This work reports the results of bandwidth measurements and tests, performed for earlier on designed and fabricated pilot lengths of new silica laser-optimized graded-index multimode fibers (LOMFs) with extremely enlarged core diameter up to 100 μm and "typical" "telecommunication" cladding diameter 125 μm. Presented optical fibers are targeted for harsh environment short-range multi-Gigabit onboard cable systems and industrial networks. Proposed LOMF 100/125 differs by specially optimized graded refractive index profile, that provides low differential mode delay (DMD) for selected guided modes. We present some results of tests, performed for fabricated pilot 520 m length of described LOMF 100/125, focused on researches of bandwidth features. They contain DMD map and transfer function measurement as well as 10GBase-LX/SX channels eye-diagram and bit-error-ratio reports with following direct detection of the maximal acceptable optical fiber length for guaranteed 10Gbps channel supporting.
A novel method of optical image registration using matrix of piezoelectric crystals is introduced. This technique allows measurement of beam profiles without using attenuation systems even at high power levels of incident radi- ation. Each element of the sensor matrix is the crystal piezoelectric resonator that has its own set of eigenmodes, which frequencies strongly depend on temperature. Due to an inverse piezoelectric effect the eigenmodes can be excited noncontactly via the application of the probe radiofrequency electric field providing that its frequency corresponds to any of the crystal eigenmode frequencies. Due to the residual optical absorption each element is heated in compliance with the incident radiation power. A calibration procedure is preliminary performed by transmitting collimated laser radiation separately through each single matrix element.
Most modern systems of the optical image registration are based on the matrices of photosensitive semiconductor heterostructures. However, measurement of radiation intensities up to several MW/cm2 -level using such detectors is a great challenge because semiconductor elements have low optical damage threshold. Reflecting or absorbing filters that can be used for attenuation of radiation intensity, as a rule, distort beam profile. Furthermore, semiconductor based devices have relatively narrow measurement wavelength bandwidth.
We introduce a novel matrix method of optical image registration. This approach doesn’t require any attenuation when measuring high radiation intensities. A sensitive element is the matrix made of thin transparent piezoelectric crystals that absorb just a small part of incident optical power. Each crystal element has its own set of intrinsic (acoustic) vibration modes. These modes can be exited due to the inverse piezoelectric effect when the external electric field is applied to the crystal sample providing that the field frequency corresponds to one of the vibration mode frequencies. Such piezoelectric resonances (PR) can be observed by measuring the radiofrequency response spectrum of the crystal placed between the capacitor plates. PR frequencies strongly depend on the crystal temperature. Temperature calibration of PR frequencies is conducted in the uniform heating conditions. In the case a crystal matrix is exposed to the laser radiation the incident power can be obtained separately for each crystal element by measuring its PR frequency kinetics providing that the optical absorption coefficient is known. The operating wavelength range of such sensor is restricted by the transmission bandwidth of the applied crystals.
A plane matrix constituting of LiNbO3 crystals was assembled in order to demonstrate the possibility of application of the proposed approach. The crystal elements were placed between two electrodes forming a capacitor which was interconnected to the lock-in detection system. The radiofrequency response to the applied voltage from the generator was measured simultaneously for all elements.
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