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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

Controlling the JSI at the source.(a) In a five-resonator photon-pair source, this 2D plot obtained by numerical simulation shows the contours of the function Ψ defined in equation (1) as a function of the wavelengths of the two generated photons, relative to the band centre. Shown to the top and the right are the transmission amplitudes in the two bands. The number of transmission resonances in each band is equal to the number of resonators (five) and, together, they form 5 × 5=25 phase-matching points in the 2D plane at which photon-pair generation can be efficient. The wavelength of the pump determines which diagonally oriented slices of this phase-matching diagram comprise the JSI of the photon pair, with three particular possibilities for the JSI marked by regions ‘b’, ‘c’ and ‘d’. (b) The JSI of the two-photon state when the pump wavelength is positioned at the edge of its transmission band, showing a state with one major peak in the JSI. Such a state is suitable for heralding1728. (c) The JSI when the pump wavelength is positioned in the middle of its transmission band, showing a state with five distinct peaks, which is suitable for an entangled pair source1729. (d) The JSI when the pump is tuned to another resonance in its transmission band, with three peaks as an intermediate case. In each figure, the horizontal axes are in units of normalized wavelength (one unit equals the separation between adjacent peaks) measured relative to the band centre, and the vertical axes and colour scales are normalized so that the area under the JSI is unity. The K values represent the Schmidt numbers, that is, the dimensionality of the singular-value decomposition of the JSI.
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f1: Controlling the JSI at the source.(a) In a five-resonator photon-pair source, this 2D plot obtained by numerical simulation shows the contours of the function Ψ defined in equation (1) as a function of the wavelengths of the two generated photons, relative to the band centre. Shown to the top and the right are the transmission amplitudes in the two bands. The number of transmission resonances in each band is equal to the number of resonators (five) and, together, they form 5 × 5=25 phase-matching points in the 2D plane at which photon-pair generation can be efficient. The wavelength of the pump determines which diagonally oriented slices of this phase-matching diagram comprise the JSI of the photon pair, with three particular possibilities for the JSI marked by regions ‘b’, ‘c’ and ‘d’. (b) The JSI of the two-photon state when the pump wavelength is positioned at the edge of its transmission band, showing a state with one major peak in the JSI. Such a state is suitable for heralding1728. (c) The JSI when the pump wavelength is positioned in the middle of its transmission band, showing a state with five distinct peaks, which is suitable for an entangled pair source1729. (d) The JSI when the pump is tuned to another resonance in its transmission band, with three peaks as an intermediate case. In each figure, the horizontal axes are in units of normalized wavelength (one unit equals the separation between adjacent peaks) measured relative to the band centre, and the vertical axes and colour scales are normalized so that the area under the JSI is unity. The K values represent the Schmidt numbers, that is, the dimensionality of the singular-value decomposition of the JSI.

Mentions: Before discussing the experimental results, we first discuss theoretically how the JSI can be varied, and why the coupled-resonator structure is useful. In any pair source device, simultaneous energy-matching and phase-matching requirements determine the JSI of the two-photon state generated by a pump beam of a particular frequency. Our device consists of a periodic sequence of coupled microresonators, in which optical excitations propagate from input to output by nearest-neighbour coupling, similar to the tight-binding model of propagation in solid-state physics31. The coupling of N resonators creates N transmission resonances within each passband (see Supplementary Fig. 2). It is important to realize that each of the N resonators contribute via coherent superposition to each (Bloch) resonance, that is, these N resonances are the ‘supermodes’ of the combined structure, not N individual, uncoupled resonances. Figure 1a represents an idealized map of Ψ in terms of the quantity defined in the integrand of equation (1), that is, the product of the two-dimensional phase-matching points for N=5 coupled microresonators and the transfer functions at the two passbands of the generated photon pair. Along the horizontal and vertical axes, we have plotted the transmission spectra at the and passbands, showing the five supermode transmission resonances. When the pump frequency is fixed, we obtain the equation , where is the pump frequency and and are the frequencies of the spontaneously generated photon pair. In the two-dimensional (2D) plane shown in Fig. 1a; this equation defines the JSI to be one of the diagonally oriented boxes shown with dotted white lines. Different choices of result in the selection of different regions and correspondingly different JSIs, for example, the regions marked by the labels ‘b', ‘c' and ‘d' correspond to the JSIs shown in Fig. 1b–d, respectively. (Other choices are also possible, corresponding to the unmarked diagonals in Fig. 1a).


