bluuebunny/crossref_metadata_2025 huggingface dataset:
Image quality analysis of a rainbow hologram by using a spatial and spectral extended light source
Authors: Cai L. Z. , Zhang Y. W.
Published: February 2023

For rainbow holograms, a spatial and spectral extended light source (white light source) is used for reconstruction. The effect of spectral extension on the image blur (color blur) has been analyzed by several authors, 1-2 but the effects of spatial extension or both extensions together have not been studied. In this paper, a new concept of effective width of extended light source, which may be regarded as a characteristic of rainbow holograms, is proposed. It is proved that owing to the existence of two small apertures (slit and viewer's pupil) both the effective area of spatial extension of the light source and the effective range of its spectral extension are significantly limited. Thus the two extensions have approximately equal effects on the image blur. A strip white light source can be used to reconstruct the rainbow hologram without serious degradation of image quality except for the change of apparent properties of the image.
Imaging characteristics of a reverse parabolic defocusing GRIN rod lens
Authors: Liao Tingdi , Qiu Jinghui , Lin Jindou
Published: February 2023

In recent years studies have been made of ray propagation and paraxial imaging through light focusing GRIN rods but few light defocusing ones. 1-3 Here we further study ray propagation and paraxial imaging characteristics of a reverse parabolic defocusing GRIN rod.
Axial gradient index doublet objective for optical disk systems
Authors: Kittaka Shigeo , Yamane Tsuyoshi , Kaite Yoshikazu , Toyama Minoru
Published: February 2023

A plano-convex axial gradient index (Z-GI) lens is able to correct both spherical aberration and coma. However, it is difficult to fabricate a Z-GI singlet with a numerical aperture (N.A.) of over 0.3, because a large refractive index change (Δn) and a precise refractive index profile are required. To make the N.A. larger, a homogeneous meniscus lens was added to a Z-GI singlet. Several types of Z-GI doublet with large N.A. (0.53-0.60) were designed and fabricated as the objectives for optical disk systems. The specifications of a Z-GI doublet are given as follows: λ: 780 nm N.A.: 0.55 focal length: 3.07 mm conjugate length: ∞ working distance: 1.10 mm disk thickness: 1.20 mm (n = 1.57).
Complex ternary matched filters yielding high signal-to-noise ratios
Authors: Dickey F. M. , Vijaya Kumar B. V. K. , Romero L. A. , Connelly J. M.
Published: February 2023

Matched spatial filters provide the highest output signal-to-noise ratio in pattern recognition applications but have not become practicable due to the complex nature of the spatial filters required. Lately much research effort has been devoted to methods of avoiding complex filters. This research has suggested binary and ternary real valued approximations to the phase-only filter. Dickey and Hansche1 suggested a quad-phase-only filter that does not suffer from having the simple symmetry of real valued filters and can have improved signal-to-noise ratio. The authors suggest a complex ternary matched filter (CTMF). This CTMF filter function has the form: where IR1 and IR2 are support functions, sr and S1 are the real and imaginary parts of the object function Fourier transform, and β is the threshold line angle. The algorithm introduced by Kumar and Bahri2 can be used to optimize this filter. The optimized CTMF produces signal-to-noise ratios very near the optimal phase-only filter and does not suffer from having the simple symmetry of real valued filters.
Photochemical Hole Burning of Ionic Dye Molecules
Authors: Sakoda K. , Kominami K. , Iwamoto M.
Published: February 2023

We previously reported the first observation of a photochemical hole burned above 77 K.1 In this paper, the hole burning characteristics of several related dye doped polymers were investigated. The samples we studied were (A) porphin derivatives with ionic substituents such as sulfothienyl groups and (B) two fluorescein derivatives, both dispersed in polyvinyl alcohol. The following results were obtained: (1) The hole width in the former shows a power law dependence on the burning temperature between 20 and 120 K, and the value of the power is 1.7-1.8. (2) The energy difference between the zero phonon hole and the side hole is fairly large in the former, which brings about a weak temperature dependence of the Debye-Waller factor. (3) Persistent spectral holes can be burned in the latter, which is reported for the first time. (4) The mechanism of the hole burning in the latter does not involve the intramolecular charge transfer proposed for similar organic dye molecules such as resorufin.2
Resonance Floquet-Block analysis for grating couplers and grating-surface-emitting lasers
Authors: Noll R. J. , Macomber S. H.
Published: February 2023

The rigorous Floquet-Block mode expansion1 used in the past to discuss off-resonance grating waveguide coupling is extended to the on-resonance condition using the method of grating eigenfunctions.2 The results of this theory are applied to a discussion of the grating/waveguide coupling problem as well as to the outcoupling of surface-emitting DFB and DBR lasers. Of special concern are second-order grating devices with thick metal gratings which cannot be handled by perturbation theory.
Enhanced photorefractive effect in SBN:60:Cr and SBN.60:Rh with external dc fields
Authors: Sayano Koichi , Yariv Amnon , Neurgaonkar Ratnakar R.
Published: February 2023

