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| 2. |
- Engström, David, 1976, et al.
(författare)
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Analog low-loss full-range phase modulation by utilizing a V-shaped switched ferroelectric liquid-crystal cell in reflective mode
- 2006
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 31:19, s. 2906-2908
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the analog (V-shaped switching) mode in ferroelectric liquid crystals in reflective mode for analog phase modulation applications. We have found that several combinations of cell thicknesses and input polarization states exist for which near-lossless analog phase modulation with a range of ~2π rad is obtained, and we demonstrate one such combination experimentally. Despite a slight deviation from the ideal conditions, e.g., the tilt angle was 38° instead of the desired 45°, virtually pure 1.6π rad phase modulation was obtained; the measured values agree very well with our numerical simulations of the real device.
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| 3. |
- Engström, David, 1976, et al.
(författare)
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Diffraction-based determination of the phase modulation for general spatial light modulators
- 2006
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Ingår i: Applied Optics. - 1539-4522. ; 45:28, s. 7195-7204
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Tidskriftsartikel (refereegranskat)abstract
- We describe a characterization method based on diffraction for obtaining the phase response of spatial light modulators (SLMs), which in general exhibit both amplitude and phase modulation. Compared with the conventional interferometer-based approach, the method is characterized by a simple setup that enables in situ measurements, allows for substantial mechanical vibration, and permits the use of a light source with a fairly low temporal coherence. The phase determination is possible even for a SLM with a full amplitude modulation depth, i.e., even if there are nulls in the amplitude transmission characteristic of the SLM. The method successfully determines phase modulation values in the full 2pi rad range with high accuracy. The experimental work includes comparisons with interferometer measurements as well as a SLM characterization with a light-emitting diode (LED).
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| 5. |
- Engström, David, 1976, et al.
(författare)
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Three-level phase modulator based on orthoconic antiferroelectric liquid crystals
- 2006
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 31:21, s. 3158-3160
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Tidskriftsartikel (refereegranskat)abstract
- Surface-stabilized orthoconic antiferroelectric liquid crystals (OAFLCs) have a director tilt of θ=45° and are, with no field applied, negatively uniaxial with the optic axis perpendicular to the cell substrates. We demonstrate that OAFLCs can be utilized to achieve lossless phase modulation with three almost equidistant phase levels. This turns out to be true also for polymer-stabilized OAFLCs, where the polymer network increases the switching speed of the device without affecting the phase modulation appreciably.
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| 6. |
- Galt, Sheila, 1956, et al.
(författare)
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Demonstration of distortion suppression in photonic time-stretch ADC using back propagation method
- 2007
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Ingår i: MWP 2007 - 2007 IEEE International Topical Meeting on Microwave Photonics. - 1424411688 ; , s. Pages 141-144
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Konferensbidrag (refereegranskat)abstract
- We experimentally demonstrate the performance of the recently proposed "OBP" algorithm based on optical phase retrieval by numerical back-propagation. Using this technique, distortion due to the modulator transfer function as well as the group velocity dispersion in a photonic time-stretch ADC (TS-ADC) can be suppressed, and frequency fading eliminated thanks to the use of a dual output "phase diverse" modulator. The algorithm was tested with a swept input signal frequency from 10 to 50 GHz as well as with a two-tone signal, and is shown to recover the signal even in the presence of fading with a distortion suppression of up to 26 dB. These results also constitute the first experimental demonstration of channel combining in a phase diverse TS-ADC. © 2007 IEEE.
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| 7. |
- Modh, Peter, 1968, et al.
(författare)
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Linear Cascade VCSEL Arrays With High Differential Efficiency and Low Differential Resistance
- 2006
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 18:1, s. 100-102
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated monolithic linear cascade ver- tical-cavity surface-emitting laser (VCSEL) arrays intended for low loss fiber-optic radio-frequency links. Arrays with up to four VCSELs connected in series, with a spacing of 250 m, were fab- ricated on an insulating substrate. A thick layer of BCB was used to facilitate series connection through contact metallization and enable high frequency operation. The threshold current is 0.6 mA, independent of the number of VCSELs in the array. Differential efficiency, maximum output power, voltage, and differential re- sistance scale linearly with the number of VCSELs. For a four VCSEL array, we achieve a high differential efficiency of 160%, a maximum output power of 24 mW, and a low differential resis- tance of 220 . Basic link measurements, using a series connected VCSEL array, a parallel fiber ribbon, and a parallel connected detector array revealed a differential current gain exceeding unity in the low frequency limit.
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| 8. |
- Stigwall, Johan, 1977, et al.
(författare)
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Analysis of the resolution-bandwidth-noise trade-off in wavelength-based photonic analog-to-digital converters
- 2006
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Ingår i: Applied optics. - 0003-6935. ; 45:18, s. 4310-4318
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Tidskriftsartikel (refereegranskat)abstract
- The performance of wavelength-based photonic analog-to-digital converters (ADCs) is theoretically analyzed in terms of resolution and bandwidth as well as of noise tolerance. The analysis applies to any photonic ADC in which the analog input signal is converted into the wavelength of an optical carrier, but special emphasis is put on the spectrometerlike setup in which the wavelength is mapped to a spatial spot position. The binary output signals are then retrieved by an array of fan-out diffractive optical elements that redirect the beam onto the correct detectors. In particular, the case when the input signal controls the wavelength directly such that it will chirp in frequency during each sampling pulse or interval is studied. This chirping obviously broadens the spot on the diffractive optical element array; the effect of this broadening on noise tolerance and comparator accuracy is analytically analyzed, and accurate numerical calculations of the probability of error are presented.
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| 9. |
- Stigwall, Johan, 1977, et al.
(författare)
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Demonstration and analysis of a 40 gigasample/s interferometric analog-to-digital converter
- 2006
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 24:3, s. 1247-1256
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Tidskriftsartikel (refereegranskat)abstract
- A novel interferometric scheme for photonic analog-to-digital conversion is for the first time experimentally demonstrated at a real-time sample rate of 40 gigasamples/s. The scheme includes sampling as well as binary encoding, and the input signal in the experiment was a 1.25-GHz sinusoidal tone that was successfully digitized with a nominal resolution of 21 digital levels. Single-sample measurements yielded an effective number of bits (ENOB) of 2.6, which was limited by thermal detection noise while multisample averaged measurements resulted in an ENOB of 3.6 bits, mainly limited by phase drift. Apart from the experimental results, this paper covers an extensive theoretical analysis of the system, including calculations on the fundamental maximum bandwidth, the required optical power, the generated binary code, and its error robustness, as well as the impact of detection noise on the signal-to-noise ratio of the digitized signal. The major benefits of this interferometric scheme are that only one standard phase modulator is required and that the phase swing does not have to be larger than /spl plusmn//spl pi/ to reach the full digital value space.
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