bluuebunny/crossref_metadata_2025 huggingface dataset:
A CCD System to Detect Fast-Moving Asteroids
Authors: Gehrels T. , Boesgaard H. , Doose L. R. , Frecker J. E. , McMillan R. S. , Perry M. L. , Scotti J. V. , Shoemaker E. M. , Tholen D.
Published: February 2023

A rendezvous by a space probe with an asteroid will allow the composition of the asteroid to be studied in great detail. Since some "asteroids" are the cores of extinct comets, such spacecraft will also permit the properties of these mysterious objects to be clarified.
Analysis of narrow-band filtergrams for bidimensional spectroscopy of the solar atmosphere.
Authors: Caccin B. , Falciani R. , Roberti G. , Smaldone L.A.
Published: February 2023

A series of "monochromatic" images of extended sources obtained with a wavelength tunable filter at different points along the profile of a strong Fraunhofer line provide data that occupy a threedimensional volume of two spatial and one spectral dimension. These data can be used to retrieve the line profile at any desired point on the acquired image, with a spectral resolving power that can be made comparable with that of a moderate resolution spectrograph (λ/Δλ≲25000), according to the trade-off between the spectral and the time resolution that, together with the constraints on the total amount of data, fixed the maximum number of images available along the line profile.
Computer-aided design of integrated optics: closing the synthesis loop
Authors: Young Terry P.
Published: February 2023

The numerical techniques for analyzing integrated optics include the well-known finite-element (FEM), finite-difference (FDM), and beam-propagation (BPM) methods, and a number of lesser known and emergent techniques (see Ref. 1 and references cited therein).
Observation of modulational instability for normal dispersion
Authors: Rothenberg Joshua E.
Published: February 2023

Optical modulational instability (MI), the spontaneous generation of intensity modulation, has received much attention recently as a novel nonlinear-optical process and as a source of high-repetition-rate sub picosecond pulses. In a detailed analysis1 it was pointed out that MI would only be seen for anomalous group-velocity dispersion(GVD,β = 0). This effect was first observed in the nonlinear propagation of infrared light in optical fibers.2 The situation of waves nonlinearly coupled through cross phase modulation in a biréfringent fiber was treated3 for anomalous GVD. A straightforward extension of this analysis shows that MI occurs even for normal dispersion.4 We find that gain exists in a band of frequencies centered about

Ω
≅
δ
/
β
,
 
where
 
δ
=

v

g

(

s
l
o
w

)

−
1

−

v

g

(

f
a
s
t

)

−
1

is the group-velocity mismatch of the two polarization modes. Each wave develops intensity modulation, and the slow wave develops a single sideband frequency downshifted by Ω, and the fast wave is upshifted by Ω. This behavior is in contrast to previously observed optical MI,2 in which the pump develops dual sidebands and thus represents a new class of MI.
Tunable femtosecond soliton generation from continuous diode lasers using pulsed stimulated Raman amplification
Authors: Greer E. J. , Patrick D. M. , Vukusic J. I. , Wigley P. G. J. , Taylor J. R.
Published: February 2023

The single-pass soliton–Raman generation process1 provides an expansive spectral continuum that contains several solitons of sub-picosecond duration. However, the spectral extent of the continuum and the number of solitons contained in it are not particularly controllable, although they are a function of the pump power. Consequently, the soliton–Raman continuum is of limited use as a practical wavelength-tunable, femtosecond-pulse source. By using spectral filtering, a wavelength band of interest can be selected. This method does give rise to considerable overall system energy loss, but the solitons so selected can be used for pump-probe experiments.2
Modulational instability in a stimulated Brillouin fiber ring laser
Authors: Itoh Hiroki , Asobe Masaki , Sudo Shoichi
Published: February 2023

Modulational instability (MI) in optical fibers is a nonlinear process in which a cw turns into high-repetition-rate pulses as a result of an interplay between the nonlinearity and anomalous dispersion.1 MI can be induced by mixing two waves that propagate in the same direction, and the pulse repetition rate is fixed at the frequency difference between the two waves.1 Stimulated Brillouin scattering (SBS) is another nonlinear effect in optical fibers. In a SBS fiber ring laser, pumping with large power can generate not only first SBS Stokes that circulates backward but also second SBS Stokes that circulates forward. We have achieved MI that is induced by mixing the pump light at 1.32 μm with the second Stokes light in a SBS fiber ring laser.
Interferometric quantum-well waveguide modulators
Authors: Zucker J. E. , Jones K. L. , Miller B. I. , Koren U. , Wegener M. , Chang T. Y. , Sauer N. , Chemla D. S.
Published: February 2023

Semiconductor Mach-Zehnder waveguide interferometers are attractive for high-speed intensity modulation because they have, in push-pull configuration, zero frequency chirp and low half-wave voltage Vπ.1,2 Monolithic integration of a laser and modulator for high-bit-rate optical communications requires that both the active length L and Vπ be kept small. In bulk semiconductors, the Pockels effect yields the product Vπ x L ~ 3 V cm for voltage applied across 1 μm. In this paper we demonstrate Vμ x L as small as 0.4 V cm by utilizing large quantum-well (QW) electrorefractive effects.
Substituted polysilanes for integrated optics
Authors: Schellenberg F. M. , Byer R. L. , Miller R. D.
Published: February 2023

