Tapered Diode Laser Research Articles

Theoretical investigation on the effective coupling optical system between an astigmatic tapered diode laser beam and single-mode optical fibers

In this study, we theoretically investigate the coupling efficiency of tapered diode lasers to single-mode fibers in four different coupling systems using an astigmatic beam propagation algorithm. The fast-axis lens and slow-axis lens have been used to mitigate astigmatism, which is a characteristic of the tapered diode laser and then the beam coupling into different single-mode fibers. Designers should carefully balance the pursuit of high coupling efficiency with the need to minimize astigmatism sensitivity in the design of coupling systems.

Unidirectional ring laser operation and tunable single-frequency emission using differential parametric gain.

In this Letter, a novel approach for unidirectional operation of a 1064 nm solid-state ring laser is demonstrated based on difference frequency mixing. Unidirectional operation is achieved exploiting the directional parametric gain from a single-pass diode laser, facilitated through a periodically poled LiNbO3 crystal. In addition to achieving unidirectional operation, the nonlinear process further enables the generation of single-frequency mid-infrared light. Using a single-pass tapered diode laser, tunable in the range from 780 to 815 nm, the generated mid-infrared signal covers the 2.9 to 3.5 µm range while optimizing the phase-match condition of the difference frequency generation process.

High gain, multi-pass, femtosecond Yb:KYW crossed-crystals amplifier pumped by high-brightness tapered laser diodes

High gain, multi-pass, femtosecond Yb:KYW crossed-crystals amplifier pumped by high-brightness tapered laser diodes

Improving beam quality of tapered laser diodes by integrated metalens

High-power and high-beam-quality laser sources are required in numerous applications. Here, we theoretically investigate a tapered laser diode with integrated metalens, which can improve the lateral beam quality. By carefully designing the slot length and width at different lateral positions behind the front facet, the mode mismatch between the ridged cavity and the tapered cavity is overcome while ensuring high transmittance (>96%). The beam quality is greatly improved, and the lateral far-field divergence is reduced. The simulation results show that the lateral far-field divergence (second-moment level) decreases from 7.2° to 5.9°, and the M2 (second-moment level) decreases from 2.3 to 1.2. The proposed structure shows a good thermal stability in the simulation.

Compact all-solid-state femtosecond Yb amplifier using a high-brightness multi-watt tapered laser diode

In this work, we present a novel amplification module based on a high-brilliance tapered pump laser diode. A monolithic distributed Bragg grating permits to stabilize the diode wavelength, that was kept at 978.5 nm with a full-width at half-maximum bandwidth <0.2 nm during our experiments. Such a compact and reliable single laser source achieves a maximum output power of about 6.5 W, in a linearly polarized beam with high spatial quality (M2 < 1.5). This allows to optimize the performance of compact amplification modules designed to maximize the gain-per-Watt of absorbed pump power and the optical-to-optical extraction efficiency. To assess the potential of such pump unit, we designed a single-pass and double-pass amplification module based on a 3-mm-long 9.5%-doped Yb:KYW crystal, seeded by a either a cw or a femtosecond oscillator providing a maximum average power of ∼500 mW with output wavelength tunable between 1025 nm and 1035 nm. By tightly focusing the pump beam and carefully optimizing the mode-matching between the almost TEM00 pump and seed beam we achieved a single pass small signal gain G0 > 7 at about 3.5 W absorbed pump power and a maximum output power of 2.2 W, corresponding to an optical-to-optical extraction efficiency close to 50%. The excellent beam quality of the seeder was very well preserved during amplification, resulting in a measured Mx2× My2 <1.1 both in single and double pass.

