Power Diode Laser Research Articles

High-power pulsed laser diodes emitting in the range

This paper examines approaches for increasing the output pulse power of laser diodes based on MOVPE InGaAs/AlGaInAs/InP heterostructures and emitting in the range . We demonstrate that optimising waveguide layer parameters may ensure an increase in the quantum efficiency of the laser diodes and a reduction in their internal optical loss. Characterisation results are presented for laser diodes based on the proposed heterostructures.

Improvement of characteristics of InGaN-based laser diodes with undoped InGaN upper waveguide layer

In the structure of conventional InGaN-based laser diodes, considerable optical absorption loss exists in the p-doped region, especially in the p-doped upper waveguide layer. A structure of InGaN-based laser diodes with an undoped InGaN upper waveguide layer instead of p-doped GaN was designed and optimized. Instead of being located between AlGaN EBL and AlGaN cladding layer, the undoped InGaN layer was positioned between the AlGaN electron blocking layer and the active region of multi-quantum well. The optical and electrical characteristics of this type of laser diodes were simulated by the commercial software lastip, and it was found that the optical absorption loss was obviously lowered. Further theoretical analysis showed that the undoped InGaN upper waveguide layer eliminated the influence of electron leakage current, leading to a reduction of threshold current density and an increase of output light power of the InGaN-based laser diodes.

Studies of upconversion emission of Yb3+, Er3+:Lu2O3 nanoceramics

The translucent Yb3+ and Er3+ doped Lu2O3 ceramics composed of nanocrystalline grains were sintered using a low temperature and high pressure method. The upconversion emission associated with the 2H11/2→4I15/2, 4S3/2→4I15/2 (green), 4F9/2→4I15/2 (red) and 4I9/2→4I15/2 (IR) transitions was observed upon intense infrared laser excitation. The dependence of the upconversion intensity on incident laser diode power in Yb3+, Er3+:Lu2O3 nanoceramics was investigated. In particular it was found that the green/red intensity ratio of upconversion transitions increased with the power of the incident laser light. This effect was due to heating of the nanoceramics with increasing excitation power and may be utilized for high temperature thermometry.

Experimental research on profile measurement based on laser optical feedback

A novel method of profile measurement for reflective surface based on optical feedback is proposed in this paper. With so-called self-mixing structure, a fraction of the light emitted from a laser diode (LD) is reflected back by the target under test and returns the laser cavity and changes the operation mode of this LD. When the laser operates in coherence collapse regime, the output power of LD is affected by the optical feedback coefficient, while the coefficient is decided by the defocusing amount and the reflectivity of the target under test. Therefore, through scanning coins three-dimensionally and measuring the output power of LD, we obtain the profile information of samples. Compared with the conventional interferometry, this technique is advantageous of accuracy, compactness and low cost.

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 500m to 20km between the optical line terminal (OLT) and different optical network units (ONUs). It will result in difference power losses (ΔPloss) from 4 to 5dB. 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 1.1dB in this experiment.

Amorphous-to-crystalline phase transformation in (GeTe) x (Sb2Te3) (x = 0.5, 1, 2, 8) thin films

In this work, several experimental methods were used to evaluate the phase transformation characteristics of Ge-Sb-Te pseudobinary thin films that were comprehensively utilized as phase change materials. Except for Ge8Sb2Te11 (x = 8), the phase transition of the (GeTe)x(Sb2Te3) (x = 0.5, 1, 2) thin films from the amorphous to the hexagonal structure via the fcc structure was confirmed by X-ray diffraction the measurements. Additionally, the X-ray photoelectron spectra analysis revealed that the Ge-Te bond was weakened for Ge2Sb2Te5 (x = 2) and all of bonds were strengthened for Ge8Sb2Te11 (x = 8) during the amorphous to crystalline transition. The optical energy gaps (EOP) were around 0.71 and 0.50 eV, and the slopes of the absorption in the extended region (B) were ∼5.1 × 105 and ∼10 × 105 cm−1·V−1 for the amorphous and the fcc crystalline structures, respectively. Finally, the speed of the amorphous-to-crystalline phase transition for the (GeTe)x(Sb2Te3) (x = 0.5, 1, 2) films was characterized by using a nano-pulse scanner with a 658-nm laser diode (power: 1 ∼ 17 mW, pulse duration: 10 ∼ 460 ns).

Optimization of the cavity facet coating in high power GaN-based semiconductor laser diodes

A method to calculate the reflectivity of the coated cavity facet was proposed, and the distribution of the optical power near the two coated cavity facets was calculated for GaN-based laser diodes. A new design method for reducing the optical power at the two cavity facets without changing the output power of laser diodes was discussed, which is helpful to optimize the cavity facet coating and raise the threshold current at which catastrophic optical damage occurs.

