Space-domain lock-in amplifier based on a liquid-crystal spatial light modulator

Lousberg, Grégory; Lundeberg, L.D.A.; Boïko, D. L.; Kapon, E.

doi:10.1364/ol.31.000990

Cited by 8 publications

(10 citation statements)

References 15 publications

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“…We employ Young's interference measurements between pairs of array elements by using a configurable aperture generator based on a liquid crystal spatial light modulator. 8 We observe a decay of the mutual coherence with increasing distance between array VCSELs, as well as deviations from perfect phase difference between adjacent emitters expected for the highest-order supermode. Possible origins of these coherence features are discussed.…”

Section: -5mentioning

confidence: 63%

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Spatial coherence measurements in arrays of coupled vertical cavity surface emitting lasers

Lundeberg

Lousberg

Boïko

et al. 2007

Applied Physics Letters

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The spatial coherence and the optical phase distribution across a two-dimensional ͑2D͒ photonic crystal implemented with coupled arrays of vertical cavity surface emitting lasers ͑VCSELs͒ are experimentally characterized. This is achieved by performing Young's interference experiments between pairs of array elements using a spatial light modulator arrangement. In contrast to far-field measurements that provide information only on the global spatial coherence, this approach can yield full mapping of the complex degree of spatial coherence. Examples of such analysis are presented for nominally uniform one-dimensional and 2D arrays of coupled VCSELs and possible mechanisms of the observed coherence degradation are discussed. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2431474͔The output power of single-mode vertical cavity surface emitting lasers ͑VCSELs͒ is typically limited to a few milliwatts because of their small aperture area required for higher-order spatial mode suppression.1 Increasing the aperture size leads to poor selection between spatial modes and, above a certain size, results in uncontrolled filamentation, which limits the output power and degrades the spatial coherence and beam quality of the device. The problem of filamentation can be overcome by coupling a large number of single-mode VCSEL, forming two-dimensional ͑2D͒ arrays of phase-locked emitters. [2][3][4][5] In addition, these arrays exhibit a high degree of spatial coherence, as inferred from their nearly diffraction limited, four-lobed far-field patterns, which indicate that they oscillate predominantly at the lowest loss out-of-phase supermode. 2-5Evaluating the features of spatial coherence of coupled-VCSEL arrays is important not only for optimizing their coupling but also for developing functionalities that rely on such coherence. An example of such application is beam steering, where control over the mutual phase of the emitters is necessary.The spatial coherence in phase-locked VCSEL arrays has traditionally been evaluated using measurements of their far-field patterns 2,3 complemented by model calculations of their supermodes. 4,5 However, this approach yields information only on the global coherence properties of the array, in particular, the deviation of the beam pattern from the expected diffraction limited distribution. Moreover, such analysis generally cannot give direct indications on the mechanisms of coherence degradation. Spectral analysis of such arrays, e.g., using spectrally resolved far-field patterns or spatially resolved emission spectra, could give more indications on spatial coherence, but is difficult due to the small spectral splitting of the supermodes in large arrays.A more complete evaluation of the spatial coherence across a VCSEL array would be to measure the complex degree of spatial coherence ␥͑x , y ; xЈ , yЈ͒ between pairs of points in the array plane ͑x , y͒. This can be accomplished by performing Young's interference experiments, in which the interference pattern corresponding to two selected...

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Section: -5mentioning

confidence: 63%

“…8. The near-field pattern of the array was imaged on the spatial light modulator, which was programed to select the desired VCSEL pairs.…”

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confidence: 99%

Spatial coherence measurements in arrays of coupled vertical cavity surface emitting lasers

Lundeberg

Lousberg

Boïko

et al. 2007

Applied Physics Letters

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“…It uses spatially modulated light source to create structured illumination with adjustable patterns that effectively samples at multiple points in the space-frequency domain [80, 81, 82]. In terms of instrumentation, spatial modulation can be achieved in a number of different ways, e.g., by using glass templates [83], micro-mirror arrays [80], liquid crystal devices [84, 85], or potentially other devices, e.g., [86, 87].…”

Section: Signal Modulationmentioning

confidence: 99%

“…A special application of the Fourier method is the so-called lock-in method, which, by synchronizing the timing of photo-detection to that of the light pulse train, creates an equivalent narrow-band bandpass filter in the time-frequency domain to dramatically improve the signal-to-background contrast [95]. Analog to that in the time-frequency domain, the lock-in method can also be used in the space-frequency domain to augment the contrast of spatially modulated signals [82]. …”

Section: Signal Modulationmentioning

confidence: 99%

Instrumentation in Diffuse Optical Imaging

Zhang

2014

Photonics

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Diffuse optical imaging is highly versatile and has a very broad range of applications in biology and medicine. It covers diffuse optical tomography, fluorescence diffuse optical tomography, bioluminescence, and a number of other new imaging methods. These methods of diffuse optical imaging have diversified instrument configurations but share the same core physical principle – light propagation in highly diffusive media, i.e., the biological tissue. In this review, the author summarizes the latest development in instrumentation and methodology available to diffuse optical imaging in terms of system architecture, light source, photo-detection, spectral separation, signal modulation, and lastly imaging contrast.

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“…This coherence analysis can be refined by measuring and resolving the contribution of each mode to the emission spectrum. A more complete evaluation demonstrated recently consists in measuring the spatial degree of coherence of each VCSEL pair by performing Young's interference experiments [3]. Remarkably, the mode structure can be analyzed using the mutual coherence function, based on the modal coherence theory discussed by Wolf and Agarwal [4].…”

Section: Imentioning

confidence: 99%

Eigenmode analysis of phased-coupled VCSEL arrays using spatial coherence measurements

Lamothe¹,

Lundeberg²,

Kapon³

2011

Opt. Lett.

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We apply the modal coherence theory to evaluate the spatial mode structure of a 2×2 phase-coupled array of vertical cavity surface emitting lasers (VCSELs). The eigenmode structure is extracted for different pump currents by measuring the degree of spatial coherence of all VCSEL pairs in the array. The results reveal the impact of optical disorder and spatial hole burning on the modal discrimination. The approach is useful more generally for the evaluation of spatial mode content of other laser array.

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Space-domain lock-in amplifier based on a liquid-crystal spatial light modulator

Cited by 8 publications

References 15 publications

Spatial coherence measurements in arrays of coupled vertical cavity surface emitting lasers

Spatial coherence measurements in arrays of coupled vertical cavity surface emitting lasers

Instrumentation in Diffuse Optical Imaging

Eigenmode analysis of phased-coupled VCSEL arrays using spatial coherence measurements

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