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.

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.

An Open Rectangular Waveguide Grating for Millimeter-Wave Traveling-Wave Tubes

Millimeter-wave traveling-wave tube （TWT） prevails nowadays as the amplifier for radar, communication and electronic countermeasures. The rectangular waveguide grating is a promising all-metal interaction circuit for the millimeter-wave TWT with advantages of high power capacity, fine heat dissipation, scalability to smaller dimen- sions for shorter wavelengths, compact structure and robust performance. Compared with the traditional closed structure, the open rectangular waveguide grating （ORWG） has wider bandwidth, lower cut-off frequency, and higher machining precision for higher working frequencies due to the open transverse. It is a potential structure that can work in the millimeter wave and even Terahertz band. The rf characteristics including dispersion and interaction impedance are investigated by both theoretic calculation and software simulation. The influences of the structure parameters are also discussed and compared, and the theoretical results agree well with the simula- tion results. Based on the study, the ORWG will favor the design of a broadband and high-power millimeter-wave TWT.

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.

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.

Study on the adaptability of augmented reality smartglasses for astigmatism based on holographic waveguide grating

Background Augmen ted reality(AR)smartglasses are considered as the next generation of smart devices to replace mobile phones,and are widely concerned.But at present,AR smartglasses are usually designed according to the human normal eyes.In order to experience AR smartglasses perfectly,abnormal eye users must first wear diopters.Methods For people with astigmatism to use AR smartglasses without wearing a diopter lens,a cylindrical lens waveguide grating is designed in this study based on the principle of holographic waveguide grating.First,a cylindrical lens waveguide substrate is constructed for external light deflection to satisfy the users'normal viewing of the real world.Further,a variable period grating structure is established based on the cylindrical lens waveguide substrate to normally emit the light from the virtual world in the optical machine to the human eyes.Finally,the structural parameters of grating are optimized to improve the diffraction efficiency.Results The results show that the structure of cylindrical lens waveguide grating allows people with astigmatism to wear AR smartglasses directly.The total light utilization rate reaches 90%with excellent imaging uniformity.The brightness difference is less than 0.92%and the vertical field of view is 10°.Conclusions This research serves as a guide for AR product designs for people with long/short sightedness and promotes the development of such products.

Tunable wavelength filters using polymer long-period waveguide gratings based on metal-cladding directly defined technique

In this work, long-period waveguide grating-based tunable wavelength filters using organic–inorganic grafting poly（methyl methacrylate）（PMMA） materials are designed and fabricated by metal-cladding directly defined technique.The thermal stabilities and optical properties of the organic–inorganic grafting PMMA core materials are analyzed. Structures and performance parameters of the waveguide gratings and self-electrode heaters are designed and simulated. The contrast of the filter is about 15 d B and the resonant wavelength can be tuned by different electric powers applied to the metal-cladding self-electrode heaters. The temperature sensitivity is 3.5 nm/℃ and the switching time is about 1 ms. The technique is very suitable for realizing the optoelectronic integrated wavelength-division-multiplexing systems.

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.

Waveguide Bragg Grating for Fault Localization in PON

Femtosecond laser direct inscription is a technique especially useful for prototyping purposes due to its distinctive advantages such as high fabrication accuracy,true 3D processing flexibility,and no need for mold or photomask.In this paper,we demonstrate the design and fabrication of a planar lightwave circuit(PLC)power splitter encoded with waveguide Bragg gratings(WBG)using a femtosecond laser inscription technique for passive optical network(PON)fault localization application.Both the reflected wavelengths and intervals of WBGs can be conveniently tuned.In the experiment,we succeeded in directly inscribing WBGs in 1×4 PLC splitter chips with a wavelength interval of about 4 nm and an adjustable reflectivity of up to 70% in the C-band.The proposed method is suitable for the prototyping of a PLC splitter encoded with WBG for PON fault localization applications.

