Laser Diode Array Research Articles

24‐wavelength distributed Bragg reflector laser array with surface gratings

A small footprint diode laser array of 24 individually addressable distributed Bragg reflector lasers is presented. Third-order gratings etched into the surface of an AlGaAs vertical waveguide structure act as Bragg reflectors. The ridge waveguides have an 87 µm-wide spacing and the emission wavelengths are spread on a 0.5 nm-wide grid around a centre wavelength of 905 nm. All 24 lasers on the array emit single mode with side mode suppression ratios > 50 dB and output powers >17 mW at 40 mA pump current.

FPGA-based phase control of acousto-optic modulator Fourier synthesis system through gradient descent phase-locking algorithm.

We present a new application of the stochastic parallel gradient descent (SPGD) algorithm to fast active phase control in a Fourier synthesis system. Pulses (4.9ns) with an 80MHz repetition rate are generated by feedback from a single phase-sensitive metric. Phase control is applied via fast current modulation of a tapered amplifier using an SPGD algorithm realized on a field-programmable gate array (FPGA). The waveforms are maintained by constant active feedback from the FPGA. We also discuss the extension of this technique to many more semiconductor laser emitters in a diode laser array.

Transmitter Optical Subassembly Using a Polarization Beam Combiner for 100 Gbit/s Ethernet over 40-km Transmission

A transmitter optical subassembly (TOSA) has been developed for a 100-Gbit/s Ethernet system for a long optical transmission distance over a 40-km single-mode fiber (SMF). To obtain a high optical output power and a high dynamic extinction ratio, the TOSA consists of two two-channel distributed feedback laser diode array chips integrated with electro-absorption modulators (EADFB laser array chips) with a 2 × 1 multimode interference (MMI) optical coupler and a polarization beam combiner for wavelength multiplexing. The TOSA is 8.7 mm × 28.7 mm × 6.5 mm including an LC-type receptacle. The TOSA has a twin collimator path for two EADFB laser array chips. The wavelength multiplexer consists of a mirror, a half-wavelength plate, and a polarization beam combiner. The TOSA could improve the optical output power by around 2 dB compared with a TOSA with a four-channel EADFB laser array chip and a 4 × 1 MMI optical coupler. An optical modulation amplitude of over 0.5 dBm and a mask margin exceeding 21% were obtained for each lane when all lanes were operated simultaneously with an EA modulator driving voltage of 1.5 V at a bit rate of 25.78125 Gbit/s, which fully satisfies the 100GBASE-ER4 specifications. We demonstrated error-free operation for an SMF transmission of over 40 km. Moreover, we confirmed that the TOSA was capable of error-free SMF transmission over 60 km with a power penalty of less than 1.4 dB.

High-Efficiency Mid-Infrared Picosecond MgO:PPLN Single Resonant Optical Parametric Oscillator**Supported by the National Natural Science Foundation of China under Grant Nos 61275142, 61308042, and 51321091, the National Key Scientific Instrument and Equipment Development Project under Grant No 2011YQ030127, and the China Postdoctoral Science Foundation under Grant No 2014T70633.

We demonstrate a high-efficiency mid-infrared picosecond optical parametric oscillator (OPO) based on MgO doped periodically poled lithium niobate (MgO:PPLN) with a laser diode array (LDA) pumped Innoslab amplifier as the pumping source. Under a 16 W synchronously pumping power, 4.5 W of idler light at 2896 nm is obtained. A tuning range of idler light from 2688 nm to 3016 nm is achieved, within which the highest optical-optical conversion efficiency from pump power to OPO output is 35.1%. Moreover, a signal light of ∼500 mW from 1644 to 1700 nm with a repetition rate of 233.8 MHz is generated.

Feasibility of human lung ventilation imaging using highly polarized naturally abundant xenon and optimized three-dimensional steady-state free precession.

