Improved performance of tunable single-mode laser array based on high-order slotted surface grating

Turn-key Kerr soliton generation and tunable microwave synthesizer in dual-mode Si3N4 microresonators

This study investigates the thermal compensation mechanism in dual-mode Si3N4 microresonators that demonstrates the ease of generation of single-solitons with nearly octave-wide spectral bandwidth. The deterministic creation of soliton frequency combs is achieved by merely switching the wavelength of a tunable laser or a semiconductor diode laser in a single step. The pump frequency detuning range that can sustain the soliton state is 30 gigahertz (GHz), which is approximately 100 times the resonance linewidth. Interestingly, these dual-mode resonators also support the coexistence of primary combs and solitons, enabling their utilization as functional microwave synthesizers. Furthermore, these resonators readily facilitate the generation of diverse multi-solitons and soliton crystals. This work presents a simplified system to access high-performance and versatile Kerr solitons, with wide-ranging applications in optical metrology, microwave photonics, and LiDAR.

Single-mode InGaAsP/InP BH lasers based on high-order slotted surface gratings

A single-mode InGaAsP/InP buried heterostructure (BH) laser based on high-order slotted surface gratings has been fabricated. The introduction of surface slotted grating can simplify the fabrication process of single-mode BH lasers notably. The laser shows a good single-mode emission performance, with larger than 30 dB side-mode suppression ratio (SMSR) when the current is between 200 and 400 mA. Calculations show that the gain coupling mechanism plays a key role for the slot grating to select the emission wavelength. The linewidth of the laser is measured. The fitted Gaussian and Lorentzian linewidths are 1500 and 550 kHz, respectively.

Quasi-continuous tunable semiconductor laser based on the gain-lever effect with full C-band coverage fabricated by standard lithography

A quasi-continuous tunable semiconductor laser covered full C-band is demonstrated. The quasi-continuous tuning range of the tunable semiconductor laser is significantly improved by optimizing the length of the phase section using the gain-lever effect, achieving a 36 nm range that covered the whole C-band. In the tuning range, 46 channels with 100 GHz spacing are achieved, and all channels exhibit a side mode suppression ratio above 30 dB. No regrowth or high-precision lithography is involved in the fabrication process of the tunable semiconductor laser, which has the potential to provide a cost-effective light source for dense wavelength division multiplexing systems.

Wide range thermal and athermal operation of slotted surface grating lasers

Athermalisation is a procedure in which the wavelength of a semiconductor laser remains unchanged even as the temperature is altered. This is achieved by altering the currents that flow through the laser so as to maintain the wavelength and avoid mode hops. In this study, we demonstrate that lasers operating with a large red-shift with respect to the gain peak yield the best performance in terms of the highest temperature operation and also in terms of the widest athermal operating range. In particular, a device with red detuning of approximately 25 nm yields the best results. This device is athermalised continuously (without mode hops) from 5 to 106 ^oC, and discontinuously to 115 ^oC while maintaining wavelength stability of $\pm$0.4 GHz/0.003 nm and side mode suppression ratio of above 40 dB in most of the continuous range and above 30 dB in the discontinuous regime. Operating in this manner will enable semiconductor lasers to be used without a thermoelectric cooler in applications where the temperature changes substantially.

1.3 μm wavelength tunable single-mode laser arrays based on slots

Two twelve-channel arrays based on surface-etched slot gratings, one with non-uniformly spaced slots and another with uniformly spaced slots are presented for laser operation in the O-band. A wavelength tuning range greater than 40 nm, with a side-mode suppression ratio (SMSR) > 40 dB over much of this range and output power greater than 20 mW, was obtained for the array with non-uniform slots over a temperature range of 15 °C - 60 °C. The introduction of multiple slot periods, chosen such that there is minimal overlap among the side reflection peaks, is employed to suppress modes lasing one free spectral range (FSR) from the intended wavelength. The tuning range of the array with uniformly spaced slots, on the other hand, was found to be discontinuous due to mode-hopping to modes one FSR away from the intended lasing mode which are not adequately suppressed. Spectral linewidth was found to vary across devices with the lowest measured linewidths in the range of 2 MHz to 4 MHz.

Back-side-on-BOX heterogeneously integrated III-V-on-silicon O-band discrete-mode lasers

We demonstrate foundry-fabricated O-band III-V-on-silicon discrete-mode lasers. The laser fabrication follows the back-side-on-buried-oxide laser integration process and is compatible with complex, multilayer, silicon-on-insulator based platforms. A series of devices were characterized, with the best devices producing on-chip powers of nearly 20 mW with Lorentzian linewidths below 20 kHz and a side mode suppression ratio of at least 60 dB.