On-chip digitally tunable positive/negative dispersion controller using bidirectional chirped multimode waveguide gratings

A silicon-based digitally tunable positive/negative dispersion controller(DC)is proposed and realized for the first time using the cascaded bidirectional chirped multimode waveguide gratings(CMWGs),achieving positive and negative dispersion by switching the light propagation direction.A 1×2 Mach-Zehnder switch(MZS)and a 2×1 MZS are placed before and after to route the light path for realizing positive/negative switching.The device has Q stages of identical bidirectional CMWGs with a binary sequence.Thus the digital tuning is convenient and scalable,and the total dispersion accumulated by all the stages can be tuned digitally from−(2^(Q)−1)D0 to(2^(Q)−1)D_(0) with a step of D_(0) by controlling the switching states of all 2×2 MZSs,where D_(0) is the dispersion provided by a single bidirectional CMWG unit.Finally,a digitally tunable positive/negative DC with Q=4 is designed and fabricated.These CMWGs are designed with a 4-mm-long grating section,enabling the dispersion D_(0) of about 4.16 ps∕nm in a 20-nm-wide bandwidth.The dispersion is tuned from−61.53 to 63.77 ps∕nm by switching all MZSs appropriately,and the corresponding group delay is varied from−1021 to 1037 ps.

Study of the double rectangular waveguide grating slow-wave structure

A slow-wave structure （SWS） with two opposite gratings inside a rectangular waveguide is presented and analysed. As an all-metal slow-wave circuit, this structure is especially suited for use in millimetre-wave travelling wave tubes （TWTs） due to its advantages of large size, high manufacturing precision and good heat dissipation. The first part of this paper concerns the wave properties of this structure in vacuum. The influence of the geometrical dimensions on dispersion characteristics and coupling impedance is investigated. The theoretical results show that this structure has a very strong dispersion and the coupling impedance for the fundamental wave is several tens of ohms, but the coupling impedance for -1 space harmonic wave is much lower than that for the fundamental wave, so the risk of backward wave oscillation is reduced. Besides these, the CST microwave studio is also used to simulate the dispersion property of the SWS. The simulation results from CST and the theoretical results agree well with each other, which supports the theory. In the second part, a small-signal analysis of a double rectangular waveguide grating TWT is presented. The typical small-signal gain per period is about 0.45 dB, and the 3-dB small-signal gain bandwidth is only 4%.

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.

Tunable Filters Based on Cascaded Long-Period Polymer Waveguide Gratings

Long-period waveguide grating based filters have attracted attention due to their flexible fabrication,a variety of materials and structures,low back reflection,low insertion loss,and excellent performance in the tuning range and temperature sensitivity.To our knowledge,for the first time,a two-segment polymer long-period waveguide grating was cascaded to implement a filter with a narrower bandwidth.Experimental results showed that the device had a maximum extinction ratio of 24 dB at 1577 nm,and the 12 dB bandwidth was 10 nm.The temperature sensitivity of the fabricated device was 1.79 nm/℃.

PDL Reduction in Arrayed-Waveguide Gratings by Control of Stress in the Waveguide

We have demonstrated polarization insensitive AWGs by controlling the doping concentration of Boron in overcladding and the etching depth of waveguide. The proposed method uses the conventional fabrication process and does not degrade optical properties and reliability characteristics.

Low-crosstalk silicon photonics arrayed waveguide grating

In this Letter,we demonstrate a 1×4 low-crosstalk silicon photonics cascaded arrayed waveguide grating,which is fabricated on a silicon-on-insulator wafer with a 220-nm-thick top silicon layer and a 2μm buried oxide layer.The measured on-chip transmission loss of this cascaded arrayed waveguide grating is～4.0 dB,and the fiber-towaveguide coupling loss is 1.8 dB/facet.The measured channel spacing is 6.4 nm.The adjacent crosstalk by characterization is very low,only -33.2 dB.Compared to the normal single silicon photonics arrayed waveguide grating with a crosstalk of ～-12.5 dB,the crosstalk of more than 20 dB is dramatically improved in this cascaded device.