Optimizing an interleaved p-n junction to reduce energy dissipation in silicon slow-light modulators

Reducing power dissipation in electro-optic modulators is a key step for widespread application of silicon photonics to optical communication. In this work, we design Mach–Zehnder modulators in the silicon-on-insulator platform, which make use of slow light in a waveguide grating and of a reverse-biased p-n junction with interleaved contacts along the waveguide axis. After optimizing the junction parameters, we discuss the full simulation of the modulator in order to find a proper trade-off among various figures of merit such as modulation efficiency, insertion loss, cutoff frequency, optical modulation amplitude, and dissipated energy per bit. Comparison with conventional structures (with lateral p-n junction and/or in rib waveguides without slow light) highlights the importance of combining slow light with the interleaved p-n junction, thanks to the increased overlap between the travelling optical wave and the depletion regions. As a surprising result, the modulator performance is improved over an optical bandwidth that is much wider than the slow-light bandwidth

Effects of fabrication errors on the focusing performance of a sector metalens

Using e-beam lithography, a 16-sector spiral metalens was fabricated in an amorphous silicon, capable of converting linearly polarized incident light into an azimuthally polarized optical vortex. When illuminated by a 633-nm linearly polarized laser beam, the metalens generated a near-surface subwavelength focal spot equal to 0.75 of the incident wavelength at full-width of half-maximum intensity. The focusing performance of the spiral metalens was numerically shown to be sensitive to the deviation of the factual microrelief from the calculated height. For the designed microrelief height, a circularly polarized incident beam was focused into a bright ring with a reverse energy flow occurring at its center. For the microrelief height other than the designed one, the energy backflow effect did not occur

Wavelet (valić) transformacija

Valić transformacija daje sofisticiranu vremensko-frekvencijsku analizu i koristi se u brojnim algoritmima u raznim područjima znanosti. Nakon teorijske pozadine i usporedbe sa frekvencijskom analizom, bit će prezentirane neke primjene u području sažimanja slike i uklanjanju šuma iz signala. Pojašnjen je i algoritam za prepoznavanje osoba pomoću očnog uzorka

Antiturcica Iterata – another Look at Croatian anti-Turkish Writings during the Renaissance

