Crystal ion slicing was used in conjunction with conventional annealed proton exchange in Z-cut LiNbO/sub 3/ to result in prepatterned microns-thick single-crystal LiNbO/sub 3/ films with channel guides and a measured waveguide propagation loss of 0.2-0.7 dB/cm. Full optical circuit transfer, including a buffer layer and a patterned metal electrode structure for active control was demonstrated

Optical waveguides fabricated on a yttrium iron garnet (YIG) substrate are integrated onto a semiconductor surface by using rid ge waveguides patterned onto a prefabricated recess in the YIG surface. The recess separates the waveguides from the semiconductor substr ate with an air-gap. This structure makes it possible to avoid coupling light within the YIG waveguides into the semiconductor substrate which has a higher refractive index. The excess optical loss due to the coupling can be as low as <or=0.1 dB/cm with a 1- mu m-wide air-g ap. The calculated coupling loss is confirmed by comparing the guided TE and TM modes

The dielectric response has been studied in 10- mu m-thick, single-crystal potassium tantalate films formed by crystal ion slic ing. Scanning microwave microscopy shows that the implanted, pre-etched samples exhibit a bulk-like permittivity and low-loss tangent (0. 0009) at 1.7 GHz. The separated free-standing films have somewhat higher loss tangents due to residual-ion-induced stress. Selective rela xation of this stress by etching or annealing reduces the dielectric loss

In this letter, we have designed and fabricated low-loss ultrasmall corner mirrors and T-branches on thin silicon-on-insulator material system. The measured performance of the devices agrees with simulations using finite-difference time-domain calculations. These devices demonstrate the potential of this high-refractive-index-contrast material system for high-density planar optical integrated circu its

Summary form only given. We have developed a numerical modeling tool for calculating the cavity modes in VCSELs based on bidirectional BPM. We demonstrated its use in simulating oxide-confined VCSELs. This tool can actually be applied to all types of VCSELs in general

Summary form only given. There has recently been a surge of interest in thin SOI-based integrated optics, where the silicon guiding layer is less than a micrometer thick. Optical devices on this platform can be potentially integrated with SOI-based CMOS technology, which is currently being favored for high speed and low-voltage applications. For integrated optics, equally important is the fact that the high refractive index difference between the Si-core and the SiO/sub 2/ substrate ( Delta n = 2.0) can be utilized to significantly reduce the dimensions of photonic integrated circuits. The thin-SOI structures used in our study contains a 0.34 mu m Si guiding layer on a 1.0 mu m thick buried oxide layer

We present an optical modeling approach for calculating vertical-cavity surface emitting laser (VCSELs) modes based on the bidirectional beam propagation method. Compared with existing approaches, it is flexible, efficient, and convenient. To demonstrate and validate the approach, we examined several design problems for oxide-confined VCSEL devices. Specifically, we modeled the blue-shift phenomenon in small oxidized VCSELs and compared our calculations with previous results. We also examined the dependence of the threshold gain on different oxide-aperture shaped designs and on the thickness and placement of an aperture layer.

We have fabricated a bicell detector consisting of a single freestanding film of single-crystal lithium niobate (LiNbO3) 10-mu m thick, having two adjacent domains of opposite spontaneous polarization, and hence, two adjacent pyroelectric detector regions of equal and opposite sensitivity. The film was created by applying the process of crystal ion slicing and electric field poling (domain engineering) to a Z-cut LiNbO3 wafer. The detector's noise equivalent power was 6 nW.Hz-12/ at 16 Hz, and the ambient temperature-dependent variation of the detector's response near room temperature was 0.1was -24 dB relative e to that of a single-domain detector.

We present an evaluation of the parameters involved in designing low-loss right-angle waveguide bends based on a high index contrast materials system. We apply the finite difference time domain method (FDTD) to several two-dimensional bend structures and study the effects of varying the bend geometry. Such a study is relevant for the understanding of bend mechanisms and for the optimization and fabrication of high-density high-contrast integrated optical components. The study indicates that high bend transmission can be achieved with the addition of a low-Q resonant cavity; however, similar or even better performance can be achieved with a structure that combines a corner mirror with a phase retarder. The use of a double corner mirror structure is shown to further increase the bend transmission, with little increase in bend area

We survey the properties of photonic crystal fibers with elliptical air holes, examining mode shapes, birefringence, group velocity walkoff and dispersion, and cutoff conditions. We find new types of behavior for each quantity and demonstrate the possibility achieving large birefringence with zero walkoff in the single-mode regime. We show that the dispersive properties of the vector modes are closely tied to those of the so-called fundamental space filling modes, and that at long wavelengths, the fibers exhibit a single-polarization single-mode regime of propagation without the presence of material anisotropy

We study the dispersive properties of photonic crystal fibers (PCF's) with elliptical air holes. The unusual guidance of PCF leads to novel behavior of the birefringence, group-velocity walk-off, and dispersion parameters, including the possibility of zero walk-off with high birefringence in the single-mode regime. A number of these effects are closely tied to the underlying radiation states of the air-hole lattice

Photonic crystals containing defects produce enhanced Faraday rotation but existing designs have low intensity output. We show that designs with two-defects possess sufficient freedom to attain high transmission over a large range of rotation angles in very short lengths. We optimize such systems for 45 degrees rotation in optical isolators

