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Quantum technologies containing key GaN laser components will enable a new generation of precision sensors, optical atomic clocks and secure communication systems for many applications such as next generation navigation, gravity mapping and timing since the AlGaInN material system allows for laser diodes to be fabricated over a wide range of wavelengths from the u.v. to the visible. We report our latest results on a range of AlGaInN diode-lasers targeted to meet the linewidth, wavelength and power requirements suitable for quantum sensors such as optical clocks and cold-atom interferometry systems. This includes the [5s2S1/2-5p2P1/2] cooling transition in strontium+ ion optical clocks at 422 nm, the [5s2 1S0-5p1P1] cooling transition in neutral strontium clocks at 461 nm and the [5s2s1/2 − 6p2P3/2] transition in rubidium at 420 nm. Several approaches are taken to achieve the required linewidth, wavelength and power, including an extended cavity laser diode (ECLD) system and an on-chip grating, distributed feedback (DFB) GaN laser diode.

We report on GaN lasers with extremely narrow linewidth (~1MHz) at ‘magic wavelengths’ for cold-atom quantum sensors and optical atomic clocks, using extended cavity GaN laser diodes and DFB GaN laser diodes.

Owing to increased performance capabilities over their LED counterparts, Gallium Nitride (GaN) based Laser Diodes (LDs) are becoming more prevalent in several applications, including lighting, visible light communications, medical spectroscopy, and atom cooling. For many of these applications, a tunable, precise wavelength is necessary such that chromatic aberrations are minimized and that specific wavelengths with narrow linewidth can be utilized for atomic transitions or filtered communications systems. This paper discusses one method of achieving single-mode lasing operation in GaN LDs, namely the deeply-etched sidewall grating Distributed Feedback (DFB) LD. Optical characteristics of such devices will be discussed, as well as their feasibility for optical communications.

Laser diodes based on Gallium Nitride (GaN) are useful devices in a wide range of applications including atomic spectroscopy, data storage and optical communications. To fully exploit some of these application areas there is a need for a GaN laser diode with high spectral purity, e.g. in atomic clocks, where a narrow linewidth blue laser source can be used to target the atomic cooling transition. We report on the continuous wave, room temperature operation of a distributed feedback laser diode (DFB-LD) with high-order notched gratings. The design, fabrication and characterization of DFB devices based on the (Al,In) GaN material system is described. A single peak emission at 408.6 nm with an optical power of 20 mW at 225 mA and a side mode suppression ratio (SMSR) of 35 dB was achieved. Additionally, we demonstrate the use of a GaN DFB-LD as a transmitter in visible optical communications system. We also present results from a DFB-LD optimized for laser cooling of Sr+.

We report on the generation of high speed polarization modulated data via direct electrical binary data injection to the phase shifter section of a monolithically integrated laser diode integrated with a polarization controller. The device is fabricated on standard InP/AlGaInAs multiple quantum-well material and consists of a semiconductor laser, a passive polarization mode convertor, and an active differential phase-shifter section. We demonstrate the generation of 300 Mb/s polarization shift keyed data.

We report for the first time Coherent Population Trapping (CPT) in Cs-filled Kagome Hollow Core Fibers. Dark resonance contrasts of up to 9 % and linewidths as narrow as 1.8 MHz were observed.

We, for the first time, present electroabsorption modulator lasers based on side-wall gratings and the identical epitaxial layer scheme using very simple fabrication processes. The devices show stable single-mode operation with little mode-hopping and a side mode suppression ratio of more than 45 dB, which is maintained until the applied current exceeds 6 times that of the threshold value. The drive voltage required to obtain a 12-dB extinction ratio is ${-}{\rm 2}~{\rm V}$ . The devices can be operated with a 3-dB bandwidth of 7 GHz allowing for error-free large signal modulation at 5 Gb/s with a dynamic extinction ratio of 11 dB.

The monolithic integration of four 1.50-μm range AlGaInAs/InP distributed feed-back lasers with a 4 × 1 multimode-interference optical combiner, a curved semiconductor optical amplifier and an electroabsorption modulator using relatively simple technologies-sidewall grating and quantum well intermixing-has been demonstrated. The four channels span the wavelength range of 1530-1566 nm and can operate separately or simultaneously. The epitaxial structure was designed to produce a far field pattern at the output waveguide facet, which is as small as 21.2°× 25.1°, producing a coupling efficiency with an angled-end single mode fiber at twice that of a conventional device design.