A major thrust of photorefractive materials research has been to increase the coupling constant Γ and speed up response time. Previous two-beam coupling experiments using SBN:60 have shown that the space charge field Esc, and therefore the coupling constant, can be increased to some degree by optimizing the characteristic fields En and Ed.1,2 However, since Esc tends toward the smaller of EN and Ed for no external field, any attempt to incrase Esc by increasing En will have minimal effect since Esc will be limited by the diffusion field Ed. By applying an external dc electric field E0, the photoexcited carriers will tend to be driven into the traps half a grating period away, and Esc will be limited by En = eNA/ϵK for large E0. Experimentally, Γ has been found to increase by almost a factor of 3 to over 10 cm−1 in Cr-doped SBN:60 with an applied field of 10 kV/cm. In addition, for Rh-doped SBN:60, the response time has been found to get significantly faster with an applied field, decreasing by more than an order of magnitude from ~2 s for E0 = 0 to 0.1 s with E0 = 10. These results suggest potential applications in field-enhanced optical limiting, switching, and thresholding.
Femtosecond hot carrier relaxation in GaAs
Authors: Gong T. , Nighan W. L. , Young D. A. , Fauchet P. M.
Published: February 2023

Pulses of 100-fs duration, 2-μJ energy, and at a repetition rate of 8 kHz are generated from a copper vapor laser amplified CPM dye laser. A small fraction of the pulse is split off as a pump beam and the remainder is used to generate a white light continuum as a probe beam. The sample is a 0.15-μm thick GaAs film obtained using the lift-off procedure of Yablonovitch et al.1 We report time resolved transmission measurements at probe photon energies from 1.38 to 2.07 eV and carrier densities from 1017 to 1019 cm-3. Earlier work was restricted to a carrier density of ~1018 cm-3 and probe photon energy above the bandgap.2 Different hot carrier processes, such as carrier-carrier scattering, carrier-phonon scattering, state filling, and bandgap renormalization, and their dependence on carrier density are discussed.
Light-induced permanent codirectional mode-coupling gratings in Ge-doped optical fiber
Authors: Ouellette François
Published: February 2023

Exposition of a multimode Ge-doped optical fiber to high power cw argon laser light leads to the creation of a permanent mode-coupling grating in the fiber core. This grating has the right periodicity and transverse index structure to induce codirectional mode coupling and is written through the photosensitivity of the fiber.1 The experiments are done as follows. First the fiber is exposed to 600-mW cw argon laser light at 514 or 488 nm for 30 min or more. Afterward, the fiber transmission is measured as a function of wavelength around the irradiating wavelength, using a white light source and a monochromator. The fiber is placed between two polarizers. If the input and output polarizers are crossed, one observes narrow peaks (0.1 nm) at well-defined wavelengths that depend on the fiber used. This occurs since the fundamental mode polarization does not rotate, but that of the higher-order modes does. If more strippers are installed at the input and output of the fiber and the polarizers are parallel, one observes narrow dips in the transmission spectrum. A number of fibers have been tested and more than 50% coupling has been observed in 1-m fiber strands.
Degenerate four-wave mixing in metallophthalocyanines
Authors: Lindle J. R. , Shirk James S. , Bartoli F. J. , Hoffman C. A. , Kafafi Zakya H. , Young J.
Published: February 2023

The metallophthalocyanines have recently received some attention as a new class of nonlinear optical (NLO) organometallic materials.1,2 In addition to the extensive delocalized π system, the presence of the metal introduces metal-to-ligand and ligand-to-metal charge transfer (MLCT and LMCT) states. While these properties are known to give rise to large third-order optical nonlinearities, the precise mechanism for the nonlinearities in transition-metal substituted phthalocyanines is not yet understood.
Collisions of dark solitons in optical fibers
Authors: Thurston R. N. , Weiner A. M.
Published: February 2023

We have used numerical simulations to study dark soliton collisions in optical fibers. The starting field consists of two gray solitons either on an infinite background or on a finite duration background pulse. The phase profiles of the input gray solitons are chosen so that they have equal and opposite velocities with respect to the background. According to simulations that use the conventional nonlinear Schrodinger equation, the dark solitons pass through each other and emerge unchanged except for a temporal shift, in confirmation of the soliton nature of the input pulses. As the blackness1 (i.e., the soliton depth) is increased toward 1.0, the relative velocity of the solitons decreases toward zero and the temporal shift resulting from the collision increases. The blackness dependence of the shift is determined. When the blackness is less than about (3/4)0.5 (minimum intensity greater than one-quarter of the maximum), there is a single minimum in the resultant intensity at the time of intersection. For blacker pulses, there is always a double minimum in the intensity. When the Raman contribution to the nonlinear index is included,2 the slower soliton becomes blacker and more shifted than the faster one. These calculations lay the groundwork for possible experiments aimed at observation of dark soliton collisions.
Performance of photonic switches using cascade-structured integrated optic devices
Authors: Koai Kwang T. , Su Shing-Fong
Published: February 2023

