Digital synthesis of programmable photonic integrated circuits

Programmable photonic waveguide meshes can be programmed into many different circuit topologies and thereby provide a variety of functions.Due to the complexity of the signal routing in a general mesh,a particular synthesis algorithm often only accounts for a specific function with a specific cell configuration.In this paper,we try to synthesize the programmable waveguide mesh to support multiple configurations with a more general digital signal processing platform.To show the feasibility of this technique,photonic waveguide meshes in different configurations(square,triangular and hexagonal meshes)are designed to realize optical signal interleaving with arbitrary duty cycles.The digital signal processing(DSP)approach offers an effective pathway for the establishment of a general design platform for the software-defined programmable photonic integrated circuits.The use of well-developed DSP techniques and algorithms establishes a link between optical and electrical signals and makes it convenient to realize the computer-aided design of optics–electronics hybrid systems.     

Micro-scale Fabry–Perot interferometer with high spectral resolution and tunable transmission frequency via chiral waveguide-emitter coupling

A micro-scale Fabry–Perot interferometer with high spectral resolution and tunable transmission frequency is proposed. In this scheme, two partially reflecting mirrors with a separation of several wavelengths is fabricated in a waveguide, and a two-level emitter is located between the mirrors and coupled to the waveguide with chiral interaction. We analytically show that the single emitter plays the role of a strongly dispersive medium and the full width at half maximum (FWHM) of the transmission fringes around the resonance frequency of the emitter can be narrowed by 5 orders of magnitude. The proposed micro-scale interferometer can have the same spectral resolution as meter-scale traditional interferometers. We also show that the central frequency of the narrowed transmission fringe can be tuned by adjusting the asymmetry of the emitter-waveguide coupling. Our scheme has potential applications in the fields of integrated optical circuit and quantum information processing.     

Photonic‐on‐a‐chip: a thermal actuated Mach‐Zehnder interferometer and a molecular thermometer based on a single di‐ureasil organic‐inorganic hybrid

An integrated photonic‐on‐a‐chip device based on a single organic‐inorganic di‐ureasil hybrid was fabricated for optical waveguide and temperature sensing. The device is composed by a thermal actuated Mach‐Zehnder (MZ) interferometer operating with a switching power of 0.011 W and a maximum temperature difference between branches of 0.89 ºC. The MZ interferometer is covered by a Eu³⁺/Tb³⁺ co‐doped di‐ureasil luminescent molecular thermometer with a temperature uncertainty of 0.1ºC and a spatial resolution of 13 µm. This is an uncommon example in which the same material (an organic‐inorganic hybrid) that is used to fabricate a particular device (a thermal‐actuated MZ interferometer) is also used to measure one of the device intrinsic properties (the operating temperature). The photonic‐on‐a‐chip example discussed here can be applied to sense temperature gradients with high resolution (10⁻³ ºC·µm⁻¹) in chip‐scale heat engines or refrigerators, magnetic nanocontacts and energy‐harvesting machines.     

风场探测干涉仪中基准光程差的选择原理

为了确定风场成像干涉仪（Wind Imaging Interferometer,WINDII）中存在的基准光程差的值,首先从风场探测机理出发,分析了影响基准光程差的因素.针对WINDII分别从调制度、相位及相近谱线同相的要求三个方面加以剖析,依次获得了它们与基准光程差之间的定量关系.综合考虑三个条件的要求,最终得出了基准光程差的选择原理.并用此理论对几种不同的风场成像干涉仪的基准光程差值进行了验证.     

Femtosecond pulse generation using stimulated Raman scattering in integrated silicon optical waveguide device

To generate ultrafast femtosecond optical pulses, we propose a model of an integrated device consisting of a Mach-Zehnder interferometer (MZI) with two symmetric 3 dB directional couplers and a straight waveguide based on the single-mode silicon-on-insulator (SOI) optical waveguide. The principle of pulse generation in the presented device is based on the strong stimulated Raman scattering (SRS) in silicon; the center wavelength of the pulse generated is tunable by changing the center wavelength of the co-propagating pump pulse. Numerical results show that, when a continuous wave (CW) with a weak power at 1670 nm wavelength and a pump pulse with a high peak power at 1550 nm wavelength are co-propagating, a narrow femtosecond pulse with a pulse width (full width at half maximum, FWHM) of ∼60 fs (FWHM of the pump pulse is 166.5 fs) can be achieved in the device proposed. In addition, when the waveguide length, pump peak power, and pump-pulse width are fixed, the properties of generated femtosecond pulse depend strongly on the incident chirp of the pump pulse and the CW power.     

