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Programmable linear optical processors (LOPs) can have widespread applications in computing and information processing due to their capabilities to implement reconfigurable on-chip linear transformations. A conventional LOP that uses a mesh of Mach-Zehnder interferometers (MZIs) requires $2N+1$ stages of phase shifters for $N \times N$ matrices. However, it is beneficial to reduce the number of phase shifter stages to realize a more compact and lower-loss LOP, especially when long and lossy electro-optic phase shifters are used. In this work, we propose a novel structure for LOPs that can implement arbitrary matrices as long as they can be realized by previous MZI-based schemes. Through numerical analysis, we further show that the number of phase shifter stages in the proposed structure can be reduced to $N+2$ for a large number of random target matrices. This work contributes to the realization of compact, low-loss, and energy-efficient programmable LOPs.

Supplement 1

Optical unitary converter (OUC) that can convert a set of N mutually orthogonal optical modes into another set of arbitrary N orthogonal modes is expected to be the key device in diverse applications, including the optical communication, deep learning, and quantum computing. While various types of OUC have been demonstrated on photonic integration platforms, its sensitivity against a slight deviation in the waveguide dimension has been the crucial issue in scaling N. Here, we demonstrate that an OUC based on the concept of multi-plane light conversion (MPLC) shows outstanding robustness against waveguide deviations. Moreover, it becomes more and more insensitive to fabrication errors as we increase N, which is in clear contrast to the conventional OUC architecture, composed of 2 $\times$ 2 Mach-Zehnder interferometers. The physical origin behind this unique robustness and scalability is studied by considering a generalized OUC configuration. As a result, we reveal that the number of coupled modes in each stage plays an essential role in determining the sensitivity of the entire OUC. The maximal robustness is attained when all-to-all-coupled interferometers are employed, which are naturally implemented in MPLC-OUC.

Supplementary document.

Single crystals of three neutral charge-transfer complexes and a cation radical salt based on a C₂v-symmetric polycyclic aromatic hydrocarbon, benzo[ghi]perylene (bper), were obtained. The 1 : 1 complex with 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) involves DA-type alternating π-columns, whereas the alternating π-columns in the 2 : 1 TCNQ complex are flanked by another bper molecule. The in-plane rotation of bper in the 1 : 1 complex was significantly suppressed compared with that of coronene in (coronene) (TCNQ), which is associated with the lower molecular symmetry of bper. Whereas the 3 : 1 TCNQ complex involves DDA-type alternating π-columns flanked by another bper molecule, bper molecules in the 3 : 1 cation radical salt with Mo₆O₁₉²⁻ have a columnar structure with a [101]-like charge-ordered pattern associated with intermolecular interactions in the bay region of bper. The dimerisation of charge-rich bper molecules results in an increased energy gap at the Fermi level, and consequently, semiconducting behaviour of the salt has a larger activation energy than that of the isostructural coronene salt in the partially charged state. The lower molecular symmetry of bper also affects the degeneracy of the frontier-orbitals; the energy difference between the HOMO and the HOMO−1 of bper is significantly larger than that of coronene, which is comparable to the intermolecular transfer integrals.

N-methylimidazole (MeIm) solvates of vanadium(II), chromium(II) and iron(II) phthalocyanines: [V(II)(MeIm)2{Pc(2-)]0).MeIm (1) and [M(II)(MeIm)2{Pc(2-)}](0).2C6H4Cl2 (M = V (2), Cr (3), and Fe (4)) have been obtained and studied in a crystalline form. It has been shown that central metal atoms have +2 oxidation state in 1-4 and dianionic Pc(2-) macrocycles are formed. Optical spectra of 1−3 (V(II), Cr(II)) are different from that of 4 (Fe(II)) due to the appearance of intense absorption bands in the NIR range at 1187 nm for 1 and 2 and 1178 nm for 3 and manifestation of multiple bands in the visible range. Absorption in the NIR range is explained by unusually small HOMO−LUMO gaps for MeIm solvated Cr(II)Pc and V(II)Pc. Essential diradicaloid character of the Pc macrocycles in [Cr(II)(MeIm)2{Pc(2-)}](0), in which α- and β-orbitals are distributed in different regions of the macrocycle has also been shown. In this case, the diradicaloid character is comparable to that of aromatic hydrocarbon heptacene. Magnetic properties of 1−3 are defined by metal atoms with S = 3/2 spin state for V(II) and S = 1 for Cr(II). Compounds 1−3 manifest broad isotropic EPR signals at 4.2 K with g = 2.0188 and linewidth (deltaH) of 81.8 mT for 1 (V(II), g = 1.8300 and linewidth deltaH = 161.0 mT for 2 (V(II), and g = 2.0534 and deltaH = 60.27 mT for 3 (Cr(II)). These signals shifted to smaller g-factors with the temperature increase. Integral intensity of narrow EPR signals from Pc(•3-) does not exceed 0.1% from those of broad signals in 1−3. Complex 4 is EPR silent due to the presence of diamagnetic Fe(II) and Pc(2-)., JSPS KAKENHI 17H05153/15K17901/26288035; JST(ACCEL) 27 (100150500010)

