Output mode characteristics of an in-phase locked gain waveguide array CO_2 laser

In this paper, experimental and theoretical studies of the output mode characteristics of an in-phase locked gain waveguide array CO2 laser are reported. The experimental results of the optical oscillation mode frequency, the far-field intensity distribution and the burnt pattern of the sliced waveguide array laser are obtained. A revised mode expression of the rectangle waveguide, which is suited for this waveguide array CO2 laser, is proposed. The theoretical simulation results based on the revised mode expression are shown to be in good agreement with the experimental results.

Subwavelength self-imaging in cascaded waveguide arrays

Self-imaging is an important function for signal transport,distribution,and processing in integrated optics,which is usually implemented by multimode interference or diffractive imaging process.However,these processes suffer from the resolution limit due to classical wave propagation dynamics.We propose and demonstrate subwavelength optical imaging in one-dimensional silicon waveguide arrays,which is implemented by cascading straight and curved waveguides in sequence.The coupling coefficient between the curved waveguides is tuned to be negative to reach a negative dispersion,which is an analog to a hyperbolic metamaterial with a negative refractive index.Therefore,it endows the waveguide array with a superlens function as it is connected with a traditional straight waveguide array with positive dispersion.With a judiciously engineered cascading silicon waveguide array,we successfully show the subwavelength self-imaging process of each input port of the waveguide array as the single point source.Our approach provides a strategy for dealing with optical signals at the subwavelength scale and indicates functional designs in high-density waveguide integrations.

General coupled-mode analysis of a geometrically symmetric waveguide array with nonuniform gain and loss

The exceptional point(EP)is one of the typical properties of parity–time-symmetric systems,arising from modes coupling with identical resonant frequencies or propagation constants in optics.Here we show that in addition to two different modes coupling,a nonuniform distribution of gain and loss leads to an offset from the original propagation constants,including both real and imaginary parts,resulting in the absence of EP.These behaviors are examined by the general coupled-mode theory from the first principle of the Maxwell equations,which yields results that are more accurate than those from the classical coupled-mode theory.Numerical verification via the finite element method is provided.In the end,we present an approach to achieve lossless propagation in a geometrically symmetric waveguide array.

Floquet spectrum and optical behaviors in dynamic Su–Schrieffer–Heeger modeled waveguide array

Floquet topological insulators(FTIs) have been used to study the topological features of a dynamic quantum system within the band structure. However, it is difficult to directly observe the dynamic modulation of band structures in FTIs. Here, we implement the dynamic Su–Schrieffer–Heeger model in periodically curved waveguides to explore new behaviors in FTIs using light field evolutions. Changing the driving frequency produces near-field evolutions of light in the high-frequency curved waveguide array that are equivalent to the behaviors in straight arrays. Furthermore, at modest driving frequencies,the field evolutions in the system show boundary propagation, which are related to topological edge modes. Finally, we believe curved waveguides enable profound possibilities for the further development of Floquet engineering in periodically driven systems, which ranges from condensed matter physics to photonics.

Ultra-wideband low radar cross-section metasurface and its application on waveguide slot antenna array

A novel approach devoted to achieving ultra-wideband radar cross section reduction（RCSR） of a waveguide slot antenna array（WGSAA） while maintaining its radiation performance is proposed. Three kinds of artificial magnetic conductors（AMCs） tiles consisting of three types of basic units resonant at different frequencies are designed and arranged in a novel quadruple-triangle-type configuration to create a composite planar metasurface. The proposed metasurface is characterized by low radar feature over an ultra-wideband based on the principle of phase cancellation. Both simulated and measured results demonstrate that after the composite metasurface is used to cover part of the antenna array, an ultrawideband RCSR involving in-band and out-of-band is achieved for co-and cross-polarized incident waves based on energy cancellation, while the radiation performance is well retained. The proposed method is simple, low-cost, and easy-tofabricate, providing a new method for ultra-wideband RCSR of an antenna array. Moreover, the method proposed in this paper can easily be applied to other antenna architectures.

Design and fabrication of multi-channel photodetector array monolithic with arrayed waveguide grating

We have provided optical simulations of the evanescently coupled waveguide photodiodes integrated with a 13- channels AWGs. The photodiode could exhibit high internal efficiency by appropriate choice of layers geometry and refrac- tive index. Aseamless joint structure has been designed and fabricated for integrating the output waveguides of AWGs with the evanescently coupled waveguide photodiode array. The highest simulation quantum efficiency could achieve 92% when the matching layer thickfiess of the PD is 120 nm and the insertion length is 2 μm. The fabricated PD with 320-nm-thick match.ing layer and 2-μm-length insertion matching layer present a responsivity of 0.87 A/W.

