Progress in Semiconductor Integrated Optics

S.Y. Wang

MA1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Low-Drive-Voltage GaAs/AIGaAs Quantum Well Waveguide Phase Modulators

J. E. Zucker, T. L. Hendrickson, and C. Burrus

MA2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Phase Modulation in Impurity-Induced-Disordered AlGaAs/GaAs Quantum-Well and Double-Heterostructure Waveguides

T. R. Hausken, T. C. Huang, K. W. Lee, R. J. Simes, N. Dagli, and L. A. Coldren

MA3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Large Electroabsorption Effect in InGaAs/InP Multiple Quantum Well Waveguide Modulator Grown by MO-CVD

Thomas H. Wood, Elizabeth C. Carr, Charles A. Burrus, Barry I. Miller, and Uziel Koren

MA4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Temperature Dependence in GaAs/AlGaAs Multiple Quantum Well Waveguides

Y. J. Chen and G. J. Sonek

MA5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Waveguide Modulator for Argon Laser consisting of Vapor-grown Single-crystal ZnSe on GaAs substrates

M.H. Jupina, B.G. Kim, E. Garmire, and N. Shibata

MB1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

High-speed and low-chirp GaInAsP/InP optical intensity modulator

H. Soda, K. Nakai, H. Ishikawa, and H. Imai

MB2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Narrowband InGaAsP/InP Waveguide Grating-Folded Directional Coupler Multiplexer/Demultiplexer

R. C. Alferness, L. L. Buhl, M. J. R. Martyak, M. D. Divino, C. H. Joyner, and A. G. Dentai

MB3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Electro-refraction in Semiconductor Waveguide Structures

K.W. Steijn, R.P. Leavitt, and J.W. Little

MB4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Scattering and Coherent Coupling in Low-loss GaAs Waveguides and Bends

R.J. Deri, R. J. Hawkins, E. Kapon, and L.M. Schiavone

MB5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Bend Losses of Miniature Single Mode GaAs/AlGaAs Waveguides

Hiroaki Takeuchi and Kunishige Oe

MB6 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Buried Low-Loss Fiber-Compatible Single-Mode Ion-Exchanged Channel Waveguides

H.C. Cheng, H. Zhenguang, A. Miliou, R. Srivastava, and R.V. Ramaswamy

MC1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Two-step thermal ion exchange process for single-mode waveguides embedded in glass

Masafumi Seki, Ryoichi Sugawara, and Hideki Hashizume

MC2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Low-loss single-mode plastic waveguide fabricated by photopolymerization

K. Miura, I Sawaki, and H. Nakajima

MC3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Patterned Channel Waveguides on Printed Circuit Boards for Photonic Interconnection Applications

Davis H. Hartman, James W. Howse, Robert R. Krchnavek, and Ivan Ladany

MC4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Integrated Four-Channel Mach-Zehnder Multiplexer Fabricated With Phosphorous Doped SiO2 Waveguides on Si

C. H. Henry, B. H. Verbeek, N. A. Olsson, K. J. Orlowsky, R. F. Kazarinov, and B. H. Johnson

MC5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

A Focusing Grating Coupler for Polarization Detection

Shogo Ura, Hiroshi Sunagawa, Toshiaki Suhara, and Hiroshi Nishihara

MC6 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

LiNbO3 - A Practical Optoelectronic Waveguide Technology?

R.C. Booth, A.R. Beaumont, and M. Lawrence

MD1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Diffusion of Protons in H+: LiNbO3 Waveguides from a Melt of Limited Volume

Sandeep T. Vohra and Alan R. Mickelson

MD2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Very Low-Loss Proton-Exchanged LiNbO3 Waveguides With A Substantially Restored Electro-Optic Effect

A. Loni, R.M. De La Rue, and J.M. Winfield

MD3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Low-Loss Proton-Exchanged LiNbO3 Waveguides With No Electrooptic Degradation

P. G. Suchoski, M. M. Abou el leil, T. K. Findakly, and F. J. Leonberger

MD4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

High Index, Low Loss Waveguides in LiNbO3 with Ti Ion Implantation

Paul R. Ashley, William S. C. Chang, and Chris J. Buchal

MD5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Analysis of Intersecting Waveguides: Novel Physical Effects Explained and Explored

L. McCaughan

ME1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Narrowband Double-Pass Wavelength Filter with Broad Tuning Range

F. Heismann, W. Warzanskyj, R. C. Alferness, and L. L. Buhl

ME2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Guided-Wave Polarization Splitter Based on Two-Mode-Interference

