bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Two Wavelength Demultiplexing InGaAsP Photodetector
Authors: Campbell J. C. , Dentai A. G. , Lee T. P. , Burrus C. A.
Published: February 2023

Wavelength-division multiplexing is a technique that may be used to improve the efficiency, and increase the utility, of lightwave systems by expanding the information transmission rate without increasing the bit rate.1,2 Recently, we have reported a new device that uses stacked eiptaxial InGaAsP layers to integrate both detection and demultiplexing functions into a single photodetector.3,4 A difficulty in the fabrication of this structure results from dissolution of the lower-bandgap quaternary layer during the LPE growth of subsequent higher-bandgap layers. Further the dissolution is most severe for quaternary layers with bandgap energies smaller than 1.0 eV, and this has restricted operation of these devices to wavelengths ⪝ 1.25 µm. In this paper we will describe an "inverted" structure that has successfully eliminated this problem. Coupled with the achievement of lower doping levels in the LPE layers the resulting new structure exhibits substantial improvements in both the optical properties (quantum efficiency, optical cross-talk, long-wavelength cutoff) and the electrical properties (modulation bandwidth, electrical cross-talk).
Stacked Planar Optics - New Integrated Optics
Authors: Iga K. , Oikawa M. , Misawa S. , Banno J.
Published: February 2023

As the optical fiber transmission is widely applied to communication systems, we require a technology of large-scale production and integration of the optical circuits. In the conventional micro-optics1,2 we use distributed index rod lenses (or GRIN rods) as lens devices and this type of lens makes us difficult to make optical circuits in a single batch process. Stacked planar optics we propose here is based on the idea that we construct optical circuits by stacking planar optical devices such as planar micro-lenses, holes, apertures, filters, reflectors, polarizers and so on which are arranged on a substrate as a 2-dimensional array as shown in Fig 1. In this structure a number of optical circuits or the array of them can be formed monolithicaliy, and thus mass-production is possible by separating individual components.
Static and Dynamic Characteristics of Bistable Semiconductor Injection Lasers
Authors: Harder Ch. , Lau K. Y. , Yariv A.
Published: February 2023

As an optical counterpart to bistable electronic elements, such as schmidt-trigger, flip-flops and multivibrators, a bistable injection laser is projected to play an important role in the fast advancing field of opto-electronic signal processing. Lasers with inhomogeneous injection have been proposed more than a decade ago [1], [2] as highly compact bistable optical devices. Unfortunately inhomogenously pumped injection lasers showed to date no or only a small hysteresis [3], [4] and were in addition beset by pulsations in the optical output [5] for reasons not well understood.
W-Shaped Diffused Stripe (WDS) GaAs/GaAIAs Double Heterostructure Lasers Grown by Metalorganic Chemical Vapor Deposition
Authors: Hong C. S. , Liu Y. Z. , Coleman J. J. , Dapkus P. D.
Published: February 2023

Low-threshold single-mode lasers are needed in the integrated optics application. We report here a simple laser structure which has a built-in lateral confinement for both the current and the light. The structure reported here is similar to the conventional Deep Diffused Stripe (DDS) lasers1,2 but without the need for precise control of diffused dopings as required in the latter. The new structure consists of an n-p-n instead of all n double-heterostructure (DH) layers grown on an n-GaAs substrate. The stripe region is formed by deep Zn diffusion to the p-type active layer with a W-shaped diffusion front (see Fig. 1). The n-p-n structure outside the stripe region automatically forms a reverse-biased junction, while the W-shaped diffusion front provides a lateral refractive-index profile for an optical waveguide.3 With an over-all 6 to 7 μm stripe width, the devices have threshold currents as low as 30 mA. An excellent light-current (L-I) linearity and single-mode operation of these lasers are observed up to about two times their threshold currents. Preliminary results indicate that these lasers also have good modulation characteristics.
A new (A1Ga) As buried convex waveguide structure laser with a truncated convex active region
Authors: Hanamitsu K. , Shima K. , Takusagawa M.
Published: February 2023

A buried heterostructure (BH) laser1) has many attractive features such as low threshold and stable fundamental transverse mode oscillation. Recently, we reported a new type of a channeled substrate buried heterostructure laser2) called as a buried convex waveguide structure (BCS) laser3). The BCS laser consistently succeeded in stable fundamental transverse mode oscillation, but the fundamental transverse mode oscillation was limited below 5-6 mW/facet. The suppresion of the higher order modes in the convex waveguide is due to the fact that thickness fluctuations of the tapered portion bring about large scattering loss for higher order modes4). The large difference of the scattering loss between fundamental mode and higher order modes makes it possible to obtain stable fundamental mode lasing up to high power level. This may be realized in a truncated convex waveguide where the fundamental mode mainly distributes in the center flat region with small loss but the higher order modes distribute over the tapered portion giving large scattering loss. In this paper, we report an improved BCS laser with a truncated convex active region which enables to realize stable fundamental mode lasing up to 20 mW/facet, and its reproducible fabrication technique.
AℓGaAs Lasers With Micro-cleaved Mirrors Suitable for Monolithic Integration
Authors: Blauvelt H. , Bar-Chaim N. , Fekete D. , Margalit S. , Yariv A.
Published: February 2023

