用参量法通过LiNbO3晶体产生太赫兹的理论设计

按照参量振荡器的基本原理,从理论上设计了一个太赫兹参量振荡器。根据动量守恒、能量守恒条件以及相位匹配条件,应用铌酸锂(LiNbO3)晶体,给出了理论设计过程。画出了频率在太赫兹波段,波长与折射率的关系曲线,分析了太赫兹参量振荡器的非共线相位匹配条件,确定了晶体形状及其切割角、输出太赫兹波的可调谐范围,并画出了晶体为铌酸锂时相应的曲线,根据有效的输出功率,最后设计出最佳的太参量振荡器的结构。     

High-power picosecond terahertz-wave generation in photonic crystal fiber via four-wave mixing

We demonstrate picosecond terahertz (THz)-wave generation via four-wave mixing in an octagonal photonic crystal fiber (O-PCF). Perfect phase-matching is obtained at the pump wavelength of 1.55?μm and a generation scheme is proposed. Using this method, THz waves can be generated in the frequency range of 7.07-7.74?THz. Moreover, peak power of 2.55?W, average power of 1.53?mW, and peak conversion efficiency of more than -66.65?dB at 7.42?THz in a 6.25?cm long fiber are realized with a pump peak power of 2?kW.     

Arrayed silicon prism coupler for a terahertz-wave parametric oscillator

Using room-temperature parametric oscillation of a LiNbO(3) crystal pumped by a Q-switched Nd:YAG laser with a simple configuration, we have realized a widely tunable coherent terahertz- (THz-) wave source in the range between 1 and 3 THz. Inasmuch as the THz wave is affected by total internal reflection at the crystal edge, we used a Si prism coupler to couple out the THz wave. We introduce an arrayed Si-prism coupler that increases the efficiency and decreases the diffraction angle. By use of the arrayed-prism coupler, there is a sixfold increase in coupling efficiency and a 40% decrease in the far-field beam diameter, compared with the use of a single-prism coupler. We discuss the negative effect of the free carriers at the Si-prism surface that is excited by the scattered pump beam, and the positive effect of cavity rotation on the unidirectional radiation of the THz wave from a Si prism.     

Pulsed optical parametric amplification based on photonic crystal fibres

In this paper, we simulate pulsed one-pump fibre optical parametric amplifiers (1-P FOPAs) based on photonic crystal fibres in telecommunication region. At first, a PCF is designed such that its zero-dispersion wavelength is located at 1535 nm in order to fulfil the phase-matching condition for the parametric amplification in the telecommunication region. Then, the dispersion coefficients of the PCF including β₂, β₃, β₄ and β₅ as well as the nonlinear parameters are calculated at the pump, signal and idler wavelengths. Finally, the coupled nonlinear Schrödinger equations are numerically solved and the impacts of pump power and the pulse shape on the evolution of each pulse along the 1-P FOPA are investigated. The results show that the peak powers of the pump, signal and idler are periodically varied and each pulse is distorted and broadened as it propagates down the fibre optical parametric amplifiers. Also, the pulse distortion and broadening increase with the increase in both propagation distance and the input peak power.     

A parametric quartz crystal oscillator

Parametric oscillators have been well studied but currently are not used often. Nevertheless, they could be a low-phase noise solution, at least outside the frequency bandwidth of the resonant circuit. The theoretical aspect of parametric oscillations is briefly reviewed in this paper. Indeed, the basic theory of a simple resistance-inductor-capacitor (RLC) circuit working in parametric conditions easily can be extended toward a resonant loop that includes a quartz crystal resonator. Then, as an application, this study is transposed to a quartz crystal oscillator that has been modeled and tested as a first prototype. Simulation results are compared with those actually obtained.     

High-efficiency mid-infrared ZnGeP2 optical parametric oscillator in a multimode-pumped tandem optical parametric oscillator

We demonstrate a high-efficiency ZnGeP(2) optical parametric oscillator (OPO) pumped by another KTP OPO in a multimode-pumped tandem OPO configuration. The maximum optical-to-optical and slope efficiencies were 32% and 42.5%, respectively. Our setup also provides tunable multiband radiation in the 2.03-2.32-mum range and the 2.9-6.2-mum range simultaneously.     