Linear polysilanes are polymers consisting of a long catenated silicon backbone, with two side groups, usually carbon based, attached to each Si atom in the backbone chain. Electronic and structural properties can vary significantly with the side group, but common to all polysilanes is a degree of electron delocalization along the σ-bonded backbone. This delocalization results in large oscillator strengths for excitations polarized parallel to the backbone. Absorption of UV photons decays either by UV fluorescence or scission of the polymer backbone, making these materials useful as deep UV photoresists for microlithography. These large oscillator strengths also give rise to large optical nonlinear susceptibilities.
New beam-propagation algorithm based on the method of lines
Authors: Pregla R. , Gerdes J.
Published: February 2023

When using the standard beam-propagation method (BPM), we can analyze optical waveguide structures in a clear way. Attention must be paid, however, to the following restrictions of the applicability of the BPM: no large transverse index steps, no large propagation steps compared with the wavelength, and propagation under paraxial conditions. Another problem arises from the finiteness of the computational window. The field intensity should be equal to zero, and radiation modes should not be reflected at the window edges. To achieve these conditions, we usually place artificial absorbers at the edges. This leads to additional storage and computing time.
Switching characteristics of Ti:LiNbO3 devices-a comparison of simulation techniques
Authors: Chu F. S. , Liu Pao-Lo
Published: February 2023

The propagation-beam, or beam-propagation, method has been extensively used to simulate waveguide devices.1-3 Both three-dimensional (3D) and two-dimensional (2D) calculations have been used. The 2D calculation requires substantially less computer time, however, it uses the effective index, which is an approximation to the real index profile.4 The effective-index method has been demonstrated to provide accurate results for single-mode structures. On the other hand, Y junctions are commonly used in waveguide devices. At the branching point, a Y junction may support more than one mode locally. It is interesting to compare 2D and 3D results for waveguide devices with Y junctions.
MgO/Ti bilaterally diffused LiNbO3 optical switch
Authors: Tanaka Nobuyuki , Banno Tatsuya , Katsuda Hirohiko , Shiota Takao , Inada Koichi
Published: February 2023

The Ti diffusion method is well known for making low-loss waveguides. However, the coupling and bending loss must be reduced for small-scale integration. These losses are mainly attributed to the asymmetric spot of waveguide.1 A symmetric waveguide spot is appropriate for reducing both the coupling and the bending loss. To achieve this, several proposals such as MgO/Ti double diffusion have been made.2 However, there is a trade off between reduction of loss and other switching performances.2
Effect of intrinsic phase mismatch on linear modulator performance
Authors: Howerton M. M. , Bulmer C. H. , Burns W. K.
Published: February 2023

Both the symmetric 1×2 directional coupler and the asymmetric Mach-Zehnder interferometer can function as linear modulators that are passively biased about the optimum operating point.1,2 Their performance is comparable for ideal devices, and results near the theoretical limit have been experimentally obtained.3,4 Our interest here is to study factors leading to nonideal behavior in order to predict device yield. To accomplish this we have (1) developed models incorporating the intrinsic phase mismatch Δβo between the two waveguides; (2) measured that Δβo distributions for both devices; and (3) experimentally demonstrated that Δβo impacts performance (linear dynamic range and sensitivity) as predicted by theory.
Suppression of acoustic effects in lithium niobate integrated-optical modulators
Authors: Betts G. E. , Ray K. G. , Johnson L. M.
Published: February 2023

Acoustic effects can degrade the performance of LiNbO3 integrated-optical modulators at frequencies below a few hundred MHz. Acoustic problems have been reported in traveling-wave modulators1 and in lumped-element modulators using both baseband2 and resonant3 drive circuits. The most serious problem is the appearance of ripples in the frequency response owing to acoustic resonances, as shown in Fig. 1. These are typically sharp (as little as 100 kHz wide) and are polarization dependent. Acoustic interactions also cause frequency-dependent changes in the modulator electrode impedance; this causes problems primarily in resonant-matched devices. Finally, acoustic waves can cause cross talk between modulators on the same substrate. We report here the characterization of acoustic effects and methods for their reduction.
Fabrication and enhanced performance of reduced-confinement GaAlAs tapered-waveguide antennas
Authors: Bossi D. E. , Goodhue W. D. , Johnson L. M. , Finn M. C. , Rauschenbach K. , Rediker R. H.
Published: February 2023

Tapered-waveguide antennas reduce the far-field divergence of beams emitted from integrated-optical waveguides. Previously, we presented preliminary results on reduced-confinement GaAlAs antennas,1 which, unlike horn antennas, are compatible with two-dimensional antenna development. We now report a new fabrication technique that permits improved and reproducible performance of these antennas, and we describe a numerical simulation that allows us to verify and accurately predict performance limitations of reduced-confinement antennas.
Dynamic etch mask technique for fabricating tapered semiconductor optical devices
Authors: Shahar A. , Tomlinson W. J. , Seto M. , Yi-Yan A. , Deri R. J.
Published: February 2023

A critical problem for the realization of practical integrated-optical circuits in semiconductor materials is that the optimum optical waveguide mode sizes are different for different types of circuit elements. Previously reported techniques for tapering the composition and/or depth of waveguides have been limited in their capabilities, ease of implementation, or ranges of applications.1-3 We report here a new technique, using a dynamic etch mask, that makes it possible to fabricate semiconductor waveguide and device structures with a smooth, gradual, tapered etch depth in various orientations at arbitrary locations on a sample.
Realization of small-bend radii in Ti:LiNbO3 waveguides through indiffusion from a stepped MgO layer
Authors: Majd M. , Schüppert B. , Petermann K.
Published: February 2023

