1,721,156 research outputs found
Tunable Optical Filtering Techniques in Waveguides Using Liquid Crystals and Composites
No full textWe present several approaches to make integrated optic filters, which include either liquid crystals or composite structures including polymers. The presence of liquid crystals allows tunability of the filters controlled by means of low power electric signals. All-optical tuneable filters are also presented in which optical nonlinear properties of liquid crystals are deployed to drive the device
Tuneable optical filtering techniques in waveguides using liquid crystals and composites
No full textCommutatore di luce a cristalli liquidi per comunicazioni tutto-ottiche
No full textRiportiamo le analisi teoriche, i criteri di progetto, la realizzazione e la caratterizzazione sperimentale di un commutatore ottico integrato a cristalli liquidi ferroelettrici. Recentemente i cristalli liquidi ferroelettrici (CLF) si sono rivelati materiali interessanti per la realizzazione di matrici di commutazione ottiche ad elevato numero di porte da impiegare in reti di telecomunicazioni tutto-ottiche a larga banda. Tale interesse è legato a tempi di commutazione dell’ordine dei microsecondi, alla proprietà di bistabilità delle celle a cristallo liquido ferroelettrico stabilizzate alle superfici e ai bassi costi di realizzazione legati all’impiego della tecnologia già consolidata degli schermi piatti. In questa memoria è riportata la caratterizzazione di un commutatore ottico integrato basato su una struttura ad accoppiatore direzioanle verticale costituito da uno strato di cristallo liquido ferroelettrico stabilizzato alle superfici collocato tra due guide d’onda ottiche singolo modo ottenute mediante scambio ionico in ambiente salino su vetro BK7. Un segnale ottico in ingresso ad una delle due guide può essere trasferito all’altra guida commutando la posizione delle molecole e quindi l’indice di rifrazione del CLF attraverso un controllo elettrico. E’ stato misurato con un rapporto di estinzione in uscita superiore a 16 dB per soli 6 V applicati. La completa commutazione avviene in un tempo pari a 270 s o addirittura inferiore, con una lunghezza d’accoppiamento pari a meno di 4 mm, che può peraltro essere drasticamente ridotta a meno di 100 m come risulta dalle simulazioni eseguite con BPM che verranno illustrate nella presentazione. Migliori rapporti di estinzione possono essere ottenuti con una deposizione di uno strato di allineamento più uniforme. Inoltre si possono ottenere regioni di commutazione di lunghezza inferiori al millimetro utilizzando più piccoli elettrodi di ITO, permettendo così un’integrazione ottica su larga scala, determinante per la realizzazione di grandi matrici di commutazione ottiche a basso costo e basso crosstalk
All-Optical Switching and Filtering Based on Liquid Crystals and Photosensitive Composite Organic Materials
No full textWe present our recent experimental results on guided wave devices that can be switched and tuned by optical driving signals. Two different waveguide structures recently implemented are reported. The first one uses liquid crystals (LCs) as a core in a SiO2/Si V-groove and optical signals whose power is in the order of few milliwatts to control propagation. The second structure is an all-optical tunable filter that includes photosensitive composite materials. The latter combines the simple and low-cost ion exchange waveguide technology with a composite LC methyl red azo-dye photosensitive compound to obtain full optical tunability. © 2013 Copyright Taylor and Francis Group, LLC
BPM analysis of an integrated optical switch using polymeric optical waveguides and SSFLC at 1.55 μm
No full textAn optical switch using polymeric waveguides and ferroelectric liquid crystals (FLC) has been modelled by using a 3D vectorial beam propagation method (BPM) at the wavelength of 1.55 μm used in optical communications. The switch structure is a vertical directional coupler consisting of a surface stabilised FLC (SSFLC) embedded between two polymeric optical waveguides and ITO layers as electrodes. A polymeric buffer layer has been introduced to reduce losses due to ITO absorption. Polymeric waveguides and buffers used in our analysis can be obtained by different compositions of P(PFS-GMA) (poly(pentafluorostyrene-coglycidyl methacrylate)). Several devices have been modelled with different values of the refractive indexes of the individual layers. Simulations show the benefits in terms of loss reduction due to the presence of the buffer. An optimised device presents an extinction ratio of more than 50 dB and losses lower than 1 dB with a coupling length of only 174 μm
BPM analysis of integrated optical switches using polymeric optical waveguides and SSFLC at 1.55 m
No full textOptical switches using polymeric waveguides and ferroelectric liquid crystals (FLC) have been modelled by using a 3D vectorial beam propagation method (BPM) at the wavelength of 1.55 micron used in optical communications. The structure is a vertical directional coupler consisting of a surface stabilised FLC (SSFLC), by using FELIX-M4851-025 mixture from Clariant, embedded between two polymeric waveguides and ITO layers as electrodes. The working principle of the switch is identical to the device reported in [1].
A polymeric buffer layer has been introduced to reduce losses due to ITO absorption. Polymeric waveguides and buffers used in our analysis can be obtained by different compositions of the P(PFS-GMA) (poly(pentafluorostyrene-co-glycidyl methacrylate)). Polymer films with different refractive indexes by varying the PFS amount (copolymer composition) were reported in literature [2]. We figured out an optimised device with an extinction ratio of more than 50 dB and losses of less than 1 dB with a coupling length of only 174 micron by using 3 micron thick polymeric waveguides with a refractive index of 1.475 at the wavelength of 1.55 micron. Such waveguides can be made by using a PFS content of 60 mol %. A buffer layer with a thickness of 6 micron and a refractive index of 1.462, corresponding to an amount of 100 % of PFS, has been included. Furthermore the device consists of a 5 micron FLC layer aligned by teflon layers with a thickness of 40 nm and ITO layers of 20 nm to drive it. The FLC cone axis is tilted by 51° from light propagation. The same device without buffer gives an extinction ratio of 29.33 dB and higher losses of 1.36 dB.
Simulations show the benefits in terms of loss reduction due to the presence of the buffer. In particular it is possible to increase ITO thickness to have a more homogeneous and conductive layer without increasing optical losses. In fact ITO thickness of 40 nm in the device without buffers leads to losses of 5.55 dB that can be decreased to 1.35 dB by using buffer layers whose thickness is 6 micron.
References
[1] R. Asquini, A. d’Alessandro, “A bistable optical waveguided switch using a ferroelectric liquid crystal layer”, paper MM4, LEOS 2000, 13th Annual Meeting, Puerto Rico, 13-16 November 2000.
[2] C. Pitois, S. Vukmirovic, A. Hult, D. Wiesmann, M. Robertsson, “Low-Loss Passive Optical Waveguides Based on Photosensitive Poly(pentafluorostyrene-co-glycidyl methacrylate)”, Macromolecules, 32, pp. 2903-2909, 1999
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