Aiming at the problem of the resolution reduction in a miniaturized grating spectrometer, we presented a method to improve its spectral resolution by inserting a tunable Fabry-Perot filter into its optical path before the grating. The Fabry-Perot filter was designed to filter out a partial spectrogram and separate the original undistinguishable spectral lines so as to make their actual wavelengths can be detected. The different cavity length of the Fabry-Perot filter is corresponding to the different separated partial spectrogram. Combining all the separated partial spectrograms, an entire spectrogram with improved resolution can be achieved. Experimentally, the spectral resolution of a grating dispersive system was improved from 2 nm to 1.2nm in a broad spectral range by insetting a homemade tunable Fabry-Perot filter, which demonstrated the feasibility of this scheme. The tunable Fabry-Perot filter is fit for miniaturization by using MEMS technology and is able to work as an independent module. The method proposed provides a potential way to improve the spectral resolution without reducing the spectral range of the existing miniaturized grating spectrometers.
The structure combining the microlens and DOE is not sensitive to the incident beam and can control the overall shape
profile flexibly. So that the structure called DOE array is designed in this paper in order to shape the unstable laser beam
to the four polar uniformity distribution. The paper gives the principle of the DOE array and the design process. The
array element determines the profile of the output beam. It is designed using the G-S algorithm and the Adaptive
Addition algorithm (A-A). The number of the DOEs is optimized and analyzed. The simulative diffraction efficiencies
are 89% and non-uniformities are less than 3% when the incident beams are Gaussian, supper-Gaussian, paraboloid and
random distributions. In experiment, diffraction efficiency of 77% and maximum non-uniformity of 5.6% are got on the
condition of the different input laser beam. So the effect on the instability of the incident beam could be decreased.
Phase modulation characteristics of subwavelength metallic square holes are investigated for 2D imaging purpose. Based
on Maxwell equations, the transmission model of three-dimension subwavelength metallic holes is founded by a mode
expansion technique. The relationship between the widths of the holes and the phase from -π to π is established when the
thickness of metallic film is given. Then the influences of coupling electromagnetic (EM) fields as well as the incident
angle on phase retardation are investigated and calculated through varying the center distance between double holes. A
slab lens is demonstrated by using hole-array formed on a metallic film, which verifies the theoretic analysis.
Dead spaces are generated in the fast-axis direction of the laser diode stack (LDS) because of the construction of the LDS. A new method of using a plane-parallel plate array to eliminate dead spaces between the bars of the LDS is presented. The design method of the plane-parallel plate is also investigated, and the beam parameter product is used to evaluate the quality of the beams. As an example, the plane-parallel plate array for an LDS consisting of four bars is designed and simulated. The simulation results show that the dead spaces are eliminated, the spots size is compressed from 6.5 mm×10 mm to 3.5 mm×10mm, and the energy loss is about 2%.
An innovative beam-shaping method for laser diode stacking is presented by employing a pair of reflective two-wedge-angle prism arrays. Each subprism with two variable wedge angles is designed for deflecting the partial emission from different bars to the dead spaces of the stack, according to the configuration of the real laser diode (LD) stack and the requirement of the system. The formula to determine the parameters of each subprism is deduced by way of geometrical analysis. A beam-shaping system for stack laser diodes with three bars is designed and simulated, and the results show that the stack laser beam is well transformed into a required distribution efficiently.
Coupling high-power laser diode array (LDA) beams into a multi-mode fiber is an important way to expand the LDA applications. Transforming LDA beam is an essential step for fiber-coupled LDA. Diffractive grating arrays are used to transform a bar LDA beam with the output power of 40 watts to realize the symmetry of BPPs in fast and slow axis directions in the paper. First, the specifications of the diffractive grating are calculated according to focusing and coupling bar LDA. Second, the 8-level binary diffractive gratings are fabricated based on the binary optical elements processing platform in our lab. Third, the experiment was carried out and results are gotten. The results show that the focusing spot size is about 200μm in diameter and the numerical aperture NA is 0.22, which agree with the calculated and simulated.
To collimate effectively the beam emitted from the stacked laser diode in which the lasing surfaces of the diode bars are not located in a plane, a new type of fast-axis collimator, refractive cylindrical microlens array with tunable focal lengths, is presented in this paper. Each lens of the array has the same diameter of 300μm but different focal lengths, ranged from 430μm to 540μm. By means of the mask moving lithography and replication technology, the microlens array was successfully fabricated. The measured fast-axis divergence of the stacked laser diode beam after the collimator was 25mrad, about half of the one (40mrad) for the microlens array with common focal lengths of 400μm.
A profile formation and control approach has been developed for manufacturing micro-optical elements with continuous profile and deep relief depth. Based on Dill's exposure model, an effective expression for determining the exposure dose function is established by using a supposition of equivalent exposure threshold inside a resist layer. An analytical simplified formula is further deduced by taking absorbance as constant B, and the approximate condition is discussed. For evaluating the simplified formula, the profile error was calculated and analyzed by simulation. With the exposure dose function, the binary mask for manipulating the light distribution by means of a moving-mask lithographic method can be designed. Experimental results are given and show the comparative performance to the required profile and relief depth. A series of refractive microlens arrays with aspherical profiles, a wide range of numerical apertures (0.005 to 0.6), and high fill factors were accomplished in the lab and may be applied to many systems.
