An integrated-optic device using electrooptic polymer waveguide onSi substrate for modulating focus spot intensity distribution

A device integrating a focusing grating coupler (FGC) and a modulator in an electrooptic polymer slab waveguide on a Si substrate is proposed and demonstrated. The modulator consists of two-finger upper electrodes and a lower electrode sandwiching the slab waveguide. The electrodes are used for both the poling process and modulating the phase of the guided wave. The intensity distribution on the focal plane of the FGC is modulated from one spot to two spots, of which peak intensity is half that of the one-spot state when the applied voltage varies from zero to the halfwave voltage     

High-speed electrooptic modulation in GaAs/GaAlAs waveguide devices

A figure of merit is constructed for broad-band electrooptic modulators which compares bandwidth with launched generator voltage standardized to a common wavelength. Comparison of various published results in terms of this figure shows that a lumped-element III-V semiconductor device performance may be no more than a factor of two below that of typical (i.e., LiNbO3) traveling wave devices and are probably easier to implement-especially in an integrated format. Accurate modeling, which incorporates all transit time and velocity match effects, is described and found to agree well with experimental results. Experimental GaAs/GaAlAs modulators have been made, using a Mach-Zehnder interferometer configuration. At a wavelength of 1.15 μm and with unterminated drive a bandwidth of 6.5 GHz was obtained with Vpiof 17.3 V. A shorter (34.6-v) device was ∼ 1.25-dB down at 8.4 GHz. The corresponding figures of merit are close to the maximum expected for the configurations used.     

Ultrafast all-optical modulation of infrared radiation viametal-semiconductor waveguide structures

We present a novel optical-optical semiconductor switching technique for application to infrared laser beam modulation and ultrashort infrared laser pulse switching. This method relies on the ultrafast optical excitation, with femtosecond above-bandgap laser radiation, of an air-filled metal-clad semiconductor waveguide. Guided electromagnetic wave analysis combined with time-varying dielectric properties of the semiconductor layer are used to investigate the ultrafast switching speed of the structure. The device is capable of modulation at various infrared wavelengths. In particular, we investigate intensity modulation of the quasi-TE₁₀ mode for 10.6-μm laser radiation. At an electron-hole photoinjection density of ~1.8×10¹⁸ cm^-3, an extinction ratio of 83 dB is demonstrated. This ratio is significantly higher than that exhibited by current optical-optical semiconductor switches. Potential applications to all-optical Mach-Zehnder metal-clad semiconductor modulators and self-limiting switches are also discussed     

Monolithic integration of waveguide polymer electrooptic modulators on VLSI circuitry

We demonstrated some of the critical technology that is needed for the monolithic integration of polymer electrooptic modulators and VLSI circuitry by fabricating and testing a phase slab modulator on nonplanar VLSI circuits. We demonstrated the survival of GaAs MESFET's to the high-voltage poling and polymer modulator fabrication procedures. We also implemented an electrical interconnect scheme between the electronics and photonics layers.     

A proposal for internal electrooptic intensity and frequency modulation of diode lasers

Modulation of a GaAs diode laser by a GaP electro-optic diode modulator internal to the laser cavity is proposed. Application of a reverse voltage to the modulator diode changes the state of polarization of the oscillating mode. One polarization component of the mode is efficiently coupled out of the cavity by reflection off a Brewster angle laser diode face. Solutions of the threshold equations for the mode frequencies, threshold gain, and the amplitude ratio and the relative phase of the polarization components of the oscillating mode exhibit novel behavior. This allows the laser-modulator combination to be used as either an intensity or a frequency modulated source. This frequency modulation regime in a coupling modulation configuration is an unexpected result and can be applied to other types of lasers. Calculations of the modulation characteristics based on measured properties of the GaP modulator diodes are presented. Operated as a Gürs-Müller coupling modulator (intensity modulation) the device could produce a depth of intensity modulation over 50 percent with a bandwidth of 1 to 3.5 GHz while dissipating only 0.1 watt in the modulator. Operated as a pure frequency modulator the device could have a 2.5 GHz bandwidth, again with 0.1 watt modulator dissipation. The modulator diode can also be used to produce pulse-code modulation. Up to one gigabit per second could be produced with the same modulator dissipation.     

