Silicon-based compact eight-channel wavelength and mode division (de)multiplexer for on-chip optical interconnects.

A compact wavelength and mode division (de)multiplexer is proposed for multiplexing a total of eight guided TE modes of a 220 nm thick silicon-on-insulator waveguide with input channels at two wavelengths of 1.55 and 2 µm for wavelength division multiplexing. The (de)multiplexer is composed of four sequentially arranged sections with bus waveguides of increasing widths. The first section uses an asymmetric directional coupler to couple one TE mode at 1.55 µm, while each of the next three sections consists of two collocated directional couplers to simultaneously couple two TE modes of the bus waveguide, one at each wavelength of 1.55 and 2 µm. Three linear adiabatic tapers are designed to connect the consecutive bus waveguides. The fundamental TE mode of the bus waveguide at 1.55 or 2 µm is coupled by using another adiabatic taper from a single-mode input waveguide. The simulation results show that over a broad bandwidth of >100n m the insertion loss and crosstalk for both wavelength bands is <1.15d B and <-27d B, respectively. In addition, a compact device footprint with a total coupling length of ∼61µm is achieved due to the use of collocated directional couplers in three sections.

SOI-based compact mode- and polarization-division multiplexer for on-chip optical interconnects: design and simulation.

A compact seven-channel hybrid mode- and polarization-division multiplexer based on a silicon-on-insulator (SOI) waveguide platform is proposed for on-chip optical interconnects. Three independent signals are coupled into the TE0, TM0, and TE1 mode of a three moded waveguide using a taper, a polarization beam splitter, and an asymmetric directional coupler in the first coupler section. In the adiabatically connected second and third sections, two collocated asymmetric directional couplers are used to couple two TE modes (TE2, TE3) and two TM modes (TM1, TM2) to reduce the footprint of the device. A coupling length of ∼44.29µm is achieved with low insertion loss <0.09dB and crosstalk better than -30dB at the designed wavelength of 1.55 µm.

Long period fiber grating based sensor for the detection of triacylglycerides.

In this paper, stable, label free enzyme based sensor using long period fiber grating (LPG) is described for the detection of triacylglycerides. A stable covalent binding technique for lipase enzyme immobilization on an optical fiber is reported. An active and stable attachment of the functional group of the enzyme on the fiber surface is achieved using this method. Enzyme immobilization is confirmed by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. The stability is confirmed by lipase p-nitrophenyl palmitate (PNP) assay. In contrast to widely used amperometric based biosensor, where a number of enzymes are required, only one enzyme, namely, lipase is required in our sensor. The sensor shows optimum response within one minute at a temperature of 37°C and pH of 7.4. The sensor is based on the shift in resonance wavelength of the LPG transmission spectrum due to the interaction of triacylglycerides with the enzyme. The biosensor is highly specific towards triacylglycerides and is unaffected by the presence of many other interfering substances in serum. Interaction between the bio-molecules and the long period grating surface is also modeled theoretically using a four layer model for the LPG fiber with the bio-recognition layer and the results obtained are consistent with experimentally obtained results. The sensor shows a high sensitivity of 0.5 nm/mM and a low detection limit of 17.71 mg/dl for the physiological range of triacylglycerides in human blood.

Long period grating refractive-index sensor: optimal design for single wavelength interrogation.

We report the design criteria for the use of long period gratings (LPGs) as refractive-index sensors with output power at a single interrogating wavelength as the measurement parameter. The design gives maximum sensitivity in a given refractive-index range when the interrogating wavelength is fixed. Use of the design criteria is illustrated by the design of refractive-index sensors for specific application to refractive-index variation of a sugar solution with a concentration and detection of mole fraction of xylene in heptane (paraffin).