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In this article, we report the demonstration of directly modulated grating-assisted microcylinder surface-emitting lasers (GAMSELs) with low threshold. Two second-order gratings are added onto the side and top of the microcylinder cavity to select a single mode with a radially polarized emission pattern and efficiently emit the mode vertically, respectively. Laser with cavity radius of 6.05 μm is demonstrated with continuous-wave lasing ranging from 1 °C to 50 °C. This radius is approaching the theoretically smallest radius for the microcylinder laser to work at O band. A low threshold of 3.6 mA at 15 °C is obtained for the GAMSEL laser. Single-mode lasing with side-mode suppression-ratio (SMSR) larger than 40 dB is also shown here. GAMSELs with different cavity radii are demonstrated as laser arrays. 3 dB direct modulation bandwidth of 12 and 14 GHz of GAMSELs with radius of about 8 and 10 μm are obtained, respectively. Besides, effects of the duty cycle of the top and side gratings, scattering losses of the cavity, gain peak of the epitaxial wafer and ion implantation are experimentally investigated.

High performance InP-based polarization beam splitters (PBSs) with a symmetrical Mach–Zehnder interferometer (MZI) are theoretically and experimentally demonstrated. The p-i-n waveguide is exploited to employ the phase shifters in the two arms of the MZI. Injection current and reverse bias inducing electro-optic (EO) effects in each of the MZI arms are analysed in detail when the waveguides are aligned along both the [011] and $[ {01\bar{1}} ]$ directions. Results indicate that the birefringence from reverse bias help to realize the PBS combining with the polarization-independent carrier-induced refractive index change from the injection current. Theoretical prediction shows that the polarization extinction ratio (PER) is over 35 dB at 1550 nm for the PBSs with the waveguides aligned along both directions. Furthermore, the PBS with the waveguides aligned along the [011] direction can be adjusted more easily to work at the best operating point and get the higher birefringence which requires lower reverse bias exhibiting better performance across the C-band compared with the $[ {01\bar{1}} ]$ direction. The fabricated PBSs exhibit a PER over 19 dB (14 dB) in the wavelength range from 1525 to 1570 nm with one arm injected of 2.88 mA (0.2 mA) current and the other arm reversed biased at 5.63 V (7.89 V) when the waveguides aligned along the [011] ( $[ {01\bar{1}} ]$ ) direction. The PER of both PBSs is expected to be 20 dB across the C-band with the help of a birefringence contribution arising from inserting waveguide arms of different widths.

Cylindrical vector (CV) beams are highly desirable for wide applications ranging from manipulation to communications. Despite diverse schemes of CV beam emitters, the efficient generation of vector...

A narrow-linewidth thermally tuned multi-channel interference (MCI) laser integrated with a semiconductor optical amplifier (SOA) and spot size converter (SSC) is demonstrated in this paper. A MCI laser integrated with SOA through chirped grating is successfully realized for the first time, which achieves a tuning range of more than 42.5 nm with side-mode suppression ratios (SMSRs) higher than 48 dB and Lorentzian linewidth below 100 kHz. InGaAlAs multiple quantum wells (MQWs) and thermal tuning are used to reduce linewidth. The integration of SSC greatly improves the coupling efficiency between the laser and a lensed fiber. The MCI laser integrated with SSC achieves more than 16 dBm output power coupled into a lensed fiber. Air layers are fabricated in the phase sections to increase the heating efficiency. The total thermal tuning power is below 20 mW across the whole tuning range.

The high-performance thermally tuned multi-channel interference widely tunable semiconductor laser was demonstrated for the first time, achieving tuning range of more than 60nm, SMSRs of up to 56dB and Lorentzian linewidth of less than 100kHz.

Based on InP platform, we design and optimize a compact integrated device to realize efficient lasing of azimuthally polarized beam. Single-mode selection, emission and high speed can be achieved under electrical pumping.

Lorentzian linewidth of electro-optically tuned multi-channel interference widely tunable laser has been demonstrated to be less than 350 kHz in the entire tuning range. © 2020 The Author(s)

850 nm single-mode surface-emitting DFB laser based on surface gratings has achieved a threshold current of 1.8 mA and a side-mode suppression-ratio of 47 dB for a large-area oxidized-aperture (2×50 µm2).

A new design of radially polarized surface-emitting laser (RPSEL) is presented for the first time. RPSEL which has a second-order grating shallowly etched on top of a microcylinder cavity is easy to fabricate. The grating selects a specific whispering-gallery mode with the proper emission pattern (radially polarized emission) to lase and simultaneously scatters the mode vertically to form the surface emission. Through numerical simulations, RPSEL is predicted to be a single-mode laser with radially polarized surface emission. RPSEL can be rather easily realized at different wavelengths such as the near infrared 1310 and 1550 nm wavelength bands. Furthermore, it can be fabricated with microcylinder cavities with very small radii even down to wavelength-scale, therefore it has the potential to realize very high modulation bandwidth and very low threshold current.

