A compact dual wavelength Nd:YVO4/MgO:PPLN infrared laser was developed successfully which was composed of Nd:YVO4 crystal, MgO:PPLN crystal and a cavity mirror(M1). The fundamental laser was consisted of the first face of Nd:YVO4 and M1, and the optical parametric oscillation(OPO) cavity defined by the second face of Nd:YVO4 and M1. The infrared laser output with wavelengths of 1539 nm and 3447 nm was obtained using intracavity cw OPO technology. The output power of 1539nm and 3447nm were 670mW and 236mW at the pumped LD power of 6.0 W, and the optical conversion efficiency was 15.1%. The higher conversion efficiency was mainly attributed the 2mm thickness of MgO:PPLN crystal. Intracavity dual wavelength laser can be used in spectrum detection, drunk driving test and so on.
This system uses SOI optical waveguide ring resonator chip. By using the method of selecting single direction light path, we got the resonance curve and backscattering curve of the resonant, while the system is working under different light powers. The changing rules of FWHM and resonant depth under different light powers is analyzed. And the action mechanism of optical power on the cavity resonance curve and backscattering is analyzed. Finally, the optimal working optical power of SOI integrated optical gyroscope system is determined.
Based on the asymmetric directional coupler, a polarization beam splitter based on silicon on Insulator (SOI) platform is designed for the wavelength range of 1500nm-1600nm in optical communication in this letter. The asymmetric directional coupler is composed of a regular strip shape waveguide and a sub-wavelength grating waveguide. The influence of the grating period, grating depth, and duty cycle on its polarization characteristics is analyzed. The simulation results show that the polarization extinction ratio (PER) of TE polarization is 20-23 dB and the insertion loss (IL) is 0.01-0.04dB, in the wavelength range of 1500–1600nm, while the PER of TM polarization is 15-26 dB and the IL is 0.3-0.6dB. Especially, the PER and IL are 21 dB (26 dB) and 0.31 dB (0.26 dB) for TE (TM) at the wavelength of 1550 nm. Moreover, the minimum feature size of this device is 25 μm2 . It can be effectively used in semiconductor photoelectronic devices.
Alexandrite crystal is a broadband tunable gain medium with good performance in near infrared band. At room temperature, the wavelength tuning range of the alexandrite laser is about 700~818nm, UV or deep-UV (DUV) lasers can be obtained by single or multiple optical nonlinear frequency conversions. The laser oscillations can be generated when alexandrite crystals absorb pumping light energy, and a considerable part of pumping energy will be converted into thermal energy of crystals which will lead to a thermal effect. It will affect the output laser efficiency, the stability of resonator and the quality of output laser beam. In this paper, by establishing the thermal conduction model of the crystal, the stable temperature field distribution, deformation field distribution, and thermal stress field distribution in the crystal can be obtained by solving the corresponding equations. Then the thermal effects caused by these three fields are analyzed respectively, and the corresponding focal lengths of thermal are calculated which shows an inverse relationship between the focal length of the thermal and the absorption pumping power when other conditions remain unchanged. The stable parameter range of the laser cavity can be obtained according to the stable conditions of the resonator, and it will play a guiding role in solving the thermal effect of the crystal and improving the performance of the laser.
The readily accessible commercial electron beam lithography (EBL) has high-accuracy and mask-free characteristics which enable fast exploration of novel on-chip devices. However, current EBL technique would be challenging to solve the dilemma between high accuracy and large writing field. Here we report an effective recipe to fabricate such multiscale photonic devices. It is realized by improving the standard procedure of stitching small writing fields with alignment markers. The key is the small patterns stitching and exposure alignment process. We divide the large design structure into several small patterns and take pictures of their corresponding alignment markers by the EBL instrument itself with exactly the same parameters used in the subsequent e-beam exposure. As such, the exposure alignment errors caused by calibration procedures are completely eliminated. We precisely write the divided patterns to desired locations by their surrounding markers and finally achieve gapless and precise stitching within the whole photonic circuit. The protocol is demonstrated by a Mach-Zehnder Interferometer (MZI) structure on a 200nm thick Si3N4 chip, in which nano-scale grating coupler have been clearly developed. Compared with traditional EBL technique, the connection accuracy of a waveguide between adjacent writing fields has been significantly improved to be less than 10 nm even without a laser interferometric stage. Moreover, due to the stitching mechanism, the maximum chip size for exposure becomes limitless and could reach up to the entire wafer. Our technique greatly expands the fabrication size of EBL while maintaining its high resolution and opens more opportunities to the development of integrated photonic circuits.
A novel ultralow loss bent waveguide for single-mode operation was designed based on the Euler spiral. The proposed 180° bend (U-bend) was composed of two identical 90° Euler bends with gradient width from 1.6μm to 0.45μm and a 0.45μm wide, 2μm long strip waveguide. The proposed U-bend had ultralow losses (<−0.0005dB) and very low mode excitation ratios (MERs) of high-order modes (<−35dB) over a broad wavelength-band by lumerical simulation software. The effective radius Reff of the designed U-bend was as small as 42.547μm and the transmission ratio of fundamental-mode was 0.99988 that almost equal to 1. After simulation and computation, only the fundamental-mode could be retained and propagated in the designed U-bend waveguide with ultralow loss.
