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Nonlinear propagation in periodic media has been studied for decades, yielding demonstrations of numerous phenomena including strong temporal compression and slow light generation. Gap solitons, that propagate at frequencies inside the stopband, have been observed in optical fibres but have been elusive in photonic chips. In this manuscript, we investigate nonlinear pulse propagation in a chip-based nonlinear Bragg grating at frequencies inside the stopband and observe clear, unequivocal signatures of gap soliton propagation, including slow light, intensity-dependent transmission, intensity-dependent temporal delay and gap soliton compression. Our experiments which are performed in an on-chip ultra-silicon-rich nitride (USRN) Bragg grating with picosecond time scales, reveal slow light group velocity reduction to 35%–40% of the speed of light in vacuum, change in the temporal delay of 7 ps at low peak powers between 15.7 W–36.6 W, which is accompanied by up to 2.7× temporal compression of input pulses. Theoretical calculations using the nonlinear coupled mode equations confirm the observations of intensity-dependent temporal delay. Of fundamental importance, this demonstration opens up on-chip platforms for novel experimental studies of gap solitons as the basis of all-optical buffers, delay lines and optical storage.

The generation of optical pulse trains from continuous-wave light has attracted growing attention in recent years because it provides a simple way to obtain high repetition rate ultrashort pulses. While pulse generation has been extensively demonstrated in optical fibers, pulse train generation from weak, continuous wave light in photonic chips has posed significant challenges because of the short interaction length and therefore difficulty in acquiring sufficient new frequency content, and/or absence of the appropriate dispersion environment. In this manuscript, we report the pulse train generation of a low continuous-wave signal to 18 ps, by leveraging cross-phase modulation induced by co-propagating pump pulses with a peak power of 3.7 W in an ultra-silicon-rich nitride grating. The pulse train generation dynamics are documented both experimentally and theoretically to arise from cross-phase modulation-induced generation of new spectral content, and dispersive re-phasing. This is a new approach in which picosecond pulse generation may be achieved from low power, continuous-wave light.

Topological boundary states are well localized eigenstates at the boundary between two different bulk topologies. As long as bulk topology is preserved, the topological boundary mode will endure. Here, we report topological nonlinear parametric amplification of light in a dimerized coupled waveguide system based on the Su-Schrieffer-Heeger model with a domain wall. The good linear transmission properties of the topological waveguide arising from the strong localization of light to the topological boundary is demonstrated through successful high-speed transmission of 30 Gb/s non-return-to-zero and 56 Gb/s pulse amplitude 4-level data. The strong localization of a co-propagating pump and probe to the boundary waveguide is harnessed for efficient, low power optical parametric amplification and wavelength conversion. A nonlinear tuning mechanism is shown to induce chiral symmetry breaking in the topological waveguide, demonstrating a pathway in which Kerr nonlinearities may be applied to tune the topological boundary mode and control the transition to bulk states.

We demonstrate a complementary metal–oxide–semiconductor (CMOS)-compatible optical parametric Bragg amplifier on an ultra-silicon-rich nitride chip. The amplifier design incorporates advantageous group index properties in a nonlinear Bragg grating to circumvent phase matching limitations arising from the bulk material and waveguide dispersion. The grating structure further augments the effective nonlinear parameter of 800 W−1/m, considerably lowering the power required for the observation of strong parametric gain. On/off optical parametric gain of 20 dB is achieved using a low peak power of 1.6 W, in good agreement with numerical calculations. This represents a 7 dB improvement in the parametric gain compared to the absence of grating enhancement which is attributed to the Bragg grating induced superior phase matching.