Single crystals of racemic charge-transfer complexes comprising a helical polycyclic aromatic hydrocarbon molecule, [6]helicene, as the electron donor (D) and 7, 7, 8, 8-tetracyano-p-quinodimethane (TCNQ) analogs as the electron acceptor (A) were obtained via either co-sublimation or solvent evaporation. All complexes consist of heterochiral DA-type alternating π-columns with a [⋯(P)-[6]helicene⋯TCNQ⋯(M)-[6]helicene⋯TCNQ⋯] repeating unit, which show a peculiar wavy feature primarily related to the nonplanar geometry of the [6]helicene molecules. [6]Helicene molecules form a two-dimensional sheet intersecting the columns, and the molecular arrangement (namely, either homochiral or heterochiral arrangement) in the sheets depends on the TCNQ analog. Theoretical calculations were carried out to discuss the origin of the molecular deformation of [6]helicene molecules in the CT solids in terms of intermolecular interactions.

Reduction of aluminum(III), gallium(III), and indium(III) phthalocyanine chlorides by sodium fluorenone ketyl in the presence of tetrabutylammonium cations yielded crystalline salts of the type (Bu4 N(+) )2 [M(III) (HFl-O(-) )(Pc(.3-) )](.-) (Br(-) )⋅1.5 C6 H4 Cl2 [M=Al (1), Ga (2); HFl-O(-) =fluoren-9-olato(-) anion; Pc=phthalocyanine] and (Bu4 N(+) ) [In(III) Br(Pc(.3-) )](.-) ⋅0.875 C6 H4 Cl2 ⋅0.125 C6 H14 (3). The salts were found to contain Pc(.3-) radical anions with negatively charged phthalocyanine macrocycles, as evidenced by the presence of intense bands of Pc(.3-) in the near-IR region and a noticeable blueshift in both the Q and Soret bands of phthalocyanine. The metal(III) atoms coordinate HFl-O(-) anions in 1 and 2 with short Al-O and Ga-O bond lengths of 1.749(2) and 1.836(6) Å, respectively. The C-O bonds [1.402(3) and 1.391(11) Å in 1 and 2, respectively] in the HFl-O(-) anions are longer than the same bond in the fluorenone ketyl (1.27-1.31 Å). Salts 1-3 show effective magnetic moments of 1.72, 1.66, and 1.79 μB at 300 K, respectively, owing to the presence of unpaired S=1/2 spins on Pc(.3-) . These spins are coupled antiferromagnetically with Weiss temperatures of -22, -14, and -30 K for 1-3, respectively. Coupling can occur in the corrugated two-dimensional phthalocyanine layers of 1 and 2 with an exchange interaction of J/kB =-0.9 and -1.1 K, respectively, and in the π-stacking {[In(III) Br(Pc(.3-) )](.-) }2 dimers of 3 with an exchange interaction of J/kB =-10.8 K. The salts show intense electron paramagnetic resonance (EPR) signals attributed to Pc(.3-) . It was found that increasing the size of the central metal atom strongly broadened these EPR signals.

We grew large single crystals of the cluster magnet Nb3Cl8 with a magnetic triangular lattice and investigated its magnetic properties and crystal structure. In Nb3Cl8, the [Nb3]8+ cluster has a single unpaired spin, making it an S = 1/2 triangular lattice anti-ferromagnet. At low temperatures, Nb3Cl8 exhibits a magnetic–nonmagnetic phase transition driven by a charge disproportionation, in which the paramagnetic [Nb3]8+ clusters transform into alternating layers of nonmagnetic [Nb3]7+ and [Nb3]9+ clusters. The observed exotic phenomenon with the strong correlation between the magnetism and structure are based on the nature of the cluster magnetism.