Novel wavelength-accurate InP-based arrayed waveguide grating

A 13-channel, InP-based arrayed waveguide grating （AWG） is designed and fabricated in which the on-chip loss of the central channel is about -5 dB and the crosstalk is less than -23 dB in the center of the spectrum response. However, the central wavelength and channel spacing are deviated from the design values. To improve their accuracy, an optimized design is adopted to compensate the process error. As a result, the central wavelength 1549.9 nm and channel spacing 1.59 nm are obtained in the experiment, while their design values are 1549.32 nm and 1.6 nm, respectively. The route capability and thermo-optic characteristic of the AWG are also discussed in detail.

A 32-channel 100 GHz wavelength division multiplexer by interleaving two silicon arrayed waveguide gratings

A 32-channel wavelength division multiplexer with 100 GHz spacing is designed and fabricated by interleaving two silicon arrayed waveguide gratings(AWGs).It has a parallel structure consisting of two silicon 16-channel AWGs with200 GHz spacing and a Mach-Zehnder interferometer(MZI)with 200 GHz free spectral range.The 16 channels of one silicon AWG are interleaved with those of the other AWG in spectrum,but with an identical spacing of 200 GHz.For the composed wavelength division multiplexer,the experiment results reveal 32 wavelength channels in C-band,a wavelength spacing of 100 GHz,and a channel crosstalk lower than-15 dB.

Design and Fabrication of a 400 GHz InP-Based Arrayed Waveguide Grating with Flattened Spectral Response

A four-channel 400 GHz channel spacing InP-based arrayed waveguide grating with a flattened wavelength re- sponse by employing a multimode interference coupler at the input waveguide of the filter is prepared. The fabricated devices show a flattened spectral response with a broadened 3-dB bandwidth up to 3.5 nm, interchan- nel non-uniformity of 〈0. 7dB and excellent match to the simulation results.

An Array Consisting of 10 High-Speed Side-Illuminated Evanescently Coupled Waveguide Photodetectors Each with a Bandwidth of 20 GHz

We design and fabricate a parallel system with 10 high speed side-illuminated evanescently coupled waveguide photodetectors （ECPDs）. The 10 ECPDs exhibit a uniform 3dB bandwidth of 20 GHz and low dark current of about i nA at 2 V reverse bias. The 10 ECPDs also exhibit uniform photo-responsivity of about 0.23A/W with an active region of 5 × 25μmS. The photodetector array has a total bandwidth of more than 200 GHz and can be integrated with other optoelectronic devices.

Progress and realization platforms of dynamic topological photonics

Dynamic topological photonics is a novel research field, combining the time-domain optics and topological physics.In this review, the recent progress and realization platforms of dynamic topological photonics have been well introduced.The definition, measurement methods and the evolution process of the dynamic topological photonics are demonstrated to better understand the physical diagram. This review is meant to bring the readers a different perspective on topological photonics, grasp the advanced progress of dynamic topology, and inspire ideas about future prospects.

Ultralow cross talk arrayed waveguide grating integrated with tunable microring filter array

The silicon-based arrayed waveguide grating(AWG)is widely used due to its compact footprint and its compatibility with the mature CMOS process.However,except for AWGs with ridged waveguides of a few micrometers of cross section,any small process error will cause a large phase deviation in other AWGs,resulting in an increasing cross talk.In this paper,an ultralow cross talk AWG via a tunable microring resonator(MRR)filter is demonstrated on the SOI platform.The measured insertion loss and minimum adjacent cross talk of the designed AWG are approximately 3.2 and-45.1 d B,respectively.Compared with conventional AWG,its cross talk is greatly reduced.

Electromagnetic coupling reduction in dual-band microstrip antenna array using ultra-compact single-negative electric metamaterials for MIMO application

In this paper, an ultra-compact single negative（SNG） electric waveguided metamaterial（WG-MTM） is first investigated and used to reduce the mutual coupling in E ＆ H planes of a dual-band microstrip antenna array. The proposed SNG electric WG-MTM unit cell is designed by etching two different symmetrical spiral lines on the ground, and has two stopbands operating at 1.86 GHz and 2.40 GHz. The circuit size is very compact, which is only λ_0/33.6 ×λ_0/15.1（where λ_0 is the wavelength at 1.86 GHz in free space）. Taking advantage of the dual-stopband property of the proposed SNG electric WG-MTM, a dual-band microstrip antenna array operating at 1.86 GHz and 2.40 GHz with very low mutual coupling is designed by embedding a cross shaped array of the proposed SNG electric WG-MTM. The measured and simulated results of the designed dual-band antenna array are in good agreement with each other, indicating that the mutual coupling of the fabricated dual-band antenna array realizes 9.8/11.1 d B reductions in the H plane, 8.5/7.9 d B reductions in the E plane at1.86 GHz and 2.40 GHz, respectively. Besides, the distance of the antenna elements in the array is only 0.35 λ_0（where λ_0 is the wavelength at 1.86 GHz in free space）. The proposed strategy is used for the first time to reduce the mutual coupling in E ＆ H planes of the dual-band microstrip antenna array by using ultra-compact SNG electric WG-MTM.

