Photonics

Improving Lens Performance With Transmitted Wavefront Error Testing

During design and manufacturing, optical systems and lenses are toleranced and tested to ensure the smallest possible performance error. Matching most optics manufacturing companies’ capabilities, lenses are traditionally toleranced with individual surface specifications — surface power and irregularity, or form, error. These tolerances and the associated tests control performance of a single surface, not the entire lens. Because lens designs are built around transmission characteristics such as spot size and RMS wavefront error, the performance of the entire lens, not the individual surfaces, is the true target. Transmitted wavefront error (TWE), which is the error in transmission of light through a lens, is the true target. For aspheric surfaces, traditional single-surface, three-dimensional surface form metrology is not easy. Aside from testing the true target, it may be easier and faster to make use of TWE for aspheric lenses. Using innovative metrology and developing a feed-forward manufacturing strategy, tolerancing and testing TWE can reduce risk in optical designs, improve performance and reduce cost and lead time.

Posted in: ptb catchall, Applications, Photonics, Application Briefs

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Optical Magnetometer Incorporating Photonic Crystals

Sensitivity would be increased by orders of magnitude. NASA’s Jet Propulsion Laboratory, Pasadena, California According to a proposal, photonic crystals would be used to greatly increase the sensitivities of optical magnetometers that are already regarded as ultrasensitive. The proposal applies, more specifically, to a state-of-the-art type of quantum coherent magnetometer that exploits the electromagnetically-induced-transparency (EIT) method for determining a small change in a magnetic field indirectly via measurement of the shift, induced by that change, in the hyperfine levels of resonant atoms exposed to the field.

Posted in: Tech Briefs, ptb catchall, Photonics, Briefs

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Raman-Suppressing Coupling for Optical Parametric Oscillator

Loading of desired modes is reduced, relative to loading of undesired modes. NASA’s Jet Propulsion Laboratory, Pasadena, California A Raman-scattering-suppressing input/output coupling scheme has been devised for a whispering-gallery-mode optical resonator that is used as a four-wave-mixing device to effect an all-optical parametric oscillator. Raman scattering is undesired in such a device because (1) it is a nonlinear process that competes with the desired nonlinear four-wave conversion process involved in optical parametric oscillation and (2) as such, it reduces the power of the desired oscillation and contributes to output noise.

Posted in: Tech Briefs, ptb catchall, Photonics, Briefs

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WGM-Resonator/Tapered-Waveguide White-Light Sensor Optics

Light patterns formed by these optics contain information on absorption spectra. NASA’s Jet Propulsion Laboratory, Pasadena, California Theoretical and experimental investigations have demonstrated the feasibility of compact white-light sensor optics consisting of unitary combinations of (1) low-profile whispering-gallery-mode (WGM) resonators and (2) tapered rod optical waveguides. These sensors are highly wavelength-dispersive and are expected to be especially useful in biochemical applications for measuring absorption spectra of liquids.

Posted in: Tech Briefs, ptb catchall, Photonics, Briefs

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Cold Atom Source Containing Multiple Magneto-Optical Traps

This source allows a smaller package relative to single-trap sources of similar performance. NASA’s Jet Propulsion Laboratory, Pasadena, California An apparatus that serves as a source of a cold beam of atoms contains multiple two-dimensional (2D) magneto-optical traps (MOTs). (Cold beams of atoms are used in atomic clocks and in diverse scientific experiments and applications.) The multiple-2D-MOT design of this cold atom source stands in contrast to single-2D-MOT designs of prior cold atom sources of the same type. The advantages afforded by the present design are that this apparatus is smaller than prior designs.

Posted in: Tech Briefs, ptb catchall, Photonics, Briefs

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Opto-Electronic Oscillator Using Suppressed Phase Modulation

Phase noise would be much lower than in prior OEOs. NASA’s Jet Propulsion Laboratory, Pasadena, California A proposed opto-electronic oscillator (OEO) would generate a microwave signal having degrees of frequency stability and spectral purity greater than those achieved in prior OEOs. The design of this system provides for reduction of noise levels (including the level of phase noise in the final output microwave signal) to below some of the fundamental limits of the prior OEOs while retaining the advantages of photonic generation of microwaves. Whereas prior OEOs utilize optical amplitude modulation, this system would utilize a combination of optical phase modulation and suppression thereof. The design promises to afford, in the opto-electronic domain, the low-noise advantages of suppression of carrier signals in all-electronic microwave oscillators.

Posted in: Tech Briefs, ptb catchall, Photonics, Briefs

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Alternative Controller for a Fiber-Optic Switch

This controller communicates via a serial instead of a parallel port. NASA’s Jet Propulsion Laboratory, Pasadena, California The figure is a simplified diagram of a relatively inexpensive controller for a DiCon VX (or equivalent) fiber-optic switch — an electromechanically actuated switch for optically connecting one or two input optical fibers to any of a number of output optical fibers. DiCon VX fiber-optic switches are used primarily in research and development in the telecommunication industry. This controller can control any such switch having up to 32 output channels.

Posted in: Tech Briefs, ptb catchall, Photonics, Briefs

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