Low-loss optical waveguide bends are desired to realize integrated-optical devices with practical dimensions. On the basis of InGaAsP/InP, bend radii down to 150 μm are possible.1 However, an important material for integrated optics is LiNbO3 because of its large electro-optical coefficient and easy fabrication process. However, because of the weak confinement by Ti:LiNbO3 waveguides, large bend radii in the range of centimeters must be used.
Integrated-optical waveguides in silicon by germanium indiffusion
Authors: Schüppert B. , Schmidtchen J. , Petermann K.
Published: February 2023

Silicon is an attractive material for monolithic integration of optical and electronic components for wavelengths above 1.1 μm. In this concept even laser diodes may be integrated by means of heteroepitaxy of III–V compounds on silicon, and detectors can be fabricated by heteroepitaxial growth of germanium1, whereas electronic components can be realized by standard techniques. Rib waveguides have been realized in Ref. 2 for an n/n
+
silicon and proposed in Ref. 3 for a Ge-doped epilayer grown on an undoped substrate. The basic idea of our technique for integrated-optical waveguides in silicon is to indiffuse an element with a larger refractive index than that of silicon into a lightly n-doped epilayer, which is grown on a heavily doped n+ substrate. Because losses increase with an increase of free carriers, the element for indiffusion must belong to group IV of the periodic system. Both conditions are met by Ge that is deposited as a GeSi alloy onto the epilayer, either by quasi-simultaneous evaporation of Ge
x
Si(1-
x
) using a jumping E-beam or by evaporating a system of thin alternating Ge and Si layers. The channel waveguides are formed through standard lift-off techniques (Figs, 1a–1c). To avoid evaporation during diffusion, a SiO2-overlay is sputtered onto the epilayer (Fig. 1d). After diffusion at 1200C for 69 h (Fig. 1e) the SiO2 overlay is removed by etching (Fig. 1f). A typical depth profile of Ge is shown in Fig. 2, yielding a diffusion depth of d = 2.1 μm and a diffusion constant of D = 1.6 × 10-2 μm2/h. Various waveguides with different stripe widths, alloy ratios, and layer thicknesses have been fabricated, and the spot sizes have been measured to be in the range of 4–8 μm for the vertical and 6–12 μm for the horizontal spot. Fitting the measured vertical spot sizes to theoryyields the maximum index enhancement as a function of Ge content, which is shown in Fig. 3. The Ge content before indiffusion is given in terms of the product of the deposited layer thickness τ and the alloy ratio x from which the maximum Ge concentration at the surface after indiffusion can be calculated if we assume that the material is completely indiffused.
Enhanced photorefractivity in germanosilicate fibers: effects of bleaching with 488-nm light
Authors: Hand D. P. , Poyntz-Wright L. J. , Russell P. St. J.
Published: February 2023

Permanent index changes, Δn, of the order of 10-4 at 633 nm are induced in germanosilicate optical fibers by exposure to light at 488, 266, and 240 nm.1-3 This photorefractivity has great potential in the fabrication of efficient grating-based devices for a wide range of WDM and lasing applications. It has been explained2 in terms of alterations in the UV absorption spectrum yielding (through the Kramers-Kronig relation) almost dispersion-free Δn values between 500 nm and 1.5 μm. The predominant cause is the movement of electrons from broken oxygen deficient Ge–Si bonds (associated absorption peak at 240 nm) to Ge(2) traps (when occupied by an electron an absorption peak appears at 213 nm) (see Fig. 1). The Ge–Si bonds can be broken by single-photon absorption of 240-or 266-nm light (permitting gratings of any period to be fabricated by side writing), or (much more slowly) by two-photon absorption (TPA) of 488-nm light. However, an undesirable side effect of 266-nm treatment is that the absorption induced for approximately the same Δn value is some two orders of magnitude larger than that obtained with 488-nm light (30 dB/m at 633 nm). This absorption is attributed to the creation of Ge(1) color centers,4 with a broad absorption peak centered at 281 nm and extending into the visible (Fig. 1). Because the balance between bleaching and trapping at Ge(1) and Ge(2) dopant sites is different for 266-nm light, it seemed possible that the population of Ge(1) centers could be depleted by 488-nm light, perhaps even enhancing the induced Δn.
Phase Fluctuations in Seeded Second Harmonic Frequency Generation in Optical Fibers
Authors: Krol D.M. , Broer M.M. , Stolen R.H. , Tom H.W.K.
Published: February 2023

We demonstrate here the significant effect relative phase fluctuations have on seeded second harmonic generation (SHG) in optical fibers. A changing relative phase between IR (1.06 μm) and green (0.532 μm) seeding beams results in a continuous washing-out of the χ(2) grating. Consequently only a weak SH signal is observed immediately after seeding. A stable relative phase on the other hand increases the seeded second harmonic (SH) intensity by approximately a factor of 103.
Low Threshold Strained Quantum Well Lasers at 1.5 Micron Wavelength
Authors: Koren U. , Oron M. , Young M. G. , Miller B.I. , De Miguel J.L. , Raybon G. , Chien M.
Published: February 2023

