Metasurfaces are opening up promising flexibilities to reshape the wavefront of electromagnetic waves, and a notable optical phenomenon is observed with the tailored surface plasmon. However, meta-devices with metallic material face challenges of low transmission efficiency, especially in the visible spectrum. In this work, a multilayer metamaterial strategy is proposed to improve the transmission. By adding dielectric material as space layer is inserted along the propagation direction, vertical cavities are formed to modulate the transmission and reflection. The multilayer structure is numerically studied to discuss the transmission efficiency. A maximum transmission efficiency of 90% is achieved by adding a spin on glass material to the silver layer at the visible spectrum. The transmission efficiency with and without space layer is discussed as a control. Significantly, the surface plasma and the phase could still be modulated by adjusting the geometrical parameters of the multilayer metamaterial for diversified functionalities.
A dispersive Fourier transformation-based ranging method utilizing a femtosecond laser frequency comb is demonstrated. The target and measurement signals interfere through a Mach-Zehnder interferometer and then enter a single-mode fiber with a sufficiently large group velocity dispersion (GVD) to be stretched and extended. The spectral interference information is mapped to the time-domain waveform. The time-frequency conversion function, obtained through calibration, converts the time-domain data into the frequency-domain data. After applying a Fourier transform, the measured distance is determined using the peak-interval method. In multiple measurements with an interval of 200 μm, the average error is within tens of microns., which can be further reduced with a higher-precision displacement table.
A real-time online ranging system is proposed using the frequency domain peak interval measurement method. By utilizing an NPR-locked, all-fiber, wide-spectrum erbium-doped femtosecond laser, a gain distribution with a center wavelength of 1560nm is obtained, with a repetition frequency of up to 14.54MHz, and then a femtosecond laser source with a spectral width of 38nm at -3dB can be obtained by adjusting its polarization state, which can improve ranging accuracy. By a combination of an upper computer system an all-fiber Michelson interferometer, real-time capture and processing of spectral interference data can be achieved, thereby realizing real-time acquisition of relative displacement distance. Experimental results show that within the coherence length, the measurable relative distance is around 2cm, and the measurement accuracy can reach 5μm.
We proposed an absolute distance measurement method with a large non-ambiguity range based on a polarization-multiplexed dual-comb fiber laser. By fully exploiting the intracavity linear loss based gain profile tilting and residual birefringence, polarization-multiplexed dual-comb pulses with tunable repetition rate difference and overlapping spectra in the 1530-nm gain region are obtained. The repetition frequency difference could be continuously tuned from ~89 to ~194 Hz. The alternative sampling under different repetition rate difference is experimentally verified to be effective approach to extend the non-ambiguity range in the single-cavity dual-comb ranging. The non-ambiguity range could reach thousands of kilometer while the precision could reach at least on the order of hundreds of micrometers. These results indicate a simple and intriguing route with a free-running laser source to obtain ranging with large non-ambiguity range, showing high potential in the applications such as satellite formation flying, large-scale 3D surface morphology measurement and so on.
This paper introduces a new absolute distance measurement system. A single-cavity double-comb laser based on single-wall carbon nanotube mode-locking is used as a light source by adjusting the intraccavity loss, and two optical combs with slight differences in wavelength and repetition rate and constant repetition frequency difference are generated for absolute distance measurement based on asynchronous optical sampling. The measured fuzzy distance is about 1.5 meters, and the measurement uncertainty is 15μm.
We experimentally investigated the build-up dynamics of single-cavity dual-wavelength-comb pulses emitted from a ring fiber cavity with Lyot filter configuration. Dual-wavelength lasers are firstly observed by adjusting the polarization controller to control Lyot filter effect. When the pump powers of the bidirectional pumps are set as 57 mW and 49 mW respectively, dual-wavelength pulses with the center wavelengths of 1546.2 nm and 1563.6 nm and spectral bandwidths of 2 nm and 1.6 nm are obtained. Subsequently, time-stretched dispersive Fourier transform spectroscopy is adopted to monitor the build-up process of dual-wavelength pulses. When switching on the pump diode, the three-stage build-up process from background noise to stable dual-wavelength pulses is experimentally observed. The build-up time is at the level of hundreds of milliseconds. These results provide a deep understanding of single-cavity dual-wavelength-comb pulse generation and contribute to the design and control of the single-cavity dual-comb pulses.
