This PDF file contains the front matter associated with SPIE Proceedings Volume 11182, including the Title Page, Copyright information, Table of Contents, Introduction and the Author and Conference Committee lists

Low-cost tunable lasers are key enablers for wide deployment of dense wavelength division multiplexing (DWDM) technology in upcoming 5G wireless networks. Simple and compact tunable V-cavity laser (VCL) have been previously reported with direct modulation up to 10Gbps. The transmission distance was limited to below 10km due to wavelength chirp and chromatic dispersion of optical fiber in the telecom C-band. Here we present an electro-absorption modulated tunable V-cavity laser (VCL) based on InGaAlAs/InP multiple quantum wells. The modulator is monolithically integrated with the half-wave coupled VCL, which are fabricated with a single shallow etch for ridge waveguides and a single deep etch step for reflecting facets and trenches. No grating nor epitaxial regrowth is required. A deep-etched trench serves as the partial reflecting front mirror for the laser, while providing an excellent electrical isolation between the laser and the modulator. 50-channel wavelength tuning with 100 GHz spacing is achieved, with side-mode suppression ratio as high as 47 dB. Error-free transmission over 50 km is demonstrated at 10 Gbps, with receiver sensitivity better than -23 dBm.

We propose a silicon modulator in a multi-mode waveguide based on the anti-symmetric Bragg grating (AS-BG). When the incident light is in the fundamental transverse electric (TE₀) mode, the reflected light of the AS-BG is in the first order transverse electric (TE₁) mode, rather than the TE₀ mode. Therefore, the reflected TE₀ mode is radiated in a tapered waveguide (WG) that connects a multi-mode and single-mode WG. As a result, the back reflection of the Bragg grating (BG) based silicon modulator avoids the utilization of an optical circulator, especially when ingrating with a semiconductor laser, which is susceptible to the external light.

Silicon photonics has become very popular because of the compatibility with mature CMOS technologies. However, it is still very difficult for pure silicon to realize various photonic devices for large-scale photonic integrated circuits due to the material intrinsic properties. Currently silicon-plus photonics, which introduces some specific optoelectronic materials on silicon to overcome the shortcomings of silicon, is becoming more and more attractive a very important role. This paper gives a review and discussion on silicon-plus photonics, including the structures, devices and applications for on-chip light-manipulation and photodetection.

1550nm laser diodes have been widely used in the field of optical fiber communication and optical fiber sensing systems. However it is a relatively new and important light source for Lidar. Most of the 1550nm commercial lasers for Lidar application are diode pumped fiber lasers or fiber amplifiers. This article introduces 1550nm monolithic MOPA (Master-Oscillator Power Amplifier) diode laser chips, single-mode PM fiber pigtailed butterfly packaging and their applications in the field of Lidar, especially for wind sensing and autonomous driving.

Monolithic integration of III–V semiconductor materials on planar on-axis silicon (001) is one of the most promising method for low-cost and scalable photonic integrated circuits. Here, we present InAs/GaAs quantum dots microdisk lasers monolithically grown on on-axis Si (001) substrate with ultra-low lasing threshold under room-temperature continues-wave optical pumping. The promising lasing characteristics of the microdisk lasers with ultra-low threshold and small footprint represent a major advance towards large-scale, low-cost integration of laser sources on silicon-based platform.

We study the phase requirement in phased-array antennas. Firstly, we present a tunable and wideband microwave photonic phase shifter based on polarization-dependence of the LiNbO3 Mach-Zehender modulator (MZM).With the proposed device, the phase of the optical microwave signal output from the polarizer can be tuned from 0 to 360 degree by simply adjusting the polarization direction of the lights whereas the amplitude keeps constant. A full range tunable phase shifting in the frequency range of 10 - 35 GHz is achieved. Secondly, we focus on the photodetector (PD) phase response with different input optical power and different PD. We study the Phase Retardation in InGaAs Photodetectors. The phase response of different PDs will affect the phased-array antennas.

