S-type Er-Yb Co-doped Phosphate Glass Waveguide Amplifier Integrated with Cascaded Multilayer Medium Thin Film Filter

A new S-type of erbium-ytterbium co-doped phosphate glass waveguide amplifier integrated with cascaded multilayer medium thin film filter is proposed,this S-type geometry waveguide structure is used to achieve a long path in a compact chip,and obtained higher gain with lower Er-doped concentration. The cascaded multilayer medium thin film filter is utilized to achieve a broader flattening gain bandwidth.The intrinsical gain spectrum is obtained by solving rate and power propagation equations,the effect of transmittance spectrum of thin film filter on flattening gain is discussed.

Tunable optical filter using second-order micro-ring resonator

In this paper, we design and fabricate a silicon integrated optical filter consisting of two cascaded micro-ring resonators and two straight waveguides. Two micro-heaters are fabricated on the top of two micro-rings respectively, which are employed to modulate the micro-rings to perform the function of a tunable optical filter by the thermo–optic effect. The static response test indicates that the extinction ratio and 3-d B bandwidth are 29.01 d B and 0.21 nm respectively, the dynamic response test indicates that the 10%–90% rise and 90%–10% fall time of the filter are 16 μs and 12 μs, respectively,which can meet the requirements of optical communication and information processing. Finally, the power consumption of the device is also characterized, and the total power consumption is about 9.43 m W/nm, which has been improved efficiently.

Integrated nano-structured silicon waveguides and devices for high-speed optical communications

With progress in fabrication technology, integrated photonics plays an increasingly important role in high-speed optical communications, from monolithic transmitters and receivers for advanced optical modulation formats to on-chip subsystems for optical signal processing. We review our recent work on the highly tailorable physical properties of silicon waveguides for communication and signal processing applications, using slot structures. Controllable chromatic dispersion, nonlinearity, and polarization properties of the waveguides are presented, and the enabled wideband wavelength conversion, optical tunable delay, and signal processing of polarization-multiplexing data channels are discussed.

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 between 1.470 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 dB/RIU and 548.95 dB/RIU, respectively. And the average and linear detection resolution of the sensor are 1.3010-6 RIU （RIU：refractive index unit） and 1.8210-5 RIU, respectively. This sensor has a fast and cost-effective fabrication process which can be used in the cases of requiring portability and disposability.

Compact TE-pass polarizer based on lithium-niobate-on-insulator assisted by indium tin oxide and silicon nitride

An indium tin oxide(ITO) and silicon nitride(Si_(3)N_(4)) assisted compact TE-pass waveguide polarizer based on lithiumniobate-on-insulator is proposed and numerically analyzed.By properly designing the ITO and Si_(3)N_(4) assisted structure and utilizing the epsilon-near-zero effect of ITO,the TM mode is strongly confined in the ITO layer with extremely high loss,while the TE mode is hardly affected and passes through the waveguide with low loss.The simulation results show that the polarizer has an extinction ratio of 22.5 dB and an insertion loss of 0.8 dB at the wavelength of 1.55 μm,and has an operating bandwidth of about 125 nm(from 1540 nm to 1665 nm) for an extinction ratio of>20 dB and an insertion loss of<0.95 dB.Moreover,the proposed device exhibits large fabrication tolerances.More notably,the device is compact,with a length of only 7.5 μm,and is appropriate for on-chip applications.

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.

Monolithic DWDM source with precise channel spacing

We report a low-cost manufacturing approach for fabricating monolithic multi-wavelength sources for dense wavelength division multiplexing(DWDM)systems that offers high yield and eliminates crystal regrowth and selective area epitaxy steps that are essential in traditional fabrication methods.The source integrates an array of distributed feedback(DFB)lasers with a passive coupler and semiconductor optical amplifier(SOA).Ridge waveguide lasers with sampled Bragg side wall gratings have been integrated using quantum well intermixing to achieve a fully functional four-channel DWDM source with 0.8 nm wavelength spacing and residual errors<0.13 nm.The output power from the SOA is>10 mW per channel making the source suitable for use in passive optical networks(PONs).We have also investigated using multisection phase-shifted sampled gratings to both increase the effective grating coupling coefficient and precisely control the channel lasing wavelength spacing.An 8-channel DFB laser array with 100 GHz channel spacing was demonstrated using a sampled grating with twoπ-phase-shifted sections in each sampling period.The entire array was fabricated by only a single step of electron beam lithography.

