Optical Wavelength Filters Research Articles

Analysis of the Principle and Applications for Surface Plasmon Polariton

The integrated optics technology based on Surface Plasmon Polaritons (SPPs) is gradually emerging as a breakthrough for optical devices, owing to its high field localization and strong energy density. Currently, SPP-based technologies, such as optical modulators and wavelength filters, have demonstrated significant application value. However, the research on SPPs is predominantly focused on the visible and near-infrared bands due to difficulties in wavevector matching for excitation, insufficient theoretical investigations of SPPs, and limitations of micro-nanofabrication techniques. Consequently, research on SPPs in information transmission bands like the far-infrared is still scarce. Therefore, this paper starts from the electromagnetic theory fundamentals of SPPs and explores their redshift characteristics and excitation mechanisms. Subsequently, it summarizes research and modulation techniques in the infrared band, comparing and analyzing the advantages and limitations of optical devices based on the principles of SPPs. Finally, it presents some limitations of current SPP research and the development prospects of far-infrared devices.

Encryption chain based on measurement result and its applications on semi-quantum key distribution protocol

This study proposes a new encoding method, also known as an encryption chain based on the measurement result. Then, using the encryption chain to propose a unitary-operation-based semi-quantum key distribution protocol (SQKD) protocol. In the existing SQKD protocols, semi-quantum environments adopt a round-trip transmission strategy. In round-trip transmission, the classical participant must resend the received photons to the quantum participant after implementing local operations. Therefore, round-trip transmissions are vulnerable to Trojan horse attacks. Hence, the classical participant must be equipped with a photon number splitter and an optical wavelength filter device against Trojan horse attacks. This is illogical for semi-quantum environments because the burden on the classical participant is significantly increased as it involves the prevention of Trojan horse attacks. The proposed SQKD protocol is congenitally immune to Trojan horse attacks and involves no extra hardware because it is designed based on a one-way transmission as opposed to a round-trip transmission. When compared to the existing SQKD protocols, the proposed SQKD protocol provides the best qubit efficiency, and classical participants only require two quantum capabilities, which enhance its practicability. Moreover, the proposed SQKD protocol is free from collective attacks, Trojan horse attacks, and intercept-resend attacks. Thus, the proposed scheme is more efficient and practical than the existing SQKD protocols.

Wavelength-Tunable Optical Two-Tone Signals Generated Using Single Mach-Zehnder Optical Modulator in Single Polarization-Mode Sagnac Interferometer

We demonstrate 60 GHz separation optical two-tone signal generation at arbitrary C-band wavelengths without involving complicated optical wavelength filtering. By utilizing a polarizer, the selective suppression of undesired low-order optical sidebands has been proven and optimized based on model analysis. By utilizing this scheme in conjunction with the optimized parameters, more than 20 dB of suppression of undesired optical sidebands have been successfully achieved over a 40 nm wavelength range. This scheme allows us to generate optical two-tone signals at the desired wavelength.

Design and simulation of high-sensitivity refractometric sensors based on defect modes in one-dimensional ternary dispersive photonic crystal

Photonic crystals are widely used in sensors, lasers, optical wavelength filters, and dispersion compensations used in optical communication networks. We propose to exploit the defect modes of one-dimensional ternary photonic crystals based on silicon, analyte, and silica layers for a refractive index sensor. The defect modes are created by inserting an analyte layer in the middle of the structure between two adjacent silica and silicon layers. Exploiting the defect modes in the transmission spectrum leads to hypersensitivity. The results show that the thicknesses of the layers and defect part are, respectively, about 155, 700, 155, and 1200 nm in optimum conditions. Our optimum structure is about 11 µm long, and sensitivity of this structure is more than 450 nm/RIU and 600 nm/RIU for the perpendicular light incident and incident angle of 45°, respectively. The effect of dispersion is investigated on the sensor operation, too. Numerical simulations exhibit that sensitivity is decreased to 410 nm/RIU for incident perpendicular rays. Also, the optimum thickness of the defect layer is changed significantly when considering the dispersion effects, so dispersion plays a significant role in the proposed sensor.

Design of lithium niobate phase-shifted Bragg grating for electro-optically tunable ultra-narrow bandwidth filtering.