Colliding-pulse mode-locked lasers (MLLs) offer many advantages compared to other types of MLLs as they provide relatively stable and better pulse-shaped mode-locking operation [1]. Colliding-pulse MLLs (CPM) with narrow far-field patterns are highly desirable for simple and high-yield passive optical alignment, as a low divergence angle improves the coupling efficiency and imposes less stringent alignment tolerances between the laser and a single-mode fiber (SMF). However, conventional epi-structure designs result in large beam divergence angles and highly asymmetric far-field patterns [2]. A great deal of work has been carried out over the past several years towards the development of spot-size converted lasers to improve the coupling efficiency with SMF. Many of the techniques, such as butt-coupling or lateral-taper-vertical-shift, require etch-and-regrowth over the active region, which is not readily applicable to AlGaInAs/InP-based lasers due to rapid oxidation of exposed Al-containing surfaces [3]. In addition, mode-locked lasers emitting optical pulse trains with low phase noise and timing jitter are also desirable for optical time-division-multiplexed (OTDM) communication systems and optical signal processing. The timing jitter of passive CPM operation can be reduced either by lowering the internal loss of the cavity or by increasing the saturation energy (E sat ) of the gain section [4]. To obtain a high E sat in the gain section, one should try to use either a low optical confinement factor (Γ) or a large spot size (A), i.e. maximize A/Γ. E sat can also be improved by decreasing the differential gain (dg/dN), which can be achieved by reducing the number of quantum wells (QWs) in the gain medium.

We present a laterally-coupled AlGaInAs/InP DFB laser emitting two longitudinal modes simultaneously within the same cavity and integrated with EAM. A stable 0.82 THz beating signal was observed over a wide range of bias parameters.

The monolithic integration of four 10-GHz 1.55- μm AlGaInAs/InP mode-locked surface-etched distributed Bragg reflector lasers with a 4 × 1 multimode-interference optical combiner, a curved semiconductor optical amplifier, and electroabsorption modulator using relatively simple technologies-surface-etched distributed Bragg reflector and quantum-well intermixing-has been demonstrated. Our techniques have the advantage of eliminating crystal regrowth and antireflection coating processes that are required in traditional methods. The four channels can operate separately or simultaneously. They also can be synchronized at the same pulse repetition frequency by the injection mode-locked technique.

The 10-GHz passively mode-locked AlGaInAs/InP 1.55- μm extended cavity lasers integrated with optimized surface-etched distributed Bragg mirrors have been fabricated. A quantum-well intermixing process was used to provide low-absorption loss gratings with accurate wavelength control. The lasers produce 2.99-ps sech2-pulses with a time-bandwidth product (TBP) of 0.51.

We report a sampled grating distributed Bragg reflector (SGDBR) laser with two different gratings which mode-lock independently at respective pulse repetition frequencies of 640 and 700 GHz. The device operates in distinct regimes depending on the bias conditions, with stable pulse trains observed at 640 GHz, 700 GHz, the mean repetition frequency of 666 GHz, and the sum frequency of 1.34 THz (due to nonlinear mixing). Performance is consistent and highly reproducible with exceptional stability observed over wide ranges of drive bias conditions. Furthermore, a monolithically integrated semiconductor optical amplifier is used to amplify the pulse trains, providing an average output power of 46 mW at 666 GHz.

We report for the first time generation of 640 GHz and 1.28 THz pulse repetition frequencies with high reproducibility, controllability and a wide operation range using passively mode-locked side-wall sampled-grating distribute Bragg reflector lasers.

We report 40 GHz passively mode-locked 1.55 μm AlGaInAs/InP lasers with integrated tapered semiconductor optical amplifiers producing nearly transform limited pulses with a pulse width of 4.3 ps and average output power of 200 mW.

We present an ultralow RF linewidth (192 Hz) and subpicosecond phase noise (260 fs) using a passively mode-locked quantum-well laser with feedback via a dual optical fiber loop.

Monolithic ∼1.55µm colliding-pulse mode-locked AlGaInAs/InP lasers with 3 and 5 quantum wells are compared. The 3 well device emitted pulses at 162GHz, with a width of 0.98ps, energy of 0.16pJ and time-bandwidth product of 0.47.

