Efficient and high-power laser-diode single-end-pumped Nd：YVO4 continuous wave laser at 1342nm

A compact, efficient and high-power laser diode （LD） single-end-pumped Nd：YVO4 laser with continuous-wave emission at 1342 nm is reported. With a single crystal single-end-pumped by fibre-coupled LD array, an output power of 7.36W is obtained from the laser cavity of concave-convex shape, corresponding to an optical-to-optical efficiency of 32.8%. The laser is operated in TEM00 mode with small rms amplitude noise of 0.3%. The influences of the Nd concentration, transmissivity of the output mirror and the cavity length on the output power have been studied experimentally.

First-Stokes Wavelengths at 1175.8 and 1177.1 nm Generated in a Diode End-Pumped Nd:YVO_4/LuVO_4 Raman Laser

A diode end-pumped acousto-optic Q-switched Nd:YVO_4/LuVO_4 Raman laser is demonstrated. Both YVO_4 and LuVO_4 can work as Raman gain, and slightly different active vibration modes of both crystals can result in different first-Stokes wavelengths. The output characteristic as the Raman competition between YVO_4 and LuVO_4 crystals for the laser systems with both shared cavity and coupled cavity is experimentally investigated.For the shared cavity, simultaneous Raman conversion in both YVO_4 and LuVO_4 crystals is achieved with dualwavelength emission at 1175.8 and 1177.1 nm. The maximum output power of 1.03 W and the conversion efficiency of 10.3% are obtained. The 0.84 W single first Stokes wavelength at 1177.1 nm with LuVO_4 Raman conversion is achieved with the coupled cavity. The results show that the coupled cavity with short Raman cavity can obtain a narrow pulse width. The separated laser crystal and Raman gain media with different vanadates in shared cavity have advantages in achieving dual-wavelength lasers with small frequency intervals.

High-power and high optical conversion efficiency diode-end-pumped laser with multi-segmented Nd：YAG/Nd：YVO-4

A novel flat-flat resonator consisting of two crystals（Nd：YAG ＋ Nd：YVO4） is established for power scaling in a diode-end-pumped solid-state laser. We systematically compare laser characteristics between multi-segmented（Nd：YAG ＋ Nd：YVO4） and conventional composite（Nd：YAG ＋ Nd：YAG） crystals to demonstrate the feasibility of spectral line matching for output power scale-up in end-pumped lasers. A maximum continuous-wave output power of 79.2 W is reported at 1064 nm, with Mx2= 4.82, My2= 5.48, and a pumping power of 136 W in the multi-segmented crystals（Nd：YAG ＋ Nd：YVO4）. Compared to conventional composite crystals（Nd：YAG ＋ Nd：YAG）, the optical-optical conversion efficiency of multi-segmented crystals（Nd：YAG ＋ Nd：YVO4） from 808 nm to 1064 nm is enhanced from 30% to 58.8%,while the laser output sensitivity as affected by the diode-laser temperature is reduced from 55% to 9%.

Compact,efficient diode-end-pumped Nd:GdVO_4 slab continuous-wave 912-nm laser

A fiber-coupled laser-diode （LD） end-pumped Nd：GdVO4 slab continuous-wave （CW） 912-nm laser and an LD bar end-pumped Nd：GdVO4 slab CW 912-nm laser are both demonstrated in this paper. Using the fiber-coupled LD of end-pumped type, a highest CW 912-nm laser output power of 10.17 W is obtained with a high optical to-optical conversion efficiency of 24.6% and a slope efficiency of 34.5%. The measured M2 factors of beam quality in x and y directions are 5.3 and 5.1, respectively. Besides, an LD bar of end-pumped type is used to realize CW 912-nm laser output, which has the advantages of compactness and low cost. When the pump power is 38.8 W, the output power is 8.87 W and the measured M^2 factors of beam quality in x and y directions are 16 and 1.31, respectively. In order to improve the beam quality of the 912-nm laser at x direction, a new quasi-concentric laser resonator will be designed, and an LD bar end-pumped Nd：GdVO4 slab high-power CW 912-nm TEM00 laser will be realized in the future.

GaN based ultraviolet laser diodes

In the past few years,many groups have focused on the research and development of GaN-based ultraviolet laser diodes(UV LDs).Great progresses have been achieved even though many challenges exist.In this article,we analyze the challenges of developing GaN-based ultraviolet laser diodes,and the approaches to improve the performance of ultraviolet laser diode are reviewed.With these techniques,room temperature(RT)pulsed oscillation of AlGaN UVA(ultraviolet A)LD has been realized,with a lasing wavelength of 357.9 nm.Combining with the suppression of thermal effect,the high output power of 3.8 W UV LD with a lasing wavelength of 386.5 nm was also fabricated.

Gallium nitride blue laser diodes with pulsed current operation exceeding 15 W in optical output power

Since Shuji Nakamura first demonstrated the nitride laser in 1996[1],the domain of semiconductor laser technology has undergone a period of remarkable growth[2,3].Al In Ga N-based diode lasers(LDs)have proven their exceptional capabilities across a spectrum of pivotal applications,including high-density data storage,laser displays,laser lighting,and quantum technology[4].

