Polymer slab waveguides for the optical detection of nanoparticles in evanescent field based biosensors

We present a polymer optical waveguide integration technology for the detection of nanoparticles in an evanescent field based biosensor. In the proposed biosensor concept, super-paramagnetic nanoparticles are used as optical contrast labels. The nanoparticles capture target molecules from a sample fluid and bind to the sensor surface with biological specificity. The surface-bound nanoparticles are then detected using frustration of an evanescent field. In the current paper we elaborate on the polymer waveguides which are used to generate a well-defined optical field for nanoparticle detection

State-to-state cross sections for rotational excitation of NH3 and OH by collisions with HE, AR and H2

Contains fulltext : mmubn000001_149126417.pdf (publisher's version ) (Open Access)Promotores : J. Reuss en J. ter Meulen160 p

Longitudinal mode-switching dynamics in a dual external-cavity laser diode

We study the potential speed of an optical neural network that uses the longitudinal cavity modes of an external-cavity laser diode as neurons. For this purpose, we used a laser diode coupled to two external cavities, each corresponding to one longitudinal cavity mode. The process of longitudinal mode switching is investigated for the case of intracavity optical modulation. In this experiment, the feedback for the mode in one cavity is modulated, and the length of the other cavity can be controlled. Three limitations are imposed on the switching speed. A number of external-cavity round trips are needed to switch from one mode to the other. It is observed that, depending on the amount of optical feedback in both cavities, between 7 and 21 round trips are needed. When the experimental results for varying cavity length are extrapolated to zero cavity length, a residual delay of a few nanoseconds remains. It is believed that this delay is due to a change in carrier density, needed to switch from one mode to another. Modified rate equations are used to model our experiments. The results of numerical simulations are in good agreement with the experimental results and predict the residual delay. The model also predicts a turn-on delay that is related to relaxation oscillations and imposes a third limitation on the operation speed of our optical neural network. Implications of our findings on the potential operation speed of the optical neural network are discussed and suggestions are made for optimizatio

Optical-mode neural network by use of the non-linear response of a laser diode to external optical feedback

We present an intelligent all-optical neural network using a single laser diode that is provided with controlled external feedback. The outputs of the laser neural network (LNN) are represented in the optical domain by the longitudinal cavity modes of the laser diode. The inputs to the LNN are applied by means of adjusting the external feedback of each longitudinal mode through an optical vector-matrix multiplier. Supervised training of some basic input-output mappings is demonstrated by means of a stochastic learning algorithm. The stability and reproducibility of the LNN setup is examined

Loop-mirror laser neural network using a fast liquid-crystal display

In our laser neural network (LNN) all-optical threshold action is obtained by application of controlled optical feedback to a laser diode. Here an extended experimental LNN is presented with as many as 32 neurons and 12 inputs. In the setup we use a fast liquid-crystal display to implement an optical matrix vector multiplier. This display, based on ferroelectric liquid-crystal material, enables us to present 125 training examples/s to the LNN. To maximize the optical feedback efficiency of the setup, a loop mirror is introduced. We use a d-rule learning algorithm to train the network to perform a number of functions toward the application area of telecommunication data switching

Optical neuron by use of a laser diode with injection seeding and external optical feedback

We present an all-optical neuron by use of a multimode laser diode that is subjected to external optical feedback and light injection. The shape of the threshold function, that is needed for neural operation, is controlled by adjusting the external feedback level for two longitudinal cavity modes of the laser diode individually. One of the two modes corresponds to the output of the neuron, light injection at the wavelength of this mode provides excitatory input. Light injection in the other mode provides inhibitory input. When light corresponding to two input signals is injected in the same mode, summation of input signals can be achieved. A rate-equation model is used to explain the operating principle theoretically. The proposed injection seeding neuron is built using free-space optics to demonstrate the concept experimentally. The results are in good agreement with the predictions from the rate-equation model. Some experimental results show threshold functions that are preferable from a neural-network point of view. These results agree well with injection locking theory and experiments reported in literatur

Mobility and height detection of particle labels in an optical evanescent wave biosensor with single-label resolution

Particle labels are used in biosensors to detect the presence and concentration of analyte molecules. In this paper we demonstrate an optical technique to measure the mobility and height of bound particle labels on a biosensor surface with single-label resolution. The technique is based on the detection of the particle-induced light scattering in an optical evanescent field. We show that the thermal particle motion in the optical evanescent field leads to intensity fluctuations that can accurately be detected. The technique is demonstrated using 290 bp (99 nm) DNA as an analyte and using polystyrene particles and magnetic particles with diameters between 500 and 1000 nm as labels. The particle intensity histograms show that quantitative height measurements are obtained for particles with uniform optical properties, and the intensity versus position plots reflect the analyte–antibody orientation and the analyte flexibility. The novel optical detection technique will lead to biosensors with very high sensitivity and specificity