A. Neyer and D. Dang

ME3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

New Polarization Scrambler Using Ti:LiNbO3 Rotating Waveplate

David A. Smith and Reinhold Noe

ME4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Stability of Ti:LiNbO3 Waveguide Modulators in an Optical Transmission System

C.R. Giles and S. K. Korotky

ME5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

New Formulations of the Beam Propagation Method: Application to Rib Waveguides

David Yevick and Björn Hermansson

MF1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Semiconductor Finite Elements for Integrated Optics

T. P. Young, G. A. Armstrong, and W.P. Smith

MF2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Zero Crosstalk Conditions for Crossed Δβ Switches with Symmetric Branches

W.K. Burns

MF3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

A Simplified Method of Calculating Power Transfer between Nonparallel Dielectric Waveguides

Paul Pedersen and J. L. Nightingale

MF4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

A New Technique for Analysing Planar Optical Waveguides

P.O. Kendall, M.J. Adams, P. McIlroy, S. Ritchie, and M.J. Robertson

MF5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

A highly sensitive excite and probe technique to measure optically induced refractive index changes in Ti:LiNbO3 -waveguide resonators

R. Volk and W. Sohler

MF6 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Heterodyne Measurement of Optical Modulator Frequency Response

David W. Dolfi and David K. Donald

MF7 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

GHz Bandwidth Magnetooptic Interaction in YIG-GGG Waveguide Using Magnetostatic Forward Volume Waves

D. Young and C. S. Tsai

MF8 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

A Tree-Structured 4×4 Switch Array in Lithium Niobate with Attached Fibers and Proton-Exchange Polarizers

M. A. Milbrodt, J. J. Veselka, K. Bahadori, Y. C. Chen, G. A. Bogert, D. G. Coult, R. J. Holmes, J. R. Erickson, and W. A. Payne

MF9 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Optical switch matrix with simplified nxn tree-structure

H. Okayama, A. Matoba, R. Shibuya, and T. Ishida

MF10 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

ThF4-Buffered GaAs Waveguide Modulators for CO2 Lasers*

J. D. Farina, R. T. Brown, and P. K. Cheo

MF11 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Low Loss and Low Drive Voltage Electrooptical Phase Modulator at 10.6 Microns

D. Delacourt, R. Blondeau, C. Brylinski, M.A. Di Forte-Poisson, and M. Papuchon

MF12 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Thermal Tapering of Ion-Exchanged Channel Guides in Glass

A. Mahapatra and J.M. Connors

MF13 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

All-optical Switching and Codirectional Mode Conversion in Nonlinear Gratings

S. Trillo and S. Wabnitz

MF14 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Single Frequency Pumped Doubly Resonant Integrated Optical Parametric Oscillator of Very High Efficiency

H. Suche and W. Sohler

MF15 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Nonlinear Prism Coupling and Power Limiting in Ion-Exchanged Waveguides

H. Zhenguang, R. Srivastava, and R.V. Ramaswamy

MF16 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Endless polarization control system with integrated optical Ti:LiNbO3 polarization transformers

Reinhold Noé, Helmut Heidrich, and Detlef Hoffmann

PDP1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

1.5μm Tunable Wavelength Filter with Wide Tuning Range and High Constant Gain Using Phase Controllable DFB LD

T. Numai, S. Murata, and I. Mito

PDP2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Polarization Independent 4×4 Switch Matrix in LiNbO3 for Communicative and Distributive Switching

P Granestrand, B Lagerström, P Svensson, L Thylen, B Stoltz, K Bergvall, and H Olofsson

PDP3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Suppression of Sidelobes in Far-Field Radiation from Non-uniformly-spaced Waveguide Arrays for Optical Beam Steering

J. H. Abeles, G. Keramidas, W. K. Chan, R. J. Deri, and R. J. Hawkins

PDP4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Optical Switching in Semiconductor MQW Optical Switch Due to Field Induced Reflection

K. G. Ravikumar, T. Kikugawa, K. Shimomura, A. Izumi, S. Arai, Y. Suematsu, and K. Matsubara

PDP5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Polarization Independent LiNbO3 4×4 Matrix Switch

H. Nishimoto, S. Suzuki, and M. Kondo

PDP6 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Dopant Diffusion Loss Mechanism in High-Birefringent Fiber Fused Couplers

C.W. Pickett, W. K. Burns, and C. A. Villarruel

PDP7 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Broadly-Tunable Dynamic-Single-Mode Multiple-Quantum-Well Semi-Insulating-Blocked Distributed-Bragg-Reflector Lasers at 1.5 μm

