Mart Diemeer

Polymeric thermo-optic space switches for optical communications

Solid state optical space switches based on the thermo-optic (t.o.) effect in polymeric optical waveguides have now reached the commercial stage. The application of these switches is in network protection and network reconfiguration functions for fiber optic communications systems. The requirements for these applications include polarization and wavelength independence, low insertion loss, low cross talk, low drive power with step-like (digital) response, millisecond switching times and small size. In addition the reliability of the component must meet the demanding requirements of telecom applications. It will be shown that polymeric t.o. space switches can meet all functional requirements due to the exceptional thermal and t.o. effects of polymers combined with their tunability and processing versatility. Furthermore, it will be shown that polymer optical chips components can withstand extreme lifetime tests with success.

Modal dispersion phase matching over 7 mm length in overdamped polymeric channel waveguides

Phase‐matched second harmonic generation over 7 mm is demonstrated using the modal dispersion of a composite 4‐dimethylamino‐4′‐nitrostilbene/polyetherimde channel waveguide. For a 1‐mm‐long sample a record figure of merit for polymers of η=P2ω/(PωL2)=14%/W cm2 was measured at 1550 nm. This is comparable to the value reported for LiNbO3 at that wavelength. The efficiency in longer samples is limited by fundamental and harmonic waveguide losses.

Design and fabrication of electro-optic polymer modulators and switches

Electro-optic (EO) polymers are interesting materials for realising active functions in integrated optics devices, since they can have relatively high EO coefficients and they can be easily combined or integrated with several (passive) materials. EO interaction can be exploited for obtaining modulation or switching in polymer-based devices using several principles (e.g. Mach–Zehnder, Digital Optical Switch or tuned coupling to surface plasmons), which have been investigated and tested using a number of different materials. We compare these principles in view of several aspects of practical importance: realistic values of EO coefficients and wavelength-dependent attenuation, optical, electrical and chemical compatibility of substrate, guiding and cladding layers, channel definition by etching (inverted) ridge waveguides or by photo-bleaching, local and global poling methods, polarisation-dependence, and the design of efficient high-bandwidth travelling wave electrodes. In most of the investigated devices, we employ a waveguiding structure based on silicon and its oxynitrides, exploiting the fact that the refractive index of silicon oxynitride can be accurately adjusted over a wide range by adjusting its composition. We will discuss the practical difficulties encountered and show the obtained results with phase- and intensity modulators and switches.

Guided wave modulators and switches fabricated in electro-optic polymers

In this paper the fabrication of directional couplers (2×2 switches) and Mach–Zehnder interferometers (intensity modulators) using electro‐optic polymeric multilayer structures, is described. Results show attractively low switching voltages (<10 V for 1.4 cm long devices) and very good on‐off ratios (17 dB) for the directional couplers. In the case of the Mach–Zehnder interferometers, Vπ‐values of 4.5 V have been obtained, also for 1.4 cm long devices.

Recent Developtents In Optically Nonlinear Polymers And Related Electro-Optic Devices

Side chain polymers, containing hyperpolarizable moieties as pendant groups, have been applied as optically nonlinear materials. Electro-optic properties have been induced via electric field poling of nultilayer structures incorporating the nonlinear polymers. For a poling field strength of 156 Wpm, the obtained i r33 coefficient was equal to 28 pn/V at the wavelength of 1.3 pm, which is close to r33 = 32 of the inorganic single crystal lithium niobate. Low loss mcnomode charnel waveguides (< 1 dB/cm @ 1.3 μm wavelength) have been realized in the optically nonlinear polymer nultilayers. Tunable Fabry-Perot etalons, monamode phase and intensity modulators and monomode Mach-Zehnder interferameters, have been made and tested; their performances will be discussed. Owing to their considerable electro-optic coefficients and attractive processing properties, polymers are becoming serious alternatives for the currently often applied lithium niobate.

Key trade‐offs for second harmonic generation in poled polymers

We discuss the critical trade‐off between the spectral dispersion in the second order nonlinearity d(2) and the linear absorption coefficient for second harmonic generation (SHG) by the mixing of copropagating or counterpropagating fundamental beams in poled polymers. The 4‐dimethylamino–4′‐nitrostilbene side‐chain polymer is used as a specific example. The predictive power of the classical two‐level model for SHG is also assessed.

POLYMER WAVEGUIDES WITH OPTIMIZED OVERLAP INTEGRAL FOR MODAL DISPERSION PHASE-MATCHING

Modal dispersion phase-matched second harmonic generation is demonstrated in new poled polymer waveguide geometries with a nonlinear optical core consisting of two side-chain polymers with different glass transition temperatures. After poling above and between the respective glass transitions, the sign of the nonlinear optical coefficient is reversed in the two polymers, thereby improving the overlap integral. Conversion efficiencies up to 7%/W cm2 were achieved in the first experiments.

Optically nonlinear polymeric switches and modulators

Side chain polyrrers containing hyperpolarizable noieties as the periant groups have been applied as optically ncrilinear traterials to produce polyxreric integrat1 electro-optical devices . Phase nixiulators, intisity nixiulators (1ch-Zebzx1er interferaiters) aixi optical 2*2 sce switches ( 2*2 directixa1 nixie couplers) have been uncle . Driving voltages as 1ci as 2 Volts (V ) have been obtain1 for a 24 nm active 1gth çkmse ncdulator; 4.4 Volts (V ) for a 14 inn active 1angthch-Zebrx1er interferarter, ath 9 Volts for a 14 nm active length directionI node ccupler. Intisity nixiulation ratios of about -23 dB atti -17 dB have been derived for the intensity nixiulator atd nixie ccxipling switch, respectively. The device properties , theni.l arxi electrical stabilities , etc. will be discussed. The results obtained shcw that optically txnlinear polyiTers are attractive caixlidates for the realizaticzi of polyireric integrated electro-optical devices. In additicn, several passive veguiding devices have beai nnde.

Low-cost and low-loss multimode waveguides of photodefinable epoxy

To satisfy the urgent need for low-cost multimode planar waveguides, we developed photodefined, multimode-fiber compatible waveguides with low-cost commercially available epoxies showing low losses from 550 to 1100 nm and around 1300nm

Optically nonlinear polymeric devices

Optically nonlinear side chain polymers have been used to make a number of polymeric electro-optic and thermo-optic switching devices. The following devices are described and their performances discussed: a 2 X 2 electro-optical directional mode coupler; a 1 X 2 Mach-Zehnder switch comprising a Y-splitter combined with 2 parallel arms and a directional coupler section; a polarization and wavelength independent switch comprising a Y- junction; and an electro-thermo-optical Mach-Zehnder interferometer. In addition, the stability of some of the devices is presented and discussed. The directional mode coupler shows -17 dB modulation depth for 7.5 Volts switching voltage; the Mach-Zehnder switch required 10 Volts for 14 dB switching ratio; the Y-junction switch needed 50 mW for >20 dB modulation; the electro-thermo-optical Mach-Zehnder required as low as 0.5 mW to achieve (pi) -phase shift. The results show that optically nonlinear side chain polymer are attractive materials for the realization of polymeric switching devices.