In a practical photonic switching system using integrated optic devices, crosstalk and control are more of a problem than optical loss. In this paper, performances of photonic gate-type matrix switch1 and a time slot interchanger2 using cascaded-structured integrated optic modulators and switches are analyzed. Both have shown improved signal-to-crosstalk ratios (SXR) and the possibility of using a common control voltage without tuning for the switching components. We also compare these two photonic systems with those using conventional components by considering other performance factors such as optical insertion loss, device count, switch capability, and possible switch size, etc.
Optical self-routing through a three-structured space-division photonic switch using pulse-interval binary encoding
Authors: Goel Kamal K. , Perrier Philippe A. , Prucnal Paul R. , Milbrodt Michele A. , Desurvire Emmanuel
Published: February 2023

Optical processing has been demonstrated to remove the data flow bottleneck that results at a switch controller when routing decisions are processed electronically.1,2 Here, optical control of a tree-structured (1 × N) space division photonic switch is reported. A lithium niobate integrated-optic duobanyan switch, with N = 4, is used for the demonstration.3 Each data bit 1 is subencoded with a binary route address by dividing the bit interval into a frame of M + 1 time slots, where M is the number of stages in the switch (M = log
2
N). The 0th slot is occupied by a reference pulse. Binary information in time slot j, j = 1,…, M, determines the state of the switching elements in the jth stage of the switch. To route a bit to the desired switch output port, an optical routing controller decodes the route through the switch, stage-by-stage, and sets all switching elements in each stage of the switch accordingly. Since a time reference is transmitted along with the data, no external synchronization is required at the optical routing controller. Extension of this self-routing technique to N × N switching architectures, based on a tree structure,4 as well as its use in packet/circuit switching, are discussed.
Sub-natural Resonance Fluorescence Spectra
Authors: Narducci L.M. , Oppo G.-L. , Ru P. , Tredicce J.R. , Scully M.O.
Published: February 2023

This study concerns the shape of the resonance fluorescence spectrum emitted by a V-type three-level atom driven by two coherent fields which are resonant with the transitions connecting the ground state and the second and third level, respectively. We are especially interested in monitoring the spontaneous emission from the top level to the ground state. If the field connecting levels 1 and 2 is absent or small, the spontaneous emission from level 3 is characterized by the standard Mollow spectrum. If instead the 1-2 transition is saturated, the spectrum of resonance fluorescence from the top level is characterized by the following signatures: (i) the appearance of sidebands due to Rabi splitting effects, (ii) a reduction of its integrated area because of coherent population trapping1, and (iii) a significant reduction of its linewidth if the natural lifetime of level 2 is longer than level 3. The latter effect is especially interesting and rather unexpected, as the decay properties of an optical transition are being transferred to another by controlling the relative magnitudes of the driving fields. We have carried out our calculations with the help of the regression theorem and also developed a simple physical interpretation in terms of appropriate dressed states2.
Stable 428 nm Second-Harmonic Output Using Frequency Locking of a GaAlAs Diode laser to a KNbO3 Nonlinear Resonator
Authors: Kozlovsky W. J. , Lanth W.
Published: February 2023

Frequency doubling of a GaAlAs diode laser using a build-up cavity with a KNbO3 crystal is an attractive approach for developing an efficient, compact blue light source.1-3 If the laser and resonator frequencies are precisely matched the 856-nm fundamental radiation builds up to a high intensity which results in efficient second-harmonic generation of 428-nm light. Small changes of the diode-laser wavelength due to current (~5 GHz/mA) or temperature (~40 GHz/°C) variations and shifts of the cavity resonance induced by self-heating phenomena2 result in substantial fluctuations of the infrared power inside the resonator and thus in the blue output. At low laser powers, passive self-locking based on optical feedback has been demonstrated.1 Here, have used a simple, effective, electronic frequency locking technique that resulted in the generation of 9.5 mW of stable blue output from a frequency-doubled GaAlAs diode laser. In order to lock the GaAlAs diode laser frequency to the monolithic ring KNbO3 resonator of ~200 MHz linewidth, we modified the Pound-Drever technique often used for stabilizing dye and Argon lasers4 by exploiting the convenient modulation and tuning properties of the semiconductor laser. To produce small sidebands around the ~10 MHz-wide laser emission line, a weak 291 MHz current was superimposed on the dc injection current by capacitive coupling. By using a double-balanced mixer for heterodyne detection of the light reflected from the input surface of the resonator, a strong servo signal indicative of the match of the laser and resonator frequencies was generated.4 This servo signal was amplified and used to control the dc-current of the diode laser so that frequency stabilization was obtained by tuning of the laser frequency so that it tracked the cavity resonance. With the servo loop closed, the GaAlAs laser frequency remained locked on resonance for several hours, producing a stable 428-nm output power of 9.5 mW from the 63 mW of near-infrared power incident on the KNbO3 resonator.
Mutually pumped phase conjugation in Kerr media
Authors: Saxena R. , Yeh Pochi
Published: February 2023