Broadband lasers have extensive applications in many fields such as spectroscopy, photochemistry, medicine, and biology, so they have obtained significant attention, particularly for their enormous potential in broadband imaging, pollution monitoring, and semiconductor material processing. This paper presents a 1-micron femtosecond laser with a broadened spectrum, achieved by integrating both intracavity and extracavity spectral broadening methods. Initially, a 1-micron single-mode fiber is introduced into the laser cavity to reduce the total dispersion. Subsequently, the collimated output laser is directed onto a negative dispersion grating. After being reflected by the dual grating system, the laser is measured, all while maintaining a stable mode-locked state. To address spectral distortion caused by the loss in non-target gain intervals, dual filtering is employed to retain only the 1064 nm gain interval. Through the balance between these two negative dispersions, the laser’s spectral width is expanded by approximately six times from its original 5 nm to 30 nm. During the experiments, the laser demonstrated remarkable stability and compared to using only intracavity single-mode fiber expansion or extracavity grating expansion, this approach offers superior results and greater potential. It aids in the precise measurement of pollutants and plays a crucial role in enhancing the resolution of broadband imaging.
We proposed the triple-wavelength pulses across the 1530- and 1550-nm gain regions are emitted from a carbon nanotube mode-locked ring fiber laser by simultaneously exploiting intracavity loss-based gain profile tuning, Lyot filter effect, and nonlinear polarization evolution. A polarization beam splitter with 2×1-m intracavity polarization-maintaining fiber pigtails is additionally introduced in a typical ring fiber cavity. Polarization-dependent loss is firstly adjusted to equalize the 1530- and 1550-nm gain regions. Except for the triple-wavelength pulses based on Lyot filter and loss-based gain profile tuning, another type of triple-wavelength pulses, i.e. single-wavelength pulse centered at 1530-nm gain region and spectral-overlapping dual-wavelength pulses centered at 1550-nm gain region, are observed by additionally introducing nonlinear polarization evolution. These intriguing results show the feasibility of multi-wavelength pulse generation based on multiple soliton formation mechanisms and the high potential to construct a single-cavity multiple-comb source with versatile pulse characteristics.
Based on PbS quantum dots and single-walled carbon nanotube, we have successfully demonstrated a Er-doped fiber laser capable of switching between two different types of output pulses. By finely adjusting both the pump power and the states of polarization controller, flexible switchable Q-switched and mode-locked pulses can be achieved. At pump power of 29 mW, Q-switched pulses are obtained at a central wavelength of 1560.2 nm. When the pump power increases from 29 mW to 92 mW, the Q-switched rate varies from 25 kHz to 75.22 kHz. Accordingly, the output pulse energy rises from 3 nJ to 5.46 nJ, and the output power changes from 0.08 mW to 0.41 mW. When the pump power is set in the ranges of 92 mW to 107 mW, the fiber laser enters the transition region of Q-switching operation. In this region, evident Q-switched instability with large fluctuations is observed, which is independent of the polarization states. When the laser pump power exceeds 107 mW, the Q-switched pulse disappears, and mode-locked pulses are obtained by altering the state of the polarization controller. The central wavelength of the mode-locked pulses output spectrum is 1561.1 nm, and the corresponding 3 dB spectral bandwidth is 4.22 nm. Coupled Ginzburg-Landau equation are provided to reveal the underlying principles of the transition of these pulse trains. Our work provides a new prospect for achieving fiber lasers capable of flexibly switching output pulse types, further expanding their applications in fields such as laser microprocessing, optical communication and medical lasers.