Over the past two decades (EDO-TTF)₂PF₆(EDO-TTF = 4, 5-ethylenedioxytetrathiafulvalene), which exhibits a metal–insulator (M–I) phase transition with charge–ordering (CO), has been investigated energetically because of attractive characteristics that include ultrafast and massive photoinduced spectral and structural changes. In contrast, while its crystal structure has much in common with the (EDO-TTF)₂PF₆ crystal, the organic alloy system of [(EDO-TTF)₀.₈₉(MeEDO-TTF)₀.₁₁]₂PF₆ (MeEDO-TTF = 4, 5-ethylenedioxy-4′-methyltetrathiafulvalene) exhibits a quite different type of M–I phase transition that is attributed to Peierls instability. Here, an optical study of the static absorption spectra and the time-resolved changes in the absorption spectra of [(EDO-TTF)₀.₈₉(MeEDO-TTF)₀.₁₁]₂PF₆ are reported. The observed absorption spectra related to the electronic structure are highly anisotropic. With a reduction in temperature (T), the opening of a small optical gap and a small shift in the center frequency of the C=C stretching mode are observed along with the M–I phase transition. Additionally, photoinduced transient states have been assigned based on their relaxation processes and transient intramolecular vibrational spectra. Reflecting small valence and structural changes and weak donor–anion interactions, a photoinduced transient state that is similar to the thermal-equilibrium high-T metallic phase appears more rapidly in the alloy system than that in (EDO-TTF)₂PF₆.

Electrochemical oxidation of a polycyclic aromatic hydrocarbon, coronene, with D6h symmetry in the presence of tetrahedral GaCl4– anions gave two cation salts, (coronene)(GaCl4) (1) and (coronene)5(GaCl4)2 (2), with unprecedented charge arrangements. Salt 1 involves π-stacking columns in a zigzag manner, which are composed of the crystallographically equivalent coronene monocations. First-principle calculations revealed that the dimerization of coronene cations gives rise to a band gap opening at the Fermi level, and thus, semiconducting behavior. On the other hand, in salt 2, two crystallographically independent coronene molecules (A and B) form π-stacking columns with an AABB repeating unit, which are flanked by another coronene molecule (C). The crystallographic features, such as interplanar distances and in-plane molecular distortions arising from the Jahn–Teller effect, as well as the first-principle calculations, strongly suggested the emergence of charge disproportionation within the π-stacking columns. As in the case of 1, the calculated band structure exhibits a band gap opening at the Fermi level, which corresponds to the observed semiconducting behavior.

Semiconductor lasers capable of generating a vortex beam with a specific orbital angular momentum (OAM) order are highly attractive for applications ranging from nanoparticle manipulation, imaging and microscopy to fibre and quantum communications. In this work, an electrically pumped OAM laser operating at telecom wavelengths is fabricated by monolithically integrating an optical vortex emitter with a distributed feedback (DFB) laser on the same InGaAsP/InP epitaxial wafer. A single-step dry etching process is adopted to complete the OAM emitter, equipped with specially designed top gratings. The vortex beam emitted by the integrated laser is captured, and its OAM mode purity characterized. The electrically pumped OAM laser eliminates the external laser required by silicon- or silicon-on-insulator (SOI)-based OAM emitters, thus demonstrating great potential for applications in communication systems and quantum domain., 9 pages, 5 figures

In these days, many universities open the enlightening courses for the youth. Graduate School of Science, Kyoto University offers the course for the high school students, in which not only the lectures but also the experiences of experiments are provided. This document shows the instructional aids for a course carried out in the fiscal year 2014. In this class, the basic concepts to understand the conducting organic materials are explained and then the trainees prepared the metallic charge-transfor complex (TTF)(TCNQ) along with the insulator, (TTF)(Chloranil) which changes the color by cooling in liquid nitrogen.

Compounds of the formula (EDO-TTF-Cl)_2XF_6 (EDO-TTF-Cl = 4-chloro-4',5'-ethylenedioxytetrathiafulvalene, X = As, Sb) were prepared to examine the substituent size effect on the packing structure of the donor molecules. In these salts, a head-to-tail type donor stacking was observed. Although the AsF6 salt is a quasi-one-dimensional dimer Mott insulator, the SbF_6 salt shows quasi-one-dimensional metallic behavior. Detailed crystal structure analyses revealed the correlation between the anion size and the intermolecular slipping among the donor molecules. The donor morphology, which plays an important role in the overlapping mode selectivity, is characterized by the magnitude and configuration of the out-of-plane substituent size.