Taper is a basic device widely used in photonics technology which transmits light between the waveguides with different widths. Tapers are usually designed to be trapezoidal in shape, which is simple but has many limits. If the taper is designed to be too short, the broken lines at the junction positions between the strip waveguides (SWGs) and the taper will excite high-order modes and cause high fundamental mode loss. As a result, the traditional tapers are always with a long length which limits the miniaturization of photonic systems. To solve this problem, we proposed a method based on forth-order Bezier curve that made the taper has both small size and good performances on the transmission loss of fundamental mode and the mode excitation ratios (MERs) of high-order modes. According to the obtained results, the proposed Bezier curve method decreased the length of a taper from 100μm to 30μm on the premise of maintaining the performances.
High-power special-shaped infrared radiation sources are usually used for detection systems such as compact photoacoustic spectrometers for gas detection. In this article, the light emitting characteristics of a rod-shaped infrared thermal radiation light source was obtained experimentally. Then, based on the luminous characteristics and the illuminance requirements on the target photoacoustic cell, combined with the basic principle of conservation of light energy during transmission, the shaping system for the special-shaped infrared radiation source for photoacoustic spectroscopy was designed and optimized, aiming to achieve efficient collection and utilization of light source beams.
All-solid-state (ASS) ultraviolet (UV) laser is an organic combination of ASS laser technique and nonlinear frequency conversion technique. By using different kinds of nonlinear optical crystals and optimizing the system structure, the conversion efficiency and output power of fifth-harmonic-generation (5HG) of ASS lasers has been constantly updated. And the expected UV laser with high beam quality and stability was obtained through reasonable system design. In this paper, the research status of 5HG for ~1 μm near-infrared ASS lasers were briefly reviewed, different approaches for producing 5HG were compared, and the advantages and disadvantages of the corresponding approaches are analyzed.
It is hard to judge quality of CaF2 window from its nominal specification, because suppliers are used to testing products performance under relatively weak spectral lines from lamp, which can not tell the real operation behavior of CaF2 window under intense laser irradiation. We report a method of testing the transmissivity of three different grade commercially available CaF2 windows under high pulse repetition rate laser irradiation at 193nm, and the lab prototype of test module distinguishes them well with a repeatability better than 2%.
Due to complex kinetics of formation and loss mechanisms, such as ion-ion recombination reaction, neutral species harpoon reaction, excited state quenching and photon absorption, as well as their interactions, the performance behavior of different laser gas medium parameters for excimer laser varies greatly. Therefore, the effects of gas composition and total gas pressure on excimer laser performance attract continual research studies. In this work, orthogonal experimental design (OED) is used to investigate quantitative and qualitative correlations between output laser energy characteristics and gas medium parameters for an ArF excimer laser with plano-plano optical resonator operation. Optimized output laser energy with good pulse to pulse stability can be obtained effectively by proper selection of the gas medium parameters, which makes the most of the ArF excimer laser device. Simple and efficient method for gas medium optimization is proposed and demonstrated experimentally, which provides a global and systematic solution. By detailed statistical analysis, the significance sequence of relevant parameter factors and the optimized composition for gas medium parameters are obtained. Compared with conventional route of varying single gas parameter factor sequentially, this paper presents a more comprehensive way of considering multivariables simultaneously, which seems promising in striking an appropriate balance among various complicated parameters for power scaling study of an excimer laser.
A self-seeded discharge-excited ArF excimer laser oscillator using a dual-cavity configuration with long cavity lengths was developed and characterized. Proper designs for effective mode-locking in long cavity-lengths are proposed and demonstrated experimentally, which will significantly improve the energy and monochromaticity. By using the techniques of efficient mode-locking, self-seeded laser outputs with nearly the same linewidths with the seeders and larger energies are obtained. And the mode-locking can be achieved at different laser linewidths and wavelength centers.
A coherence length tunable solid-state laser based on Fabry-Perot (F-P) etalon with high stability is constructed. Principles of the coherence length tuning method by rotating the F-P etalon are theoretically analyzed and experimentally verified. By using Nd:YAG as the gain medium, an all-solid-state 1064 nm laser with 375 mW output power, 0.37% high power stability(RMS), high beam quality, and tunable coherence lengths from 9.37 cm to 20.05 cm is achieved. This method could be extended to multiband center wavelengths for their tuning of coherence length.
The inscription method of FBGs on large-mode-area double-clad fibers (LMA-DCFs) with phase mask technique was
described. A pair of LMA FBGs was prepared and the center wavelengths of them were both around 1076nm with 3 dB
bandwidths of about 0.5nm. The reflectivities of them are 99% and 10% in the fundamental mode, respectively. In order
to be protected and to withstand high-power laser, the FBGs were metally packaged, and then applied to an Yb3+-doped
LMA-DCF laser as the laser cavity. An output power of 314 W centered at 1075.71 nm with a slope efficiency of 60%
was achieved.
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