Supercontinuum generation is demonstrated in a 3-mm-long ultra-silicon-rich nitride (USRN) waveguide by launching 500 fs pulses centered at 1555 nm with a pulse energy of 17 pJ. The generated supercontinuum is experimentally characterized to possess a high spectral coherence, with an average |g12| exceeding 0.90 across the wavelength range of the coherence measurement (1260 nm to 1700 nm). Numerical simulations further indicate a high coherence over the full spectrum. The experimentally measured supercontinuum agrees well with the theoretical simulations based on the generalized nonlinear Schrödinger equation. The generated broadband spectra using 500 fs pulses possessing high spectral coherence provide a promising route for CMOS-compatible light sources for self-referencing applications, metrology, and imaging.

We experimentally demonstrate picosecond pulse generation from a low-power continuous-wave signal, generating 18ps pulses, by leveraging cross-phase modulation of pump pulses with a low peak power of 3.7 W in an ultra-silicon-rich nitride Bragg grating.

A 1.2-octave-spanning supercontinuum generation is demonstrated in a 3-mm-long ultra-silicon-rich-nitride waveguide using 17pJ, 500fs pulses. The generated supercontinuum possesses a spectral coherence (|g12|) exceeding 0.94 on average across the measured wavelength range.

We demonstrates the first optical prametric amplification using nonlinear Bragg grating where enhanced phase matching is enabled by utilizing the rapid increase and decrease in effective index near the stopband. An on/off parametric gain of 20dB is achieved in a 3-mm ultra-silicon rich nitride Bragg grating at a low peak power of 1.6W.

Bragg-soliton dynamics in a 2-stage ultra-silicon-rich-nitride (USRN) chip-based device, consisting of a cladding-apodized modulated Bragg grating (CMBG) stage and a USRN channel waveguide stage, is studied and optimized for enhanced supercontinuum generation. We observe that the enhancement is strongly dependent on the Bragg-soliton effect temporal compression developing in the CMBG stage, which is linked to both device and input pulse parameters. With the optimal parameter combination, a supercontinuum spanning 610 nm at the −30 dB level is experimentally demonstrated in the 2-stage USRN device, representing a 5× enhancement compared to that in a reference waveguide. Good agreement is obtained between the experimentally measured supercontinuum and simulations based on the generalized nonlinear Schrödinger equation and is consistent with design rules based on Bragg soliton compression. This device provides an encouraging path to generate supercontinuum in compact chip-based platforms, which does not need ultrashort, femtosecond scale pulses, greatly relaxing the pulse width and pulse power requirement.

Topological boundary states are well localized eigenstates at the boundary between two different bulk topologies. As long as bulk topology is preserved, the topological boundary mode will endure. Here, we report topological nonlinear parametric amplification of light in a dimerized coupled waveguide system based on the Su-Schrieffer-Heeger model with a domain wall. The good linear transmission properties of the topological waveguide arising from the strong localization of light to the topological boundary is demonstrated through successful high-speed transmission of 30 Gb/s non-return-to-zero and 56 Gb/s pulse amplitude 4-level data. The strong localization of a co-propagating pump and probe to the boundary waveguide is harnessed for efficient, low power optical parametric amplification and wavelength conversion. A nonlinear tuning mechanism is shown to induce chiral symmetry breaking in the topological waveguide, demonstrating a pathway in which Kerr nonlinearities may be applied to tune the topological boundary mode and control the transition to bulk states.

Optical pulses are fundamentally defined by their temporal and spectral properties. The ability to control pulse properties allows practitioners to efficiently leverage them for advanced metrology, high speed optical communications and attosecond science. Here, we report 11× temporal compression of 5.8 ps pulses to 0.55 ps using a low power of 13.3 W. The result is accompanied by a significant increase in the pulse peak power by 9.4×. These results represent the strongest temporal compression demonstrated to date on a complementary metal–oxide–semiconductor (CMOS) chip. In addition, we report the first demonstration of on-chip spectral compression, 3.0× spectral compression of 480 fs pulses, importantly while preserving the pulse energy. The strong compression achieved at low powers harnesses advanced on-chip device design, and the strong nonlinear properties of backend-CMOS compatible ultra-silicon-rich nitride, which possesses absence of two-photon absorption and 500× larger nonlinear parameter than in stoichiometric silicon nitride waveguides. The demonstrated work introduces an important new paradigm for spectro-temporal compression of optical pulses toward turn-key, on-chip integrated systems for all-optical pulse control.