We investigate enhancement of magnetooptical rotation in periodic magnetic garnet thin-film stacks with defects using a combination of coupled-mode theory and matrix calculations. We prove that a combination of high rotation per unit length and high output is unattainable for a symmetric grating with a single central defect. We demonstrate that the addition of a second defect introduces sufficient degrees of freedom to allow high transmission for a much larger range of rotation angles than was previously possible. We present a number of designs with emphasis an achieving 45 degrees rotation in very short propagation lengths

We perform a theoretical study of enhancement of magnetooptical rotation on reflection of light from a periodic system with a defect. Using calculations based on a coupled mode approach and the transfer matrix method we demonstrate that an asymmetric placing of a single defect allows arbitrary Kerr rotations with better than 99% reflectivity from very short devices

We report on the implementation of crystal ion slicing in potassium tantalate (KTaO/sub 3/). Deep-ion implantation is used to create a buried sacrificial layer in (001) single-crystal wafers of KTaO/sub 3/. 10- mu m-thick single-crystal films have been fabricated by adjusting the stress level in the implantation damage layer to induce room-temperature etchless exfoliation. Crack propagation is found to depend critically on implantation dose, with a threshold dose for exfoliation near 1*10/sup 16/ cm/sup -2/. A significant implantation-induced etch selectivity between the sacrificial layer and the rest of the sample is also found. Capacitance measurements show that the films exhibit a bulk-like dielectric constant and loss tangents below 0.01 at low temperatures

Existing algorithms for bidirectional optical beam propagation proposed to simulate reflective integrated photonic devices do not propagate evanescent fields correctly. Thus inaccuracy and instability problems can arise when fields have significant evanescent character. We propose complex representations of the propagation operator by choosing either a complex reference wave number or a complex representation of Pade approximation to address this issue. Therefore correct evolution of both propagating waves and evanescent waves can be simultaneously realized, significantly reducing the inaccuracy and instability problems. Both test problems and practical problems are presented for demonstration

Electron cyclotron resonance plasma etching is used to fabricate submicrometer-scale GaInAsSb/AlGaAsSb multiple-quantum-well structures. Smooth and anisotropic features at low substrate bias were obtained under appropriate conditions. The etch quality was investigated with photoluminescence spectroscopy; luminescence data from the etched features agree well with a model that assumes a low-damage etching process

We report on the fabrication and chi /sup (2)/ measurements of thin 10- mu m-thick films of periodically poled LiNbO/sub 3/, obtained by crystal ion slicing. The d/sub 33/ optical coefficient in the films is probed by sum-frequency generation with a short-pulse laser source at 1550 nm and compared with that of the bulk. Efficient, room-temperature TM( omega , m=0)-to-TM( omega + omega , m=0) mode conversion is obtained in the films. These measurements show that domain periodicity is preserved during ion implantation and that the thin films have bulklike nonlinearity and material dispersion

Recent interest in employing single-crystal yttrium iron garnet (YIG) films for miniaturized microwave integrated circuit applications has prompted us to study detaching liquid phase epitaxy (LPE) grown YIG films from their gadolinium gallium garnet (GGG) substrates via crystal ion slicing (CIS). We report studies of magnetization and ferromagnetic resonance (FMR) of narrow linewidth gallium-doped YIG (GaYIG) films in various stages of separation from their <111> oriented GGG substrates. All samples were diced from the same three-inch wafer of Y/sub 3/Fe/sub 4.6/Ga/sub 0.4/O/sub 12/ with 4 pi M/sub eff/ of 1070 G and 9.45 GHz FMR linewidth of 0.4+or-0.1 Oe. The CIS separation process involved (1) implantation with helium ions, (2) flash annealing to remove surface damage, and (3) chemical etching to detach the YIG at the implantation damaged layer. The starting films were 10.8- mu m thick. Separation occurred 7 to 8 mu m from the front surface in the YIG. The implantation (5*10/sup 16/ cm/sup -2/ dosage, 3.8 MeV bias) increased the uniaxial anisotropy of these films. A small cubic anisotropy ( 5 G 60 degrees in-plane periodicity) persisted in both implanted and unimplanted samples. Upon implantation the FMR linewidth increased from 0.4 to 3+or-0.5 Oe. The detached samples have linewidths ranging from 1.7 to 2.5 Oe. The temperature dependence of the linewidths is roughly exponential decreasing as the temperature is lowered for the unprocessed sample, increasing with reduced temperature for all processed samples. Post-detachment annealing restores the FMR linewidth to 0.55+or-0.5 Oe

A novel 1*4 coupler multiplexer permutation switch (CMPS) is proposed for applications in wavelength-division-multiplexing (WDM) optical networks. The structure of the CMPS integrates the multiplexing and switching functions into a single compact device. It consists of a single-mode/multimode-waveguide grating-assisted, backward-coupler multiplexer followed by a 1*4 digital optical switch (DOS). The specific design uses an InP-based 1*4 CMPS with InGaAsP-InP multiple-quantum-well (MQW) DOS. The calculated values of crosstalk for the coupler multiplexer and the DOS are <-25 dB and -23 dB, respectively, giving an overall crosstalk <-21 dB for channel bandwidths of 10-13 GHz. The device channels are unequally spaced, which reduces unwanted four-wave mixing (FWM), but are fitted to the ITU standard wavelength grid