In order to form the proper aspherical microlens array profile with larger NA on photosensitive materials, a method is developed based on the characteristics of resist and processing parameters during development, for designing the exposure distribution, an experience formula has been proposed in the paper. Using the moving mask method, the exposure energy distribution function related to the photolithographic mask function can be determined by the experience formula. The profile control procedure is formed especially for the deeper relief profiles, after the binary mask data are slightly modified, the micro-structure with aspherical lens profile can be fabricated on the selected thicker resist, the micro relief profile error can be controlled in a certain range. The micro-profile is farther transferred to fused silica by ICP etching system. By our method, the fast microlens array elements with good fidelity and reasonable roughness have been fabricated and applied to the laser diode collimating system.
A conclusion that a single conventional optical system could not realize fiber coupled high-power laser diode array is drawn based on the BPP of laser beam. According to the parameters of coupled fiber, a method to couple LDA beams into a single multi-mode fiber including beams collimating, shaping, focusing and coupling is present. The divergence angles after collimating are calculated and analyzed; the shape equation of the collimating micro-lenses array is deprived. The focusing lens is designed. A fiber coupled LDA result with the core diameter of 800 um and numeric aperture of 0.37 is gotten.
A new method for microlens profile design was developed based on the analysis to the main parameters of microlens array, including micro profile formation, the numerical aperture ( NA ), the maximum sag depth for the refractive lens and the minimum zones width for the diffractive lens. With the relationships among the parameters, the microlens array in different profile can be determined effectively. The moving mask method[1] is used to realize the required profiles, an unique photolithography system have been built for implementing the mask moving exposure in both X and Y directions for the creation of microlens array. By modifying the binary moving mask, optimizing the photosensitive materials and the processing technique, the microlens profile error can be controlled in the range of 0.4µm~3µm depending on effective reliefdepth of the microlens. In our method, both diffractive and refractive microlens array with larger NA and higher fill factor can be fabricated for satisfying a plenty of purposes.
Performances of diffractive and refractive microlens array have been studied and compared. Besides the diffractive microlens array which can be fabricated by means of the microfabrication technologies, method for manufacturing continuous profile refractive microlens array with larger sag depth has been developed for solving the unique problems like diode laser alignment. Both diffractive and refractive microlens array with different numerical aperture and other parameters are fabricated according to the application requirements, experimental results are given.
In this paper, the process of fabrication of binary optical elements by thin film deposition has been introduced. An eight-level phase microlens array has been fabricated with 20 X 20 rectangularly shaped microlenses, focal length of 100 mm and lens size of 0.8 mm for the wavelength of 0.6328 μm. Our measurements show that all the step heights are nearly identical and the controlled precision of step heights was better than 1 nm.
Aerial images of a 0.35micrometers contact hole with the different phase shifting masks are calculated based on Hopkins model, and the optimal parameters of different phase shifters are gotten. Attenuated PSM in enhancing resolution and improving the depth of focus is of the most among them, especially when partial coherence factor is smaller. The calculated and simulated software is programmed. The software could produce all kinds masks automatically and calculate the aerial images at different illumination parameters, numeric aperture (NA), defocus conditions and add optimal phase shifter at these areas where resolution is smaller than the critical dimension (CD). At last, it could transform process old CIF format data file which is used to control E-beam exposure tool and filter it into two files by some sifting rule. The Att-PSMs is made and exposure experiments are carried out.
The structure, principle and manufacturing process of a single layer attenuated phase-shifting mask which is compatible with the traditional Cr mask fabrication technology are introduced in the paper. Partial experimental results are provided.
Attenuated phase shifting mask and that with optical proximity correction is adopted to improve resolution of photolithography based on some calculation results. The first factor k1 of the photolithography could be to 0.50, and the optimal transmission is about to 8 to approximately 10%. And a new kind of method of making attenuated phase shifting mask by encoding is put forward, and the theoretical calculation results are accordant to the conventional attenuated shifting mask.
In this paper, the principle of two typical i-line ((lambda) equals 365 nm) and excimer laser ((lambda) equals 248 nm) uniform illumination optical systems based on Cohler illumination is reviewed, the principle and method of the calculation and simulation of intensity distribution of the illumination system for sub-micron photolithography consisting of aspherical surfaces, non-co-axial surfaces and lens array are put forward, that is ray-tracing based on the Snell theorem and spot diagram. At the same time, a program CALOSD made by us is described, two typical results of calculation and simulation of intensity distribution of illumination optical systems are given.
In this paper, a novel color-encoder which has dual functions of a beamsplitter and a beamshaper is proposed. This encoder could acquire very good uniformity of light field with high diffractive efficiency. An algorithm which combining tracing algorithm, G-S algorithm and Y-G algorithm is used to design this encoder, the result by computer simulation calculation shows: the diffraction efficiency is up to 93.3%, non-uniformity is less than 0.01%. And a new approach to encode and make a phase element by using color- printer techniques is proposed in this paper as well.
An off-axis type refractive/diffractive Gregorian telescopic optical system without any aspherical element and center obscuration is presented in this paper. A binary optical element is used to correct aberrations and its size is reduced to 1/3 or 1/4 of the Schmidt corrector. Using OSLO SIX4.2 (Sinclair Optics Inc.) optical design software, an off-axis infrared refractive/diffractive hybrid telescopic system is designed with the parameters: aperture (phi) equals 120 mm, effective focal length f equals -1000 mm, wavelength (lambda) equals 4.3 micrometers , the field of view 2 degree(s) X 6 degree(s), resolution Res equals 50 um, modulation transfer function >= 0.4 when the spatial frequency v <EQ 10 cycles/mm.
Deep etched diffractive optical elements could acquire some significant properties, for example, deep etched Fresnel lens could be used as fast lens, deep etched blazed grating has high dispersive index. So it is a new subject of binary optics. In this paper, a new kind of element, deep etched multi-phase level fractional Talbot grating is presented. Compared with common fractional Talbot grating, it has the property of high fill factor.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.