We report 40 GHz passively mode-locked 1.55 µm AlGaInAs/InP lasers with integrated semiconductor optical amplifiers producing nearly transform limited pulses with a pulse width of 4 ps and a peak power over 550 mW.

A novel 20 GHz 1.55 µm passively colliding-pulse mode-locked AlGaInAs/InP laser was demonstrated with a small RF linewidth (10 kHz), low timing jitter of 218 fs (4–80 MHz) and low divergence angle (14.7° × 27.3°).

We measured the absorption recovery times in reverse biased AlInGaAs multiple quantum well material designed to emit at around 1.5 μm wavelength. Absorption recovery times as low as 2.5 ps were found at -4V bias, with values below 5 ps consistently found for biases above 3 V. The short absorption recovery times obtained under reverse bias were confirmed by using cross-absorption modulation in the material to demonstrate wavelength conversion of a 10 GHz pulse train, showing both up and down conversion of the incident pulses.

Monolithic AlInGaAs compound-cavity lasers for harmonic ML at multi-GHz frequencies have been fabricated and assessed. Optical pulses of ∶ 1 ps long at 160 GHz have been obtained. The optimal cavity and reflector design has been investigated experimentally and theoretically.

Mode-locked laser diodes (MLLDs) are excellent candidates for generating ultrashort high frequency pulses for a number of applications, including optical clocking, sampling, and clock recovery. Although more prone to noise than active MLLDs, passive MLLDs do not require any external electrical oscillator. But many applications for such lasers require highly stable optical pulses with sub-picosecond timing jitter and in this paper we report a technique for reducing the RF phase noise in a passive MLLD. Regenerative mode locking is a technique used to significantly reduce the timing jitter by providing a self-referencing mechanism to continuously correct the phase timing of the pulses [1, 2]. However, many of the current techniques used are based on electrical extraction and high-Q RF filtering of the pulses, which adds several components and considerable system complexity. Here we present a simplified all-optical regenerative mode locking technique which can provide significant reductions in phase noise and timing jitter.

In recent years there has been a high level of interest in the properties of fast semiconductor saturable absorbers operating at λ ∼ 1.5»m. The applications for these include the fabrication of passively modelocked lasers[1] and wavelength conversion of optical data streams through cross-absorption modulation. To enable these effects to be utilised at the highest repetition rates, very fast absorption recovery times are required, in materials that can be conveniently integrated with optical gain elements. Several methods for achieving very short absorption recovery times have been demonstrated such as the inclusion of high densities of crystal defects in the material and the use of intersubband transitions. However, it is not possible to integrate these with gain elements operating at the same wavelength without the use of expensive and technologically demanding epitaxial regrowth processes.

The monolithic integration of four 10 GHz multi-colored mode-locked lasers with a 4×1 MMI, a SOA and an electroabsorption modulator has been demonstrated. The lasers produce 2.49 ps Sech2-pulses with TBP of 0.389.

We have characterized the reflectivity, modal discrimination, and passive mode locking performance of diode lasers with intracavity reflectors (ICR) composed of a different number of slots. Upon analysis, we demonstrate that a monolithic semiconductor mode-locked laser comprising a compound cavity formed by a single deeply etched ICR slot fabricated using the 1.55 μm AlGaInAs strained quantum-well material provides the best harmonic (M = 4) mode-locking performance, with Gaussian-pulses generated at a pulse repetition rate of 161.8 GHz and a pulse duration of 1.67 ps, providing a time-bandwidth product of 0.81.

High-power 40 GHz 1.55 μm passively mode-locked surface-etched distributed Bragg reflector lasers monolithically integrated with semiconductor optical amplifiers (SOAs) are reported. These are based on an optimized AlGaInAs/InP epitaxial structure with a three quantum-well active layer and a far-field reduction layer. The device produces near transform-limited sech2 pulses with the shortest measured pulse duration at 3.19 ps, and the narrowest measured radio frequency linewidth at 110 kHz. The highest average output power at ~155 mW with a peak power of >0.6 W was attained from the SOA-end facet while mode-locked. The beam divergences from the SOA side were narrow and symmetric (26.7° × 26.8°), which is highly desirable for butt coupling to a single-mode fiber.

We present a laterally coupled 1.55 μm AlGaInAs/InP distributed feedback laser monolithically integrated with a curved tapered optical amplifier, providing an output power of 210 mW with single transverse and longitudinal mode operation exhibiting a record low linewidth of 64 kHz.