Thermally tuned multi-channel interference (MCI) lasers are really advantageous for applications of coherent optical communication systems, in which light sources with narrow linewidth are critical requirements. To optimize the thermally tuned MCI lasers, simulations of thermal effects are quite important. In this paper, we analyze the thermal tuning efficiency of such lasers using the finite element analysis software Comsol. First, the effect of the air insulation thickness on the thermal tuning efficiency is simulated and we found that the thicker air insulation the larger phase shift. Then, influences of different microheater lengths on the temperature distribution of waveguide core are analyzed in detail. Simulation results indicate that the waveguide core temperature is increasing with the microheater length. In addition, considering the lasing wavelength depends on the temperature change of InP, the curve of phase shift versus thermal tuning power is obtained. It is predicted that the microheater power of πphase shift is about 5.4 mW for a 100 μm-long suspended thermal tuning waveguide. Finally, for the verification of our simulations, some test structures of the suspended thermal tuning waveguide with the air insulation are experimentally fabricate. By measuring the phase of the output light under different thermal power, about 5.7 mW microheater power is needed for π-phase shift of the 100 μmlong suspended thermal tuning waveguide, which is consistent with the simulation result. It can be concluded that the thermal simulations and structure designs will be beneficial for the realization of the thermally tuned MCI lasers in the future.

Semiconductor lasers based on microcylinder/microring cavities supporting high-quality factor modes are promising candidates of optical sources for optical interconnect. However, their multi-mode lasing performance and non-directional emission characteristic restrict their applications. In this paper, a single mode surface-emitting laser at O-band based on a second-order grating shallowly etched on the top of the microcylinder/microring cavity is proposed and demonstrated. The second-order top grating cannot only scatter the whispering gallery modes vertically to form surface emission but also select a single mode to lase. The laser is electrically pumped and continuous wave operated in a wide temperature range with side-mode suppression-ratio larger than 40 dB. The upward surface-emitting optical power exceeds 1 mW. Except for O-band, the laser can be easily realized at other long-wavelength communication bands, such as C-band and L-band.

A multi-channel interference (MCI) widely tunable semiconductor laser is described in detail with improved performance in this paper. The MCI laser without the common phase section was packaged into a standard 14-pin butterfly package. The device realized a tuning range of more than 40 nm with side mode suppression ratios (SMSRs) higher than 48 dB and about 7 dBm fiber power. By making the gain section and the phase sections to be surface ridge waveguides, threshold currents of the laser have become less than 18 mA across the tuning range. Besides, tuning characteristics of the MCI laser were experimentally studied in detail for the first time. The MCI laser can be treated as a combination of eight Fabry-Pérot (FP) cavity lasers which share the same gain section. It is found that when the eight arm phase sections are completely in phase at the lasing wavelength, the operating currents are at maxima of the output power curves. The relationship between the lasing wavelength and the injection currents of the eight arm phase sections has been introduced and analyzed.

We propose a design of single-mode orbital angular momentum (OAM) beam laser with high direct-modulation bandwidth. It is a microcylinder/microring cavity interacted with two types of second-order gratings: the complex top grating containing the real part and the imaginary part modulations and the side grating. The side grating etched on the periphery of the microcylinder/microring cavity can select a whispering gallery mode with a specific azimuthal mode number, while the complex top grating can scatter the lasing mode with travelling-wave pattern vertically. With the cooperation of the gratings, the laser works with a single mode and emits radially polarized OAM beams. With an asymmetrical pad metal on the top of the cavity, the OAM on-chip laser can firstly be directly modulated with electrical pumping. Due to the small active volume, the laser with low threshold current is predicted to have a high direct modulation bandwidth about 29 GHz with the bias current of ten times the threshold from the simulation. The semiconductor OAM laser can be rather easily realized at different wavelengths such as the O band, C band, and L band.

In this letter, we report the first experimental demonstration of the multi-channel interference (MCI) widely tunable semiconductor laser. Mode selection of the MCI laser is achieved by the constructive interference of eight arms with unequal length difference. Compared with conventional widely tunable semiconductor lasers based on distributed Bragg reflectors, fabrication of the MCI laser is simpler with large fabrication tolerances. A quasi-continuous tuning range of about 52.3 nm (1538.96–1591.26 nm) has been demonstrated at a temperature of 23 °C with side-mode suppression-ratios greater than 44 dB across the whole tuning range (typically greater than 48 dB).

A novel design of grating-assisted microcylinder surface-emitting laser (GAMSEL) is presented. GAMSEL has two gratings: top grating and side grating. Both gratings have the number of periods close to the azimuthal mode number of the whispering gallery mode (WGM) supported by the microcylinder cavity, therefore, they behave like second-order gratings of a straight waveguide. The top grating scatters the WGM vertically so as to form the surface emission while the side grating selects the mode having the proper emission pattern to lase. Through the cooperation of the two gratings, GAMSEL becomes a single-mode surface-emitting laser. Due to its small volume, GAMSEL is predicted through simulation to have a threshold current about 1 mA and a direct modulation bandwidth higher than 40 GHz. Besides, relying on the lateral microcylinder cavity, GAMSEL does not require highly reflective mirrors as vertical-cavity surface-emitting lasers do, which makes this design easily apply to different wavelengths such as the near infrared 1310- and 1550-nm wavelength bands.