Efficient continuous-wave eye-safe region signal output from intra-cavity singly resonant optical parametric oscillator

We report an efficient continuous-wave (CW) tunable intra-cavity singly resonant optical parametric oscillator based on the multi-period periodically poled lithium niobate and using a laser diode (LD) end-pumped CW 1064 nm Nd:YVO4 laser as the pump source. A highly efficiency CW operation is realized through a careful cavity design for mode matching and thermal stability. The signal tuning range is 1401–1500 nm obtained by varying the domain period. The maximum output power of 2.2 W at 1500 nm is obtained with a 17.1 W 808 nm LD power and the corresponding conversion efficiency is 12.9%.

Efficient Pump Beam Multiplexer Based on Single-Mode Fibers

An efficient pump beam combining technique using single-mode fibers was introduced. Well-defined modes formed from a single-mode fiber bundle were efficiently coupled into an output multimode fiber. The coupling rate can be maintained up to an input fiber number of 331. The total power of a multimode output fiber combined with single-mode fibers can greatly exceed the output power of a multimode laser diode pigtailed with the same multimode fiber.

High Efficiency Laser Diode Power Supply

A continuous light-emitting laser diode power supply has been present,in this paper. The power supply is up to 50 W and the current is continuous adjustable below 5A . The supply is easy controlled, miniaturization, high efficiency, non-impact and slow-start to meet the characteristics of laser diode. The efficiency of the supply is better then 93% by application test.

Focal laser interstitial thermotherapy (LITT) at 980 nm for prostate cancer: treatment feasibility in Dunning R3327-AT2 rat prostate tumour

To examine the feasibility and reproducibility of laser interstitial thermotherapy (LITT) as a minimally invasive method for the treatment of prostate cancer. Heterotopic tumours of prostatic adenocarcinoma (Dunning R3327-AT2) were induced in 10 male Copenhagen rats. After preoperative magnetic resonance imaging (MRI), a 10-mm cylindrical diffusing fibre developed by our research department was inserted under ultrasonographic guidance into the tumour. LITT was performed with a 980-nm diode laser (power 5 W) for 75 s (fluence rate of 1145 J/cm(2)). Non-enhanced T2-weighted and dynamic gadolinium-enhanced T1-weighted MRI examinations were performed at baseline, 1 and 48 h after the procedure and correlated with histological findings. The necrosis lesions induced by LITT were visible on MRI. The mean (SD) ellipsoid necrosis volumes were 0.748 (0.075) mL at 1 h and 0.982 (0.052) mL at 48 h after the LITT procedure, and significantly different (P < 0.001). Histological analysis showed a strong correlation (r = 0.87) with the mean necrosis volume obtained by MRI at 48 h after LITT. In a prostatic adenocarcinoma model, 980-nm LITT induces reproducible necrosis volumes. Further characterization of the response to LITT in an animal model and in human tissues will be important in establishing the efficacy of the procedure for prostate cancer focal therapy.

Diode lasers emitting at 1190 nm with a highly strained GaInAs quantum well and GaAsP compensating layers MOCVD-grown on a GaAs substrate

Laser heterostructures with an active region consisting of a highly strained GaInAs quantum well located between GaAsP compensating layers were grown by metal-organic chemical vapor deposition on GaAs substrates. Stripe mesa-structure laser diodes of 100 μm aperture emitting at 1190 nm were fabricated. The highest emission power of these diodes in the CW mode amounted to 4.5 W per output mirror. Due to the presence of compensating GaAsP barriers, the GaInAs quantum well remains unrelaxed, which eliminates the spread in the maximum emission power of laser diodes produced from the same heterostructure.

Thermal Analysis of Heat-Assisted Magnetic Recording Optical Head with Laser Diode on Slider

For the optical head used in heat-assisted magnetic recording (HAMR), mounting a laser diode chip on the slider offers a more integrated, compact, and stable design. However, the heat generated by the laser diode will cause the head temperature to increase, which may decrease the laser output power and change the slider flying status. In this paper, the thermal analysis of the HAMR head including the laser diode and a transducer is conducted. The effects of the laser diode power, the power absorbed by the transducer, boundary thermal resistance between the laser diode chip and the slider substrate, and slider fly speed and fly height on the laser temperature increase, the transducer temperature increase, and the air-bearing surface temperature distribution are studied. The deformation of the air-bearing surface caused by its temperature change is also analyzed.

Thermal Analysis of Heat-Assisted Magnetic Recording Optical Head with Laser Diode on Slider

For the optical head used in heat-assisted magnetic recording (HAMR), mounting a laser diode chip on the slider offers a more integrated, compact, and stable design. However, the heat generated by the laser diode will cause the head temperature to increase, which may decrease the laser output power and change the slider flying status. In this paper, the thermal analysis of the HAMR head including the laser diode and a transducer is conducted. The effects of the laser diode power, the power absorbed by the transducer, boundary thermal resistance between the laser diode chip and the slider substrate, and slider fly speed and fly height on the laser temperature increase, the transducer temperature increase, and the air-bearing surface temperature distribution are studied. The deformation of the air-bearing surface caused by its temperature change is also analyzed.