InGaAs/InGaAsP multiple quantum well (MQW) lasers at 1.3-1.5 micron wavelength have yielded several advantages over bulk lasers at this wavelength range, such as low internal loss , high quantum efficiency, low threshold current operation and small linewidth enhancement factors [1-3]. There have been several reports predicting that further improvements are possible by employing strained layer quantum wells [4,5], as the effective mass of holes in the heavy hole sub-band of quantum well layers can be significantly reduced in the plane of the wells by compressive strain. This should result in lower threshold currents and other improvements of the laser parameters. Recently, the operation of InGaAs /InGaAsP strained layer MQW lasers at 1.5 micron was reported [6] with efficiency and output powers similar to the high values reported previously for unstrained MQW lasers. However, the expected reduction in threshold current and linewidth enhancement factor have not been observed.
InGaAs/InAlAs Multiple Quantum Well (MQW) Optical Modulators Employing a Thick p-i-n MQW Core
Authors: Kawano Kenji , Kotaka Isamu , Wakita Koich , Mitomi Osamu , Nojima Syunji , Asai Hiromitsu , Kawamura Yuichi
Published: February 2023

There has been considerable recent interest in external optical modulators [1]-[5]. MQW optical modulators with more than a 40 GHz modulation bandwidth and 7 V driving voltage at a 1.54 μm wavelength have been reported by the authors [5]. However, the insertion loss was too high due to the large coupling loss caused by small spotsize (<0.4 μ m) in the vertical direction.
Balanced Operation of an InGaAs/InGaAsP Multiple-Quantum-Well Integrated Heterodyne Receiver
Authors: Koch T. L. , Choa F. S. , Koren U. , Gnall R. P. , Hernandez-Gil F. , Burrus C. A. , Young M. G. , Oron M. , Miller B. I.
Published: February 2023

Heterodyne receiver photonic integrated circuits (PIC’s), incorporating continuously tunable local oscillator (LO) lasers, directional couplers and photodetectors, offer the potential for dramatic simplification of coherent lightwave technology by eliminating the coupling and packaging of the corresponding discrete devices[1,2].
Elucidation of the Origin of Photoinduced Second-Harmonic Generation in Glass Optical Fibers
Authors: Mizrahi Victor , Hibino Yoshinori , Stegeman George
Published: February 2023

Since the first report1 of efficient second-harmonic generation (SHG) in glass optical fibers four years ago, a number of models have been put forward to explain the effect. These can be roughly divided into two categories. In some models2,3,4 it is proposed that an internal d.c. electric field is set up which, acting on the χ(3) of the glass, serves as an effective χ(2). In other models5,6,7 it is proposed that the macroscopic χ(2) originates from an orienting of dipoles ("defects") in the glass. We have examined the polarization properties of the second-harmonic light generated by a single mode germania doped fiber. From the observed behavior we deduce that the effective χ(2) of the fiber behaves as a χ(3) of a nondispersive isotropic material (glass) acted on by a transverse d.c. electric field; in other words, we are likely dealing with an electric-field induced second-harmonic generation (EFISH) phenomenon.
Monolithic integration of multilayer filter and waveguide photodetectors
Authors: Baba T. , Tamura S. , Kokubun Y. , Watanabe S.
Published: February 2023

Multilayer optical filters are suitable for waveglength multiplexers/demultiplexers because of their high performance of broad wave length range (large tolerance), high suppression ratio, and large freedom of design. However, it is difficult to integrate them monolithically with waveguide-type devices, as achieved by grating,1 directional couplers,2,3 and ARROW.4 In this study we investigate a novel technique to fabricate multilayer filters on a vertical surface of substrate monolithically and demonstrate the integration of multilayer filter and photodetector, which can be applied to an integrated device of optical waveguide, demultiplexer, and waveguide photodetector, as shown in Fig. 1.
Stimulated Raman scattering in optical fibers: polychromatic single-field numerical experiments
Authors: Hawkins Raymond J. , Stolen R. H.
Published: February 2023

The response-function based computational approach to Raman scattering in single-mode optical fibers was introduced, in part, as a method for treating situations in which the spectral distinction between pump and Stokes broke down. This happens, for example, in the case of femtosecond optical pulses whose bandwidth exceeds the bandwidth of X3. The Raman response function has been used with considerable success to predict the propagation properties of many pulses in the femtosecond regime.1,2 It is not, however, promoted as an approach for longer pulses. In this paper we report on the use of the Raman response function in predicting the propagation properties of picosecond pulses in optical fibers and discuss the results of a numerical reproduction of the laboratory experiments of Raman scattering reported by Stolen and Johnson.3
Raman effect in biréfringent optical fibers
Authors: Menyuk C. R. , Gordon J. P. , Islam M. N.
Published: February 2023

In recent experiments by Islam,1,2 soliton in birefringent optical fibers have been used for switching. These pulses are 300 fs long so that the Raman effect plays an important role in the soliton evolution. In deriving the form of the Raman interaction, we use a phenomenological approach.
Analysis of second-order nonlinear interactions in an optical waveguide by the Galerkin method
Authors: Maruta Akihiro , Kawata Yasuhiro , Matsuhara Masanori
Published: February 2023

In recent years experimental and theoretical research on the frequency converter utilizing second-order nonlinear interactions between light waves in an optical waveguide, mainly on the second-harmonic generation (SHG) device, has been carried out actively.1-3Earlier theoretical works, however, have some drawbacks.
Novel analysis method for mode-locked semiconductor lasers
Authors: Helkey R. J. , Morton P. A. , Bowers J. E.
Published: February 2023

