Showing papers by "Amnon Yariv published in 1997"

Optical electronics in modern communications

Abstract: 1. Electromagnetic Theory 2. The Propagation of Rays and Beams 3. Propagation of Optical Beams in Fibers 4. Optical Resonators 5. Interaction of Radiation and Atomic Systems 6. Theory of Laser Oscillation and its Control in the Continuous and Pulsed Regimes 7. Some Specific Laser Systems 8. Second-Harmonic Generation and Parametric oscillation 9. Electronic Modulation of Laser Beams 10. Noise in Optical Detection and Generation 11. Detection of Optical Radiation 12. Interaction of Light and Sound 13. Propagation of Coupling Modes in Optical Dielectric Waveguides-Periodic Waveguides 14. Holography and Optical Data Storage 15. Semiconductor Lasers-Theory and Applications 16. Advanced Semiconductor Lasers: Quantum Well Lasers, Distributed Feedback Lasers, Vertical Cavity Surface Emitting Lasers 17. Phase Conjugate Optics - Theory and Applications 18. Two-Beam Coupling and Phase Conjugation in Photorefractive Media 19. Optical Solitons 20. A Classical Treatment of Quantum Optics Appendices A. The Kramers-Kroning relations B. The Electrooptic Effect in Cubic 43m Crystals C. Noise in Traveling Wave Lasers Amplifiers D. Transformation of a coherent

Coupled-mode analysis of fiber-optic add drop filters for dense wavelength-division multiplexing.

Abstract: We present a coupled-mode theory of fiber-optic add drop filters, which involve directional coupling between two fibers combined with fiber Bragg gratings defined inside the coupling region. The analysis self-consistently accounts for both the directional and the reflection coupling, and the propagation constants and structure of the supermodes of the combined structure are derived. We present a detailed analysis of a filter design based on identical fibers. The calculated device parameters satisfy the requirements for dense wavelength-division multiplexing applications.

Effect of noise on the power spectrum of passively mode-locked lasers

Abstract: We analyze the effects of noise on the power spectrum of pulse trains generated by a continuously operating passively mode-locked laser. The shape of the different harmonics of the power spectrum is calculated in the presence of correlated timing fluctuations between neighboring pulses and in the presence of amplitude fluctuations. The spectra at the different harmonics are influenced mainly by the nonstationary timing-jitter fluctuations; amplitude fluctuations slightly modify the spectral tails. Estimation of the coupling term between the longitudinal cavity modes or the effective saturable absorber coefficient is made from the timing-jitter correlation time. Experimental results from an external cavity two-section semiconductor laser are given. The results show timing-jitter fluctuations having a relaxation time much longer than the repetition period.

Improved laser modulation response by frequency modulation to amplitude modulation conversion in transmission through a fiber grating

Abstract: We have demonstrated that transmission through a fiber grating can increase the system response of a directly modulated semiconductor laser by over 7 dB at all modulation frequencies up to 25 GHz. When combined with dispersive optical fiber, the grating produced a system response that was larger, flatter, and had a larger bandwidth, providing a frequency-domain demonstration of dispersion compensation through an unchirped grating. The effect can be understood as frequency modulation to amplitude modulation conversion by the grating, and was accurately predicted by a Fourier domain analysis of the laser signal and grating.

Nonparaxial equation for linear and nonlinear optical propagation

Abstract: The formalism of coupled-mode theory, specialized to the continuum of radiation modes, allows us to extend the standard parabolic wave equation to include nonparaxial terms and vectorial effects, and, in particular, to generalize the nonlinear Schrodinger equation that describes propagation in the presence of an intensity-dependent refractive index.

Semiconductor device with electrostatic control

Abstract: A semiconductor light-emitting device having one or more depletion regions that are controlled by one or more control electrodes to vary the spatial distribution of the carriers in an active layer. The voltages on the control electrodes can be controlled to modulate the current density in the active layer and the output light intensity. The polarization of a surface emitting diode laser based on this device can be controlled or modulated.

An experimental and theoretical study of the suppression of interferometric noise and distortion in AM optical links by phase dither

Abstract: The effects of phase dither on the magnitude and spectral distribution of interferometric fiber optic noise and intermodulation products is considered. A theory is presented as well as experimental data which show major reduction of AM noise brought about by intentional narrow band and wide band phase dither of the laser output.

