Optimum Output Coupling Research Articles

Dynamically tunable broadband output coupling of optical oscillators based on non-cyclic geometric phase mirror

We present a uniquely versatile and efficient mirror system capable of real-time fine-tuning in reflection and transmission properties across a broad wavelength range and at a high optical power. Leveraging the principles of the non-cyclic geometric phase (GP) acquired by the clockwise and counterclockwise beams of the Sagnac interferometer satisfying the anti-resonant condition on propagation through the quarter-wave plate, half-wave plate, and quarter-wave plate combination having fast axes oriented at 45° (fixed), θ (variable), and −45° (fixed) with respect to the vertical, respectively, our mirror system offers dynamic transmission control across 0–100% without the need for realignment. Notably, the GP-based mirror (GP-mirror) preserves the polarization state of the reflected beam, making it ideal for polarization-sensitive applications. The wavelength insensitivity of the GP enables seamless operation of the mirror across a wide wavelength range. As a proof-of-principle, we use the GP-mirror as the output coupler of a continuous-wave, green-pumped, doubly resonant optical parametric oscillator (DRO) based on a 30-mm-long MgO:sPPLT crystal and obtain stable operation at high powers over a wide wavelength tuning range. For a pump power of 5 W, the DRO provides an output power of 2.45 W at an extraction efficiency as high as 49% when operated at optimum output coupling. The DRO shows a maximum pump depletion of 89% and delivers an optimum output power across a tuning range ≥90 nm. The demonstrated concept offers a promising approach for advancing the capabilities and control of coherent optical sources tunable across different spectral regions and in all time scales from continuous-wave to ultrafast femtosecond domain.

Universal Output Characteristics of Single-Mode Operation in Low-Loss Large- V -Number Multimode Waveguide Lasers with Transverse Spatial Hole Burning

We study the performance limit of single-mode operation in low-loss large-V-number planar waveguide lasers, with transverse spatial hole burning as the dominating mechanism for transverse-mode competition. By introducing normalized variables, we develop a simple semianalytical model to describe the universal output characteristics of single-mode emission before the onset of high-order modes, which can be easily scaled to a wide range of laser configuration parameters. Our model is validated using exact numerical solutions, which show applicability beyond that of the low-loss approximation. Our analysis establishes a minimum criterion of the loss ratio between the fundamental and first higher-order mode for a robust single-mode operation. This criterion is much weaker than that of conventional wisdom based on the pure wave-propagation argument, which we attribute to a resonator enhancement effect. Our universal outcome can be denormalized to establish the relationship between single-mode extraction efficiency and optimum output coupling in a multimode laser with arbitrary modal loss ratios over a wide range of single-pass unsaturated gain and loss.

Tunable single-mode cw energy-transfer dye laser directly optically pumped by a diode laser

Within this work a tunable single-mode continuous wave energy transfer dye laser operation in green-yellow spectral region was achieved under direct optical pumping by an economy-class diode laser at λ = 445 nm. The laser is operated on a binary dye mixture: Coumarin 498 (donor) and Pyrromethene 556 (acceptor); the latter exhibits only negligible absorption at the pump wavelength, and thus its lasing is almost exclusively due to the excitation energy transfer. This binary energy transfer dye mixture was studied for the first time. Basic lasing properties at various acceptor concentrations were examined; donor concentration was fixed at the value optimum for its lasing under the optical pumping conditions applied. For the final acceptor concentration the optimum output coupling was determined for selected wavelengths from the measurements of the output power in variable output coupling scheme. Single-mode operation sufficiently stable for high-resolution spectroscopic applications was also achieved and tested. Further investigations of the energy transfer mechanisms and efficiency in the binary dye mixture applied are in progress and will be reported separately.

