Abstract:
A data conversion system acquires samples of low frequency signal components of an applied analog signal at a first data conversion rate and samples of high frequency signal components of the applied analog signal at a second data conversion rate that is higher than the first data conversion rate. The data conversion system applies a first correction filter to the acquired samples of the low frequency signal components to provide a first filtered signal and applies a second correction filter to the acquired samples of the high frequency signal components to provide a second filtered signal. The data conversion system interpolates the first filtered signal to provide an interpolated signal, and sums the interpolated signal with the second filtered signal to provide an output signal.
Abstract:
The tunable optical filter includes an elastic substrate, a diffractive element in the elastic substrate, an actuator for stretching the elastic substrate to control the pitch of the diffractive element, a first optical path and a second optical path. The diffractive element optically couples the second optical path to the first optical path at an optical frequency determined by the pitch of the diffractive element.
Abstract:
An optical spectrum analyzer is provided with a user selectable sensitivity. Required operating parameters are set in response to user selection of sensitivity to permit measurement of an input light beam at the selected sensitivity. Setting the required parameters includes setting a required gain of a video channel to permit measurement of a specified maximum light signal and to provide the selected sensitivity, setting a required video bandwidth of the video channel to provide the selected sensitivity at the required gain of the video channel and setting a sweep rate to provide the selected sensitivity at the required video bandwidth. When the normal bandwidth of the video channel is not adequate to provide the selected sensitivity, the electrical signal is passed through a digital filter having a filter coefficient set to provide the required video bandwidth. A peak detector is incorporated in the video channel to accurately measure signal amplitudes in a fast scanning condition.
Abstract:
A data conversion system acquires samples of low frequency signal components of an applied analog signal at a first data conversion rate and samples of high frequency signal components of the applied analog signal at a second data conversion rate that is higher than the first data conversion rate. The data conversion system applies a first correction filter to the acquired samples of the low frequency signal components to provide a first filtered signal and applies a second correction filter to the acquired samples of the high frequency signal components to provide a second filtered signal. The data conversion system interpolates the first filtered signal to provide an interpolated signal, and sums the interpolated signal with the second filtered signal to provide an output signal.
Abstract:
Wavelength reference standard using multiple gasses and calibration methods using same. A wavelength reference using absorption lines of multiple gasses provides stable reference wavelengths over multiple regions of interest of the optical spectrum. The gasses may be in separate cells or combined in one cell. Improved calibration using the reference is achieved by performing calibration measurements at a plurality of known wavelengths and using an average calibration constant derived from the plurality of measurements. In a second embodiment, improved calibration is achieved by performing calibration measurements at a plurality of known wavelengths and calculating a higher order calibration model, such as a least-squares linear fit. Both approached may be extended by segmenting the wavelength range and using calculated calibration values for each segment.
Abstract:
Optical wavelength reference apparatus with wide wavelength range. Illuminated by a wideband source, a first reference such as absorption lines in a gas cell is used as a transfer standard, calibrating the response of the secondary reference over the range of the first reference. The performance of the second reference is extrapolated to a wider wavelength range, retaining the stability and accuracy characteristics of the first reference. Suitable secondary devices include etalons such as Fabry-Perot filters and Mach-Zehnder interferometers.
Abstract:
A double-pass scanning monochromator for use in an optical spectrum analyzer includes an input optical fiber for emitting an input light beam, a diffraction grating for diffracting the input light beam to produce a spatially dispersed light beam, a slit for passing a selected portion of the dispersed light beam, a motor for rotating the diffraction grating, a shaft angle encoder for sensing grating position, and an output optical fiber. The light that passes through the slit is directed to the diffraction grating and is recombined by the diffraction grating to produce an output light beam. The light beam to be analyzed is incident on the diffraction grating during first and second passes. A polarization rotation device rotates the polarization components of the light beam by 90.degree. between the first and second passes so that the output of the monochromator is independent of the polarization of the input light beam. The output optical fiber is translated by a micropositioning assembly in a plane perpendicular to the output light beam during rotation of the diffraction grating to automatically track the output light beam and to provide optical chopping.
Abstract:
A double pass scanning monochromator for use in an optical spectrum analyzer includes an input optical fiber for emitting an input light beam, a diffraction grating for diffracting the input light beam to produce a spatially dispersed light beam, a slit for passing a selected portion of the dispersed light beam, a motor for rotating the diffraction grating, a shaft angle encoder for sensing grating position, and an output optical fiber. The light that passes through the slit is directed to the diffraction grating and is recombined by the diffraction grating to produce an output light beam. The light beam to be analyzed is incident on the diffraction grating during first and second passes. A polarization rotation device rotates the polarization components of the light beam by 90.degree. between the first and second passes so that the output of the monochromator is independent of the polarization of the input light beam. The output optical fiber is translated by a micropositioning assembly in a plane perpendicular to the output light beam during rotation of the diffraction grating to automatically track the output light beam and to provide optical chopping.
Abstract:
Devices and methods for processing multi-wavelength light beams and the single-wavelength components of such light beams are disclosed. In accordance with some embodiments, a spectral filter includes collimating and focusing optical elements, an apodizing filter, a diffraction grating, and a spatial filter. The collimating optical element collimates an input light beam while the apodizing filter spatially filters this beam. In general, the apodizing filter includes a range of transmissivity that varies according to a distance from a predetermined location on the apodizing filter. The diffraction grating diffracts the input beam which is focused by the focusing optical element onto the spatial filter to generate a filtered output beam. Embodiments of the invention may be employed as spectral filters, optical spectrum analyzers, optical mutiplexers, optical de-multiplexers, and the like.
Abstract:
An apparatus for optically shifting the frequency of an input signal beam includes a first Raman medium that receives an input signal beam, a first pump beam, and a first reference beam to responsively generate an intermediate signal beam comprising a Raman sideband of the first Raman medium. A second Raman medium is optically coupled in series with the first Raman medium. The second Raman medium receives the intermediate signal beam, a second pump beam, and a second reference beam to responsively generate an output signal beam comprising a Raman sideband of the second Raman medium. The generated output signal represents the input signal that is shifted in frequency by a frequency shift that corresponds to the frequency difference between the first and second reference beams.