Recently, the nonlinear multimodal interference-based all fiber saturable absorber has been the focus of attention on ultrafast fiber lasers, owing to its intriguing properties of versatility, high damage threshold and instantaneous response time. Although, challenges present in the technology, such as complex perturbation induced by quasi-degenerate modes in multimode fiber, it is presented as an effective solution to control the output characterization and study the nonlinear dynamics in fiber lasers. In this work, we experimentally and numerically demonstrate the spectral sidebands in a passively Er-doped fiber laser based on multimodal interference technique. Kelly-type and triangular-type sidebands are achieved, and can be switchable by changing the polarization states of cavity, which are asymmetric distribution on both sides of the output spectrum. When the polarization states are varied, a wide sideband is obtained, which the width of sideband can be tuned from 0.13 nm to 2.3 nm. Coupled complex Ginzburg-Landau equation are provided to reveal the underlying principles of the tunable features in sidebands. The results of numerical simulation show the relevance between filtering induced by modal interference, high-order dispersion, polarization modal dispersion and experimental results. Our work lays a foundation for understanding of nonlinear dynamics in mode locking fiber lasers based on multimodal interference effect and provides a new way to generating versatile ultrafast source in engineering and scientific research.
We experimentally demonstrated a fast and effective intelligent optimization algorithm to obtain the self-correcting ultrashort pulse emission from a nonlinear polarization rotation mode-lock fiber laser. The temporal trace corresponding to the optical spectrum is measured by the time-stretched dispersive Fourier transform technique, which functions as the monitoring signal. Subsequently, the genetic algorithm is proposed to finely control the electronic polarization controller for self-correcting pulse generation. The target state could be realized after five generations of iterations. By combining dispersive Fourier transform technique and genetic algorithms, the total adjustment time can be minimized to six seconds. These findings indicate an effective route to obtain robust and self-correcting ultrashort fiber lasers.
A packaging scheme for optical transmission modules based on PAM4 with a data transmission rate of up to 200Gbit/s is proposed to meet the design requirements of 200Gbit/s PAM4 optical transceiver modules. Package integrates four PAM4 electrical/optical conversion ways internally, with a single channel data transmission rate of 50Gbit/s. This article introduces the composition and technical difficulties of the 200Gbit/s PAM4 optical emission module, and then models, simulates, and optimizes the 50Gbit/s data transmission channel. Finally, the sample testing is completed. The test results show that the single channel PAM4 data rate of the sample can reach 50Gbit/s, and the overall PAM4 data rate can reach 200Gbit/s, meeting the design requirements of the optical transceiver module.
We proposed the simultaneous wavelength extensions of single-cavity dual-wavelength pulses by using a single erbium-doped fiber amplifier and one section of high nonlinear fiber. By additionally introducing a polarization dependent isolator, polarization dependent loss based gain profile tuning is adopted to obtain dual-wavelength pulses centered at 1533.7 and 1554.8nm. When both dual-wavelength pulses are simultaneously launched into the same erbium-doped fiber amplifier with the bidirectional pump power, the spectral range of the output pulses could be expanded to be from 1500 to 1600nm. Subsequently, the amplified dual-wavelength pulses further pass through a section of high nonlinear fiber, extending the spectrum from 1.2μm to more than 1.75μm. Dual-wavelength pulses are amplified simultaneously by using only one amplifier, showing the feasibility of the simplification of single-cavity dual-comb pulse amplification. These results show the high potential in the applications such as multi-color laser generation and spectroscopy.