Design and Fabrication of Polymer Arrayed Waveguide Grating

In this paper, based on the principle of Arrayed Waveguide Grating (AWG)theory, some important parameters are optimized for polymer AWG around the central wavelength of1.55μm with the wavelength spacing of 1.6 nm. Then, a 9 X 9 polymer AWG is designed and thefabricating process are described . The cladding material is poly-methyl-methacrylate-co-glyciclylmethacrylate (PMMA-GMA) and the core material is the mixture of PMMA-GMA and bis-phonel-A epoxy. Inorder to obtain a better shape of the waveguide after the Reactive Ion Etching (RIE) using oxygen,an aluminum mask is used on polymer instead of conventional photoresist as mask in the fabricationprocess. The measuring results indicate that the fabricated optical waveguide achieves single-modetransmission.

Characterization of Birefringence and Dispersion Properties in an Arrayed Waveguide Grating

We have characterized polarization dependent loss(PDL), differential group delay(DGD), and chromatic dispersion of an AWG and a simple method was proposed to estimate the chromatic dispersion from the measured DGD of the device.

Analysis of fabrication results for 17×17 polymer arrayed waveguide grating multiplexers with flat spectral responses

Based on transmission theory, a 17 x 17 polymer arrayed waveguide grating （AWG） multiplexer para meter optimization is performed, and the influence of the fabrication results on the transmission characteristics are analyzed. In this paper, we mainly discuss three of the main errors in the fabrication of polymer AWG devices. One is 3n 1, which is caused by the tuning of the core refractive index n 1, the second is 8b, which results from the rotating-coating of the core thickness b, and the other is the non-ideal core cross-section, which is caused by steam redissolution. The effects of the above fabrication errors on the transmission characteristics of the AWG device are investigated, and compensation techniques are proposed. By comparing the theoretical simulation and experimental results, the shift in the transmission spectrum is reduced by 0.028 nm, the 3 dB bandwidth is increased by about 0.036 nm, the insertion loss is reduced by about 3 dB for the central channel and 4.5 dB for the edge channels, and the crosstalk is reduced by 1.5 dB.

16 channel 200 GHz arrayed waveguide grating based on Si nanowire waveguides

A 16 channel arrayed waveguide grating demultiplexer with 200 GHz channel spacing based on Si nanowire waveguides is designed. The transmission spectra response simulated by transmission function method shows that the device has channel spacing of 1.6 nm and crosstalk of 31 dB. The device is fabricated by 193 nm deep UV lithography in silicon-on-substrate. The demultiplexing characteristics are observed with crosstalk of 5-8 dB, central channel＇s insertion loss of 2.2 dB, flee spectral range of 24.7 nm and average channel spacing of 1.475 nm. The cause of the spectral distortion is analyzed specifically.

Array Waveguide Grating Based Fiber Lasers

Two array waveguide grating (AWGs) based fiber ring lasers are experimentally demonstrated. Either of them achieves wavelength discrete tuning of 32 nm, or yields simultaneously lasing up to four channels with -7 dBm output power for each channel.

Fabrication of 17×17 polymer/Si arrayed waveguide grating with flat spectral response using steam-redissolution technique

Arrayed waveguide grating（AWG） is a key device in the wavelength-division multiplexing（WDM） system, and the flat spectral response of the AWG device is required.In this paper,the RIE process has been improved.By using the steam-redissolution technique,the insertion loss and the crosstalk have been reduced.Experimental results show that the central wavelength is 1550.86 nm,the channel spectral response flatness is about 1.5 dB,3-dB bandwidth is about 0.478 nm,insertion loss is 10.5 dB,and crosstalk is about-22 dB.The insertion loss of an AWG device is reduced by about 3 dB for the central channel and 4.5 dB for the edge channels,and the crosstalk is reduced by 2.5 dB after the steam-redissolution.

16-channel dual-tuning wavelength division multiplexer/demultiplexer

A 16-channel dual tuning wavelength division multiplexer/demultiplexer based on silicon on insulator platform is demonstrated, which is both peak wavelength tunable and output optical power tunable. The wavelength division multiplexer/demultiplexer consists of an arrayed waveguide grating for wavelength division multiplexing/demultiplexing, a heater for peak wavelength tuning and a variable optical attenuator based on p–i–n carrier-injection structure for optical power tuning. The experimental results show that the insertion loss on chip of the device is 3.7 dB–5.7 dB and the crosstalk is 7.5 dB–9 dB. For the tunability of the peak wavelength, 1.058-nm wavelength tunability is achieved with 271.2-mW power consumption, and the average modulation efficiency is 3.9244 nm/W; for the tunability of the optical power, the optical power equalization is achieved in all 16 channels, 20-dB attenuation is achieved with 144.07-mW power consumption,and the raise/fall time of VOA is 35 ns/42 ns.