T. L. Koch, U. Koren, and B. I. Miller

PDP8 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

An InGaAs/InGaAsP Distributed Feedback Quantum Well Laser With an Intracavity Phase Modulator

U. Koren, T.L. Koch, B.I. Miller, and A Shahar

PDP9 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Bandwidth Broadening of Travelling-Wave Integrated-Optic Modulators

E.M. Zolotov, V.M. Pelekhaty, A.M. Prokhorov, and R.F. Tavlykaev

PDP10 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Payoffs of Integrated Optics Technology to Fiber Optic Sensor Systems

Ramon P. De Paula and William J. Minford

TuA1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

High Dynamic Range, Linear Modulators for Electric Field Sensing

C. H. Bulmer, M.M. Howerton, W.K. Burns, and S. C. Hiser

TuA2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Use of Integrated Guided-Wave Optics to Measure and/or Process Optical Wavefronts with High-Temporal Resolution*

R. H. Rediker, T.A. Lind, B.E. Burke, and B. G. Zollars

TuA3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Integrated Optic High Frequency Phase Comparator

L. M. Walpita, S. C. Wang, and W. S. C. Chang

TuA4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Multichannel Integrated Optic Device Modules in LinbO3 for Digital Data Processing*

C. S. Tsai, D. Y. Zang, and P. Le

TuA5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Low noise flip-chip integrated photoreceiver with an InGaAs-PIN photodiode and a GaAs IC

T. Horimatsu, Y. Oikawa, M. Makiuchi, and M. Sasaki

TuB1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

A Fast Organic-on-Inorganic Semiconductor Photodetector

F.F. So, S.R. Forrest, H.L. Garvin, and D.J. Jackson

TuB2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Photo-Electronic Bistable Device with Selectable Output Light Channels

Y. Tashiro, K. Kasahara, N. Hamao, M. Sugimoto, and T. Yanase

TuB3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Effects of Facet Reflection in a Monolithically Integrated Optical Device Consisting of a DFB Laser and an Amplifier/Modulator

K. Tada, J. Hashimoto, and Y. Nakano

TuB4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Active Mode-Locking of a 13-μm Extended-Cavity Silicon Chip Bragg Reflector Laser

G. Raybon, R. S. Tucker, G. Eisenstein, and C. H. Henry

TuB5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Amplification of High Repetition Rate Picosecond Pulses Using An InGaAsP Traveling-Wave Optical Amplifier

G. Eisenstein, J. M. Wiesenfeld, R. S. Tucker, and G. Raybon

TuB6 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

The Digital Optical Switch: Theory and Applications

Y. Silberberg, P. Perlmutter, and J. E. Baran

TuC1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Integrated-Optical 2×2 Switch with Y-Branch Mode Splitters*

L. M. Johnson and H. V. Roussell

TuC2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Low Crosstalk and Polarization Independent Ti:LiNbO3 Optical Waveguide Switch for OTDR

Y. Tanisawa, T. Aoyama, R. Ishikawa, M. Kondo, and Y. Ohta

TuC3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Polarization independent LiNbO3 switch with reduced fabrication tolerances employing Δβ and Δκ modulation

P Granestrand, L Thylen, and B Stoltz

TuC4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Optical Two-Guide Coupler Switches In GaAs: Ideal and Nonideal Operation*

Lynne A. Molter, Hermann A. Haus, Leonard M. Johnson, and Joseph P. Donnelly

TuC5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

A synthesized digital switch using a 1x2 directional coupler with asymmetric Δβ phase reversal electrode

Suwat Thaniyavarn

TuC6 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Voltage-tunable wavelength filtering with a non-symmetric interferometer

Janet Lehr Jacket and John Johnson

TuC7 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Low Loss Channel Waveguides and Electrooptic Modulators in KTiOPO4

John D. Bierlein and August Ferretti

TuD1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Optical Waveguides in Lithium Tantalate by Vapor Diffusion Below Curie Temperature

D.W. Yoon, O. Eknoyan, and H.S. Jung

TuD2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Ferroelectric Microdomains In Lithium Niobate Optical Modulators

L.L. Pendergrass and R.J. Jungerman

TuD3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Laser Micro-Fabrication of Ti:LiNbO3 Waveguide Devices

T. Krauss, M.M. Oprysko, K. Grebe, B. Fan, and A. Speth

TuD4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

LiNbO3 blazed grating fabricated by reactive ion-beam etching

S. Ogata, H. Hosokawa, and T. Yamashita

TuD5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Grating Outcoupling From Large Area Rib Waveguide Arrays Fabricated on Titanium Indiffused Lithium Niobate Substrates