Cross-cascaded AWG-based wavelength selective switching integrated module using polymer optical waveguide circuits

100-GHz cross-cascaded arrayed waveguide gratings （AWGs）-based wavelength selective optical switching optical cross-connects （OXCs） modules with Mach-Zehnder interferometer （MZI） thermo-optic （TO） variable optical attenuator （VOA） arrays and optical true- time-delay （TTD） line arrays is successfully designed and fabricated using polymer photonic lightwave circuit. Highly fluorinated photopolymer and grafting modified organic-inorganic hybrid material were synthesized as the waveguide core and cladding, respectively. The one-chip transmission loss is -6 dB and the crosstalk is less than -30 dB for the transverse-magnetic （TM） mode. The actual maximum modulation depths of different thermo-optic switches are similar, -15.5 dB with 1.9 V bias. The maximum power consumption of a single switch is less than 10 mW. The delay time basic increments are measured from 140 to 20 ps. Proposed novel module is flexible and scalable for the dense wavelength division multiplexing network.

Integrated thin film lithium niobate Fabry–Perot modulator[Invited]

Integrated traveling-wave lithium niobate modulators need relatively large device lengths to achieve low drive voltage. To increase modulation efficiency within a compact footprint, we report an integrated Fabry–Perot-type electro-optic thin film lithium niobate on insulator modulator comprising a phase modulation region sandwiched between two distributed Bragg reflectors. The device exhibits low optical loss and a high tuning efficiency of 15.7 pm/V. We also confirm the modulator's high-speed modulation performance by non-return-to-zero modulation with a data rate up to 56 Gbit/s.

Highly efficient tunable optical filter based on liquid crystal micro-ring resonator with large free spectral range

A highly efficient tunable optical filter of liquid crystal （LC） optical micro-r/rig resonator （MRR） was proposed. The 4-pro-radius ring consists of a silicon-on- insulator （SOI） asymmetric bent slot waveguide with a LC cladding. The geometry of the slot waveguide resulted in the strong electro-optic effect of the LC, and therefore induced an increase in effective refractive index by 0.0720 for the quasi-TE mode light in the slot-waveguide. The ultra-wide tuning range （56.0 nm） and large free spectral range （FSR） （-28.0nm） of the optical filters enabled wavelength reconfigurable multiplexing devices with a drive voltage of only 5 V. The influences of parameters, such as the slot width, total width of Si rails and slot shift on the device＇s performance, were analyzed and the optimal design was given. Moreover, the influence of fabrication tolerances and the loss of device were both investigated. Compared with state-of-the-art tunable MRRs, the proposed electrically tunable micro-ring resonator owns the excellent features of wider tuning ranges, larger FSRs and ultralow voltages.

Single-waveguide-based microresonators for optical sensing

Optical biosensors with a high sensitivity and a low detection limit play a highly significant role in extensive scenarios related to our daily life. Combined with a specific numerical simulation based on the transfer matrix and resonance condition, the idea of novel single-waveguide-based microresonators with a double-spiral-race- track （DSR） shape is proposed and their geometry optimizations and sensing characteristics are also investigated based on the Vernier effect. The devices show good sensing performances, such as a high quality factor of 1.23 x 105, a wide wavelength range of over 120 nm, a high extinction ratio （ER） over 62.1 dB, a high sensitivity of 698.5 nm/RIU, and a low detection limit of 1.8 × 10^-5. Furthermore, single-waveguide-based resonators can also be built by cascading two DSR structures in series, called twin-DSRs, and the results show that the sensing properties are enhanced in terms of quasi free spectral range （FSR） and ER due to the double Vernier effect. Excellent features indicate that our novel single-waveguide-based resonators have the potential for future compact and highly integrated biosensors.

