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Acousto-optic modulation (AOM) is regarded as an effective way to link multi-physical fields on-chip. We propose an on-chip AOM scheme based on the thin-film lithium niobate (TFLN) platform working at the higher-order TE1 mode, rather than the commonly used fundamental TE0 mode. Multi-physical field coupling analyses were carried out to obtain the refractive index change of the optical waveguide (>6.5×10−10 for a single phonon) induced by the enhanced acousto-optic interaction between the acoustic resonator mode and the multimode optical waveguide. By using a Mach-Zehnder interferometer (MZI) structure, the refractive index change is utilized to modulate the output spectrum of the MZI, thus achieving the AOM function. In the proposed AOM scheme, efficient mode conversion between the TE0 and TE1 mode is required in order to ensure that the AOM works at the higher-order TE1 mode in the MZI structure. Our results show that the half-wave-voltage-length product (VπL) is 0 mode (e.g., VπL > 0.04 V·cm for AOM, VπL > 1 V·cm for EOM). Finally, the proposed AOM has lower loss when compared with EOM because the electrode of the AOM can be placed far from the optical waveguide.

We demonstrate a flat broadband time-stretched swept source based on extra-cavity spectral shaping. By adjusting the polarization-dependent gain profile and driving current of the booster optical amplifier (BOA), extra-cavity spectral shaping is optimized to generate output with a 1-dB bandwidth of ∼100 nm, 3-dB bandwidth of ∼140 nm and output power of ∼21.4 mW. The short-term and long-term stabilities are characterized. The average cross correlation of 183,485 round trips is 0.9997 with a standard deviation of 2×10−5, indicating high single-shot spectral similarity and high coherence. The noise floor of relative spectral energy jitter is −141.7 dB/Hz, indicating a high short-term spectral energy stability. The proposed highly stable flat broadband time-stretched swept source is applied to an optical coherence tomography (OCT) system. The axial resolution is 10.8 µm. The proposed swept source can serve as excellent light sources in ultra-fast coherent detection systems for high precision sensing and imaging.

We propose a practical scheme to demonstrate the combination and subsequent self-similar compression of two pulses with the same or different central wavelengths while propagating through a nonlinear fiber with exponentially decreasing dispersion. To initiate these processes, two raised cosine pulses with the same or different wavelengths is modulated using a phase modulator to acquire the same chirp at the input of the fiber. While propagating through the nonlinear fiber, these chirped pulses first coalesce into a single pulse and during further propagation get compressed into a single ultrashort high-power pulse. The output pulse possesses a large compression factor, high proportion of energy and peak power compared to a single input pulse. We also report the combination and compression of five raised cosine pulses with different wavelengths to achieve an appreciable compression effect, indicating that this system works well even with a small number of input pulses. The proposed scheme provides a simple way to generate high power ultrashort pulse with high energy and good quality in a short length of fiber.

Microcavity based optical frequency combs are commonly generated with a tunable continuous wave laser pump making it unsuitable for chip-level integration. We proposed a new dual-comb generation scheme in coupled nonlinear microcavities with a single frequency pump.

Kerr soliton frequency comb generation in nonlinear microcavities with compact configurations are promising on-chip sources. Current Kerr comb generation by using a single microcavity with a tunable CW pump laser or high-power femtosecond pulse pump are difficult to be integrated on chip. In this paper, we propose an on-chip soliton comb generation scheme by tuning the coupling coefficient of two coupled microcavities instead of tuning the wavelength of the cw pump laser or using a pulsed pump laser in a single microcavity. The two microcavities are assumed to be identical. We showed by numerical simulation that Kerr comb generation is possible in both the blue and red detuned regions of the main microcavity in the coupled cavity system. We further found that the range and boundary of the soliton generation region of the couple microcavities depend on the coupling coefficient between the coupled cavities. To ensure that the modes being coupled have identical optical paths, we designed a Sagnac loop structure which couples the clockwise and counterclockwise modes in a single microcavity and demonstrated Kerr comb generation in both the blue and red detuned regions by tuning the coupling coefficient. The proposed Kerr comb generation scheme can be utilized for chip-scale integrated soliton comb sources, which will contribute to the development of on-chip applications.