Bonding between liquid-phase-epitaxy-grown yttrium iron garnet films and various semiconductors is realized by direct wafer bonding. The semiconductor substrates can serve as a platform for integration or as a handle platform for the transfer of mesoscopic garnet films. To effect film transfer, a sacrificial layer is formed in the garnet by deep ion implantation prior to bonding. Shear stress at the garnet/semiconductor interface can be controlled by temperature tuning during the bonding process. A debonding temperature threshold of 400 degrees C is found and related to the interfacial thermal stress due to difference in thermal expansion coefficients of the bonded materials. Film separation is realized by the application of thermally induced stress at the sacrificial layer

A waveguide optical isolator based on nonreciprocal interference is demonstrated. Ridge waveguides are fabricated in a Mach-Zehnder configuration on a single film of bismuth-, lutetium-, neodymium-iron garnet. With this design, no polarizers are required to achieve extinction in the backward propagation direction. This isolator exhibits a 19 dB extinction ratio at lambda =1.54 mu m. A flat wavelength dependence, to within 2 dB, has been observed in the range between 1.49 and 1.57 mu m

A single-section, compact, passive polarization converter has been designed and fabricated on GaAs-AlGaAs. The device uses an optimized waveguide structure with angled-facets to obtain 90 degrees -polarization rotation in a single section; this waveguide structure eliminates the need for longitudinal variation and hence avoids any section-to-section coupling losses. A transverse electric (TE) to transverse magnetic (TM) polarization conversion of 96achieved for a conversion length of approximately=720 mu m

Electro-optic modulation is demonstrated in 10- mu m-thick single-crystal LiNbO/sub 3/ films obtained by crystal ion slicing. This technique uses ion implantation of single-crystal bulk samples followed by selective etching. The measured electro-optic response of these films is comparable, within experimental error, to that of single-crystal bulk LiNbO/sub 3/ and is superior to previously reported values for epitaxial polycrystalline thin films. The product of half-wave voltage and modulator length, V/sub pi /L, is 8 V cm. Post lift-off annealing is shown to be of key importance in improving the modulator extinction ratio

Recently, an ion-implantation based technique, known as crystal ion slicing has been shown to yield single-crystal LiNbO/sub 3/ films on semiconductors and other platforms. In this technique, ion implantation is used to define a sacrificial layer which is then etched away in a dilute hydrofluoric acid solution. The thickness of the film is defined by the implantation energy. We report measurements of the electro-optical response of film and report on the techniques used to prepare the films and to emphasize their performance. We show that the electro-optic response of these films is comparable to that of single-crystal bulk, and is superior to values previously reported in the literature for polycrystalline films. Further the thin film geometry used has been shown to yield lower half-wave voltage for device operation

Reports on fabrication and characterization of the first zeroth-order half-wave plates of LiNbO/sub 3/ obtained by crystal ion slicing (CIS). Polarization rotation was demonstrated in 10- mu m-thick freestanding LiNbO/sub 3/ films with 30-dB conversion ratios and negligible material loss. Polarization-independent performance was demonstrated in a hybrid-optic device comprising a CIS wave plate integrated with single-mode silica-based channel waveguides

Microwave-optical velocity matching and 50 Omega impedance matching are difficult to achieve with LiNbO/sub 3/ traveling wave modulators. We perform a detailed study (simulations) of the microwave and optical performance characteristics for modulators using thin layer (few micrometers), X-cut LiNbO/sub 3/ and find significant improvements in velocity and impedance matching together with a lower V/sub pi /L

Summary form only given. Several methods for bidirectional beam propagation have been suggested to treat reflective devices. Accurate and efficient modeling of devices such as Bragg gratings, AR coatings and add-drop multiplexers has been demonstrated. However, a significant weakness remains in current bidirectional BPM techniques-evanescent waves are generated at interfaces but are not propagated correctly by the conventional BPM propagator. This leads both to errors in transmission and reflection coefficients and introduces instabilities to the simulation algorithms. The solution to these inaccuracy and instability problems is to find a better propagator, which does not map the real axis to itself. Our approach is to use a complex-valued reference wave number

Accurate modeling of photonic devices is essential for the development of new, higher performance optical components required by current and future high-bandwidth communication systems. The paper reviews one of the predominant techniques for such modeling, the beam propagation method (BPM), and describes several applications along with experimental results. BPM can be used for both mode solving and the simulation of propagation in nearly arbitrary structures, and as a result, is commonly used in commercial design tools

Summary form only given. Magnetic garnets such as bismuth-substituted yttrium iron garnet (Bi-YIG) are of great interest for the fabrication of optical isolators and circulators exploiting Faraday rotation. While their magnetic properties are relatively strong, nonetheless propagation lengths of order 0.5-1.0 mm are required to produce 45 degrees rotations for isolation at communications wavelengths. Although such materials yield compact bulk isolators, thinner films are required for a number of integrated applications-non-guided propagation across a rotator inserted in a waveguide requires structures less than approximately=30 microns to control diffraction loss. We use a coupled mode equation (CME) description and exact matrix calculations to investigate the relation between rotation and output intensity. We find that appropriate placement of defects permits simultaneous optimization of both. With such structures very short high-quality isolators could be built

Summary form only given. We have studied the second order optical nonlinearity of crystal ion slicing periodically poled LiNbO/sub 3/ films. Temperature- and electro-optic response experiments were discussed

