Abstract: In order to avoid errors inherent in the measurement of electrical phase differences or pulse arrival time in relative group delay measurements, different optical signals have their intensity modulated at a common high frequency and different permutations are selected. The amplitudes of corresponding electrical signals are detected and phase differences are computed on the basis of trigonometrical relationships. Because the modulation frequency is known, time differences can be deduced. Apparatus for measuring the phase differences conveniently comprises a slotted wheel (26) which passes selected ones or both of the optical signals. One of the optical signals may be split to produce a third signal with a predetermined phase shift, e.g. about 90 degrees at the modulation frequency and the amplitudes of some possible permutations of the three optical signals used to compute the phase difference. The measurements may be used to compute chromatic dispersion, polarization mode dispersion, elongation, and so on.

Abstract: An optical spectrum analyzer comprises a diffraction grating (DG), a polarization decomposing unit (PDM) for decomposing the input light beam into first and second light beams having mutually-perpendicular linear states of polarization, and two output ports (FP2/1, FP2/2) each for receiving from the grating, substantially exclusively, a respective one of the polarized light beams (LT, LR) after diffraction by the diffraction grating (DG).

Abstract: Apparatus for measuring very low levels of polarization mode dispersion of optical devices, that is inexpensive, robust and portable, comprises a broadband source and a polarizer for directing substantially completely polarized broadband light into the device under test with the polarization in a plane substantially perpendicular to the propagation direction of the light. Light leaving the device is analyzed spectrally to produce a spectrum of intensity in dependence upon wavelength or frequency of such light for each of at least two mutually orthogonal polarization axes in a plane perpendicular to the propagation axis of the light leaving the device. The spectra are used to compute Stokes parameters s1, s2 and |s3| for each of a plurality of wavelengths within the bandwidth of the broadband light.

Abstract: An all-reflective optical system uses a mirror with a hole to transmit a focused laser beam to an on-axis elliptical mirror. The reflected beam from the ellipse is predominately reflected off the mirror with a hole and focused to a distant adjustable focus. This focus spot can be positioned by X-Y scanning mirrors.

Abstract: An optical time domain reflectometer suitable for determining its front panel insertion loss comprises a four-port coupler having first and second ports connected to a light source and an optical detector, respectively, and third and fourth ports connected to a front panel connector and a reference reflector, respectively. In use, a fiber-under-test is connected to the front panel connector. The coupler splits light from the light source between the front panel connector and the reference reflector and couples light returning from the front panel connector and reflector to the detector. The optical path between the front panel connector and the coupler is longer than the optical path between the reference reflector and the coupler by such a distance that a Fresnel reflection pulse from the reference reflector, produced by a pulse emitted by the light source, will be received by the detector before a corresponding reflection pulse returned from the front panel connector.

Abstract: Attenuation of an optical fiber is measured by transmitting an optical signal having a predetermined wavelength to the fiber, and FSK modulating the optical signal with information identifying the wavelength and transmitted power of the optical signal. At a receiver, the optical signal is detected and the information is recovered by demodulation. Wavelength-dependent sensitivity information for the detector is read from a store in dependence upon the wavelength information and used to control the gain of an amplifier for amplifying a subsequently transmitted continuous wave optical signal used for attenuation measurement. The received power level of this optical signal is converted into a digital value and used with the transmitted power information to determine the fiber attenuation at the predetermined wavelength. Reference power levels are determined by connecting a jumper between a port and an external detector.

Abstract: Attenuation of an optical fiber is measured by transmitting an optical signal having a predetermined wavelength to the fiber, and FSK modulating the optical signal with information identifying the wavelength and transmitted power of the optical signal. At a receiver, the optical signal is detected and the information is recovered by demodulation. Wavelength-dependent sensitivity information for the detector is read from a store in dependence upon the wavelength information and used to control the gain of an amplifier for amplifying a subsequently transmitted continuous wave optical signal used for attenuation measurement. The received power level of this optical signal is converted into a digital value and used with the transmitted power information to determine the fiber attenuation at the predetermined wavelength.

Abstract: The invention relates to a non-contact laser engraving apparatus and process. A laser beam is directed onto a work piece by a mask arrangement. The mask can be transparent or reflective. Optical means are used to transfer the laser beam and thus the image produced by the mask onto the work piece. In one embodiment parallel support tables hold the mask and the work piece in fixed, spaced apart, parallel arrangement. The support tables and/or the laser beam source are moved relative to each other such that the beam scans the mask and thus the work piece.