To demonstrate the potential for high quality MRI of pulmonary ventilation using naturally abundant xenon (NAXe) gas. MRI was performed at 1.5 Tesla (T) and 3 T on one healthy smoker and two healthy never-smokers. 129Xe gas was polarized to ∼25% using an in-house spin-exchange optical pumping polarizer fitted with a laser diode array with integrated volume holographic grating and optical train system. Volunteers inhaled 1 L of NAXe for an 8 to 15 s breathhold while MR images were acquired with full-lung coverage using a three-dimensional steady-state free precession sequence, optimized for maximum signal-to-noise ratio (SNR) at a given spatial resolution. For the purpose of image quality comparison, the MR acquisition was repeated at 1.5 T with 400 mL enriched xenon and 200 mL 3He. All NAXe lung images were of high quality, with mean SNRs of 25-40 (voxel 4.2 × 4.2 × 8/10 mm3) and ∼30% improvement at 3 T versus 1.5 T. The high SNR permitted identification of minor ventilation defects in the healthy smoker's lungs. NAXe images were of comparable SNR to those obtained with enriched xenon and 3He. Optimization of MR pulse sequences and advances in polarization technology have facilitated high quality pulmonary ventilation imaging with inexpensive NAXe gas.

Beam multiplexing of diode laser arrays**Project supported by the National Science Foundation of China (No. 61275145).

Design and experimental studies on the wavelength multiplexing and polarization multiplexing of diode laser arrays were carried out. First, the structure of a AlGaInAs/GaAs/AlGaAs quantum well under compressive strain was used because the characteristic of wavelength was easier to adjust. We obtained diode laser arrays lasing in five different wavelengths, about 760 nm, 800 nm, 860 nm, 930 nm, and 976 nm. At the same time, four edge filters were designed, and an experimental study on the beam multiplexing of diode laser arrays was carried out. Second, two beams with different polarization states were composited using a half wave plate and a polarizing beam-splitter prism. After that, the beam focusing system was designed. Ultimately, ten beams of diode laser arrays in five wavelengths and two polarization states were composited, the total output power was 196 W and the overall efficiency was 76%. The size of the output focus spot was 144 × 1330 μm2, and the power density of the focused light was as high as 1.02 × 105 W/cm2. Compared with a single diode laser array, the power density of the composite beam was improved by 4.3 times.

Spectral beam combining for a diode laser array by using a grating pair

A grating and a collimating lens are used to replace the transformer lens in the traditional spectral beam combining structure. As a result, the degradation of the beam quality and the cross-talk are prevented. A spectral beam combining with narrow line-width is achieved. A standard semiconductor laser array is employed in this experiment. An output power of 44.8 W and an electro-optic conversion efficiency of 38.9% are achieved. The spectral line-width is 4.1 nm. A beam quality factor of 1.3711.7 in fast and slow axis directions are obtained. The beam quality of the output is close to that of a single emitter of the array in both directions.

Designing and optimizing highly efficient grating for high-brightness laser based on spectral beam combining

A highly efficient nano-periodical grating is theoretically investigated for spectral beam combining (SBC) and is experimentally implemented for attaining high-brightness laser from a diode laser array. The rigorous coupled-wave analysis with the S matrix method is employed to optimize the parameters of the grating. According the optimized parameters, the grating is fabricated and plays a key role in SBC cavity. The diffraction efficiency of this grating is optimized to 95% for the output laser which is emitted from the diode laser array. The beam parameter product of 3.8 mm mrad of the diode laser array after SBC is achieved at the output power of 46.3 W. The optical-to-optical efficiency of SBC cavity is measured to be 93.5% at the maximum operating current in the experiment.