We have packaged a rectangular 3 mm*4 mm, 10- mu m-thick Z-cut lithium niobate (LiNbO/sub 3/) film produced by crystal ion slicing (CIS) and evaluated its performance as a pyroelectric optical detector. We justify the difficulty of preparing the film by showing that the freestanding detector has much greater sensitivity than the same detector bonded to a substrate. We compare the sensitivity of three CIS-film detectors with that of a detector based on a 230- mu m-thick LiNbO/sub 3/ plate and describe the detectors' spatial uniformity and noise-equivalent power

A polarization-independent waveguide optical isolator based on nonreciprocal interference is proposed. The design uses simultaneous TE and TM nonreciprocal phase shifts obtained from geometric asymmetry in horizontal and vertical axes of waveguide cross section along with opposing transverse and vertical magnetic fields in interferometer arms. A design to achieve such an isolator is described. Both TE and TM nonreciprocal phase shifts comparable to the theoretical counterparts have also been experimentally observed from a single waveguide

Summary form only given. The recent development of a novel crystal ion slicing technique (CIS) has made it possible to obtain high-quality single-crystal LiNbO/sub 3/ micron-thick films for heterogeneous integration of optical systems. These films can be integrated onto planar substrates based on technologically important materials systems [e.g. semiconductor] otherwise incompatible with single-crystal LiNbO/sub 3/. The technique employs the formation and subsequent preferential etching of a buried damage sacrificial layer obtained by implanting energetic He/sup +/. We report on a technique for rapid fabrication of the single-crystal LiNbO/sub 3/ films and the second harmonic generation (SHG) in the freestanding films. A bulk LiNbO/sub 3/ crystal phase-matched (PM) for SHG at 1.55 mu m is cut from a z-poled single crystal

Summary form only given. Direct wafer bonding is an attractive technique for the heterogeneous integration of dissimilar materials, including III-V and silicon-on-insulator structures (SOI). Recently a novel technique (crystal ion slicing) has been reported by some of the authors for the epitaxial liftoff of magnetic garnet films for magnetooptic isolators. This technique makes use of fast etching in a sacrificial layer generated by the deep implantation of energetic ( 4 MeV) helium ions. The metal-oxide films detached by this process have been subsequently bonded onto semiconductor substrates with epoxy. In the paper we report on direct wafer bonding of ion-implanted bismuth-substituted yttrium iron garnets (Bi-YIG) films onto InP substrates at room temperature and selective etching of the implantation-induced sacrificial layer in the bonded material. The low bonding temperatures prevents annealing out of the implanted region

We report on optical frequency mixing in epitaxial liftoff thin films of single-crystal LiNbO/sub 3/ integrated onto heterogeneous planar glass platforms. These films are found to have a nonlinear optical response comparable to that of the bulk. Second-harmonic generation is investigated as a function of crystal orientation, ion implantation, and modal and temperature dispersion. Ion implantation-induced shifts in the refractive indices are shown to be useful for achieving phase matching

Measurements up to 45 degrees nonreciprocal phase shift using the transverse magneto-optical effect have been made in a hybrid Mach-Zehnder waveguide/fiber interferometer. BiLu-IG waveguides of various thicknesses and lengths have been used to study the length and thickness dependence of the effect at lambda =1.55 mu m. This interferometric scheme is also employed to observe optical isolation; an extinction ratio of 11 dB is obtained for the 45 degrees nonreciprocal phase shift, in agreement with theoretical predictions

Recently proposed tapered MMI devices have been shown to allow for substantial reductions in device geometries, but as of this time such ultracompact devices have not been realized. The fabrication and testing of a series of parabolically tapered 3-dB 2*2 MMI devices have been accomplished in the InP-InGaAsP double heterostructure system. The results validate previous predictions and yield device geometries about 40previous 3-dB 2*2 MMI device. The measured splitting ratios of these devices are compared to the results of numerous beam propagation method simulations, based on the finite-difference method, and good correlation is obtained

A novel approach to the bidirectional beam propagation method, which can treat multiple dielectric interfaces, is developed and implemented using iterative methods. Comparisons with two previously published results demonstrate its accuracy, as well as its efficiency in computation time and memory. Finally, its capability in simulating and designing complex structures is also demonstrated via a three-channel add-drop multiplexer

Crystal ion slicing (CIS) is a novel approach to produce films from bulk crystalline materials. A LiNbO/sub 3/ film with dimensions of 1.29*0.9*0.01 mm was detached from a poled bulk crystal. The ferroelectric domain characteristics and phase transition behavior of the detached film were studied using transmission optical microscopy and recorded continuously by VCR tape recorder through a CCD camera. The sample was heated gradually from room temperature to 1190 degrees C, and then cooled down to room temperature. The phase transition from the ferroelectric to paraelectric was observed at 1163 degrees C. High density domain structures were also observed when the sample was cooled to room temperature after it was annealed at a temperature around the Curie temperature. The experimental results show that the virgin CIS LiNbO/sub 3/ film is still in a ferroelectric state and preserves the single domain state of a poled bulk crystal. The CIS film has clear advantages over the film prepared by other techniques for various integrated applications

We report on a large etch selectivity enhancement in the epitaxial liftoff of He/sup +/-implanted single-crystal lithium niobate (LiNbO/sub 3/) films upon rapid thermal annealing. A buried sacrificial layer is formed by ion implantation. Heat treatment is found to reduce the time needed for film detachment by a factor as large as 100. Implant damage and postanneal stress-induced etch selectivity become nearly independent of implantation energy upon annealing. Large (0.5*1 cm/sup 2/) 5-10- mu m-thick single-crystal LiNbO/sub 3/ films of excellent quality are detached in just a matter of a few hours

