Coherent Detection of High-Rate Optical PPM Signals

Quantum-limited performance is achievable.

A method of coherent detection of high-rate pulse-position modulation (PPM) on a received laser beam has been conceived as a means of reducing the deleterious effects of noise and atmospheric turbulence in free-space optical communication using focal-plane detector array technologies. In comparison with a receiver based on direct detection of the intensity modulation of a PPM signal, a receiver based on the present method of coherent detection performs well at much higher background levels.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Mathematical analysis, Lasers, Lasers, Performance tests, Turbulence

White-Light Whispering-Gallery-Mode Optical Resonators

Overlapping resonator modes are exploited to obtain wide, high-Q spectra.

Whispering-gallery-mode (WGM) optical resonators can be designed to exhibit continuous spectra over wide wavelength bands (in effect, white-light spectra), with ultrahigh values of the resonance quality factor (Q) that are nearly independent of frequency. White-light WGM resonators have potential as superior alternatives to (1) larger, conventional optical resonators in ring-down spectroscopy, and (2) optical-resonator/electro-optical modulator structures used in coupling of microwave and optical signals in atomic clocks. In these and other potential applications, the use of white-light WGM resonators makes it possible to relax the requirement of high-frequency stability of lasers, thereby enabling the use of cheaper lasers.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Lasers, Optics, Spectroscopy, Lasers, Optics, Spectroscopy

Middleware Bridges the Optical/Mechanical Design Gap

Mechanical CAD (computer-aided design) programs have become very sophisticated during the past few years. Unfortunately, there is still a portion of the engineering spectrum that cannot be handled well in a traditional CAD program: optical modeling. If you are creating a complicated optical system (think of a camera zoom lens), then it is best to perform almost all of the design in a specialized optical design software program and then transfer the optical design to a CAD program for the later stages of the design process where items like housings, threads, cams, and motors are designed and integrated into the model.

Posted in: Articles, Features, ptb catchall, Photonics, CAD / CAM / CAE, CAD, CAM, and CAE, Design processes, Optics, Optics

Photonics Tech Briefs Presents 2005 Products of the Year

Photonics Tech Briefs (PTB) recently presented the 2005 Readers’ Choice Products of the Year at a special awards dinner held at The Water Club in New York City. The top three products chosen by the readers of PTB were honored at the event.

Posted in: Articles, Features, ptb catchall, Photonics, Optics, Sensors and actuators, Optics, Sensors and actuators, Product development

Tunable, Highly Stable Lasers for Coherent Lidar

Designs have been refined to satisfy competing requirements for stability and tenability.

Practical space-based coherent laser radar systems envisioned for global winds measurement must be very efficient and must contend with unique problems associated with the large platform velocities that the instruments experience in orbit. To compensate for these large platform-induced Doppler shifts in space-based applications, agile-frequency offset-locking of two single-frequency Doppler reference lasers was thoroughly investigated. Such techniques involve actively locking a frequency-agile master oscillator (MO) source to a comparatively static local oscillator (LO) laser, and effectively producing an offset between MO (the lidar slave oscillator seed source, typically) and heterodyne signal receiver LO that lowers the bandwidth of the receiver data-collection system and permits use of very high-quantum-efficiency, reasonably-low-bandwidth heterodyne photoreceiver detectors and circuits. Similar techniques are being applied in atmospheric CO2 differential-absorption lidar work, where MO sources need to be actively offset-locked to CO2 reference cells for continuous absolute-calibration purposes. Active MO/LO offset-locking is also highly applicable to lidar problems involving very high target velocities with respect to a static or moving lidar platform.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Calibration, Lasers, Lidar, Lasers, Lidar

Optical Systems Improve Nerve Stimulation

An infrared laser-based nerve stimulation system eliminates electrical stimulation artifacts, and improves nerve target specificity.

The stimulation of nerve tissue is a technique that is used in both research and clinical applications. Neuroscientists use nerve stimulation to study the fundamental principles of the nervous system and to research Parkinson’s disease, Alzheimer’s disease, and nerve regeneration, among others. Medical professionals use nerve stimulation for everything from pain and depression management to brain mapping. Today’s stimulators use electrical current to stimulate nerves, resulting in significant limitations. Thanks to a novel optical stimulation technique pioneered by Vanderbilt University, Aculight has developed a compact, laser-based neural stimulator that overcomes these obstacles.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Optics, Optics, Medical equipment and supplies

DPSS UV Source Targets Gas Lasers and Life Sciences

System is designed for applications that relied on pulsed nitrogen gas lasers.

Spectra-Physics Corp., Tucson, Arizona

Nitrogen lasers have been used for more than 15 years in life science and forensic applications and will continue to play a role in many scientific and industrial applications. But researchers, OEMs, and system integrators working on innovative, cutting-edge applications need higher-performance lasers. The Explorer, a diode-pumped solid-state OEM laser system with flexible power and control electronics, is a low-power, actively Q-switched, ultraviolet (UV) laser system that operates at 349 nm for bioinstrumentation applications that in the past have relied on pulsed nitrogen gas lasers.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Lasers, Lasers, Biological sciences, Gases

Optical Profilometers Using Adaptive Signal Processing

Sizes would be reduced, leading to development of hand-held profilometers.

A method of adaptive signal processing has been proposed as the basis of a new generation of interferometric optical profilometers for measuring surfaces. Many current optical surface-measuring profilometers utilize white-light-interferometry and, because of optical and mechanical components essential to their operation, are comparable in size to desktop computers. In contrast, the proposed profilometers would be portable, hand-held units. Sizes could be thus reduced because the adaptive-signal-processing method would make it possible to substitute lower-power coherent light sources (e.g., laser diodes) for white light sources and would eliminate the need for most of the optical components of current white-light profilometers. Furthermore, whereas the height scanning ranges of current surface-measuring profilometers are of the order of millimeters, the adaptive-signal-processing method would make it possible to attain scanning ranges of the order of decimeters in the proposed profilometers.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Measurements, Optics, Optics, Test equipment and instrumentation

Optical Surface Analysis Advances Defect Inspection of Optoelectronics

Production defect data leads to better yield management practices.

KLA-Tencor Corp., San Jose, California

Faced with increasing demand, manufacturers of power devices, microdisplays, and high-brightness light-emitting diodes (HB-LEDs) are focusing on tightening manufacturing process windows to reduce defects. The transparent nature of the substrates used to make many optoelectronic devices such as glass, silicon carbide, and sapphire makes manual defect inspection using optical microscopes an ambiguous and time-consuming process incapable of high-volume production. To meet the need for improved defect inspection, Optical Surface Analyzer (OSA) instruments provide automated defect inspection for optoelectronic device wafers from 2" to 300 mm in diameter.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Measurements, Electronic equipment, Optics, Electronic equipment, Optics, Inspections

Improved Photon-Emission-Microscope System

An advanced photon-emission microscope is combined with the latest image-processing software.

An improved photon-emission-microscope (PEM) instrumentation system has been developed for use in diagnosing failure conditions in semiconductor devices, including complex integrated circuits. This system is designed primarily to image areas that emit photons, at wavelengths from 400 to 1,100 nm, associated with device failures caused by leakage of electric current through SiO2 and other dielectric materials used in multilayer semiconductor structures. In addition, the system is sensitive enough to image areas that emit photons during normal operation. This system supplants a prior PEM system based on a photon-intensified, gated, charge-coupled-device (CCD) camera.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Failure analysis, Charge coupled devices, Integrated circuits, Semiconductor devices, Charge coupled devices, Integrated circuits, Semiconductor devices, Diagnostics

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