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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

Experimentally generating photon pairs with different JSIs.Distinctly different JSIs can be obtained by tuning either the chip temperature or the pump wavelength. (a–c) Three JSIs measured with a fixed pump wavelength (1,563.61 nm) while tuning the TEC controlling the chip temperature to 27.7 °C (a), to 30.2 °C (b) and to 37.3 °C (c). (d–f) Three JSIs measured with a fixed TEC temperature setting of 30.2 °C while tuning the pump wavelength to be 1,563.03 nm (d), 1,563.61 nm (e) and 1,563.79 nm (f). In each case, the range of wavelengths over which data were acquired was the same. The Richardson–Lucy algorithm was used to deconvolve the point-spread function of the filters in front of the SPADs with 50 iterations. The Schmidt numbers are K=1.95 (a), 5.72 (b), 7.02 (c), 1.88 (d), 5.72 (e) and 5.47 (f). In each panel, the horizontal axes are in units of normalized wavelength (one unit equals a wavelength separation of 0.6 nm) measured relative to the respective band centre, which for ‘Photon 1’ was 1,548.8 nm and for ‘Photon 2’ was 1,578.7 nm. The vertical axes and colour scales are normalized so that the area under each JSI is unity, reflecting the fact that JSI is a probability density.
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f4: Experimentally generating photon pairs with different JSIs.Distinctly different JSIs can be obtained by tuning either the chip temperature or the pump wavelength. (a–c) Three JSIs measured with a fixed pump wavelength (1,563.61 nm) while tuning the TEC controlling the chip temperature to 27.7 °C (a), to 30.2 °C (b) and to 37.3 °C (c). (d–f) Three JSIs measured with a fixed TEC temperature setting of 30.2 °C while tuning the pump wavelength to be 1,563.03 nm (d), 1,563.61 nm (e) and 1,563.79 nm (f). In each case, the range of wavelengths over which data were acquired was the same. The Richardson–Lucy algorithm was used to deconvolve the point-spread function of the filters in front of the SPADs with 50 iterations. The Schmidt numbers are K=1.95 (a), 5.72 (b), 7.02 (c), 1.88 (d), 5.72 (e) and 5.47 (f). In each panel, the horizontal axes are in units of normalized wavelength (one unit equals a wavelength separation of 0.6 nm) measured relative to the respective band centre, which for ‘Photon 1’ was 1,548.8 nm and for ‘Photon 2’ was 1,578.7 nm. The vertical axes and colour scales are normalized so that the area under each JSI is unity, reflecting the fact that JSI is a probability density.

Mentions: Figure 4 shows that different JSIs were obtained experimentally from the same photon-pair source. In Fig. 4a–c, the optical pump wavelength was kept constant at λp=1,563.61 nm, and the chip temperature was tuned from 27.7 °C (Fig. 4a) to 30.2 °C (Fig. 4b) and to 37.3 °C (Fig. 4c). This range of temperature variations can be achieved by conventional thermoelectric controllers, such as those incorporated within commerical semiconductor lasers1. In Fig. 4d–f, the chip temperature was kept constant at 30.2 °C and the pump wavelength was tuned from 1,563.03 nm (Fig. 4d) to 1,563.61 nm (Fig. 4e) and to 1,563.79 nm (Fig. 4f). This range of wavelength variation required of the pump is comparable to the range of tunability offered in compact commercial tunable semiconductor lasers1, which can therefore be conveniently used to pump the silicon chip. Other different JSIs can also be obtained; however, we limit our report to these three examples because each frame shown in Fig. 4 took many hours to acquire since the optical filters were individually scanned over the 2D grid. Supplementary Note 3 and Supplementary Fig. 4 discuss a measurement example in which the de-blurring algorithm was not needed, for example, to decide between three distinct JSI alternatives, where the measurement took only 30 s. In Fig. 4a,c, the JSI showed a single peak, but because of the elliptical shape of the peak, the Schmidt number K is greater than 1. To reduce K without shaping the pump pulse, the device design should be adjusted to support a slightly broader spectral envelope for the pump pulse. The results of Fig. 4 show that temperature tuning and pump wavelength tuning result in similar effects, and either method of selecting different JSIs can be adopted in practice.


