Wavelength-Tunable Microring Resonator on Lithium Niobate

A wavelength-tunable microring resonator with integrated microheater on lithium niobate is presented. Ridge structure on lithium niobate is formed by a wet-etching technique for enhancing the lateral index contrast of the waveguide. The resonant wavelength of the microring resonator is tuned through thermooptic effect by injecting current into the integrated microheater. The tuning characteristics of through port and drop port are measured and the tuning rates in the microring resonator with a radius of 100 mum for transverse-magnetic and transverse-electric polarizations are 2.54 x 10^-2 nm/mA and 3.40 x 10^-3 nm/mA.     

Tunable Optical Add–Drop Multiplexer Based on Silicon Photonic Wire Waveguides

A wavelength tunable optical add–drop multiplexer based on silicon photonic wire waveguides with Bragg-grating-reflectors was demonstrated by tuning the dropping wavelength through thermooptic effect. A 6.6-nm dropping wavelength shift was obtained at a 0.82-W heating power. For the device that is presently polarization-dependent, the 3-dB channel-dropping bandwidth was 0.4 nm and the extinction ratio at the dropping wavelength for port THROUGH was better than 17 dB for assuming 1.6-nm wavelength spacing dense wavelength-division multiplexing. The average tuning speed was about 200$muhboxs$.     

Low-loss and high-extinction-ratio silica-based strictlynonblocking 16×16 thermooptic matrix switch

A low-loss and high-extinction-ratio silica-based 16×16 thermooptic matrix switch is demonstrated. The switch, which employs a double Mach-Zehnder interferometer switching unit and a matrix arrangement which reduces the total waveguide length, is fabricated with 0.75% refractive index difference waveguides on a 6-in silicon wafer. The average insertion loss and the average extinction ratio are 6.6 and 55 dB, respectively. The total power consumption is 17 W     

16-band integrated dynamic gain equalization filter with less than2.8-dB insertion loss

We demonstrate a low-loss 16-band dynamic gain equalization filter consisting of two perfectly sampled waveguide grating routers (WGRs) and an array of thermooptic attenuators. This integrated silica waveguide filter has <2.8-dB fiber-to-fiber insertion loss, <0.2-dB polarization-dependent loss at minimum attenuation and <0.7-dB at 10-dB extra attenuation, and <5.0-W electrical power consumption over the C-band. We also demonstrate a new technique for reducing the loss of WGRs     

Fully packaged polymeric four arrayed 2×2 digital opticalswitch

A fully packaged polymeric four arrayed 2×2 digital optical switch is fabricated. Crosslinkable fluorinated polymers with a large thermooptic coefficient and a low loss are used for a low electrical power consumption and a low insertion loss. We improve the uniformity, crosstalk, and insertion loss with introducing a rib waveguide, a channel waveguide, and a tapered waveguide in the polymeric four arrayed 2×2 digital optical switch. The deviation of crosstalks is ±2 dB at 250 mW. The crosstalks are less than -30 dB for all four 2×2 digital optical switch elements with each total electrical power of 250 mW. The fall and rise times are less than 5 ms. The polarization-dependent losses are in the range of 0.2-0.7 dB. The total insertion losses range from 3.5 to 4.0 dB     

Rearrangeable nonblocking SOI waveguide thermooptic 4/spl times/4 switch matrix with low insertion loss and fast response

A rearrangeable nonblocking 4/spl times/4 thermooptic silicon-on-insulator waveguide switch matrix at 1.55-/spl mu/m integrated spot size converters is designed and fabricated for the first time. The insertion losses and polarization-dependent losses of the four channels are less than 10 and 0.8 dB, respectively. The extinction ratios are larger than 20 dB. The response times are 4.6 /spl mu/s for rising edge and 1.9 /spl mu/s for falling edge.     

