MMI Devices with Weak Guiding Designed in Three Dimensions Using a Genetic Algorithm

We discuss the design of weakly guided multimode interference (MMI) devices using a genetic algorithm. For devices exhibiting a nonnegligible vertical waveguide offset, such as those produced using ion exchange in glass, three-dimensional modeling is required to properly evaluate the device performance. A combination of semivectorial finite difference modeling in two transverse dimensions and mode propagation analysis (MPA) in the propagation direction is used to evaluate the merit of each trial design. An example is provided of a 1 x 4 power splitter designed for ion exchange, which shows considerable improvement over that obtained by self-imaging theory

Determination of Ion Exchange Parameters by a Genetic Algorithm

Modeling the process of ion exchange in glass requires accurate knowledge of the self-diffusion coefficients of the incoming and outgoing ions. Furthermore, correlating the concentration profile of the incoming ions to a change in refractive index requires knowledge of the correlation coefficient. We present a method by which these three parameters can be quickly determined experimentally, using a genetic algorithm. Comparison with published data is presented

Ion-Exchanged Glass Waveguides with Low Birefringence for a Broad Range of Waveguide Widths

Optical communications networks require integrated photonic components with negligible polarization dependence, which typically means that the waveguides must feature very low birefringence. Recent studies have shown that waveguides with low birefringence can be obtained, e.g., by use of silica-on-silicon waveguides or buried ion-exchanged glass waveguides. However, many integrated photonic circuits consist of waveguides with varying widths. Therefore low birefringence is consequently required for waveguides having different widths. This is a difficult task for most waveguide fabrication technologies. We present experimental results on waveguide birefringence for buried silver–sodium ion-exchanged glass waveguides. We show that the waveguide birefringence of the order of 106 for waveguide mask opening widths ranging from 2 to 10 μm can be obtained by postprocessing the sample through annealing at an elevated temperature. The measured values are in agreement with the values calculated with our modeling software for ion-exchanged glass waveguides. This unique feature of ion-exchanged waveguides may be of significant importance in a wide variety of integrated photonic circuits requiring polarization independent operation

Ion-Exchanged Glass Waveguide Technology: A Review

We review the history and current status of ion exchanged glass waveguide technology. The background of ion exchange in glass and key developments in the first years of research are briefly described. An overview of fabrication, characterization and modeling of waveguides is given and the most important waveguide devices and their applications are discussed. Ion exchanged waveguide technology has served as an available platform for studies of general waveguide properties, integrated optics structures and devices, as well as applications. It is also a commercial fabrication technology for both passive and active waveguide components

Sanoista miestä, kuvista presidenttiä: Ehdokas Sauli Niinistö lehtikuvissa 2005–2017