Investigation of the gain match in high brightness 980 nm tapered diode laser

High brightness, high power tapered diode-laser regularly consists of an index-guided ridge-waveguide section and a gain-guide tapered section. The gain match between the ridge and tapered sections were studied in this paper. The gain peak wavelength of the ridge section is expected to be larger than that in the tapered section because of the higher optical power density by numerical simulation. It is found that the gain peak mismatch between the ridge and tapered sections results in broadened optical spectra and low output powers according to the experimental results. The mismatch is suppressed by lowering the junction temperature of the ridge section which shifts the gain peak of the ridge section to a shorter wavelength. Alternatively, the shift of the gain spectra was also realized by increasing the transparency carrier density with an additional optical loss in the ridge waveguide introduced by He + ion implantation. Tapered diode lasers with such designs have a beam quality factor M2 (1/e2) = 1.1 with an output power of 8 W and a narrow spectra width of 2 nm.

Dual-wavelength operation of a tapered laser diode based on a composite DBR grating near 1.03 µm.

A novel monolithic dual-wavelength tapered laser diode based on a composite distributed Bragg reflection (DBR) grating is demonstrated. The composite DBR grating, composed of two sub-gratings with different effective refractive indices, is designed. With the aid of the lateral expansion effect of the optical field in the ridge waveguide, the dual-wavelength operation of tapered laser diode is realized by using the composite DBR grating as a narrow linewidth filter. At the ridge current of 190-300 mA and the heat sink temperature of 20℃, the tapered laser diode obtains dual-wavelength emission with wavelengths of 1025.4 nm and 1036.2 nm, respectively. The linewidths of both wavelengths are less than 36 pm, and the minimum power difference between the two wavelengths is 1.2 dB. The spectral distance between the two wavelengths can be modulated from 10.4 nm to 10.9 nm by adjusting the heat sink temperature of the tapered laser diode from 13.8℃ to 20.7℃.

Micro-integrated high-power narrow-linewidth external-cavity tapered diode laser at 762 nm for daylight imaging

Solar radiation is a challenge for laser-based daylight imaging since it decreases the signal-to-noise ratio (SNR) of the imaging. Here we demonstrate a micro-integrated external-cavity tapered diode laser system for daylight imaging. It emits light at a wavelength of 762 nm, chosen because of its overlap with an oxygen absorption band in the solar radiation spectrum. The integrated laser system consists of a tapered diode amplifier as gain medium and an external volume Bragg grating for spectrum stabilization and narrowing, thus a narrow bandpass optical filter can be used to improve the SNR further. The laser system can be operated in both continuous wave (CW) mode and pulsed mode by modulating the injected current to the amplifier. In CW mode operation, 1.3 W of output power is obtained with an emission spectral linewidth of 4 pm, and a beam propagation factor in the slow axis, M2, of 1.7 (4σ). In pulsed mode operation with a trigger signal of a 50μs pulse width and a 10 kHz repetition rate, 2.0 W of peak output power is achieved with an emission spectral bandwidth of 0.2 nm, and an M2 in the slow axis of 1.9 (4σ). The modulation depth is almost 100%.

Mode-locked Cr:LiSAF laser far off the gain peak: tunable sub-200-fs pulses near 1 µm.

We report, to the best of our knowledge, the first mode-locking results of a Cr:LiSAF laser near the 1 µm region. The system is pumped only by a single 1.1 W high-brightness tapered diode laser at 675 nm. A semiconductor saturable absorber mirror (SESAM) with a modulation depth of 1.5% and non-saturable losses below 0.5% was used for mode-locking. Once mode-locked, the Cr:LiSAF laser produced almost-transform-limited sub-200-fs pulses with up to 12.5 mW of average power at a repetition rate of 150 MHz. Using an intracavity birefringent filter, the central wavelength of the pulses could be smoothly tuned in the 1000-1020 nm range. Via careful dispersion optimization, pulse widths could be reduced down to the 110-fs level. The performance in this initial study was limited by the design parameters of the SESAM used, especially its passive losses and could be improved with an optimized SESAM design.

783 nm wavelength stabilized DBR tapered diode lasers with a 7 W output power.

