use of evanescent terahertz (THz) waves without directly detecting the THz wave. The technique is demonstrated for measuring changes in the electric field of near-infrared light, transcribed from changes in the electric field of THz waves. The method will enable sensing of various materials in the THz-frequency region, to provide knowledge about chemical reactions that require real-time tracking. [ABSTRACT FROM AUTHOR]

Resonant metasurfaces provide a unique platform for enhancing multiwave nonlinear interactions. However, the difficulties over mode matching and material transparency place significant challenges in the enhancement of these multiwave processes. Here we demonstrate efficient nonlinear sum-frequency generation (SFG) in multiresonant GaP metasurfaces based on guided-wave bound-state in the continuum resonances. The excitation of the metasurface by two near-infrared input beams generates strong SFG in the visible spectrum with a conversion efficiency of 2.5 × 10 -4 W -1 , 2 orders of magnitude higher than the one reported in Mie-type resonant metasurfaces. In addition, we demonstrate the nontrivial polarization dependence on the SFG process. In contrast to harmonic generation, the SFG process is enhanced when using nonparallel polarized input-beams. Importantly, by varying the input pump beam polarization it is possible to direct the SFG emission to different diffraction orders, thereby opening up new opportunities for nonlinear light sources and infrared to visible light conversion.

A theoretical and experimental study of phase-controlled beam combining based on noncollinear frequency doubling is described. Optimized second-harmonic power and improved output intensity distribution are simultaneously achieved by a closed-loop phase control system via an adaptive algorithm. It is shown that the profile of the combined beam at the second-harmonic with 12 noncollinear frequency inputs can be shaped to a near-fundamental Gaussian mode, with a power enhancement of more than two orders of magnitude, compared to the second-harmonic signal generated with a single beam. [ABSTRACT FROM PUBLISHER]

Periodic anharmonic modulation of output intensity is studied for semilinear coherent oscillator with photorefractive crystal that possesses two types of movable charge carriers. The pulse amplitude and modulation frequency are shown to depend considerably on grating spacing of photorefractive grating. We calculate these dependences within the model proposed earlier [A. Shumelyuk, A. Hryhoraschuk, S. Odoulov, Phys Rev. A, 72, 023819 (2005)] and show satisfactory agreement with the experimental data. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate tunable modulation format conversion of quadrature phase shift keying (QPSK) to four-level pulse amplitude modulation (PAM4) using nonlinear wave mixing in periodically-poled Lithium-Niobate (PPLN) waveguides. The conversion operation is accomplished by: (a) rotating the data constellation by applying a phase offset, and (b) offsetting the data constellation in the radial direction by adding a constant bias optical power. In this manner, the constellation data points can be tailored to have different amplitude levels, thus realizing the PAM4 format. In a tunable fashion, we convert 20- and 30-Gbit/s QPSK channels to PAM4, and open eye diagrams and low bit-error-rates (BER) are obtained at the receiver. We investigate the impact of phase rotation on the eye diagram of the received signal, and we determine that a phase rotation of ∼ 71°provides substantially good performance. Wavelength tunability of the output PAM4 is demonstrated by tuning the wavelength of the pump. In addition, open eye is also obtained when a high phase noise laser is used for modulating QPSK signal. [ABSTRACT FROM AUTHOR]

The achievement of wideband high-gain optical parametric amplification has not been shown in micrometer-scale cavities. In this paper we have computationally investigated the optical parametric amplification process in a few micrometer-long dispersive microresonator. By performing a gain medium resonance frequency dependent analysis of optical parametric amplification, we have found that it is possible to achieve a wideband high-gain optical amplification in a dispersive microresonator. In order to account for the effects of dispersion (modeled by the polarization damping coefficient) and the resonance frequency of the gain medium on optical parametric amplification, we have solved the wave equation in parallel with the nonlinear equation of electron cloud motion, using the finite difference time domain method. Then we have determined the resonance frequency values that yield an enhanced or a resonant case of optical parametric amplification, via gain factor optimization. It was observed that if the microresonator is more dispersive (has a lower polarization damping coefficient), then there are more resonance frequencies that yield an optical gain resonance. At these gain resonances, a very wideband, high-gain optical amplification seems possible in the micron scale, which, to our knowledge, has not been previously reported in the context of nonlinear wave mixing theory. [ABSTRACT FROM AUTHOR]