Nonlinear integrated optics leveraging platforms with high nonlinear figure of merit offer energy efficient optical signal processing capabilities. Over the last five years, CMOS-compatible ultra-silico-rich nitride (USRN) has emerged as a promising platform on which to implement various nonlinear optics functions. Bandgap engineered to maximize the Kerr nonlinearity while maintaining two-photon absorption free behavior at telecommunications wavelengths, USRN possesses a nonlinear refractive index that is 100× larger than that in stoichiometric silicon nitride. In this article, we review the recent progress made in USRN-based nonlinear integrated optics devices. The impacts it has made spanning from high gain optical parametric amplification and observations of soliton effects in photonic waveguides and photonic crystal waveguide structures will be discussed. Finally, we assess the future outlook of CMOS-compatible USRN-based nonlinear optics.

Strong temporal compression in an integrated ultra-silicon-rich nitride temporal compressor consisting of separate nonlinear and anomalously dispersive stages is demonstrated. 11× compression of 5.8ps pulses at a low input peak power of 13.3W and 9.4× increase in the pulse peak power is achieved.

Integrated photonic nanostructures provide powerful degrees of design freedom for the engineering of light confinement and advanced lightwave manipulation functions. The ability to tailor field profiles in these on-chip devices allows enhanced light-matter interaction, strong modal confinement and the ability to engineer dispersion. Here, we present recent developments in photonic integrated circuits towards the generation of solitons, amplification, and optical waveform manipulation. By harnessing CMOS platforms with a high nonlinear figure of merit, the existence of on-chip Bragg solitons, Bragg soliton fission and solitons in photonic waveguides are experimentally observed. These demonstrations are made possible by 1,000X larger dispersion close to the band edge in on-chip Bragg gratings, an effect that arises from the interaction of forward and backward propagating fields. In addition, efficient parametric processes facilitate wavelength conversion of light and high gain amplification of signals. These efficient nonlinear mechanisms provide a possible pathway in which to realize new approaches to efficiently manipulate optical waveforms.

Nonlinear properties of GeSe2-As2Se3-PbSe are studied using z-scan measurements from 2.5μm–5.5μm. The largest nonlinear refractive index is observed at 2.8μm, corresponding to the two-photon edge. A sub-peak at 4.6μm arises from mid-gap defect states.

Nonlinear CMOS Photonics allows for seamless integration with CMOS electronics and ease of manufacturability. We discus developments in USRN-based nonlinear optics. We demonstrate 8.7 soliton-effect compression in USRN waveguides, on-chip Bragg-soliton compression and fission.

Nonlinear phenomena at the 1550nm wavelength are studied in ultra-silicon-rich nitride devices. Photonic crystals in one are demonstrated to introduce 1000x enhancement in the group velocity dispersion properties and a 40x increase in the nonlinear parameter. The large Kerr nonlinearity and negligible two-photon absorption allow strong nonlinear effects including 42.5dB optical parametric gain and Bragg soliton based temporal compression to be demonstrated.