Slotless dispersion-flattened waveguides with more than five zero-dispersion wavelengths

We propose a new type of dispersion-flattened waveguide without a slot-assisted structure that can obtain an ultra-flat group velocity dispersion profile with five or six zero-dispersion wavelengths in the mid-infrared region.The dispersion profile becomes less sensitive to the waveguide dimensions due to the absence of the slot-assisted structure,making waveguide fabrication more friendly.The dispersion profile varies between−0.472 and 0.365 ps/(nm·km)over a 2665 nm bandwidth from 2885 nm to 5550 nm with a flatness of 3183.99 nm2·km/ps.Two different combinations of materials are demonstrated for dispersion flattening of the proposed waveguide structures.We also provide design guidance for the proposed waveguide structures with other combinations of materials.

Silicon intensity Mach–Zehnder modulator for single lane 100 Gb/s applications

In this paper, a substrate removing technique in a silicon Mach–Zehnder modulator(MZM) is proposed and demonstrated to improve modulation bandwidth. Based on the novel and optimized traveling wave electrodes,the electrode transmission loss is reduced, and the electro-optical group index and 50 Ω impedance matching are improved, simultaneously. A 2 mm long substrate removed silicon MZM with the measured and extrapolated 3 dB electro-optical bandwidth of >50 GHz and 60 GHz at the-8 V bias voltage is designed and fabricated.Open optical eye diagrams of up to 90 GBaud∕s NRZ and 56 GBaud∕s four-level pulse amplitude modulation(PAM-4) are experimentally obtained without additional optical or digital compensations. Based on this silicon MZM, the performance in a short-reach transmission system is further investigated. Single-lane 112 Gb∕s and 128 Gb∕s transmissions over different distances of 1 km, 2 km, and 10 km are experimentally achieved based on this high-speed silicon MZM.

Design of a C-band polarization rotator-splitter based on a mode-evolution structure and an asymmetric directional coupler

A C-band polarization rotator-splitter based on a mode-evolution structure and an asymmetric directional coupler is proposed. The mode-evolution structure is designed in a bi-level taper through which the TM;mode can evolve into the TE;mode. Then the TE;mode is coupled to the TE;mode at the cross port using the asymmetric directional coupler. The input TE;mode propagates along the waveguide without mode conversion and output at the through port. From the experimental results, the extinction ratio is lower than 30 dB and the excess loss is less than 1 dB for input TE;mode at the whole C-band. For input TM;mode, the ER and the EL are, respectively,lower than-10 and 1.5 dB.

Ultra-compact broadband polarization beam splitter with strong expansibility

Based on the traditional directional coupler, we proposed a scheme to design on-chip polarization beam splitters using an inverse design method. In our scheme, the coupling area of the designed devices are only 0.48 μm× 6.4 μm. By manipulating the refractive index of the coupling region, the devices can work in C-band,L-band, O-band, or any other communication band. Different from conventional design methods, which need to adjust the design parameters artificially, if the initial conditions are determined, the proposed scheme can automatically adjust the design parameters of devices according to specific requirements. The simulation results show that the insertion losses of the designed polarization beam splitters can be less than 0.4 dB(0.35 dB) for TE(TM)mode at the wavelengths of 1310, 1550, and 1600 nm, and the extinction ratios are larger than 19.9 dB for the TE and TM modes at all three wavelengths. Besides, the extinction ratios of both polarization states are more than 14.5 dB within the wavelength range of 1286–1364 nm, 1497–1568 nm, and 1553–1634 nm. At the same time,the insertion losses are smaller than 0.46 dB.

Demonstration of ultralow-threshold 2 micrometer microlasers on chip

We demonstrate ultralow-threshold thulium-doped, as well as thulium-holmium-codoped, microtoroid lasers on silicon chips, operating at the wavelength of around 2 ?m. High quality factor whispering gallery mode(WGM) microtoroid cavities with proper thulium and holmium concentrations are fabricated from the silica sol-gel films. The highly confined WGMs make the microcavity lasers operate with ultralow thresholds, approximately 2.8 ?W and 2.7 ?W for the thulium-doped and the thulium-holmium-codoped microlasers, respectively.