Effect of transmission through fiber gratings on semiconductor laser intensity noise

Abstract: The effect of transmission through a fiber Bragg grating on the relative intensity noise of semiconductor laser light is investigated. We first present a model of the grating as a linear frequency discriminator that exchanges correlated power between frequency noise and intensity noise caused by spontaneous emission. This correctly explains observed increases in intensity noise of up to 30 dB at low frequencies, obeying an inverse-square frequency dependence. Next, we show that there exist conditions under which a grating can reduce intensity noise and that these are determined by the phase relationship between correlated intensity and frequency fluctuations. Finally, we demonstrate a 2 dB reduction of intensity noise at frequencies up to 15 GHz, and present a numerical calculation based on the complex transmittance of the grating that correctly describes the effect of grating dispersion.

Optical system using a radial harmonic pupil filter for generating collimated beams

Abstract: A Fourier hologram, placed at rear focal plane (Pi), with the distribution of a radial harmonic function creates, in the far field, near focal plane (Pf), a pseudo non-diffracting beam. The properties of this pseudo non-diffracting beam can be set by appropriate characterization of the radial harmonic function. Various operations can also be carried out to change the position of the beam relative to the focal point (Z=0). The beam can be shifted in space, twisted, or tilted.

Phase-shifting masks for photolithography

Abstract: A method of designing phase shifting masks with improved resolution. Auxiliary transmissive phase regions with properly selected locations and dimensions are introduced to eliminate unwanted interference patterns. A usual opaque region between the transmissive features that are phase-conflicting to one another is partially or entirely replaced with a transmissive region of an opposite phase with respect to the phase of the transmissive features. In positive photoresist layouts, the light-absorbing features are partially or entirely made transmissive while an opposite and uniform phase is maintained throughout the transmissive background. Segmenting features with at least one auxiliary phase region and adjusting attenuation of different features can further improve the performance.

Direct Measurement of Population-Induced Broadening of Quantum Well Intersubband Transitions

Abstract: The dependence of the absorption spectral linewidth of quantum well intersubband transitions on the electron population in the well is experimentally demonstrated. We show that the dependence of the spectral linewidth on the population is substantial and accounts for some of the broadening previously attributed to donor scattering.

Effect of noise on the power spectrum of passively modelocked lasers

Abstract: Modelocking is a common technique employed to produce ultrashort optical pulses from lasers over a wide range of wavelengths. Actively modelocked lasers, for example, are driven by a stable external frequency reference. In this case the timing fluctuations are related to the modulator signal and can be treated as stationary processes. The theory revealed spectral characteristics that are commonly referred to as a spike and a pair of pedestals, with the spike resulting from a delta-function-like shape at each harmonic owing to the external locking source. One pedestal, or side band, at each harmonic is due to amplitude fluctuations and the second is due to timing-jitter fluctuations. The latter is harmonic-number dependent. For more than a decade, this theory was applied to the fundamentally different case of passively modelocked lasers, but the results were not adequately explained.

Lasers incorporating two-dimensional photonic crystal mirrors

Abstract: Photonic bandgap crystals are expected to be of use in defining microcavities for modifying spontaneous emission and as highly reflective mirrors. There are several reports of microfabricating one-dimensional structure. Here, we describe the incorporation of a microfabricated two-dimensional photonic lattice in an edge-emitting semiconductor laser structure. We demonstrate laser operation in a cavity formed between a cleaved facet and a microfabricated periodic lattice.

Broader, flatter optical spectra of passively mode-locked semiconductor lasers for a wavelength-division multiplexing source.

Abstract: Using the time domain master equation for a complex electric-field pulse envelope, we find analytical results for the optical spectra of passively mode-locked semiconductor lasers. The analysis includes the effect of optical nonlinearity of semiconductor lasers, which is characterized by a slow saturable amplifier and absorber. Group velocity dispersion, bandwidth limiting, and self-phase modulation were considered as well. The FWHM of the spectrum profile was found to have a strong dependence on group velocity dispersion and self-phase modulation. For large absolute values of the chirp parameter, the optical spectra result in equispaced continuous wave frequencies, a large fraction of which have equal power.

