Robert Shih

Normal incident InGaAs/GaAs multiple quantum well infrared detector using electron intersubband transitions

A normal incident infrared detector has been fabricated using electron intersubband transition in a InGaAs/GaAs quantum well structure. With the light polarized in the plane of the layers (normal incident) a nominally forbidden absorption peak was observed. Such an absorption is most likely a result of spin‐flip intersubband transitions induced by the spin‐orbit coupling. In addition, for the light polarized in the plane of incidence, the usual intersubband absorption due to envelope function transition is observed. The responsivity of 0.2 A/W was obtained for the normal incident infrared on the detector. This work demonstrates the fabrication of high sensitivity quantum well infrared detectors operating in the normal incident mode without fabricating grating structures on the device for focal plane applications.

Nonlinear microwave susceptibility measurement of an artificial Kerr medium

A suspension of short graphite fibers was shown to provide an effective medium for nonlinear microwave interactions. Using a 18‐GHz pump beam with up to 20 W continuous power, changes in the 94‐GHz refractive index were measured by interferometry. The induced birefringence and anisotropic absorption indicate an alignment of the fibers with the electric field of the pump beam. The resulting nonlinear refractive index coefficient of n2=2.6×10−4 cm2/W is of sufficient magnitude to demonstrate microwave bistability.

Electro‐optic phenomena in gelatin‐based poled polymer

An electro‐optic polymer with nitrophenol and photo lime gel has been constructed and demonstrated. The transmission spectrum of nitrophenol/gelatin shows an ultrawide optical bandwidth, from 340 to 2800 nm. A relatively stable and large electro‐optic effect, γ33=10–40 pm/V, was observed at 632.8 nm. The poling stability is attributed to the two‐dimensional cross‐linked nature of the gelatin. This result indicates that both passive and active integrated optical devices can be fabricated onto the same polymer thin film to form a fully polymer‐based miniature integrated optical circuit.

Nonlinear microwave optics in liquid suspensions of shaped microparticles

The use of shaped microparticle suspension for such active processes as phase conjugate via degenerate four-wave mixing at microwave and millimeter wavelengths is addressed. The theoretical method used to describe the interaction of shaped microparticles with coherent radiation is outlined. The generation of up to 250 mW phase conjugate radiation in a medium composed of rod-shaped carbon fibers suspended in a passive fluid dielectric that is maintained in a waveguide is reported. The theory for the nonlinear optical behavior of shaped particle suspensions is shown to be in excellent agreement with the available experimental data. >

Graded index polymer channel waveguide array for backplane optical interconnects

Various components needed for optical backplane applications have been demonstrated from gelatin-based polymer integrated op[tic material. An array of waveguides have been realized with packaging density as high as 1250 channels per cm and loss of 0.1 dB per cm. A 1-to-8 Y-junction splitter and a 32 x 32 star coupler have been fabricated using photolithographic techniques. The unification of the star coupler and a modulator array is for backplane optical interconnects is under investigation.

Microwave phase conjugation via degenerate four-wave mixing in an artificial Kerr medium

Collinear microwave phase conjugation was observed in an artificial Kerr medium consisting of short graphite fibers suspended in a binary liquid mixture. Using an 18 GHz pump beam with up to 20 W continuous power, characterization of the changes in the 94 GHz refractive index were made by interferometry. A nonperturbative method for describing the response of the medium was used to analyze the phase-shift measurements for the static berefringence and the time response as functions of microwave intensity.

Single‐mode optically activated phase modulator on GaAs/GaAlAs compound semiconductor rib waveguides

We report on an optically activated phase modulator (OAM) and modulator array on GaAs‐GaAlAs compound semiconductor rib waveguides. A rib waveguide device with an optical activation window of 5 μm in diameter was fabricated. Optical activation was produced by using a HeNe 632.8 nm wavelength as the free‐carrier generator and a 1.3 μm laser as the signal carrier. A 33% modulation depth was observed and 10−2 index modulation was experimentally confirmed on an OAM working in the phase modulation regime. OAMs working in both phase‐ and cutoff‐modulation regimes were further determined by considering the variation of the waveguide confinement factor. An 8.2 dB modulation depth was observed on an OAM working at the cutoff regime. Furthermore, the activation source for the free‐carrier generation is in the mW power region, which significantly reduces the size and cost of all optical switching devices.

Single-mode optically activated phase modulator on GaAs/GaAlAs compound semiconductor channel waveguides

We report on optically-activated phase modulator (OAM) and modulator array on GaAs- GaAlAs compound semiconductor channel waveguides. A channel waveguide device with an optical activation window of 5 micrometers in diameter was fabricated. Optical activation was produced by using a HeNe 632.8 nm wavelength as the free-carrier generator and a 1.3 micrometers laser as the signal carrier. Thirty-three percent modulation depth was observed and 10-2 index modulation was experimentally confirmed on an OAM working in the phase modulation regime. OAMs working in both phase- and cutoff-modulation regimes were theoretically determined by considering the fluctuation of the waveguide confinement factor. 8.2 dB modulation depth was observed on an OAM working at the cutoff regime. Furthermore, the activation source is in the mW power region which significantly reduces the size and cost of all optical switching devices.

Polymer-based channel waveguide array for large fanout optical interconnects

Various components needed for optical backplane applications have been demonstrated from gelatin-based polymer integrated optic material. An array of waveguides have been realized with packaging density as high as 1250 channels/cm and loss of 0.1 dB/cm. A 1-to-8 Y- junction splitter and a 32 X 32 star coupler have been fabricated using photolithographic techniques. The unification of the star coupler and a modulator array for backplane optical interconnects are under investigation.

Electro-optic effect in gelatin-based nonlinear polymer

Photo lime gel has become increasingly important because of its potential for use in integrated holographic elements. However, it has been a passive optical component. An electro-optic modulator with nitrophenol and gelatin has been constructed and demonstrated for the first time. The transmission spectrum of nitrophenol/gelatin shows an ultrawide optical bandwidth, from 340 nm to 2800 nm. A relatively stable and large electro-optic effect, (gamma) 33 equals 10 - 40 pm/V, was observed at 632.8 nm. This result indicates that both passive and active integrated optical devices can be fabricated onto the same polymer thin film to form a fully polymer-based miniature integrated optical circuit.