Evaluation of Attenuation Methods for an Integrated, Weak Coherent Source for Quantum Key Distribution

Quantum key distribution (QKD) systems that use weak coherent states often rely on attenuated lasers to generate signals with an average of less than one photon per pulse. Two ways of attenuating laser light in a weak, coherent, integrated QKD transmitter chip are compared in terms of noise, namely attenuation with Mach-Zehnder (MZ) interferometers and attenuation with semiconductor optical amplifiers (SOAs) biased as attenuators. Results from simulations and experiments on the optical spectrum of the output of the transmitter chip show that under reverse bias conditions the SOAs result in similar noise levels as the MZs. The footprint of the SOAs on the chip, however, is more than 50 times smaller than that of the MZs. This makes them the better candidate for the integrated, weak coherent QKD source

Evaluation of Attenuation Methods for an Integrated, Weak Coherent Source for Quantum Key Distribution

Quantum key distribution (QKD) systems that use weak coherent states often rely on attenuated lasers to generate signals with an average of less than one photon per pulse. Two ways of attenuating laser light in a weak, coherent, integrated QKD transmitter chip are compared in terms of noise, namely attenuation with Mach-Zehnder (MZ) interferometers and attenuation with semiconductor optical amplifiers (SOAs) biased as attenuators. Results from simulations and experiments on the optical spectrum of the output of the transmitter chip show that under reverse bias conditions the SOAs result in similar noise levels as the MZs. The footprint of the SOAs on the chip, however, is more than 50 times smaller than that of the MZs. This makes them the better candidate for the integrated, weak coherent QKD source

Large Multi-Wavelength Waveguide Hologram on InP Membrane On-Si Platform

We present a 416 μm × 416 μm waveguide hologram that can focus light from single-mode waveguides to a 50 μm × 50 μm narrow spot located 10 mm above the chip for three distinct wavelengths. To the best of our knowledge, this waveguide hologram stands as the most expansive grating coupler achieved on a photonic integration platform with a high refractive index contrast. To achieve nearly uniform emission across its expansive area, we etch the hologram's nanostructures into a relatively low refractive index layer atop the waveguide. Additionally, we have developed a novel semi-analytical model that enables us to efficiently calculate the emission pattern of large-area waveguide holograms with varying nanostructure sizes. This model enables us to optimize the nanostructure's sizes across the hologram to achieve a Gaussian intensity profile in the far-field. Leveraging this approach, we design and fabricate a tri-wavelength focusing emitter on the InP Membrane On-Silicon (IMOS) Platform, targeting wavelengths of 1310 nm, 1450 nm, and 1600 nm. Our calculated far-field intensity profiles closely align with experimental measurements. We observe the coupler achieves near-vertical focusing at 9.4 mm across the target wavelengths. Though an initial design mistake resulted in an imbalance in coupling efficiency across different wavelengths. Nevertheless, our model clearly predicts this imbalance. Our model allows one to conveniently optimize the intensity profile of various waveguide holograms used in optical sensing, Augmented Reality or optical imaging

Integrated optical phased array with on-chip amplification enabling programmable beam shaping

We present an integrated optical phased array (OPA) which embeds in-line optical amplifiers and phase modulators to provide beam-forming capability with gain and beam steering in the 1465–1590 nm wavelength range. We demonstrate up to 21.5 dB net on-chip gain and up to 35.5 mW optical output power. The OPA circuit is based on an InP photonic integration platform and features the highest measured on-chip gain and output power level recorded in an active OPA (i.e., with amplification), to the best of our knowledge. Furthermore, the OPA enables the independent control of both amplitude and phase in its arms and through this we demonstrate programmable beam shaping for two cases. First, we carried out a Gaussian apodization of the power distribution profile in the OPA emitter waveguides, leading to 19.8 dB sidelobe suppression in the far-field beam, which is the highest value recorded for active OPAs, and then we demonstrated beam forming of 0th, 1st, and 2nd order 1D Hermite–Gaussian beams in free-space

Analysis of hybrid mode-locking of two-section quantum dot lasers operating at 1.5 micron