Wavelength stabilized distributed Bragg reflector (DBR) tapered diode lasers at 783 nm will be presented. The devices are based on GaAsP single quantum wells embedded in a large optical cavity leading to a vertical far field angle of about 29° (full width at half maximum). The 3-inch (7.62 cm) wafers are grown using metalorganic vapor phase epitaxy. In a full wafer process, 4 mm long DBR tapered lasers are manufactured. The devices consist of a 500 µm long 10th order surface DBR grating that acts as rear side mirror. After that, a 1 mm long ridge waveguide section is realized for lateral confinement, which is connected to a 2.5 mm long flared section having a full taper angle of 6°. At an injection current of 8 A, a maximum output power of about 7 W is measured. At output powers up to 6 W, the measured emission width limited by the resolution of the spectrometer is smaller than 19 pm. Measured at 1/e2 level at this output power, the lateral beam waist width is 11.5 µm, the lateral far field angle 12.5°, and the lateral beam parameter M2 2.5. The respective parameters measured using the second moments are 31 µm, 15.2°, and 8.3. 70% of the emitted power is originated from the central lobe.

Measuring the sensitivity to optical feedback of single-frequency high-power laser diodes

Laser diodes, in general, are sensitive to optical feedback, especially with regard to maintaining single-frequency operation. Until now, however, the feedback sensitivity of high-power devices such as single-frequency distributed Bragg reflector (DBR) tapered laser diodes has not been investigated in quantitative detail. In this paper, we analyze the impact of very weak optical feedback between − 105 d B and − 40 d B on a high-power DBR tapered laser diode. The measurement setup is validated using a typical DFB laser diode. The results are in good agreement with the theory at low-feedback levels.

Influence of Guided Wave Mode on Output Characteristics of Tapered Diode Laser

Influence of Guided Wave Mode on Output Characteristics of Tapered Diode Laser

Microsecond pulse-mode operation of a micro-integrated high-power external-cavity tapered diode laser at 808 nm.

We investigate microsecond pulse-mode operation of a micro-integrated high-power diode laser based on volume Bragg grating external-cavity feedback around 808 nm. The laser system contains a tapered amplifier consisting of a ridge-waveguide section and a tapered section with separated electrical contacts. Thus, the diode laser system can be pulsed by modulating the injected current either to the ridge waveguide section (IRW) or to the tapered amplifier section (ITA). With a trigger signal of a 50 µs pulse width and a 10 kHz repetition rate, comparing the modulation depth, peak output power, beam propagation factor, and spectral bandwidth, we conclude that the pulse-mode operation achieved by modulating the ITA gives better results than by modulating the IRW due to the decreased thermal effect. At a constant IRW of 0.2 A and a modulated ITA of 6.0 A, 4.3 W of peak output power is obtained with an emission spectral bandwidth with an upper bound of 0.2 nm, and a beam propagation factor in the slow axis, Mslow2, of 2.6 (1/e2). The modulation depth is almost 100%. The results show that the tapered diode laser system may be a good candidate for microsecond pulse-mode solid-state lasers.

Scalable structure of coherent polarization beam combining based on tapered diode laser amplifiers

We develop a scalable multi-stage beam combining system based on the superposition of four tapered diode laser amplifiers using the coherent polarization beam combining. By employing the combination of master oscillator power amplification and active phase control of each amplifier, a stable output power of 6.9 W is obtained with a nearly diffraction-limited beam quality. The combining efficiency is 72%, and the brightness is improved by a factor of 3.3 compared to that of a single amplifier. Our system provides a new solution to obtain a high-coherence and high-brightness diode laser beam.

Micro-integrated high-power narrow-linewidth external-cavity tapered diode laser at 808 nm.

A novel compact micro-integrated high-power narrow-linewidth external-cavity diode laser around 808 nm is demonstrated. The laser system contains a tapered amplifier consisting of a ridge-waveguide section and a tapered section with separated electrical contacts. Thus, the injection currents to both sections can be controlled independently. An external volume Bragg grating is utilized for spectral narrowing and stabilization. The diode laser system is integrated on a 5mm×13mm aluminum nitride micro-optical bench on a conduction cooled package mount with a footprint of 25mm×25mm. The diode laser system is characterized by measuring the output power and spectrum with the injection currents to the ridge-waveguide section (IRW) and tapered amplifier section (ITA) changed in steps of 25 and 50 mA, respectively. At IRW=200mA and ITA=6.0A, 3.5 W of output power is obtained with an emission spectral linewidth with an upper bound of 6 pm, and a beam propagation factor in the slow axis, M2, of 2.6 (1/e2). The characterization of the temperature stabilization of the laser system shows an increase of the wavelength at a rate of 6.5 pm/K, typical for the applied volume Bragg grating.