Single-wavelength ring-cavity fiber laser employed pre-amplification technique to reduce threshold by circulating spontaneous brillouin scattering

<span>In this paper, two types of ring-cavity fiber laser structures that operate as a single wavelength laser were investigated on the threshold performance. The two structures are namely Brillouin fiber laser and Brillouin erbium fiber laser. In the first structure, the Brillouin pump signal was amplified before being injected into the laser cavity which namely as Brillouin fiber laser. Meanwhile, for second structure respectively, the Brillouin pump signal was pre-amplified in the laser cavity which namely as Brillouin Erbium fiber laser. We found that the stimulated Brillouin scattering threshold power was lowered significantly by circulating the spontaneous Brillouin scattering in the gain medium utilizing the pre-amplification technique. The optimum stimulated Brillouin scattering threshold power was about 1.4 mW, and this was achieved at optimum output coupling ratio of 95%. By comparing to the first structure in which the Brillouin pump signal was amplified before entering the laser cavity, stimulated Brillouin scattering threshold power was only achieved at 2.62 mW at a similar wavelength. The pre-amplification technique proposed in this paper has been shown to improve the performance of single-wavelength ring-cavity fiber lasers via significant reduction of the stimulated Brillouin scattering threshold power which was around 1.22 mW.</span>

Study on the performance improvement of high power gas terahertz laser by optimizing L-shaped cavity

A high power gas terahertz laser based on L-shaped cavity was demonstrated. We, for the first time, investigated the output performances of D2O gas 385 μm THz laser by optimizing the output coupler transmittance of the L-shaped cavity both in theory and experiment. Under the pump energy of 1.6 J, the optimum output coupler transmittance was about 0.78 and the optimum gas pressure was about 500 Pa. Up to 8.4 mJ pulse energy at 385 μm was achieved at output coupler transmittance of 0.8, corresponding to a photon conversion efficiency of 43.7%. Pulse width of 120 ns, and beam quality factor M2 of 1.58 were obtained at the highest output energy. In addition, the experimental results are in agreement with the theoretical simulation results.

Lasing characteristics of 10 GHz signal spacing in a ring cavity multi-wavelength Brillouin fiber laser employing fiber Bragg grating

This paper experimentally demonstrated a ring cavity multi-wavelength Brillouin fiber laser employing fiber Bragg grating (FBG) that operated in the C-band region. The FBG plays a significant role to reflect signals and filter selected wavelengths. A number of generated Brillouin Stokes (BS) signals and tuning range ability were investigated. A 9[Formula: see text]km length of single mode fiber was utilized to provide a Brillouin gain medium for generating stimulated Brillouin scattering effect. In this work, at optimum output coupling ratio of 90% and Brillouin pump (BP) wavelength of 1550[Formula: see text]nm, up to a maximum of 26 BS signals were recorded by injecting 63.1[Formula: see text]mW of amplified BP powers. The BS signals were also tunable within the ranges of 1544–1556[Formula: see text]nm in accordance with the FBG properties at 3[Formula: see text]dBm bandwidth of 5[Formula: see text]nm.

Antiresonant ring output-coupled continuous-wave optical parametric oscillator

We demonstrate the successful deployment of an antiresonant ring (ARR) interferometer for the attainment of optimum output coupling in a continuous-wave (cw) optical parametric oscillator (OPO). The cw OPO, configured as a singly-resonant oscillator (SRO), is based on a 50-mm-long MgO:PPLN crystal and pumped by cw Ytterbium-fiber laser at 1064 nm, with the ARR interferometer integrated into one arm of the standing-wave cavity. By fine adjustment of the ARR transmission, a continuously variable signal output coupling from 0.8% to 7.3% has been achieved, providing optimum output coupling for signal and optimum power extraction for the idler, at different input pumping levels. The experimental results are compared with theoretical calculations for conventional output-coupled cw SRO, and the study shows that by reducing the insertion loss of the ARR elements, the performance of the ARR-coupled cw SRO can be further enhanced. We also show that the use of the ARR does not lead to any degradation in the cw SRO output beam quality. The proof-of-principle demonstration confirms the effectiveness of the technique for continuous, in situ, and fine control of output coupling in cw OPOs to achieve maximum output power at any arbitrary pumping level above threshold.

Possibility for mode-locked operation of a femtosecond UV storage ring free-electron laser using a low-loss Fabry–Perot resonator

A storage ring free-electron laser (SR-FEL) is inherently a self-mode-locked optical system. The gain broadening due to electron energy spread affects the small signal gain in order to determine the output coupling. Here, the dependence of the small signal gain, the optimum output coupling, and pulse duration on both electron energy spread and loss of a Fabry–Perot resonator in UV SR-FEL were investigated. It was shown that the output coupling strongly affects the mode-locked pulse duration and the present picosecond pulses can be shortened to femtosecond ones using a proper low-loss resonator.