Supercontinuum generation (SCG) through soliton fission provides high‐brightness, spectrally‐rich light needed for hyperspectral imaging, broadband spectroscopy, and fluorescence microscopy. The prospect of miniaturization has led to many demonstrations of this phenomenon in integrated platforms. However, due to the moderate dispersion and nonlinearity generally available in channel waveguides, femtosecond pulses have typically been required to date, as the use of picosecond pulses would require unpractically long devices to achieve soliton fission. Here, spectral bandwidth enhancement of the supercontinuum process through Bragg grating induced soliton‐effect compression and soliton fission is demonstrated. This approach uses picosecond pulses on a complementary metal oxide semiconductor (CMOS)‐compatible, millimeter‐scale platform, consisting of a monolithically integrated cladding‐modulated Bragg grating with a channel waveguide. The strong dispersion near the stopband of the grating enables compression and fission of picosecond higher‐order solitons, which enhances the spectral broadening in the channel waveguide. A 4.3 spectral bandwidth enhancement is reported, with respect to a reference waveguide of the same length. The output spectra are further studied both through simulations and experiments and determined to possess high spectral coherence. These results highlight a simple route to significantly augment the bandwidth of nonlinear processes such as SCG while maintaining low power and compact footprint.

Correlated photon pair generation is demonstrated using ultra-silicon-rich nitride waveguides. Waveguides with a length of 10 mm, nonlinear parameter of 530 W−1/m and anomalous dispersion are used to achieve spontaneous four-wave mixing. A generated coincidence rate of 2.40 × 105 counts per second is achieved, and derived from a measured coincidence rate of ∼ 1 counts per second at the maximum coupled power of 5 mW, in line with the expected quadratic dependence of spontaneous four-wave mixing efficiency on power. Utilizing picosecond pulses as the pump, we achieve a measured coincidence rate of up to 1.8 counts per second, resulting in a generated coincidence rate of 2.20 × 10−2 counts per pulse at the maximum peak power of 8.33 W. 2.3 times larger coincidence-to-accidental ratio is also obtained using a pulsed pump compared to that achieved with a continuous-wave pump. Further enhancements via the use of ring resonators may be adopted.

Nonlinear optical properties of ultra-silicon-rich nitride are investigated. The nonlinear refractive index and two-photo and three-photon absorption coefficients are measured in the range of 0.8pm-1.6pm covering the C- and L-bands.

We demonstrate pulse compression using ultra-silicon-rich nitride grating devices. Frequency chirp from a waveguide is temporally synchronized by a dispersive grating to achieve temporal compression by a factor of 4.3. When reversed, spectral compression of 2.3× is achieved.

The nonlinear optical properties of GeSbS chalcogenide glass are characterized in the wavelength range from 1.1-5.5μm. High order multi-photon up to the 11th order, multiphoton induced photoluminescence and nonlinear refractive indices are experimentally measured.

We demonstrate the optical pulse compression of 2ps laser down to 230fs pulse resulting in 8.7 times compressed using a USRN waveguide. The process is facilitated by high-order soliton formation arising from a large nonlinear parameter and anomalous group velocity dispersion.