All polymer asymmetric Mach-Zehnder interferometer waveguide sensor by imprinting bonding and laser polishing

We present an all polymer asymmetric Mach–Zehnder interferometer(AMZI) waveguide sensor based on imprinting bonding and laser polishing method. The fabrication methods are compatible with high accuracy waveguide sensing structure. The rectangle waveguide structure of this sensor has three sensing surfaces contacting the test media, and its sensing accuracy can be increased 5 times compared with that of one surface sensing structure. An AMZI device structure is designed. The single mode condition, the length of the sensing arm, and the length deviation between the sensing arm and the reference arm are optimized. The length deviation is optimized to be 19.8 μm in a refractive index range between1.470 and 1.545. We fabricate the AMZI waveguide by lithography and wet etching method. The imprinting bonding and laser polishing method is proposed and investigated. The insertion loss is between-80.36 dB and-10.63 dB. The average and linear sensitivity are 768.1 d B/RIU and 548.95 dB/RIU, respectively. And the average and linear detection resolution of the sensor are 1.30×10~(-6) RIU(RIU: refractive index unit) and 1.82×10~(-5) RIU, respectively. This sensor has a fast and cost-effective fabrication process which can be used in the cases of requiring portability and disposability.     

Efficient Integrated Graphene Photonics in the Visible and Near‐IR

Graphene photonics has emerged as a promising platform for providing desirable optical functionality. However, graphene's monolayer‐scale thickness fundamentally restricts the available light matter interaction, posing a critical design challenge for integrated devices, particularly in wavelength regimes where graphene plasmonics is untenable. While several plasmonic designs have been proposed to enhance graphene light interaction in these regimes, they suffer from substantial insertion loss due to metal absorption. Here we report a non‐resonant metamaterial‐based waveguide platform to overcome the design bottleneck associated with graphene device. Such metamaterial structure enables low insertion loss even though metal is being utilized. By examining waveguide dispersion characteristics via closed‐form analysis, it is demonstrated that the metamaterial approach can provide optimized optical field that overlaps with the graphene monolayer. This enables graphene‐based integrated components with superior optical performance. Specifically, the metamaterial‐assisted graphene modulator can provide 5‐fold improvement in extinction ratio compared to Si nanowire, while reducing insertion loss by one order magnitude compared to plasmonic structures. Such a waveguide configuration thus allows one to maximize the optical potential that graphene holds in the telecom and visible regimes.     

集成马赫-曾德尔热光耦合器的可调谐振环优化设计

根据耦合模理论,推导出可调谐光波导谐振环的光强和相位传递函数的表达式,并分析了可调谐谐振环的传输特性.结果表明,谐振环中集成的马赫-曾德尔耦合器的参量设定和调谐方式直接影响谐振环的谐振频率移动范围和调制功率.通过改变耦合器参量对谐振环进行优化设计,在中心波长为1550 am附近,谐振环半径2 cm,传输损耗0.08 dB/cm的情况下,实现了清晰度和最佳谐振深度的调谐,谐振频率的移动范围低于0.027 GHz,降低了谐振环对频率调制器的调频要求,同时降低了耦合器的调制功率.     