Recently, there has been substantial interest in the monolithic integration of semiconductor lasers with other optoelectronic devices. (1-3) The conventional method of obtaining optical feedback in a semiconductor laser is to cleave opposite facets of the substrate. However, with this method, the number of optoelectronic devices that can be integrated onto the chip with the laser is severely restricted by the laser cavity length, which is typically about 300 μm.
An Integrated Optics Picosecond Transient Digitizer
Authors: Stegeman G.I. , Normandin R.
Published: February 2023

When two equifrequency contra-propagating waves mix near the surface of a material, a harmonic field is generated normal to the surface (1-3). This phenomenon has previously been utilized in Ti: indiffused LiNbO3 waveguides to perform the convolution of picosecond optical waveforms (4). Here we demonstrate another novel application of this interaction, namely to a transient digitizer for the recording of multi-picosecond optical signals with sub-picosecond time resolution.
Piezoelectric PVF2 (polyvinylidene fluoride) Compensator for Fiber Interferometer
Authors: Koo K. P. , Sigel G. H.
Published: February 2023

A phase-drift compensator is needed for optical fiber interferometric sensors to correct for normal environmental effects such as temperature and air-current fluctuations.1 Previously, piezeoelectric PZT compensators using ~ 10 meters of fiber have been reported.1,2 Light weight piezoelectric PVF2 material has been found to have large phase shifting capability (~ 4 radians/V-m) in a fiber interferometer.3 Taking advantage of this property, a PVF2 compensator using modest length of fiber (60 cm) has been successfully implemented for the first time.
Low-Loss Ti:LiNbO3 Waveguide Bends at λ = 1.3 μm
Authors: Minford W. J. , Alferness R. C.
Published: February 2023

Low-loss waveguide bends are necessary for many proposed integrated optical circuits to improve the packing density, and for certain devices, e.g., directional couplers. Previous bend loss measurements have been reported for Ti: LiNbO3 at λ = 0.633 μm and 1.06 μm, with losses as low as 0.3 ± 0.3 dB for an S-shaped transition between straights separated by 3 mm longitudinally with an lateral offset of 0.10 mm.1 For comparable transition regions bend losses of 2-3 dB were measured using two constant curvature segments,2 4 dB using a straight-segment transition,3 and 1.8 dB using three straight segments with coherent coupling.4
Photodetector and Compatible Low-Noise Amplifiers for Long-Wavelength Light-Wave Receivers
Authors: Campbell J. C.
Published: February 2023

This paper reviews photodetector/low-noise-amplifier combinations for light-wave receivers. Included are recent experimental results and theoretical limits for avalanche photodiodes and a PIN photodiode/amplifier combination as well as some promising new structures.
A Gallium Arsenide Electrooptical Interferometric Modulator*
Authors: Donnelly J. P. , DeMeo N. L. , Ferrante G. A. , Nichols K. B. , O'Donnell F. J.
Published: February 2023

Interferometers in which the effective length of one arm can be electronically varied are important optical components for signal processing and high-speed laser modulation. Integrated optical Mach-Zehnder interferometers have been fabricated in LiNO3 but, to our knowledge, there have been no reports of such an interferometer in the III-V semiconductors. Interferometers in the III-V's have the potential of being integrated with lasers, detectors and high speed electronic devices for a truly monolithic integrated optical circuit. In this paper we report initial results on a GaAs interferometer capable of amplitude modulation via the electrooptic effect.
Planar Waveguide 8-port Branched Circuit
Authors: Okuda Eiji , Wada Hiroshi , Yamasaki Tetsuya
Published: February 2023

An optical branched circuit is one of the important devices in optical communication systems. Several different types of such optical device have been reported.1),2),3) We previously reported a 4-port branched circuit with planar gradient-index glass waveguide fabricated by an electric field assisted two stage ion migration process.4)
Single-Mode Fiber Devices
Authors: Stolen R. H.
Published: February 2023

Optical fibers were once thought of strictly as a transmission medium. It was expected that any processing of the optical signal would take place outside of the fiber; either by conventional electronics, or by devices based on planar integrated optics. Over the years this situation has changed, as many optical components, that are made directly with single-mode fiber, have been reported. Such components include directional couplers, polarizers, phase modulators, polarization transformers, filters, and optical amplifiers. Most of these components require control over the state of polarization, and take advantage of recent improvements in polarization preserving fibers. At the same time there has been a steady improvement in single-mode fiber splicing techniques. It is thus becoming possible to think of fairly complex devices based on combinations of several inline single-mode fiber components.
Fused-Fiber-Array Structure and its Application to Polarizing Directional Coupler
Authors: Kawachi Masao , Kobayashi Morio , Noda Juichi
Published: February 2023

Fiber-optic devices such as polarizers and directional couplers are required for single-mode fiber communications and fiber sensor systems. In order to fabricate these fiber-optic devices, it is necessary to modify the fiber structures. Such modifications have been usually achieved by etching, polishing or fusion/tapering of the fibers.1)
Efficient Fibre-chip Coupling using Ion-milled Alignment Grooves on Lithium Niobate at λ = 1.3μm.
Authors: Nutt Alan C. G. , Bristow J.P.G. , McDonach A. , Laybourn P.J.R.
Published: February 2023