High order axially symmetric polarized beams (ASPBs) can create multiple focused spots under tight focusing conditions, and thus have been highly recommended for optical manipulation, but the feasible experiments have never been demonstrated. Cells trapping and manipulation based on optical tweezers using high order ASPBs are presented theoretically and experimentally to verify its feasibility and effectiveness. The focused intensities and corresponding gradient forces for high order ASPBs are first analyzed and calculated if two kinds of particles are trapped respectively based on the electromagnetic theory. Then an optical tweezers based on an inverted microscopy using high order ASPBs is built up, and the yeast cells (~10μm) are trapped and manipulated to shift and rotate using two kinds of ASPBs with P=1 and P=3. One yeast cell is stably trapped and shifted with a speed about 40μm/s and four yeast cells are trapped and rotated simultaneously with a rotation speed about 45°/s, which can also be further modulated and the track of the focusing spot can be programmed by computer. Finally, the optical trap stiffnesses are calculated theoretically using the Boltzmann statistics method and further measured experimentally when the filling factors of the objective lens are 0.50, 0.80 and 1.00 respectively and three microcopy objective lenses with numerical apertures 0.40, 0.65 and 0.85 are used, and the measured results agree well with the calculated results, which shows the trapping performances can be flexibly modulated by setting the system parameters and provides some novel choices for optical manipulations. All these findings benefit the expansion of the practical applications of vector beam OTs in some fields, especially in the field of biomedicine.
We demonstrate a Q-switched mode-locked Er-doped fiber laser using an all-fiber grade-index multimode fiber-based modulator which generates dark-bright pair between bright pulse sequences and alternate bright and dark pulses. A section of dispersion compensation fiber (Nufern UHNA4) considered as a candidate normal group victory dispersion fiber is used to adjust the net dispersion of cavity. At a pump power of 410 mW, evident Q-switched instability modulating mode-locked bright pulses are observed, and the duration of Q-switched envelope changes from 1.8 μs to 8 μs along with the variation of power. Changing the state of polarization controller, the mode-locked bright pulse train is tuned to dark pulse train with reducing the duration of Q-switched envelope to 1.2 μs. What’s more, dark-bright pair between bright pulses train and alternate bright and dark pulses are also observed under second harmonic operations with suitable PC states. Coupled complex Ginzburg-Landau equation, field coupling model for propagation in multimode fiber, and fiber nonlinear effects are provided to reveal the underlying principles of the transition of these pulse trains. Because of the principal modes and filtering effect in multimode fibers, the formation and stable propagation of the dark-bright pair are precisely achieved. At the same time, the physical mechanism behind the unusual pairing of dark and bright pulses is that under certain conditions, cross-phase modulation can counteract the time extension of optical pulses caused by the combination of self-phase modulation and normal dispersion. Thus, the cross-phase modulation induced chirping on dark solitons enables dark-bright pair between bright pulse sequences to coexist.
A single-cavity triple-comb all-fiber laser is proposed by wavelength/polarization multiplexing. A variable optical attenuator is introduced to equalize the 1530-nm and 1550-nm gain profile of erbium-doped fiber for dual-wavelength pulses. Their repetition rate difference reach kHz level. Meanwhile, by further adjusting the intracavity polarization state, polarization-multiplexed dual-comb pulses with tens-of-Hz repetition rate difference in the 1550-nm gain region are obtained. The more than one-order-of-magnitude difference between the maximum and minimum repetition frequency difference and qualified passive mutual coherence of triple-frequency pulses is highlighted. These results indicate a highly potential triple-comb source for multiple-comb metrology such as triple-comb ranging and frequency measurement and so on.
In line structured light vision measurement, due to the occlusion of the object, the complete information might not be collected. We propose a method to acquire the object’s all point data by dual-camera cooperative measurement. First, the transformation models between cameras and motion coordinates are constructed. Subsequently, the light plane is calibrated by special points from the images of the calibration plate which is raised 3 times with an appointed distance. Finally, the data points are fused and optimized with particular matrix. The results show that the average fusion error is reduced from 0.5668 mm to 0.1253 mm. This method improves the reconstruction accuracy greatly.
During the caries treatment, three-dimensional measurement of tooth profile and caries location is one of key steps in the therapeutic process of caries. We propose a three-dimensional vision measurement of tooth crown and dental caries with line structured light. First, an integrated calibration using right angled spot target is executed and the parameters are obtained rapidly. Subsequently, the profile of the tooth crown is reconstructed and the dental caries area is identified. The results show that the reprojection error could reach tens of micrometers and the caries’ area is measured as ~ 2.83 mm2. These results indicate high potential in the diagnosis and treatment of dental caries.