Simulation of Tunable Power Multimode Interference Couplers with Deep Rib Structure

The muhimode interference （MMI） couplers, which operate at 1. 55 microns in deep rib InGaAsP/InP waveguide with large lateral confinement and tunable power splitting ratios, are of high interest in integrated optics. The gold contacts are applied on the top of waveguides where tuning is desired and the plasma effect will lead to negative refractive index change. The three-dimensional （3D） finite difference beam propagation method（FD-BPM） is used to model the tunable MMI couplers. The length of a 2 × 2 overlap-MMI is determined by FD-BPM, so the longitudinal position of tuning spots is obtained. The position of gold contacts with two types, the edge-pads or center-pad, are also determined. In our design, the length of MMI is 180 microns. If the width of pads is 50 microns and the refractive index is tuned from 0 to -0. 027, the power ratio is tuned from 50 ： 50 to the maximum 88.5 ： 11.4. For deep rib structure, the effective index（EI） method can not be used to simplify the 3D waveguide to plane waveguide because of its lower precision, and so the direct 3D FD-BPM simulation is necessary for the design of 3D MMI couplers.     

Electrooptically wavelength-tunable polarization converter utilizing strain-optic effect on X-cut LiNbO/sub 3/

A new electrooptically wavelength-tunable polarization converter by strain-optic effect on LiNbO/sub 3/ is presented. The polarization conversion is achieved by the tilt of waveguide principal axis caused by the stress induced by the proton-exchanged region on the single side of the waveguide. Simply increasing the proton-exchange time can enlarge the stress-distributed region and its interaction with the input light, thus, the conversion efficiency can be enhanced. By electrooptic effect, the wavelength of maximum conversion can be tuned at a rate of 0.081 nm/V with a maximum conversion efficiency of 92.4%.     

Ferrite-Loaded, Circularly Polarized Microwave Cavity Filters

CircuIarly polarized cavities have made possible a group of compact, high-Q, microwave waveguide filters having useful directional properties. When these cavity filters are ferrite loaded, frequency sensitive circulators result and magnetic tuning becomes possible. This paper presents several new three- and four-port ferrite-loaded filters, some with 3-db waveguide couplers, which can be used as tunable band-pass filters, tunable band-rejection filters, or as passive, selective duplexers. As duplexers, they can be operated at a fixed frequency or can be magnetically tuned over a one to five per cent frequency range at X band depending upon the allowable loss. Experimental loss, bandwidth, isolation, and tuning data are presented. Temperature stability and power handling capacity are also discussed.     

Integration of a multimode interference coupler with a corrugated sidewall Bragg grating in planar polymer waveguides

We demonstrate the integration of a 3-dB multimode interference coupler with a corrugated sidewall Bragg grating in planar polymer waveguides by direct electron beam writing. Both transmission and reflection spectra of the Bragg grating are measured through this integrated device directly. We use the thermooptic effect to tune the integrated waveguide grating, achieving a tuning range of 6.2 nm and a bandwidth variation of 0.3 nm within a temperature change of 62/spl deg/C.     

Millimeter-wave tune-all bandpass filters

Distributed microelectromechanical varactors on a coplanar waveguide have been used to design a two- and four-pole bandpass tune-all filters. The two-pole initial bandwidth is 6.4% at 44.05 GHz with a mid-band insertion loss of 3.2 dB and with matching better than 15 dB. The four-pole initial bandwidth is 6.1% at 43.25 GHz with a mid-band insertion loss of 6.5 dB and with matching better than 10 dB. The use of microelectromechanical system bridges allows a continuous tuning for both center frequency and bandwidth. The varactors biasing network has been designed so that the center frequency and bandwidth can be tuned separately. The two-pole filter center frequency can be changed from 44.05 to 41.55 GHz (5.6% tuning range), while the bandwidth can be independently changed from 2.8 to 2.05 GHz. The four-pole filter center frequency can be changed from 43.25 to 40.95 GHz (5.3% tuning range) and the bandwidth can be changed from 2.65 to 1.9 GHz.     