Modeling of electrooptic polymer electrical characteristics in a three-layer optical waveguide modulator

The electrical characteristics of electrooptic polymer waveguide modulators are often described by the bulk reactance of the individual layers. However, the resistance and capacitance between the layers can significantly alter the electrical performance of a waveguide modulator. These interface characteristics are related to the boundary charge density and are strongly affected by the adhesion of the layers in the waveguide stack. An electrical reactance model has been derived to investigate this phenomenon at low frequencies. The model shows the waveguide stack frequency response has no limiting effects below the microwave range and that a true dc response requires a stable voltage for over 1000 h. Thus, reactance of the layers is the key characteristic of optimizing the voltage across the core layer, even at very low frequencies (>10/sup -6/ Hz). The results of the model are compared with experimental data for two polymer systems and show quite good correlation.     

Integrated optical waveguide polarizer based on photobleaching-induced birefringence in an electrooptic polymer

A TE-pass waveguide polarizer is fabricated by utilizing the photobleaching-induced birefringence at room temperature in an electrooptic polymer. The polarizer consists of the photobleached waveguide supporting only TE mode, which is integrated in the middle of the etched rib waveguide supporting both TE and TM modes. It has a simple structure and requires no high temperature process like poling. The measured polarization extinction ratio is about 21 dB at the wavelengths of 1.3 and 1.55 /spl mu/m, and the estimated excess loss is about 0.4 dB.     

Broadband transition between air-filled waveguide and substrate integrated waveguide

A Ka-band broadband transition between an air-filled waveguide and a substrate integrated waveguide (SIW) is proposed. The transition is realised by using a radial probe inserted into the height-tapered metal waveguide. Results show that an insertion loss less than 2.5 dB and a return loss better than 14 dB in the frequency band 28.3-39.5 GHz are obtained for a back-to-back structure     

Lightpath concentrators for all-optical networks

In some deployments of all-optical networks, it is necessary to concentrate the lightpaths from some fibers to fewer fibers. An N/spl times/M lightpath concentrator is an optical component for this purpose, and it concentrates the lightpaths from N incoming fibers to M outgoing fibers. In this paper, three designs of N/spl times/M lightpath concentrators are proposed. The first design is a generalization of optical crossconnects, and it requires M/spl times/M optical switches. The second design incorporates the concept of partial concentration so that it requires only m/spl times/m optical switches (where m相似文献   

Topologies for wavelength-routing all-optical networks

Three regular meshed topologies are compared in light of their possible use for the implementation of large all-optical wavelength-routing communication networks (or interconnection systems). These systems provide all source-destination pairs with end-to-end transparent channels that are identified through a wavelength and a physical path. The considered topologies are the K-dimensional bidirectional square lattice, the twin shuffle, and the de Bruijn graph. The comparison is based on the maximum and average distance between source and destination (number of traversed nodes), on the degree of connectivity for each node (number of input and output fibers), and on the minimum number of wavelengths in the WDM comb necessary to discriminate all source-destination pairs     

Deep-ridge distributed feedback waveguide for polarisationindependent all-optical switching

Structural birefringence in a deep-ridge distributed feedback (DFB) waveguide for polarisation independent all-optical switching is investigated. The coupling coefficient of the DFB structure is also polarisation independent between the TE and TM modes     

Recovery time for a silicon waveguide all-optical switch

Dye laser pulses were used to switch the propagation path of an infra-red (λ=1.3 μm) beam propagating in a planar silicon waveguide. Recovery time ranged from 1.2 to 15 ns, depend on both the pulsed laser wavelength and the illumination geometry     

Design and simulation of waveguide electrooptic beam deflectors

Numerical simulation based on the scalar beam propagation method, was used to investigate the performance of waveguide electrooptic beam deflectors. The deflectors under investigation consist of a stack of electrooptically controlled prisms in a waveguide. The results were compared to earlier simplified analysis. It was found that for given overall device dimensions, the number of interfaces between prisms in a prism-type electrooptic deflector has significant influence on the device performance when it is small. To avoid wavefront distortion, unwanted reflection from the interfaces, and asymmetry in the deflection angles caused by small number of interfaces, one should use more than about ten interfaces in a typical deflector. Additional insights of device operation and design issues are discussed     

Broadband transition between half mode substrate integrated waveguide and rectangular waveguide

A broadband transition between a half mode substrate integrated waveguide and a rectangular waveguide with an antipodal fin-line in its quasi-TEM mode is presented. Experimental results show about 1.3 dB insertion loss and below 215 dB return loss for a back-toback double transition over 10 GHz bandwidth from 26.5 to 40 GHz (the single transition insertion loss is about 0.65 dB). The transition may be used in low-loss and low-noise front-end circuits of the microwave and millimetre-wave bands.     