In modern radar system, pulse compression technique has been widely used to increase the detection distance and range resolution. To enlarge the pulse compression ratio, the microwave signals are often phase modulated, such as phase-coded or frequency chirped. Conventionally, the phase-modulated microwave signals generated by electrical methods suffer from low microwave carrier frequency, limited bandwidth, low data rate and high transmission loss. Photonic-assisted generation and transmission of phase-modulated signals is a promising candidate to overcome these limitations In this paper, we review our recent works about the photonic generation and transmission of phase-modulated microwave signals, including the simultaneously frequency up-conversion and phase-coding, background-free frequency-doubled phase-coded microwave signal generation, phase-coded microwave pulse generator by optoelectronic oscillation (OEO), as well as transmission of dual-chirped microwave signals with chromatic-dispersion-induced power fading (CDIP) compensation and elimination technology. These works represent the new progresses in photonic approaches to generate and transmit phase-modulated microwave signals, which has great potential in the modern radar system.

For the requirement of cold atom interference technology, a 780nm narrow line width extended cavity diode laser device is developed and verified. Based on the simulation modeling of extended cavity and light beam, the laser structure, hermetic package, hybrid integration process and thermal control design is introduced. Then the integration of LD and multiple micro-optical elements are realized with a self-building integration platform, and the die-bonding process is also indicated in details. Finally, the integrated device is tested and verified to have 100KHz line width in 780.24nm, with a 50mW output power.

Large smile, the emitters in a laser diode are vertically displaced, is always a big obstacle to affect the directly application of high power laser diode. In this report, a symmetrical structure, that bonding two submounts on the top and bottom of heat sink to control the smile effect by balancing the packaging induced stress, is designed. A cm bar with less than 1 um smile value delivering more than 200W continuous wave (CW) mode output power with power conversion efficiency (PCE) 65% is reported. The lifetime can reach more than 20000 hours. We also report the applications of high power and low smile vertically stacked laser bars, like forming a wider line for glass surface treatment and a rectangular beam for cladding. A 2x14mm² rectangular beam was built with 32 bars vertical stack to produce 6kW CW mode output power with a beam uniformity of more than 80%.

In this paper, the far-field characteristic of the vertical-cavity surface-emitting laser (VCSEL) incorporating a highcontrast subwavelength grating (HCG) is analyzed by finite-difference time-domain (FDTD) method. Full three-dimensional simulations are carried out by utilizing FDTD solutions software. We study the parameters of HCG made from GaAs/AlOx which is defined by wet oxidation of an Al_0.98Ga_0.02As spacer layer. We have simulated HCG-VCSELs with different HCG periods and oxide aperture diameters. Various far-field patterns including single-lobe, double-lobe, triple-lobe shapes are obtained with the designed HCG-VCSEL. More interestingly, by tuning the HCG periods and the oxide aperture diameter, the far-field emission patterns transform from double-lobe to single-lobe shapes. By proper design of the two parameters, one can obtain Gaussian-like beam outputs, double-lobe or multi-lobe beams. The fullwidth half-maximum (FWHM) of the far-field divergent angle of the Gaussian-like fundamental mode obtained with grating periods of 23 and oxide aperture diameter of 8 μm is less than 5 degree. This opens a new path for engineering a VCSEL’s emission properties and provides guideline for actual device fabrication.

Traditional NIR laser night vision systems can only obtain 2D images without target range information, and are also easily affected by fog, rain, snow and foreground/background. To solve the problems above, 3D laser night vision based on range-gated imaging has been developed. This paper reviews 3D range-gated imaging advances and focuses on 3D rangeintensity correlation imaging (GRICI) due to its better real time performance and higher spatial resolution. In GRICI systems, the typical illuminator is eye-invisible pulsed semiconductor laser, and the image sensor chooses gated ICCD or ICMOS with mega pixels and ns-scaled gate time. To realize 3D night vision, two overlapped gate images with trapezoidal or triangular range-intensity profiles are grasped by synchronizing the puled laser and the gated sensor. The collapsed range is reconstructed by the range-intensity correlation algorithm, and furthermore 2D and 3D images can both be obtained at the same frame rate. We have established 3D NIR night vision systems based on triangular GRICI, and the experimental results demonstrate that 3D images realize target extraction from background and through windows or smoke. The range resolution minimum is about less than 0.2m at the range of 1km in our GRICI-NV3000, and the range maximum of 3D imaging is about 5km in our GRICI-NV6000.