For most photonics devices and systems, loss is desperately averted, since it will increase the power consumption and degrade the performance. However, in some non-Hermitian systems, loss can induce a modal gain when the parity-time symmetry is broken, which offers a new way to manipulate the lasing of active cavities. Here we experimentally observe the counterintuitive phenomenon in a single laser cavity assisted by the polarization-dependent loss. A parity–time symmetric system is constituted by the two orthogonally polarized photonic loops in a single laser cavity, which can guarantee the consistency of two coupling loops. The measured output power of the cavity depends on the cross-polarization loss, which reveals virtually opposite relationships before and after the critical point. It provides a novel, to the best of our knowledge, understanding of polarization loss and shows great potential for lasing manipulation in a single cavity with polarization control.

We present optical frequency comb generation in normal dispersion microresonators with blue-detuned pump. A new bistability regime in the blue-detuned region is theoretically analyzed and numerically simulated for the first time.

We demonstrate a microheater with the metal heater placed very close to the waveguide based on broken PT symmetry. It can achieve a high-speed modulation, simultaneously without introducing a nonnegligible loss.

We demonstrate an on-chip photonic convolutional accelerator, which can perform configurable optical convolution operations to achieve specific image processing. It indicates great potential for on-chip image processing in AI hardware acceleration.

Optical frequency combs based on microcavities with Kerr nonlinearity are promising frequency comb sources for many applications. A typical Kerr soliton comb is generated in a nonlinear microcavity with anomalous dispersion pumped by a red-detuned continuous-wave laser. Modulation instability (MI) is the basis for Kerr soliton comb generation. In a microcavity with nearly zero dispersion, the first pair of MI modes can grow only with a red-detuned pump laser. In this paper, we find that MI generation is possible with blue-detuned pump lasers for coupled microcavities with nearly zero dispersion. We study a microcavity with Kerr nonlinearity coupled with an auxiliary microcavity, which has negligible nonlinearity. By theoretical analysis, we show that the coupled microcavities can create a region supporting MI generation in the blue-detuned side of the resonances of the nonlinear main cavity, whereas there is no blue-detuned MI generation in a single nonlinear microcavity. The properties of the blue-detuned MI region are determined by the coupling coefficient between the two microcavities, the loss of the auxiliary cavity, and the detuning between the modes of the two microcavities. The size and location of the blue-detuned MI region can be varied by tuning these parameters. Numerical simulations of MI generation based on the blue-detuned MI region in the coupled microcavities are presented. By considering more modes, MI comb generations with coupled microcavities having anomalous and normal dispersion are also numerically simulated.

We present deterministic excitation of single soliton in LiNbO3 microcavities by a trigger approach with either weak or strong fundamental-second-harmonic mode coupling.

In this paper, we present a miniature fiber-optic Fabry–Perot interferometric pressure sensor based on an in situ printed fiber-top air cavity. With an in-house optical 3D μ-printing setup, a suspended SU-8 diaphragm with light scatter is directly printed on the end face of standard optical fiber to form a sealed Fabry–Perot cavity. The fabricated Fabry–Perot microinterferometer shows a linear response to the change of pressure with a sensitivity of 2.93 nm/MPa in the range of 0 ∼ 700 kPa. The response of the sensor to the change of temperature in the range from 30 °C to 65 °C is measured to be ∼38 pm/°C. Such an ultra-small fiber-optic pressure sensor has remote monitoring capability and is promising for a great number of measurement and testing applications ranging from miniature manometers to bioprobes.

Nonlinear fiber-optic transmissions based on Nonlinear Fourier Transform (NFT) is an emerging area in optical communications with more and more experiments demonstrating their potentials. We review recent developments in signal processing techniques for NFT systems.

