Richard W. Ridgway

Generation and Modulation of a 94-GHz Signal Using Electrooptic Modulators

Wireless data transmission at 10.6 Gb/s on a 94-GHz carrier is achieved using photonic components operating at frequencies less than 18 GHz, including a laser diode, two lithium niobate modulators, and an arrayed waveguide grating. A uni- traveling-carrier photodiode is used to convert the doubly modulated optical signal to a modulated millimeter-wave (mmW) carrier. Two antennas are used to transmit and receive the data-encoded mmW signal. A Schottky-diode detector is used to detect the on-off keyed data on the mmW signal at power levels greater than -20 dBm. MMW wireless signals are measured out to a distance of 800 m.

Data Transmission Using Differential Phase-Shift Keying on a 92 GHz Carrier

Wireless data transmission with binary phase-shift keying modulation encoded on a 92 GHz carrier is achieved using photonic components. A high-speed photodiode is used to convert the doubly-modulated optical signal to a modulated millimeter-wave carrier. A W-band Mach-Zehnder interferometer with a one-bit time delay is used to directly detect the differential phase-shift keyed millimeter-wave wireless signal without the use of a local oscillator. Field tests with antennas separated by 890 m demonstrate the ability to discriminate two phase states for differential binary phase shift keying (DBPSK) and four phase states for differential quadrature phase shift keying (DQPSK) at data rates of 2.3 Gb/s and 4.6 Gb/s, respectively.

Integrated optic sensor with macro-flow cell

An integrated-optic channel waveguide device is configured as a biosensor. The device measures a refractive index change on the waveguide surface, so it is called a biorefractometer. With an appropriate overlay or selective coating, the device can monitor proteins in blood or pollutants and bio-warfare agents in water. We describe the design, fabrication, and testing of a sensor employing a waveguide Mach-Zehnder interferometer configuration. The device is fabricated in a glass substrate using potassium ion exchange. A patterned glass buffer layer defines the sensing and reference arms of the interferometer. A silicone-rubber macro-flow cell confines the liquid above the integrated-optical waveguide device. Salt solution data show that the biorefractometer has a sensitivity ((Delta) neff/(Delta) nLiquid) of 2 X 10-3 and can measure refractive index changes of about 0.005. Data obtained for antigen-antibody binding of the protein IgG indicate that a 10 percent signal change occurs in approximately 1 minute for a 10 (mu) g/ml concentration level.

Integrated Optic Biosensor for Environmental Monitoring

An integrated-optic biosensor monitors the concentration of liquid pollutants on the surface of a planar substrate composing single-mode channel waveguides. The concept uses a Mach- Zehnder interferometer structure to measure thickness and/or refractive index changes on the waveguide surface. These changes occur as pollutant molecules interact directly with the interferometers active arm or with a hydrophobic coating on the surface of the arm. Interferometer output data were obtained for various solutions including PPM levels of benzene and toluene in water. Theoretical analysis indicated that a hydrophobic coating on the waveguide would provide sensor specificity and detect pollutants at PPB levels.

Integrated optic sensor for measuring aflatoxin-B1 in corn

An integrated optic refractometer device was developed to perform a rapid one-step, homogeneous immunoassay. The device measures refractive index changes at the surface of a planar, singlemode, ion-exchange waveguide using difference interferometry. Anti-aflatoxin- B1 antibodies were attached to the waveguide surface to provide a bioselective coating for detecting and quantifying the aflatoxin-B1 antigen level in a sample. The detection limit of this small antigen must be determined using a competitive assay format. To determine feasibility of the competitive assay, we determined the biosensor response to a larger molecular weight competing antigen, namely HRP-labeled aflatoxin-B1. This labeled antigen will compete with unlabeled aflatoxin for binding sites on the sensor surface. Increased sample aflatoxin levels will result in a decreased time-dependent phase change of the helium-neon laser light beam. Phase change data were determined for various concentration levels of HRP-labeled aflatoxin- B1 antigen. The assay measurements were made over a 5-minute time period. Results indicated that a competitive assay is feasible. Future assay efforts should be able to demonstrate measurement of aflatoxin-B levels found in contaminated corn samples.

Integrated optic biosensor

A micro-sized biosensor is formed using integrated-optic channel waveguides in a Mach- Zehnder interferometer configuration. The device measures refractive index changes on the waveguide surface, so it is called a biorefractometer. With an appropriate overlay or selective coating, the sensor can monitor proteins in blood or pollutants and bio-warfare agents in water. The waveguides are fabricated in a glass substrate using potassium ion exchange. A patterned glass buffer layer defines the interferometers sensing and reference arms. A silicone-rubber cell arrangement brings sample analytes into contact with proteins immobilized on the integrated-optical waveguide surface. Data obtained for antigen-antibody binding of the proteins human Immunoglobulin-G and staph enterotoxin-B indicate that a 50 - 100 ng/ml concentration levels can be measured in less than ten minutes.

Integrated optic device for biochemical sensing

A novel immunosensor concept monitors antigen-antibody binding on the surface of a planar single-mode waveguide. The concept can be used as the basis for a label-free homogeneous immunoassay because only changes in the thickness and refractive index of the antigen-antibody layer are monitored by observing small changes in the effective index of the waveguide. BSA +anti- BSA binding was examined theoretically using a four-layer model and effective index measurements were obtained which agreed with the calculated values. Analysis indicated that the small effective index changes can possibly be measured with high sensitivity and at low cost using an integrated optic interferometer format.

Design of a 10-Gb/s satellite downlink at millimeter-wave frequencies

System requirements, including carrier frequency, transmitted power and antenna gain are presented for a 10 Gb/s satellite downlink operating at millimeter-wave frequencies. Telecommunications-grade optical components and a high-speed photodiode are used to generate and modulate millimeter-wave carrier frequencies between 90 GHz and 100 GHz at data rates in excess of 10 Gb/s. Experimental results are presented that determine the minimum received power level needed for error-free wireless data transmission. Commercially available W-band power amplifiers are shown to increase the transmitted power level and extend the error-free propagation distance to distances of 10 km. Experimental results and documented atmospheric attenuation values for clouds, fog and rain are used to estimate link budgets for a wireless downlink located on a low-earth-orbiting satellite operating at an altitude of 350 km.

Modulation of light using Kerr-clad silica waveguide

A silica waveguide employing an electrooptic Kerr material as a functioning cladding is shown to modulate light at RF frequencies. The modulator uses a Kerr electrooptic material as the functional cladding on a silica waveguide structure. The modulator is designed to operate at 70 C and the electrooptic material has an index of refraction that is less than the silica waveguide at that temperature. Kerr-based materials have a refractive index that varies as the square of the applied voltage. This quadratic relationship is exploited by combining a DC bias voltage with the RF drive signal in order to reduce the drive voltage of the modulator.

The integration of modulators and multiplexers on silica planar lightwave circuits

An integrated optical device comprising two arrayed waveguide gratings (AWGs) and an electrooptic modulator array is described. When used in conjunction with a broadband light source, the integrated optic device can provide multiple high data rate signals from a single optical light source. The first AWG spectrally slices the light from the broadband light source. Each optical signal is then modulated using an electrooptically-clad silica waveguide Mach-Zehnder interferometer. The second AWG multiplexes the modulated optical signals onto a single output fiber. The paper describes the design of the modulator-multiplexer circuit. Experimental results of the modulator portion of the circuit show the modulation of light at 1550 nm in a electrooptically-clad silica waveguide at data rates of 1 GB/s.