Design and Simulation of Broadband Beam Splitter on a Silicon Nitride Platform for Optical Coherence Tomography

ABSTRACT

Integrated photonics enables the miniaturization of bulk optical components for biosensing applications such as optical coherence tomography (OCT) and is therefore promising for future lab-on-chip solutions. Here, we report the design and simulation of a compact low loss broadband beam splitter with arbitrary coupling ratios on silicon nitride platform for OCT systems. The reported coupler uses asymmetric waveguide-based phase control section for 10:90, 20:80, 30:70, 40:60, and 50:50 splitting ratios and is broadband over 100 nm with the central wavelength of 850 nm. The couplers are realized for transverse electric, transverse magnetic, and fully vectorial modes, and maximum excess loss for all mode types is reported to be less than 0.19 dB. The design tolerance of waveguide width and thickness of the designed coupler is further calculated and is within fabrication limit.     

Model of a Rectangular Waveguide Laser Resonator with Mirrors of Arbitrary Radius of Curvature

The authors developed a multimode model of a rectangular waveguide laser resonator with mirrors of arbitrary radius of curvature; this model makes it possible to take into account the influence of intracavity elements and the quality of the electrode surface on the optical loss of normal modes in the system. Results of calculation within the framework of the model developed are in good agreement with the data of measurements of the optical loss carried out using a scanning interferometer of the middle IR range.     

Finite element analysis of optically controlled non-linear directional coupler switches

Optically controlled two-way optical switches are useful for high-speed photonic switches and rapidly reconfigurable optical interconnection networks. A directional coupler forms such a switch because the field can be switched from one waveguide to the other by altering the optical length of the waveguide. Nonlinear materials are incorporated in the waveguide so that the optical path length may be altered by using an optical control beam to vary the intensity of light. A finite element method is described that enables the modelling of the non-linear dual waveguide structure for arbitrary waveguide shapes. Spurious modes are avoided in the transverse magnetic field method and non-linearity is handled by iteration and assuming an equivalent non-linear relative permittivity.     

多模干涉马赫曾德尔光开关模型

根据N×N多模干涉耦合器的基本原理 ,确定了多模干涉耦合器的结构参数。通过分析多模干涉耦合器的输入光场与其映像间的相位关系 ,提出了模传输矩阵的分析方法 ,并用此方法分析了N×N普通干涉多模干涉耦合器、N×N相移器以及N×N普通干涉多模干涉马赫 曾德尔光开关 ,得到了它们的模场传输方程 ,分析了光开关在光场从任一输入端输入 ,从任一输出端输出时开关的驱动条件。用上面的方法分析了 4× 4光开关的结构及驱动条件     

Theoretical Design of a Pump‐Free Ultrahigh Efficiency All‐Optical Switching Based on a Defect Ring Optical Waveguide Network

A theoretical design of a defect ring optical waveguide network is proposed to construct a pump‐free ultrahigh efficiency all‐optical switch. This switch creates ultrastrong photonic localization and causes the nonlinear dielectric in the defect waveguide to intensely respond. At its ON state, this material defect without Kerr response helps to produce a pair of sharp pass bands in the transmission spectrum to form the dual channel of the all‐optical switch. When it is switched to its OFF state, the strong Kerr response induced refractive index change in the high nonlinear defect waveguide strongly alters the spectrum, leading to a collapse of the dual channels. Network equation and generalized eigenfunction method are used to numerically calculate the optical properties of the switch and obtain a threshold control energy of about 2.90 zJ, which is eight orders of magnitude lower than previously reported. The switching efficiency/transmission ratio exceeds 3× 10¹¹, which is six orders of magnitude larger than previously reported. The state transition time is nearly 108 fs, which is approximately two orders of magnitude faster than the previously reported shortest time. Furthermore, the switch size can be much smaller than 2.6 µm and will be suitable for integration.     

Internal Reflection Spectroscopy

Abstract

This review‐type article deals with small, stable, compact, inexpensive, and low‐resolution interferometers mainly based on continuous or back and forth rotational motion to create the optical path difference. These interferometers are suitable for low‐resolution Fourier Transform Infrared (FTIR) spectroscopy. The paper introduces the most typical interferometers illustrated with figures. For example, interferometers with retroreflectors such as corner cubes are presented. This work aims at developing a tilt compensated optical design where the optical path difference of the interferometer will be achieved with rotational scanning. The most important property of this optical design is large mechanical tolerances to make manufacturing easy and inexpensive. New interferometers based on rotational motion are described. The mechanical angle tolerances of these interferometers can be up to three orders of magnitude larger than the angle tolerances in commonly used corner cubes.     

