Bragg Reflector Tapered Diode Laser Research Articles

Intensity Noise Transfer Through a Diode-Pumped Titanium Sapphire Laser System

In this paper, we investigate the noise performance and transfer in a titanium sapphire (Ti:S) laser system. This system consists of a distributed Bragg-reflector tapered diode laser, which is frequency doubled in two cascaded nonlinear crystals and used to pump the Ti:S laser oscillator. This investigation includes electrical noise characterizations of the utilized power supplies, the optical noise of the fundamental light, the second harmonic light, and finally the optical noise of the femtosecond pulses emitted by the Ti:S laser. Noise features originating from the electric power supply are evident throughout the whole transfer chain. It is demonstrated that improving the electrical noise provides an easy method for reducing the relative intensity noise (RIN) in all stages. The frequency doubled light is shown to have a higher RIN than the fundamental light. In particular, the cascaded system is seen to exhibit higher RIN than a setup with only a single nonlinear crystal. The Ti:S is shown to have a cutoff frequency around 500 kHz, which means that noise structures of the pump laser above this frequency are strongly suppressed. Finally, the majority of the Ti:S noise seems to originate from the laser itself, which partly can be explained by the effect of relaxation oscillation frequency.

Reduction of Optical Feedback Originating From Ferroelectric Domains of Periodically Poled Crystals

Optical feedback originating from the interfaces of the periodically poled domains of a nonlinear crystal is usually blocked by a bulky optical isolator to avoid an influence on the pump source. Here, a nonlinear bulk crystal with a slanted design of the periodic poling is used to suppress the optical feedback toward the laser source. This crystal is compared with a conventionally poled crystal, in which the incident radiation propagates perpendicular to the domains. Both crystals are made of magnesium oxide doped congruent lithium niobate (PPMgO:CLN). A distributed Bragg reflector tapered diode lasers with a maximum optical power of 7.0 W at a wavelength of 1122 nm and each nonlinear crystal are employed in a single-pass setup. In comparison with the conventional crystal, the optical feedback of the crystal with slanted domains is reduced by 13.4 dB enabling a stable narrow-band operation of the pump laser source without an optical isolator. The impact of the optical feedback on the diode laser with respect to the optical output power and the spectral behavior is investigated. For the crystal with slanted domains, a frequency doubled output power up to 0.39 W at 561 nm is generated without reaching the coherence collapse regime, as observed in case of the conventional crystal. These results are promising for miniaturization of the setup without a need for a bulky optical isolator.

Generation of sub-50fs soliton pulses from a mode-locked Yb,Na:CNGG disordered crystal laser.

We experimentally demonstrated a diode-pumped sub-50 fs Yb,Na:CNGG disordered crystal laser. Pumped by a 980 nm distributed Bragg-reflector tapered diode laser and passively mode-locked with a semiconductor saturable absorber mirror (SESAM), soliton pulses as short as 62 fs and 45 fs were obtained without and with external compression, respectively. The ultrashort pulses had a repetition rate of ~104 MHz at the central wavelength of 1061 nm. To the best of our knowledge, this is the first demonstration of sub-50 fs pulses from the Yb3+-doped CNGG type disordered crystal lasers.

Direct Modulation Capabilities of Micro-Integrated Laser Sources in the Yellow–Green Spectral Range

In this letter, the millisecond modulation capabilities of high power multisection diode laser systems and their application to second harmonic generation (SHG) are investigated. Different modulation methods of the optical output power of a distributed Bragg-reflector tapered diode laser and a master oscillator power amplifier (MOPA), both emitting at 1120 nm, are compared. The modulated optical output power features a rectangular pulse shape with pulse lengths in the low millisecond regime and peak optical power above 5 W. Based on these results, the most suitable method for the modulation of the second harmonic emission is identified and applied to micro-integrated modules with an MOPA pump source and different crystals for SHG. At an emission wavelength of 560 nm, rectangular millisecond pulses with a peak power of more than 245 mW are achieved.

Highly efficient multimode diode-pumped Yb:KYW laser

Record high differential efficiency (53.2%) and full optical efficiency (48%) for a multimode diode-pumped Yb:KYW laser have been achieved. The characteristics of the laser and methods for improving its efficiency using a distributed Bragg reflector tapered diode laser (DBR TDL) are discussed.

Injection Current-Dependent Single-Mode Fiber Coupling of a DBR Tapered Diode Laser Beam

In this letter, we investigate experimentally the influence of injection current-induced beam astigmatism change in a distributed Bragg reflector tapered diode laser on launching of its nearly diffraction limited, simple astigmatic laser beam into a single-mode fiber (SMF). In particular, the optical power and the laser beam properties in front and behind the SMF are examined in dependence on the current injected into the taper section of the diode laser. The fiber coupling measurements are conducted at two fixed configurations of the applied optical system, each of which is optimized for a different taper current value. A maximum power of 3.5 W ex SMF at a coupling efficiency of 67% is reached.