Genetic algorithm optimization of high order surface etched grating tunable laser array

A genetic algorithm is developed with a view to optimizing surface-etched grating tunable lasers over a large optimization space comprised of several variables. Using this approach, a new iteration of slotted lasers arrays are optimized showing significant improvements over previous designs. Output power, lower grating order, fabrication tolerance and performance at high temperatures are among key parameters improved. The new designs feature a much lower grating order (24-29) than used previously (37). The biggest improvement is a near doubling to slope efficiency to 0.1-0.13 mW/mA, with wavelengths from the array covering the C-band . The designs show a reduced sensitivity to etch depth variations. Designs with linewidths down to 100 kHz are also simulated. This algorithm can be readily applied to different wafer materials to efficiently generate slotted lasers designs at new wavelengths.

850 nm GaAs/AlGaAs DFB lasers with shallow surface gratings and oxide aperture

We present and experimentally demonstrate a novel oxide-confined ridge-waveguide distributed feedback (DFB) laser with the first-order surface grating using only a single growth step. The metal contacts are laterally offset from the ridge waveguide to inject current thus avoiding unwanted light absorption from the electrodes. The oxide aperture is defined by selective wet oxidation of aluminium-rich material, which confines the injection current from the electrodes to the active layer under the ridge waveguide. This allows that a thin ridge layer can be used with relatively higher refractive index compared to the active layer and thus the grating can be shallowly etched but provides a strong coupling effect. The fabricated 150 µm-long DFB laser exhibited a relatively low threshold current of 8 mA and a side mode suppression ratio (SMSR) up to 50 dB at the injected current of 32 mA around 4 times threshold at 20 °C. Stable single mode operation has been observed for the fabricated DFB laser over the temperature range from 10 to 50 °C. The variation of wavelength with temperature Δλ/ΔT was 0.06 nm/°C. The proposed laser may have advantages combined both DFB lasers and vertical-cavity surface-emitting lasers (VCSELs), such as single mode, stabilized polarization, potentially narrow linewidth and low power consumption. In addition, the laser is regrowth free, thus has advantages of low cost and high reliability.

Tuning behaviour of slotted vernier widely tunable lasers

A detailed thermo-optic model combining the 1D transfer matrix method and a 3D finite element method is developed and used to simulate a widely tunable vernier laser based on surface etched slots. The model is used to investigate the experimentally observed tuning patterns. At low injection currents, carrier tuning dominates, while at high currents, thermal tuning is the dominant mechanism. These lasers are very simple to fabricate and have a wide tuning over 50 nm, but SMSR and linewidth performance is not yet optimised. Simulations give an insight into the observed tuning efficiency and linewidth performance of the lasers, with high carrier densities in the grating regions being identified as a key area, which is presently limiting these parameters.

Single-mode semiconductor lasers fabricated by standard photolithography for direct modulation

The output characteristics, modal properties, far-field profiles, and dynamic modulation responses of semiconductor lasers with surface higher-order gratings fabricated by the standard photolithography are presented. Single-mode semiconductor lasers with 20^th- and 37^th-order gratings for the 1.55 µm wavelength range are realized. The single-mode semiconductor lasers with 20^th-order gratings have lower threshold currents and higher slope efficiencies than those with 37^th-order gratings. The surface higher-order grating placed closed to the output facet can deteriorate the vertical far-field profile of the semiconductor laser. However, the properties of the semiconductor laser's single-mode operation are not affected by the surface higher-order grating's position in the ridge waveguide. The -3 dB bandwidth of these single-mode semiconductor lasers can achieve 9 GHz at 100 mA, which is the highest, to the best of our knowledge, for such a kind of single-mode semiconductor laser with a surface higher-order grating.

Eight-channel laser array with 100 GHz channel spacing based on surface-slotted structures fabricated by standard lithography

An eight-channel laser array with 100 GHz channel spacing based on surface-slotted structures is demonstrated. Wavelength selection is realized by using a group of micrometer-order slots fabricated by standard lithography technology. An output power of over 14 mW and a side-mode suppression ratio of better than 35 dB for each laser within the array are achieved. A laser array without tuning for 100 GHz channel spacing by standard lithography was realized for the first time, to the best of our knowledge. The laser array can be used to enhance the capacity of communication links and provides a promising light source for photonic-integrated circuits.

Athermal operation of multi-section slotted tunable lasers

Two distinct athermal bias current procedures based on thermal tuning are demonstrated for a low-cost, monotlithic, three section slotted single mode laser, achieving mode-hop free wavelength stability of ± 0.04 nm / 5 GHz over a temperature range of 8-47 °C. This is the first time that athermal performance has been demonstrated for a three-section slotted laser with simple fabrication, and is well within the 50 GHz grid spacing specified for DWDM systems. This performance is similar to experiments on more complex DS-DBR lasers, indicating that strong athermal performance can be achieved using our lower-cost three section devices. An analytical model and thermoreflectance measurements provide further insight into the operation of multi-section lasers and lay the foundation for an accurate predictive tool for optimising such devices for athermal operation.