棱镜-波导耦合实现聚合物波导的全光调制

提出了一种基于改进的棱镜一波导耦合技术实现全光调制的方法。以有机聚合物热光效应为例,泵浦光从等腰三角棱镜顶端垂直入射到光波导上,这样泵浦光和探测光能较容易地耦合到应力点上,从而实现泵浦光对探测光的调制,验证了利用该装置实现全光调制的可行性。观测到基于聚甲基丙烯酸甲酯（PMMA）和蒽醌（An7）染料混合薄膜波导的热光效应的全光调制现象,随着泵浦光功率的增大,探测光功率线性减少,调制响应时间约为20ms。该方法也可以用于具有更快响应时间的基于三阶非线性克尔效应的全光调制或全光开关。     

Physical topology design for all-optical networks

When designing an all-optical network, the designers face a choice of laying down more fibers or increasing the number of wavelengths. Although either choice could be used to support new connections, one increases the link cost and the other increases the node (wavelength equipments) cost. The tradeoffs between link and node cost are not well understood. Using the efficient physical topology design algorithm that we propose, we study this tradeoff. We use the asymptotic growth rate of the provisioned capacity as a metric to compare various design alternatives. A higher asymptotic growth rate translates directly into a higher deployment cost for large networks. Our study shows that taking fiber length into consideration can lead to lower capacity requirement. We also find that a sufficiently large fiber-to-node ratio is necessary in order to minimize the asymptotic growth in the provisioned capacity, increase capacity utilization and minimize the need for wavelength conversion. We study a real network and find that its fiber-to-node ratio is too low. As a result, large provisioned capacity is required and less than 55% of the capacity is usable. By increasing the ratio, we can reduce the provisioned capacity and achieve close to 80% utilization.     

Novel piezoelectric-barrier heterostructure for all-optical light modulation

We propose a novel quantum heterostructure especially designed to be used as an optically-controlled light modulator device with moderate optical power densities and without the need of electrical contacts. The device exploits the piezo-electric effect in strained semiconductor layers and its principle relies on the fact that upon optical excitation, a substantial space charge field perpendicular to the quantum well plane is established in every period of the heterostructure, owing to efficient photocarrier separation in piezoelectric barrier layers. We present preliminary results which demonstrate a photo-induced electric field of more than 30 kV/cm with about 100 W/cm² inducing large spectral shifts in the photo-luminescence spectra of a CdHgTe quantum well.     

Trading coupling loss for modulation efficiency in electrooptic modulators

Phase modulators utilizing the electrooptic effect in Li-NbO3are most efficient if the waveguide, and hence the guided mode, is positioned as closely as possible to the modulation electrode which is located at the surface of the crystal. However, placing the guided wave near the crystal surface tends to deform its shape so that the coupling loss between the waveguide mode and an optical fiber is increased. In this paper, we study the tradeoffs between coupling loss and modulation efficiency that result from moving the waveguide further below the crystal surface.     

Improved electrode geometry for electrooptic frequency translation in a channel waveguide

The technique of optical frequency translation by a rotating electric field in a trigonal electrooptic crystal has been adapted to a buried channel waveguide structure. To implement the field rotation under the constraints of a planar geometry, an electrode configuration was adopted consisting of three coplanar, collinear metal strips driven in phase quadrature, with the light guide under the central strip. Elimination of a cyclic modulation of field amplitude, characterizing the results of a previous study by the author, was achieved by appropriately widening the outer electrodes relative to the central one and by choosing a suitable channel depth. Spurious sidebands previously generated by an effective counter-rotating field component are thus removed. It is shown that with a residual modal birefringence equivalent tolambda/20-differential phase retardation, the device here described can achieve 98 percent translation into the single first-order sideband with less than 0.5 percent combined spurious carrier and second-order upper sideband.