Several mutually pumped phase conjugation configurations have been experimentally demonstrated and theoretically studied in photorefractive media.1 Although these materials are very efficient at low operating power, the process is inherently slow due to the need to generate a large number of photo-induced charge carriers.2 This paper examines the possibility of the same process occurring in a transparent Kerr medium which offers the advantage of faster response times. Due to an electrostrictive nonlinearity in the medium, a photon from either of the two input beams can be spontaneously converted into a frequency downshifted Stokes photon and an acoustic phonon, a process better known as Brillouin scattering.3 The presence of phonons due to noise will also help in Stokes scattering the incident photons. Each pair of incident beam and its coherently generated scattered beam will then write a grating that is moving at the phonon velocity. Reading of this moving hologram by the other incoherent input beam may generate the cross-readout phase conjugated beam that is frequency shifted from the read beam by the frequency of the acoustic field. The nonlinear medium thus acts like a phase conjugate mirror to both of the incident beams. Since the read-write processes occur simultaneously, the dynamics of the beam coupling are described by NFWM equations in the nonlinear medium with appropriate boundary conditions. Our calculations show that it is indeed possible to phase conjugate the two mutually incoherent input beams simultaneously when the coupling strength is above a threshold value. If one of the input beams is very weak compared to the other input beam, it is phase conjugated with a very high reflection coefficient. We have also examined the effects of seeding the phase conjugated beams.
Complexity of three-dimensional optical Fredkin gate interconnections
Authors: Mirsalehi Mir M. , Shamir Joseph , Rhee Uh-Sock , Caulfield H. John
Published: February 2023

A recently proposed 3-D optical Fredkin gate interconnection network1 is further analyzed. It is shown that any arbitrary permutation of an array of N × N channels can be performed by cascading 3N – 1 switching layers. The complexity of this architecture, which is defined as the total number of switching elements, is determined and compared with a similar parameter for the 2-D architecture. It is shown that the 3-D architecture becomes superior to the 2-D architecture as the number of channels N
c
increases. In particular, the 3-D architecture is found very suitable for the cases where N
c
is a square number.
Improved minimum-resolvable temperature-difference model for IR imaging system
Authors: Gao M. L. , Karim M. A. , Zheng S. H.
Published: February 2023

The currently used static minimum-resolvable-temperature-difference (MRTD) model for IR imaging systems, referred to as the Ratches model,1 is severely limited in scope. In practice, the predictive MRTD does not match the measured MRTD. The cause of these discrepancies, which are generally referred to as the high- and low-frequency problems, can be traced to the limitations of the eye-brain model that is a part of MRTD. A recent work2 has pointed out that eye-brain characteristics are not exponential functions, as most experts believe, but are sinusoidal functions.
Dynamic minimum-resolvable temperature-difference for IR imaging systems characterization
Authors: Gao M. L. , Karim M. A. , Zheng S. H.
Published: February 2023

The currently used minimum-resolvable-temperature-difference (MRTD) model for characterizing IR imaging systems, referred to as the Ratches model, is a static performance model.1 However, when the object in the scene moves, its picture on the cathode-ray-tube screen may be so severely degraded that the object may not be recognizable. Accordingly, MRTD, which is determined by the static modulation transfer function, fails to account for such target degradation. A recent work, however, has identified a dynamic modulation transfer function (DMTF) for a phosphor-based cathode-ray-tube display device.2 In our work, we first develop the DMTF for IR imaging systems and then use it to identify a dynamic MRTD (DMRTD). In particular, we identify the DMRTD of a staring IR system.
Nonlinear scanning image processing
Authors: Duncan Bradley D. , Poon Ting-Chung , Pieper Ronald J.
Published: February 2023

Image processing often employs sophisticated digital algorithms or precisely aligned coherent optical techniques. Although these methods are typically efficient in their image processing capabilities, neither method readily lends itself to simple, real-time implementation. For binary image processing, the importance of optical morphological filtering has recently been recognized.1,2 Through the optical implementation of mathematical morphology, systems capable of performing operations, such as median filtering, skeletonization, edge extraction, and impulsive noise removal have been studied. Though often real-time in nature, these systems usually require complex optical arrangements or nonlinear electronic-feedback networks. We present an edge-extraction technique for binary images that implements morphological transformations through the use of a technically simple hybrid optical/electronic system. The optical portion of our system consists of an optical-scanning arrangement that requires only minimal optical alignment. The electronic portion of our system uses simple analog circuitry, which requires no feedback and eliminates the need for sophisticated digital/electronic processing. The same system is also used to extract edges from gray-scale objects by subtracting binary slices obtained through a threshold-decomposition operation.2 The processing speed of our system is essentially limited by how fast we can scan an object. We have obtained good results in extracting edges in real time from both binary and gray-scale objects.
Optical heteroassociative memory for character translation
Authors: Yu Francis T. S. , Lu Taiwei , Yang Xiang Y.
Published: February 2023

