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Controlling the spectrum of photons generated on a silicon nanophotonic chip.

Kumar R, Ong JR, Savanier M, Mookherjea S - Nat Commun (2014)

Bottom Line: Here we design a photon-pair source, consisting of planar lightwave components fabricated using CMOS-compatible lithography in silicon, which has the capability to vary the JSI.By controlling either the optical pump wavelength, or the temperature of the chip, we demonstrate the ability to select different JSIs, with a large variation in the Schmidt number.Such control can benefit high-dimensional communications where detector-timing constraints can be relaxed by realizing a large Schmidt number in a small frequency range.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California 92093, USA.

ABSTRACT
Directly modulated semiconductor lasers are widely used, compact light sources in optical communications. Semiconductors can also be used to generate nonclassical light; in fact, CMOS-compatible silicon chips can be used to generate pairs of single photons at room temperature. Unlike the classical laser, the photon-pair source requires control over a two-dimensional joint spectral intensity (JSI) and it is not possible to process the photons separately, as this could destroy the entanglement. Here we design a photon-pair source, consisting of planar lightwave components fabricated using CMOS-compatible lithography in silicon, which has the capability to vary the JSI. By controlling either the optical pump wavelength, or the temperature of the chip, we demonstrate the ability to select different JSIs, with a large variation in the Schmidt number. Such control can benefit high-dimensional communications where detector-timing constraints can be relaxed by realizing a large Schmidt number in a small frequency range.

No MeSH data available.


Related in: MedlinePlus

JSI.(a) The JSI can be interpreted as the section of the N × N array of phase-matching points in the  plane which are selected by the input pump (of a particular energy ) based on the principle of energy conservation to lie along the diagonal regions shown by dotted white lines. The width of the selected region that defines the JSI is given by the spectral width of the pump envelope . The pump itself must be resonant with one of the supermodes in its transmission band; the possible choices of the pump frequency are shown by the black circles along the diagonal line, defined by . The JSI comprises from 1 upto N peaks; here N was taken as 11 in this representative calculation of the device used in the experiment, which consisted of 11 coupled silicon microring resonators. The horizontal axis represents the optical frequency of the ‘signal’ photon, and the vertical axis represents the optical frequency of the ‘idler’ photon; in both cases, the (ideal) transmission of one passband is shown to the top and right edges of the plot, respectively. (b) The experimentally measured transmission spectrum at the signal and idler passbands shows lower transmission at some of the band-edge resonances compared with the band centre, and a nonuniform spacing between the peaks because of fabrication disorder that affects the precise coupling coefficients between the resonators. Correspondingly, the calculated JSI shows about five peaks should have higher brightness than the others. Whereas all the peaks would be visible if the measurement process was noiseless, it is expected that the measured JSI in this device show between one and five peaks.
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f2: JSI.(a) The JSI can be interpreted as the section of the N × N array of phase-matching points in the plane which are selected by the input pump (of a particular energy ) based on the principle of energy conservation to lie along the diagonal regions shown by dotted white lines. The width of the selected region that defines the JSI is given by the spectral width of the pump envelope . The pump itself must be resonant with one of the supermodes in its transmission band; the possible choices of the pump frequency are shown by the black circles along the diagonal line, defined by . The JSI comprises from 1 upto N peaks; here N was taken as 11 in this representative calculation of the device used in the experiment, which consisted of 11 coupled silicon microring resonators. The horizontal axis represents the optical frequency of the ‘signal’ photon, and the vertical axis represents the optical frequency of the ‘idler’ photon; in both cases, the (ideal) transmission of one passband is shown to the top and right edges of the plot, respectively. (b) The experimentally measured transmission spectrum at the signal and idler passbands shows lower transmission at some of the band-edge resonances compared with the band centre, and a nonuniform spacing between the peaks because of fabrication disorder that affects the precise coupling coefficients between the resonators. Correspondingly, the calculated JSI shows about five peaks should have higher brightness than the others. Whereas all the peaks would be visible if the measurement process was noiseless, it is expected that the measured JSI in this device show between one and five peaks.

Mentions: Figure 2a shows the construction of the JSI using the calculated transfer function of an 11-ring coupled-resonator structure, which models the device that was fabricated. The peaks are not of the same size and strengths because near the band edges, the resonances are sharper and the transmission magnitude decreases (see Supplementary Fig. 3). In recent work, Helt et al.34 have analysed the effect of loss in pair generation using SPDC where the fundamental and second-harmonic wavelengths are widely separated; a comparable analysis of loss in SFWM, where the pump, signal and idler wavelengths are much closer, remains to be developed. The JSI expected from the measured transmission at the signal and idler wavelengths is shown in Fig. 2b; this figure differs from the ideal because of at least two possible reasons: (i) the increased loss at band edges because of the increase in the slowing factor near the band-edge, (ii) errors in fabrication resulting in a different coupling coefficient than intended between the feeder waveguides and the first/last microring resonators (that is, imperfect apodization). Whereas these issues can be addressed with improved fabrication, here we expect that the JSI can be varied between one and five peaks. As discussed in Supplementary Note 2, the JSI can consist of any number of peaks ranging from 1 to N if the pump spectral width is narrow, and upto N2 if the pump spectral width can be changed. Chains of upto N =235 coupled silicon microring resonators have been demonstrated with an end-to-end spectral width of the transmission band of only ~5 nm33; however, those structures are not suitable for pair generation because, although the propagation loss per ring was quite low (~0.08 dB per ring), the total transmission loss was not low enough for such long chains.