Study of materials for protecting the output mirrors of semiconductor lasers based on AlGaAs/GaAs heterojunctions

The optical properties of thin films of zinc selenide, aluminum oxide, and silicon nitride obtained by electron-beam evaporation using ion assistance have been investigated. It is shown that the resulting zinc selenide films have high roughness and weak protective properties. By using reactive sputtering, silicon nitride films are obtained that increase the limiting power of lasers by a factor of 2.5. Using silicon nitride as an example, it is shown that the optical characteristics of the films can be controlled by varying the parameters of the sputtering process. It is shown that aluminum oxide films obtained with ion assistance increase the limiting power of laser diodes by a factor of 2 by comparison with similar films obtained with no ion assistance.

Measurements of radiation vibrations of turbomachine blades using an optical-fiber displacement-sensing system

Turbomachine blades are critical equipment in the energy, chemical, aviation, and shipbuilding industries. Turbomachine-blade vibrations can cause high cycle fatigue, which reduces the blade lifetime. Their stable operation is a determining factor of safe and efficient production. In order to monitor and detect the turbomachine-blade vibrations and check whether whole or partial performance is normally operating, we design a reflective intensity-modulated optical-fiber sensing system for radial vibration detection of turbomachine blades and introduce the basic principles of the detection system in detail. We study some key technologies such as the control system of the laser-diode (LD) constant power and an optical-fiber coupling system with the optical-fiber-bundle structure. We analyze the sensor output characteristics and present some numerical simulations. In view of our experimental results, we show that the system elaborated can eliminate the effects caused by light-intensity fluctuations, optical-fiber flexural losses, and changes in the surface reflection coefficient, and can detect the radial vibrations of turbomachine blades in the presence of strong electromagnetic interference and under high temperatures.

A novel endoscopic fluorescent clip for the localization of gastrointestinal tumors

Accurate tumor localization is essential for gastrointestinal surgery, especially in cases of early cancer. This study was designed to develop a novel fluorescent clip for rapid and exact visualization of tumor sites. A transparent polymer matrix containing highly bright fluorochromes was coated on the front end of endoscopic clips. The fluorescent clips were placed on the mucosal surface of a porcine colon and stomach, and the operator then attempted to identify the fluorescent clips from the outer serosal side of the colon and stomach. A 532-nm diode laser and filter glass were used for visualizing the fluorescence signals through the colonic tissue. A 650-nm diode laser and a digital charge-coupled device (CCD) camera equipped with a bandpass emission filter were used for the imaging of the fluorescent clips through the thick stomach tissue. When a green light from a 532-nm diode laser (power density=0.35 mW/cm2) was applied on the serosal surface of the porcine colon, we could identify all clips that had been placed endoscopically on the mucosal surface of the inner colonic wall. By using the light from a 650-nm diode laser (power density=0.7 mW/cm2), we identified all fluorescent clips through the stomach wall in real time. Similar results were also obtained with the filtered xenon lamp. An endoscopic fluorescent clip can be useful for the rapid and exact localization of tumors, and this technique can also be useful during laparoscopic surgery.

Efficient generation of 1096 nm and 1572 nm by simultaneous stimulated Raman scattering and optical parametric oscillation in one KTiOPO4 crystal

The simultaneous stimulated Raman scattering (SRS) and optical parametric oscillation (OPO) for the 1064 nm radiation were realized in one KTP crystal for the first time. At an incident diode laser power of 8.6 W, the maximum average output powers at 1096 nm and 1572 nm were 1.1 W and 0.36 W, respectively. The conversion efficiency to Stokes with respect to the incident diode power was as high as 12.8%. The corresponding minimum pulse widths at 1096 nm and 1572 nm were 2.8 and 1.1 ns, respectively.

렌즈형 광섬유를 이용하여 펄스형 반도체 레이저 Beam Shaping 및 증폭 기술 연구

We investigate an optical technique for beam shaping and optical amplification of a pulsed laser diode without variation of its original properties, such as repetition rate and pulse duration. The horizontal and longitudinal sizes of the pulsed laser diode are 300 and , respectively, and its output power is . The multimodal and elliptical pulse shape of the laser diode is converted to the single-modal and Gaussian pulse shape by using a lensed optical fiber. Since the single-modal lensed fiber coupling from the multimodal pulsed laser diode degrades the output power severely, the output power of the pulsed laser diode is dramatically enhanced by using an optical amplification method based on master oscillated power amplification (MOPA). The pulse qualities of the laser diode are not changed after amplifying the pulse power and the output power was finally measured to be .

A Novel Deign Method of Laser Diode Power Supply

In this paper, a digital control continuous light-emitting laser diode power supply has been present. According to the characteristics of laser diode, the is easy controlled, miniaturization, high efficiency, non-impact and slow-start. The mathematical model of current source circuit and the design method of transform the analog control model to the digital control model is established to improve the performance of laser diode current source. The efficiency of supply is better then 92%.