Multi-species blood identification is especially useful in animal quarantine, import and export, criminal cases, forensic examination, and wildlife conservation. Raman spectroscopy is a non-destructive, label-free, and highly specific method for providing chemical information on materials and serving as an analytical tool to characterize biological samples. Machine learning approaches in conjunction with Raman tweezers are proposed to extract the Raman spectral characteristics of single red blood cells (RBCs), then the cells based on the spectral characteristics are classified, and some classification prediction models to achieve single cell identification of different blood species are achieved finally.
Multiple myeloma may develop resistance to certain drugs during chemotherapy, which have a fatal impact on treatment efficacy. At present, the drug resistance detection methods for multiple myeloma, such as proteomic identification and clone formation analysis, are relatively complex, and the accuracy and detection time are not ideal. In our work, laser tweezers Raman spectroscopy was used to collect 412 groups of spectra of two kinds of cells, namely, MM.1R and MM.1S, which were respectively resistant to dexamethasone and sensitive to dexamethasone. We selected support vector machine, random forest, linear discriminant analysis and other algorithms to train the pretreated Raman spectra, and the recognition accuracy on the test set was above 95%. This result shows that the combination of laser tweezers Raman spectroscopy and artificial intelligence algorithm can quickly detect drug resistance of cancer cells.
We experimentally demonstrate a simple, effective and intelligent scheme to obtain image monitoring of femtosecond laser processing of biological hard tissues. A simple mobile phone camera is adopted for imaging of different processing status of biological hard tissue. Subsequently, an automatic recognition method based deep learning is proposed to recognize the relationship between the optical images and manufacturing effect for the fast parameter optimization of laser processing. Correspondingly, the laser processing parameter could be well controlled to obtain qualified laser processing of biological hard tissue. These results indicate an efficient and accurate image monitoring route for intelligent femtosecond laser processing of biological
In this work, we demonstrate a single-walled carbon nanotubes-based wavelength multiplexed fiber laser, which generates dual-comb pulse in the train of soliton rain. The fiber laser cavity is manipulated in repetition frequency of 16.58 MHz, 3 dB spectral bandwidth of 8.4 nm. Two asynchronous pulses constitute the soliton rain pulse sequences, which the intensity difference is about 5.72 dB between the dual frequencies. A piece of graded-index multi-mode fiber as a filter based on the multi-mode interference effect is introduced into cavity to improving the signal to noise ratio to ~62 dB, and locate the central wavelength of the dual-comb at 1556.7 nm and 1561.5 nm. The repetition rate difference of the dual-frequency is about 169 Hz with the resolution bandwidth of 1 Hz. The time delay of the dual-frequency pulse detected by cross-correlation method is 5.78 ms, which is well matched with the results in radio frequency spectrum. Different from the stable period of the general cross-correlation signal, our experimental results show several different sub-periods due to the existence of the drifting solitons in the soliton rain sequences. Meanwhile, the number of different sub-periods in the correlation decreases from six to three as the pump power reduced from 100 mA to 97.3 mA. Our work provides a new sight into the quasi-steady multi-soliton dynamics process in fiber lasers, and will be promising solutions for interference ranging, and synchronization and timing.