For the first time a detailed study of hybrid mode-locking in two- section InAs/InP quantum dot Fabry-Pérot-type lasers is presented. The output pulses have a typical upchirp of approximately 8 ps/nm, leading to very elongated pulses. The mechanism leading to this typical pulse shape and the phase noise is investigated by detailed radio-frequency and optical spectral studies as well as time-domain studies. The pulse shaping mechanism in these lasers is found to be fundamentally different than the mechanism observed in conventional mode-locked laser diodes, based on quantum well gain or bulk material. ©2009 Optical Society of America

High-Power Continuously Tunable Terahertz Beat Note Generation Based on a Generic Photonic Integration Platform

We generate a continuously tunable terahertz beat note, with a maximum output power of 50 mW and frequency range from 807 to 915 GHz, by using the device implemented on a generic photonic integration platform

Radio-frequency signal generation using actively frequency stabilised monolithically integrated inp-based lasers

We demonstrate the generation of radio-frequency (RF) signals using stabilized integrated semiconductor lasers. The lasers are monolithically integrated on the same chip using InP active-passive integration technology. They are locked to different resonances of the same external optical cavity using the Pound-Drever-Hall locking technique. The locking is implement with single control loop for each laser and by voltage controlled tuning thus avoiding significant thermal effects. The generated RF signal can be tuned discretely to frequencies that are multiples of the external optical cavity free spectral range. Examples of beat tones at 12.436, 24.8735 and 40.4194 GHz are demonstrated. The linewidth of the generated signals at all frequencies is less than 40 kHz. The single-side-band phase noise is about -54 dBc/Hz for frequencies offsets from the carrier at 12.436 GHz between 1 kHz and 10 kHz and -60 and -67 dBc/Hz at 100 kHz and 1 MHz respectively

An InP-Based DBR Laser with an Intra-Cavity Ring Resonator with 130 kHz Linewidth and 65 dB SMSR

We demonstrate a monolithic extended cavity InP-based single-mode laser with DBR mirrors and an intra-cavity ring resonator with 15 mA threshold current fabricated with a generic integration technology. A 130 kHz linewidth has been measured and an SMSR well over 60dB

Multi-stable operation of a semiconductor ring laser due to spatial hole-burning

We have theoretically analyzed multi-stability of a symmetric ring laser operating in one single longitudinal mode in the presence of coherent back scattering and inversion-grating-induced mutual coupling of the clockwise and counter-clockwise modes. Our model takes into account the inversion grating created by the standing-wave pattern of the interfering counter-propagating fields and avoids the frequently used ad-hoc introduction of cross and self-saturation coefficients. Our study confirms that linear coupling due to waveguide irregularities or weak interface reflections leads to an effective pump strength below which the clock and anti-clock wise modes are symmetrically coupled whereas above which the grating-induced coupling leads to multi-stability

Theoretical and experimental investigation of unidirectionality in an integrated semiconductor ring mode-locked laser with two saturable absorbers

The lack of integrated optical isolators in standard integrated semiconductor photonics platforms leaves integrated lasers vulnerable to back reflections. A hypothesis is that by making a ring laser operate unidirectionally, external reflections will couple back into the non-lasing direction, and the sensitivity toward reflections will be reduced. In this paper, unidirectionality is pursued by placing two saturable absorbers asymmetrically in a ring mode-locked laser. In the case of passive mode-locking, and for internal reflections below -75 dB, simulations, based on the slowly varying envelope approximation, show extinction ratios of up to 37 dB between the two propagation directions. For larger reflections, the extinction ratio degrades linearly with reflection magnitude. The extinction ratio is shown to increase when the reverse bias of the saturable absorbers is modulated actively with a phase difference. Our simulations show that unidirectional operation reduces the amplitude noise in the frequency range from 1 MHz to 10 GHz from around 0.022% to 0.004% when compared to bidirectional operation, whereas the timing jitter of the pulse train increases from around 172 to 412 fs. Experiments show that the extinction ratio of a realization of this mode-locked laser design is limited to around 3 dB. Simulations suggest that this is due to internal butt-joint reflections in the laser cavity