780 nm wavelength distributed feedback lasers have been integrated onto a Si 3 N 4 photonic platform on a Si substrate and coupled into waveguides for laser locking to either a ring resonator or rubidium vacuum cell. © 2019 The Author(s)

High-Q microring resonators have applications in gyroscopes, frequency comb generation, and feedback systems to control narrow linewidth integrated lasers [1-3]. This paper demonstrates the highest Q values measured for microring resonators at 780 nm wavelength. These sub mm integrated cavities can be used to provide an error signal for locking a distributed feedback laser (DFB), Fig. 1(a), using the Pound-Drever-Hall (PDH) method. High stability DFBs can also be achieved using a micro-electro-mechanical system (MEMS) cell containing 87 Rb vapour and taking advantage of the absorption line at 780.24 nm. This provides an absolute reference for locking the laser but only to the 87 Rb transition wavelengths. The microring resonator can be tailor made for any wavelength but is susceptible to thermal effects; this could in part be overcome using a top cladding with a thermo-optic coefficient that counteracts that of the waveguide core.

There has been recent interest in developing chip-scale cold atom systems for a range of timing and sensing applications. Here we present DFB lasers at 780 nm flip-chip bonded onto a Si substrate with the light coupled into Si 3 N 4 waveguides and a micro-ring locking cavity.

Summary form only given. The UK Quantum Technology Hub in Sensors and Metrology [1] has the aim of developing integrated, small and practical cold atom systems for a range of sensor and timing applications which includes rotation, magnetism, gravity and atomic clocks. The approach is similar to that pioneered by the chip scale atomic clock [2] where atoms held in microfabricated vacuum chambers have atomic transitions excited and probed by diodes lasers [3] and photodetectors. That system used coherent population trapping for the clock transitions whilst we are aiming to first produce lasers for cooling and trapping ions inside vacuum chambers before microwave pulses or controlled lasers are used to create superposition states, recombine them and measure the interference from the final state populations. For cooling 87 Rb atoms, 780.24 nm lasers with linewidths below ~5 MHz are required whilst the lasers for controlling and measuring superposition states typically external cavity lasers have been used to achieve linewidths from 20 kHz [3] down to a few Hz [4]. Most single mode diode lasers aimed at laser cooling have used DBR gratings with regrowth [5] but this is challenging when using AlGaAs materials due to oxidation.Here we present single mode 780.24 nm DFB AlGaAs/GaAs lasers with output powers up to 50 mW and sidemode suppression ratios above 46 dB (Fig. 1(a)) using sidewall etched gratings (Fig. 1(b)) and no regrowth. The lasers demonstrate clear DFB performance allowing tuning through the required 780.24 nm without any mode hopping. Initial tests for short ridge devices indicate linewidths of ~10 MHz and initial lifetime tests have exceeded 200 hours. We will discuss methods being pursued to increasing the power and reducing the linewidth through longer ridges [5], coupled cavities and by integrating SOAs. Control of the population of electrons in hyperfine split states requires two laser outputs spaced by ~3.617 GHz. Fig 1(c) demonstrates the principle of two DFB lasers operated on the same waveguide where the present line spacing has been increased to 30 GHz to allow a clear measurement by our OSA. Careful control of the gratings and the current enable 3. 617 GHz to be achieved. We will present results comparing two coupled DFB lasers (Fig. 1(c)), direct modulation, external AOMs and integrated AOM approaches and discuss which are best suited for integrated cold atom systems.

We demonstrate operation of a GaAs-based self-aligned stripe (SAS) distributed feedback (DFB) laser. In this structure, a first order GaInP/GaAs index-coupled DFB grating is built within the p-doped AlGaAs layer between the active region and the n-doped GaInP opto-electronic confinement layer of a SAS laser structure. In this process no Al-containing layers are exposed to atmosphere prior to overgrowth. The use of AlGaAs cladding affords the luxury of full flexibility in upper cladding design, which proved necessary due to limitations imposed by the grating infill and overgrowth with the GaInP current block layer. Resultant devices exhibit single-mode lasing with high side-mode-suppression of >40 dB over the temperature range 20 degrees C-70 degrees C. The experimentally determined optical profile and grating confinement correlate well with those simulated using Fimmwave.

