Imaging with non-classical photons allows to bypass the Rayleigh resolution limit and classical shot-noise level. One step towards imaging demonstration with large photon numbers is the separation of non-classical photon states from the classical photons, thus increasing dynamic range and signal to background contrast on the detector. We demonstrate the feasibility of such separation by an échelle grating at high diffraction orders. In our demonstration, a PPKTP crystal generates entangled photon pairs in type-0 SPDC. The crystal is cw pumped and produces non-collinear degenerated photon pairs at 810nm. The classical light states are produced by a VCSEL at nearly same wavelength. After diffraction on echelle grating, the spatial far-field patterns and the photon arrival times are recorded by a novel 32×32 SPAD array sensor with 160 ps timing resolution. It allows real-time monitoring of the first- and second order correlation patterns. Within the observation window, we detected correlated biphoton arrivals in the four diffraction orders corresponding to their de Broglie wavelength, which is a half of the classical wavelength. Respectively a half of these diffraction orders is prohibited for classical photons. Placing a slit mask in these orders allows us to transmit only non-classical photon state and block the classical ones. We report on a series of experiments elucidating spatial and temporal correlations at the output of such quantum –classical photon discriminator. Those results could be used for the separation of biphotons from classical photons at the same wavelength in high-intensity light sources.
European Space Agency (ESA) considers Mode-Locked Semi-Conductor Lasers as a promising technology for precision metrology systems in space such as High Accuracy Absolute Long Distance Measurement. We report our progress towards challenging ESA requirements: picosecond pulse duration, pulse energy 200 pJ, Pulse Repetition Frequency (PRF) 1-3 GHz, PRF stability < 5·10<sup>-9</sup> at 1 second and PRF tunability 20 MHz. The laser should have small power consumption, be compact and robust against launch vibrations. We have reported in the past two such mode-locked (ML) laser diodes, each reaching only 90 pJ pulse energies: (<i>i</i>) very long (13.5mm) monolithic tapered laser and (<i>ii</i>) inverse bow-tie external cavity (EC) laser. The subject of the present communication is a novel passively mode-locked monolithic tapered laser achieving 201 pJ pulses. Large optical cavity with 2QWs heterostructure provides a low internal loss (~1 cm<sup>-1</sup>) together with high quantum efficiency (< 90 %) and low series resistance. To reach high energy output pulses, the tapered gain section gets a low (< 0.1 %) reflectivity dielectric coating. For passive mode-locking at fundamental cavity frequency, the saturable electroabsorber section is located at the back side of the gain chip with a high reflectivity coating (< 95 %). The monolithic cavity is made 13.5mm long by introducing an intermediate section for PRF tuning around 3 GHz. We reached passive ML at 2.9 GHz PRF with pulse energy of 201 pJ, compressed pulse width of 2.6 ps and electric power consumption of 8.2 W. PRF can be continuously tuned by 9.8 MHz. Active current modulation for hybrid ML resulted in PRF relative stability at 9.16·10<sup>-10</sup> level on 1s intervals, while with a phase lock loop (PLL) acting on the DC gain section current we reached PRF stability of 1.15·10<sup>-10</sup> on 1 s measurement interval.
We report on multi-section inverse bow-tie laser producing mode-locked pulses of 90 pJ energy and 6.5 ps width (895 fs after compression) at 1.3 GHz pulse repetition frequency (PRF) and consuming 2.9 W of electric power. The laser operates in an 80 mm long external cavity. By translation of the output coupling mirror, the PRF was continuously tuned over 37 MHz range without additional adjustments. Active stabilization with a phase lock loop actuating on the driving current has allowed us to reach the PRF relative stability at a 2·10<sup>-10</sup> level on 10 s intervals, as required by the European Space Agency (ESA) for inter-satellite long distance measurements.
Mode-locked semiconductor laser technology is a promising technology candidate considered by European Space Agency (ESA) for optical metrology systems and other space applications in the context of high-precision optical metrology, in particular for High Accuracy Absolute Long Distance Measurement. For these applications, we have designed, realized and characterized a multi-section monolithic-cavity tapered laser diode with a record cavity length of 13.5mm. The laser operates at 975nm wavelength with average output power up to 600mW. It is based on a MOVPE grown laser structure with Aluminium free active region enabling high optical gain, low internal losses and low series resistance. It reaches passive mode-locking operation on fundamental cavity round trip frequency of 2.88GHz with chirped pulse width of 6.2ps and time bandwidth product of 8 for the average output power of 250mW. Alongside with passive mode-locking operation, we discuss other lasing regimes in these very long tapered lasers.
