Intensity-modulating characteristics of a laser diode subjected to optical injection

We have found that the optical power of a laser diode (LD) does not change with the injected light intensity that is modulated when its injection current is at some specific values. The amplitude of optical power change of the LD varies periodically with the increase of the injection current. It is made clear through theoretical analysis that these phenomena are caused by gain compression and interband carrier absorption of the LD that depend on longitudinal mode competition, bandgap-shrinkage effects, thermal conduction, and so on. Our experimental results make it easy to eliminate optical power change of LDs. We only need to choose a proper value of the injection current.     

InGaN/GaN量子阱垒层和阱层厚度对GaN基激光器性能的影响及机理

采用LASTIP软件研究了InGaN/GaN(In组分为15%)量子阱垒层和阱层厚度对GaN基蓝紫光激光器性能的影响及机理. 模拟计算结果表明, 当阱层太薄或太厚时, GaN基激光器的阈值电流增加、输出功率下降, 最优的阱层厚度为4.0 nm左右; 当阱层厚度太薄时, 载流子很容易泄漏, 而当阱层厚度太厚时, 极化效应导致发光效率降低, 研究还发现, 与垒层厚度为7 nm 相比, 垒层厚度为15 nm时激光器的阈值电流更低、输出功率更高, 因此适当地增加垒层厚度能显著抑制载流子泄漏, 从而改善激光器性能.     

GaN-based violet laser diodes grown on free-standing GaN substrate

A violet laser diode (LD) structure is grown on a free-standing c-plane GaN substrate and 4~μ m× 800~μ m ridge waveguide LDs are fabricated. The electrical and the optical characteristics of LDs under different facet-coating and chip-mounting conditions are investigated under pulse mode operation. The active region temperatures of p-side up and p-side down mounted LDs are calculated with different injection currents. The calculated thermal resistances of p-side up and p-side down mounted LDs are 4.6~K/W and 3~K/W, respectively. The threshold current of the p-side down mounted LD is much lower than that of the p-side up mounted LD. The blue shift of the emission wavelength with increasing injection current is observed only for the LD with p-side down mounting configuration, due to the more efficient heat dissipation.     

非对称结构大功率940 nm量子阱激光器

为改善940 nm大功率InGaAs/GaAs半导体激光器输出特性,通过模拟计算了非对称波导层及限制层结构的光场分布,并参照模拟制作了非对称结构半导体激光器器件。采用低压金属有机物气相沉积（LP-MOCVD）生长技术,获得了低内吸收系数的高质量外延材料,通过实验数据计算得到激光器材料内吸收系数仅为0.44 mm-1。进而通过管芯工艺制作了条宽100 m、腔长2000 m的940 nm半导体激光器器件。25 ℃室温10 A直流连续（CW）测试镀膜后器件阈值电流251 mA,斜率效率1.22 W/A,最大输出功率达到9.6 W,最大光电转化效率超过70%。     

非对称结构大功率940nm量子阱激光器

为改善940 nm大功率InGaAs/GaAs半导体激光器输出特性,通过模拟计算了非对称波导层及限制层结构的光场分布,并参照模拟制作了非对称结构半导体激光器器件。采用低压金属有机物气相沉积(LP-MOCVD)生长技术,获得了低内吸收系数的高质量外延材料,通过实验数据计算得到激光器材料内吸收系数仅为0.44mm~(-1)。进而通过管芯工艺制作了条宽100μm、腔长2000μm的940 nm半导体激光器器件。25℃室温10 A直流连续(CW)测试镀膜后器件阈值电流251 mA,斜率效率1.22 W/A,最大输出功率达到9.6 W,最大光电转化效率超过70%。     

A High Conversion Efficiency Q-Switched Intracavity Nd:YVO_4/KTA Optical Parametric Oscillator under Direct Diode Pumping at 880nm

We report a high conversion efficiency Q-switched Nd:YVO_4/KTiOAsO_4(KTA) intracavity optical parametric oscillator(IOPO) operating near 3.5 um based on direct 880 nm laser diode(LD) pumping. A maximum average idler output power of 2.6 W with a pulse width of about 7.9 ns is achieved under an absorbed LD power of 45.4 W at a pulse repetition rate(PRR) of 10 kHz. The maximum optical-optical conversion efficiency from LD power to OPO mid-infrared(MIR) output of 6.74% is achieved. To our knowledge, this is the highest conversion efficiency for a KTA-IOPO by exploiting a Q-switched laser as the parent fundamental pump source. The beam quality factors M~2 of the MIR beam at the full output power with a PRR of 10 kHz are within 2.12 in both the horizontal and vertical directions, indicating a near Gaussian mode.     