Subpicosecond mode-locked lasers have been analyzed analytically1,2 and numerically.3,4 The analytic methods neglect important physical mechanisms, and the numerical methods require excessive computation time.
Computer-aided thermal analysis of semiconductor integrated ring lasers
Authors: Chen Wei , Laybourn Peter J. R. , Jezierski Andrjez F.
Published: February 2023

Integrated semiconductor ring lasers with an output waveguide have been produced.1 They have attracted considerable attention because high-quality mirrors are not needed, the output termination has little influence on oscillation conditions, and the small dimensions make the longitudinal mode spacing increase so that single-mode operation is possible. A rib waveguide configuration was used to maximize light confinement and to minimize bending loss in the small cavity (Fig. 1). However, the temperature increases within the ring-laser structure are expected to be excessive as the heat source is more concentrated and the heat generated is difficult to dissipate because of the extremely small dimensions. A thermal model of the ring-laser device has been developed. Laser-device substrate and lasing rib were considered separately in this cylindrical symmetry model. For simplicity, no convection or radiation has been taken into account, and all the heat was assumed to transfer to the heat sink, which is forced down to an adjustable temperature, e.g., 20°C. The temperature distribution within the ring-laser structure has been calculated by using a finite-difference technique2 and plotted by using a Ghost 80 computer plot package (Fig. 2). The thermal resistance for the whole laser device has also been calculated (Fig. 3). All modeling was done on an IBM 3090 computer with a vector facility. The resulting temperature profiles agree with IR imaging thermal measurement results fairly well.3 The temperature gradient is strongest just beneath the rib, and the distribution is the same for an increase in input power or in heat-sink temperature. Only the temperature corresponding to each isotherm increases.
Comparative study of the reflectivity of coated and angled facets
Authors: Buus J. , Faries M. C. , Robbins D. J. , Vassallo C. , Besse P. A. , Gu J. S. , Atternäs L , Thylén L. , Nilsson J. , Jaskorzynska B.
Published: February 2023

Optical amplifiers based on semiconductor laser-like structures are attracting increasing attention for application in lightwave systems. To achieve low gain ripple in a traveling-wave amplifier, the facet reflectivity must be very low, placing stringent tolerance requirements on the facet coating. As an alternative to facet coating, it has been proposed that a low reflectivity could be achieved by combining a less critical coating with an angled facet.1
Bismuth-doped yttrium iron garnet-gadolinium gallium garnet waveguides with application to magneto-optic Bragg cells
Authors: Tsai Chen S. , Wang C. L. , Pu Y.
Published: February 2023

Similar to guided-wave acousto-optic (AO) interactions1 in which the surface acoustic waves (SAWs) induce a moving optical grating through the photoelastic effect, guided-wave magneto-optic (MO) interactions result from the moving optical grating induced by the magnetostatic waves (MSW) through the Faraday and the Cotton-Mouton effects.2 Of particular interest to us is a noncollinear coplanar geometry2 in YIG-GGG waveguides,3 as shown in Fig. 1 in which an incident guided-light wave is Bragg diffracted and mode-converted (TE- to TM-mode and vice versa). The Bragg-diffracted light is scanned in the waveguide plane as the frequency of the MSW is tuned. Analogous to the AO Bragg diffraction in which the resulting modulator is called the AO Bragg cell, the resulting MO modulator is called the MO Bragg cell.2
Direct loss measurement for optical devices incorporating coupled waveguides
Authors: Shahar A. , Yi-Yan A. , Tomlinson W. J. , Kapon E. , Seto M. , Deri R. J.
Published: February 2023

Directional couplers are important building blocks in the design of a variety of integrated-optics devices. A precise knowledge of the device loss is important, both for practical use in systems applications and for effective design through a thorough understanding of the device operation. To the best of our knowledge, all the loss measurement techniques for coupled waveguides in use today use indirect methods under the assumptions that both a calibration waveguide and the device have the same input coupling efficiency and the same propagation loss per unit length. These assumptions are invalid for many cases and are a major source of uncertainty in the measurement of losses of such devices.
Analysis of discontinuities in planar dielectric waveguides using a hybrid finite-element/boundary-element method
Authors: Dillon B. M. , Ferrari R. L. , Young T. P.
Published: February 2023

The evaluation of the effect of discontinuities, typically junctions, tapers, or bends, in dielectric waveguides is important in the design of many integrated-optical devices. The planar nature of the waveguides used in many of these devices means that a good approximation to the discontinuity characteristics can be obtained by modeling an equivalent planar waveguide that is obtained by applying the effective index method1 to the three-dimensional waveguide. A similar approximation is used when the beam-propagation method2 is applied to these type problems.
Mode structure of rib waveguides
Authors: Kellner A. L. , Bradley J. C.
Published: February 2023

This paper summarizes research that was done to determine the modes in rib waveguides with complex dielectrics. The general method of computation is the product method used by Bradley and Kellner.1 The calculations can be carried out by using complex algebra in the product method so that no substantial changes occur in the procedure except for dielectric interfaces. We derive the results appropriate for treating complex dielectric interfaces and report results of these calculations that characterize the active region in a waveguide modulator.
Calculation of modal discrimination in leaky-mode diode-laser arrays using a triangular-mesh finite-difference method
Authors: Hadley G. Ronald
Published: February 2023