Semiconductor optical amplifier-based multi-wavelength ring laser utilizing photonic crystal fiber

A multi-wavelength laser source is demonstrated with a semiconductor optical amplifier (SOA) as a gain medium. A multi-wavelength comb with equal spacing is achieved due to Fabry–Pérot modes of the SOA which oscillates in the ring cavity. A 100 m long photonics crystal fiber (PCF) is inserted in the ring cavity to provide a nonlinear gain by four-wave mixing (FWM) so that the output comb spectrum can be greatly broadened and flattened. The stability of the ring laser is also increased due to the efficient FWM phenomenon occurring in the PCF. The SOA-based laser can generate 35 lasing lines with equal spacing of 0.28 nm and extinction ratios of more than 30 dB at room temperature. The number of channels of the multi-wavelength laser can be controlled flexibly by changing the ratio of the coupler used in the ring cavity configuration as well as controlling the polarization state of the oscillating laser.     

Multimodal coherent anti-Stokes Raman spectroscopic imaging with a fiber optical parametric oscillator

We report on multimodal coherent anti-Stokes Raman scattering (CARS) imaging with a source composed of a femtosecond fiber laser and a photonic crystal fiber (PCF)-based optical parametric oscillator (FOPO). By switching between two PCFs with different zero dispersion wavelengths, a tunable signal beam from the FOPO covering the range from 840 to 930 nm was produced. By combining the femtosecond fiber laser and the FOPO output, simultaneous CARS imaging of a myelin sheath and two-photon excitation fluorescence imaging of a labeled axons in rat spinal cord have been demonstrated at the speed of 20 μs per pixel.     

Long-pulse, amplitude-modulated optical parametric oscillator

A singly resonant optical parametric oscillator (OPO) based on periodically poled LiNbO(3) is pumped by a Nd:YAG-based oscillator-modulator-amplifier source. This pump source, operating at 1.064 μm, provides the ability to control the temporal characteristics of the OPO waveform. We illustrate pulse tailoring by demonstrating three pulse formats: a pulse with a sharply rising edge, a square pulse, and an amplitude-modulated square pulse. The OPO output is tuned over 1.45-1.67-μm (signal) and 2.9-4.0-μm (idler). We demonstrate a 7-μJ, 2-μs square pulse with 5-MHz sinusoidal amplitude modulation.     

Limited efficiency of a silver selenogallate optical parametric oscillator caused by two-photon absorption

The nonresonant two-photon absorption (TPA) coefficient in silver selenogallate (AgGaSe(2)) crystals was measured for both ordinary and extraordinary polarizations in the 1300-1600-nm wavelength range. We found a cutoff wavelength for the TPA at between 1400 and 1500 nm, which corresponds to half of the bandgap energy of the AgGaSe(2) crystal. Below the cutoff wavelength we measured the TPA coefficient to be approximately 0.035 cm/MW for the extraordinary polarization and two to three times lower for the ordinary polarization. We compared the AgGaSe(2) samples from two manufacturers and observed a factor of 2 difference in the TPA coefficients. Because of the high TPA, the 1.32-mum pumped AgGaSe(2) optical parametric oscillator conversion efficiency was clipped at a low level.     

Linear and nonlinear optical properties of hollow core photonic crystal fiber

We review the optical guidance properties of hollow-core photonic crystal fibers. We follow a historical perspective to introduce the two major optical guidance mechanisms that were identified as operating in these fibers: photonic bandgap guidance and inhibited coupling guidance. We then review the modal properties of these fibers and assess the transmission loss mechanisms in photonic bandgap guiding hollow-core photonic crystal fiber. We dedicate a section to a review of the technical basics of hollow-core photonic crystal fiber fabrication and photonic microcell assembly. We review some of the early results on the use of hollow-core photonic crystal fiber for laser guiding micro-sized particles, as well as the generation of stimulated Raman scattering, electromagnetically induced transparency and laser frequency stabilization when the fiber core is filled with a gas-phase material. We conclude this review with a non-exhaustive list of prospects where hollow-core photonic crystal fiber could play a central role.     

Tunable continuous-wave doubly resonant optical parametric oscillator by use of a semimonolithic KTP crystal

A temperature-tuned continuous-wave doubly resonant optical parametric oscillator (OPO) consisting of a semimonolithic KTP crystal and a concave mirror has been designed and built. Under single-axial-mode-pair operation, we obtained a combined output power of the signal and idler light fields up to 365 mW at a pump power of 680 mW. The output wavelength of the OPO can be temperature tuned by as much as 9 nm. We achieved 2.8-GHz continuous frequency tuning of the OPO by tuning the pump laser frequency.     