Low loss and high extinction ratio strictly nonblocking 16×16thermooptic matrix switch on 6-in wafer using silica-based planarlightwave circuit technology

We describe a silica-based 16×16 strictly nonblocking thermooptic matrix switch with a low loss and a high extinction ratio. This matrix switch, which employs a double Mach-Zehnder interferometer (MZI) switching unit and a matrix arrangement to reduce the total waveguide length, is fabricated with 0.75% refractive index difference waveguides on a 6-in silicon wafer using silica-based planar lightwave circuit (PLC) technology. We obtained an average insertion loss of 6.6 dB and an average extinction ratio of 53 dB in the worst polarization case. The operating wavelength bandwidth completely covers the gain band of practical erbium-doped fiber amplifiers (EDFAs). The total power consumption needed for operation is reduced to 17 W by employing a phase-trimming technique which eliminates the phase-error in the interferometer switching unit     

Flexible Bragg Reflection Waveguide Devices Fabricated by Post-Lift-Off Process

Bragg reflection waveguide devices are fabricated on a flexible substrate by using a post-lift-off process in order to obtain highly uniform grating patterns on a wide range. In this process, the flexible substrate formed by spin-coating on a silicon wafer is lifted-off at the end of fabrication procedures. The flexible Bragg reflector exhibits very sharp transmission spectrum with a 3-dB bandwidth of 0.1 nm and a 10-dB bandwidth of 0.4 nm, which is provided by the grating pattern with excellent uniformity. Athermal operation of the flexible Bragg reflector is also demonstrated through the optimization of thermal expansion property of the plastic substrate by controlling the thickness of two polymer substrate materials. The flexible substrate made of 0.7-mum SU-8 layers sandwiching 100-mum NOA61 film provides an optimized thermal expansion property compensating the thermooptic effect of the polymer waveguide. The temperature dependence of the Bragg reflector is reduced to -0.011 nm/degC by the plastic substrate.     

A Micromachined Reconfigurable Metamaterial via Reconfiguration of Asymmetric Split‐Ring Resonators

A micromachined reconfigurable metamaterial is presented, whose unit cell consists of a pair of asymmetric split‐ring resonators (ASRRs); one is fixed to the substrate while the other is patterned on a movable frame. The reconfigurable metamaterial and the supporting structures (e.g., microactuators, anchors, supporting frames, etc.) are fabricated on a silicon‐on‐insulator wafer using deep reactive‐ion etching (DRIE). By adjusting the distance between the two ASRRs, the strength of dipole–dipole coupling can be tuned continuously using the micromachined actuators and this enables tailoring of the electromagnetic response. The reconfiguration of unit cells endows the micromachined reconfigurable metamaterials with unique merits such as electromagnetic response under normal incidence and wide tuning of resonant frequency (measured as 31% and 22% for transverse electric polarization and transverse magnetic polarization, respectively). The reconfiguration could also allow switching between the polarization‐dependent and polarization‐independent states. With these features, the micromachined reconfigurable metamaterials may find potential applications in transformation optics devices, sensors, intelligent detectors, tunable frequency‐selective surfaces, and spectral filters.     

Arrayed waveguide lens wavelength add-drop in silica

We present experimental results of an integrated 16-channel, 100-GHz-channel-spacing wavelength add-drop in silica. It consists of two interleave-chirped waveguide grating routers connected by an array of waveguides containing thermooptic phase shifters. The fully packaged device has 6.6-7.6-dB fiber-to-fiber insertion loss and a switching extinction ratio >27 dB (>33 dB for a single polarization) when used as an add-drop, It is compact, allowing for at least four such devices per 5-in-diameter wafer     

Channel drop filter using a single defect in a 2-D photonic crystal slab waveguide

This paper describes a theoretical and experimental analysis of the channel drop filter using a single defect formed near the two-dimensional (2-D) photonic crystal slab waveguide. First, we calculate the transmission spectrum of a 2-D photonic crystal waveguide and show that high transmittance for a wide wavelength range (/spl sim/60 nm) is obtained in the 1.55-/spl mu/m region. We also show that a defect state having a wavelength within the high transmission wavelength range can be formed in the photonic bandgap by introducing a single defect of appropriate radius. Next, we fabricate several devices and show that the emission wavelength from each defect can be tuned by changing the defect radius. The measured tuning characteristics coincide well with the calculated results. From the near-field pattern of the device, we estimate the emission efficiency of the present device at almost a few tens percent. We clarify the structural condition in order to obtain the maximum output efficiency and show that tuning of emission wavelength while maintaining high output efficiency is possible by selecting appropriate defect radius and position. Based on these results, we propose an ultrasmall channel drop filter for a wavelength-division-multiplex optical communication system.     