Power characteristics of homogeneously broadened index-antiguided waveguide lasers

A model is reported that describes a bidirectional homogeneously broadened index-antiguided (IAG) slab laser having arbitrary single-pass gain and distributed losses. Maximum extraction efficiency and corresponding optimum output coupling are determined for various values of unsaturated gain and loss per pass. A method is proposed to determine the intrinsic laser parameters from output power measurements.

Analytical analysis of second-order Stokes wave in Brillouin ring fiber laser

This paper details a theoretical modeling of Brillouin ring fiber laser which incorporates the interaction between multiple Brillouin Stokes signals. The ring cavity was pumped at several Brillouin pump (BP) powers and the output was measured through an optical coupler with various coupling ratios. The first-order Brillouin Stokes signal was saturated with the presence of the second-order Stokes signal in the cavity as a result of energy transfer between them. The outcome of the study found that the optimum point for the first-order Stokes wave performance is at laser power reduction of 10%. Resultantly, at the optimum output coupling ratio of 90%, the BFL was able to produce 19.2 mW output power at BP power and Brillouin threshold power of 60 and 21.3 mW respectively. The findings also exhibited the feasibility of the theoretical models application to ring-type Brillouin fiber laser of various design parameters.

Multiwavelength Brillouin fiber laser with enhanced reverse-S-shaped feedback coupling assisted by out-of-cavity optical amplifier

A multiwavelength widely tunable Brillouin optical comb with an enhanced reverse-S-shaped feedback coupling assisted by out-of-cavity optical amplifier is demonstrated. The enhancement is done by locating the amplifier and the Brillouin pump into the reverse-S-shaped fiber section. The oscillating modes in the cavity are directly influenced solely by the Brillouin gain. A wide tuning range of 45 nm is obtained that is only limited by the erbium amplification bandwidth. An average of eleven laser lines that can be tuned to over 45 nm wavelengths is obtained at 40% optimum output coupling ratio.

High-power, continuous-wave Ti:sapphire laser pumped by fiber-laser green source at 532 nm

We report the first experimental demonstration of efficient and high-power operation of a Ti:sapphire laser pumped by a simple, compact, continuous-wave (cw) fiber-laser-based green source. The pump radiation is obtained by direct single-pass second-harmonic-generation (SHG) of a 33 W, cw Yb-fiber laser in a 30-mm-long MgO:sPPLT crystal, providing 11 W of single-frequency green power at 532 nm in TEM 00 spatial profile with power and frequency stability better than 3.3% and 32 MHz, respectively, over 1 h. The Ti:sapphire laser is continuously tunable across 743–970 nm and can deliver an output power up to 2.7 W with a slope efficiency as high as 32.8% under optimum output coupling of 20%. The laser output has a TEM 00 spatial profile with M 2<1.44 across the tuning range and exhibits a peak-to-peak power fluctuation below 5.1% over 1 h.

激光二极管抽运低温运转Yb:YAG片状激光器理论和实验研究

A Yb:YAG disk laser with V-shaped stable resonator and active-mirror configuration, end-pumped by a 940-nm InGaAs laser diode array, is demonstrated. Performances and optimization of the disk laser at low temperature over a range of 130-200 K are investigated theoretically and experimentally. Laser output energy of 1.46 J/pulse operating at 10-Hz repetition rate is obtained with the optimum output coupler transmission of 30%, and the corresponding optical-to-optical efficiency is 48.7%.

Optimization of output coupling ratio on the performance of a ring-cavity Brillouin-erbium fiber laser

The operation of a single-wavelength Brillouin-erbium fiber laser (BEFL) system with a Brillouin pump preamplified technique for different output coupling ratios in a ring cavity is experimentally demonstrated. The characteristics of Brillouin Stokes power and tunability were investigated in this research. The efficiency of the BEFL operation was obtained at an optimum output coupling ratio of 95%. By fixing the Brillouin pump wavelength at 1550 nm while its power was set at 1.6 mW and the 1480 pump power was set to its maximum value of 135 mW, the Brillioun Stokes power was found to be 28.7 mW. The Stokes signal can be tuned within a range of 60 nm from 1520 to 1580 nm without appearances of the self-lasing cavity modes in the laser system.