Quantum imaging uses entangled photons to overcome the limits of a classical-light apparatus in terms of image quality, beating the standard shot-noise limit, and exceeding the Abbe diffraction limit for resolution. In today experiments, the spatial properties of entangled photons are recorded by means of complex and slow setups that include either the motorized scanning of single-pixel single-photon detectors, such as Photo-Multiplier Tubes (PMT) or Silicon Photo- Multipliers (SiPM), or the use of low frame rate intensified CCD cameras. CMOS arrays of Single Photon Avalanche Diodes (SPAD) represent a relatively recent technology that may lead to simpler setups and faster acquisition. They are spatially- and time-resolved single-photon detectors, i.e. they can provide the position within the array and the time of arrival of every detected photon with <100 ps resolution. SUPERTWIN is a European H2020 project aiming at developing the technological building blocks (emitter, detector and system) for a new, all solid-state quantum microscope system exploiting entangled photons to overcome the Rayleigh limit, targeting a resolution of 40nm. This work provides the measurement results of the 2nd order cross-correlation function relative to a flux of entangled photon pairs acquired with a fully digital 8×16 pixel SPAD array in CMOS technology. The limitations for application in quantum optics of the employed architecture and of other solutions in the literature will be analyzed, with emphasis on crosstalk. Then, the specifications for a dedicated detector will be given, paving the way for future implementations of 100kpixel Quantum Image Sensors.
Mode-locked semiconductor laser technology is a promising technology candidate considered by European
Space Agency (ESA) for optical metrology systems and other space applications in the context of high-precision
optical metrology, in particular for High Accuracy Absolute Long Distance Measurement. For these
applications, we have realised a multi-section monolithic-cavity tapered laser diode with a record cavity
length of 13.5 mm. The laser operates at 975 nm wavelength. It is designed for the emission of ultra-short
optical pulses (<1 ps) at a repetition rate of 3 GHz with an average optical power of 600 mW. It is based on a
MOVPE grown laser structure with Aluminium free active region enabling high optical gain, low internal
losses and low series resistance. The first results obtained under CW pumping of such centimetre-long laser at
20 °C heatsink temperature show the lasing threshold current as low as 1.27 A and the differential external
efficiency as high as 0.55 W/A.
We demonstrate picosecond pulse generation in the blue-violet wavelength region by passive intra-cavity mode-locking in GaN-based ridge waveguide laser diodes with monolithically integrated absorbers. For cavity lengths of 1.2 and 0.6 mm we observe repetition frequencies of 40 and 90 GHz, and pulse lengths of 7 and 4 ps, respectively. The results are explained by an extremely short, tunneling dominated carrier life time in the saturable absorber at high negative bias. The fast depletion of the charge carriers in the absorber is investigated by bias-dependent life-time measurements in the absorber.
It is well known that totally incoherent light cannot exhibit first-order interference with photons that are uncorrelated,
i.e., the normalized first-order correlation function is g<sup>(1)</sup>(0) = 0, whereas the second-order correlation
function is g<sup>(2)</sup>(0) = 1. Less familiar is the fact that both chaotic and coherent sources can exhibit first-order interference,
so that merely using the term "interference" is ambiguous. If fact, some previous QIQC presentations
have centered around whether or not two-photon correlations are actually a form of two-photon interference.<sup>1</sup>
Another area of ambiguity concerns the detection of quantum state coherence using interference.<sup>2</sup> In an attempt
to disambiguate the concept of interference, we examine associated photon states using chaotic sources and the
Hanbury Brown and Twiss (HBT) detection of bunched photons. The unambiguous determination of coherent
quantum states has important applications for:
(1) Atomic Bose-Einstein condensate (BEC) determined using scattered laser interference<sup>3</sup>
(2) Exciton-Polariton BEC determined using emitted photon interference<sup>4</sup>
(3) Coherent light states.
(4) Characterizing photon statistics.
(5) Characterization of extended sources.
In this paper, we present imaging results for topics 3-5. The difficulties of HBT data acquisition are generally
underappreciated. An advantage of our approach is super-linear speedup through the development of a new
imaging device consisting of a 2-dimensional array of single-photon avalanche detectors.<sup>5, 6</sup> A 4 × 4 array
enables 120 HBT coincidence experiments to be run in parallel to generate the 2-dimensional distribution of
g(2)(x) spatial correlations, thus making plausible the term "g<sup>2</sup> camera" for this quantum imaging device.
We continue our previous program<sup>1</sup> where we introduced a set of quantum-based design rules directed at quantum engineers
who design single-photon quantum communications and quantum imaging devices. Here, we report on experimental
progress using SPAD (single photon avalanche diode) arrays of our design and fabricated in CMOS (complementary metal
oxide semiconductor) technology. Emerging high-resolution imaging techniques based on SPAD arrays have proven useful
in a variety of disciplines including bio-fluorescence microscopy and 3D vision systems. They have also been particularly
successful for intra-chip optical communications implemented entirely in CMOS technology. More importantly for our
purposes, a very low dark count allows SPADs to detect rare photon events with a high dynamic range and high signal-to-noise ratio. Our CMOS SPADs support multi-channel detection of photon arrivals with picosecond accuracy, several
million times per second, due to a very short detection cycle. The tiny chip area means they are suitable for highly miniaturized
quantum imaging devices and that is how we employ them in this paper. Our quantum path integral analysis of the
Young-Afshar-Wheeler interferometer showed that Bohr's complementarity principle was not violated due the previously
overlooked effect of photon bifurcation within the lens--a phenomenon consistent with our quantum design rules--which
accounts for the loss of which-path information in the presence of interference. In this paper, we report on our progress
toward the construction of quantitative design rules as well as some proposed tests for quantum imaging devices using
entangled photon sources with our SPAD imager.