A new type of diode-laser array that emits a near-diffraction-limited beam at drive currents up to 10 times threshold has recently been reported.1 These devices, denoted leaky-mode arrays because of their tendency to lase on radiation modes, show great potential as high-power sources of focusable radiation. Realization of this potential, however, necessitates accurate modeling, which has so far proved difficult because of several problems. First, the use of the effective index method has been shown to be inaccurate for these arrays so that full two-dimensional (2D) waveguide modeling is necessary.2 Second, the use of highly absorbing GaAs regions requires a fully complex calculation. Finally, the accurate simulation of radiation modes necessitates lateral boundary conditions that are totally absorbing; i.e., they reflect no radiation back into the problem region.
Measurement and Dispersion of Two-Photon Parameter for All-Optical Switching
Authors: DeLong K. W. , Mizrahi Victor , Stegeman G. I. , Saifi M. A. , Andrejco M. J.
Published: February 2023

We calculate the dispersion of a two-photon figure of merit for all-optical switching, and show that in semiconductors operation below the two-photon bandgap is desirable. We present measurements of two-photon absorption in titanium doped and lead glass fibers.
Kerr-type nonlinearities in lightguides: coupled-mode field representations
Authors: Hénault A. , Black R. J. , Gonthier F. , Lacroix S. , Cada M.
Published: February 2023

Third-order nonlinearities in optical waveguides have received considerable recent attention,1with particular interest in the possibility of devices for all-optical signal processing. In the small-intensity limit (linear case), field decomposition for longitudinally invariant lightguides allows for independently propagating modes, which are wave equation solutions after separation of transverse and longitudinal parts.2,3For intensity-dependent refractive indices, the illuminated guide is no longer longitudinally invariant, and thus this separation is not permitted. However, as is possible for tapered guides, we can describe the field as a combination oflocal modes,which couple as the light propagates. As local modes we can use modes of the linear-index guide. Alternatively, we may use solutions of the nonlinear wave equation (NLWE) for the transverse field dependence.4For approximate monomode propagation this can provide a more natural field representation in particular. However, these modes are only solutions of the transverse NLWE if considered in isolation; i.e., each nonlinear mode modifies the nonlinear index differently. For few-mode propagation, although a coupled nonlinear-local-mode approach may involve fewer local modes depending on the structure, increased complexity in the formalism results when non-orthogonality of the nonlinear modes is accounted for. In contrast, the linear-local-mode treatment has the attraction of simplicity. In Figs. 1-3 we consider the nonlinearly coupled linear-guide local-mode field representation and convergence thereof given initial bimodal excitation, assuming a Kerr-type nonlinear index and slowly varying approximations.3When we adopt the notation of Ref.3with difference between the effective indices of the two initially excited modesδneff,the Kerr coefficientn21,core half-widthρ, andPref=ρδneff/n2,I, forP/Pref<1, the two-mode representation is highly accurate for describing the nonlinear phase shifting and small nonlinear coupling. AsP/Pref≈ 1 is approached, the field evolution is well described in terms of 3 or 4 local modes. ForP/Pref≥2, "violent pulsations"2are observed, and the local-mode representation may not necessarily be uniformly convergent. These results may be compared with field evolution obtained by using the beam-propagation method.
Novel waveguiding phenomena in nonlinear semiconductor Bragg reflector structures
Authors: Lambkin P. M. , Shore K. A.
Published: February 2023

Nonlinear waveguiding properties of planar optical waveguides have been investigated by many researchers. Recently attention has focused on promising nonlinear multilayer configurations.1 Previous investigations reported the linear guiding properties of several multilayer structures, including the Bragg reflection waveguide.2 This paper presents the first analysis of the nonlinear waveguiding behavior of a Bragg-reflector structure fabricated in semiconductor material.
Electroabsorption in InGaAs/InP multiple quantum wells at high optical intensities
Authors: Wood Thomas H. , Pastalan John Z. , Burrus Charles A. , Miller Barry I. , deMiguel Jose L , Koren Uziel , Young Martin
Published: February 2023

Electroabsorption modulators made from multiple quantum wells (MQWs) show promise for application to optical fiber systems. Because of the relatively low absorption saturation intensities of MQWs2 and bulk3 electroabsorption modulators. Here, we report, for the first time, mea surements of the saturation intensities of the electroabsorption in long-wavelength MQWs. We studied both the decrease in on/off ratio and changes in bandwidth of such devices at high input intensities. Preliminay studies of related effects have been reported in GaAs/AlGaAs MQWs.4
Electric-field-induced optical waveguide in GaAs/AIGaAs
Authors: Huang T. C. , Chung Y. , Dagli N. , Coldren L. A.
Published: February 2023

Optical waveguides are key components of optoelectronic devices. It is attractive to have an optical waveguide in which the waveguiding can be controlled electrically. Voltage-induced optical waveguides have been observed and discussed previously on LiNbO3.1,2 Here we report for the first time, to our knowledge, the electric-field-induced optical waveguide, or field-induced guide (FIG), in the GaAs/AIGaAs. Figure 1(a) shows a schematic diagram of the cross section of such a waveguide. A p-i-n multiple quantum-well (MQW) structure was grown by using molecular-beam epitaxy (MBE). A proton ion implantation was carried out to convert the regions between the FIGs into semi-insulating material so that an electrical controllable channel was formed in the non-proton ion-implanted region because only this region contains an electrical field across the transverse (top-to-bottom) dimension.
Vertical impedance matching for enhanced evanescent coupling in waveguide/photodetectors
Authors: Deri R. J. , Wada O. , Makiuchi M. , Hawkins R. J.
Published: February 2023