Polarization compensation: a passive approach to a reducing heterodyne interferometer nonlinearity

Cyclic errors that are due to optical leakage limit the precision of displacement measurements made with optical interferometers. A method for real-time estimation of leakage components is introduced and is used to implement a novel passive technique for suppression of cyclic nonlinearities that uses only adjustments of existing polarizers and quarter-wave plates. This approach is used to reduce the cyclic error from 3 nm to 300 pm for an interferometer operating at a wavelength of 1320 nm.     

Interferometric precision measurements with Bose–Einstein condensate solitons formed by an optical lattice

We propose the precision measurement of both angular rotation and of the gradient magnetic of a field based on the use of matter wave interferometers with soliton states of a Bose-Einstein condensate (BEC). We consider the formation of these soliton states in a BEC with negative scattering length by an optical lattice produced by two counterpropagating laser beams. We determine the parameters of both the initial condensate and the optical radiation necessary for the formation of coherent solitons. We demonstrate that this interferometer can be used to measure magnetic field gradient with a precision of 10^-2 pT/cm. Our calculations show that the sensitivity of a gyroscope based on a ring, two-port matter wave interferometer can achieve 2.6×10^-7 rad s^-1. The precision of this method is more than ten times greater than in that of rotating interferometer with cooled atoms.     

Integrated waveguide sensor utilizing organic photodiodes

We present a novel optical sensor platform, combining monolithically integrated ring‐like sensor waveguides together with ring‐shaped thin‐film organic photodiodes (OPDs) on one substrate. The OPDs serve as integrated light detectors, simplifying the detection system by minimizing the number of required optical components. The waveguide structures, including a means of coupling light in and out of the waveguides, serve as sensing elements. The functionality of the concept is demonstrated by an integrated carbon dioxide sensor, utilizing absorbance as sensing principle. The integrated optical sensor platform is suitable for the parallel detection of multiple parameters in a single sensor chip using sensor arrays. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Development of a Fourier-transform waveguide spectrometer for space applications

We describe the development of a waveguide Fourier-transform spectrometer for space-borne high-resolution sensing. A prototype device is designed to monitor the water vapor absorption band near 1,364?nm with a resolution of 0.05?nm. It has no moving parts and is based on a unique concept of arrayed interferometers implemented in silicon-on-insulator planar waveguide chip. The optical input is formed by many independent waveguides, providing a significantly increased light gathering capability (étendue) compared to single-waveguide input configurations. Enhancements of the spectrometer capabilities are achieved by stacking planar waveguide layers and by using surface gratings to couple light into the waveguides.     

Three‐dimensional ultra‐broadband integrated tapered mode multiplexers

The demonstration of a three‐dimensional tapered mode‐selective coupler in a photonic chip is reported. This waveguide‐based, ultra‐broadband mode multiplexer was fabricated using the femtosecond laser direct‐write technique in a boro‐aluminosilicate glass chip. A three‐core coupler has been shown to enable the multiplexing of the LP₀₁, LP and LP spatial modes of a multimode waveguide, across an extremely wide bandwidth exceeding 400 nm, with low loss, high mode extinction ratios and negligible mode crosstalk. Linear cascades of such devices on a single photonic chip have the potential to become a definitive technology in the realization of broadband mode‐division multiplexing for increasing optical fiber capacity.     

Investigation of a UV-laser generated waveguide in a planar polymer chip using an improved interferometric method

Polymeric integrated-optical waveguides are prepared in a planar polymer chip by UV-laser lithographic methods. The waveguide samples are irradiated by an excimer laser at a wavelength Λ=248 nm with various irradiation parameters (different fluencies and irradiation doses). Mach-Zehnder interferometer is employed and the refractive index depth profiles of the waveguide samples are obtained. This profile covers two regions having exponential and Gaussian shapes. The model field distributions strongly depend on the refractive index of each region. The mode field distribution and the effective mode indices for each region have been calculated on the basis of a theoretical model and the experimentally measured data.