Polarization-insensitive modulation, i.e., overcoming the limit of conventional modulators operating under only a single-polarization state, is desirable for high-capacity on-chip optical interconnects. Here, we propose a hybrid graphene-silicon-based polarization-insensitive electro-absorption modulator (EAM) with high-modulation efficiency and ultra-broad bandwidth. The hybrid graphene-silicon waveguide is formed by leveraging multi-deposited and multi-transferred methods to enable light interaction with graphene layers in its intense field distribution region instead of the commonly used weak cladding region, thus resulting in enhanced light–graphene interaction. By optimizing the dimensions of all hybrid graphene-silicon waveguide layers, polarization-insensitive modulation is achieved with a modulation efficiency (ME) of ~1.11 dB/µm for both polarizations (ME discrepancy &lt, 0.006 dB/µm), which outperforms that of previous reports. Based on this excellent modulation performance, we designed a hybrid graphene-silicon-based EAM with a length of only 20 µm. The modulation depth (MD) and insertion loss obtained were higher than 22 dB and lower than 0.23 dB at 1.55 µm, respectively, for both polarizations. Meanwhile, its allowable bandwidth can exceed 300 nm by keeping MD more than 20 dB and MD discrepancy less than 2 dB, simultaneously, and its electrical properties were also analyzed. Therefore, the proposed device can be applied in on-chip optical interconnects.

We numerically demonstrate a mechanism to get stable pulse train from discrete Fourier domain mode locked laser. The FSR of comb filter and linewidth of tunable bandpass filter should be optimized to obtain stable output.

We deterministically excited thermally self-stabilized single dissipative Kerr soliton in a microresonator using an energetic trigger pulse. The soliton automatically balances the thermal perturbation and is stabilized without any active thermal compensation.

We present an inter-ring detuning control scheme to generate spatiotemporal soliton in symmetric serially coupled dual micro-ring resonators. By using our proposed model, we numerical demonstrate tunable different orders solitons generation form identical initial state.

We proposed a normalized model to describe the general behaviors of polarization pulling in fiber optical parametric amplifiers (FOPAs). We adopted a modified interpolation function to analyze the simulation results and found that FOPAs using fibers with moderate PMD coefficient can achieve strong polarization pulling with relatively small gain.

In this paper, we demonstrated experimentally the intermodal four-wave mixing effect by launching femtosecond pulses centered at 1550 nm into deeply normal dispersion region in the fundamental guided-mode of an air-silica photonic crystal fiber with two zero dispersion wavelengths. When intermodal phase-matching condition is satisfied, the energy of the pump waves at 1550 nm in the fundamental guided-mode is converted to the anti-Stokes waves around 1258 nm and Stokes waves around 2018 nm both in the second-order guided-mode. When femtosecond pulses at input average power P av of 90 mW are propagated inside 22-cm-long photonic crystal fiber, the conversion efficiencies η as and η s of the anti-Stokes and Stokes waves generated are 8.5% and 6.8%, respectively. We also observed that the influences of the fiber bending and walk-off effect between the fundamental and second-order guided-modes on intermodal four-wave mixing-based frequency conversion process are very small.

We numerically study parabolic similariton generation in tapered hydrogenated amorphous silicon photonic wires. Simulation results show that initial Gaussian pulses can evolve into parabolic similaritons with the linear chirp at 1550 and 2150 nm, respectively.

Communications for nonlinear optical fiber channels based on Nonlinear Fourier Transform(NFT) has gained attraction as a new communication strategy for nonlinear optical communications. We review recent developments and discuss key challenges in this area.

We experimentally generate second-harmonics within deep-ultraviolet wavelength range of 334.5 to 306 nm. We combine four-wave mixing and surface nonlinearity polarization by coupling femtosecond pump pulses at ∼800 nm into an air-silica photonic crystal fiber.

We investigate broadband spectral compression assisted by soliton self-frequency shift in a proposed chalcogenide strip waveguide. Simulation results show that a compression ratio of 7.2 and a wavelength shift of 190 nm can be achieved.

Microwave signal generation using sideband injection locking in a Fabry-Perot laser diode is studied numerically. The frequency tuning range in frequency doubling and maximum RF output power in frequency doubling, tripling, and quadrupling is compared.

We have numerically studied two beam injection locking in an Fabry-Perot laser diode. We show that the injection locking properties of the first beam depends whether the second beam is injected on the red or blue side of the cavity mode of the Fabry-Perot laser diode.