Bismuth-substituted yttrium iron garnet (Bi-YIG) is the material of choice in the fabrication of optical isolators. Recently some of us have demonstrated an ion-implantation based technique for detaching single-crystal Bi-YIG films from their gadolinium gallium garnet growth substrates, and for their subsequent bonding onto semiconductor wafers. In this article we study the magnetic properties of bubble-type Bi-YIG films with large out-of-plane uniaxial anisotropy in various stages of the separation process. We find that the implantation reduces the perpendicular anisotropy field from approximately 1435 to 750 Oe as a result of increased residual strain. Annealing partially restores the anisotropy to 900 Oe depending on annealing conditions. Chemical etching of the implanted sample separates the Bi-YIG film from the substrate at the sacrificial layer. Upon detachment the perpendicular anisotropy of the sample is nearly fully restored to its original value. The 9 GHz ferromagnetic resonance (FMR) linewidth of these films is large (440-520 Oe) and is only weakly affected by the processing

A new technique for forming nonperipheral cleaved facets on GaAs epilayers for hybrid optical integration is demonstrated. Local photoelectrochemical etching is used to form an undercut region under the epilayer structure. The undercut region is then cleaved by subsequent ultrasonic agitation. Undercut widths of 70-170 mu m+or-5 mu m are obtained at a bias voltage of 2 V and laser powers of 200-600 mu W. Optical measurements show that these facets have minimal (0.4 dB) excess loss. A thin-film polarizer is inserted into the groove to test facet performance; the test shows a minimal degradation of the extinction ratio (<0.3 dB) over its free-space counterpart

The epitaxial separation of single-crystal magnetic and ferroelectric oxide films is presented. Ion implantation is used to create a buried damage layer beneath the surface. The high etch-selectivity of this sacrificial layer makes it possible to detach high quality single-crystal films from bulk samples. Magnetic and electrical properties of the films are discussed

Conventional beam propagation methods (BPM) only deal with the forward propagating optical field, and, thus, they are useful only if the structure has a sufficiently slowly-varying index along the propagation direction such that the accumulated reflections are negligible. However, many practical guided-wave optical devices involve junctions of different waveguides, laser facets, grating structures, anti-reflection or high-reflection coatings, etc. In all these structures there exists a refractive index discontinuity or variation along the direction of propagation of the optical field, hence consideration of coupling the forward and backward waves must be included for accurate modeling. We present an iterative approach to dealing with problems involving multiple dielectric interfaces, which has significantly reduced memory requirements

Photonic integrated circuits based on MMI couplers have been implemented for a variety of optical signal processing functions. However, it is difficult to obtain high-performance for N*N MMI couplers with large N due to the modal phase errors in self-imaging. For example, MMI-based phased-array (PHASAR) demultiplexers are of interest because of their application to WDM systems. One important factor that limits the crosstalk of these MMI-PHASARs is the performance degradation of N*N MMI couplers due to modal phase errors. In this study, a new design approach by optimizing the index-contrast to reduce phase error is described which yields a device design with extremely low imbalance and insertion loss

We report on the implementation of crystal ion slicing in lithium niobate (LiNbO/sub 3/). Deep-ion implantation is used to create a buried sacrificial layer in single-crystal c-cut poled wafers of LiNbO/sub 3/, inducing a large etch selectivity between the sacrificial layer and the rest of the sample. 9- mu m-thick films of excellent quality are separated from the bulk and bonded to silicon and gallium arsenide substrates. These single-crystal films have the same room-temperature dielectric and pyroelectric characteristics, and ferroelectric transition temperature as single-crystal bulk. A stronger high-temperature pyroelectric response is found in the films

A new design approach for N*N multimode interference (MMI) couplers with large N is described which yields a device design with extremely low imbalance and insertion loss. Analytical expressions for the phase errors in MMI devices are derived from basic principles; these expressions enable significant phase-error reduction to be obtained by optimizing the index-contrast. This optimization in conjunction with the proper placement of the access waveguides allows significant improvement in the device performance. An application of the design approach is illustrated through the design of an 8*8 MMI-based, phased-array demultiplexer with low crosstalk

An integrated, cascaded, asymmetric GaAs-AlGaAs Mach-Zehnder (MZ) interferometer, for use in wavelength filtering and time-domain multiplexing, has been designed, fabricated, and tested, This device employs several new passive components, including height-tapered Y-branches, for uniform splitting and recombining, and index-tailored waveguide bends, for low-loss operation. The waveguide bend is designed with a predistorted index profile for minimizing both transition loss and radiation loss. The circuit is fabricated with a resistless, light-induced local etching technique, which enables rapid iterative fabrication of the device geometry to achieve the desired operating path delays. Acting as a wavelength filter, the fabricated device has a -24.3 dB minimum-to-maximum extinction ratio and a -10.5 dB side-lobe suppression ratio. Acting as a pulse-rate multiplexer, the device generates a four-pulse train with a 10-ps pulse-to-pulse separation and an amplitude uniformity of 80for each input pulse

The use of carbon nanotubes as tips in atomic force microscopy for a systematic study of dry etching pattern transfer in GaAs is described. The GaAs samples are patterned via electron beam lithography and then etched using magnetron reactive ion or chemically assisted ion beam processing. The technique allows diagnosis, in air, of etched features with scale sizes of <100 nm