双光栅实现半导体激光阵列波长组束

双光栅实现半导体激光阵列波长组束

Effect of 660 nm Light-Emitting Diode on the Wound Healing in Fibroblast-Like Cell Lines

Light in the red to near-infrared (NIR) range (630–1000 nm), which is generated using low energy laser or light-emitting diode (LED) arrays, was reported to have a range of beneficial biological effects in many injury models. NIR via a LED is a well-accepted therapeutic tool for the treatment of infected, ischemic, and hypoxic wounds as well as other soft tissue injuries in humans and animals. This study examined the effects of exposure to 660 nm red LED light at intensities of 2.5, 5.5, and 8.5 mW/cm2for 5, 10, and 20 min on wound healing and proliferation in fibroblast-like cells, such as L929 mouse fibroblasts and human gingival fibroblasts (HGF-1). A photo illumination-cell culture system was designed to evaluate the cell proliferation and wound healing of fibroblast-like cells exposed to 600 nm LED light. The cell proliferation was evaluated by MTT assay, and a scratched wound assay was performed to assess the rate of migrating cells and the healing effect. Exposure to the 660 nm red LED resulted in an increase in cell proliferation and migration compared to the control, indicating its potential use as a phototherapeutic agent.

二极管激光阵列光栅-外腔谱合成系统中光束串扰行为及其对合成效率的影响

二极管激光阵列光栅-外腔谱合成系统中光束串扰行为及其对合成效率的影响

Thermal Effects of High-Power Side-Pumped Alkali Vapor Lasers and the Compensation Method

A side-pumping configuration with six laser diode arrays is designed for the diode pumped alkali vapor lasers. A physical model is established to describe the thermal effects in a high-power side-pumped cesium vapor laser. Distributions of the radial temperature and the optical path difference in the cesium vapor cell are simulated and analyzed. Influences of the pump power, the pump beam waist, and the cell temperature on the thermal focal length are calculated and discussed. We propose a very simple and promising design of a scheme to compensate for the thermal lens of the cesium vapor laser. The compensation results are also presented.

5.2-W high-repetition-rate eye-safe laser at 1525 nm generated by Nd:YVO₄₋YVO₄stimulated Raman conversion.

We report herein an efficient eye-safe Raman laser, which is based upon Nd:YVO₄₋YVO₄ and in-band pumped by a wavelength-locked laser diode array at 878.6 nm. By virtue of mitigated thermal load and improved pump absorption, a maximum average output power of 5.2 W at 1525 nm is obtained under the incident pump power of 30.6 W with the pulse repetition frequency of 140 kHz, corresponding to an optical efficiency of 17.0%.

A <inline-formula> <tex-math notation="TeX">\(10 \times 10\) </tex-math></inline-formula>-Gb/s DFB-LD Array Integrated With PLC-Based AWG for 100-Gb/s Transmission

We describe a hybrid integration module of a 10 × 10-Gb/s distributed feedback laser diode array (DFB-LDA) and a planar light-wave circuit-based arrayed waveguide grating (AWG). For fabrication of the DFB-LDA, we adopted a selective area growth technique to tailor the channel gain properly, and E-beam lithography to accurately control the channel lasing wavelength and grating phase. For implementation of the AWG, we introduced a 2%-Δ structure to reduce the coupling loss between the AWG and DFB-LDA, and designed the tapered and parabolic waveguides at the junctions of the free propagation regions to widen the spectral passband width (i.e., a -1-dB spectral width of 3 nm). The developed module shows a side-mode suppression ratio of >45 dB, a clear eye opening with a dynamic extinction ratio of >4.4 dB at 10 Gb/s, and a power penalty of <;1.5 dB after a 2-km transmission for all channels.

The elliptical micro-lens array in the application of the LDA beam shaping

Based on the analysis of semiconductor laser-diode array (LDA) beam characteristics, a new scheme of beam collimation and focusing is proposed. The elliptical micro-lens shaping the beam of LDA has been analyzed by theoretical and simulated by optical ray tracing. The efficiency for laser beam coupling into the optical fiber is 73.2% of the whole system.