Tunable optical wavelength filters are indispensable components in optical communication systems. In this paper, an ultra-narrowband tunable filter inscribed in lithium niobate (LN) wafer is designed. Two sections of Bragg grating and a pair of electrodes are fabricated in the LN waveguide. The operation wavelength could be tuned by adjusting the electric voltage applied on the electrode pair owing to the electro-optic effect of LN crystal. Simulation results indicate that the filtering bandwidth of the proposed phase-shifted Bragg grating is determined by grating lengths no longer than 1pm. The tuning sensitivity is dependent on the distance between the two gratings. In addition, the proposed structure overcomes the difficulty in controlling the phase shift of the grating pair, ensuring its potential applications in optical sensing systems.

Imaging of IR700DX Labeled Mouse Breast Tumor Using a Custom Angle-Selective Fluorescence Contact Imaging System.

Cancer treatment faces the challenge of identifying small clusters of residual tumor cells in the resection cavity after the gross section of tumor is surgically removed. Despite the introduction of targeted fluorescent probes to guide cancer surgeries, large, bulky, optical components restrict the ability of fluorescence imaging devices to detect small clusters of tumor cells in the complex surgical cavity. We have developed a small size-scale contact fluorescence image sensor that incorporates angle-selective gratings and a thin 15 m amorphous silicon optical wavelength filter for detecting residual cancer tissue in vivo. Using a custom fluorescent probe combining a fluorescent dye, IR700DX, with a targeted antibody, Trastuzumab, we label and visualize breast tissue in in vivo mouse models of breast cancer. When imaging tumorbearing mice injected with the probe, HER2+ breast cancer tissue intensity is 3.80.8 times brighter than other tissue. Excised cancer tumors and residual cancer attached to healthy tissue are imaged using the custom image sensor. Residual cancer tissue can be detected in real-time and is imaged with a high SNR of 45 dB using an integration time of only 40 ms.

Scrambling-based cryptography with a programmable SLM-based filter-triggered chaotic tent/hologram mapping algorithm for secure H.264/AVC video streaming over a WDM network

Traditional chaos-based encryption techniques use pseudorandom codes to implement encryption (e.g., XOR; exclusive or operation) directly, resulting in the violation of requirements for media compression formats for image transmission. In this study, a programmable spatial light modulator (SLM)-based optical wavelength filter was investigated for implementing a scrambling-based cryptographic scheme in WDM networks. A new chaotic tent/hologram mapping algorithm (THmA) and advanced THmA are proposed for triggering the programmable SLM-based filter array. Similarly, an approximately symmetric scheme was used to configure a scrambling SLM-based decryption scheme for performing decryption operations when the initial value and control parameters of the chaotic sequence as individual secret keys are communicated in advance over a private channel. The proposed scheme was evaluated using video application-layer experiments. The results revealed that compared with conventional reconfigurable schemes involving triggered registers and switches behind an AWG router, the number of code space sizes involved in the proposed cryptographic scheme increased by more than 1.31E + 89 times, thereby avoiding eavesdropping attacks in the physical layer. Furthermore, on the basis of the reduced peak signal-to-noise ratio of the encrypted videos and the unidentifiability of the videos to unauthorized users, the scrambling efficiency of the proposed scheme was sufficiently high.

High-finesse Fabry\u2013Perot cavities with bidimensional Si3N4 photonic-crystal slabs

Light scattering by a two-dimensional photonic-crystal slab (PCS) can result in marked interference effects associated with Fano resonances. Such devices offer appealing alternatives to distributed Bragg reflectors and filters for various applications, such as optical wavelength and polarization filters, reflectors, semiconductor lasers, photodetectors, bio-sensors and non-linear optical components. Suspended PCS also have natural applications in the field of optomechanics, where the mechanical modes of a suspended slab interact via radiation pressure with the optical field of a high-finesse cavity. The reflectivity and transmission properties of a defect-free suspended PCS around normal incidence can be used to couple out-of-plane mechanical modes to an optical field by integrating it in a free-space cavity. Here we demonstrate the successful implementation of a PCS reflector on a high-tensile stress Si3N4 nanomembrane. We illustrate the physical process underlying the high reflectivity by measuring the photonic-crystal band diagram. Moreover, we introduce a clear theoretical description of the membrane scattering properties in the presence of optical losses. By embedding the PCS inside a high-finesse cavity, we fully characterize its optical properties. The spectrally, angular- and polarization-resolved measurements demonstrate the wide tunability of the membrane’s reflectivity, from nearly 0 to 99.9470±0.0025%, and show that material absorption is not the main source of optical loss. Moreover, the cavity storage time demonstrated in this work exceeds the mechanical period of low-order mechanical drum modes. This so-called resolved-sideband condition is a prerequisite to achieve quantum control of the mechanical resonator with light.

