We report on diffraction performances of deep-etched transmission gratings in fused silica at the wavelength of 1.55μm. Profile parameters of the depth and line density are optimized to achieve the first order Bragg transmitted efficiency of more than 98% theoretically under TE- or TM-polarized incident lights. Spectra performance of a 630 lines/mm grating with the depth of 3.0μm in the C+L bands is presented in which the diffraction efficiency of each spectrum can be above 90%. By holography and inductive coupled plasma (ICP) etching, we have made a fused silica grating with the period of 610lines/mm and the depth of 0.73μm, the first order Bragg diffraction efficiency of which can reach 17% at the wavelength of 1.31 µm and 10% at 1.55 μm. Our results provide an important guideline for transmission gratings in fused silica as (de)multiplexers for dense wavelength division multiplexing (DWDM) application.
Inductively coupled plasma (ICP) technology is a new advanced version of dry-etching technology compared with the widely used method of Reactive Ion Etching (RIE). Extensive experiments have been done successfully and the fabrication results of microoptical elements have proved that the new ICP technology is very effective in dry etching field. Plasma processing of the ICP technology is complicated due to the mixed reactions among discharge physics, chemistry and surface chemistry. Existing models concentrate only on part of the whole problem, for example, on plasma physics, or on chemistry reactions. Despite the efforts to understand and model the etching process, simulation of the surface phenomena with accurate and general model coefficients is still lacking. Need for a simulation is even greater when high-density plasma methods such as inductively coupled plasma (ICP) technology are used due to strong polymer deposition effects. In the paper we analyze the physical reactions and chemical reactions that may occur in the chamber in detail, and a surface dynamic model is used to explain the complex reactions occurring in the reaction chamber. At last, we present an experiment that demonstrates the applicability of the surface dynamic model theory very well. The surface dynamic model of the ICP technology presented in this paper provides us a theory basis so that we can take effective measures to control the etching process of ICP technology and to improve the etching quality of microoptical elements greatly.
Driven by the fast development in optical fiber interconnections, there exists an increasingly growing demand for wider bandwidth. DWDM technology can extremely enhance the number of wavelengths (de)multiplexed. Among many DWDM devices, free-space diffraction gratings (FSDG) play an important role, with the advantages of parallel and athermal processing as well as low polarization-dependent losses. In our work, we describe by means of the rigorous coupled-wave analysis (RCWA) that high-density holographic photoresist gratings, if being in optimized profile parameters, can realize high diffraction efficiencies, e.g., the first Bragg diffraction efficiency can theoretically achieve more than 90% both in TE and TM polarizations. And we have successfully fabricated the 600 lines/mm photoresist gratings whose first Bragg diffraction efficiency can experimentally reach 80% with the grating depth 2.9μm. The experiment process is presented in detail, and the experimental result is in good agreement with the theoretical one.
Femtosecond pulse shaping for time-to-space conversion of ultrafast optical waveforms is presented, analyzed, and experimentally implemented. Here the temporal pattern for the designed multiple pulses optimized with a preassumed Gaussian spectral distribution of an ultrashort pulse is described. With the simulation of a Gaussian spectral distribution, we realize that the uniformity of the generated multiple ultrafast temporal pulses is relevant to the repeated number, the accuracy of the transition points and the pixel number for the modulation periods of the mask in the spectral plane. Especially, the change of the Gaussian spectral phase of the modulated phase plate with the wavelength that many people do not consider formerly is analyzed in detail in this work. On the other hand, experiments of the shaped femtosecond pulse measurement with the frequency-resolved optical gating (FROG) characterization technique are given in this paper.
Ultrafast temporal pattern generation and recognition with femtosecond laser technology is presented, analyzed, and experimentally implemented. Ultrafast temporal pattern generation and recognition are realized by taking advantage of two well-known techniques: the space-time conversion technique and the ultrafast pulse measurement technique. Here the temporal pattern for the designed multiple pulses, optimized with a preassumed Gaussian spectral distribution of an ultrashort pulse, is described. With the simulation of a Gaussian spectral distribution, we realize that the uniformity of the generated multiple ultrafast temporal pulses is relevant to the repeated number of modulation periods in the mask in the spectral plane. Moreover, the change of Gaussian spectral phases with the wavelengths in the modulated phase plate is considered. Experiments of ultrafast temporal pattern recognition by the frequency-resolved optical gating (FROG) characterization technique are also given.
Comparing with thin film filters and arrayed waveguide gratings, holographic gratings can realize the highest channel capacity, the lowest insertion loss, etc., which are desirable for DWDM applications. In this paper, we have calculated the diffraction efficiencies of grating structures, such as rectangular, sinusoidal and symmetric triangular gratings with the technique of the rigorous coupled-wave analysis. The presumed conditions, such as TE- and TM- polarization, the aspect ratio of holographic gratings, have been investigated. It is shown that our results are in good agreement with other previous works. Further, we’ve established an experimental setup for fabricating the planar binary holographic gratings. The gratings we’ve made have a relatively high groove or line density (e.g., 600,900 and 1200 lines/mm), and they’ve achieved high angular dispersion between each individual wavelength in their first diffraction order with relatively high transmitted diffraction efficiencies (e.g., for the 600 lines/mm grating, the efficiency is near 65%), which are able to demultiplex 1.31μm and 1.55μm wavelengths in CWDM (coarse wavelength division multiplexing). The fabricated high-density gratings should have important applications for DWDM in the near future.
We describe a new kind of symmetric color separation grating (SCSG), which can be applied to separate the frequency-tripling (3ω)light from the basic (1ω) and frequency-doubling (2ω)lights. The profile of the proposed SCSG is a three-level symmetric structure in one period, thus it is easy to fabricate it with the much improved tolerance of mask misalignment without the decrese of the efficiency of the frequency-tripling light. We have analyzed the principles of the SCSGs by employing the scalar diffraction theory and fabricated them experimentally by means of binary optics technology. The theoretical and experimental results demonstrated that the proposed SCSGs can be made in a comparatively easy way for the symmetric structure that can effectively avoid the effect of the fabrication error due to mask misalignment, thus higher manufacturing yield and lower cost can be achieved.
The systematic ablation plasma study with the measurement of ion emission in laser-target interaction is presented. We have obtained the scaling laws of ablation parameters with laser intensities for aluminum plasmas in the intensity range of 1011 - 1013 W/cm2, under both of the line-focused and the spot-focused laser irradiation.