Session C05: AMO1: Optical Measurement

Taking High Resolution Images with a Lensless, Single Pixel Camera

Structured illumination imaging is a method of capturing an image without the need for an imaging lens or a multi-pixel detector.  By projecting known patterns of light onto an object, and measuring how much light the object scatters, information about the object can be collected, and then processed into an image.  In our lab we are using laser interference to generate structured illumination patterns.  This technique has some significant advantages over previous work, including the ability to achieve microscopic resolution with no optics near the object imaged, a depth of field and field of view which are independent of the resolution, and the ability to surpass the resolution limit of conventional imaging without any expensive high numerical aperture optic.  And because the technique doesn't require a precise lens or multi-pixel detector, it could easily be applied to imaging with x-rays, radar waves, acoustic waves, or other waves for which these elements are difficult to manufacture.  

Construction and Characterization of an Avalanche Photodiode Detector

Traditional photodetectors built using photodiodes are relatively inexpensive, robust, and have high quantum efficiencies, but their responsivity is small. Photomultiplier tubes have much higher responsivities due to electron avalanche multiplication, but have lower quantum efficiency, are more expensive, and fragile. Avalanche photodiodes have many of the advantages of standard photodiodes, but also utilize electron avalanche multiplication.  We are working on constructing a small, precise, and inexpensive avalanche photodiode detector utilizing modern voltage converter and amplifier chips. This detector would use a commercially available avalanche photodiode instead of a regular photodiode to achieve a higher internal gain while maintaining a large quantum efficiency to allow more accurate measurements of low intensity light.   

Effect of Scaling on the Optical Q of SiN Optomechanical Oscillators

Cavity optomechanical oscillators (OMOs) have several applications in timing, communications and sensors. For all applications, it is interesting to investigate the effect of reduced device size on optical quality factor, Q. In this study, we measure the optical Q at 1550 nm of released SiN whispering gallery mode resonator OMOs coupled to SiN waveguides. We chose a free space optical setup for flexible mode matching and long-term stability. The setup takes advantage of a top down camera and co-linear, co-focused 635 nm and 1550 nm lasers for easier waveguide coupling. We also describe improvements in automation for real time resonance identification and analysis. The devices measured are discs and anchored ring resonators with varying waveguide coupling gaps and device radii ranging from 10 μm to 60 μm which are suspended with various spoke widths. We achieved Q=2x10⁶ in 50 μm radius discs. A comparison of optical Q as a function of the parameters stated above will be made to determine designs for optomechanical characterization.