Effects of TMIn flow rate during quantum barrier growth on multi-quantum well material properties and device performance of GaN-based laser diodes

Multidimensional influences of indium composition in barrier layers on GaN-based blue laser diodes(LDs)are discussed from both material quality and device physics perspectives.LDs with higher indium content in the barriers demonstrate a notably lower threshold current and shorter lasing wavelength compared to those with lower indium content.Our experiments reveal that higher indium content in the barrier layers can partially reduce indium composition in the quantum wells,a novel discovery.Employing higher indium content barrier layers leads to improved luminescence properties of the MQW region.Detailed analysis reveals that this improvement can be attributed to better homogeneity in the indium composition of the well layers along the epitaxy direction.InGaN barrier layers suppress the lattice mismatch between barrier and well layers,thus mitigating the indium content pulling effect in the well layers.In supplement to experimental analysis,theoretical computations are performed,showing that InGaN barrier structures can effectively enhance carrier recombination efficiency and optical confinement of LD structure,thus improving the output efficiency of GaN-based blue LDs.Combining these theoretical insights with our experimental data,we propose that higher indium content barriers effectively enhance carrier recombination efficiency and indium content homogeneity in quantum well layers,thereby improving the output performance of GaN-based blue LDs.

Characteristic analysis of 1.06μm long-cavity diode lasers based on asymmetric waveguide structures

In long-cavity edge-emitting diode lasers,longitudinal spatial hole burning(LSHB),two-photon ab⁃sorption(TPA)and free carrier absorption(FCA)are among the key factors that affect the linear increase in out⁃put power at high injection currents.In this paper,a simplified numerical analysis model is proposed for 1.06μm long-cavity diode lasers by combining TPA and FCA losses with one-dimensional(1D)rate equations.The ef⁃fects of LSHB,TPA and FCA on the output characteristics are systematically analyzed,and it is proposed that ad⁃justing the front facet reflectivity and the position of the quantum well(QW)in the waveguide layer can improve the front facet output power.

Fiber Coupling of Laser Diode Bar to M ultimode Fiber Array

A piece of multimode optical fiber with a low num er ical aperture (NA) is used as an inexpensive microlens to collimate the output r adiation of a laser diode bar in the high numerical aperture (NA) direction.The emissions of the laser diode bar are coupled into multimode fiber array.The radi ation from individual ones of emitter regions is optically coupled into individu al ones of fiber array.Total coupling efficiency and fiber output power are 75% and 15W,respectively.

Quantitative Moisture Measurement with a Cavity Ring-down Spectrometer using Telecom Diode Lasers

Moisture measurement is of great needs in semiconductor industry, combustion diagnosis, meteorology, and atmospheric studies. We present an optical hygrometer based on cavity ring-down spectroscopy （CRDS）. By using different absorption lines of H20 in the 1.56 and 1.36 gm regions, we are able to determine the relative concentration （mole fraction） of water vapor from a few percent down to the 10-12 level. The quantitative accuracy is examined by comparing the CRDS hygrometer with a commercial chilled-mirror dew-point meter. The high sensitivity of the CRDS instrument allows a water detection limit of 8 pptv.

High Power 808nm AlGaAs/GaAs Quantum Well Laser Diodes with Broad Waveguide

The 808nm laser diodes with a broad waveguide are designed and fabricated.The thickness of the Al_ 0.35 - Ga_ 0.65 As waveguide is increased to 0.9μm.In order to suppress the super modes,the thickness of the Al_ 0.55 Ga_ 0.45 As cladding layers is reduced to only 0.7μm while keeping the transverse radiation losses of the fundamental mode below 0.2cm -1 .The structures are grown by metal organic chemical vapour deposition.The devices show excellent performances.The maximum output power of 10.2W in the 100μm broad-area laser diodes is obtained.

1.3μm InGaAs/InAs/GaAs Self-Assembled Quantum Dot Laser Diode Grown by Molecular Beam Epitaxy

The growth of multi-layer InGaAs/InAs/GaAs self-assembled quantum dots （QDs） by molecular beam epitaxy （MBE） is investigated,and a QD laser diode lasing at 1.33μm in continuous operation mode at room temperature is reported. The full width at half maximum of the band edge emitting peaks of the photoluminescence （PL） spectra at room temperature is less than 35meV for most of the multi-layer QD samples,revealing good,reproducible MBE growth conditions. Moreover,atomic force microscopy images show that the QD surface density can be controlled in the range from 1×10^10 to 7 ×10^10 cm^-2 . The best PL properties are obtained at a QD surface density of about 4×10^10cm^-2. Edge emitting lasers containing 3 and 5 stacked QD layers as the active layer lasing at room temperature in continuous wave operation mode are reported.

Diode Pumped Monolithic Unidirectional Nonplanar Single-Frequency Ring Laser

Diode pumped monolithic nonplanar ring laser has been developed, yielding single frequency laser and has the advantages of compactness, reliability and high efficiency. Its principles are given in detail and a monolithic nonplanar ring laser is designed. As a result, a laser of hundreds milliwatts cw single frequency output was built up, placed in a magnetic field and pumped by LD. The optical conversion efficiency was more than 15% and the slope efficiency more than 30%. The laser beam had a good quality, with M 2 about 1 2.