Harmonic mode-locking in an external cavity tapered diode laser with saw-toothed microstructure

In the present study, we report the passive harmonic mode-locking (HML) of the external cavity tapered semiconductor laser system with saw-toothed microstructure. The stable picosecond pulse trains were observed up to the third order HML. The mechanism behind the system was analyzed and single-pulse energy of 59 pJ with a repetition rate of 412 MHz and pulse duration of 3.9 ps was realized.

Efficient Tm:YAG and Tm:LuAG lasers pumped by 681 nm tapered diodes.

In this paper, we present highly efficient continuous-wave (cw) laser operation of Tm:YAG and Tm:LuAG lasers pumped by high-brightness red tapered diodes. The single-emitter tapered diode lasers (TDLs) provide up to 1W of pump power around 680nm. By adjusting the operation temperature of the TDL, the pump central wavelength could be matched to the strong absorption peak of Tm3+ ions in this region (H63→F33 excitation). This absorption peak is around threefold stronger than the usually employed 785nm transition (H63→H34). In the cw laser experiments, we have achieved slope efficiencies exceeding 55% at room temperature, which is far above the Stokes limited slope efficiency (34%), indicating presence of a strong two-for-one cross-relaxation process. Pumping with high-brightness tapered diode lasers further facilitated usage of smaller pump spots (enabling quite low lasing thresholds) and generation of near-diffraction limited output beam profiles from standard z-type cavities. To the best of our knowledge, this is the first report of diode pumping of Tm-doped solid-state lasers around 680nm as well as the first usage of TDLs as pump sources in Tm-doped laser systems.

A Yb:KYW Laser Pumped by a Powerful Single-Mode Tapered Diode Laser

A powerful single-mode distributed Bragg reflector diode laser with a low-noise power supply is developed. The output characteristics of the tapered diode laser are investigated. Using such a laser as a pumping source, the free running mode of a Yb:KYW laser is achieved and investigated. It is shown that a compact precision femtosecond frequency synthesizer based on Yb:KYW laser pumped by a similar type of diode laser can be created.

2.7 W diffraction-limited yellow lasers by efficient frequency doubling of high-brightness tapered diode lasers

Abstract Modulated yellow lasers may enable more efficient photocoagulation for treatments of ophthalmic diseases. In this regard, we present a laser system emitting 2.7 W of true-yellow light at 576 nm by frequency doubling the emission of a tapered diode laser emitting 7 W at 1153 nm. The frequency doubling is based on a single-pass configuration using a cascade of two 40-mm periodically poled lithium niobate (PPLN) crystals. The stabilization of the yellow power over 10 h showed a standard deviation of 0.10% and a relative intensity noise of 0.032% rms. Moreover, we demonstrate the generation of yellow pulses with 900 mW of amplitude and a high extinction ratio in the microsecond and millisecond regimes, as required for photocoagulation.

Numerical simulation and experiment of high brightness tapered lasers

The optical properties of a tapered laser, which can be used to improve laser beam quality and generate a high brightness optical beam, are simulated and the tapered laser is fabricated. The beam quality, the index difference, and the index difference dependence on taper angle are studied. A tapered diode laser with a ridge waveguide is introduced and formed through etching the wafer with asymmetrical waveguide structure and double quantum wells. A high brightness power is achieved due to the combination of the ridge waveguide and the taper waveguide. In the experiment, the laser delivers 978 nm, 8 W CW with an 11.96 A current. The beam quality factor M2 in the vertical and lateral directions is measured at 1.42 and 2.21, respectively.