To make realistic use of the vast range of integrated optic devices, both active and passive, on lithium niobate, as in other substrates, it is necessary to produce efficient, reliable and repeatable fibre to waveguide couplers. High efficiency can be achieved (Ref.1) by micro manipulating the fibre butted to the waveguide, while also taking steps to reduce modal field mismatch. Manipulating the fibre is however a complex and time-consuming operating which does not easily lend itself to multi-port devices. The use of silicon 'V' grooves (Ref.2) can aid fibre alignment and reduce the complexity of the operation while maintaining a high coupling efficiency. However, the component utilises two technologies and the alignment of multi-port devices face down onto the silicon surface poses problems. Problems may also arise from silicon and lithium niobate having different thermal expansion coefficients.
Fundamental Diffraction Limits of the Performance of Chirped Grating Lenses
Authors: Delavaux Jean-Marc P. , Chang William S. C.
Published: February 2023

Although highly efficient chirped grating lenses have been reported[1−7], their performance that will combine high efficiency η with large angular field of view Δθ or high η with low F-number is limited by the phase distortion in the diffraction process and by fabrication tolerances. In this paper, we will show how the coupling coefficient Kc and the minimum periodicity Λmin will limit the lens performance (i.e. η, Δθ and F). The efficiency is also sensitive to the variation of the line width to space width ratio obtained in the lithographic process. However, it is insenstive to the position accuracy of the individual grating grooves.
High-Speed PLZT Optical Switches
Authors: Yamazaki Osamu , Wasa Kiyotaka , Kawaguchi Takao , Manabe Yoshio , Adachi Hideaki , Higashino Hidetaka , Setsune Kentaro
Published: February 2023

PLZT [(Pb,La)(Zr,Ti)O3] thin film is one of the most promising materials for optical integrated circuits. The PLZT films have potential for their stronger electrooptic effect than conventional Ti-diffused LiNbO3 and for monolithic integration with other active devices fabricated on a same substrate. Several workers have tried to prepare PLZT films of optical quality1,2). Using an rf-planar magnetron sputtering system, we succeeded in epitaxial growth of PLZT single crystal film on sapphire from PLZT(28/0/100) target and confirmed an electrooptic effect of the film3). Basic operation of optical switches have been also confirmed4). In this paper, we report high frequency operation, optical damage of the PLZT switches and propose a butt-coupling technique in a layered structure.
Acousto-Optic Birefringent Fiber Frequency Shifters
Authors: Risk W.P. , Youngquist R.C. , Kino G.S. , Shaw H.J.
Published: February 2023

Single-mode birefringent fiber guides two orthogonally polarized waves. These waves travel at slightly different speeds, giving rise to a beat pattern as the net polarization state evolves with propagation down the guide. A periodic stress pattern, with spatial period equal to the beat length of the fiber, can produce coupling between these two modes1. If the stress pattern is itself a travelling wave, light coupled from one polarization to the other will be shifted in frequency by the frequency of the acoustic wave.
InGaAsP/InP λ=1.3μm Channelled Substrate Buried Heterostructure Lasers with Vapor Phase Epitaxial Current Confinement Layers
Authors: Wilt D. P. , Karlicek R. F. , Strege K. E. , Dautremont-Smith W. C. , Dutta N. K. , Flynn E. J. , Johnston W. D. , Nelson R. J.
Published: February 2023

We have fabricated 13 μm InGaAsP/InP channelled substrate buried heterostructure lasers with vapor phase epitaxial (VPE) grown current confinement structures to increase throughput and reduce the cost of devices. The cross section of the device fabricated is indicated in Figure 1. Three layers of InP are grown by hydride transport VPE to form the npn base structure which is v-groove etched and regrown by liquid phase epitaxy.
Noise and Dynamic Aspects of Semiconductor Lasers
Authors: Yariv Amnon , Vahala Kerry
Published: February 2023

Recent experimental progress in the field of semiconductor-laser noise and spectra are summarized and the dynamic extension of the conventional (Schawlow-Townes) noise theory and conventional (Lamb) laser theory, which are needed to account for the new observations are described.
Microwave Direct Frequency Modulation of Cleaved-Coupled-Cavity InGaAsP Channeled Substrate Lasers
Authors: Tucker R. S. , Bowers J. E. , Burrus C. A.
Published: February 2023

It is well known that directly modulated semiconductor lasers exhibit changes in oscillation frequency due to variations in the refractive index and cavity temperature [1]. Frequency modulation (FM) and frequency shift keying (FSK) are potentially useful in coherent lightwave communications but pulse spreading resulting from fiber dispersion associated with undesired FM can seriously degrade the performance of high-speed long-haul intensity modulation systems.
Fabrication of Titanium-In-Diffused Lithium Niobate Optical Waveguides by Laser Annealing at 10.6 μm
Authors: Parmenter M. , Holman R. L. , Wood V. E. , Busch J. R. , Long G.
Published: February 2023

The most common method for fabricating high quality planar and channel waveguides in electrooptic lithium niobate is titanium in-diffusion.1 This process typically involves uniform heating, in a furnace, of polished lithium niobate single crystal substrates on which dense, thin titanium metal films have been deposited. The process, nowadays, is normally conducted for 5-6 hours in moistened oxygen2 at 1000°C. As the diffusion furnace is heated to 1000°C, or during an intentional pre-soak at 600°C, the titanium film oxidizes to titanium dioxide. This oxide precursor then reacts with the crystal surface layers in a complex mechanism culminating in the diffusive incorporation of titanium ions within the lithium niobate lattice.
Integrated-Optical Channel-Waveguide Frequency Shifter*
Authors: Johnson L. M. , Becker R. A. , Kingston R. H.
Published: February 2023