Three dimensional polarization dependence of OH bands absorption in potassium niobate crystals

Abstract: Absorption band countered on wave numbers 3504 and 6843 cm−1 have been observed in potassium niobate crystals. These absorption bands correspond to the transition energies of O–H stretching vibration, from the ground state to the first excited state and to the second excited state, respectively. Absorption bands around 3992 and 4476 cm−1 are attributed to the combination of O–H vibration plus libration. The integrated absorption intensities around 3504, 3992, and 4476 cm−1 are three dimensional polarization dependent which indicates the motion properties of hydrogen ions in the lattice.

The effect of temperature on the resonant tunneling and electric field domain formation in multiple quantum well superlattices

Abstract: Analyzing the photocurrent spectra and the I–V characteristics of weakly coupled GaAs/AlGaAs multiquantum well structures, different transport regimes are distinguished. At low temperatures (below ∼50 K), due to the electron coherence over a few periods of the superlattice, electron transport is dominated by sequential resonant tunneling. At higher temperatures, evidences for the increased contribution of nonresonant transport processes, and the subsequent modification in the electric field distribution in the device, are presented.

Amplitude-equation formalism for four-wave- mixing geometry with transmission gratings

Abstract: An amplitude equation is derived for a four-wave-mixing geometry with nearly counterpropagating, mutually incoherent, nondiffracting pump beams, spatially overlapping in a photorefractive material with a nonlocal response. This equation extends the earlier linear two-dimensional theory to the weakly nonlinear regime. The analysis also starts from a more complete equation for the photorefractive effect, which leads to the prediction of novel effects especially apparent in the nonlinear regime. Precise predictions for the spatiotemporal behavior of the grating amplitude in the nonlinear regime are presented. The range of validity of the amplitude equation is studied. The characteristics of the instability in the nonlinear regime are analyzed through a front-selection analysis.

Copper, hydrogen, and titanium incorporation in potassium lithium tantalate niobate single crystals

Abstract: In this study we propose a model that describes the diffusion of copper, hydrogen, and titanium through the liquid/solid interface in potassium lithium tantalate niobate crystals. Copper and hydrogen ions may occupy potassium/lithium vacant sites. Hydrogen ions are also able to stay at tantalate/niobate vacant sites in the presence of titanium. This model shows that the hydrogen concentration can be dramatically reduced in KLTN:Cu,X,Ycrystals (where X, Yare any first row transition metals but not Ti or Cu), and is in agreement with experimental results.

Ferroelectric domain gratings and Barkhausen spikes in potassium lithium tantalate niobate

Abstract: The observation of Barkhausen current spikes during the recording of volume phase holograms in potassium lithium tantalate niobate is reported on. These spikes are due to the ferroelectric domain reversal induced by photorefractive space charge fields. Both “small” (1 nA) and “large” (100 nA) spikes are observed, which correspond to micro and macro domain reversal, respectively. The diffraction efficiency can change as much as 50% during a single macrodomain switching.

Edge-emitting quantum well laser with integrated intracavity electrostatic gate

Abstract: Ridge waveguide, edge-emitting single quantum well GaAs lasers with an integrated gating electrode have been fabricated. These devices integrate a MESFET structure with the laser PN junction so that the SBD (Schottky barrier diode) depletion layer can be used for transverse current confinement in the laser. Device fabrication was very simple requiring only an anisotropic etch for waveguide definition followed by a single self-aligned contact deposition step. The Schottky barrier depletion layers on either side of the ridge waveguide act to confine free carriers. This structure allows for separation of the optical and electrical confinement in the transverse direction without requiring complex fabrication. The device demonstrated modulation of the pulsed lasing threshold with gate control voltage on a 30 micron wide ridge. Above threshold, increasing power output with increasing gate voltage was demonstrated with negligible gate current. The multimode lasing spectrum showed that the increased power output occurred for all modes with no shift in the mode wavelengths to within the resolution of the measurement system.

Special angle cut of potassium niobate crystal for thermal fixing

Abstract: We investigated the optimal cut of potassium niobate crystals to approach the maximum exponential photorefractive gain coefficient and the highest diffraction efficiency. Volume hologram is thermally fixed in this sample and a significant enhancement of diffraction efficiency is achieved.