Multiphoton imaging with a novel compact diode‐pumped Ti:sapphire oscillator

Multiphoton laser scanning microscopy commonly relies on bulky and expensive femtosecond lasers. We integrated a novel minimal-footprint Ti:sapphire oscillator, pumped by a frequency-doubled distributed Bragg reflector tapered diode laser, into a clinical multiphoton tomograph and evaluated its imaging capability using different biological samples, i.e. cell monolayers, corneal tissue, and human skin. With the novel laser, the realization of very compact Ti:sapphire-based systems for high-quality multiphoton imaging at a significantly size and weight compared to current systems will become possible.

High-power diode lasers at 1178 nm with high beam quality and narrow spectra.

High-power distributed Bragg reflector tapered diode lasers (DBR-TPLs) at 1180nm were developed based on highly strained InGaAs quantum wells. The lasers emit a nearly diffraction-limited beam with more than two watts with a narrow spectral width. These features are believed to make this type of diode laser a key component for the manufacturing of miniaturized laser modules in the yellow and orange spectral range by second-harmonic generation to cover a spectral region currently not accessible with direct emitting diode lasers. Future applications might be the laser-cooling of sodium, high-resolution glucose-content measurements, as well as spectroscopy on rare earth elements.

Compact Blue Light Source by Single-Pass Second Harmonic Generation of DBR Tapered Laser Radiation

We demonstrate a continuous-wave 460-nm compact visible laser module having a footprint of 75 mm × 25 mm × 25 mm. This blue light source is achieved through single-pass second harmonic generation with a distributed Bragg reflector tapered diode laser as a single-frequency pump source at ~920 nm in a periodically poled MgO-doped lithium niobate crystal with a planar waveguide. The compact blue laser module reached an optical output power of 286 mW with the highest optical conversion efficiency of 11.6% at room temperature. The power stability of the blue light from the laser module is measured at an output power of 268 mW with a variation of ±3.5% during a period of 1 h.

High-Power Single-Mode Fiber Coupling of a Laterally Tapered Single-Frequency Diode Laser

In this letter, we investigate experimentally single-mode fiber (SMF) coupling of a nondiffraction limited, astigmatic beam generated by a near-infrared distributed Bragg reflector tapered diode laser at high output powers. In particular, a systematic study of the coupling efficiency as well as spectral and spatial laser beam characteristics behind the SMF is carried out in dependence on the properties of the collimated beams in front of the SMF, which are generated at given operating points of the diode laser. A stigmatic, nearly Gaussian laser beam is obtained behind the SMF independent on the diode laser operating point and the input optical power. A maximum power of 3.5 W ex fiber at a power coupling efficiency of 65% is reached.

Watt-class green-emitting laser modules using direct second harmonic generation of diode laser radiation

Large-area high-resolution displays, using a flying-spot to create the picture, require light sources in the red, green and blue wavelength range with a high optical output power and nearly diffraction limited beam. In this paper we present experimental results of high-brightness distributed Bragg reflector tapered diode lasers at 106x nm that can be used for single-pass second harmonic generation into the green. Based on these lasers we developed compact (2.5 cm3) green laser modules with an output power of 1W at 53x nm and an electro-optical conversion efficiency of about 5%. The output power stability is better than 2% and the wavelength stability is ±10 pm. The excellent beam quality Mδ2 < 2 of the green light allows operation in flying spot application systems. Furthermore, we estimate that our concept allows power scaling up to 2W by using nonlinear planar waveguide crystals and into the multi-watt level by spectral beam combining.

Efficient concept for generation of diffraction-limited green light by sum-frequency generation of spectrally combined tapered diode lasers

In order to increase the power of visible diode laser systems in an efficient manner, we propose spectral beam combining with subsequent sum-frequency generation. We show that this approach, in comparison with second harmonic generation of single emitters, can enhance the available power significantly. By combining two distributed Bragg reflector tapered diode lasers we achieve a 2.5-3.2 fold increase in power and a maximum of 3.9 W of diffraction-limited green light. At this power level, green diode laser systems have a high application potential, e.g., within the biomedical field. Our concept can be expanded combining multiple diode lasers to increase the power even further.

Diode-pumped mode-locked Yb:YCOB laser generating 35 fs pulses

Direct sub-50-fs pulse generation is demonstrated with a mode-locked Yb:YCa4O(BO3)3 laser. With external compression, pulses as short as 35 fs are generated at 1055 nm. The oscillator operating at a repetition rate of 95 MHz is pumped by a two-section distributed Bragg reflector tapered diode laser and mode locked by a semiconductor saturable absorber mirror. The onset of self-Raman-conversion for pulse spectral bandwidths exceeding 40 nm (FWHM) is observed.