Single-sideband optical frequency shifters compatible with optical fibers would be useful in a variety of applications including fiber-optic gyros and optical heterodyne communciations. Acoustooptic frequency shifters, which are now commonly used, are not compatible with optical fiber systems since they are broad-beam devices and require angular tuning to utilize their full electrical bandwidth. Here we present experimental results on a channel-waveguide frequency shifter being developed independently by us and others1 which utilizes TE/TM mode conversion produced by a traveling refractive-index-wave perturbation. In our approach, an interdigitated electrode structure is driven with a three-phase electrical signal to generate the index perturbation so that phase matching and therefore high conversion efficiency can be obtained from arbitrarily low frequencies to several gigahertz. The use of a three-phase-drive interdigitated electrode array is similar in concept to the wide-band slab-waveguide Bragg-diffraction frequency translator reported earlier.2 In the initial device reported here, which was fabricated in Ti:LiNbO3 for operation at λ = 1.15 μm, we obtained 10% conversion efficiency at 90 MHz. Much higher conversion efficiencies should be obtainable with improved designs. Here we report on the principles of operation of these devices, their fabrication, and the experimental results.
Nondestructive technique for rapidly assessing the stability of lithium niobate electrooptic waveguide devices
Authors: Beaumont A. R. , Daymond-John B. E. , Stallard W. A. , Booth R. C.
Published: February 2023

Lithium niobate optical waveguide devices are currently being investigated for use in advanced optical fiber transmission and sensor systems.1 In many of these systems it is necessary to apply a constant bias voltage to the LiNbO3 device. However, the performance of these devices can some-times be limited by an electric field-induced temporal instability or drift.2,3
Gain measurements of InGaAsP 1.5-μm optical amplifiers
Authors: Eisenstein G. , Jopson R. M. , Linke R. A. , Burrus C. A. , Koren U. , Whalen M. S. , Hall K. L.
Published: February 2023

Optical amplifiers will be important components in future optical communication and signal processing systems. Semiconductor Fabry-Perot amplifiers (FPA), i.e., injection lasers driven below threshold, have actually been demonstrated in experimental systems.1 However, FPA suffer from extremely narrow gain bandwidth and low saturated output power.2 On the other hand, traveling wave amplifiers (TWA)3 (ideally with zero reflectivity facets) have the potential for extremely wide bandwidth operation and high saturated output power. In practice, of course, zero reflectivity facets are impossible to achieve. Therefore, all semiconductor injection amplifiers may be viewed as FPA with a continuum of facet reflectivities ranging from that of cleaved mirrors to the lowest obtainable reflectivities. Since the facet reflectivities, however low, are always finite, the amplifier gain spectrum is not flat, and these wavelength-dependent gain variations must be considered when wide-bandwidth amplification is desired. The gain spectrum of a semiconductor optical amplifier can be approximated using a simple model which incorporates a single-pass gain g in the simple Fabry-Perot transmission equations.4 The gain spectrum G(λ) is then, where R is the facet reflectivity, and δ = 2π, (i/λ), i is the amplifier length, and λ. is the wavelength inside the amplifier. K is a coupling coefficient including coupling into and out of the amplifier.
An lnGaAsP-LiNbO3 directional coupler ring laser
Authors: Eisenstein G. , Alferness Rod C. , Korotky Steven K. , Taylor M. K. , Veselka J. J. , Buhl L. L. , Stulz L. W. , Burrus C. A. , Koren U. , Tucker R. S.
Published: February 2023

LiNbO3 waveguide devices operating in the 1.3−1.6-μm wavelength region with very low total insertion losses have now been demonstrated.1 Such low losses enable the use of these devices as intracavity active elements in a variety of composite-cavity semiconductor lasers. Such lasers are important for narrow-linewidth sources in coherent communications2 and for mode locking.3 Most reported composite-cavity lasers use a passive extended cavity, but active extended cavities are attractive, since they enable a variety of control functions to be incorporated in addition to the control produced by the drive current to the gain medium.
High-speed electroabsorption modulator with strip-loaded InGaAsP planar waveguide
Authors: Noda Y. , Suzuki M. , Kushiro Y. , Akiba S.
Published: February 2023

Monolithic integration of distributed feedback (DFB) lasers and external modulators1 is a very promising approach to high-performance intensity-modulated sources in a high-bit-rate optical fiber communication system. An electroabsorption (EA) or Franz-Keldysh effect modulator2-4 is an efficient candidate for the integrated external modulator. We report characteristics of InGaAsP/InP double-heterostructure (DH) EA modulators grown by vapor-phase-epitaxy (VPE); this is the first report of high-frequency operation over 1 GHz of EA modulators.
Novel tunable pulsed dye laser holography and subsequent processing for fabrication of optoelectronic device gratings
Authors: Contolini R. J. , Osinski J. S.
Published: February 2023

A novel grating fabrication technique which has the capability for ease of fabrication of many very long cavity DFB lasers (>1000 μm), single substrate DFB/DBR laser arrays, single-substrate wavelength multiplexer/demultiplexers, and other optoelectronic devices has been developed. This technique utilizes a tunable pulsed dye laser for obtaining an interference grating in photoresist. The dye laser is characterized by a high peak power and uniform non-Gaussian beam. This is an advantage compared to typical cw fixed-frequency laser systems,1-3 whose Gaussian beams provide nonuniform photoresist exposure which is acceptable only in their central regions. The high average power of the present laser also allows exposure of large areas without significant sacrifice in exposure time, and the tunability provides ease of fabrication of any desired grating periodicity.
Dielectric grating evanescent reflectors in double-mode fibers
Authors: Liu K. , Sorin W. V. , Shaw H. J.
Published: February 2023