Tässä tutkielmassa selvitetään, miten viisi suomalaista sanomalehteä kuvittivat Sauli Niinistön asettumisen presidenttiehdokkaaksi kolmissa vaaleissa vuosina 2005–2017, sekä miten hänen muuttunut asemansa ja toisaalta mediaympäristön muutos näkyivät tutkimusaineistossa. Tutkimuksessa avataan lehtikuvien visuaalisten järjestysten, tietoisesti tai tiedostamatta, sisältämiä arvoja, asenteita ja näkökulmia. Lisäksi tutkitaan uutiskuvan ja kuvatekstin vuorovaikutusta, niiden yhdessä luomia merkityssisältöjä. Samalla pohditaan, millainen rooli median visuaalisella aineistolla on ihmisten mielikuviin poliittisista päättäjistä. Keskeisenä tutkimusmenetelmänä käytetään semioottista kuva-analyysia. Semiotiikka tutkii merkkejä ja merkityksiä sekä niiden välisiä suhteita. Semioottisen tradition mukaan teksti, kuva tai muu sanoma saavat merkityksiä vasta, kun ne ovat vuorovaikutuksessa vastaanottajien kanssa. Kuva-analyysin avulla avattavat visuaaliset järjestykset tarkoittavat visuaalisen todellisuuden säännönmukaisuuksia ja sen merkityksiä. Lähes jokainen on nähnyt tiedotusvälineissä kuvia presidenttiehdokkaista, mutta harva on tavannut heitä henkilökohtaisesti. Tutkimusaineistoista on löydettävissä kolme toisistaan poikkeavaa kokonaisuutta, jotka kertovat sekä ajan että ehdokkaan aseman muutoksesta. Vuonna 2005 sanomalehdet kuvittivat Niinistön ehdokkaaksi asettumisen asiallisesti. Vuonna 2011 visuaalisuuden määrä kasvoi selvästi, vanhat tupakointikuvat kaivettiin esiin ja erityisesti Aamulehti innostui mittavaan Niinistö-ilotteluun rakentamalla ehdokkuudesta kanteen jopa Afrikan tähti -mukaelman. Vuonna 2017 lehtikuvien määrä aineistossa väheni ja istuvan tasavallan presidentin ehdokkuuden käsittelytapa palasi visuaalista presidenttimyyttiä uusintavaksi. Niinistö kasvoi arkistokuvien kiharatukkaisesta pelimiehestä arvovaltaiseksi, etäiseksi presidenttihahmoksi. Samalla kuva-aineisto vahvistaa tulkintaa siitä, että eräs Niinistön kansansuosion selityksistä on hänen henkilöbrändiinsä kuuluva boheemi rosoisuus. Aineiston kuvista on löydettävissä monitasoisia merkityksiä ja oleellinen kysymys on, missä ne syntyvät. Kulttuurin pitkä käsivarsi vaikuttaa tässä huomaamatta, tiedotusvälineet eivät tietoisesti keskity rakentamaan suurta määrää piilomerkityksiä tulkitsijan löydettäväksi. Eräs tutkimuksen keskeisistä havainnoista on se, että aineistosta löydettävät merkitykset voivat kertoa enemmän tulkitsijasta itsestään kuin objektiivisesta todellisuudesta. Tulkintojen houkuttavuudesta huolimatta onkin tärkeää ymmärtää, ettei tämän tutkimusaineiston perusteella ole mahdollista muodostaa pitkälle meneviä johtopäätöksiä yksittäisten kuvien tai sanomalehtien vaikutuksista ehdokas Niinistön menestykseen. Samalla on kuitenkin perusteltua todeta, ettei Sauli Niinistöä olisi valittu tasavallan presidentiksi ilman tiedostusvälineiden hänestä välittämiä kuvia sekä niiden synnyttämiä merkityksiä ja mielikuvia. Tutkimus osoittaa, että visuaalisilla merkityksillä on tärkeä rooli ihmisten mielikuvien muokkaamisessa ja yhteiskunnallisen päätöksenteon taustalla vaikuttavissa tekijöissä. Tämä korostaa tarvetta ymmärtää visuaalisen median monitahoista merkityksellisyyttä ja sen vaikutusta yhteiskunnalliseen keskusteluun ja poliittiseen päätöksentekoon

Fabrication and Comprehensive Modeling of Ion-Exchanged Bragg Opitcal Add-Drop Multiplexers

Optical add–drop multiplexers (OADMs) based on asymmetric Y branches and tilted gratings offer excellent-performance in wavelength-division multiplexed systems. To simplify waveguide fabrication, ion-exchange techniques appear to be an important option in photosensitive glasses. Optimum OADM performance depends on how accurately the waveguide fabrication process and tilted Bragg grating operation are understood and modeled. Results from fabrication and comprehensive modeling are compared for ion-exchange processes that use different angles of the tilted grating. The transmission and reflection spectra for the fabricated and simulated OADMs show excellent agreement. The OADM’s performance is evaluated in terms of the measured characteristics of the Y branches and tilted gratings

Ion-Exchanged Glass Waveguides with Low Birefringence for a Broad Range of Waveguide Widths