The length of N*N multimode interference-based (MMI) devices scales as the square of the MMI region width, and as a result, the use of these structures for large-N applications can require large chip areas. We discuss the N*N applications of a recently proposed MMI structure that has smaller device dimensions than conventional multimode interference structures. Numerical simulations of such structures and design rules are presented. Limitations on device performance are discussed

Epitaxial liftoff has been used for achieving heterogeneous integration of many III-V and elemental semiconductor systems. However, it has been heretofore impossible to integrate devices of many other important material systems. A good example of this problem has been the integration of single-crystal transition metal oxides on semiconductor platforms, a system needed for on-chip thin film optical isolators. We report here an implementation of epitaxial liftoff in magnetic garnets. Deep ion implantation is used to create a buried sacrificial layer in single-crystal yttrium iron garnet (YIG) and bismuth-substituted YIG (Bi-YIG) epitaxial layers grown on gadolinium gallium garnet (GGG). The damage generated by the implantation induces a large etch selectivity between the sacrificial layer and the rest of the garnet. Ten-micron-thick films have been lifted off from the original GGG substrates by etching in phosphoric acid. Millimeter-size pieces of excellent quality have been transferred to the silicon and gallium arsenide substrates. Study of the magnetic domain structure in the detached epilayers by Faraday contrast shows no changes in film anisotropy. Optical insertion loss measurements are also presented

The length of NxN multimode interference-based devices scales as the square of the MMI region width, and as a result, the use of these structures for large-N applications can require large chip areas. We discuss the NxN applications of a recently proposed MMI structure which has smaller device dimensions than conventional multimode interference structures. Numerical simulations of such structures and design rules are presented. Keywords: multimode interference, power splitters, couplers, parabolic waveguide tapers

Metal cladding is proposed for enhancing performance of multimode interference (MMI) devices for low-index-contrast material systems and numerically investigated by the beam propagation method (BPM). Metal-cladding eliminates spurious phase errors due to the Goos-Hahnchen shift and thus yields improved imaging. The application of this concept is demonstrated by the simulation of a 1*8 MMI-based wavelength router using a typical low-index-contrast polymer channel waveguide and the results show that the crosstalk is significantly improved

We describe the use of chemically assisted ion beam etching to realize smooth, highly anisotropic features in GaSb. The measured etch rates are comparable to those of GaAs, and are fitted to a model that assumes the formation of trichloride etch product species

Explicit analytic design rules are derived for both 3 dB and full adiabatic couplers. The design rules are in excellent agreement with numerical calculations using the beam propagation method (BPM). It is shown that the length scaling for 3 dB couplers compared to full couplers makes the former more difficult to design. The design for each case is optimized to obtain the upper limit of performance and a comparison is carried out between two different design geometries for both 3 dB and full adiabatic couplers

We introduce here a new multimode interference-based 3-dB coupler that has a substantially smaller device geometry than conventional multimode interference structures. This new structure is based on a special multimode region shape and an appropriate launching technique which aids in circumventing the proximity limitations. Simulations show this structure can provide a decrease of a factor of three or more in the device size of the smallest 3-dB MMI coupler made to date

Waveguide polarizers based on embedded thin metallic stacks are proposed. Highly efficient TM polarization is obtained for metal thicknesses smaller than the optical skin depth. The optimal single-metal-layer waveguide is found to yield an extinction ratio better than 12.2 dB/mm and a linear loss below 0.075 dB/mm. Experimental confirmation for this structure is also obtained in polymeric waveguides. Polarization efficiencies better than 100 dB/mm with linear losses below 2 dB/mm are calculated for multi-stack waveguides. This high performance is found to hold even if oxidation at metal-core boundaries is considered

Waveguide polarizers based on embedded nanometer-thick metallic layers are proposed and analyzed as a function of metal thickness and number of layers. The performance is shown to approach that of commercially available free-space polarizers with only a few stacks

Bent multi-mode interference-based power splitters are realized in GaAs by laser lithography. Simulations are used to investigate sensitivities to device geometry. We present the first experimental realization of such power splitters in GaAs which were prototyped using a laser-written photolithographic process. Extensive simulations of the power-splitting behavior of devices of different dimensions and geometry show a beneficial tolerance to fabrication errors

We report on the implementation of epitaxial liftoff in magnetic garnets. Deep-ion implantation is used to create a buried sacrificial layer in single-crystal yttrium iron garnet (YIG) and bismuth-substituted YIG epilayers grown on gadolinium gallium garnet. The damage generated by the implantation induces a large etch selectivity between the sacrificial layer and the rest of the garnet. 10- mu m-thick films of excellent quality are lifted off and bonded to silicon and GaAs substrates. No noticeable degradation in magnetic coercivity due to domain pinning is observed. Stress-induced microfracturing in the thin oxide layers is also addressed

A metal-coated multimode interference (MMI) device is proposed and analyzed. Simulations show that due to its ideal mode spectrum and resulting enhanced imaging performance, the device has applications to low index contrast polymer waveguides. We demonstrate its feasibility by the design and simulation of a polymer channel waveguide MMI coated with Al. Experimental demonstration and application will be the next step for this design concept

Bent multimode interference-based variable power splitters are experimentally demonstrated in GaAs-AlGaAs using the principles of general imaging. Simulations are used to investigate sensitivities to device geometry. Results indicate that the device's splitting ratio performance is largely fabrication tolerant