Backcoupling manipulation in silicon ring resonators

In this paper, we theoretically propose and experimentally demonstrate the manipulation of a novel degree of freedom in ring resonators, which is the coupling from the clockwise input to the counterclockwise propagating mode （and vice versa）. We name this mechanism backcoupling, in contrast with the normal forward-coupling of a directional coupler. It is well known that internal reflections will cause previous research demonstrated that the peak asymmetry will be strongly influenced by the backcoupling. Thus, it is worth manipulating the backcoupling in order to gain full control of a split resonance for the benefit of various resonance-splitting-based applications. While it is difficult to directly manipulate the backcoupling of a conventional directional coupler, here we design a circuit explicidy for manipulating the backcoupling. It can be potentially developed for applications such as single sideband filter, resonance splitting elimination, Fano resonance, and ultrahigh-Q and finesse.

High-efficiency all-dielectric transmission metasurface for linearly polarized light in the visible region

We propose and numerically investigate an efficient transmission-mode metasurface that consists of quasi- continuous trapezoid-shaped crystalline silicon nanoantennas on a quartz substrate. This metasurface provides a linear phase gradient and realizes both full 2Jr phase shift and high transmission efficiency in the operating wavelength range from 740 to 780 nm. At the central wavelength around 751 nm, the total transmission efficiency is up to 88.0% and the section of the desired anomalous refraction is 80.4%. The anomalous refraction angle is 29.62°, and larger refraction angle can be achieved by changing the period of the super cell. We demonstrate a refraction angle as large as 38.59°, and the anomalous transmission efficiency reaches 76.6% at wavelength of 741 nm. It is worth mentioning that the structure is much simpler than conventional metasurfaces based on arrays of discrete nanoantennas. Our research may pave the way for designing efficient all-dielectric phase-gradient metasurfaces and applying them in integrated optical devices for wavefront control.

Ultra-short plasmonic polarization beam splitter-rotator using a bent directional coupler

We propose and analyze a silicon hybrid plasmonic polarization splitter-rotator with an ultra-short footprint using an asymmetric bent directional coupler on a silicon-on-insulator platform.Benefitting from the large birefringence induced by the bent structure and plasmonic effect,the cross-polarization coupling length is only 5.21μm.The transverse magnetic to transverse electric polarization conversion efficiency is over 99.9%,with an extinction ratio of 20.6 dB(32.5 dB)for the transverse magnetic(transverse electric)mode at 1.55μm.Furthermore,the polarization conversion efficiency is higher than 90%while maintaining cross talk below-19 dB within the bandwidth of 80 nm.

Single nanoparticle trapping based on on-chip nanoslotted nanobeam cavities

Optical trapping techniques are of great interest since they have the advantage of enabling the direct handling of nanoparticles. Among various optical trapping systems, photonic crystal nanobeam cavities have attracted great attention for integrated on-chip trapping and manipulation. However, optical trapping with high efficiency and low input power is still a big challenge in nanobeam cavities because most of the light energy is confined within the solid dielectric region. To this end, by incorporating a nanoslotted structure into an ultracompact one- dimensional photonic crystal nanobeam cavity structure, we design a promising on-chip device with ultralarge trapping potential depth to enhance the optical trapping characteristic of the cavity. In this work, we first provide a systematic analysis of the optical trapping force for an airborne polystyrene （PS） nanoparticle trapped in a cavity model. Then, to validate the theoretical analysis, the numerical simulation proof is demonstrated in detail by using the three-dimensional finite element method. For trapping a PS nanoparticle of 10 nm radius within the air-slot, a maximum trapping force as high as 8.28 nN/mW and a depth of trapping potential as large as 1.15 × 105 kBTmW-1 are obtained, where kB is the Boltzmann constant and T is the system temperature. We estimate a lateral trapping stiffness of 167.17 pN. nm-1 . mW-1 for a 10 nm radius PS nanoparticle along the cavity x-axis, more than two orders of magnitude higher than previously demonstrated on-chip, near field traps. Moreover, the threshold power for stable trapping as low as 0.087 μW is achieved. In addition, trapping of a single 25 nm radius PS nanoparticle causes a 0.6 nm redshift in peak wavelength. Thus, the proposed cavity device can be used to detect single nanoparticle trapping by monitoring the resonant peak wavelength shift. We believe that the architecture with features of an ultracompact footprint, high integrahility with optical waveguides/cir- cuits, and efficient trapping demonstrated here will provide a promising candidate for developing a lab-on-a-chip device with versatile functionalities.