In this paper, we propose and demonstrate a novel generation scheme for the optical frequency comb (OFC), which is pumped by the optical injection and enhanced by the self-recirculating modulation. A directly modulated semiconductor laser under the optical injection is driven into the nonlinear period-one oscillation dynamic, which provides a primary OFC seed source with only several sparse comb lines and poor flatness. An enhanced OFC can be generated by modulating this directly modulated semiconductor laser in a closed loop, wherein the modulating signal is derived from the primary OFC. The performance of the proposed OFC is optimized through controlling the injection parameters and the self-recirculating modulation index.

High power diode lasers (HPDLs) have been applied in more and more fields, such as material processing, pumping of solid-state lasers and fiber lasers, medical therapy. With the improvement of output power, efficiency and reliability, thermal management has been one of most critical issue for HPDLs. The junction temperature of a diode laser package has critical effects on laser characteristics, affecting wavelength, output power, threshold current, slope efficiency, and operating lifetime. Lower junction temperature is an effective means to achieve high output power and high electrooptical conversion efficiency of diode lasers. In recent years, high-power diode lasers operated at cryogenic temperature have attracted academic interests. Herein, high power diode lasers suitable at cryogenic temperature and a measurement setup at cryogenic temperature have been developed. The optical-electrical performance of microchannel cooled high power diode lasers from 0℃ ~ -60℃ have been studied theoretically and experimentally. The output power increases 18% and the conversion efficiency increases 6.3% from 0 ºC to -60 ºC. The high diode laser bars operated at cryogenic will be applied in pumping high energy lasers in the future.

We propose an on-chip optical narrowband reflector (NBR) based on two cascaded Bragg gratings (BGs). A π phase shifted anti-symmetric Bragg grating (π-PS-ASBG) and a rear uniform Bragg grating (UBG), are in-line connected. The π-PS-ASBG provides a hybrid mode resonance between the even- and odd TE (TE₀ and TE₁) modes, while the UBG is used as a rear reflector to reflect the TE₀ mode that transmitted from the π-PS-ASBG. The reflection bandwidth decreases when the coupling coefficient increases, which is different from traditional UBG. The performances are theoretically studied via both the rigorous three-dimensional finite-difference time-domain (3D-FDTD) method and multimode transmission matrix method (MTMM). The calculated 3-dB bandwidth is 0.16 nm when the whole grating length is 400 μm (π-PS-ASBG: 200 μm and UBG: 200 μm) and the coupling coefficients of the π-PS-ASBG and rear UBG are 240cm^-1 and 110cm^-1, respectively. The proposed NBR can be applied in the cases requiring narrow reflection such as narrow linewidth semiconductor lasers.

A parallel hybrid-integrated optical injection locking (PHOIL) DFB laser with narrow linewidth is experimentally demonstrated by using REC technology. The linewidth of the PHOIL DFB laser is significantly narrowed under the injection locking state. The linewidth of the PHOIL DFB laser is measured to be under 100 kHz, compared with 1034.2 kHz under free running state. The narrowest linewidth of the PHOIL DFB laser can be as low as 31.9 kHz. The nonlinear distortions of the PHOIL DFB lasers, including third-order intermodulation distortion (IMD3) and spurious-free dynamic range (SFDR), are also suppressed significantly. The IMD3 is reduced by 4.33 dB and SFDR is also increased from 77.63 dB·Hz^2/3 to 82.71 dB·Hz^2/3.