The development of multimode passive polymer optical waveguide components for board and backplane interconnect applications, such as in the the DARPA-sponsored Polymer Optical Interconnect Technology (POINT) program, require several optics design issues to be addressed, including efficiency and modal noise. For example, the mating of arrays of sources, detectors, and fibers requires appropriate fan-out structures to match the component pitch. Here, we consider designs for such structures using multimode polymer waveguides, including both abrupt and smooth bending elements. We investigate these structures using a new multimode beam propagation method (BPM) simulation CAD tool, and consider the bend losses as a function of geometry, angle, and source condition. The results are compared with experimental observations on devices fabricated for use in the POINT demonstration module. The simulation closely matches the experiment, demonstrating the utility of such efforts in practical component development

A tunable TE/TM polarization splitter, based on a Mach-Zehnder interferometer with an electrooptic switch, is demonstrated in GaAs-AlGaAs. Symmetric and asymmetric Y-branches employing height-tapered waveguides are used to achieve power splitting and mode sorting, respectively, in the interferometer. The device has an extinction ratio of 20 dB and an excess loss less than 1.5 dB for both TE and TM polarized light. The device can be reconfigured by tuning the switching voltage for operation at both 1.3- and 1.55-pm wavelengths

Cathodoluminescence has been employed to investigate the luminescence and lateral transport properties of excited carriers at 8 K in GaAs-AlGaAs quantum well material and in submicron features fabricated in this material by magnetron reactive ion etching. A carrier diffusion length of 0.85+or-0.04 mu m in quantum wells and a surface recombination velocity (5.4+or-0.8)*10/sup 3/ m/s at etched sidewalls were measured. Also, the effect of feature size on luminescence efficiency was examined and compared with model calculations using the measured values of diffusion length and surface recombination velocity

The design, fabrication, and testing of a highly multimode polymeric 8*8 star coupler is described. The design process allowed a comparison to be made of ray tracing and beam propagation methods for the design of such highly multimode waveguide devices. The results obtained with either of these two different methods agree well with actual measurements on a fabricated 8*8 multimode-input star coupler with a refractive index difference of Delta n=0.0274 and a device length of L=4.25cm. The reduction in the RMS power fluctuation in the output guides with the choice of a higher refractive index difference is demonstrated

A new approach to an integrated Y-branch power splitter, useful for strongly guiding waveguide circuits, is proposed, fabricated and tested. The device uses adiabatic mode evolution by effective-refractive-index tapering to achieve a compact, low-loss geometry. Device performance is examined numerically by twoand three-dimensional beam propagation simulations. Y-branches with an overall length of 330 mu m and losses of <0.2 dB are then fabricated in GaAs-AlGaAs. A compact and low-loss 1*4 power splitter incorporating this Y-branch is also described and demonstrated

In this paper we briefly review the approach and capabilities of the BPM method, and its applications to photonic devices and largescale PICs such as arrayed-waveguide-grating WDMs. Many numerical and analytical techniques have been developed for optical waveguide modeling. After briefly surveying these techniques, the talk will focus on the finite-difference BPM and the problems to which it can be applied. The method allows efficient simulation in 2D or 3D, can incorporate polarization via both semi- and full-vectorial approaches, can handle anisotropic media, nonlinear effects, and wide-angle circuits, and can perform mode solving as well as propagation calculations. As a specific example of the difficulties in treating large scale circuits, We give two approaches to the design of the arrayed-waveguide-grating based routers used in WDM sytems

Summary form only given. Perhaps the most important MMI structure is the 2*2 coupler, due to its use in such a variety of photonic integrated circuits. We propose here a new MMI stucture which reduces the proximity limitations by allowing the access waveguides to be well separated. This device allows for a major reduction in the device length through a taper of the MMI region width along the propagation axis. The shape of the MMI region is designed in such a manner that the splitting ratio at the end of the MMI region is preserved, even at the 3dB point. Numerical simulations of several such MMI structure designs are given

We describe studies of luminescence and lateral transport properties of excited carriers in GaAs-AlGaAs multiple quantum well (MQW) structures by cathodoluminescence measurements in a scanning electron microscope. We examine the effect of in-plane, etch-defined feature size on MQW luminescence efficiency and variability, and determine the diffusion length and its temperature dependence from 8 K to 250 K. Our measurements also provide information about nonradiative surface recombination velocity at the side walls of etch-defined MQW structures

We describe studies of luminescence and lateral transport properties of excited carriers in GaAs-AlGaAs multiple quantum well (MQW) structures by cathodoluminescence measurements in a scanning electron microscope. We examine the effect of in-plane, etch-defined feature size on MQW luminescence efficiency and variability, and determine the diffusion length and its temperature dependence from 8 K to 250 K. Our measurements also provide information about nonradiative surface recombination velocity at the side walls of etch-defined MQW structures

The development of a workable optical integrated isolator for use in photonic integrated circuits is increasingly important due to the rapid growth in fiber optical systems. No fully integrated isolator has been demonstrated as yet. The device that we propose here addresses a number of unresolved problems. Its Mach-Zehnder design eliminates the need for input and output polarizers present in conventional isolators; integration of the polarizers has been one the main stumbling blocks to achieving a fully integrated device. Low insertion losses are obtained using a vertically tapered Y-branch, recently demonstrated in our laboratories. The arms of the Mach-Zehnder interferometer are magnetized in opposite directions with a patterned thin-film magnet