Grating reflectors are interesting as narrowband filters for optical fiber wavelength-division multiplexing. In particular, gratings directly in the evanescent field of a guided mode offer possibilities for all-fiber in-line components. Previously, evanescent grating reflectors have been demonstrated with single-mode fibers.1 Although efficient reflection appears possible, single-mode reflectors have the disadvantage of needing an element such as a directional coupler to extract the reflected signal returning on the same fiber. The problem is that the forward signal is also split by the coupler. Such an arrangement incurs a minimum of 6-dB loss to the extracted reflected signal.
Passive and active GaAs and InP integrated-optic components fabricated using localized vapor phase epitaxy
Authors: Erman M. , Vodjdani N. , Theeten J. B. , Jarry P. , Stephan P.
Published: February 2023

Various fabrication methods for semiconductor waveguides have already been proposed. Recently,1 localized vapor phase epitaxy (LOCVPE) (a chloride process) was found to be an attractive alternative solution to the conventional etching-based techniques (rib or ridge waveguides). Losses of 1 dB/cm in GaAs have been measured, the LOCVPE process has been further developed, and new structures have been made on both GaAs and InP. Figure 1 illustrates three possible waveguide structures. In Fig. 1(a) an external waveguide is fabricated by epitaxial growth through a stripe opening in a dielectric overlayer. The waveguide’s cross section depends on the growth conditions but is, in all cases, limited by perfect crystallographic planes. Using a similar dielectric overlayer and performing an in situ high-temperature (720°C) chemical etching (HCI) prior to growth, an embedded waveguide can be obtained [Fig. 1(b)]. Figure 1(c) illustrates the case when a V-groove is made on a substrate which is not covered with the dielectric film, the VPE anisotropy being then adjusted to obtain a perfectly planarized waveguide structure. For all these structures, the main advantage of LOCVPE is to grow extremely smooth facets and thus to reduce the losses from scattered light. The measured losses are dominated by the free electron absorption of the substrate. The importance of this absorption for various waveguide structures as well as doping of the substrate will be discussed.
Modal dispersion of GaAs/AlGaAs multiple quantum well waveguides
Authors: Sonek G. J. , Ballantyne J. M. , Chen Y. J. , Carter G. M. , Brown S. W. , Koteles E. S. , Salerno J. P.
Published: February 2023

The current interest in GaAs/AlGaAs multiple quantum well (MOW) materials has developed because of unique electronic and optical properties due to the presence of the 2-D room temperature excitons in these structures.1 Applications of multiple quantum wells to modulators and detectors have previously been reported.2 Only recently, however, have the excitonic properties of quantum wells been exploited in optical waveguide geometries.3,4 Here we present results of a study on single-mode multiple quantum well asymmetric slab waveguides using the grating coupling technique.
Progress in Semiconductor Integrated Optics
Authors: Wang S.Y.
Published: February 2023

Ultrahigh speed photonic components are necessary to exploit the wide bandwidth available when using lightwaves as the carrier frequency for telecommunication and instrumentation applications. On the transmitter end, a high speed modulator is needed to impress the electrical signal onto the lightwave carrier. Direct modulation of a semiconductor laser is most efficient but suffers from spectral broadening [1]. Spectrally pure signal are necessary for long distance transmission in optical fibers neccesitating the development of external modulators. Over two decades ago, modulators were developed in both lithium niobate and GaAs [2]-[6]. However due to the poor material quality in GaAs resulting in high excessive insertion losses, the material of choice was lithium niobate. With numerous refinement, the modulator and switch technologies in lithium niobate have progressed to Mach Zhenders and directional couplers with bandwidths in excess of 40 GHz. With recent improvements in III-V epitaxial technologies, substrate qualities and superlattice techniques to pin defects, the III-V modulator is once again been studied [7] [8] [9]. Moreover, because III-V materials offer the obvious advantage of monolithic integration of active/passive photonic and electronic devices to form the foundation of optical electronic integrated circuits (OEIC), III-V may eventually replace lithium niobate. Travelling wave GaAs electro-optic waveguide modulators at a wavelength of 1.3 μm with bandwidth in excess of 20 GHz have been developed and characterized. The design and characteristics of both p-i-n modulators in microstrip configuration and Schottky barrier on n− – GaAs/semi-insulating (S.I.) GaAs in the coplanar strip configuration modulators will be discussed. It will be shown that microwave loss and slowing on n
+
GaAs substrates will limit the bandwidth of the microstrip modulator to less than 10 GHz for a device 8 mm in length. Modulators with bandwidths in excess of 10 GHz are fabricated on S.I. GaAs substrates. The structures of the devices are shown in Fig.(l) and (2) [10][11].
Scattering and Coherent Coupling in Low-loss GaAs Waveguides and Bends
Authors: Deri R.J. , Hawkins R. J. , Kapon E. , Schiavone L.M.
Published: February 2023