Character translation can be accomplished by a heteroassociative memory in an artificial neural network. Because of the similarity among the characters, the special features of the patterns are important in pattern recognition. In this paper, a neural-network model based on the interpattem association (IPA) concept is presented.1 Generalized logical rules are developed to construct the excitatory and inhibitory interconnections in the heteroassociative memory. An adaptive optical neural network using high-resolution liquid-crystal televisions2 is used to translate between English letters and Chinese characters. Experimental and computer-simulated results have revealed that the IPA model is more effective in recognizing input among similar characters and has a larger storage capacity than the Hopfield model. Furthermore, the IPA model has shown two major advantages: fewer interconnections and fewer gray levels.
Continuum model for the dynamics of semiconductor laser arrays
Authors: Wang Shawe-Shiuan , Winful Herbert G.
Published: February 2023

We recently presented a coupled-mode theory of the dynamics of semiconductor-laser arrays that showed the existence of certain instabilities in these arrays.1 An implicit assumption of coupled-mode theory is that of weak coupling between the elements. Under that condition, the individual laser elements retain their identities, and their uncoupled fields form proper basis modes for the coupled-mode description. This approach is strictly correct for index-guided laser arrays, in which a built-in index-guide provides lateral confinement of the mode fields within each laser. In gain-guided lasers, the lateral guiding mechanism is much weaker. For such lasers, as well as the recently demonstrated anti guide arrays, a continuum model may be more appropriate. In this paper we present a self-consistent continuum model for the dynamics of semiconductor-laser arrays. The model is based on the solution of a pair of coupled partial differential equations for the complex field and the carrier density in the array. This model has been applied successfully to both gain-guided and index-guided laser arrays. By varying the center-to-center spacing between the waveguides, we have mapped out regions of stable and unstable temporal behavior in the laser output.
Confinement of optical pulses in nonlinear slab waveguides
Authors: El-Halafawy F. Z. , Abou-El-Enein A. A. , Saleh A. A.
Published: February 2023

The confinement of optical pulses in nonlinear inhomogeneous slab waveguides is theoretically derived and parametrically investigated with a set of controlling parameters consisting of optical wavelength, slab thickness, percentage of doping, ratio of slab thickness to optical wavelength, film nonlinearity, and injected power.1,2 The model consists of a thin optical dielectric film sandwiched between semi-infinite dielectrics (substrate and cover). The three layers possess a Kerr-like nonlinearity. The electric fields, and consequently the powers trapped in each slab, are derived under simple, but accurate, forms. The confinement factor is as follows: C = Pf/(Pf + Pc + Ps), where Pf, Pc, and Ps are, respectively, the trapped power through the film, the cover, and the substrate. The correlation of C and the ratio d/λ (2d is the slab thickness and λ is the optical wavelength) is obtained under a simple series form with coefficients that depend on the set of controlling parameters. Two different slabs (AlGaAs and SiO2–GeO2) are tested and compared. Under any common set of controlling parameters, the AlGaAs waveguide possesses a high confinement coefficient compared to the GeO2–SiO2 waveguide. The ultimate confinement is obtained if the product of film refractive index and its nonlinear coefficient equals the product of the substrate.
Generalized interpattern association neural network
Authors: Yang Xiang Y. , Lu Taiwei , Yu Francis T. S.
Published: February 2023

The interpattem-association (IPA) neuralnetwork model emphasizes the effect of the special features,1 which makes it particularly suitable for application to reference patterns that are similar to one another. To achieve robustness of the neural network, some interconnection redundancy must be introduced. The IPA algorithm proposed in our previous publication is based on logic rules that determine the excitory and inhibitory interconnection. However, the interconnections were excessively redundant, and common features were not effectively suppressed.
Waveguide Schottky and P-I-N a-Si:H photodetectors
Authors: Diawara Yacouba , Currie John F. , Najafi S. Iraj
Published: February 2023

Optical detectors are important in integrated optics, and monolithic integration of photodetectors on waveguides has become an attractive technique. High-speed response and high photoconductor sensitivity are required for optoelectronic devices. Because of the high absorption coefficient and low transit time for the photogenerated carriers in a Schottky configuration, hydrogenated amorphous silicon (a-Si:H) is an interesting material for low-cost integrated photodetectors. It can easily be deposited in thin films and at low temperature (250°C) on Si or GaAs. We present photodetectors integrated on a slab ion-exchanged glass waveguide.1 By using capacitance measurements with a Schottky photodetector, we have deduced the semiconductor properties through modelling and have calculated an RC time constant of 17.6 ns. The measured parameters with shortpulse (4 ns) laser light at 0.63μm are a sensitivity of 22.35 mA/W, a detectivity D* = 3.09 × 1010 cm Hz1/2/W, and a response time of 30 ns FWHM under zero-bias conditions. The fabrication process and characterization results will be presented in detail. The performance of the P-I-N device will be compared with the Schottky device, and its advantages will be discussed.
Single-photon observation of Berry’s phase
Authors: Kwiat P. G. , Chiao R. Y.
Published: February 2023