Due to the simple configuration, qualified passive coherence between pulses, and cost-effective characteristics, single-cavity dual-comb sources attract increasing research interest. Actually, such lasers have been experimentally verified in dual-comb metrology such as dual-comb frequency measurement and spectroscopy. Unlike the single-cavity dual-comb fiber laser multiplexed in other dimensions such as wavelength, direction and mode-locked mechanism, polarization-multiplexed pulses own the unique characteristics of overlapping spectra, intrinsic spectral coherence, and tunable repetition rate difference. They are beneficial for the simplification of additional optical amplification and the satisfaction of versatile requirements of dual-comb metrology. Here, we demonstrated a single-wall carbon nanotube saturable absorber mode-locked Er-doped fiber laser to emit wavelength-switchable polarization-multiplexed dual-comb pulses. The intracavity loss is carefully tuned by an additional optical variable attenuator to define the oscillation windows. In both the 1530- and 1550-nm gain regions, spectral-overlapping, polarization-multiplexed pulses are experimentally obtained with the fine configuration of the intracavity state of polarization. The polarization dynamics and tunable repetition rate difference are experimentally revealed. The repetition rate difference is at the tens-of-hertz level, which is somewhat lower than that of the reported polarization-multiplexed fiber laser with additionally introduced polarization-maintaining fiber. Since there are no additional birefringent media, the polarization mode dispersion for polarization-multiplexed pulses is attributed to the residual birefringence. Moreover, the passive mutual coherence is also highlighted. There results provide a simple yet effective way to design switchable and versatile single-cavity dual-comb pulses.
In our work, we experimentally demonstrate wavelength multiplexed dual-comb pulses based on multi-modal interference effect in a passively single-walled carbon nanotube mode-locking all fiber ring laser. The laser cavity achieves a variety of dual-wavelength mode-locked states by switching the polarization controller in the laser cavity. A piece of 25 cm long graded-index multi-mode fiber as a filter based on the multi-mode interference effect is introduced into cavity to fixing wavelength and to improving the signal to noise ratio. With optimized length of multi-mode fiber, we observed the two different filter state which located at 1559 nm and 1562 nm, 1561 nm and 1563 nm respectively in the different polarization dual-comb states. With suitable filtering state by stretching the multi-mode fiber, the two asynchronous pulse sequences coexist with diverse operation, which propagate with singlet and double pulses, respectively. The repetition rate of the laser is 16.59 MHz and the time period corresponding to the asynchronous pulse is ~60 ns. The repetition rate difference of dual-wavelength states reaches 100 Hz. In addition, we recorded the output modulation state of the laser cavity. Our research provides experimental basis for optical fiber sensing, wavelength division multiplexing communication system and high resolution spectroscopy.
Raman spectroscopy, a “fingerprint” spectrum of substances, can be used to characterize various biological and chemical samples. To allow for blood classification using single-cell Raman spectroscopy, several machine learning algorithms were implemented and compared. A single-cell laser optical tweezer Raman spectroscopy system was established to obtain the Raman spectra of red blood cells. The Boruta algorithm extracted the spectral feature frequency shift, reduced the spectral dimension, and determined the essential features that affect classification. Next, seven machine learning classification models and deep learning model without dimensionality reduction are analyzed and compared based on the classification accuracy, precision, and recall indicators. The results show that support vector machines and convolutional neural network are the two most appropriate machine learning algorithms for single-cell Raman spectrum blood classification, and the findings provide essential guidance for future research studies.
High-quality gold nanospheres (Au NPs) were transferred to a sapphire substrate. The balanced twin-detector measurement technique was used to study the saturable absorption properties of the Au NPs. With the as-prepared Au NPs as a saturable absorber (SA), an efficient passively Q-switched laser was realized at 1.93 μm. Under an absorbed pump power of 4.5 W, a maximum output power of 400 mW was obtained with the shortest pulse width of 410 ns and repetition rate of 126 kHz. The results indicate that Au NPs are promising candidates as SAs for mid-infrared laser pulse generation.
A method is proposed to suppress speckle noise using only part of the pixels in a single-exposure digital hologram. Different holographic patterns are first generated from a single-exposure digital hologram using specially designed binary masks; then, these holographic patterns are reconstructed according to the Fresnel transform. The reconstructed images are superposed and averaged on the intensity to achieve the suppression of speckle noise. The entire denoising process does not need any additional digital holograms or specific requirements for recording a hologram. Theoretical simulation and experiment verification were carried out and confirm that the proposed method is a very convenient and effective way to suppress speckle noise in digital holography. The proposed method has wide applications in holographic imaging, holographic storage, and art display.
