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.

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.

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.

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.

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-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.

Low-Cost and Highly Sensitive Liquid Refractive Index Sensor Based on Polymer Horizontal Slot Waveguide

We analyze and explore the potential of using a polymer horizontal slot waveguide as light-analyte interactive region to implement a low-cost and highly sensitive liquid refractive index sensor.Numerical analysis shows that the optimized polymer horizontal slot waveguide is able to realize high waveguide sensitivity.With the optimized horizontal slot waveguide,polymer liquid refractive index sensors based on Mach-Zehnder interferometer(MZI)and microring resonator(MRR)are then investigated numerically,and the results show that the MZI-based sensor can achieve high sensitivity of 17024 nm/RIU and low limit of detection(LOD)of 1.76´10^(-6) RIU while the MRR-based sensor can achieve the sensitivity of 177 nm/RIU and the LOD of 1.69´10^(-4) RIU with a very small footprint.Compared with the sensors employing conventional silicon or silicon nitride vertical slot waveguide,the sensors employing polymer horizontal slot waveguide exhibit comparable performances but simpler and lower fabrication costs.

Light spectral filtering based on spatial adiabatic passage

We present the first experimental realization of a light spectral filter based on the spatial adiabatic passage technique.We demonstrate that a fully integrable CMOS-compatible system of three coupled identical total internal reflection silicon oxide waveguides with variable separation along their propagation direction can be used simultaneously as a low-and high-pass spectral filter within the visible range of wavelengths.Light is injected into the right waveguide,and after propagating along the system,long wavelengths are transferred into the left output,whereas short wavelengths propagate to the right and central outputs.The stopband reaches values up to 211 dB for the left output and approximately 220 dB for the right plus central outputs.The passband values are close to 0 dB for both cases.We also demonstrate that the filtering characteristics of the device can be controlled by modifying the parameter values,which define the geometry of the triple-waveguide system.However,the general filtering behavior of the system does not critically depend on technological variations.Thus,the spatial adiabatic passage filtering approach constitutes an alternative to other integrated filtering devices,such as interference or absorbance-based filters.

Human-like stereo sensors using plasmonic antenna embedded MZI with space–time modulation control[Invited]

A micro stereo sensor system is proposed for human sensors,where eyes,ears,tongue,nose,body,and brain are applied by six panda rings embedded in a Mach–Zehnder interferometer(MZI).The input power is applied to the upper branch of MZI and propagates within the system.The six antennas(sensors)are formed by the whispering gallery modes of the panda rings.The space–time modulation signal is applied to the MZI lower branch.The modulated stereo signals can be configured as the plasmon(electron)spin orientations,which can be identified and applied for quantum codes and quantum consciousness.