Berry's phases in optics have been studied extensively, and examples are typically discussed in quantum-mechanical terms. To our knowledge, however, experimental demonstrations have been performed only at the classical level. We report the first observation of a Berry's phase at the single-photon level. In particular, we investigated Pan-charatnam's phase,1 which is acquired whenever light is taken through a closed cycle of polarization states, e.g., with various retardation plates. Correlated pairs of linearly-polarized photons were produced by parametric fluorescence in a UV-pumped KDP crystal. One of each pair was directed into a photomultiplier tube (PMT1). The other was directed into a Michelson interferometer, one arm of which contained two quarter-wave plates, that was used to generate a Berry's phase.
Properties of sputtered glass films for waveguide applications
Authors: Hawthorne J. A. , Houde-Walter S. N. , Papernov S. , Schmid A.
Published: February 2023

Rapid quenching during sputtering makes it possible to achieve glass films with compositions not obtainable in the bulk by normal batch melting. Virtually all previously reported studies have used Corning 7059 glass and SiO2. We report the first investigation of sputtering multicomponent oxide glasses that contain large mole fractions of modifier components. A titanium borosilicate glass, originally developed for all-optical switching in diffused waveguides,1 was modified for this work: 40 mol% SiO2, 20 TiO2, 20 B2O3, 20 K2O. Linear optical properties were characterized (nd = 1.7184, vd = 27.65,αd = 0.5 cm-1). The intensity-dependent refractive-index coefficient was measured with a Mach–Zehnder interferometer and a Q-switched, mode-locked Nd :glass laser [n2 = (1.38 ± 0.81) × 10−15 cm2/W]. High-quality waveguiding films were achieved and were fully characterized. The films have high refractive indices (1.66 < nd < 1.83) and excellent transparency. Film composition and stoichiometry were checked with SIMS and ESCA. In-plane and out-of-plane optical scattering losses were measured. Thermal anneals were found to reduce scattering losses significantly. The films have excellent mechanical properties and chemical durability and were able to withstand repeated optical pulses of an average intensity of 10 GW/cm2 without visible signs of damage.
Ion-exchanged glass circuit for interferometric distance measurement
Authors: Voirin G.
Published: February 2023

The machine tools of the next generation will have to make extensive use of distance- measurement interferometers, which will have to be both inexpensive and compact. Integrated optics is well suited for regrouping all the optical processing functions of a Mach-Zehnder interferometer on a single monolithic platform. In contrast to existing silicon-based integrated optic interferometers, our approach involves interfering fields with full transverse confinement. The technology is K+ ion-exchange in BK7 glass. The waveguide circuit is first patterned by photolithography in an aluminum layer deposited on the glass plate, then it is immersed in a KNO3 bath at 380°C for 3 h. The integrated circuit can have a Michelson or a Mach- Zehnder configuration. The measuring beam is collimated in the air, sent back by the moving comer cube, and coupled back into the chip. The reference arm is reflected at the edge of the chip. Both waveguides reach the phase demodulator, where they interfere. The interference section is a wide waveguide carrying approximately 20 modes1; its length is chosen so as to provide fourfold subimages of the input branches.2 The optical power signals at these points are close to quadrature. They provide the movement direction and the displacement with an accuracy of 0.15µm without interpolation at the 633 nm wavelength.
Hybrid Kinoform Fan-Out Elements in Dichromated Gelatin
Authors: Robertson B. , Turunen J. , Ichikawa H. , Miller J. M. , Taghizadeh M. R. , Vasara A.
Published: February 2023

The successful construction of a digital optical processor or photonic switching network depends on our ability to efficiently power and interconnect together arrays of optical logic devices. Thus components capable of generating, re-routing and fanning-out arrays of beams must be available if full advantage is to be taken of the parallelism and improved communications inherent in optics. This has led to a great deal of effort being invested into the design and fabrication of optical interconnects using, for example, bulk optics, computer generated holograms and volume phase holographic optical elements. At present, one of the most promising techniques is based on CGH‘s which have a continuous phase profile. Such holographic gratings, commonly referred to as kinoforms, can theoretically reconstruct arrays of equal intensity light beams with a diffraction efficiency approaching 100%. These CGH's are therefore ideal for many applications, ie array generation and fan-out, both of which are vital for the construction of a digital optical processor or a photonic switching network. The fabrication of optical elements which have continuous surface-relief or refractive index profiles is, unfortunately, an extremely demanding task. Much of the recent work in the field of array generation has therefore been devoted to the design of kinoforms which have only a few, discrete, equally spaced phase levels. Recently however we have demonstrated an alternative technique of fabricating kinoforms which is based on the concept of the hybrid hologram1. This is a volume phase hologram recorded optically using a plane reference beam and an object wavefront generated from a binary amplitude CGH. By spatially filtering out all but the first diffraction order of the CGH it is possible to generate a uniform amplitude, continuous phase wavefront at the hologram plane, a form of wavefront ideal for recording a volume phase hologram.
Nonlinear Spectroscopy of Cold Atoms in a Spontaneous Force Optical Trap
Authors: Tabosa J. W. R. , Chen G. , Lee R. B. , Kimble H. J.
Published: February 2023

