R.P. Salathe

Optical coherence topography based on a two-dimensional smart detector array

A low-coherence reflectometer based on a conventional Michelson interferometer and a novel silicon detector chip with a two-dimensional array of pixels that allows parallel heterodyne detection is presented. We demonstrate acquisition of three-dimensional images with more than 100,000 voxels per scan at a sensitivity of -58 dB and a rate of 6 Hz.

Video-rate optical low-coherence reflectometry based on a linear smart detector array.

A low-coherence reflectometer based on a conventional Michelson interferometer and a novel silicon detector chip that allows parallel heterodyne detection is presented. Cross-sectional images of 64x256 pixels covering an area of 1.92 mm x 1.3 mm are acquired at video rate and with a sensitivity close to the shot-noise limit. Applications in surface profiling and thickness measurement are demonstrated.

Parallel optical coherence tomography in scattering samples using a two-dimensional smart-pixel detector array

Parallel optical coherence tomography in scattering samples is demonstrated using a 58 x 58 smart-pixel detector array. A femtosecond mode-locked Ti:Sapphire laser in combination with a free space Michelson interferometer was employed to achieve 4 mum longitudinal resolution and 9 mum transverse resolution on a 260 x 260 mum field of view. We imaged a resolution target covered by an intralipid solution with different scattering coefficients as well as onion cells

Spatially incoherent illumination as a mechanism for cross-talk suppression in wide-field optical coherence tomography

Comparison of two illumination modes for wide-field optical coherence tomography has revealed that spatially coherent illumination generates coherent cross talk, causing significant image degradation, and that spatially incoherent illumination, with an adequate interferometer design, provides an efficient mechanism for suppression of coherent cross talk. This is shown by comparison of a pulsed laser with a thermal light source for a U.S. Air Force resolution target covered with a scattering solution made from microbeads as well as for an ex vivo tooth.

Postfabrication resonance peak positioning of long-period cladding-mode-coupled gratings

A simple, flexible method of postfabrication positioning of resonance wavelengths of long-period cladding-modecoupled gratings is proposed. This method is based on changing the outer fiber diameter. Reducing the diameter by etching the fiber in HF acid shifts the loss peaks to higher wavelengths. A shift as large as 130 nm after 5 min of HF etching was observed for our strongest grating peak, corresponding to the cladding mode HE19. The experimental results are in excellent agreement with model calculations.

UV-irradiation-induced structural transformation of germanoscilicate glass fiber

Raman spectra of germanosilicate core fibers before and after UV irradiation were investigated. Significant changes of the Raman spectra after irradiation indicate transformation of the glass structure. A possible interpretation of the observed changes is proposed.

Air-turbine driven optical low-coherence reflectometry at 28.6-kHz scan repetition rate

An optical low-coherence reflectometer is actuated with an air bearing turbine to show the feasibility of scanning at rates lying typically one order of magnitude above previously reported high-speed scanning systems. The rotation frequency of the air turbine of 427 000 rpm leads to a repetition rate of longitudinal scans of 28.6 kHz. Coherent signals are detected over a distance of 2 mm at a longitudinal scan speed of 175 m/s.

Tunable loss filter based on metal coated long period grating

A tunable loss filter based on a long-period fiber grating and a Ti-Pt coating is presented. Electrical wavelength tuning of 11 nm with an efficiency of 16.4 nm/W and modulation with 2 s rise time were achieved.

Robust and rapid optical low-coherence reflectometer using a polygon mirror

A robust delay line comprising a rotated polygon mirror and a fixed glass parallelepiped is incorporated in an optical low-coherence reflectometer. A high degree of scalability of scan repetitiveness and scan range is obtained by producing the scan rate and scan range by means of a moving and a fixed element. The reflectometer is operated at a scan repetition rate and a scan speed of 2.58 kHz and 37 m/s, respectively.

Self-referenced method for optical path difference calibration in low-coherence interferometry.

A simple method for the calibration of optical path difference modulation in low-coherence interferometry is presented. Spectrally filtering a part of the detected interference signal results in a high-coherence signal that encodes the scan imperfections and permits their correction. The method is self-referenced in the sense that no secondary high-coherence light source is necessary. Using a spectrometer setup for spectral filtering allows for flexibility in both the choice of calibration wavelength and the maximum scan range. To demonstrate the methods usefulness, it is combined with a recently published digital spectral shaping technique to measure the thickness of a pellicle beam splitter with a white-light source.