K. Rastani and A. R. Tanguay

TuD6 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Monolithic Two-Dimensional GalnAsP/InP Laser and Lenslet Arrays*

Z. L. Liau, J. N. Walpole, and V. Diadiuk

WA1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Room temperature c.w. GaAs surface-emitting laser with integrated Bragg reflector

J. Faist, F. Morier-Genoud, D. Martin, J.D. Ganiere, and F.-K. Reinhart

WA2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Polarization Characteristics of MOCVD Grown GaAs/GaAlAs CBH Surface Emitting Lasers

M. Shimizu, F. Koyama, and K. Iga

WA3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

High Efficiency Surface-Emitting Distributed Bragg Reflector Laser Array

Keisuke Kojima, Masaaki Kameya, Susumu Noda, and Kazuo Kyuma

WA4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

InGaAsP/InP Buried-Heterostructure Lasers and Laser Arrays Fabricated by Ion-Beam-Assisted Etching

D. Yap, J. N. Walpole, and Z. L. Liau

WA5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Physics Technology and Potential Integration of Ultralow-Threshold Diode Lasers

Amnon Yariv

WB1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Corrugation Structure Based Semiconductor Optical Guided-Wave Devices

S. Murata and I. Mito

WB2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

High Power High Speed Single Mode Sipbh-DFB Lasers at 1.3 Micron Wavelength

U. Koren, T.L. Koch, P.J. Corvini, B.I. Miller, G. Eisenstein, R.S. Tucker, Y.K. Su, and R.J. Capik

WB3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Monolithically Integrated Transverse Junction Stripe Lasers with Rib Waveguides in GaAs/AlGaAs

G. Allen Vawter, James L. Merz, and Larry A. Coldren

WB4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Integrated Semiconductor Ring Laser Structures

A F Jezierski and P J R Laybourn

WB5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Efficient Degenerate Four-Wave Mixing in a Single Mode Waveguide

A. Gabel, K. DeLong, C. Seaton, and G. Stegeman

WC1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Experimental Characteristics of a Multiple-Quantum-Well-Coupled Nonlinear Directional Coupler

B.P. Keyworth, M. Cada, J.M. Glinski, A.J. SpringThorpe, and P. Mandeville

WC2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Nonlinear Directional Coupler as a Femtosecond All-Optical Switch

Y. Silberberg, A.M. Weiner, S. R. Friberg, B. G. Sfez, and P. W. Smith

WC3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Nonlinear Guided-Wave Device Characteristics

G.I. Stegeman, C.T. Seaton, E.M. Wright, N. Finlayson, and R. Zanoni

WC4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Nonlinear Optical Effects in Channel Waveguide Devices Fabricated in Semiconductor-Doped Glass

W.C. Banyai, N. Finlayson, F. Brown, C.T. Seaton, G.I. Stegeman, T.C. Cullen, and C.N. Ironside

WC5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

The Nonlinear Asymmetric Mach Zehnder Interferometer in GaAs/AIGaAs

M. O'Neill, J. Bell, B. S. Bhumbra, T. J. Cullen, C. N. Ironside, and O. Mikami

WC6 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Integrated All-Optical Modulator and Logic Gate for Fiber Optics Systems

R. Normandin, D.C. Houghton, and M. Simard-Normandin

WC7 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

High-Speed Ti:LiNbO3 Switch/Modulators: Recent Advances and Applications

Steven K. Korotky

WD1 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Integrated High-Speed Ti:LiNbO3 Δβ-Reversal Switching Circuits

J.J. Veselka, D.A. Herr, T.O. Murphy, L.L. Buhl, and S.K. Korotky

WD2 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Lithium Niobate Band Pass Response Microwave Modulator With Phase Reversal Electrodes

S.C. Hiser, W.K. Burns, C.H. Bulmer, R.D. Esman, R.P. Moeller, A. Djupsjobacka, and L. Thylen

WD3 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

High Speed Ti: LiNbO3interferometric Activated X-Switch:IAX

T. Pohlmann, A. Neyer, and E. Voges

WD4 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Picosecond Optical Sampling with LiNbO3 Waveguide and Compressed Laser Diode Pulses

Y. Yamabayashi, A. Takada, and M. Saruwatari

WD5 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

High Frequency Intrinsic Resonance in Traveling Wave Y-fed Directional Couplers

Y. Bourbin, A. Enard, M. Papuchon, C. Moronvalle, and M. Werner

WD6 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF

Guided-Wave Polymeric Electro-Optic Modulators

C.C. Teng, D.R. Haas, H.T. Man, and H.N. Yoon

WD7 Integrated and Guided Wave Optics (IGWO) 1988 View: PDF