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We characterize the nonlinear optical response of low loss Si(0.6)Ge(0.4) / Si waveguides in the mid-infrared between 3.3 µm and 4 µm using femtosecond optical pulses. We estimate the three and four-photon absorption coefficients as well as the Kerr nonlinear refractive index from the experimental measurements. The effect of multiphoton absorption on the optical nonlinear Kerr response is evaluated and the nonlinear figure of merit estimated providing some guidelines for designing nonlinear optical devices in the mid-IR. Finally, we compare the impact of free-carrier absorption at mid-infrared wavelengths versus near-infrared wavelengths for these ultra-short pulses.
RESUMO
We have investigated the nonlinear optical response of low loss Si(0.6)Ge(0.4) / Si waveguides in the mid-infrared wavelength range from 3.25- 4.75µm using picosecond optical pulses. We observed and measured the three and four-photon absorption coefficients as well as the Kerr nonlinear refractive index. The dynamics of the spectral broadening suggests that, in addition to multiphoton absorption, the corresponding higher order nonlinear refractive phenomena also needs to be included when high optical pulse intensities are used at mid-infrared wavelengths in this material.
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Highly nonlinear planar glass waveguides have been shown to be useful for all optical signal processing. However, the typical SMF-28 fiber to waveguide coupling loss of ~5dB/end remains a barrier to practical implementation. Low loss coupling to a fiber using vertical tapering of the waveguide film is analyzed for rib and nanowire waveguides and experimentally demonstrated for ribs showing polarization and wavelength independence over >300nm bandwidth. Tapers with essentially zero excess loss led to total losses from the waveguide to fiber core of 1.1dB per facet comprising only material absorption (0.75dB) and mode overlap loss (0.36dB), both of which can be eliminated with improvements to processing and materials.
Assuntos
Tecnologia de Fibra Óptica/instrumentação , Nanotubos/química , Refratometria/instrumentação , Ressonância de Plasmônio de Superfície/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Luz , Espalhamento de RadiaçãoRESUMO
We show that highly nonlinear chalcogenide glass nanowire waveguides with near-zero anomalous dispersion should be capable of generating correlated photon-pairs by spontaneous four-wave mixing at frequencies detuned by over 17 THz from the pump where Raman noise is absent. In this region we predict a photon pair correlation of >100, a figure of merit >10 and brightness of ~8×10(8) pairs/s over a bandwidth of >15 THz in nanowires with group velocity dispersion of <5 psâkm(-1) nm(-1). We present designs for double-clad Ge(11.5)As(24)Se(64.5) glass nanowires with realistic tolerance to fabrication errors that achieve near-zero anomalous dispersion at a 1420 nm pump wavelength. This structure has a fabrication tolerance of 80-170 nm in the waveguide width and utilizes a SiO(2)/Al(2)O(3) layer deposited by atomic layer deposition to compensate the fabrication errors in the film thickness.
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Vidro/química , Modelos Teóricos , Nanofios , Óptica e Fotônica/instrumentação , Óptica e Fotônica/métodos , Fótons , Óxido de Alumínio/química , Arsênio/química , Desenho de Equipamento/métodos , Germânio/química , Manufaturas , Nanotecnologia/instrumentação , Nanotecnologia/métodos , Selênio/química , Dióxido de Silício/químicaRESUMO
We report the first demonstration of on-chip cascaded stimulated Brillouin scattering (SBS). Cascaded SBS is characterized in a 4 cm long chalcogenide (As2S3) rib waveguide where the end facet reflections provide a monolithic Fabry-Perot (FP) resonator. The presence of the FP cavity reduces the Brillouin gain threshold, which enables observation of cascaded SBS at reduced pump powers. We observe up to three orders of Stokes waves in the backscattered signal at a coupled peak power of 1.34 W. Anti-Stokes waves due to four-wave mixing between the pump and the Stokes wave were observed in the forward spectrum.
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We report the first demonstration of optical phase conjugation (OPC) transmission of phase encoded and wavelength-division multiplexed (WDM) signals by the Kerr effect in a planar structured waveguide. The phase conjugated electric field of the signal is produced by four wave mixing pumped by a CW laser during co-propagating with the signal in a highly nonlinear waveguide fabricated in As(2)S(3) glass. Experiments demonstrate the capability of the device to perform dispersion-free transmission through up to 225 km of standard single mode fiber for a 3 × 40 Gb/s WDM signal, with its channels encoded as return-to-zero differential phase shift keying and spaced either 100 or 200 GHz apart. This work represents an important milestone towards demonstrating advanced signal processing of high-speed and broadband optical signals in compact planar waveguides, with the potential for monolithic optical integration.