Waveguide coupling to absorbing layers is essential for photodetector integration in OEICs. Evanescent coupling schemes (Fig. 1) are the simplest to fabricate, but exhibit weak coupling. Long devices are required for appreciable absorption, resulting in large capacitance and small bandwidth.1-3 Improved coupling is achievable by using thin waveguide layers1,2 or thin absorbers,2,3 but these designs result in difficult fiber-to-waveguide coupling or excessive photodiode capacitance, respectively. Here we present a novel method that improves evanescent coupling ≥7× over conventional structures, preserves simplicity of fabrication, and applies to all guide and absorber thickness values.
Theoretical model for the tunable resonant amplifying photodetector
Authors: Choa F. S. , Koch T. L
Published: February 2023

In a wavelength-division-multiplexed broadband fiber-optic network, a key component is a narrowband filter with good bandwidth control and a wide tunability of the center frequency. We have previously demonstrated such a device, the tunable resonant amplifying photodetector (TRAP) which can function simultaneously as a tunable filter, optical amplifier, photodetector, and FSK discriminator.1 In this paper, we present a theoretical model for this multifunction device. This theory is applicable to all types of resonant laser diode amplifiers, i.e., DFB, DBR, and Fabry-Perot.
Impedance and loss calculations for thick coplanar structures optical modulators
Authors: Gopinath Anand , Donnelly Joseph P.
Published: February 2023

Coplanar waveguides and asymmetric coplanar strip lines1 are used in lithium niobate couplers and interferometers to provide the electrical rf modulation signal. In general, the spacings between the lines of these structures are small, typically between 3 and 30μm and to reduce conductor loss, they are plated up to 3μm and thicker.2 In these cases, the strip thickness to conductor spacing ratio becomes large (0.1 upwards), and impedance and loss calculations using the thin-strip approximation are no longer acceptable. The present paper discusses a Green’s function approach to the calculations of these parameters taking into account the strip thickness.
Enhanced bistability in grating coupling into InSb waveguides
Authors: Ehrlich J. , Assanto G. , Stegeman G. I. , Chu H.
Published: February 2023

Under certain conditions, for example diffusive nonlinearities, bistability can occur under appropriate angular detuning conditions when a grating or prism is used to couple an externally incident field into a thin film waveguide.1-5 In this paper we demonstrate experimentally that the bistable response of an in-coupled guided wave can be enhanced by a second counter-propagating guided wave which utilizes the same grating as an output coupler. This is verified for both an externally controlled second beam, as well as for an integrated device in which a nonlinear distributed feedback grating provides a power-dependent reflection coefficient.
Tapered optical-fiber amplifiers and saturable absorbers
Authors: Mackenzie H. S. , Payne F. P.
Published: February 2023

The adiabatically tapered single mode optical fiber provides an attractive method for gaining access to the fiber modal field for studying nonlinear interactions with external media surrounding the taper. In this paper we describe a new class of such nonlinear devices where the medium surrounding the tapered fiber is a laser dye solution; we present preliminary results of efficient optical amplification and saturable absorption at power levels compatible with diode and doped fiber lasers.
Distortion characteristics of coupled waveguide modulators
Authors: Korotky S. K. , Halemane T. R. , de Ridder R. M. , Veselka J. J.
Published: February 2023

At present, amplitude modulation is preferred for the distribution of cable television signals, although it places stringent requirements on carrier-to-noise ratio (CNR) and linearity.1 For example, consider a system consisting of a 200-mW laser with relative intensity noise of −165 dB/Hz, fiber coupling of −35 dB, external interferometric modulator with 6-dB insertion loss, link loss of 5 dB, and receiver with rms noise current of 15 pA/(Hz)1/2 and operating at an optical modulation depth (OMD) of 1% per channel. In principle this system limits the broadcasting of 40 channels with a desired CNR of 50 dB (4-MHz bandwidth) and composite triple beat of 62 dB below the carrier (dBc) to two locations. We have analyzed the distortion characteristics of a variety of modulators based on coupled waveguides and variable phase mismatch to look for a passive means of reducing the distortion, thus allowing us to broadcast to more sites. Here we show analytically that these structures exhibit intermodulation distortion similar to the interferometric modulator.2 Measured 3IM distortion levels for samples of Ti:LiNbO3 interferometric, uniform Δβ, Δβ reversal, and weighted coupling3 projected to an OMD of 4% are in the range of −74 to −72 dBc and confirm the models.
Wavelength multiplexer/demultiplexers based on codirectional couplers on GaInAsP/InP
Authors: Bornholdt C. , Kappe F. , Nolting H.-P. , Stenzel R. , Venghaus H. , Weinert C. M.
Published: February 2023

We report on the fabrication and characterization of integrated-optics multiplexer/demultiplexers (muldex) on GaInAsP/InP suitable for fiber-optic bidirectional B-ISDN customer access connections. The broadband and narrow bandwidth muldex structures were designed by two-dimensional finite-difference calculations (FDM) and the beam-propagation method (BPM). Both structures are realized in rib-waveguide technology, using quaternary LPE-grown layers (equivalent bandgap λ
Q
= 0.97 µm and λ
Q
= 1.06 µm). Waveguides are structured by RIE etching, and rib heights are controlled by in situ ellipsometry.1 The typical width of the waveguides and of the coupler gaps are 2-3 µm.
Mach-Zehnder operation of the two-wavelength nonlinear loop mirror
Authors: Nelson B. P. , Blow K. J. , Doran N. J.
Published: February 2023