Recently, interferometric null-testing with computer-generated hologram has been proposed as a non-contact and high
precision solution to the freeform optics metrology. However, the interferometry solution owns some typical
disadvantages such as the strong sensitivity to the table vibrations or temperature fluctuations, which hinders its usage
outside the strictly controlled laboratory conditions. Phase retrieval presents a viable alternative to interferometry for
measuring wavefront and can provide a more compact, less expensive, and more stable experimental setup. In this work,
we propose a novel solution to freeform metrology based on phase retrieval and computer-generated hologram (CGH).
The CGH is designed according to the ray tracing method, so as to compensate the aspheric aberration related to the
freeform element. With careful alignment of the CGH and the freeform element in the testing system, several defocused
intensity images can be captured for phase retrieval. In this paper the experimental results related to a freeform surface
with 18×18mm2 rectangular aperture (its peak-to-valley aspherity equals to 193um) are reported, meanwhile, we also
have compared them with the measurement results given by the interferometry solution, so as to evaluate the validity of
our solution.
The aqueous outflow system (AOS) is responsible for maintaining normal intraocular pressure (IOP) in the eye. Structures of the AOS have an active role in regulating IOP in healthy eyes and these structures become abnormal in the eyes with glaucoma. We describe a newly developed system platform to obtain high-resolution images of the AOS structures. By incorporating spectral domain optical coherence tomography (SD-OCT), the platform allows us to systematically control, image, and quantitate the responses of AOS tissue to pressure with a millisecond resolution of pulsed flow. We use SD-OCT to image radial limbal segments from the surface of the trabecular meshwork (TM) with a spatial resolution of ∼5 μm in ex vivo nonhuman primate eyes. We carefully insert a cannula into Schlemm’s canal (SC) to control both pressures and flow rates. The experimental results demonstrate the capability of the platform to visualize the unprecedented details of AOS tissue components comparable to that delivered by scanning electron microscopy, as well as to delineate the complex pressure-dependent relationships among the TM, structures within the SC, and collector channel ostia. The described technique provides a new means to characterize the anatomic and pressure-dependent relationships of SC structures, particularly the active motion of collagenous elements at collector channel ostia; such relationships have not previously been amenable to study. Experimental findings suggest that continuing improvements in the OCT imaging of the AOS may provide both insights into the glaucoma enigma and improvements in its management.
Optical tweezers based on cylindrical vector beams are studied theoretically and experimentally. First, we present the basic concept of a cylindrical vector beam (CVB), whose polarization is axially symmetric to the optical axis. Second, two theoretical modes to analyze the interaction between the light beam and the particle are introduced, respectively, and some simulations have been shown. Then, the system structure and its operation principle are introduced in details, where a spatial light modulator (SLM) is used to flexibly generate the CVBs, and experimental results are also demonstrated, which show some advantages for optical manipulation of particles using CVBs.
With the aim to get harmonic distortion characteristics and frequency components of modulated output signals of a Mach-Zehnder (MZ) intensity modulator, this paper analyzes the optical intensity modulation transfer function by Tailor expandsion method according with the working principle of modulator. From the viewpoint of spectrum, the output signal is mainly comprised of the fundamental harmonic, the second intermodulation harmonic and the third intermodulation harmonic of the input signal and their magnitudes are connected with the bias voltage and Eigen-phase of MZ modulator. The second harmonic distortion and the fundamental harmonic of the modulated output signal are closely related with the drift of the best bias point. When the modulator works at the best DC bias voltage point, the modulated output signals have the minimum second harmonic distortion. If the best bias point drifts, the second harmonic distortion increases and the fundamental harmonic decreases, which changes in proportion to the sine or cosine of the drift voltage. A 1GHz sine signal with 1V amplitude imposed on the modulator, the simulation results by MATLAB presents that the waveform starts distorting along with the drifting of the best bias voltage, which the fundamental wave component starts decreasing and the second harmonic component starts increasing. While at last the fundamental wave component is zero, the frequency of output modulated signal doubles as much the frequency of input signal.
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