The molecular vibration can be probed through infrared and Raman spectroscopies, which are called "vibration spectroscopy". The vibrational spectroscopy shows the advantageous feature on the analysis of the charge disproportionation in organic solids. In this article, the analysis of the electronic structure of an organic conductor, (MeEDO-TTF)[2]PF[6], is reviewed. The black plate modification of (MeEDO-TTF)[2]PF[6] exhibited the semiconductor-to-semiconductor phase transition at around room temperature. The donor molecules in both of the high- and low-temperature phases showed similar packing patterns, based on which the tight-binding approximation afforded the similar band structures and Fermi surfaces. The vibrational spectra proved that the nearly localized charge disproportionation takes place in the high-temperature phase and the distinct charge disproportionation is developed in the low-temperature phase.

We have investigated the initial growth of InAs on Si(1 1 1) substrates produced with metal-organic vapor phase epitaxy (MOVPE) and using micro-channel selective area growth (MC-SAG). Treatment of the Si surface prior to InAs growth is essential in order to achieve high-yield nucleation of a single island in each growth area. A breakthrough for successful nucleation was the use of tertiarybutylphosphine (TBP) pre-flow. We have analyzed the effect of such surface pretreatment in terms of the shape of InAs islands at the initial stage of growth and the incubation period between the supply of the indium source and the nucleation, the latter data being obtained by means of in situ surface reflectivity measurement. XPS analyses confirmed that the TBP and tertiarybutylarsine (TBAs) pre-flow introduced, respectively, P and As on the Si surfaces resulting in a change in surface energy. The surface with As exhibited a larger surface energy and shorter incubation period, which are preferable for better nucleation. The coverage of As on the surface, however, appeared less reliable than that of P, i.e., pre-flow with TBP was superior to pre-flow with TBAs in terms of uniformity of surface coverage. This finding is useful for achieving high-yield nucleation in small growth openings in MC-SAG. ?? 2009 Elsevier B.V. All rights reserved.

We investigated the dependence of the growth mode on the Ga content in micro-channel selective-area MOVPE of InGaAs on Si(1 1 1) substrates by changing the partial pressure of a Ga source. The Ga content in the crystal was affected by the initial nucleation and the shape of InGaAs islands after growth. In the growth of InAs, a single columnar nucleus was generated in each open window and a hexagonal column was eventually grown. The content of the initial nuclei of InGaAs were close to InAs. As the partial pressure of a Ga source was increased, the number of nuclei in a growth area increased, their shape became rounded, and a slight amount of Ga was incorporated into the nuclei. The InGaAs islands showed enhanced lateral growth as the partial pressure of a Ga source was increased and incoherent growth without specific crystallographic planes became apparent at a high Ga content. The InGaAs islands that grew in the lateral direction had an inhomogeneous Ga content with a higher Ga content at the peripheral region. It appears that incorporation of Ga suppresses coherent growth of In(Ga)As in the vertical direction and enhances lateral growth, although high Ga content can induce incoherent growth. ?? 2008 Elsevier B.V. All rights reserved.

We developed a 1.5-µm-band, transverse-magnetic-mode waveguide isolator based on the nonreciprocal-loss phenomenon. The device consists of an optical waveguide with an InGaAs/InGaAlAs multiple-quantum-well amplifier and a ferromagnetic MnAs layer attached to the waveguide. The combination of the optical waveguide and the magnetized MnAs layer produces a magneto-optic effect called the nonreciprocal loss–a phenomenon where the propagation loss of light is larger in backward than in forward propagation. We present the guiding principle of the design of the structure of the device. A prototype device with a MBE-grown epitaxial MnAs layer showed a nonreciprocity of 9.8 dB/mm at a wavelength of 1.54 µm. Our device can be monolithically integrated with waveguide-based optical devices on an InP substrate.

The family of materials (EDO-TTF)2XF6 represents quasi-one-dimensional quarter filled systems exhibiting insulator-to-metal (I-M) phase transition at thermal equilibrium. (EDO-TTF)2PF6 is known to undergo a photoinduced I-M conversion with cooperative response to light excitation. Here we use femtosecond pump-probe experiments to study the photoresponse of (EDO-TTF)2SbF6 made of a larger counteranion SbF6 compared to the well studied (EDO-TTF)2PF6. In the early stage of the photoinduced process, we reveal a multicomponent coherent oscillating feature. The evolution of this feature with excitation density and temperature points to the local nature of the photoswitching in (EDO-TTF)2SbF6. At longer time scale, we did not detect the features associated with the transformation to the M phase, albeit observed in the PF6 derivative. We propose a scenario whereby the bigger size of the counteranion in (EDO-TTF)2SbF6 hinders the establishment of this transformation at macroscopic scale.

30周年記念号

30周年記念号

30周年記念号

30周年記念号

30周年記念号

30周年記念号

30周年記念号