Controlling the spectrum of photons generated on a silicon nanophotonic chip.

Kumar R, Ong JR, Savanier M, Mookherjea S - Nat Commun (2014)

JSI.(a) The JSI can be interpreted as the section of the N × N array of phase-matching points in the  plane which are selected by the input pump (of a particular energy ) based on the principle of energy conservation to lie along the diagonal regions shown by dotted white lines. The width of the selected region that defines the JSI is given by the spectral width of the pump envelope . The pump itself must be resonant with one of the supermodes in its transmission band; the possible choices of the pump frequency are shown by the black circles along the diagonal line, defined by . The JSI comprises from 1 upto N peaks; here N was taken as 11 in this representative calculation of the device used in the experiment, which consisted of 11 coupled silicon microring resonators. The horizontal axis represents the optical frequency of the ‘signal’ photon, and the vertical axis represents the optical frequency of the ‘idler’ photon; in both cases, the (ideal) transmission of one passband is shown to the top and right edges of the plot, respectively. (b) The experimentally measured transmission spectrum at the signal and idler passbands shows lower transmission at some of the band-edge resonances compared with the band centre, and a nonuniform spacing between the peaks because of fabrication disorder that affects the precise coupling coefficients between the resonators. Correspondingly, the calculated JSI shows about five peaks should have higher brightness than the others. Whereas all the peaks would be visible if the measurement process was noiseless, it is expected that the measured JSI in this device show between one and five peaks.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4263184&req=5

f2: JSI.(a) The JSI can be interpreted as the section of the N × N array of phase-matching points in the plane which are selected by the input pump (of a particular energy ) based on the principle of energy conservation to lie along the diagonal regions shown by dotted white lines. The width of the selected region that defines the JSI is given by the spectral width of the pump envelope . The pump itself must be resonant with one of the supermodes in its transmission band; the possible choices of the pump frequency are shown by the black circles along the diagonal line, defined by . The JSI comprises from 1 upto N peaks; here N was taken as 11 in this representative calculation of the device used in the experiment, which consisted of 11 coupled silicon microring resonators. The horizontal axis represents the optical frequency of the ‘signal’ photon, and the vertical axis represents the optical frequency of the ‘idler’ photon; in both cases, the (ideal) transmission of one passband is shown to the top and right edges of the plot, respectively. (b) The experimentally measured transmission spectrum at the signal and idler passbands shows lower transmission at some of the band-edge resonances compared with the band centre, and a nonuniform spacing between the peaks because of fabrication disorder that affects the precise coupling coefficients between the resonators. Correspondingly, the calculated JSI shows about five peaks should have higher brightness than the others. Whereas all the peaks would be visible if the measurement process was noiseless, it is expected that the measured JSI in this device show between one and five peaks.
Mentions: Figure 2a shows the construction of the JSI using the calculated transfer function of an 11-ring coupled-resonator structure, which models the device that was fabricated. The peaks are not of the same size and strengths because near the band edges, the resonances are sharper and the transmission magnitude decreases (see Supplementary Fig. 3). In recent work, Helt et al.34 have analysed the effect of loss in pair generation using SPDC where the fundamental and second-harmonic wavelengths are widely separated; a comparable analysis of loss in SFWM, where the pump, signal and idler wavelengths are much closer, remains to be developed. The JSI expected from the measured transmission at the signal and idler wavelengths is shown in Fig. 2b; this figure differs from the ideal because of at least two possible reasons: (i) the increased loss at band edges because of the increase in the slowing factor near the band-edge, (ii) errors in fabrication resulting in a different coupling coefficient than intended between the feeder waveguides and the first/last microring resonators (that is, imperfect apodization). Whereas these issues can be addressed with improved fabrication, here we expect that the JSI can be varied between one and five peaks. As discussed in Supplementary Note 2, the JSI can consist of any number of peaks ranging from 1 to N if the pump spectral width is narrow, and upto N2 if the pump spectral width can be changed. Chains of upto N =235 coupled silicon microring resonators have been demonstrated with an end-to-end spectral width of the transmission band of only ~5 nm33; however, those structures are not suitable for pair generation because, although the propagation loss per ring was quite low (~0.08 dB per ring), the total transmission loss was not low enough for such long chains.

Bottom Line: Here we design a photon-pair source, consisting of planar lightwave components fabricated using CMOS-compatible lithography in silicon, which has the capability to vary the JSI.By controlling either the optical pump wavelength, or the temperature of the chip, we demonstrate the ability to select different JSIs, with a large variation in the Schmidt number.Such control can benefit high-dimensional communications where detector-timing constraints can be relaxed by realizing a large Schmidt number in a small frequency range.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California 92093, USA.

ABSTRACT
Directly modulated semiconductor lasers are widely used, compact light sources in optical communications. Semiconductors can also be used to generate nonclassical light; in fact, CMOS-compatible silicon chips can be used to generate pairs of single photons at room temperature. Unlike the classical laser, the photon-pair source requires control over a two-dimensional joint spectral intensity (JSI) and it is not possible to process the photons separately, as this could destroy the entanglement. Here we design a photon-pair source, consisting of planar lightwave components fabricated using CMOS-compatible lithography in silicon, which has the capability to vary the JSI. By controlling either the optical pump wavelength, or the temperature of the chip, we demonstrate the ability to select different JSIs, with a large variation in the Schmidt number. Such control can benefit high-dimensional communications where detector-timing constraints can be relaxed by realizing a large Schmidt number in a small frequency range.

No MeSH data available.


Related in: MedlinePlus