Optical communications networks require integrated photonic components with negligible polarization dependence, which typically means that the waveguides must feature very low birefringence. Recent studies have shown that waveguides with low birefringence can be obtained, e.g., by use of silica-on-silicon waveguides or buried ion-exchanged glass waveguides. However, many integrated photonic circuits consist of waveguides with varying widths. Therefore low birefringence is consequently required for waveguides having different widths. This is a difficult task for most waveguide fabrication technologies. We present experimental results on waveguide birefringence for buried silver–sodium ion-exchanged glass waveguides. We show that the waveguide birefringence of the order of 106 for waveguide mask opening widths ranging from 2 to 10 μm can be obtained by postprocessing the sample through annealing at an elevated temperature. The measured values are in agreement with the values calculated with our modeling software for ion-exchanged glass waveguides. This unique feature of ion-exchanged waveguides may be of significant importance in a wide variety of integrated photonic circuits requiring polarization independent operation

Buried Ion-Exchanged Glass Wavelengths: Burial-Depth Dependence on Waveguide Width

A detailed theoretical and experimental study of the depth dependence of buried ion-exchanged waveguides on waveguide width is reported. Modeling, which includes the effect of nonhomogeneous time-dependent electric field distribution, agrees well with our experiments showing that burial depth increases linearly with waveguide width. These results may be used in the proper design of integrated optical circuits that need waveguides of different widths at different sections, such as arrayed waveguide gratings

Diagnostic and Prognostic Comparison of Immune-Complex-Mediated Membranoproliferative Glomerulonephritis and C3 Glomerulopathy

Membranoproliferative glomerulonephritis (MPGN) is subdivided into immune-complex-mediated glomerulonephritis (IC-MPGN) and C3 glomerulopathy (C3G). Classically, MPGN has a membranoproliferative-type pattern, but other morphologies have also been described depending on the time course and phase of the disease. Our aim was to explore whether the two diseases are truly different, or merely represent the same disease process. All 60 eligible adult MPGN patients diagnosed between 2006 and 2017 in the Helsinki University Hospital district, Finland, were reviewed retrospectively and asked for a follow-up outpatient visit for extensive laboratory analyses. Thirty-seven (62%) had IC-MPGN and 23 (38%) C3G (including one patient with dense deposit disease, DDD). EGFR was below normal (≤60 mL/min/1.73 m2) in 67% of the entire study population, 58% had nephrotic range proteinuria, and a significant proportion had paraproteins in their serum or urine. A classical MPGN-type pattern was seen in only 34% of the whole study population and histological features were similarly distributed. Treatments at baseline or during follow-up did not differ between the groups, nor were there significant differences observed in complement activity or component levels at the follow-up visit. The risk of end-stage kidney disease and survival probability were similar in the groups. IC-MPGN and C3G have surprisingly similar characteristics, kidney and overall survival, which suggests that the current subdivision of MPGN does not add substantial clinical value to the assessment of renal prognosis. The high proportion of paraproteins in patient sera or in urine suggests their involvement in disease development

Vascular Occlusion in Kidney Biopsy Is Characteristic of Clinically Manifesting Thrombotic Microangiopathy

Thrombotic microangiopathy (TMA) can sometimes manifest only histologically. Our aim was to retrospectively compare biopsy-proven adult TMA patients showing only histological (h-TMA) or both histological and clinical (c-TMA) TMA in 2006-2017. All native kidney biopsies with TMA were included. Biopsies were re-evaluated by light and electron microscopy, and immunofluorescence. Clinical characteristics, laboratory variables, and treatments were recorded from the electronic medical database. Patients were categorized into h-TMA and c-TMA and these groups were compared. In total, 30 biopsy-proven cases among 7943 kidney biopsies were identified and, of these, 15 had h-TMA and 15 c-TMA. Mean follow-up was 6.3 y, and 73.3% had secondary hemolytic uremic syndrome (HUS) and the rest were atypical HUS. Patient characteristics, treatments, and kidney, and patient survival in the groups were similar. Statistically significant differences were found in histological variables. Vascular myxoid swelling and vascular onion-skinning were almost exclusively detected in c-TMA and, thus, vascular occlusive changes indicate clinically apparent rather than merely histological TMA. In addition, regardless of clinical presentation, kidney and patient survival times were similar in the patient groups highlighting the importance of a kidney biopsy in the case of any kidney-related symptoms.Peer reviewe