Tunable channel drop filters consisting of a tilted Bragg grating and a mode sorting polymer waveguide.

Optical wavelength filters with large tuning range and narrow bandwidth are crucial for enhancing the capability of WDM communication systems. A polymeric tunable filter for C-band, comprising a tilted Bragg grating and a mode sorting waveguide junction is proposed in this work. For dropping a certain wavelength signal, the tilted Bragg grating reflects an odd mode into an even mode and then the reflected even mode propagates towards an output port of the asymmetric Y-junction due to the mode sorting. Consequently, the output port is separated from the input port, which is not possible in an ordinary Bragg reflector. The tilted Bragg reflector with an odd-even mode coupling efficiency of 61% exhibited a maximum reflectivity of 95% for a grating of 6 mm. A linear wavelength tuning of over 10 nm was achieved for an applied thermal power of 312 mW.

Road Surface Status Classification Using Spectral Analysis of NIR Camera Images

There is a need for an automated road status classification system considering the vast number of weather-related accidents that occur every winter. Previous research has shown that it is possible to detect hazardous road conditions, including, for example, icy pavements, using single point infrared illumination and infrared detectors. In this paper, we extend this research into camera surveillance of a road section allowing for classification of area segments of weather-related road surface conditions such as wet, snow covered, or icy. Infrared images have been obtained using an infrared camera equipped with a set of optical wavelength filters. The images have primarily been used to develop multivariate data models and also for the classification of road conditions in each pixel. This system is a vast improvement on existing single spot road status classification systems. The resulting imaging system can reliably distinguish between dry, wet, icy, or snow covered sections on road surfaces.

Facet preparation of polymer based optical wavelength filter using mechanical/chemical treatment technique

AbstractA photodefinable polymer of benzocyclobutene (BCB 4024‐40) from Dow Chemical™ has been demonstrated as a waveguiding material in a new structure of optical wavelength filter. The filter structure is based on the combination of restricted interference and general interference schemes of multimode interference technique. The filter is capable in optical wavelength filtering particularly for 1550/1310 nm. Because of the photosensitive nature of the polymer, the chemical wet‐etching fabrication technique needs to be adopted. For the purpose of laser coupling, a new facet polishing technique has been proposed and it is based on the combination of mechanical and chemical polishing. It is shown that the fabricated device works well with improved crosstalk of −15.7 dB (1310 nm) and −21.8 dB (1550 nm). © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1301–1313, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26781

Tunable Integrated Electro-Optic Wavelength Filter With Programmable Spectral Response

In this paper, we report on an integrated optical wavelength filter device in LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . A sequence of individually addressable polarization converters enables programmable spectral response and continuous wavelength tunability. Wavelength-selective polarization conversion is obtained using in-phase and quadrature-driven electro-optic converters. A model based on coupled-mode analysis is presented that allows to determine the filter performance. Examples of tailoring the spectral response to obtain strong sidelobe suppression and flat-top responses are discussed. Predicted theoretical results are confirmed by experiments. A 2.3 nm wide bandpass filter with more than 20 dB sidelobe suppression and a tuning range of about 20 nm are demonstrated. Moreover, even a flat-top characteristics with 4.9 nm bandwidth and about 15 dB sidelobe suppression could be demonstrated with the same device.

Efficient multiresolution time-domain analysis of arbitrarily shaped photonic devices

A multiresolution time-domain (MRTD) technique is proposed and applied to the analysis of arbitrarily shaped photonic devices. The suggested method implements the multiresolution analysis in the context of method-of-moments for the solution of Maxwell's equations. To improve the capabilities of the proposed method, the uniaxial perfectly matched layers absorber for the MRTD is rigorously incorporated and better performance is reported over the conventional finite-difference time-domain. Various numerical examples demonstrate the stability and numerical precision of the suggested MRTD method for both linear and nonlinear applications. Moreover, the application of the suggested MRTD scheme for the design of a photonic crystal-based optical wavelength filter and for the analysis of a frequency converter is presented.

