Quantum Ghost Imaging (QGI) is a scheme using entangled pairs of photons (signal and idler) in order to perform imaging with both single photons and with only a single-element detector in the spectrum of interest. It utilises the temporal coincidence of the photons to identify associated pairs, while their spatial correlation allows to obtain image information from of the idler photon from the measurement of the signal photon. It is especially useful when using nondegenerate photon pairs, allowing to keep the signal photon in the silicon detection window, while the interacting wavelength can be freely chosen.However, current schemes are limited, as they rely on time-gating and heralding. Recent advances in single photon avalanche diodes (SPADs) allow the design of new single photon cameras, which can be outfitted with dedicated in-pixel timing circuitry. This allows to register single photons in both time and space. These detectors allowed us to design a new scheme for QGI, in which the coincidence is evaluated after the measurement. It also allows us to perform depth-resolved 3D imaging based on the time-of-flight of photons, first results of which are presented here.
Quantum Ghost Imaging (QGI) is a scheme using entangled pairs of photons (signal and idler) in order to perform imaging with both single photons and with only a single-element detector in the spectrum of interest. It utilises the temporal coincidence of the photons to identify associated pairs, while their spatial correlation allows to obtain image information from of the idler photon from the measurement of the signal photon. It is especially useful when using nondegenerate photon pairs, allowing to keep the signal photon in the silicon detection window, while the interacting wavelength can be freely chosen.However, current schemes are limited, as they rely on time-gating and heralding. Recent advances in single photon avalanche diodes (SPADs) allow the design of new single photon cameras, which can be outfitted with dedicated in-pixel timing circuitry. This allows to register single photons in both time and space. These detectors allowed us to design a new scheme for QGI, in which the coincidence is evaluated after the measurement. It also allows us to perform depth-resolved 3D imaging based on the time-of-flight of photons, first results of which are presented here.
Quantum Ghost Imaging (QGI) is a scheme which uses the temporal correlation of entangled photon pairs (signal and idler) to identify detections belonging to actual entangled pairs and separate them from uncorrelated detections. By also exploiting the spatial correlation of the photon pair, this identification allows to extract image information of the idler photons by imaging the signal photons. This can even be done for non-degenerate photon pairs, allowing imaging at wavelengths without sophisticated cameras in this regime. Recent advances in detector technology, especially single photon avalanche diodes (SPADs), allow the design for new cameras capable of single photon detection with both high spatial and temporal resolution. These new detectors are especially useful for application in QGI, allowing to detect each photon individually and identify the correlated pairs after the measurement. It further allows to analyse the time-of-flight of photons and thus enables 3D imaging, the first realization of which will be presented here.
Low-light-level imaging in the infrared regime could find applications in areas ranging from technological to biological. Still, its development is limited by the inefficiency of silicon-based detectors in this regime. Quantum Ghost Imaging (QGI) can address this limitation by allowing the separation of illumination and imaging [1]. This is accomplished by generating non-degenerate correlated photon pairs, whose infrared photon probes the object and is detected by an InGaAs bucket detector, while the spatial distribution of the visible one is collected by a single-photon sensitive silicon camera. Traditional QGI setups evaluate photon correlations through “heralding”, by triggering the camera upon idler detection and thus require an image-preserving delay-line, which limits their use for remote sensing [1]. In asynchronous QGI (aQGI) cameras are replaced with SPAD arrays [2] able to record photon timestamp with picoseconds precision. By identifying pairs through timestamps comparison, the mentioned limitations are resolved [3], enabling applications with reflective or diffusive objects where the timestamp delay depends on the object's position. In this work, we propose and demonstrate an experimental QGI setup for remote sensing in reflection configuration (Fig. 1). Collinear non-degenerate pairs of single-photons at 550 nm and 1550 nm are generated by pumping a 2 mm-long type-0 ppKTP crystal with a 405 nm laser. To enable imaging of objects at varying distances, we implemented a momentum-correlation-based setup. Infrared photons interacting with the object were collected by commercially available InGaAs SPAD detectors, while the visible photons were directly captured using a prototype silicon SPAD array developed by Politecnico di Milano [4]. It is based on a 32×32 SPAD, with in-pixel TDCs, and on-chip microlenses are employed to reach a fill factor of 78%. The time resolution is adjustable down to 250 ps, with 1 μs Full Scale Range (FSR). The measurement duty cycle (i.e. the ration of the TDC FSR and the frame time) can be increased with a multi-gate acquisition scheme. To validate the efficiency of our setup, we tested it using a proof-of-principle object, as shown in Fig. 1b. The reconstructed images, captured with the object placed at 30 cm intervals in an acquisition time of only 30 s, are shown in Fig. 1c. In summary, the shown results confirm the potential of the proposed setup for remote sensing applications, particularly for reflective or diffusive objects. Moreover, the proposed approach could offers the possibility of significantly reduce acquisition times compared to standard QGI setups.