Correlated single photons provide a means to drive applications such as quantum computing and quantum communications. Correlated single photons can be generated via parametric down conversion in second–order nonlinear media or spontaneous four–wave mixing in third–order nonlinear media. In particular, complementary metal–oxide–semiconductor (CMOS) technology allows for seamless integration with electronics, providing the potential for a completely on-chip solution for quantum information processing. Ultra–silicon–rich nitride platform is a backend CMOS compatible platform, that has already been used to obtain high gain optical parametric amplification, wideband supercontinuum and enhanced nonlinearity in photonic crystal waveguides due to its large nonlinearity. In this work, we demonstrate correlated photon pair generation based on spontaneous four–wave mixing using ultra-silicon-rich nitride waveguides for the application in CMOS–based optical quantum technologies. A CW pump at a wavelength of 1555.747nm amplified using an EDFA is filtered through five wavelength division multiplexers (WDM) with a bandwidth of 1.2nm, providing 175dB suppression of EDFA induced pump sideband noise. The filtered quasi–TE pump, adjusted using a fiber polarization controller, is coupled into an ultra–silicon–rich nitride waveguide using a lensed fiber. A SiO2 cladded waveguide with a width of 550nm and height of 300nm possesses a high nonlinear parameter of 530W^-1/m with anomalous dispersion necessary for spontaneous four-wave mixing. The waveguide output is coupled into a lensed fiber and 7 cascaded WDMs are used to provide 245dB of residual pump filtration. The pump–suppressed output is spectrally separated into signal/idler part using WDMs. We refer to lower (higher) frequency photon as the signal (idler). The spontaneously generated signal and idler photons are filtered using cascaded tunable band pass filters (OTF) centered at 1571.24nm and cascaded WDMs centered at 1540.56nm, respectively. The bandwidth of the tunable OTF and WDM is 0.5nm and 1.2nm, therefore the correlated signal/idler photons are observed within the bandwidth window of 0.5nm induced by the OTF. The signal and idler photons are measured using InGaAs/InP avalanche photodetectors. The time correlation between signal and idler photons is obtained using a time interval analyzer with a detection efficiency of 20% and dead time of 15μs.The time bin is set to 81ps and the photon collection time is 240s. The coincidence peak is located ~11ns in the time–bin histogram due to the optical-path difference between the tunable OTF and WDM at respective signal and idler sides. The experimental raw coincidence counts (Hz), calculated by subtracting the accidental rate from the coincidence peak, show a quadratic increase with respect to coupled pump power. At the maximum coupled power of 5mW, the raw coincidence count is ~1Hz. We achieve a raw coincidence–to–accidental ratio (CAR) of up to 3. Therefore, we succeeded to observe correlated photon pair generation based on spontaneous four–wave mixing using the ultra–silicon–rich-nitride waveguide as a CMOS compatible platform, for future applications in quantum technologies.

Four–wave mixing (FWM) serves as the physical basis for various nonlinear phenomena including wavelength conversion, parametric amplification, and frequency combs. FWM on a chip has been implemented using CMOS platforms, chalcogenide glasses and III–V materials. On-chip, waveguide based stimulated FWM techniques have been mostly demonstrated using a coherent pump and coherent signal to focus on broadband spectral tuning for operation in high–speed and multi–channel wavelength division multiplexing network. Though FWM using incoherent light has the potential to provide large optical conversion efficiency, such demonstrations remain largely confined to fiber–experiments and involved narrow–band signals/idlers. Furthermore, the FWM based on a pulsed laser and a broadband incoherent source has yet to be implemented. In this work, we demonstrate integrated ultra–silicon–rich nitride parametric converters that perform wavelength conversion of a broadband incoherent source with a bandwidth of ~100nm at the -20dB level. A 500fs pulsed pump is combined with an incoherent superluminescent diode (SLD) as the signal and parametric gains between 12dB – 27dB is demonstrated as well as cascaded FWM. A 500fs pulsed laser centered at 1.555μm and an incoherent SLD with a 20dB bandwidth spanning from 1.6 – 1.7μm are used as the pump and signal respectively. The pump and signal are combined with a wavelength division multiplexer and coupled into an ultra–silicon–rich nitride waveguide with 10mm length, 700nm width and 400nm height. The waveguide is designed to have a larger nonlinear parameter of 330W^-1/m while possessing anomalous dispersion of -0.92ps^2/m, necessary for phase matched parametric conversion. At a coupled peak power of 4.6W, an idler spanning from 1.43 – 1.52μm at the -20dB level is generated. At a maximum input signal power of 0.71mW, a second idler appears at the blue side of the first generated idler because of cascaded FWM induced between pump of 1.555μm and the first idler peak of 1.48μm. At a coupled peak power of 2.8W, an idler spanning from 1.46 to 1.52μm is generated. The experimental idler bandwidth agrees well with the calculation based on degenerate FWM phase–matching condition. The broadened idler powers are calculated by integrating the energy of each signal and idler with respect to wavelength to obtain optical conversion efficiencies. The integrated idler power is 3.4dBm and 13.4dBm, corresponding to idler parametric gain of 12dB and 18dB respectively at a coupled peak power of 2.8 and 4.6W, respectively. The application of the SLD signal to a supercontinuum that is generated at a coupled peak power of 26W spectrally spanning 1.1 – 1.7μm is observed to generate an idler power of 14dBm within the wavelength range of 1.18 – 1.42μm as well as an idler conversion efficiency/gain of 27dB. Therefore, we achieved broadband wavelength conversion based on stimulated FWM using a pulsed pump and broadband incoherent signal that facilitate the spectrum spanning from 100nm, sufficient to cover parts of the E– and S–bands an representing large conversion efficiency and parametric gains of 12dB – 27dB.