The advent of low-loss semiconductor waveguides1-4 enables us to study loss mechanisms which were previously unobservable. Earlier reports1,2,3 of GaAs waveguides with propagation loss α < 1 dB/cm emphasized reducing losses due to material absorption and epilayer roughness; guide fabrication must be optimized to further reduce α. We recently demonstrated4,5 single­mode, low-loss (α = 0.3dB/cm) GaAs guides with the tight confinement necessary for compact waveguide bends; such performance depends critically on rib fabrication (fig. 1), indicating important loss phenomena at rib surfaces. In this paper we explore two phenomena in low-loss GaAs waveguide structures: fabrication-related propagation loss and coherent coupling in circular bends. In both cases, scattering from rib wall roughness plays a significant role.
Low-loss single-mode plastic waveguide fabricated by photopolymerization
Authors: Miura K. , Sawaki I , Nakajima H.
Published: February 2023

Plastic materials used for optical fibers are very attractive as optical waveguides because of the simple fabrication process and their low loss. There have been several reports on plastic waveguides that were fabricated by photopolymerization of the dopant monomer[1], and some had a propagation loss as low as 0.2 dB/cm[2],[3]. However, they were 2-mode or multi-mode waveguides. We now report a single-mode waveguide using polystyrene, PSt-doped poly(methyl methacrylate), PMMA. The combination of PSt/PMMA was chosen because the refractive index of PSt (n=1.59) is considerably larger than that of PMMA (n=1.49), and the solubility of PMMA in styrene is good. The fabrication process is shown in Fig. 1. The clad solution, which consisted of 10% PMMA and 90% MMA, was spin-coated at 3000 rpm on a Si substrate and baked at 90°C for 30 minutes. The core solution was also spin-coated on the PMMA clad film and baked at 60°C for 2 hours. The core solution consisted of 12% PMMA, 72% styrene, 8% aceto-phenone photoinitiater, and 8% 1,4-dioxane. The film thickness was 2 μm for the clad and 3 μm for the core. The styrene monomer for the waveguide region was polymerized by UV-light exposure through a photomask, and the unreacted monomer was removed by postbaking at 90°C for 30 minutes. Figure 2 shows the refractive index change as a function of exposure energy at the 365 nm wavelength. A maximum index change of 0.01 was obtained under this fabrication condition for the 633 nm wavelength. The channel waveguides were fabricated using a photomask which included 1- to 10-μm-wide, 60-mm-long straight waveguide patterns. Single-mode waveguides were obtained for 1 to 3 μm pattern widths with a 0.005 refractive index change. Propagation loss was measured by detecting the scattered light along the waveguide[4] (Fig. 3). The input light from the He-Ne laser was coupled through a microscopic objective lens to the waveguide and scattered light was collected by a 0.9-mm-core plastic fiber. A propagation loss of 0.1 dB/cm was obtained for the single mode waveguide (2- to 3-μm pattern width).
Zero Crosstalk Conditions for Crossed Δβ Switches with Symmetric Branches
Authors: Burns W.K.
Published: February 2023

Directional couplers with crossed Δβ electrodes1 remain widely used due to their ability to achieve good crosstalk levels. Recently several authors have discussed crosstalk issues in these devices due either to limitations of coupled mode theory itself2 or due to effects of the input and output transition (branching) structures3,4. Findakly and Leonberger4 have noted that bar states achieved with reverse phase mismatch cannot achieve zero crosstalk due to the mode coupling that occurs in the transition structures.
Dopant Diffusion Loss Mechanism in High-Birefringent Fiber Fused Couplers
Authors: Pickett C.W. , Burns W. K. , Villarruel C. A.
Published: February 2023

Fused fiber couplers 1,2 made with polarization-preserving, high-birefringent fiber have received great interest because of their low-cost fabrication potential and their application for optical polarization control in fiber-optic sensors. To date most laboratories that have attempted the fabrication of these devices have experienced mixed success in terms of achieving a reproducible fabrication process. Our experience has been that devices can be fairly readily made with some fiber samples2, but that insertion loss reaches unacceptable levels (>>1dB) with other fiber samples.
Integrated Optic High Frequency Phase Comparator
Authors: Walpita L. M. , Wang S. C. , Chang W. S. C.
Published: February 2023

We describe a novel high frequency phase comparator based on large signal modulation of an integrated optic Mach-Zehnder interferometer. In this device two high frequency electrical signals are fed into the electrodes on the two channels of the Mach-Zehnder modulator. The phase difference of the two signals is measured by determining the optical intensity of the output of the modulator.
A Fast Organic-on-Inorganic Semiconductor Photodetector
Authors: So F.F. , Forrest S.R. , Garvin H.L. , Jackson D.J.
Published: February 2023

It has been shown that certain crystalline organic semiconductors such as 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) form rectifying energy bariers1 when deposited onto inorganic semiconductor substrates; for example, Si, GaAs and InP. The organic-on-inorganic semiconductor (OI) heterostructure devices are particularly useful in fabricating many novel devices such as organic-on-inorganic semiconductor transistors2 due to the low reverse leakage current. The high index of refraction and high transmittance in the organic material also enable them to be used for optoelectronic device applications such as optical waveguides and photodetectors. In particular, since PTCDA is transparent in the infrared region it is very useful for waveguide, and various other optoelectronic device applications.
Active Mode-Locking of a 13-μm Extended-Cavity Silicon Chip Bragg Reflector Laser
Authors: Raybon G. , Tucker R. S. , Eisenstein G. , Henry C. H.
Published: February 2023