A spectroscopic investigation is reported for a sample of Cesium atoms which are cooled and confined in a Zeeman shift spontaneous force optical trap.(1'2) From measured absorption spectra for a weak probe beam both in steady state and under transient conditions, we infer that the sample consists of approximately 106 atoms trapped in a spherical volume of radius 400µm and cooled to roughly 300µK. To explore the spectral response of this sample under conditions of strong excitation by the trapping laser beams ("pump" waves), we record transmission as a function of frequency for a low intensity "probe" wave focussed through the trap. As might be expected, we observe probe spectra with broad regions of absorption and amplification characteristic of the Autler-Townes splitting for a "dressed" two-state atom. However, additional narrow features around the pump frequency have linewidths of several hundred kilohertz (well-below the natural linewidth of 5MHz) and exhibit appreciable single pass gain (≥30%) . Our preliminary attempts to describe these features theoretically provide limited qualitative agreement with experiment. In an effort to correlate the spectroscopic characteristics of the trap with its mechanical properties, we have observed recoil of the trapped atoms either along or opposite to the direction of propagation of the probe beam depending upon whether the probe experiences absorption or gain. The direction of recoil can be switched with a change in probe detuning of less than 300kHz.
Third-order susceptibility dispersion of polythiophene thin films
Authors: Torruellas W. E. , Neher D. , Stegeman G. I. , Kajzar F.
Published: February 2023

F. Kajzar et al.,1 have previously reported dispersion measurements of only the magnitude of the third order nonlinear susceptibility of polythiophene films. We have performed tunableTFIG measurements in the range of 1 to 2µm on poly(3-butylthiophene) and poly(3-decylthiophene) thin film polymers. Both the magnutide and the phase dispersions of χ(3)(3ω) agree with a three level model. This model indicates the presence of a two-photon state below the first dipole allowed one-photon state. The transition dipole moment between both excited states dominates the dispersion of the magnitude and the phase of χ(3)(3ω) near the three photon resonance.
Nonlinear-optical studies of poly (p-phenylene benzobisthiazole) and its composites with nylon
Authors: Meth J. S. , Vanherzeele H. , Jenekhe S. A. , Roberts M. F.
Published: February 2023

Conjugated heterocyclic rigid rod polymers are of special interest as nonlinear optical (NLO) materials because of their robust physical properties, which include excellent mechanical strength and thermal stability.1 Recent advances1 in the solubilization and processing of these polymers make optical- quality thin films available for NLO measurements. This paper reports χ(3)-Pi-characterization of thin films of poly(p-phenylene benzo-bisthiazole) (PBZT) and PBZT/nylon molecular composites by third-harmonic generation (THG). Solutions of PBZT or PBZT/nylon 66 in Lewis acid (GaCl3 or AlCl3-nitromethane were prepared as previously described.2 Thin films of the pure PBZT or its molecular composites with nylon were prepared in a drybox by solution casting onto 1 mm optically flat fused-silica substrates, followed by washing in water and vacuum drying. The films, which were as thin as 0.4 µm, were of fair optical quality, as evidenced by weak optical scattering and by a uniform THG response over a large area of each sample. The films were slightly yellow, with a cutoff wavelength of 0.5 µm. Third- harmonic-generation experiments were performed with a picosecond laser system that was continuously tunable in the range 0.6-4 µm.3 At 1.8 µm, we measured a nonresonant χ(3) = (1.0 ± 0.2) X 10−11 esu for pure PBZT. The χ(3) values obtained for 2:1, 1:1, and 1:2 PBZT/nylon composites correlate well with the pure material. No anisotropy in the films was detected. The large optical damage threshold of PBZT (>50 GW/cm2 for 30 ps pulses at 1.8 µm) further adds to the attractiveness of this material. We have probed the effects of two- and three-photon resonances by performing THG studies over a large wavelength range. The results will be reported at the meeting.
Mesopic lightness, brightness, and brightness contrast
Authors: Arend Lawrence E.
Published: February 2023

At mesopic mean luminances a fixed physical contrast produces less brightness contrast than at photopic mean luminances.1 This suggests that lightnesses of surfaces might also be altered at low luminances. I measured lightness, brightness, and brightness contrast in cathode-ray tube (CRT) simulations of achromatic paper patchworks. The illuminance of the standard pattern was fixed, producing 0.3, 3, or 30 cd/m2. The illuminance on the test pattern was varied from trial to trial in a lightness-constancy paradigm. Contrast efficiency declined at low mean luminances, i.e., constant brightness contrast required more luminance contrast at mesopic luminances than at photopic luminances. However, mean luminance had only a minor effect on surface lightnesses. Minor failures of lightness constancy occurred at the lowest mean luminances, but they were proportionately smaller than the loss of brightness contrast in the same pattern. These results have implications for imaging applications. Luminances in pictures frequently range downward from about 100 cd/m2, the maximum luminance of common television sets, CRT monitors, and photographs under room lights. Often, some scene content falls in the photopic range and some in the mesopic range. The results indicate that brightness contrast may decrease in low luminance regions without major changes of apparent surface color.
Two-frequency above-threshold ionization of hydrogenic atoms
Authors: Wang L. , Haus J. W. , Rzazewski K.
Published: February 2023