Self-detection of lasing characteristics for semiconductor ring laser diodes

A novel method of measurement of lasing characteristics for a ring laser diode is proposed without branching of the optical lasing power. The lasing power and the linewidth as a function of the injection current have been measured by detecting the RF power by the terminal voltage change of a ring LD. The linewidth is estimated to be 55 kHz atl=1.75l _th.     

Laser diode pumped LNYAB self-frequency-doubling lasers

The LNYAB self-doubling laser pumped by (LD) has been developed for the first time. The properties of the lasers are much better than those of NYAB self-doubling lasers pumped by LD. The LNYAB self-doubling laser pumped by LD can be operated in TEM_(00) mode with threshold pumping power of 3.6mW which is lower than that of LD pumped NYAB self-doubling lasers by 74%. The output power is 29mW at 0.531μm in green region with optical-to-optical efficiency of 4.8% which is higher than that of NYAB self-doubling laser by 20%.     

Improvement in the laser performances of an A-O Q-switched Nd:GdVO<Subscript>4</Subscript> laser by direct-diode pumping into the emitting level

The laser performances of an A-O Q-switched Nd:GdVO₄ laser are demonstrated under LD pumping at 808 and 879 nm, respectively. Results indicate that the pulse performances are improved markedly under 879-nm LD direct pumping. At a repetition rate of 100 kHz, a maximum average output power of 12.1 W, a pulse width of 20.3 ns, and a peak power of about 6 kW are reached under 879-nm pumping.     

Passively Q-switched Nd:YAG ceramic laser towards large pulse energy and short pulse width

A large pulse energy and high peak power passively Q-switched ceramic neodymium-doped yttrium aluminum garnet (Nd:YAG) laser has been demonstrated with Cr⁴⁺:YAG crystals as the saturable absorbers. By employing a continuous wave (CW) laser-diode (LD) as the pump source, as high as 11.3 W CW output power of 1064 nm was obtained under the pump power of 21.6 W, with an optical conversion efficiency of 52.3%. Inserting different initial transmissions Cr⁴⁺:YAG as saturable absorbers, under the incident pump power of 15.6 W, the largest pulse energy, shortest pulse width, and highest peak power are measured to be 188 μJ, 3.16 ns, and 59.5 kW, respectively. As we has known, this is the best passively Q-switched results ever reported by Nd:YAG ceramic material.     

双脉冲注入式LD模块的红外能级寿命可见区测试系统

Er3+的4I_13/2能级寿命的长短对评估Er3+掺杂材料在光通讯波段的应用十分重要。基于980 nm双脉冲注入式LD激发下的Er3+激发态吸收上转换发光,测量在不同双脉冲时间间隔下的上转换红光发光强度,再根据上转换红光的发光强度随双脉冲时间间隔的变化关系,推导出了Er3+红外4I_13/2能级寿命的拟合公式,实现了红外能级寿命的可见区测量。因此,结合兼具时间间隔可调和同步脉冲取样的双脉冲注入式LD模块和光电倍增管(R2658),就可以实现所有Er3+红外能级寿命的测量,这是一种十分经济的微秒量级荧光寿命测试系统。     

Improvement of performance characteristics of deep violet InGaN DQW lasers using a strip DQW active region

The effect of the laser ridge width on the performance characteristics of deep violet In_0.082Ga_0.918N/GaN double quantum well (DQW) laser diodes (LDs) has been numerically investigated. Simulation results indicated that threshold current of LDs is decreased and slope efficiency and differential quantum efficiency (DQE) are increased by decreasing ridge width, whereas output power is decreased. The results also showed that a decrease of more than 1 μm in the ridge width reduces the threshold current, whereas the slope efficiency, output power, and DQE are decreased. A new DQW LD structure with a strip active region has been proposed to obtain a lower current threshold and higher output power, slope efficiency, and DQE. The results showed the InGaN DQW LD with a strip DQW active region has the highest output power, slope efficiency, and DQE; it also has a lower threshold current compared with that of the original LD. The comparative study conducted for the LDs with output emission wavelengths of 390, 414 and 436 nm has also confirmed the enhancement in LD performance using the strip DQW active region structure.     