Diode-end-pumped CW Tm,Ho:YLF solid-state laser working at room temperature

The laser properties of laser diode end-pumped Tm and Ho co-doped lithium yttrium fluoride (YLF) laser are studied. The experiment of Tm,Ho:YLF laser is conducted for different output couplings, and the optimum output coupler transmission is 2% when the crystal is kept at room temperature. The distribution of far field intensity is measured by pin-hole scanning, the output laser is proved to be operating in the TEM00 mode, and the relation between thermal focal length and pump power is obtained. To achieve single frequency operation, two solid, uncoated fused silica etalons are used. The laser threshold pump power is 250 mW, and the maximum continuous wave single frequency output power is 118 mW at the pump power of 2.8 W. The single frequency laser may be used as a seed laser for either a larger oscillator or an amplifier.

Numerical modeling of a continuous-wave Yb-doped bulk crystal laser emitting on a three-level laser transition near 980 nm

We present a new model for cw, Yb-doped, bulk crystal lasers emitting on a three-level laser transition near 980 nm. This model takes into account the saturation of the absorption and the spatial evolution of the pump and laser beams inside the crystal, which are two important points in three-level lasers. We have validated our numerical model by building an efficient cw Yb:S-FAP (ytterbium:strontium-fluoroapatite) laser emitting at 985 nm and pumped at 899 nm by a Ti:sapphire laser. Our model can be used to define the parameters that optimize the laser output power at 985 nm, such as the relative sizes of the pump and laser beams, the optimum output coupler, or characteristics of the crystal (length, Yb concentration). By adapting this model to diode pumping, we have established the conditions to obtain cw, efficient laser operation at 985 nm of an Yb:S-FAP crystal pumped by a standard 1 × 100-µm² laser diode.

Optimization of power performance in room-temperature continuous-wave Cr 4+:YAG lasers

Experimental and numerical studies were carried out to investigate the power performance and the role of thermal loading in room-temperature Cr 4+:YAG lasers. The numerical model accounts for thermal loading effects due to the temperature dependence of the fluorescence lifetime. Experimental pump absorption, laser threshold, and laser efficiency data were first analyzed to determine the absorption, emission, and excited-state absorption cross-sections. Best-fit cross-section values were then used to perform numerical optimization studies. Results showed that a 2-cm-long crystal with a total unsaturated pump absorption of 64% at 1064 nm, should produce the maximum output power from the laser. Furthermore, the optimum output coupling of the resonator was determined to be 1.7%.

Numerical modeling and optimization of cascaded CW Raman fiber lasers

The authors solve a model which describes a nested fiber Raman cavity using Bragg reflectors by taking into account all interactions between forward and backward traveling waves. They apply the model to the cases in which a laser source at 1117 nm pumps a two-step Raman cascade leading to a 1240-nm output or a five-step cascade leading to a 1480-nm output. In order to insert into the calculations realistic fiber parameters, they have performed measurements of both Raman gain and linear losses for a few optical fibers. They derive from the numerical analysis the optimum fiber length and output coupling, and calculate, for the optimum configuration, the dependence of the output power on the pump power. The model describes with good accuracy the published experimental results.

Continuous-wave power performance of a 2.47-/spl mu/m Cr/sup 2+/:ZnSe laser: experiment and modeling

Power performance of a continuous-wave Cr/sup 2+/:ZnSe laser was investigated experimentally and numerically at 2.47 /spl mu/m. In the experiments, an astigmatically compensated z-cavity with a 3% transmitting output coupler produced as high as 250 mW of output power when excited by a NaCl:OH/sup $/color-center laser at 1.58 /spl mu/m. The measured absorbed power slope efficiency was 24.2%. Experimental pump absorption saturation and laser efficiency data were analyzed by using a numerical model to determine the absorption, emission, and excited-state absorption cross-sections. Simulations were then performed to investigate the dependence of the output power on crystal and resonator parameters. Results indicate that optimum power performance should be obtained with a 1.5-cm-long crystal which has a total unsaturated absorption of 86%. Finally, the optimum output coupling of the resonator was determined to be 10%.

Analysis of planar waveguide grating couplers with double surface corrugations of identical period

Planar waveguide grating couplers with double surface corrugations of identical period are analyzed by using the ray-optics technique and by using the rigorous diffraction grating theory. The ray-optics technique offers physical insight and renders simple analytical expressions for conditions of optimum output coupling.