Showing papers by "Wayne V. Sorin published in 1992"

A simple intensity noise reduction technique for optical low-coherence reflectometry

Abstract: It is shown that by attenuating the reference power in an optical low-coherence reflectometry (OLCR) measurement, the reflection sensitivity can be improved, even though, in many other types of optical measurements, sensitivity is improved as optical power is increased. The difference is due to the presence of inherent intensity noise associated with low-coherence sources, which can dominate over shot noise at optical powers that are as low as 1 mu W. A reflection sensitivity of -146 dB is demonstrated using this technique. >

Simultaneous thickness and group index measurement using optical low-coherence reflectometry

Abstract: Using high-resolution optical reflectometry, group index and physical thickness can both be determined by precisely measuring optical time delays through a sample. Optical low-coherence reflectometry offers both the high-spatial resolution and large dynamic range required to perform accurate measurements using this technique. >

Measurement of Rayleigh backscattering at 1.55 mu m with 32 mu m spatial resolution

Abstract: Rayleigh backscattering at a wavelength of 1.55 mu m is measured in standard single-mode fiber with a spatial resolution of 32 mu m and a dynamic range of over 30 dB. A minimum reflection sensitivity of -148 dB is the best reported to date using optical low-coherence reflectometry. >

Frequency domain analysis of an optical FM discriminator

Abstract: Measurement of optical phase and frequency deviations using a frequency-domain network analysis approach is described. The frequency domain transfer functions are given which relate the conversion of optical phase, frequency, and intensity modulation into photodetector current after passing through a quadrature biased Mach-Zehnder interferometer. It is shown that the error term in the phase and frequency transfer functions depends only to second order on any accompanying intensity modulation. Experimental data are given illustrating the analytical results. >

Method and apparatus for calibrating a polarization independent optical coherence domain reflectometer

Abstract: An optical coherence-domain reflectometry system provides an interferometer driven by a broadband incoherent light source with the device under test connected to one arm of the interferometer and a movable scanning mirror in the other arm providing a reference signal. The mirror moves at a controlled velocity to produce a Doppler shift in the reference signal frequency. The interference signal is detected and measured by a receiver. In the case where the receiver is a polarization diversity receiver, an intensity modulator and a polarization controller are incorporated into the reflectometer for use in calibrating the receiver. Calibration is also provided for a single photodetector receiver.

Coherent FMCW Reflectometry Using a Piezoelectrically Tuned Nd:YAG Ring Laser

Abstract: Coherent optical implementations of the FMCW technique [1] depend on the interferometric mixing of an optical signal probing the network under test with a reference signal obtained from the same source, whose carrier frequency is linearly, and phase-continuously, chirped [2]. Limitations on measurement range may be reduced by the choice of a laser source of long coherence length, as demonstrated in Ref. 3, but the temperature tuning employed in that particular case is relatively slow and inconvenient. A more serious problem is spatial resolution degradation due to residual nonlinearities in the frequency chirp, but this may be significantly reduced by incorporating a reference interferometer in the measurement system to track the nonlinearity and compensate for it [4]. This paper describes a coherent optical FMCW system that uses piezoelectric rather than thermal tuning of a source of long coherence length, in a fiberoptic network which includes a reference interferometer, triggering data capture by a system with a Fast Fourier Transform capability.

Optical receiver design for high optical return loss

Abstract: A new fiber pigtailed optical receiver design using a single gradient-index rod lens with a beveled exit face achieved a broadband optical return loss of >65 dB, which was limited by the diffuse reflection from the photodetector front surface. By contrast the optical return loss for a receiver with an unbeveled lens exit face and an on-axis optical path was limited to a smaller value by the specular reflection from the lens exit face.