The fiber loop mirror is an ideal device for investigating nonlinear switching by using the ultrafast Kerr nonlinearity of optical fibers, and a number of examples of its use have been published. These include pulse switching,1soliton switching,2and two-wavelength switching.3The nonlinear phase shift depends on the product of the signal intensity and the fiber loop length; thus, to reduce switching intensities, we use long loops (~100 m). To improve the long-term stability of these devices, polarization-maintaining fiber (PMF) is used. Because the group and phase velocities are considerably different for the orthogonal polarization states of a PMF, in all the previous examples we ensured that the clockwise and anticlockwise signals traveled in the same polarization state within the fiber.
Soliton breakup due to two-photon absorption
Authors: Silberberg Y. , Aitchison J. S. , Weiner A. M. , Oliver M. K. , Leaird D. E. , Jackel J. L , Smith P. W. E.
Published: February 2023

Temporal optical solitons are expected to be important for dispersion-less communication1 and for all-optical switching and logic.2 Spatial solitons have been demonstrated recently in planar waveguides.3 They could also be used in all-optical processing. In some of these applications it would be advantageous to reduce the power requirements by using materials with large nonlinearities. It has been pointed out, however, that often the increase in the nonlinear refractive index is accompanied by an increase in two-photon absorption (TPA) and that significant TPA could set a limit on the usefulness of these materials for some applications.4 Here we investigate the specific effect of TPA on the propagation of optical solitons.
Nonlinear integrated switches using spatial solitons
Authors: Heatley D. R. , Wright E. M. , Stegeman G. I.
Published: February 2023

Recent experiments1 show evidence of spatial solitons within waveguides that exhibit a Kerr nonlinearity. An all-optical switch based on this effect has been proposed previously2 and modeled numerically in one transverse dimension (1D). We now investigate the two-dimensional (2D) case, using a saturable nonlinearity to avoid critical self-focusing of the beam.
All-optical cascadable NOR gate with gain
Authors: Islam M. N.
Published: February 2023

We demonstrate an ultrafast, all-optical, cascadable NOR gate based on soliton dragging in birefringent fibers with a gain of 4.5 and a switching energy of 30 pJ. When two orthogonally polarized solitons start coincident in time and travel along the two principal axes of a fiber, they interact through cross-phase modulation and shift in time and frequency.1 In a clocked digital optical system, the time shifts from soliton dragging translate into logic operations.
Tapered waveguide InGaAs/InGaAsP multiple quantum-well lasers
Authors: Koren U. , Koch T. L. , Eisenstein G. , Young M. G. , Oron M. , Giles C. R. , Miller B. I.
Published: February 2023

Optical coupling of a semiconductor laser to a single-mode optical fiber using lensed fiber requires submicrometer alignment accuracy and leads to difficult packaging problems. Here we demonstrate the application of photonic integrated circuit (PIC) technology by using ultra-thin stop-etch epitaxial layers to integrate a controlled vertically tapered passive waveguide in a multiple quantum-well (MQW) laser cavity. This tapered waveguide adiabatically expands the mode size at the output to provide a better match to a single-mode fiber.
Compact hybrid resonant-optical reflector lasers with very narrow linewidths
Authors: Ackerman D. A. , Dahbura M. I. , Shani Y. , Henry C. H. , Kistler R. C. , Kazarinov R. F. , Kuo C. Y.
Published: February 2023

Lasers with submegahertz linewidths have importance in various applications, such as in coherent optical communications, interferometric sensors, and resonant-optical gyroscopes. For several years our laboratory has investigated a hybrid Bragg reflector laser with typical linewidths of less than 1 MHz and a narrowest linewidth of 100 kHz. The narrow line results from operating the laser at the steeply rising edge of the Bragg reflection. Understanding this mechanism led to the development1 of resonant-optical reflectors (RORs), integrated-optical elements capable of providing feedback with a reflection spectrum even sharper than previously obtained. We report hybrid ROR laser linewidths as narrow as 7.1 kHz.
Performance and fabrication of ultra-low-reflectivity semiconductor optical amplifier without antireflective coatings
Authors: Holmstrom Roger , Rideout William , LaCourse Joanne , Meland Edmund , Powazinik William
Published: February 2023

Tilted stripe 1.3-µm semiconductor optical amplifiers with internal gains in excess of 30 dB and facet residual reflectivities of less than −40 dB have been fabricated without the use of antireflective (AR) coatings. These values of facet reflectivity are nearly 20 dB lower than the best previously reported results for any uncoated device.1-4 The basic approach to reducing facet reflectivities is to tilt the waveguide relative to the cleaved facets1 by 7°. This technique has previously been reported to reduce the facet reflectivity to about −20 dB and, in combination with AR coatings, has yielded excellent results.2 However, Marcuse5 indicated that much lower facet reflectivities should be achieved without the use of AR coatings. To achieve the predicted low values of facet reflectivity, a single transverse-mode ridge waveguide semiconductor optical amplifier was designed. The purpose of this paper is to describe the excellent uncoated facet reflectivities and the performance achieved with the semiconductor optical amplifier operating at 1.3-µm wavelength and to discuss the pro-designed. The purpose of this paper is to describe the excellent uncoated facet reflectivities and the performance achieved with the semiconductor optical amplifier operating at 1.3-µm wavelength and to discuss the processing techniques developed to ensure reproducible single transverse-mode behavior.