We report femtosecond pulses from a passive C-band two-section AlGaInAs/InP mode-locked laser with a monolithically integrated passive waveguide made by quantum well intermixing. Without any external pulse compression, Lorentzian pulses are generated at a repetition frequency of ~38 GHz with 490 fs pulse duration, which is, to the best of our knowledge, the shortest pulse from any directly electrically pumped quantum well semiconductor mode-locked laser. The mode-locking range is relatively large and the ultranarrow pulse width is very stable over a broad range of driving conditions.

Optical self seeding feedback techniques can be used to improve the noise characteristics of passively mode-locked laser diodes. External cavities such as fiber optic cables can increase the memory of the phase and subsequently improve the timing jitter. In this work, an improved optical feedback architecture is proposed using an optical fiber loop delay as a cavity extension of the mode-locked laser. We investigate the effect of the noise reduction as a function of the loop length and feedback power. The well known composite cavity technique is also implemented for suppressing supermode noise artifacts presented due to harmonic mode locking effects. Using this method, we achieve a record low radio frequency linewidth of 192 Hz for any high frequency (>1 GHz) passively mode-locked laser to date (to the best of the authors’ knowledge), making it promising for the development of high frequency optoelectronic oscillators.

High output power 40 GHz 1.55 μm passively mode-locked surface-etched distributed Bragg reflector (DBR) lasers with monolithically integrated semiconductor optical amplifiers are reported. These are based on an optimized AlGaInAs/InP epitaxial structure with a three quantum well active layer and an optical trap layer. The device produces near transform limited Gaussian pulses with a pulse duration of 3.3 ps. An average output power during mode-locked operation of 130 mW was achieved with a corresponding peak power of >1 W.

We present a 10 GHz 1.55 μm all-active passively mode-locked laser based on a novel AlGaInAs/InP epitaxial structure with a three-quantum-well active layer and a passive far-field reduction layer. The device generated 1.06 ps pulses with a state-of-the-art timing jitter value of 194 fs (4-80 MHz), and a radio-frequency linewidth of 2 kHz, while demonstrating a low divergence angle (14.7° × 27.3°) with a twofold butt coupling efficiency to a flat cleaved single mode fiber, compared to the conventional five-quantum-well MLLs.

The monolithic integration of four 1.5 μm range AlGaInAs/InP distributed feedback lasers with a 4×1 multimode-interference optical combiner, a curved semiconductor optical amplifier, and an electro-absorption modulator using relatively simple technologies--sidewall grating and quantum well intermixing--has been demonstrated. The four channels span the wavelength range of 1530 to 1566 nm with a channel spacing of 12 nm. The epitaxial structure was designed to produce a far-field pattern as small as 21.2°×25.1°, producing a coupling efficiency with an angled-end single-mode fiber at twice that of a conventional device design.

We demonstrate a novel (to the best of our knowledge) 40 GHz passively mode-locked AlGaInAs/InP 1.55 μm laser with a low divergence angle (12.7°×26.3°), timing jitter of 1.2 ps (10 kHz-100 MHz), and a radio frequency linewidth of 25 kHz.

We characterized the reflectivity and the modal discrimination of intracavity reflectors (ICRs) with different numbers of slots and presented harmonic mode-locking operation of a monolithic semiconductor laser comprising a compound cavity formed by a single deeply etched slot ICR fabricated from 1.55 μm AlGaInAs strained quantum well material. Gaussian pulses were generated at a 161.8 GHz repetition rate with a pulse duration of 1.67 ps and a time-bandwidth product of 0.81.

We present a laterally-coupled 1.55 μm AlGaInAs/InP DFB laser monolithically integrated with an optical amplifier, providing an output power of 210 mW with single mode operation exhibiting a record low linewidth of 64 kHz.

Optoelectronic oscillators can provide low noise oscillators at radio frequencies in the 0.5-40 GHz range and in this paper we review two recently introduced approaches to optoelectronic oscillators. Both approaches use an optical fibre feedback loop. One approach is based on passively modelocked laser diodes and in a 40 GHz oscillator achieves up to 30 dB noise reduction. The other approach is based on resonant tunneling diode optoelectronic devices and in a 1.4 GHz oscillator can achieve up to 30 dB noise reduction.