In this paper, we report a new approach to a GaAs-AlGaAs TE/TM beam splitter which permits operation in the III-V materials system. Since III-V semiconductors do not show intrinsic material birefringence, our device is based on the birefringence induced by the electro-optical effect. Specifically, the device utilizes the large difference in propagation constants of the first-higher-order TE mode (TE/sub 01/) and the fundamental TM mode (TM/sub 00/) in the mode-sorting Y-branch

An analytical and numerical study of the accuracy of the beam propagation method that includes approximate treatments of wide-angle propagation based on Pade rational functions is presented. The investigation identifies the error terms associated with a sequence of higher order operators and the range of validity of different approximant operators is studied through examination of two-dimensional (2-D) waveguide structures. An analytical model for the general error in Pade-based wide-angle schemes is developed and compared with numerical simulations of simple waveguiding devices for which the exact solution is known. Guidelines for determining the range of error pertinent to the Pade operator are established

Microcontact printing ( mu CP) was used in conjunction with self-assembled monolayers (SAMs) of hexadecanethiolates to fabricate gold etch masks on GaAs and GaAs/AlGaAs quantum-well substrates; patterns in the mask were transferred into the semiconductor with an anisotropic dry chemical-etch process. The measured luminescence efficiency of the etched features in GaAs/AlGaAs was similar to that of samples patterned using conventional lithography; this observation indicates that no mechanical or chemical damage is incurred in the mu CP process

We present a study of pattern-transfer and etch-induced damage in photon-induced cryoetching. Features with effective radii as small as approximately=100 nm have been formed in both bulk and layered GaAs/AlGaAs materials. A measurement of the photoluminescence of etch-defined deep-submicrometer structures material suggests that this form of etching results in minimal process-induced damage. Modeling of the luminescence vs feature size for these features shows that the luminescence is limited only by carrier diffusion and non-radiative surface recombination

This letter describes the use of a compact sputter-deposited thin-film magnet that is directly integrated onto a waveguide isolator fabricated in magnetic thin-film garnets. Film magnets of different thicknesses are sputtered onto the waveguides, and isolation ratios of 29 dB are obtained with negligible excess loss. Stress-birefringent effects due to the ferromagnetic film overlayer are eliminated by the use of an aluminum compliant buffer

In this paper we will review our efforts in developing both design and fabrication capabilities for photonic integrated circuits. Design is based on software for CAD and beam propagation simulation of planar waveguide circuits. Fabrication is based on a laser-based rapid prototyping system for patterning and processing waveguide materials

Deep-etch-defined GaAs/Al/sub 0.3/Ga/sub 0.7/As square features of multiquantum well material, with dimensions as small as 160 nm, have been fabricated using magnetron reactive ion etching (MIE). Luminescence spectroscopy shows confinement of charge carriers to the features` center. The effects of rf power and etching time on the luminescence efficiency of these features and its concomitant etch-induced damage are examined

We compare low-temperature, excimer-laser-induced etching of GaAs, GaSb, InAs, and InSb surfaces covered with 1-2 monolayers of condensed Cl/sub 2/. The etch properties and a relative etch rate of GaAs GaSb<InAs<InSb are obtained. In addition, the etch rate of GaSb is characterized as a function of various system parameters, i.e., substrate temperature, chlorine pressure, and laser fluence. Spatially well resolved, anisotropic etching of 0.5 mu m features has been achieved

We report the results of a demonstration of a real time delay, optically controlled phased array radar receiver. This implementation employed a free space configuration based upon an optical switching network using liquid crystal spatial light modulators (SLM's). A three-delay unit, two-antenna array receiver was implemented at an optical wavelength of 1.3 mu m and demonstrated squint-free operation over the entire X-band (8-12 GHz) with an angular accuracy of 1.4 degrees . Finally, a novel configuration for the two-antenna element SLM architecture was proposed and demonstrated equivalent system performance with a reduction in the number of components

We have used laser direct fabrication techniques to implement optical delay lines on an epitaxial GaAs/AlGaAs substrate. These integrated photonic circuits, which are important for optically-controlled phased-array radar, include asymmetric splitters with various splitting ratios, smoothly curved 90 degrees bends, as well as linear waveguides. The delay lines were tested and found to have the desired delay and a power-output uniformity of +or-2-4%

We present a high-resolution, damage-free etching technique for GaAs and related compound semiconductors which utilizes surface-specific photochemistry at 193 nm to excite a physisorbed layer of Cl/sub 2/ on a cryogenically cooled ( approximately 140 K) sample. Etch rates as high as 0.25 AA/pulse (corresponding to 0.09 mu m/min) have been achieved. Etching is anisotropic, and etched features of 0.2-0.3 mu m linewidth have been routinely obtained. The etch rate has been characterized as a function of several system parameters including Cl/sub 2/-partial pressure, substrate-temperature, laser repetition rate and fluence, and the addition of rare gases. A phenomenological model of this cryoetching has been developed which agrees well with the experimental data. The etch damage and contamination have been studied with Auger electron spectroscopy, photoluminescence, and Schottky-barrier measurements. All results indicate that there is minimal if any damage induced by the cryoetching process

The fabrication of single quantum well (SQW) ridge waveguide ring laser in strained InGaAs is described which utilizes direct-write laser lithography followed by cryogenic UV laser-assisted etching. The laser has a threshold current of 270 mA and emits approximately 14 mW of single-frequency output