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Arsenicais/química , Calcogênios/química , Tecnologia de Fibra Óptica/instrumentação , Modelos Teóricos , Refratometria/instrumentação , Processamento de Sinais Assistido por Computador/instrumentação , Sulfetos/química , Telecomunicações/instrumentação , Simulação por Computador , Desenho Assistido por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Vidro/química , Raios Infravermelhos , MiniaturizaçãoRESUMO
We report the first demonstration of simultaneous multi-impairment monitoring at ultrahigh bitrates using a THz bandwidth photonic-chip-based radio-frequency (RF) spectrum analyzer. Our approach employs a 7 cm long, highly nonlinear (gamma approximately 9900 /W/km), dispersion engineered chalcogenide planar waveguide to capture the RF spectrum of an ultrafast 640 Gb/s signal, based on cross-phase modulation, from which we numerically retrieve the autocorrelation waveform. The relationship between the retrieved autocorrelation trace and signal impairments is exploited to simultaneously monitor dispersion, in-band optical signal to noise ratio (OSNR) and timing jitter from a single measurement. This novel approach also offers very high OSNR measurement dynamic range (> 30 dB) and is scalable to terabit data rates.
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Dispositivos Ópticos , Fotometria/instrumentação , Processamento de Sinais Assistido por Computador/instrumentação , Análise Espectral/instrumentação , Telecomunicações/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Micro-Ondas , FótonsRESUMO
We demonstrate chip-based Tbaud optical signal processing for all-optical performance monitoring, switching and demultiplexing based on the instantaneous Kerr nonlinearity in a dispersion-engineered As(2)S(3) planar waveguide. At the Tbaud transmitter, we use a THz bandwidth radio-frequency spectrum analyzer to perform all-optical performance monitoring and to optimize the optical time division multiplexing stages as well as mitigate impairments, for example, dispersion. At the Tbaud receiver, we demonstrate error-free demultiplexing of a 1.28 Tbit/s single wavelength, return-to-zero signal to 10 Gbit/s via four-wave mixing with negligible system penalty (< 0.5 dB). Excellent performance, including high four-wave mixing conversion efficiency and no indication of an error-floor, was achieved. Our results establish the feasibility of Tbaud signal processing using compact nonlinear planar waveguides for Tbit/s Ethernet applications.
Assuntos
Tecnologia de Fibra Óptica/instrumentação , Micro-Ondas , Dispositivos Ópticos , Ondas de Rádio , Análise Espectral/métodos , Telecomunicações/instrumentação , Desenho de Equipamento , Fótons , Processamento de Sinais Assistido por ComputadorRESUMO
We report the first demonstration of the use of an RF spectrum analyser with multi-terahertz bandwidth to measure the properties of femtosecond optical pulses. A low distortion and broad measurement bandwidth of 2.78 THz (nearly two orders of magnitude greater than conventional opto-electronic analyzers) was achieved by using a 6 cm long As(2)S(3) chalcogenide waveguide designed for high Kerr nonlinearity and near zero dispersion. Measurements of pulses as short as 260 fs produced from a soliton-effect compressor reveal features not evident from the pulse's optical spectrum. We also applied an inverse Fourier transform numerically to the captured data to re-construct a time-domain waveform that resembled pulse measurement obtained from intensity autocorrelation.
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Calcogênios/química , Processamento de Sinais Assistido por Computador/instrumentação , Espectroscopia Terahertz/instrumentação , Espectroscopia Terahertz/métodos , Desenho Assistido por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Ondas de Rádio , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Radiação TerahertzRESUMO
We report on the fabrication and optical properties of etched highly nonlinear As(2)S(3) chalcogenide planar rib waveguides with lengths up to 22.5 cm and optical losses as low as 0.05 dB/cm at 1550 nm - the lowest ever reported. We demonstrate strong spectral broadening of 1.2 ps pulses, in good agreement with simulations, and find that the ratio of nonlinearity and dispersion linearizes the pulse chirp, reducing the spectral oscillations caused by self-phase modulation alone. When combined with a spectrally offset band-pass filter, this gives rise to a nonlinear transfer function suitable for all-optical regeneration of high data rate signals.