Efficient high-power frequency doubling of distributed Bragg reflector tapered laser radiation in a periodically poled MgO-doped lithium niobate planar waveguide

We report on efficient single-pass, high-power second-harmonic generation in a periodically poled MgO-doped LiNbO3 planar waveguide using a distributed Bragg reflector tapered diode laser as a pump source. A coupling efficiency into the planar waveguide of 73% was realized, and 1.07 W of visible laser light at 532 nm was generated. Corresponding optical and electro-optical conversion efficiencies of 26% and 8.4%, respectively, were achieved. Good agreement between the experimental data and the theoretical predictions was observed.

Improving the modulation efficiency of high-power distributed Bragg reflector tapered diode lasers

Different measures to improve the modulation efficiency of a distributed Bragg reflector tapered diode laser emitting at 1060 nm were investigated. Due to the 6-mm long cavity, the device reached an output power of 10 W with a nearly diffraction-limited beam quality. The input currents to the ridge-waveguide (RW) and tapered gain-region sections can be independently controlled. This allows a low-current modulation of the optical output power in the Watt range. Under optimized quasi-static conditions the power could be modulated between 0.2 and 3.1 W (4.8 W) by a variation of the RW current between 0 and 50 mA (350 mA). Due to the integrated 6th order surface Bragg grating the emission wavelength remains within the spectral range of 80 pm.

Diode-pumped gigahertz femtosecond Yb:KGW laser with a peak power of 39 kW

We present a diode-pumped Yb:KGW laser with a repetition rate of 1 GHz and a pulse duration of 281 fs at a wavelength of 1041 nm. A high brightness distributed Bragg reflector tapered diode laser is used as a pump source. Stable soliton modelocking is achieved with a semiconductor saturable absorber mirror (SESAM). The obtained average output power is 1.1 W and corresponds to a peak power of 3.9 kW and a pulse energy of 1.1 nJ. With harmonic modelocking we could increase the pulse repetition rate up to 4 GHz with an average power of 900 mW and a pulse duration of 290 fs. This Yb:KGW laser has a high potential for stable frequency comb generation.

Diode-pumped mode-locked Yb:LuScO_3 single crystal laser with 74 fs pulse duration

The mode locking of the mixed sesquioxide single crystal Yb:LuScO(3) is demonstrated. This crystal is locally disordered and has the broadest emission spectrum of all sesquioxides known so far. Pulse durations as short as 111 and 74 fs were obtained using the semiconductor saturable absorber mirror and Kerr-lens mode locking, respectively. The latter regime was reached using a two-section distributed Bragg-reflector tapered diode laser as a pump source.

Compact second-harmonic generation laser module with 1 W optical output power at 490 nm

We demonstrate continues-wave 1 W at 490 nm on a 2.5 cm(3) micro-optical bench using single-path second-harmonic generation with a periodically poled MgO:LiNbO(3) bulk crystal. The pump laser is a distributed Bragg reflector tapered diode laser having a single-frequency spectrum and a pump power of 9.5 W. Based on that 1 W blue light could be achieved resulting in an optical conversion efficiency of 11%. Furthermore, the module has an output power stability of better than 2% and the blue laser beam shows an nearly diffraction limited beam quality of M(2)(sigma) = 1.2 in vertical and M(2)(sigma) = 2 in lateral direction.

Experimental and numerical study of Distributed-Bragg-Reflector tapered lasers

We report results on experimental and numerical investigations of the output characteristics of edge-emitting distributed Bragg reflector tapered diode lasers emitting around 980 nm. The experimental results are well described by the Traveling Wave model which is extended by a parametrical heating model. Dynamic instabilities occur due to different thermally induced refractive index changes.

400 mW and 16.5% wavelength conversion efficiency at 488 nm using a diode laser and a PPLN crystal in single pass configuration

Continuous wave power of more than 400 mW at 488 nm has been generated by frequency doubling of 2.45 W at 976 nm obtained from a distributed Bragg reflector tapered diode laser. This results in a wavelength conversion efficiency of 16.5% and an electrical-to-optical efficiency of more than 4.5%. We used a 50 mm long periodically poled MgO:LiNbO3 bulk crystal in single-pass configuration for the second harmonic generation. This is to the author’s knowledge the highest output power and the highest wavelength conversion efficiency at 488 nm generated by a monolithic semiconductor laser device in single pass configuration with a bulk crystal. A deviation from the quadratic dependency of the frequency doubling is explained by the decrease of the beam quality of the fundamental wave.