A thermally tuned multi-channel interference widely tunable semiconductor laser is designed and demonstrated, for the first time to our knowledge, that realizes a tuning range of more than 45 nm, side-mode suppression ratios up to 56 dB, and Lorentzian linewidth below 160 kHz. AlGaInAs multiple quantum wells (MQWs) were used to reduce linewidth, which have a lower linewidth enhancement factor compared with InGaAsP MQWs. To decrease the power consumption of micro-heaters, air gaps were fabricated below the arm phase sections. For a 75 μm long suspended thermal tuning waveguide, about 6.3 mW micro-heater tuning power is needed for a 2 π round-trip phase change. Total micro-heater tuning power required is less than 50 mW across the whole tuning range, which is lower than that of the reported thermally tuned tunable semiconductor lasers.

Cylindrical vector (CV) beams with polarization singularities have attracted intense research interest because of their important applications in optical trapping and manipulation, imaging, and high-speed optical communication. In this Letter, we propose a high-speed integrated device designed to emit fundamental CV beams, including both radially and azimuthally polarized beams. The device is composed of two grating-assisted concentric microcavities based on an InP platform. The microcavity with only a second-order grating shallowly etched on the top is optimized and used for improved azimuthally polarized CV beam emission. Another microcavity with both a triangular-shaped side grating and a rectangular-shaped top grating is employed for radially polarized CV beam lasing. The proposed devices can be further developed to be compatible with wavelength-division multiplexing and mode-division multiplexing techniques. They hold great potential in CV beam-based classical and quantum communication systems.

The multi-channel interference widely tunable laser monolithically integrated with semiconductor optical amplifier through a deeply etched slot has been demonstrated. Tuning range is about 35 nm with SMSRs higher than 40 dB.

Multi-channel interference laser with a compact and efficient shallow-deep transition was fabricated, achieving around 22 rnA threshold currents, > 40 nm tuning range covering C band, > 40 dB SMSRs.

Grating-assisted microcylinder surface-emitting laser (GAMSEL) in the O-band was demonstrated. Continuous-wave working with side-mode suppression-ratio >40dB has been realized and the output beam is radially polarized.

We designed and fabricated Mach Zehnder Modulators (MZMs) with 40GHz with a coplanar waveguide electrode (CPW) structure.

We demonstrate the MCI laser integrated with SOA through a two-port multi-mode interference reflector. A tuning range of more than 45 nm with SMSRs up to 47 dB is achieved.

In this paper, an optimization algorithm based characterization scheme for tunable semiconductor lasers is proposed and demonstrated. In the process of optimization, the ratio between the power of the desired frequency and the power except of the desired frequency is used as the figure of merit, which approximately represents the side-mode suppression ratio. In practice, we use tunable optical band-pass and band-stop filters to obtain the power of the desired frequency and the power except of the desired frequency separately. With the assistance of optimization algorithms, such as the particle swarm optimization (PSO) algorithm, we can get stable operation conditions for tunable lasers at designated frequencies directly and efficiently.

Monolithic widely tunable semiconductor lasers based on multi-channel interference (MCI) have been demonstrated with tuning range more than 53.6 nm and SMSR up to 52 dB being achieved.

A novel surface-emitting laser structure based on a microcylinder cavity etched with second-order gratings, is presented. Extensive numerical simulations show that ∼1mA threshold current and >40GHz direct modulation bandwidth can be realized with it.

A 1 × 8 multimode interferometer (MMI) based multi-channel interference (MCI) widely tunable laser integrated with semiconductor optical amplifier (SOA) through a 2-port multimode interference reflector (MIR) is reported in this paper. The 2-port MIR can be fabricated with deeply etched waveguides of the MCI laser with no extra fabrication process, which decreases the fabrication complexity greatly. To reduce the loss arising from mode mismatch between surface and deep ridge waveguides, a tapered shallow-deep transition structure is designed and fabricated with a loss of 0.09 dB ± 0.03 dB. The MCI laser with integrated SOA achieves a tuning range of 52.5 nm with side mode suppression ratios higher than 40 dB across the tuning range and more than 13 dBm output power coupled into a lensed fiber at room temperature.

A novel design of an InP-based monolithic widely tunable laser, multi-channel interference (MCI) laser, is proposed and presented for the first time. The device is comprised of a gain section, a common phase section and a multi-channel interference section. The multi-channel interference section contains a 1x8 splitter based on cascaded 1 × 2 multi-mode interferometers (MMIs) and eight arms with unequal length difference. The rear part of each arm is integrated with a one-port multi-mode interference reflector (MIR). Mode selection of the MCI laser is realized by the constructive interference of the lights reflected back by the eight arms. Through optimizing the arm length difference, a tuning range of more than 40 nm covering the whole C band, a threshold current around 11.5 mA and an side-mode-suppression-ratio (SMSR) up to 48 dB have been predicted for this widely tunable laser. Detailed design principle and numerical simulation results are presented.