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

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

Controlling the JSI at the source.(a) In a five-resonator photon-pair source, this 2D plot obtained by numerical simulation shows the contours of the function Ψ defined in equation (1) as a function of the wavelengths of the two generated photons, relative to the band centre. Shown to the top and the right are the transmission amplitudes in the two bands. The number of transmission resonances in each band is equal to the number of resonators (five) and, together, they form 5 × 5=25 phase-matching points in the 2D plane at which photon-pair generation can be efficient. The wavelength of the pump determines which diagonally oriented slices of this phase-matching diagram comprise the JSI of the photon pair, with three particular possibilities for the JSI marked by regions ‘b’, ‘c’ and ‘d’. (b) The JSI of the two-photon state when the pump wavelength is positioned at the edge of its transmission band, showing a state with one major peak in the JSI. Such a state is suitable for heralding1728. (c) The JSI when the pump wavelength is positioned in the middle of its transmission band, showing a state with five distinct peaks, which is suitable for an entangled pair source1729. (d) The JSI when the pump is tuned to another resonance in its transmission band, with three peaks as an intermediate case. In each figure, the horizontal axes are in units of normalized wavelength (one unit equals the separation between adjacent peaks) measured relative to the band centre, and the vertical axes and colour scales are normalized so that the area under the JSI is unity. The K values represent the Schmidt numbers, that is, the dimensionality of the singular-value decomposition of the JSI.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Controlling the JSI at the source.(a) In a five-resonator photon-pair source, this 2D plot obtained by numerical simulation shows the contours of the function Ψ defined in equation (1) as a function of the wavelengths of the two generated photons, relative to the band centre. Shown to the top and the right are the transmission amplitudes in the two bands. The number of transmission resonances in each band is equal to the number of resonators (five) and, together, they form 5 × 5=25 phase-matching points in the 2D plane at which photon-pair generation can be efficient. The wavelength of the pump determines which diagonally oriented slices of this phase-matching diagram comprise the JSI of the photon pair, with three particular possibilities for the JSI marked by regions ‘b’, ‘c’ and ‘d’. (b) The JSI of the two-photon state when the pump wavelength is positioned at the edge of its transmission band, showing a state with one major peak in the JSI. Such a state is suitable for heralding1728. (c) The JSI when the pump wavelength is positioned in the middle of its transmission band, showing a state with five distinct peaks, which is suitable for an entangled pair source1729. (d) The JSI when the pump is tuned to another resonance in its transmission band, with three peaks as an intermediate case. In each figure, the horizontal axes are in units of normalized wavelength (one unit equals the separation between adjacent peaks) measured relative to the band centre, and the vertical axes and colour scales are normalized so that the area under the JSI is unity. The K values represent the Schmidt numbers, that is, the dimensionality of the singular-value decomposition of the JSI.
Mentions: Before discussing the experimental results, we first discuss theoretically how the JSI can be varied, and why the coupled-resonator structure is useful. In any pair source device, simultaneous energy-matching and phase-matching requirements determine the JSI of the two-photon state generated by a pump beam of a particular frequency. Our device consists of a periodic sequence of coupled microresonators, in which optical excitations propagate from input to output by nearest-neighbour coupling, similar to the tight-binding model of propagation in solid-state physics31. The coupling of N resonators creates N transmission resonances within each passband (see Supplementary Fig. 2). It is important to realize that each of the N resonators contribute via coherent superposition to each (Bloch) resonance, that is, these N resonances are the ‘supermodes’ of the combined structure, not N individual, uncoupled resonances. Figure 1a represents an idealized map of Ψ in terms of the quantity defined in the integrand of equation (1), that is, the product of the two-dimensional phase-matching points for N=5 coupled microresonators and the transfer functions at the two passbands of the generated photon pair. Along the horizontal and vertical axes, we have plotted the transmission spectra at the and passbands, showing the five supermode transmission resonances. When the pump frequency is fixed, we obtain the equation , where is the pump frequency and and are the frequencies of the spontaneously generated photon pair. In the two-dimensional (2D) plane shown in Fig. 1a; this equation defines the JSI to be one of the diagonally oriented boxes shown with dotted white lines. Different choices of result in the selection of different regions and correspondingly different JSIs, for example, the regions marked by the labels ‘b', ‘c' and ‘d' correspond to the JSIs shown in Fig. 1b–d, respectively. (Other choices are also possible, corresponding to the unmarked diagonals in Fig. 1a).

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