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We propose a novel tuneable table-top optical source as an alternative to the free electron laser currently used for resonant infrared pulsed laser deposition of polymers. It is based on two-stage pulsed optical parametric amplification using MgO doped periodically poled lithium niobate crystals. Gain in excess of 10(6) in the first stage and pump depletion of 58% in the second stage were achieved when the system was pumped by a high-power Nd:YVO(4) picosecond laser source at 1064 nm and seeded by a CW tuneable diode laser at 1530 nm. An average power of 2 W was generated at 3.5 microm corresponding to 1.3 microJ pulse energy.
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We report the first Bragg gratings fabricated by Focused Ion Beam milling in optical waveguides. We observe striking features in the optical transmission spectra of surface relief gratings in silicon-on-insulator waveguides and achieve good agreement with theoretical results obtained using a novel adaptation of the beam propagation method and coupled mode theory. We demonstrate that leaky Higher Order Modes (HOM), often present in large numbers (although normally not observed) even in nominally single mode rib waveguides, can dramatically affect the Bragg grating optical transmission spectra. We investigate the dependence of the grating spectrum on grating dimensions and etch depth, and show that our results have significant implications for designing narrow spectral width gratings in high index waveguides, either for minimizing HOM effects for conventional WDM filters, or potentially for designing devices to capitalize on very efficient HOM conversion.
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We report on the first experimental observation of a novel type of optical vector soliton, a dipole-mode soliton, recently predicted theoretically. We show that these vector solitons can be generated in a photorefractive medium employing two different processes: a phase imprinting, and a symmetry-breaking instability of a vortex-mode vector soliton. The experimental results display remarkable agreement with the theory, and confirm the robust nature of these radially asymmetric two-component solitary waves.
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In this study we report the use of ultra-short-pulsed near-infrared lasers for precision laser ablation of freshly extracted human teeth. The laser wavelength was approximately 800nm, with pulsewidths of 95 and 150fs, and pulse repetition rates of 1kHz. The laser beam was focused to an approximate diameter of 50microm and was scanned over the tooth surface. The rise in the intrapulpal temperature was monitored by embedded thermocouples, and was shown to remain below 5 degrees C when the tooth was air-cooled during laser treatment. The surface preparation of the ablated teeth, observed by optical and electron microscopy, showed no apparent cracking or heat effects, and the hardness and Raman spectra of the laser-treated enamel were not distinguishable from those of native enamel. This study indicates the potential for ultra-short-pulsed lasers to effect precision ablation of dental enamel.
Assuntos
Preparo da Cavidade Dentária/instrumentação , Terapia a Laser , Dente Pré-Molar , Temperatura Corporal , Esmalte Dentário/diagnóstico por imagem , Polpa Dentária/lesões , Dureza , Temperatura Alta , Humanos , Microscopia Eletrônica de Varredura , Análise Espectral Raman , Propriedades de Superfície , UltrassonografiaRESUMO
The structure of Ge(5)As(x)Se(95-x) (x = 10, 20, 30, 38 at.%) and Ge(15)As(x)Se(85-x) (x = 10, 25, 34 at.%) glasses has been investigated by high-energy x-ray diffraction and extended x-ray absorption fine structure measurements. The experimental datasets have been modelled using the reverse Monte Carlo simulation technique. The model atomic configurations have been analysed in detail. It has been found that the homonuclear Ge-Ge, As-As, Se-Se and heteronuclear Ge-As bonds play an important role in the structure formation of the Ge-As-Se glasses. The total number of these bonds decreases quite slowly with the mean coordination number similarly to the nonlinear refractive index.
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Subtle atomic motion in a Bi crystal excited by a 35 fs-laser pulse has been recovered from the transient reflectivity of an optical probe measured with an accuracy of 10(-5). Analysis shows that a novel effect reported here-an initial negative drop in reflectivity-relates to a delicate coherent displacement of atoms by the polarization force during the pulse. We also show that reflectivity oscillations with a frequency coinciding with that of cold Bi are related to optical phonons excited by the electron temperature gradient through electron-phonon coupling.
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We experimentally and computationally demonstrate high transmission through arrays of coaxial apertures with different geometries and arrangements in silver films. By studying both periodic and random arrangements of apertures, we were able to isolate transmission enhancement phenomena owing to surface plasmon effects from those owing to the excitation of cylindrical surface plasmons within the apertures themselves.