Nonlinear optics leveraging CMOS-compatible, ultra-silicon-rich nitride devices is presented. Films are engineered to possess high Kerr nonlinearity and negligible two-photon absorption at telecommunications wavelengths. We demonstrate high-gain optical parametric amplifiers, wavelength conversion, supercontinuum sources and slow light enhanced devices.

We measured nitrous oxide (N 2 O) gas at concentrations as low as 2ppb using a multi-pass gas cell (MPGC) with an path length of 10m. The quantum cascade laser (QCL) was spectrally scanned in the range of 4529.4nm–4531nm having the strongest linear absorption cross-section of 3.6710−18 cm2, where the spectral absorption region of CO and CO 2 is avoided. The absorption levels at spectral lines of 4529.80nm and 4530.22nm were measured to demonstrate a relation with variation of concentration of N 2 O. This strategy could be used in low power of laser with a limit of power detector because we are using linear absorption phenomena.

We characterize the nonlinear optical properties of GeSbS chalcogenide glasses with fiber-based experiments. A waveguide nonlinear parameter of 7 W−1/m and nonlinear refractive index of 3.71 × 10−18 m2/W are estimated by self-phase modulation. A GeSbS waveguide could also generate a supercontinuum from 1280 to 2120 nm at the −30 dB level for maximum coupled power of 340 W, showing a 14 fold spectral broadening of the input spectrum explained by cascaded stimulated Raman scattering.

The formation of optical solitons arises from the simultaneous presence of dispersive and nonlinear properties within a propagation medium. Chip-scale devices that support optical solitons harness high field confinement and flexibility in dispersion engineering for significantly smaller footprints and lower operating powers compared to fiber-based equivalents. High-order solitons evolve periodically as they propagate and experience a temporal narrowing at the start of each soliton period. This phenomenon allows strong temporal compression of optical pulses to be achieved. In this paper, soliton-effect temporal compression of optical pulses is demonstrated on a CMOS-compatible ultra-silicon-rich nitride (USRN) waveguide. We achieve 8.7× compression of 2 ps optical pulses using a low pulse energy of ∼16 pJ, representing the largest demonstrated compression on an integrated photonic waveguide to date. The strong temporal compression is confirmed by numerical calculations of the nonlinear Schrodinger equation to be attributed to the USRN waveguide’s large nonlinearity and negligible two-photon absorption at 1550 nm.The formation of optical solitons arises from the simultaneous presence of dispersive and nonlinear properties within a propagation medium. Chip-scale devices that support optical solitons harness high field confinement and flexibility in dispersion engineering for significantly smaller footprints and lower operating powers compared to fiber-based equivalents. High-order solitons evolve periodically as they propagate and experience a temporal narrowing at the start of each soliton period. This phenomenon allows strong temporal compression of optical pulses to be achieved. In this paper, soliton-effect temporal compression of optical pulses is demonstrated on a CMOS-compatible ultra-silicon-rich nitride (USRN) waveguide. We achieve 8.7× compression of 2 ps optical pulses using a low pulse energy of ∼16 pJ, representing the largest demonstrated compression on an integrated photonic waveguide to date. The strong temporal compression is confirmed by numerical calculations of the nonlinear Schrodinger equation...