Vertical-cavity surface-emitting lasers (VCSELs) have wide applications in data communication, sensing, and consumer electronics, because they have many advantages, such as circular beam, low power consumption, high modulation speed, low cost, high reliability, and 2D array configuration. Metastructure like high-contrast grating (HCG) has many unique optical properties which can be used to construct novel VCSELs. Here we study the TE-polarization HCG for 940 nm wavelength range and design high-quality HCG-based vertical cavities with heterostructures aiming at HCG-VCSEL. The TE-polarization HCG-VCSEL at 940 nm is finally designed with a Q-factor of ~3.6×10⁵.

Vertical cavity surface emitting laser (VCSEL) based short reach optical solutions are widely deployed in the applications with the aggregated data rate from 10 Gb/s to 400 Gb/s and transmission distance less than 100m. Even with the great advantages of power consumption and cost, 100 Gb/s per lane multimode interconnect is still at stake due to the great challenges imposed by VCSEL design and multimode transmission. Besides the bandwidth challenge, co-design of VCSEL and electrical driver in both circuit and packaging level become significantly important with electrical and photonic chips getting close in a co-package form factor. In this paper, we will establish the theory on the VCSEL modeling and propose a comprehensive electro-optical co-design framework for power-efficient high-speed VCSEL transmitter targeting at 50 Gbaud. Bandwidth enhancement based on photon-photon resonance is also investigated with VCSELs injection locked by an optical frequency comb.

A method to obtain the thermal resistance as a function of ambient temperature is described. From the analysis of bandwidth verse internal temperature, we derive the thermal limits, providing a basis for next generation design.

Based on vertical-cavity surface-emitting lasers (VCSELs) with optical injection and polarization-rotated optical feedback, we propose and numerically demonstrate a scheme for generating synchronized random bit sequences (SRBS) for two legal users at different locations. For the scheme, the chaotic signal generated by a driving VCSEL (D-VCSEL) subject to chaotic optical injection are utilized to simultaneously drive two VCSELs (A-VCSEL and B-VCSEL) with polarization-rotated feedback, then the chaotic outputs from A (B)-VCSEL are used as physical entropy sources to generate SRBS. The simulated results show that, the SRBS at a rate up to 400 Gbits/s can be achieved after adopting suitable post-processing method. The security of this scheme can be ensured by a high-quality synchronization between A-VCSEL and B-VCSEL while relatively low-quality synchronization between D-VCSEL and A (B)-VCSEL. Moreover, the BER and the randomness of generated SRBS are also discussed.

The monolithic integration of a tunable V-coupled-cavity laser based on half-wave multimode interference reflector (MIR-VCL) with a travelling-wave Mach-Zehnder modulator (TW-MZM) on generic InP foundry platform is present in this paper. The formation mechanism of pi-coupling-phase difference and the contradiction among loss, optimal coupling phase difference and optimal coupling coefficients of half-wave coupler are analyzed. Single electrode tuning of 11 channels of about 7.3nm wavelength range is obtained, which is determined by the cavity length and the 10% cavity length difference. Among the whole wavelength tuning range, the side mode suppression ratios (SMSRs) are all above 35dB and the typical one is about 42dB. The Mach-Zehnder modulator with optimized travelling wave electrode is integrated with the MIR-VCL by two two-ports MIRs, which could provide optical feedback for laser and CW light for MZM in the meantime. The monolithic integrated transmitter on generic InP platform is free of complicated fabrication process of grating structure and has good potential for cost effective applications.

High power AlGaInP laser diodes (LDs) and bars emitting at about 685 nm have been fabricated. The epitaxial structures, including the AlInP cladding layer, asymmetric waveguide and single compressive-strained quantum well, were designed to optimize the thermal performance. The transparent window structure formed by Zn diffusion was employed to increase the output power of AlGaInP LDs. A maximum power of 4.9 W was realized for the single emitter LDs without catastrophic optical damage. Using micro-channel heat sinks, an array stacked with six 1-cm bars showed an output power of more than 300 W with 40% conversion efficiency.

