Low-power consumption InP-based optical phase arrays with non-uniformly spaced output waveguides.

Optical Phase Arrays (OPAs) are expected to be an ideal solution to achieve beam shaping, laser radar (LIDAR), free-space optical communications, and spatially resolved optical sensors, etc. We demonstrated a low-power consumption 32-channel OPA with non-uniformly spaced waveguides based on InP substrate. The phase shifters are based on a p-i-n structure which are operated with reverse bias and have a low power consumption. Besides, in order to improve the performance especially to obtain larger steering angle and narrower beam divergence without increasing the number of channels, we have optimized the spacing between the output waveguides. The fabricated OPA achieved a steering angle of 35° with the side lobe suppression ratio more than 8.2 dB across the angle range from -20° to 20° in the far field, which is the largest phase tuning steering angle reported by InP-based OPAs as far as we know. The divergence angle is about 0.46° in the phase steering dimension and the power consumption of the OPA at each steering angle is lower than 7.5 mW.

Narrow linewidth electro-optically tuned multi-channel interference widely tunable semiconductor laser.

A narrow linewidth electro-optically tuned multi-channel interference (MCI) widely tunable semiconductor laser based on carrier injection is demonstrated in this paper. The MCI laser with a common phase section and a semiconductor optical amplifier (SOA) is packaged into a 16-pin butterfly box. The laser is characterized by a strategy: shifting the longitudinal mode and then aligning the reflection peak, which obtains a quasi-continuous tuning range over 48 nm. The corresponding side mode suppression ratios (SMSRs) are higher than 40 dB and frequency deviations from ITU-grid are less than ± 1 GHz. Threshold currents are less than 28 mA. Fiber coupled output powers are higher than 20 mW and power variations with fixed gain and SOA currents are less than 0.8 dB over the whole tuning range. Lorentzian linewidths are less than 320 kHz over the entire tuning range, which is one of the lowest results for monolithic widely tunable semiconductor lasers tuned by carrier injection. These results demonstrate the potential prospects of the MCI laser with carrier injection in the field of optical sensing and optical communications.

Wide-waveguide high-power low-RIN single-mode distributed feedback laser diodes for optical communication.

We present an 8-µm-wide 800-µm-long high-power, single-mode and low RIN DFB laser using a dual-waveguide structure. The introduced passive lower waveguide has weakenes the lateral optical confinement for the ridge waveguide, and thus reduces losses caused by the p-doped layers and maintains single mode stability of the laser. The fabricated laser exhibited an output power higher than 170 mW and a relative intensity noise (RIN) below -157 dB/Hz along with a side-mode suppression-ratio (SMSR) over 55 dB. The temperature tuning from -10°C to 60°C allows an 8.6 nm wavelength tunability with a variation coefficient of 0.12 nm/K. The relaxation oscillation frequency is around 8 GHz, and the linewidth is about 250 kHz at 100 mW output power for the fabricated laser. The characteristics of the proposed high-power laser, including high slope efficiency, single mode stability and low noise, make it a suitable candidate for optical communication.

Directly modulated azimuthally polarized vector beam laser design.

Directly modulated vector beam lasers are increasingly desirable for wide applications ranging from optical manipulation to optical communications. We report the first, to our knowledge, high-speed directly modulated vector beam laser with azimuthally polarized emission. It is a microcylinder cavity interacted with a proper second-order grating on top, which enables single mode lasing and efficient surface emission. Through theoretical and numerical analysis, the laser is designed in detail. With an optimized top grating, the emission of the laser is an azimuthally polarized vector beam. With high-differential-gain material and a small active region, the laser can be directly modulated with a high 3 dB bandwidth reach of 40 GHz in simulation. The proposed high-speed directly modulated semiconductor laser with an azimuthally polarized vector beam is promising for applications in fiber space communications or quantum information.

Narrow-linewidth thermally tuned multi-channel interference laser integrated with a SOA and spot size converter.

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.

Butterfly-packaged multi-channel interference widely tunable semiconductor laser with improved performance.

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.

Concentric microcavities for cylindrical vector beam 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.

Single-mode surface-emitting microcylinder/microring laser assisted by a shallowly-etched top grating.

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.

High-performance InP-based Mach-Zehnder polarization beam splitter with a 19 dB extinction ratio across C-band.

A high-performance InP-based polarization beam splitter (PBS) using a symmetrical Mach-Zehnder interferometer is experimentally demonstrated. The waveguides are aligned along the [011] direction, which results in a small reverse bias required and easy adjustment to realize the PBS. The experimental results indicate that the polarization extinction ratio (PER) is over 19 dB in the wavelength range from 1525 to 1570 nm with one arm injected with a 4.32 mA current and the other arm reversed biased at 5.14 V simultaneously. The PER is measured to remain above 18 dB in the same wavelength range even when the width varies by ±200 nm.

1 × 8 MMI based multi-channel interference laser integrated with SOA through a 2-port multimode interference reflector.

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.

Optimization algorithm based characterization scheme for tunable semiconductor lasers.

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.

Theory and simulation of multi-channel interference (MCI) widely tunable lasers.

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.