Quantum Ghost Imaging (QGI) is a powerful imaging technique that enables probing of an object using illumination levels beyond classical limits and does not rely on a single-photon-sensitive camera in the spectrum of interest. Current “heralded” QGI setups provide high-resolution images with intensified charge-coupled device (ICCD) cameras, but their acquisition time and applicability are limited by setup complexity and detector dead time. Recently, new setups using single photon detection and time-tagging have been shown to allow more efficient acquisition while also enabling new applications, such as remote 3D imaging using “asynchronous” QGI. Here, we demonstrate novel results of two asynchronous QGI setups, using a dedicated high duty-cycle single photon avalanche diode array to drastically reduce acquisition time to sub-second regime, demonstrating video acquisition at 10 fps. As this scheme allows interoperability with arbitrary single photon timing detectors, it can be adapted to a variety of applications and is not bound by the detection window of silicon-based detectors. We further study the impact of the choice of bucket detector and pump laser, using readily available off-the-shelf detectors and lasers. Summarizing the findings, we discuss the remaining limitations for real-time imaging and give an outlook on upcoming developments and an outline of further applications of both detectors and detection scheme.
Quantum ghost imaging (QGI) is an intriguing imaging protocol that exploits photon-pair correlations stemming from spontaneous parametric down-conversion (SPDC). QGI retrieves images from two-path joint measurements, where single-path detection does not allow us to reconstruct the target image. Here we report on a QGI implementation exploiting a two-dimensional (2D) single-photon avalanche diode (SPAD) array detector for the spatially resolving path. Moreover, the employment of non-degenerate SPDC allows us to investigate samples at infrared wavelengths without the need for short-wave infrared (SWIR) cameras, while the spatial detection can be still performed in the visible region, where the more advanced silicon-based technology can be exploited. Our findings advance QGI schemes towards practical applications.
Quantum Ghost Imaging (QGI) is an intriguing imaging protocol that exploits photon-pair correlations stemming from spontaneous parametric down-conversion (SPDC). QGI retrieves images from two-path joint measurements, where single-path detection does not allow to reconstruct the target image. This technique, has been so far limited in terms of acquisition speed either by raster scanning, or by the slow electronics of intensified cameras. Here we report on a fast QGI implementation exploiting a SPAD array detector for the spatially resolving path, enabling the acquisition of a ghost image in under one minute. Moreover, the employment of non-degenerate SPDC allows to investigate samples at infrared wavelengths without the need for short-wave infrared (SWIR) cameras, while the spatial detection can be still performed in the visible region, where the more advanced silicon-based technology can be exploited. Our findings advance the state-of-the-art of QGI schemes towards practical applications.
Ghost Imaging (GI) is a fascinating imaging technique that exploits second-order correlations of light to investigate samples without directly observing them with a camera [1]. Quantum GI (QGI) version exploits correlations stemming from photon pairs generated by spontaneous parametric down-conversion (SPDC) [2]. It retrieves images from two-path correlation measurements, where single-path detection is not sufficient to obtain an image of the target. Since early demonstrations, this technique has suffered in terms of scalability due to the difficulty of efficiently performing spatially resolved single-photon detection. Early demonstrations suffered from detection efficiency limitations, due to raster scanning spatial detection. More recent camera-based experiments relying on intensified CCD cameras obtain only a limited frame rate and need complex image-preserving delay-lines [3]. More recently, SPAD arrays, two-dimensional arrangement of single-photon avalanche detectors, have been developed and employed in a number of quantum imaging and spectroscopy schemes, dramatically improving detection performances [4]. Here we report on a QGI implementation exploiting a 2D SPAD array detector for the spatially resolving path, solving limitations in terms of frame-rate and the need for optical delay lines. Our experiment enables the acquisition of an image in under one minute, and with much higher frame rate compared to the state-of-the-art. We further take advantage of non-degenerate SPDC to interrogate a Si-Au target. While light interaction with the sample happens at infrared wavelengths, no infrared cameras are needed to obtain an image, and spatial detection is performed in the visible region. This two-color scheme allows to make use of the advanced and cost-efficient silicon-technology while still investigating a sample in spectral regions where cameras are too expensive or not yet available [5]. Our findings advance the state-of-the-art of QGI schemes towards practical applications.