Our previous model of two-frequency above-threshold ionization1,2 is extended to include dipole coupling between an infinite number of continua. The continuum-continuum (C-C) matrix elements are chosen from hydrogenic atom results, and the model is analytically soluble without recourse to the rotating-wave approximation.
Fully parallel, real-time optical architectures for superior time–frequency representations of signals
Authors: Arabshahi Payman , Marks Robert J. , Atlas Les E.
Published: February 2023

A number of optical processors have been proposed for the generation of time–frequency representations of signals, such as the ambiguity function, spectrogram, and the Wigner distribution. Generalized time-frequency representations (GTFR's) have been proposed by Cohen.1 Spectrograms, Wigner distributions, the Choi–Williams distribution, and the Zhao-Atlas-Marks (ZAM) GTFR2 are subsumed as special cases. We show that Cohen's class of GTFRs can be realized optically by the straightforward augmentation of some established optical architectures by means of the simple operation of apodization. A new architecture is also proposed. In our proposal three coherent optical processors take advantage of the rapid input rate and high time-bandwidth product of one-dimensional acousto-optic transducers. Their use permits real-time processing and greatly increases the flexibility of the systems. A simple digital–optical system capable of performing manipulations on the output of the proposed architectures (such as the separation of the positive and negative portions of the GTFR) is also introduced. Finally, results of computer simulations of systems that are designed to produce the ZAM G1TR are presented and compared with spectrogram performance.
Complex spatiotemporal dynamics in lasers
Authors: Tredicce J. R. , Green C. , D’Angelo E. J. , Narducci L. M.
Published: February 2023

It is well known that transverse intensity profiles of lasers may show a nontrivial spatial structure. Usually, depending on the degree of symmetry, the spatial patterns have been associated with modes of a passive resonator or combinations of them which cause oscillations in the laser intensity (mode beating).1 It was recently shown2 that the fluctuations may be due, instead, to the nonlinear coupling between atoms and the field. Here we show that a spontaneous symmetry-breaking process is also at the origin of the formation of complex spatiotemporal dynamics in which oscillations at a single frequency, quasiperiodicity, and chaos may coexist within in the same spatial structure. We compare our experimental results with those obtained from bifurcation theory and numerical integration of the Maxwell–Bloch equations. The transition from a simple (Gaussian) profile to a complex (turbulent) profile is studied by means of the average intensity patterns, frequencies, and phases of the local intensity and cross-correlation functions.
Effects of an aperture on transverse pattern stability and dynamics in a laser
Authors: Lin H. , Abraham N. B.
Published: February 2023

In studies of a model for transverse-mode interaction and spatiotemporal dynamics in a laser, three types of simple pattern formation have been found: the lowest-order transverse mode, temporally stable transverse patterns involving many empty cavity modes (known as a cooperative-frequency-locked state1 because all modes are locked to a common optical frequency), and the beating of two cooperative-frequency-locked states.2 The aperture affects laser operation most strongly in those regions in the parameter space (e.g., laser detuning from the material resonance and transverse-mode spacing) in which the time-dependent solutions are found in the absence of the aperture. In this case the aperture works primarily to suppress the beating and to compel the formation of frequency-locked states that are made up of many empty-cavity spatial mode patterns. Surprisingly, a lesser effect is that the aperture tends to force the laser to operate simply on the lowest-order transverse cavity mode. Results of our analysis indicate that the aperture may also distort the intermode spacings for different transverse modes and that this may also affect the tendency toward single-mode or single-frequency operation.
Tapered graded-index waveguide analysis using path integrals
Authors: Constantinou Constantinos C. , Jones Raymund C.
Published: February 2023

In many fiber and integrated optical devices one needs either to connect two waveguides of different cross-sections, or to join several waveguides at a single junction. A knowledge of the coupling efficiencies of such a junction is clearly important and depends on our understanding of propagation in tapered waveguide sections. We consider paraxial propagation in the z-direction in a graded index waveguide whose refractive index is given by By suitably choosing the function c(z) we can describe tapers with linear, hyperbolic or parabolic geometries in the xz plane. We have used the Feynman Path integral method1 to obtain exact expressions for the coupling efficiency of such tapers without resorting to approximate numerical techniques. Our closed form analytical results for the coupling efficiencies reveal detailed structure which other methods of analysis do not show. Some recent experimental evidence would indicate support for the results of our calculations.2
Laser-beam alignment stabilization by self-compensation
Authors: Hsu Fu Kuo
Published: February 2023

Laser beams are usually unstable in terms of their pointing direction because of fluctuations of the resonant cavity. This angular fluctuation of laser beams can be somewhat reduced with a servomechanism.1,2 My approach uses an optical system capable of self-compensating the angular fluctuation of the laser. Because no servomechanism is required, the beam stabilizer reacts instantaneously. The stabilizer essentially uses the self-compensation principle. The input beam is first divided into two perpendicularly polarized beams, that then combine to form the output beam. Because the angular fluctuation of the input beam causes the two perpendicularly polarized component beams to deviate in exactly opposite directions, the angular error of the combined beam is automatically cancelled. This system works well for Gaussian beams, either cw or pulsed. The design and analysis of the proposed beam stabilizer are provided. Experimental demonstrations are also given.