Recently, we have demonstrated several experimental high speed transmission systems using optical time division multiplexing (OTDM) [1,2]. Unlike conventional high speed systems [3], where the data transmitted is modulated using a 50% duty cycle, these OTDM systems use short optical pulses generated by mode-locked extended-cavity semiconductor lasers [4]. Optimum performance in these OTDM systems [1,2], where up to four separate sources are time multiplexed, is limited by fiber dispersion caused by the wide spectral widths and unmatched wavelengths of the different mode-locked lasers [1,2]. In the absence of any frequency selective element within the composite cavity, the spectral characteristics of these lasers are difficult to control, and thus point to a need for a mode-locked laser structure which includes some form of frequency control. We describe here a laser which contains the desired intra-cavity frequency selective element; the external-cavity silicon chip bragg reflector (SCBR) [5] mode-locked laser. SCBR lasers with short passive cavities have demonstrated single frequency operation and very narrow linewidth [6]. We have used a long (~5 cm) passive cavity of the same type to achieve mode-locking at frequencies around 2 GHz.
The Digital Optical Switch: Theory and Applications
Authors: Silberberg Y. , Perlmutter P. , Baran J. E.
Published: February 2023

We describe a novel four-port (2X2) digital electrooptic switch where the light output exhibits a step-like response to the switching voltage. This response characteristic eliminates the need for precise voltage control for switching and it therefore enables the operation of many such elements by a single voltage source, as required for switching arrays. Moreover, the new device can switch both polarization components simultaneously and is insensitive to the precise wavelength of light. The performance of this switch does not depend critically on any of the design parameters, and therefore it is quite tolerant to variation in the fabrication process.
A synthesized digital switch using a 1x2 directional coupler with asymmetric Δβ phase reversal electrode
Authors: Thaniyavarn Suwat
Published: February 2023

We describe a new design of an electro-optic switch with a flat "digital" voltage response in which precise control of switching voltage is not required in order to achieve low crosstalk. Conventional switches require precise control of voltage in order to achieve a switched state with very low crosstalk. For example, the directional coupler requires an electro-optically induced phase shift of ΔβL/π = √3 between the waveguide pair to switch.[1] The I0-V characteristic for directional coupler with L=lc is shown in Figure 1. In order to keep the crosstalk between the two outputs below -30db, one needs to apply and maintain the switching voltage (ΔβL/π) to within a very narrow range of ±0.03 for the "cross-state" and 1.69 to 1.77 for the "straight-through" state. Therefore, even a small voltage drift can cause problem. Precise control of the applied switching voltage must be maintained at all time.
Voltage-tunable wavelength filtering with a non-symmetric interferometer
Authors: Jacket Janet Lehr , Johnson John
Published: February 2023

There is increasing interest today in the use of wavelength division multiplexing in fiber communications systems, both to increase network capacity and to provide network flexibility. Many of the network architectures currently under study require, or would benefit from, tunable single-mode wavelength filters, multiplexers, or demultiplexers. We report here the use of a non-symmetric interferometer as a voltage-tunable wavelength filter with periodic wavelength response. We show that this filter can be used as a wavelength multiplexer, using known integrated optic components, and that it can be cascaded to separate 2n channels in n stages. We have made a series of filters with channel separation of 11 to 26 nm, using standard Ti:LiNbO3 waveguides. The filters are tunable over the period of their response, requiring less than 8 volts to tune through the complete period, and are capable of high speed operation.
Grating Outcoupling From Large Area Rib Waveguide Arrays Fabricated on Titanium Indiffused Lithium Niobate Substrates
Authors: Rastani K. , Tanguay A. R.
Published: February 2023

The Integrated Optical Synthetic Aperture Radar (IOSAR) Processor [1] is one of a number of potentially powerful optical signal processing components that combine many of the throughput characteristics of bulk optical processors with the cost, size, and power advantages of guided wave optical devices. One of several novel features of the IOSAR processor is the capability of performing an inherently two dimensional image formation function in an integrated optical configuration by a combination of spatial and temporal integration. This can be accomplished as shown schematically in Fig. 1. The radar return (a linear FM chirp) is input to the processor by means of a surface acoustic wave transducer. Coherent light from a pulsed laser diode is collimated by lens L1 and focused on an array of rib waveguides by lens L2 (a spatial integration). The large area waveguide array performs an image dissection in the range dimension. Light propagating in a given rib waveguide (a given range bin) is then selectively outcoupled through a mask encoded with the azimuth doppler history onto a two dimensional CCD detector operated in the shift-and-add mode. Sequential radar returns are then integrated with appropriate shifts (a temporal integration) to perform the required azimuth compression.
Monolithic Two-Dimensional GalnAsP/InP Laser and Lenslet Arrays*
Authors: Liau Z. L. , Walpole J. N. , Diadiuk V.
Published: February 2023

Recent development of low-threshold surface-emitting diode lasers offers new possibilities for optoelectronic integration, on-wafer testing and monolithic two-dimensional (2D) laser arrays(1-9). The 2D arrays have the potential of very large number of integrated lasers and can possibly be coherently phase-locked to form a single high-power laser with high efficiency and narrow, symmetric beam divergence. In this paper, we review recent progress in GaInAsP/InP 2D laser arrays. Attempts have been made to address important issues such as array uniformity, size, performance, heat dissipation and possibility of coherent phase locking. A new technique for fabricating large-numerical-aperture lenslet arrays is also reported.
Room temperature c.w. GaAs surface-emitting laser with integrated Bragg reflector
Authors: Faist J. , Morier-Genoud F. , Martin D. , Ganiere J.D. , Reinhart F.-K.
Published: February 2023