Material Growth and Device Fabrication of GaAs Based 1.3μm GaInNAs Quantum Well Laser Diodes

Material growth and device fabrication of the first 1.3μm quantum well （QW） edge emitting laser diodes in China are reported. Through the optimization of the molecular beam epitaxy （MBE） growth conditions and the tuning of the indium and nitrogen composition of the GalnNAs QWs, the emission wavelengths of the QWs can be tuned to 1.3μm. Ridge geometry waveguide laser diodes are fabricated. The lasing wavelength is 1.3μm under continuous current injection at room temperature with threshold current of 1kA/cm^2 for the laser diode structures with the cleaved facet mirrors. The output light power over 30mW is obtained.

Material Growth and Device Fabrication of GaN-Based Blue-Violet Laser Diodes

Studies on first GaN-based blue-violet laser diodes(LDs) in China mainland are reported.High quality GaN materials as well as GaN-based quantum wells laser structures are grown by metal-organic chemical vapor deposition method.The X-ray double-crystal diffraction rocking curve measurements show the full-width half maximum of 180″ and 185″ for (0002) symmetric reflection and (10 12) skew reflection,respectively.A room temperature mobility of 850cm2/(V·s) is obtained for a 3μm thick GaN film.Gain guided and ridge geometry waveguide laser diodes are fabricated with cleaved facet mirrors at room temperature under pulse current injection.The lasing wavelength is 405 9nm.A threshold current density of 5kA/cm2 and an output light power over 100mW are obtained for ridge geometry waveguide laser diodes.

Monolithically Integrated Laser Diode and Electroabsorption Modulator with Dual-Waveguide Spot-Size Converter Output

A 1.60μm laser diode and electroabsorption modulator monolithically integrated with a novel dual-waveguide spot-size converter output for low-loss coupling to a cleaved single-mode optical fiber are demonstrated.The devices emit in a single transverse and quasi single longitudinal mode with an SMSR of 25.6dB.These devices exhibit a 3dB modulation bandwidth of 15.0GHz,and modulator DC extinction ratios of 16.2dB.The output beam divergence angles of the spot-size converter in the horizontal and vertical directions are as small as 7.3°×18.0°,respectively,resulting in a 3.0dB coupling loss with a cleaved single-mode optical fiber.

0.6μm CMOS Laser Diode Driver for Optical Access Networks

Using native CMOS technology,EDA tool,and adopting full-custom design methodology,a laser diode driver for the use of STM-1 and STM-4 optical access network,is realized by CSMC-HJ 0.6μm CMOS technology to modulate laser diodes at 155Mb/s (STM-1),622Mb/s (STM-4) with adjustable modulation current from 0 to 50mA for an equivalent 50Ω load.The maximum modulation voltage is over 2.5V pp corresponding to a 3V DC bias for output stage.The time range of rise and fall from 360ps to 471ps is measured from the output voltage pulse.The RMS jitter is no more than 30ps for four bit rates.The power consumption is less than 410mW under a power supply voltage of 5V.According to the experimental results,the laser diode driver achieves the same level as their counterparts worldwide.

Implementation of a DC-10Mb/s 0.5μm CMOS Laser Diode Driver

A DC-10Mb/s laser diode driver,compatible with TTL and CMOS levels,is presented. The optical power corresponding to‘1＇ and ‘0＇ can be set independently with resistors off-chip and stabilized with a closed loop. A novel peak-to- peak optical power monitor and stabilization mechanism is introduced. The circuit, fabricated in a CSMC 0. 5μm mixed signal CMOS process, can provide 120mA maximum drive current and 0. 6dB extinction ration fluctuation over - 20 ＋ 80℃ ,which is independent of input pattern.

1.55μm Laser Diode Monolithically Integrated with Spot-Size Converter Using Conventional Process

A novel 1 55μm laser diode with spot size converter is designed and fabricated using conventional photolithography and chemical wet etching process.For the laser diode,a ridge double core structure is employed.For the spot size converter,a buried ridge double core structure is incorporated.The laterally tapered active core is designed and optically combined with the thin and wide passive core to control the size of mode.The laser diode threshold current is measured to be 40mA together with high slop efficiency of 0 35W/A.The beam divergence angles in the horizontal and vertical directions are as small as 14 89°×18 18°,respectively,resulting in low coupling losses with a cleaved optical fiber (3dB loss).

High-Power Distributed Feedback Laser Diodes Emitting at 820nm

By etching a second-order grating directly into the Al-free optical waveguide region of a ridgewaveguide（RW） AlGaInAs/AlGaAs distributed feedback（DFB） laser diode,a front facet output power of 30mW is obtained at about 820nm with a single longitudinal mode. The Al-free grating surface permits the re-growth of a high-quality cladding layer that yields excellent device performance. The threshold current of these laser diodes is 57mA,and the slope efficiency is about 0.32mW/mA.