We report high order multi-photon absorption in Ge23Sb7S70 chalcogenide glasses up to the 11th order. Open aperture z-scan measurements with enhanced detection capabilities are performed at short-wave to mid-infrared wavelengths between 1.1 μm and 5.5 μm, enabling very high order multi-photon absorption to be experimentally observed. We report the multi-photon absorption coefficients for Ge23Sb7S70 within the measurement range corresponding to 3–11 photon absorption. The dispersive Kerr nonlinear index of the chalcogenide glass in the short-wave to mid-infrared wavelength range is measured, resulting in a peak n2 value of 4.4 × 10−18 m2/W. Enhancements to the nonlinear refractive index from the presence of defect states are observed. We further report experimentally verified multi-photon absorption excitation of photoluminescence in Ge23Sb7S70 chalcogenide glasses. The results pave the way for previously unexplored, new paradigms of photonic device design leveraging very high order multi-photon absorption effects and multi-photon excited photoluminescence.

GeSbS ridge waveguides have recently been demonstrated as a promising mid – infrared platform for integrated waveguide – based chemical sensing and photodetection. To date, their nonlinear optical properties remain relatively unexplored. In this paper, we characterize the nonlinear optical properties of GeSbS glasses, and show negligible nonlinear losses at 1.55 μm. Using self – phase modulation experiments, we characterize a waveguide nonlinear parameter of 7 W[subscript −1]/m and nonlinear refractive index of 3.71 × 10[superscript −18] m[superscript 2]/W. GeSbS waveguides are used to generate supercontinuum from 1280 nm to 2120 nm at the −30 dB level. The spectrum expands along the red shifted side of the spectrum faster than on the blue shifted side, facilitated by cascaded stimulated Raman scattering arising from the large Raman gain of chalcogenides. Fourier transform infrared spectroscopic measurements show that these glasses are optically transparent up to 25 μm, making them useful for short – wave to long – wave infrared applications in both linear and nonlinear optics., SUTD-MIT International Design Centre (IDC)

The generation of broadband light within the telecommunication band has been instrumental to the design and characterization of advanced optical devices and systems. In this paper, stimulated degenerate four-wave mixing of an ultra-silicon rich nitride waveguide is investigated using a pulsed pump at 1.555 μm and incoherent broadband sources emitting in the 1.65 μm wavelength region as a signal. The waveguide possesses a large nonlinear parameter of 330 W−1/m as well as anomalous dispersion, required for phase matched parametric processes. The broadband idler ranging from 1.43 μm to 1.52 μm is generated using a coupled peak power of 4.6 W, spanning ∼100 nm at the −20 dB level, which is sufficient to cover parts of the E- and S-bands. The spectral span of the generated idler also agrees well with the calculation based on the phase-matching condition governing degenerate four-wave mixing. Cascaded incoherent four-wave mixing is also observed. Using a supercontinuum pump spanning from 1.1 to 1.7 μm with a co...

We experimentally demonstrate switching can be occurred between D1 |F'=1>, |F'=2> and D2 |F'=2> pulses. Each of pulses is probe field of triple-A system composed of 87Rb D1 and D2 transition line.

Multiphoton absorption coefficients and nonlinear refractive indices of germanium in the near and mid-infrared (2–5 μm) are reported. The nonlinear coefficients are measured by open and closed aperture Z-scan with 150 fs pulses at a repetition rate of 1 kHz. The nonlinear refractive index of Ge has a peak value of 9.1×10−5cm2/GW at a wavelength of 3 μm. The effect of free electrons generated by multiphoton absorption is discussed by investigating the variation of multiphoton absorption coefficients at different input powers. Kramers-Kronig relations are also discussed with regard to the relationship between nonlinear refractive index and two photon absorption coefficient.