The surface-emitting laser [1,2] is expected to revolutionize semiconductor laser array technology. It will permit to reduce beam divergence and increase the emitted power through utilisation of a larger aera of the wafer. The ultrashort cavity also provides for essentially single longitudinal mode operation. It was shown recently that Fabry-Perot resonators with all-dielectric mirrors can be grown [3,4], and that these structures can lase when photopumped [5]. Similar structures can also be used for efficient photonic switching. In this paper, we demonstrate the first low threshold photopumped surface-emmiting laser that operates c.w. at room temperature.
InGaAsP/InP Buried-Heterostructure Lasers and Laser Arrays Fabricated by Ion-Beam-Assisted Etching
Authors: Yap D. , Walpole J. N. , Liau Z. L.
Published: February 2023

In recent years, dry etching techniques such as ion-beam-assisted etching (IBAE) [1] have gained considerable application in the fabrication of semiconductor guided-wave devices. In contrast to the more conventional wet-chemical etching techniques, IBAE has less material and crystallographic dependence and is capable of forming deep, vertical grooves without undercutting the mask. In this paper, we report the use of IBAE to fabricate various types of 1.3-μm wavelength InGaAsP/InP mass-transported buried-heterostructure (BH) lasers [2,3]. These devices include high performance single-stripe lasers and Y-coupled BH laser arrays [4] with deep rectangular mesas defined by IBAE, lasers with flat and cylindrical end-mirrors [5,6] which are etched and mass-transported concurrently with the mesa stripes, and arrays of diffraction-coupled BH lasers [7,8] in which the mirror at the end of the coupling region has a scalloped surface designed to improve the coupling.
Nonlinear Directional Coupler as a Femtosecond All-Optical Switch
Authors: Silberberg Y. , Weiner A.M. , Friberg S. R. , Sfez B. G. , Smith P. W.
Published: February 2023

All-optical switching devices have attracted considerable attention recently due to their potential for ultrafast switching. Using very rapid electronic nonlinearities in transparent materials, high speed switching free of thermal limitations at high rates can be achieved. A nonlinear directional coupler, first proposed by Jensen [1] and recently demonstrated by Friberg et al [2], is a promising all-optical switch. In this device switching speeds are limited only by the material response and not by transit times. Ideally, the response of such a switch is determined by the instantaneous intensity of the light; however, due to self phase modulation, group velocity dispersion and the finite bandwidth of the element, there will be a limiting switching speed. In this work we report the first study of femtosecond switching in a nonlinear directional coupler, and discuss the implications of nonlinear switching of ultrashort pulses.
Integrated All-Optical Modulator and Logic Gate for Fiber Optics Systems
Authors: Normandin R. , Houghton D.C. , Simard-Normandin M.
Published: February 2023

Advances in optically nonlinear materials and single mode fiber technology have led to a renewed interest in integrated optics. Recent advances in nonlinear integrated optics also hold promises for applications in ALL-OPTICAL processing and interfacing of fiber signals. Here we present some of our work on all-optical modulation and logic gates in silicon based channel waveguides at wavelengths of 1.32 and 1.55 micrometers. PicoJoule switching energies and subpicosecond initiation times make these waveguide devices attractive for single mode fiber systems since the lack of resonators ensures good stability in actual operation.
High Speed Ti: LiNbO3interferometric Activated X-Switch:IAX
Authors: Pohlmann T. , Neyer A. , Voges E.
Published: February 2023

Optical time division switching systems require optical switches with a great bandwidth of several GHz at moderate switching voltages ( <10 V ). Unfortunately, both types of guided wave optical switches, the directional coupler switch /1/ and the X-switch /2/ require relatively high voltages for common device length of a few millimeters. The reduction of the switching voltage by increasing the length of the device is only possible at the expense of the allowable optical bandwidth. A solution, which combines the advantageous features of low voltage operation and great optical bandwidth, is the balanced bridge interferometric switch /3/. This switch has been realized in Z-cut LiNbO3 using electrooptically tunable directional couplers as 3 dB -splitters and combiners. However, in order to utilize the excellent performance of high speed and low loss phase modulators on X-cut LiNbO3 /4/, a simpler 3 dB coupler than a directional coupler with three electrodes would be desirable. In this paper we demonstrate the implementation of electrooptic X-switches as simple and efficient 3 dB-couplers in high speed interferometric activated switches.
High Frequency Intrinsic Resonance in Traveling Wave Y-fed Directional Couplers
Authors: Bourbin Y. , Enard A. , Papuchon M. , Moronvalle C. , Werner M.
Published: February 2023

Very high speed modulation of guided light has been reported using directional coupler switches (ref. |1, 2|) or Mach-Zehnder interferometers (ref |3, 4, 5, 6|). In some applications base band operation is not necessary and band pass type modulators around a given frequency may be preferred. Such resonance has been predicted in ref |7| where switching diagrams of Y-fed directional couplers have been investigated. A Y-fed coupler as reported in ref |8|, appears to be the combination of a directional coupler switch and of a Y junction through which light is launched. This results in - 3 dB built-in optical bias and makes the device free of any electrical DC drift which is regarded to be a problem in most cases for long term operation. Those considerations lead to consider Y-fed directional couplers as very good candidates for very high speed and band pass operation as it will be discussed in the following.