Handheld probe integrating laser diode and ultrasound transducer array for ultrasound/photoacoustic dual modality imaging

Ultrasound and photoacoustics can be utilized as complementary imaging techniques to improve clinical diagnoses. Photoacoustics provides optical contrast and functional information while ultrasound provides structural and anatomical information. As of yet, photoacoustic imaging uses large and expensive systems, which limits their clinical application and makes the combination costly and impracticable. In this work we present and evaluate a compact and ergonomically designed handheld probe, connected to a portable ultrasound system for inexpensive, real-time dual-modality ultrasound/photoacoustic imaging. The probe integrates an ultrasound transducer array and a highly efficient diode stack laser emitting 130 ns pulses at 805 nm wavelength and a pulse energy of 0.56 mJ, with a high pulse repetition frequency of up to 10 kHz. The diodes are driven by a customized laser driver, which can be triggered externally with a high temporal stability necessary to synchronize the ultrasound detection and laser pulsing. The emitted beam is collimated with cylindrical micro-lenses and shaped using a diffractive optical element, delivering a homogenized rectangular light intensity distribution. The system performance was tested in vitro and in vivo by imaging a human finger joint.

Powerful all-solid-state multiwave laser for aerosol lidars

An all-solid-state multiwave laser radiator (lasing wavelengths 1064, 532, and 355 nm), integrated in a single implement with a telescope, has been developed for use in aerosol lidars. The main radiator is the master laser and an amplifier based on a YAG:Nd crystal, excited by laser diode arrays using a transverse pumping layout. In the Q-switched regime, the energy of the output pulses of the YAG:Nd laser radiator reaches 400 mJ (1064 nm). With simultaneous lasing at three wavelengths, the radiator forms radiation pulses at 1064, 532, and 355 nm, with energies of 170, 150, and 80 mJ, respectively. The pulse width is 8–11 ns at a repetition rate of 10 Hz. The developed multiwave laser radiator is effective for use as a component of aerosol lidars with an atmospheric probing range of up to 40 km.

Wide-aperture laser diode array in the external V-shaped cavity

The operation of a wide-aperture laser diode array with the radiation wavelength in external V-shaped symmetric and asymmetric cavities is experimentally studied. The regimes of stable oscillation are studied as functions of the feedback beam direction. The spectra and the intensity distribution of radiation in the far zone are presented for the laser diode in symmetric and asymmetric cavities. Tuning of the radiation wavelength is demonstrated using the Littman geometry in the asymmetric cavity.

A high-frequency laser with intracavity second-harmonic radiation conversion

The possibility of suppressing the radiation depolarization that appears in the active element of a YAG:Nd3+ laser pumped by linear laser-diode arrays with a pump-pulse-repetition rate of 1 kHz has been experimentally investigated. It is shown that the total suppression of the depolarization of the laser radiation is impeded by the appearance of birefringence in the crystals of the electrooptic shutters and the active medium of the Faraday rotator. This paper discusses the layout of a cavity with beam splitting at the polarization components, which made it possible to obtain an output pulse energy at the second harmonic greater than 10 mJ with intracavity conversion of radiation with a pulse width of 25 ns.

Output characteristics of diode laser array by three different spectral beam combing structures

Based on spectral beam combining technology, with diffraction grating and external cavity feedback, each element of an array of diode laser is locked at different wavelengths in a narrow linewidth by inserting a beam shaping system. And the output beam is an approximately parallel light along the direction of combination. Beam quality improvement and linewidth narrowing of an array of diode laser are achieved. The standard diode laser array used in our experiment has 19 elements, with a width of 100 m and a period of 500 m for each element. Experiment is conducted on different spectral beam combing setups, including spectral beam combing after collimation in both fast and slow axes, spectral beam combing after beam shaping and beam combing in an external cavity with narrow-line width. The combining output beam has the same beam quality as that of a single emitter and the linewidth of such a beam is narrow. The experiment results are analyzed.