Today’s quantum technology relies on the realization of large-scale non-classical systems in practical formats to enable quantum-accelerated computing, secure communications and enhanced sensing. Optical on-chip quantum frequency combs, characterized by many equidistantly spaced frequency modes, allow the storage of large amounts of quantum information and together with control mechanisms can provide practical large-scale quantum systems. In this contribution, we present recent advances on the controlled generation and use of quantum frequency combs for information processing. First, we demonstrate an electrically-pumped laser-integrated quantum light source of two- and high-dimensional maximally entangled photons. We exploit a hybrid InP-SiN approach which allows to include a filter, a gain section and a parametric photon pair source in a single system. Second, we demonstrate the generation of high-dimensional bi-photon quantum frequency combs with tunable entropies by exploiting a novel excitation technique and spectral filtering. Using this, we reveal unidirectional bosonic quantum walks, asymmetric energy transfer, and directional entanglement transport.
Chilas develops off-the-shelf laser sources based on hybrid integration of Photonic Integrated Chips (PICs). Combining the high optical powers of semiconducting optical amplifiers (SOAs) with low-loss wavelength tunable mirror structures on Si3N4 PICs results in compact and robust tunable laser sources. These extended cavity diode lasers (ECDLs) exhibit unique characteristics like wide tuning ranges (>100 nm), ultra-narrow linewidths (<1 kHz) and high output powers. Here we present up to 162.5 mW of optical output power by combining two SOAs inside a single cavity, thereby scaling the output power without the need of additional optical amplification on the output port. The presented laser operates inside the telecom C-band, but the strategy can be tailored to other wavelengths like 850 nm, 780 nm and 690 nm, where Si3N4 plays a key role. This new generation of hybrid integrated ECDLs, exhibiting high optical output powers, wide wavelength tuning ranges and ultra narrow linewidths, opens up a wide range of applications.
Hybrid integrated diode lasers offer a robust and small-sized solution for applications in telecommunications, quantum optics and metrology due to their wide tunability and ultra-narrow linewidth. Here, we present the fabrication, packaging and successful operation of the first fully integrated, aluminum oxide (Al2O3) based, hybrid diode laser operating at 405 nm. Low-loss, high-confinement waveguides are fabricated with a measured propagation loss of only 2.8 ± 0.3 dB/cm. The hybrid laser consists of a GaN SLED butt-coupled to an Al2O3 feedback circuit comprising of two microring resonators that form a frequency selective Vernier filter. The chip assembly is packaged in a hermetically sealed, butterfly housing for optimal performance and durability. The laser shows a maximum output power of 0.74 mW and is tunable over the entire gain bandwidth of 4.4 nm.
We present a hybrid-integrated extended cavity diode laser tunable around 637 mn, with a total tuning range of 8 nm, allowing to address the zero-phonon line of nitrogen vacancy centers. The laser provides wide mode-hop free tuning over 43.6 GHz and a narrow intrinsic linewidth below 10 kHz. The maximum output power is 2.5 mW in a single-mode fiber, corresponding to an on-chip power of 4.0 mW. The laser is assembled in a standard laser housing and fiber-pigtailed.
Optical frequency combs based on broadband-gain bulk lasers, due to the low intrinsic linewidth and sub-GHz repetition rates, have gained tremendous interest for applications such as high-resolution spectroscopy, dual-comb spectroscopy or LIDAR. However, susceptibility to mechanical and acoustic perturbations, the complexity of optical pumping and the larger physical size of these lasers has motivated research toward chip-based integrated extended cavity diode lasers with low-loss Si3N4 waveguide feedback circuits for low repetition rates. In diode lasers, mode-locking via saturable absorbers is generally used for generating frequency combs, however, the short upper-state carrier lifetime results in repetition rates of at least a few GHz. Here, we demonstrate absorber-free, passive mode-locking as well as hybrid mode-locking at sub-GHz repetition rates using a long Si3N4 feedback circuit with three highly frequency-selective microring resonators for extending the cavity roundtrip length to more than 0.6 m. This enables frequency-domain mode-locking in the form of a continuous wave, with a line spacing of around 500 MHz. Hybrid mode-locking, in addition to passive mode-locking, is demonstrated by adding a weak AC drive current with a frequency close to 500 MHz. This stabilizes the repetition rate and reduces the Gaussian component of the laser’s RF linewidth attaining a negligible Lorentzian component. Our numerical simulations predict that further lowering of the repetition rate and line spacings might be achievable with further cavity length extension.
We demonstrate the first fully on-chip electrically-pumped laser-integrated quantum photonic source, which consists of a laser cavity, an InP gain section, and a Vernier filtering stage. This sub-millimeter-sized hybrid chip generates high-quality, low-noise (CAR ~80) entangled photon states with a remarkably high pair detection rate (~620 Hz) over four resonant modes within the C-band. We confirmed the realization of high-dimensional entangled states with fidelity of ~ 0.99 and visibility of ~ 96%. This fully integrated, practical, and field-deployable quantum light source brings scalability to applications ranging from quantum processing circuits, quantum internet to quantum satellite systems.
Hybrid integration of semiconductor optical amplifiers with frequency-selective feedback circuits, implemented using low-loss Si3N4 waveguides, enables robust chip-sized lasers with outstanding properties. Deploying ring resonators as a tunable feedback filter provides single-mode operation over a wide wavelength range. Moreover, these rings resonantly enhance the cavity length, which results in ultra-narrow intrinsic linewidth, as low as 40 Hz.
Here, we present an overview on state-of-the-art developments regarding these lasers. We compare linewidth and tuning results for different feedback circuit configurations. Finally, we report on the first demonstration of a hybrid-integrated semiconductor laser that operates in the visible wavelength range.
Visible diode lasers with wide wavelength tunability and narrow spectral linewidth are of high importance in bio-photonics and metrology. Hybrid integrated diode lasers, using waveguide circuits for spectrally selective feedback, provide wide tunability and sub-100-Hz intrinsic linewidths in a robust chip format. So far, these lasers have only been realized at infrared wavelengths. Here we present the first operation of a hybrid integrated diode laser in the visible. The laser, formed by a diode amplifier which is hybrid integrated with a Si3N4 ring-resonator based feedback circuit, is tunable over 11 nm around 685 nm and delivers 5 mW output power.
Ultra-narrow linewidth tunable hybrid integrated lasers are built from a combination of indium phosphide (InP) and silicon nitride-based TriPleX™. By combining the active functionality of InP with the ultra-low loss properties of the TriPleX™ platform narrow linewidth lasers in the C-band are realized. The InP platform is used for light generation and the TriPleX™ platform is used to define a long cavity with a wavelength-selective tunable filter. The TriPleX™ platform has the ability to adapt mode profiles over the chip and is extremely suitable for mode matching to the other platforms for hybrid integration. The tunable filter is based on a Vernier of micro-ring resonators to allow for single-mode operation, tunable by thermo-optic or stress-induced tuning. This work will show the operational principle and benefits of the hybrid lasers and the state of the art developments in the realization of these lasers. High optical powers ( <100 mW) are combined with narrow linewidth (< 1 kHz) spectral responses with tunability over a large (>100 nm) wavelength range and a low relative intensity (< -160 dB/Hz).
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