Nondestructive measurement of loss performance in channel waveguide devices with phase modulator

A novel method using a phase modulator is proposed for the nondestructive measurement of propagation loss in a channel waveguide. The phase modulator was fabricated on a Ti-diffused LiNbO3 crystal. Tuning the effective optical length of a waveguide by application of an electrical field on the phase modulator, the contrast of the resultant Fabry-Perot resonator in a channel waveguide device can be measured. The associated propagation attenuation coefficients are determined from the experimental results. Coordination of the phase modulator with an optical channel waveguide device not only allows measurement of the bending loss, but improvement in the relative intensity noise owing to the reduction of the reflected power.     

Soliton switching in twin-core fibers with gain and loss

Soliton propagation and switching in twin-core nonlinear fibers with gain and loss have been investigated based on a pair of coupled nonlinear Schr?dinger equations. We have found the fiber with equal amount of gain in both cores has the minimum ascending energy Δɛ of 1.5K, while the fiber with a certain amount of gain in one core and the same amount of loss in the other core has the minimum switching thresholdɛ _th of 2.05K. A new vector field is defined and its potential function is derived, which explains the switching behavior of the minimumɛ _th switch satisfactorily.     

A modal cutoff approach to the study of buried channel waveguide couplers

We investigate the higher-order supermodes of symmetric buried channel waveguide (BCW) couplers with cores of square, rectangular, and trapezoidal geometries. We show how the cutoff wavelengths of these supermodes can be used to interpret the spectral response of a practical single-mode BCW coupler. Our results highlight the design constraints imposed by second-order supermodes. We also compare the behaviour of these couplers with that of circular-core couplers to illustrate how the geometry of each core affects the coupler cutoff characteristics.     

X-junctions in buried channel waveguides

The excess loss across an acute-angle symmetric X-junction composed of two weakly guiding single-mode buried channel waveguides of square core cross-section is shown to be very small provided the junction angle is greater than a few degrees. Numerical and approximate analytical results are presented, as well as a simple criterion for the onset of cross-talk as the junction angle decreases.     

Improvement of polarization extinction in silicon waveguide devices

The SOI based waveguide devices are found to be highly polarization sensitive. Unwanted polarization excitations can be attenuated by integrating a TE- or TM-pass polarizer. A large attenuation of TM-polarized light has been observed when a thin film of metal is coated on the top of silicon rib waveguide, while TE-polarized light remains almost unaffected. The attenuation of TM-polarized light is attributed to the plasmonic absorption of the evanescent field in the metal cladding. Typically, with an Al cladding of thickness ～ 100 nm and a length of 1 mm on top of a single-mode (λ ～ 1550 nm) SOI rib waveguide structure, TE vs TM extinction ratio of ～ 15 dB has been obtained. Integrating such waveguide polarizers in a directional coupler and MZI based DWDM channel interleaver, we have also achieved an improvement in polarization extinction by ～ 15 dB.     

硅基波导慢光器件及其应用

硅基波导慢光器件是构建全光智能互连和实时高速测控等下一代信息技术的关键器件,在光通信和光信息处理等诸多领域具有显著的技术优势和巨大的应用潜力.随着器件结构的不断创新以及微电子制造技术的不断升级换代,硅基波导慢光器件愈来愈走向实用化.文章介绍了慢光的基本原理,概述了当前国内外硅基波导慢光器件的研究进展,着重分析了基于微环谐振腔的硅基波导慢光器件,并指出了它在具体应用领域中的发展前景.     

硅基波导慢光器件及其应用

硅基波导慢光器件是构建全光智能互连和实时高速测控等下一代信息技术的关键器件,在光通信和光信息处理等诸多领域具有显著的技术优势和巨大的应用潜力.随着器件结构的不断创新以及微电子制造技术的不断升级换代,硅基波导慢光器件愈来愈走向实用化.文章介绍了慢光的基本原理,概述了当前国内外硅基波导慢光器件的研究进展,着重分析了基于微环谐振腔的硅基波导慢光器件,并指出了它在具体应用领域中的发展前景.     

Nonlocality in PT-symmetric waveguide arrays with gain and loss

We demonstrate that light propagation in waveguide arrays that include PT-symmetric structures can exhibit strongly nonlocal sensitivity to topology of the array at fixed other parameters. We consider an array composed of lossless waveguides, that includes a pair of PT-symmetric waveguides with balanced gain and loss, and reveal that PT-symmetry breaking thresholds are different for planar and circular array configurations. These results demonstrate that PT-symmetric structures can offer new regimes for optical beam shaping compared to conservative structures.     

Advances in channel waveguide lithium niobate integrated optics

Recent advances in single-mode channel waveguide lithium niobate integrated optics are reviewed. Fabrication technology, the range of devices, and applications in telecommunications, signal processing and sensing are discussed.     

PECVD SiC optical waveguide loss and mode characteristics

We report the fabrication of single mode SiC (silicon carbide) waveguides and the measurement of their propagation loss. By studying the effect of sidewalls scattering loss due to surface roughness and by reducing it, minimal propagation loss of 2.3 dB/cm for the TM polarization is measured in the visible at 0.633 μm. This loss can be used as a benchmark for further development of SiC microphotonic components and circuit for sensor systems in harsh environment.     