We demonstrate a semiconductor PCSEL array that uniquely combines an in-plane waveguide structure with nano-scale patterned PCSEL elements. This novel geometry allows two-dimensional electronically controllable coherent coupling of remote vertically emitting lasers. Mutual coherence of the PCSEL elements is verified through the demonstration of a two-dimensional Young's Slits experiment. In addition to allowing the all-electronic control of the interference pattern, this type of device offers new routes to power and brightness scaling in semiconductor lasers, and opportunities for all-electronic beam steering.

The realization of a 1 × 2 coherently coupled photonic crystal surface emitting laser array is reported. New routes to power scaling are discussed and the electronic control of coherence is demonstrated.

The impact of subjecting a n-GaN surface to an in-situ argon plasma in an atomic layer deposition (ALD) tool immediately before deposition of an Al2O3 dielectric film is assessed by frequency dependent evaluation of Al2O3/GaN MOSCAPs. In comparison with a control with no pre-treatment, the use of a 50 W argon plasma for 5 min reduced hysteresis from 0.25 V to 0.07 V, frequency dispersion from 0.31 V to 0.03 V and minimum interface state density (D-it) as determined by the conductance method from 6.8 x 10(12) cm(-2) eV(-1) to 5.05 x 10(10) cm(-2) eV(-1). (C) 2015 Published by Elsevier B.V.

This paper presents first results of a new high performance enhancement-mode (E-mode) gallium nitride (GaN) based metal-oxide semiconductor high electron mobility transistor (MOS-HEMT) that employs an ultrathin 3 nm aluminium gallium nitride (Al(0.25)G(0.75)aN) barrier layer and relies on an induced two dimensional electron gas (2DEG) for operation. Devices have been demonstrated on both sapphire and silicon substrates. Single finger devices on a sapphire substrate were fabricated using 10 nm and 20 nm, and on a silicon substrate using 30 nm of plasma enhanced chemical vapour-deposited (PECVD) silicon dioxide (SiO2) as the gate dielectric. They demonstrated threshold voltages of + 3 V, + 2 V, + 0.8 V and very high maximum drain currents of over 620 mA/mm, 550 mA/mm and 450 mA/mm, respectively. These results show that the proposed device concept can be a building block for future power electronic devices. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A new high-performance normally-off gallium nitride (GaN)-based metal-oxide-semiconductor high electron mobility transistor that employs an ultrathin subcritical 3 nm thick aluminium gallium nitride (Al 0.25 Ga 0.75 N) barrier layer and relies on an induced two-dimensional electron gas for operation is presented. Single finger devices were fabricated using 10 and 20 nm plasma-enhanced chemical vapor-deposited silicon dioxide (SiO 2 ) as the gate dielectric. They demonstrated threshold voltages (V th ) of 3 and 2 V, and very high maximum drain currents (IDSmax) of over 450 and 650 mA/mm, at a gate voltage (V GS ) of 6 V, respectively. The proposed device is seen as a building block for future power electronic devices, specifically as the driven device in the cascode configuration that employs GaN-based enhancement-mode and depletion-mode devices.

In this paper we demonstrate coherently coupled PCSELs. By utilising allsemiconductor PCSELs, realised by MOVPE re-growth [6], we fabricate PCSELs coupled by an electrically driven region (“coupler”), shown schematically in Fig. 2, allowing the electronic control of coherence between emitters. This is made possible due to the small modal refractive index change between coupler and PCSEL in our all-semiconductor device. Both coupled PCSELs have a threshold current of ~65mA and matched emission wavelengths of 986.5nm due to nominally identical photonic crystal structures.