Synthesis of guided wave optical interconnects

A guided wave optical interconnect has been designed which reduces or eliminates clock skew by ensuring simultaneous delivery of clock pulses to chips mounted on a wafer. The interconnect consists of a multimode trunk waveguide and a set of branch waveguides, one per chip, each of which couples one mode out of the trunk waveguide. The elimination of clock skew is accomplished by taking advantage of the different group velocities of the modes inherent in multimode waveguides and suitably tailoring the propagation constants of the trunk waveguide according to the location of the respective chip on the wafer. Inverse scattering theory, specifically, the method of Darboux transformations, is used to design the refractive index profiles of the trunk waveguides, using the set of propagation constants selected during the first stage of the design as input data. It is shown that, by using transverse coupling and suitable design of the trunk and branch waveguides, efficient coupling from the trunk to the branch waveguides can be ensured. Techniques for ensuring a symmetric trunk refractive index profile are investigated     

Theory of parametric oscillation phase matched in GaAs thin-film waveguides

The operation of a parametric oscillator phase matched in a GaAs thin-film waveguide is considered. Parametric equations of motion for interacting waveguide fields at three frequencies are developed. From these equations we derive expressions for parametric gain and oscillation threshold. A specific orientation of GaAs allows optically smooth cleaved surfaces to form the oscillator cavity. Conditions for which three waveguide modes at three different frequencies can be phase matched are presented for several specific waveguide-substrate structures. These conditions are in each case determined for a wide variety of mode orders, for a laser pump wavelength of 1.06 μ, and for a large range of signal wavelengths. The deviation in thin-film thickness that can be tolerated while maintaining phase matching over a given interaction length is calculated. We find that transverse coupling strength and oscillation threshold powers are widely variable for different phase matched mode order combinations. Oscillator frequency tuning is investigated by first deriving expressions for variations in waveguide parameters required to effect tuning over a specific range and then evaluating these expressions for some of the previously determined phase-matching situations.     

A Tunable Metamaterial Frequency-Selective Surface With Variable Modes of Operation

A reconfigurable miniaturized-element frequency-selective surface (FSS) is presented in this paper. A standard waveguide measurement setup is used to evaluate the performance of the design. The proposed FSS consists of two periodic arrays of metallic loops, with the same periodicity, on either side of a very thin dielectric substrate. The tuning of the reconfigurable surface is shown numerically to be possible by incorporating tuning varactors into the structure. Using varactors on both layers, a reconfigurable frequency response is achieved, which has two modes of operation: bandstop and bandpass. In addition to two completely different modes of operation, the center frequency, as well as the bandwidth of the response can be tuned independently. Frequency tunability with a constant bandwidth over 3–3.5 GHz is shown. A bandwidth tuning at a fixed center frequency is also demonstrated. Simulation results are verified experimentally by fabricating prototypes of the design at $S$-band loaded with lumped capacitors. To demonstrate the tunability, different pairs of fixed-valued capacitors, as opposed to varactors, are used in a waveguide measurement setup to avoid difficulties associated with biasing varactors in the waveguide.      

Silicon thermooptical micromodulator with 700-kHz -3-dB bandwidth

A silicon Fabry-Perot waveguide modulator, operating at the fiber optic communication wavelengths of 1.3 and 1.55 μm, has been entirely fabricated using microelectronic techniques. The planar optical cavity has been defined by plasma etching and has a length of 100 μm. The device, based on the thermooptic effect, is electrically driven and exhibits a maximum modulation depths of 60%. The measured -3 dB bandwidth is 700 kHz, which is by far the best result ever reported, to our knowledge, for thermooptic effect based modulators