高峰值266nm紫外激光器

报道了一种激光二极管(LD)端面泵浦的Nd:YAG声光Q开关高峰值功率266nm紫外激光器。该激光器采用紧凑的平平腔结构,LBO和BBO分别作为其二倍频和四倍频晶体。分别利用高偏振比LD阵列(40∶1)、低偏振比LD阵列(5∶1)及低偏振LD阵列腔内放置布氏片结构进行了实验。当注入功率为25W、调制频率为10kHz时,以上结构分别得到功率0.85,0.61和0.72W的266nm紫外光输出。其中,采用高偏振比LD阵列的输出功率最高,单脉冲能量为85μJ,脉宽为5ns,峰值功率高达17kW,泵浦光到紫外光的光-光转换率达3.4%。     

高峰值266 nm紫外激光器

报道了一种激光二极管（LD）端面泵浦的Nd：YAG声光Q开关高峰值功率266 nm紫外激光器。该激光器采用紧凑的平平腔结构,LBO和BBO分别作为其二倍频和四倍频晶体。分别利用高偏振比LD阵列（40∶1）、低偏振比LD阵列（5∶1）及低偏振LD阵列腔内放置布氏片结构进行了实验。当注入功率为25 W、调制频率为10 kHz时,以上结构分别得到功率0.85,0.61 和0.72 W的266 nm紫外光输出。其中,采用高偏振比LD阵列的输出功率最高,单脉冲能量为85 μJ,脉宽为5 ns,峰值功率高达17 kW,泵浦光到紫外光的光 -光转换率达3.4%。     

High-power simultaneous dual-wavelength emission of an end-pumped Nd:YAG laser using the quasi-three-level and the four-level transition

An efficient continuous-wave (CW) simultaneous dual-wavelength lasing (SDWL) of an LD end-pumped Nd:YAG laser utilizing a quasi-three-level transition at 946 nm and a four-level transition at 1064 nm is reported. A theoretical model has been introduced to determine the threshold conditions for SDWL. The temperature distributions of a Nd:YAG crystal under different pump powers have been analyzed. In the experiments, a CW SDWL output power of 5.12 W at a temperature of 273 K has been achieved with a pump power of 17 W, giving a slope efficiency of 16.36%.     

Experimental study of the characteristics of high-power laser diode radiation in the above-threshold mode for degradation analysis

The angular dependence of the intensity and contrast of the radiation of laser diodes (LDs) with a CW power of 1.25 W has been investigated in the above-threshold mode. An original method for detecting fundamental lasing is used to analyze the mode structure of the LD radiation at low pump currents. It is shown that this radiation contrast measurement makes it possible to detect the LD degradation in earlier stages than in power measurements.     

Free-running emerald laser pumped by laser diode

Free-running emerald laser pumped by 660-nm laser diode (LD) was reported. Free-running output powerof 24 mW has been obtained with overall efficiency of 1.4% and slope efficiency of 11.9% when the LD incident power was 2.56 W. The laser threshold value of emerald crystal was estimated to be 0.7 W.     

Adaptive upstream optical power adjustment depending on required power budget in PON access

According to the present passive optical network (PON) standard, the fiber transmission lengths are from 500 m to 20 km between the optical line terminal (OLT) and different optical network units (ONUs). It will result in difference power losses (ΔP_loss) from 4 to 5 dB. Hence, we propose to adjust adaptively the output optical power of the upstream laser diode (LD) depending on the different fiber lengths. With the different fiber transmission lengths, we can properly adjust the bias current and modulation index of upstream LD for energy-saving. We characterize and analyze experimentally the relationship of output optical power and modulation amplitude Vamp under different fiber transmissions in PON access. Moreover, due to the adaptive power control of upstream signal, the optical upstream equalization also can be retrieved with power variation of 1.1 dB in this experiment.     

Sinusoidal phase-modulating laser diode interferometer insensitive to intensity modulation for real-time displacement measurement with feedback control system

In sinusoidal phase modulating laser diode (LD) interferometer, the injection current of the LD is sinusoidally modulated to realize the modulation of the wavelength. However, the light intensity of LD is also modulated, which affects the measurement accuracy. An all-fiber sinusoidal phase modulating LD interferometer for real-time displacement measurement is proposed where the influence of the intensity modulation is eliminated with a new algorithm. It is made clear that an optimal depth of the sinusoidal phase modulation (SPM) exists in the algorithm. Moreover, the SPM depth is locked at the optimal value by controlling the injection current with a feedback control system. The feasibility of the proposed interferometer for displacement measurement is verified by experiments.     

高效新型自倍频Yb∶GdYAB激光器的理论和实验研究

通过研究自倍频现象的物理过程,理论推导了自倍频激光器输出功率的表达式,分析了影响自倍频激光器高效运转的具体参量.研究发现,除了晶体自身的性质外,在具体实验中晶体放置的位置、角度以及晶体的温度等,都不同程度地影响着自倍频激光器的输出功率.在此基础上,实现了LD端面泵浦的新型Yb∶GdYAB自倍频激光器运转,当晶体吸收功率为2.56 W时,获得了总功率为441 mW的自倍频绿光输出,从二极管到绿光的光-光转换效率达到了17.2%,并具有较好的功率稳定性和模式.