Fourier domain mode locked (FDML) fiber lasers enable megahertz wavelength sweeping rate but suffer from the short coherent length. Discretization of the swept spectrum by a comb filter was demonstrated effective to enhance the coherent length. In this paper, we propose a novel discretization method of the FDML signal with an intracavity intensity modulator. We propose and successfully demonstrate a time and Fourier domain jointly mode locked fiber laser with a Fabry-Perot comb filter and an intensity modulator in the cavity. A 50 GHz free spectral range comb filter in the Fourier domain mode locked fiber swept laser slices the spectrum into a series of comb lines and chops the swept signal into short pulses in time domain. The temporal signal is detected by a photodetector to generate a series of ultrashort pulses to drive the intensity modulator to further polish the intracavity pulses. We experimentally realized the proposed time and Fourier domain jointly mode locked fiber laser. Discrete wavelength swept laser output with a wavelength spacing of ~0.4 nm in a 41 nm sweeping range has been achieved.

We correct the value of coefficient Γ presented in Opt. Express23, 32747 (2015)10.1364/OE.23.032747, which describes the relationship between the mean output degree of polarization and the average gain of fiber optical parametric amplifiers.

In this paper, we experimentally investigate high-order modulation over a single discrete eigenvalue under the nonlinear Fourier transform (NFT) framework and exploit all degrees of freedom for encoding information. For a fixed eigenvalue, we compare different 4 bit/symbol modulation formats on the spectral amplitude and show that a 2-ring 16-APSK constellation achieves optimal performance. We then study joint spectral phase, spectral magnitude and eigenvalue modulation and found that while modulation on the real part of the eigenvalue induces pulse timing drift and leads to neighboring pulse interactions and nonlinear inter-symbol interference (ISI), it is more bandwidth efficient than modulation on the imaginary part of the eigenvalue in practical settings. We propose a spectral amplitude scaling method to mitigate such nonlinear ISI and demonstrate a record 4 GBaud 16-APSK on the spectral amplitude plus 2-bit eigenvalue modulation (total 6 bit/symbol at 24 Gb/s) transmission over 1000 km.

This paper reports a flexible piezoresistive shear and normal force sensor based on eutectic gallium–indium (EGaIn) with fabrication and testing results, which includes further study on the hysteresis analysis in the normal force direction. By using EGaIn as a gauge material, it can detect force on a flexible and stretchable substrate without breaking the gauge wires. However, the liquid-metal gauge wire needs to be packaged and protected in an elastomeric substrate, which creates hysteresis on the sensed resistance with respect to the change of applied force. This paper shows measurement results in static force and also under different speeds of loading force cycles. The relationship between the applied normal force and hysteresis of signal was observed, mainly owing to larger deformation and slower recovering time of the elastomeric substrate that defines the shape of the liquid-metal gauge wire for resistance measurement.

We proposed a theoretical model to investigate the polarization pulling effect in bi-directionally pumped degenerate Raman assisted fiber optical parameter amplifiers (RA-FOPAs) using randomly birefringent fibers. The contributions of chromatic dispersion, polarization mode dispersion (PMD), Raman gain, and nonlinear effects to the phase matching in RA-FOPAs are investigated. We characterize four different states of polarization pulling in RA-FOPAs. We found that broadband polarization attraction can be obtained in the optimum phase-matching state of the bi-directionally pumped RA-FOPAs when the parametric pump power is chosen to avoid deep saturation of the Raman gain.

The demonstration of a 253-cm-long lanthanum-codoped Bi/sub 2/O/sub 3/-based erbium-doped fiber which provides gain of greater than 20 dB and noise figure less than 6.7 dB to 142 dense wavelength-division-multiplexing channels simultaneously over an extended wavelength range of 58 nm from 1554 to 1612 nm is reported. The 3-dB (gain of 17-20 dB) bandwidth of the erbium-doped fiber amplifier is 54 nm when it is pumped with 350 mW of 1480-nm light. The power conversion efficiency of the fiber is about 54%.