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

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

Experimentally generating photon pairs with different JSIs.Distinctly different JSIs can be obtained by tuning either the chip temperature or the pump wavelength. (a–c) Three JSIs measured with a fixed pump wavelength (1,563.61 nm) while tuning the TEC controlling the chip temperature to 27.7 °C (a), to 30.2 °C (b) and to 37.3 °C (c). (d–f) Three JSIs measured with a fixed TEC temperature setting of 30.2 °C while tuning the pump wavelength to be 1,563.03 nm (d), 1,563.61 nm (e) and 1,563.79 nm (f). In each case, the range of wavelengths over which data were acquired was the same. The Richardson–Lucy algorithm was used to deconvolve the point-spread function of the filters in front of the SPADs with 50 iterations. The Schmidt numbers are K=1.95 (a), 5.72 (b), 7.02 (c), 1.88 (d), 5.72 (e) and 5.47 (f). In each panel, the horizontal axes are in units of normalized wavelength (one unit equals a wavelength separation of 0.6 nm) measured relative to the respective band centre, which for ‘Photon 1’ was 1,548.8 nm and for ‘Photon 2’ was 1,578.7 nm. The vertical axes and colour scales are normalized so that the area under each JSI is unity, reflecting the fact that JSI is a probability density.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Experimentally generating photon pairs with different JSIs.Distinctly different JSIs can be obtained by tuning either the chip temperature or the pump wavelength. (a–c) Three JSIs measured with a fixed pump wavelength (1,563.61 nm) while tuning the TEC controlling the chip temperature to 27.7 °C (a), to 30.2 °C (b) and to 37.3 °C (c). (d–f) Three JSIs measured with a fixed TEC temperature setting of 30.2 °C while tuning the pump wavelength to be 1,563.03 nm (d), 1,563.61 nm (e) and 1,563.79 nm (f). In each case, the range of wavelengths over which data were acquired was the same. The Richardson–Lucy algorithm was used to deconvolve the point-spread function of the filters in front of the SPADs with 50 iterations. The Schmidt numbers are K=1.95 (a), 5.72 (b), 7.02 (c), 1.88 (d), 5.72 (e) and 5.47 (f). In each panel, the horizontal axes are in units of normalized wavelength (one unit equals a wavelength separation of 0.6 nm) measured relative to the respective band centre, which for ‘Photon 1’ was 1,548.8 nm and for ‘Photon 2’ was 1,578.7 nm. The vertical axes and colour scales are normalized so that the area under each JSI is unity, reflecting the fact that JSI is a probability density.
Mentions: Figure 4 shows that different JSIs were obtained experimentally from the same photon-pair source. In Fig. 4a–c, the optical pump wavelength was kept constant at λp=1,563.61 nm, and the chip temperature was tuned from 27.7 °C (Fig. 4a) to 30.2 °C (Fig. 4b) and to 37.3 °C (Fig. 4c). This range of temperature variations can be achieved by conventional thermoelectric controllers, such as those incorporated within commerical semiconductor lasers1. In Fig. 4d–f, the chip temperature was kept constant at 30.2 °C and the pump wavelength was tuned from 1,563.03 nm (Fig. 4d) to 1,563.61 nm (Fig. 4e) and to 1,563.79 nm (Fig. 4f). This range of wavelength variation required of the pump is comparable to the range of tunability offered in compact commercial tunable semiconductor lasers1, which can therefore be conveniently used to pump the silicon chip. Other different JSIs can also be obtained; however, we limit our report to these three examples because each frame shown in Fig. 4 took many hours to acquire since the optical filters were individually scanned over the 2D grid. Supplementary Note 3 and Supplementary Fig. 4 discuss a measurement example in which the de-blurring algorithm was not needed, for example, to decide between three distinct JSI alternatives, where the measurement took only 30 s. In Fig. 4a,c, the JSI showed a single peak, but because of the elliptical shape of the peak, the Schmidt number K is greater than 1. To reduce K without shaping the pump pulse, the device design should be adjusted to support a slightly broader spectral envelope for the pump pulse. The results of Fig. 4 show that temperature tuning and pump wavelength tuning result in similar effects, and either method of selecting different JSIs can be adopted in practice.

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