Otpor »Turcima«, održavanje granice prema Osmanskome Carstvu, jedna je od dominantnih tema u ranonovovjekovnoj Hrvatskoj. Sukladno tome, »turska tema« prisutna je i u književnosti. Problematizirana je u velikom vremenskom rasponu, na različitim jezicima, u različitim žanrovima, s različitim intencijama. Važnu podskupinu tekstova ove tematike – izravne i neizravne pozive na otpor osmanskim napadima i osvajanjima u razdoblju 1436-1600 – ovdje smo pokušali popisati što potpunije i što konzistentnije. Uvodno dajemo pregled istraživanja i interpretacija hrvatskoga protuturskog korpusa od 1945. do 2014. Potom upozoravamo na probleme vezane uz konstituiranje korpusa i iznosimo načela po kojima smo korpus uspostavili. Zatim opisujemo korpus prema očuvanosti popisanih tekstova, prema pisanom mediju u kojem su prenošeni (rukopisi ili tiskovine), prema jeziku (latinski, hrvatski, talijanski), načinu izražavanja (proza, poezija), književnim vrstama, kronologiji (upozoravamo i na diskontinuitete, na godine kad se javlja manje protuturskih tekstova), te prema prostorima koji su u tekstovima posebno isticani. Razmatramo i autore, prema broju tekstova, prema porijeklu i društvenom statusu. Naposljetku skiciramo sinoptičku interpretaciju korpusa, posebnu pozornost poklanjajući tekstovima koji se pojavljuju istodobno ili su vremenski bliski. Bibliografska skica hrvatskog protuturskog korpusa prilog je radu, a dostupna je i kao baza podataka na internetu.In the 15th and 16th centuries, Croatian writing about the Ottoman threat was both a reaction to the continuous crisis of several states, their societies, and culture, and an attempt to overcome this crisis by developing new ideas and new ways of consolidating the society. It has been claimed that this desperate attempt laid the foundations of modern Croatia. To be able to identify continuities and discontinuities of the so-called Croatian anti-Turkish writings, we have compiled a list of as many such works as possible. In Croatian literary history, the anti-Turkish writings seem to have first been presented as a group by Mihovil Kombol in 1945. In 1974, Marin Franičević tried to consider together texts from this group written in different languages (Latin and Croatian). In 1983, Vedran Gligo selected and published a canonical collection of sixteen (Latin) »anti-Turkish speeches« from the Renaissance. At the same time, Tomislav Raukar interpreted the anti-Turkish theme as a stimulus to Early Modern Croatia. In 2004, Davor Dukić proposed an imagological interpretation of the anti-Turkish corpus. All researchers, however, worked with a restricted number of texts, and there was not even an estimate of the actual size of the corpus. To construe a corpus with some pretence to comprehensiveness, we had to establish whether (and to what degree) a text addresses the anti-Turkish theme, whether it could be considered a »Croatian« text, whether it could be considered a literary and a public as opposed to a documentary or a private text). Such considerations led us to exclude some famous texts (such as Judita by Marko Marulić),while including e. g. an Oratio contra Turcam which Ivan Pergošić reprinted from the book by Johannes Avenarius. The fuzzy boundaries between confidentiality and publicity have been demonstrated by the fate of reports by the papal nuntio Antonius Fabregues, whose official dispatches about the Battle of Krbava field have appeared also in print as propagandistic broadsheets. In our corpus, a Croatian anti-Turkish work is a text urging Christian action against the Turks in defence of Dalmatia, Croatia, Hungary, and Christian Europe as a whole, written by an author significantly connected with Croatia, and calling to arms either by direct appeals or by a more indirect strategy of reporting, celebrating and lamenting events in the Christian-Turkish struggle. The corpus currently comprises basic bibliographic data on 141 texts written between 1436 and 1600. It exists as a list (see the Appendix to the article) and as a database published by the TeMrežaH project (temrezah.ffzg.unizg.hr/antiturcica-biblio.html). We have included data on a few texts that are not preserved, and on texts by unknown authors. Ninety-four texts first appeared as manuscripts, 44 in print (two exist in roughly contemporaneous handwritten and printed versions). Two texts (poems in Croatian from 1565 and 1596) were first printed almost a hundred years after the events they describe (in 1655). One hundred and four texts are in Latin, 26 in Croatian, nine in Italian; 75 texts are in prose, 66 in verse. An especially active period of production falls in 1493-1548 (when three fifths of all texts in the corpus were written). There are three longer periods of silence, when just a few anti-Turkish texts appear: the years 1504-1509, 1546-1560, 1575-1591. Christian Europe is the central topic in 46 texts, the Kingdom of Hungary in 31, Croatia itself in 20, Dalmatia (and Dubrovnik) in 20, the Levant in 15, the Venetian Republic in 11; this distribution follows the geopolitical situation of Croatian regions during the Renaissance, but Croatia and Dalmatia are treated in about the same number of texts, while the Kingdom of Hungary was thematised significantly more often than Venice. The texts were written by 61 authors (seven are anonymous), 40 of which wrote just one text; fourteen are known as authors only because of their anti-Turkish works. The five authors with most anti-Turkish texts are Fran Trankvil Andreis, Damjan Beneša, Marko Marulić, Ludovik Paskalić, Ivan Vitez od Sredne. Beneša and Paskalić were absent from the Croatian »canon« of anti-Turkish authors. Four of the authors are not Croatian by birth (Tideo Acciarini, Antonio Fabregues, Francesco Marcello, Bernard Zane), but they were all connected to Dalmatia by office, as teachers, diplomats or Church officials. Most of the authors can be regarded as humanists (17) or priests (24, or 34 including priests serving as diplomats); there were 15 diplomats, five of them lay persons. The authors whose anti-Turkish writings appear during the longest chronological span are Fran Trankvil Andreis from Trogir (53 years), Mavro Vetranović from Dubrovnik (writing in Croatian over 45 years), and Frano Božićević Natalis from Split (35 years). A chronological analysis also reveals two main generations of anti-Turkish writers. The first one was active during 1500-1535, and the second during 1520-1570. Among the authors those from Dalmatia and Dubrovnik prevail; they belong mostly to the civic patriciate, to the lesser nobility, or even to the general citizenry. A synoptic analysis of dates, genres, authors and contexts suggests a discontinuity in the corpus of Croatian anti-Turkish writings: some time after 1530-1540 public speeches and appeals disappear, to be replaced by administrative reports to the authorities of the Habsburg empire, by sensational testimonies about travels or battles, and by highly individual »grassroots« entreaties, often, seemingly, without significant political support, often without the benefit of print or of larger print runs. The discontinuity may be connected with the agony of the Kingdom of Hungary and Croatia (after the Battle of Mohács), and with the gradual disappearance of the generation of Croatian humanists that had tried to play significant roles in this kingdom

Wavelength stability in a hybrid photonic crystal laser through controlled nonlinear absorptive heating in the reflector

This work was supported by the Science Foundation Ireland under Grants SFI12/RC/2276 and 16/ERCS/3838, Engineering and Physical Sciences Research Council (EPSRC) (doctoral grant EP/L505079/1 and equipment grant EP/L017008/1); European Research Council (ERC) (Starting Grant 337508); and Scottish Enterprise.The need for miniaturized, fully integrated semiconductor lasers has stimulated significant research efforts into realizing unconventional configurations that can meet the performance requirements of a large spectrum of applications, ranging from communication systems to sensing. We demonstrate a hybrid, silicon  photonics-compatible photonic crystal (PhC) laser architecture that can be used to implement cost-effective, high-capacity light sources, with high side-mode suppression ratio and milliwatt output output powers. The emitted wavelength is set and controlled by a silicon PhC cavity-based reflective filter with the gain provided by a III–V-based reflective semiconductor optical amplifier (RSOA). The high power density in the laser cavity results in a significant enhancement of the nonlinear absorption in silicon in the high Q-factor PhC resonator. The heat generated in this manner creates a tuning effect in the wavelength-selective element, which can be used to offset external temperature fluctuations without the use of active cooling. Our approach is fully compatible with existing fabrication and integration technologies, providing a practical route to integrated lasing in wavelength-sensitive schemes.Publisher PDFPeer reviewe