Field distribution and mode interaction in twin-core fiber

A new direct method for the measurement of the longitudinal power distribution in multicore fibers using the luminescence of active ions is proposed. The method is employed in the study of the effect of curvature of twin-core fiber on the interaction of modes that propagate in different cores. The experimental distributions are in qualitative agreement with the model of mode interaction in curved fiber with allowance for the photoelastic effect. The results are used to determine the length of the mode interaction and the difference of the core refractive indices.     

Optically tunable microcavity in a planar photonic crystal silicon waveguide buried in oxide

We present all-optical tuning and switching of a microcavity inside a two-dimensional photonic crystal waveguide. The photonic crystal structure is fabricated in silicon-on-insulator using complementary metal-oxide semiconductor processing techniques based on deep ultraviolet lithography and is completely buried in a silicon dioxide cladding that provides protection from the environment. By focusing a laser onto the microcavity region, both a thermal and a plasma dispersion effect are generated, allowing tuning and fast modulation of the in-plane transmission. By means of the temporal characteristics of the in-plane transmission, we experimentally identify a slower thermal and a fast plasma dispersion effect with modulation bandwidths of the order of several 100 kHz and up to the gigahertz level, respectively.     

Modal redistribution and power loss in on-fibre devices

The mode coupling and optical power loss taking place in on-fibre devices are investigated. These devices are fabricated by removing the cladding of a multimode fibre and replacing it with a new material such as electro-optic or magneto-optic. Under an application of an external field the index of this modified cladding increases, leading to coupling among guided modes and coupling to radiation modes, resulting in optical power loss. The coupling among guided modes and the power loss are calculated as a function of the change in the index under the field and the length of the active region for the case when HE_1m modes are excited individually or in a group. Results indicate that on-fibre devices may be used as low-loss devices for applications involving sensors and delay lines.     

Subwavelength grating waveguide devices in siliconon-insulators for integrated microwave photonics

We provide an overview of our recent work on developing subwavelength grating(SWG) waveguide devices as an enabling technology for integrated microwave photonics. First, we describe wavelength-selective SWG waveguide filters, including ring resonators, Bragg gratings, and contradirectional couplers. Second, we discuss the development of an index variable optical true time delay line that exploits spatial diversity in an equal-length waveguide array. These SWG waveguide components are fundamental building blocks for realizing more complex structures for advanced microwave photonic signal processing.     

脊形波导中导模传输与损耗的分析与计算

本文运用有效折射率法把脊形波导化成等效二维平板波导后,再运用微分法求出弱吸收情况下波导模的吸收损耗,其方法简便,精确度高.     

Direct imaging of multimode interference in a channel waveguide

By use of a near-field scanning optical microscope in collection mode, multimode interference was directly measured in an annealed proton-exchanged LiNbO3 waveguide. Periodic transitions from a single-peaked Gaussianlike intensity distribution to a double-peaked intensity distribution were observed. The intensity distribution along the waveguide was calculated, and the results agree well with the experimental observation.     

Wavelength conversion in a Ti:PPSMgLN channel waveguide

A periodically poled titanium (Ti)-diffusion waveguide in near-stoichiometric MgO:LiNbO₃ (SMgLN) was fabricated that exhibits a second harmonic generation (SHG) efficiency of 63%. The device shows very high resistance to photorefractive damage at room temperature. All optical wavelength conversion by difference frequency generation (DFG) has been demonstrated in a periodically poled SMgLN (PPSMgLN) with Ti-diffusion channel waveguides. The wavelength conversion efficiency was measured to be −7.3 dB with the pump power of 150 mW and the signal power of 50 mW at room temperature.     

Second-harmonic generation in a direct-bonded periodically poled LiNbO(3) buried waveguide

We report the fabrication of a 12-mum -thick periodically poled LiNbO(3) planar waveguide buried in LiTaO(3) by direct bonding of precision-polished surfaces. Frequency doubling of the 1064-nm output of a cw diode-pumped Nd:YAG laser was performed in a 5.5-mm-long device with a 6.50-mum -period grating at an elevated temperature of 174 degrees C. The resultant green second-harmonic output exhibited fundamental-spatial-mode characteristics at a 4.3%W(-1) conversion efficiency.     

Surface acoustic wave distribution and acoustooptic interactions in silica waveguide Bragg devices

The efficiency of acoustooptic interaction in single-mode strip silica waveguide is analyzed theoretically for the first time by determining the overlap integral between the optical and acoustic field distributions. The results show that there is a good overlap of the optical and SAW fields in the low SAW frequency range. At high acoustic frequencies, the overlap integral decreases with increasing acoustic frequency. At 216 MHz, the maximum of 0.8544 for the overlap integral is obtained provided that the H/Λ equals 0.02.     

Propagation loss in a two-dimensional triangular photonic crystal waveguide

By means of a plane-wave-based transfer-matrix method, we present an extensive study of propagation loss in two-dimensional (2D) photonic crystal waveguides with limited cladding wall thickness. We examine the dependence of propagation loss on both the propagation direction and the waveguide wall thickness. It is shown that the propagation loss is a function of excitation frequency, wall thickness and waveguide outermost surface morphology. The conclusion that the propagation loss essentially decays exponentially with respect to the cladding wall thickness of a waveguide is valid only to a certain degree. In addition, we find that the propagation loss exhibit very complex behavior with respect to the excitation frequency.