The coherent control of optical images has garnered attention because all information embedded in optical images is expected to be controlled in a parallel way. One of the most important control processes is switch for information delivery. We experimentally demonstrated phase-controlled optical image switching in a double-Lambda system where the transmission of the image through a medium was switched. Two independent laser sources were adopted for a double-Lambda system such that images inscribed in two weak probe light beams were incoherent with each other. Arbitrary phase was added to the optical images to show that switching could be accomplished just with the relative phase difference between the probe pixels. (C) 2013 Optical Society of America

Phase-controlled optical image switching with low light intensity was demonstrated in a double-Λ system. Switching by interference in a double-Λ system was observed as having a 90 % switching depth between incoherent image pixels.

Using numerical method, the authors investigate various features of the closed four-level system in the ultrafast regime. The probe absorption changes upon the phases of the fields to exhibit EIT, dispersion-like absorption, or enhanced absorption.

This paper presents a nano positioning mechanism with flexure hinge and damper. The nano stage represented in this paper consists of a leaf spring guides and the voice coil motor (VCM) since it provides long working range and the control is easy. However, when the leaf spring is used alone, mechanism has very small damping, which reduces the system stability and causes mechanical vibration in positioning. Especially, in measurement system, since the excessive vibration leads the reduction of the system bandwidth, the elimination of the mechanical vibration is very important. In this paper, the simple eddy current brake system is used as a damper. With a proper damping ratio, the transient response is improved and the settling time of the nano stage is shortened. Numerical and experimental results show the validity of the proposed damped flexure hinge stage.

A four-mount active vibration isolation system (AVIS) is developed using voice coil actuators. The flexible body modes in the upper plate of the AVIS can cause an instability problem due to control signal whose frequency is close to the resonant frequency of the flexible modes. The loop shaping technique is applied to reduce the amplitude of the control signal. The performances of the active vibration isolation system proposed in the work are investigated by comparing with the passive isolation system using the atomic force microscope (AFM) images.

We theoretically studied a triple-Λ system comprising three pairs of coupling-probe fields. Three probe fields were phase-dependently switched with a switching depth above 80%, at which the group-velocity matching of all probe pulses was available under slow light-propagation conditions. We considered the probe susceptibility as the superposition of three-photon transitions to systematically understand the multi-photon interference in a triple-Λ system, which can be applied to systems with N−Λ (N≥1). This helped us to tailor the probe susceptibility by adjusting the detuning and phases of the coupling and probe fields. This work can be applied to all-optical switching gates for triple-photons and can enhance the speed of processing optical information.

We have demonstrated anticorrelated light switching between multiphoton transition channels in a nonresonant double-Λ system. Two-color probe transitions, using rubidium D1 (795 nm) and D2 (780 nm), were included in our double-Λ system. In anticorrelated light switching, one of two probe transitions is selected as transparent while the other is selected as opaque. In this configuration, we observed completely different behavior from that seen in a resonant double-Λ system, in which both probe transmissions are transparent or opaque simultaneously. Furthermore, we observed a noise correlation between two-color probe transmissions when the phase fluctuation of the two probe lasers was converted to the intensity fluctuation. The relative phase fluctuation between the two probe lasers induced an anticorrelation between the intensity noises of two probe lasers in a nonresonant double-Λ system, while a correlation was induced in a resonant double-Λ system. The intensity fluctuation (correlated or anticorrelated) was easily controlled by detuning the double-Λ system. The noise anticorrelation effect is clearly interpreted as arising from the anticorrelated light switching in a nonresonant double-Λ system. This system can be used for noise control as well as optical switching between incoherent two-color laser lights.

We present a simple method for compensating a chirp of a white light continuum for femtosecond time-resolved spectroscopy. The quantity of the chirp was directly measured by referring to rising step of transient absorption time evolutions of a target material (polythiophene-fullerene thin organic blend film) itself. The analyzed chirp information in this manner was used for a correction procedure; each wavelength of the chirped white light continuum was correlated to an optical delay stage position for calibrating exactly with respective zero-delays. Consequently, it was possible to simultaneously measure both ultrafast kinetics and chirp independent time-resolved spectra with this method.