High-stability erbium-doped photonic crystal fiber source

A single-pass backward configuration superfluorescent fiber source (SFS) based on erbium-doped photonic crystal fiber (EDPCF) with a high mean wavelength stability was proposed. The EDPCF was used to improve the intrinsic temperature dependence of the SFS. Using the optimal EDPCF length of 24.2 m and pump power of 204 mW, a 20.7 ppm mean wavelength stability of a prototype SFS was demonstrated with increased temperature from -40 °C to 60 °C. The mean wavelength had an ultra stability of 10.3 ppm with increased temperature from -20 °C to 60 °C.     

Group-velocity-matched optical parametric oscillator in tilted quasi-phase-matched gratings

An achromatic phase-matching scheme is reported for an optical parametric oscillator in tilted quasi-phase-matched gratings. The spectral angular dispersion is introduced in interaction waves such that each wave component satisfies the two-dimensional (noncollinear) quasi-phase matching. This is equivalent to simultaneous quasi-phase matching and group-velocity matching for ultrashort pulses. The phase-matching bandwidth for 10 mm periodically poled KTP increases by a factor of 12 at lambdas = 1.7 microm compared with one-dimensional quasi-phase matching. The effective interaction length will increase as a result of the matching.     

Passively Q-switched 1.57-microm intracavity optical parametric oscillator

We demonstrate an eye-safe KTP-based optical parametric oscillator (OPO) driven intracavity by a diode-pumped 1064-nm Nd:YAG laser, passively Q-switched by a Cr4+:YAG crystal. The characteristics of this system, which operates at 1570 nm with a repetition rate as high as 50 Hz, are studied as a function of Cr4+:YAG optical density. Under optimum conditions the OPO generates 1.5-mJ, 3.4 +/- 0.1-ns pulses in a single transverse mode. For a Cr4+:YAG Q-switch element with an optical density of 0.5 the conversion efficiency of the intracavity energy is approximately 45% with the ratio of OPO to Nd:YAG peak-pulse intensity exceeding unity. These and other OPO characteristics compare favorably with a simple rate equation model of the OPO dynamics.     

Modelling of a variable optical switch based on the parametric amplification in a photonic crystal fibre

We model an optical switch with a variable gain based on the optical parametric amplification in a photonic crystal fibre (PCF). By solving the coupled amplitude equations, the switch gain as a function of the power, wavelength and the state of polarization (SOP) of the control wave as well as the signal wavelength is simulated. The results show that the switch gain is increased by increasing the control power and the maximum gain is obtained for a specific SOP of the control wave. Also, the proposed switch has ultrahigh speed and provides a very wide and flat gain over the C-band without changing the operating wavelength.     

The non-degenerate optical parametric oscillator in the strong-coupling regime

Abstract

A fully quantum treatment of the non-degenerate optical parametric oscillator in the extreme quantum limit of small photon numbers and very high nonlinear coupling strength is presented. When the nonlinear coupling constant becomes comparable with the cavity decay rate, the sharp threshold that is usually encountered disappears, a situation reminiscent of microlasers. Furthermore the output light exhibits unusual statistical properties such as strong super-Poissonian behaviour of the pump mode for (very) large coupling constants.     

High-efficiency continuously tunable single-frequency doubly resonant optical parametric oscillator

We report a high-efficiency continuously tunable single-frequency doubly resonant optical parametric oscillator (OPO) based on periodically poled KTiOPO4. Pumped by a frequency-doubled Nd:YLF laser at 526.5 nm, the OPO has a low threshold of 30 mW and can deliver up to 156 mW single-frequency output at 0.8 μm and 89 mW single-frequency output at 1.5 μm with 390 mW of pump power. Coarse and continuous frequency tuning are also demonstrated experimentally.     

High ionic strength glucose-sensing photonic crystal

We demonstrate a colorimetric glucose recognition material consisting of a crystalline colloidal array embedded within a polyacrylamide-poly(ethylene glycol) (PEG) hydrogel, or a polyacrylamide-15-crown-5 hydrogel, with pendent phenylboronic acid groups. We utilize a new molecular recognition motif, in which boronic acid and PEG (or crown ether) functional groups are prepositioned in a photonic crystal hydrogel, such that glucose self-assembles these functional groups into a supramolecular complex. The formation of the complex results in an increase in the hydrogel cross-linking, which for physiologically relevant glucose concentration blue shifts the photonic crystal diffraction. The visually evident diffraction color shifts across the visible spectral region over physiologically important glucose concentration ranges. These materials respond to glucose at physiological ionic strengths and pH values and are selective in their mode of response for glucose over galactose, mannose, and fructose. Thus, we have developed a new recognition motif for glucose that shows promise for the fabrication of noninvasive or minimally invasive in vivo glucose sensing for patients with diabetes mellitus.