A multiple gas detection system based on a V-cavity coupled diode laser around 1550nm has been developed. The Vcavity coupled diode laser exhibits side mode suppression ratio (SMSR) over 40dB and digitally switching over 20nm. The absorption lines of CO, CO₂ and H₂S are separately around 1567.3nm, 1573nm, 1578nm, which are distributed over the tuning range of the diode laser. The technique of tunable diode laser absorption spectrum (TDLAS) is adopted in the gas detection for the advantage of high sensitivity and resolution. What’s more, the systems based on direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) are established to measure gas concentration. As a result, a linear relationship between detection signal and gas concentration is worked out and the R-square coefficient of the linear fitting is better than 0.99 for CO and CO₂.

Quantum cascade laser (QCL) emitting in the mid-wave infrared atmospheric windows (3 to 5 μm) will be of immediate use to several civilian applications, including airborne self-defense protection system and trace gas sensing and free space optical communications. When the output power of a single QCL is too low, the beams of different lasers can be combined by incoherent beam combining. For incoherent beam combining the laser beams are arranged side by side on the aperture of the laser system and combine in the farfield. Incoherent beam combining has been applied very successfully to diode lasers with high robustness and reliability due to it is neither limited to any number of lasers nor to any laser characteristics. This technique is demonstrated to be compatible with QCLs in this work. In this paper, the method of incoherent beam combination of 4 independent QCL emitters with a 0.1 W continuous wave power at room temperature each is studied. Results show that the incoherent power superposition of mid-infrared QCLs can be achieved by beam combining with an efficiency of not less than 90%. The output farfield divergence angle is about 5 mrad, which is consistent with the farfield divergence angle of the four subbeams.

The underwater optical vision guidance technique is important for AUV short-range docking. Most of the docking lights are blue or green LED lights. However, LED lights have large divergence angle and cannot meet long range optical guidance. In this paper, we designed a blue laser diode docking light named as Beijixing with adjustable divergence angle and carried out the experiment. The divergence angle variation model of the docking light propagating in water is established according to the optical properties of water and the beam-spread function. The experimental results show that at a distance of 18m, when the divergence angle is 0.06° with strong directivity, the images captured by Nano SeaCam appear saturated, and the spot images captured by StarfishCam are light columns, which are difficulty for spot centroid extraction. When the angle is 10°, the light spots captured by Nano-SeaCam overlap, but StarfishCam can distinguish the spots. The research is beneficial for the design of docking lights for underwater optical vision guidance in AUV docking.

The optical frequency comb (OFC) is an emerging laser light source, which has laid the foundation for high resolution, high sensitivity, wide bandwidth and fast measurement. Angular velocity measurement as an important direction in the field of measurement has been paid attention. Nowadays, fibre optic gyroscope (FOG) is usually used to measure angular velocity. The Sagnac effect is the theoretical basis of FOG. Therefore, it is especially important to verify whether the FOG has Sagnac effect. Through theoretical derivation, when the FOG is used as a light source in combination with Sagnac interferometer and the Sagnac interferometer rotates at different angular velocities, the trigonometric function reflects the mutual transformation of the intensity of the light emitted by the interferometer and angular velocities, and the corresponds nonlinear relationship. This proves that FOG has Sagnac effect. When repetition frequency of FOG is locked ,this system can be used to measure angular velocity. In the experiment, we use 1km single-mode fiber as the rotating part of Sagnac interferometer, and measure the light intensity value at 20 different angular velocities. Measuring 10 times at each angular velocity for the mean value, which are used to fit the trigonometric function curve. The results show that the correlation coefficient of the fitting curve is greater than 0.99, and standard deviations of the measurement points are less than 0.06V. The corresponding angle error values at different angular velocities are converted into the distance errors, which are less than 0.032um.