Design and simulation of apodized wavelength filters using Gaussian-distributed sidewall grating

An accurate design for an apodized integrated optical wavelength filter using Gaussian-distributed sidewall Bragg grating is proposed, 2-dimensionally simulated and analyzed using the finite-difference time-domain method. It is verified that for various grating periods, the central wavelengths of the reflection bands are all fixed at designed 1.55 μm with the side lobes well suppressed.

Design and Application of Compact and Highly Tolerant Polarization-Independent Waveguides

In this paper, the design, fabrication, and application of a highly tolerant polarization-independent optical-waveguide structure suited for operation in the third communication window is presented. The waveguide structure has been optimized toward minimized sensitivity to technological tolerances and low fabrication complexity. The tolerance analysis has been based on the typical processing tolerances of the widely applied silicon-oxynitride technology, being plusmn3times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> in refractive index, plusmn1% in thickness, and plusmn0.1 mum in channel width. The optimized waveguide design fulfills the criterion of a channel birefringence within 5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> , including processing tolerance. It also enables a fiber-to-chip coupling loss below 1 dB/facet and is suited for the realization of low-loss bends with a radius down to 600 mum. Based on this waveguide design, a passband-flattened optical wavelength filter with 50-GHz free spectral range has been realized and tested. The measured TE-TM shift of 0.03 nm confirms the polarization dependence of the optical waveguides being as low as 3times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup>

A novel 1 × 2 multimode interference optical wavelength filter based on photodefinable benzocyclobutene (BCB 4024–40) polymer

AbstractA novel 1 × 2 multimode interference (MMI) optical wavelength filter for 1310 and 1550 nm operation based on photodefinable BenzoCyclobutene (BCB 4024–40) polymer is demonstrated. The device is fabricated on BK7 glass substrate with thin layer of SiO2 as cover. A cost effective chemical etching technique is used in the fabrication process to take advantage of the photosensitive nature of the polymer. The filter length is significantly reduced by adopting the restricted MMI scheme, lower beat length ratio, and cascaded MMI couplers. At 1550 nm filtering operation, the measured crosstalk is −20.6 dB and at 1310 nm filtering is −14.4 dB. The measured insertion loss is around 3.2–3.5 dB for both ports. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1024–1028, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22327

Electro-optic Ti:PPLN waveguide as efficient optical wavelength filter and polarization mode converter

We report the first experimental demonstration of electrically controlled Solc-type optical wavelength filters and TE-TM mode converters based on Ti-diffused periodically poled lithium niobate (Ti:PPLN) waveguides. A maximum mode conversion efficiency or a peak spectral transmittance of ~99% in the telecom C-L bands was obtained from a 9-mm long, 21.5-21.8-mum multiple-grating Ti:PPLN waveguide device with a switching voltage of as low as 22 V or 0.99 Vxd(mum)/L(cm), where d is the electrode separation and L is the electrode length. The spectral range of this device can be tuned by temperature at a rate of ~0.758 nm/ degrees C.

Design Considerations of a Television Camera Detecting Oil Slicks on the Sea

This paper describes a television camera system that automatically captures exclusive images of an oil slick on the sea. The system includes two optical wavelength filters (WFs), two charge coupled devices (CCDs), and a differential image circuit that produces an absolute value of a difference signal between two output images from CCDs. The operating principle is based on the fact that, due to the multiple-beam interference in the oil slick, there is a marked difference of intensity between light reflected from the surface of the sea and that from the slick. The probabilities to sense slicks under various conditions were calculated using two types of WF, i.e., a space-invariant WF and a space-variant WF, and it was found that the latter was far superior to the former.

Fiber Fabry-Pe/spl acute/rot interferometer with precision glass-ceramic jacketing

A novel passive-alignment fiber Fabry-Pe/spl acute/rot interferometer (FFPI) was developed by direct jacketing of an optical fiber with a low-expansion glass-ceramic (GC). It was first demonstrated that a transmission spectrum with no peak splitting is obtained by the FFPI developed. The polarization-dependent loss of this FFPI was also improved to one-third of the conventional FFPI fabricated with a ferrule and an organic adhesive. The transmission peak wavelength of the FFPI shows a sensitive linear temperature dependency. The FFPI with a GC jacket is expected as a promising candidate for narrow-band optical wavelength filters or temperature sensors that can be easily embedded in standard optical fiber connectors.

Mach-Zehnder interferometer with a uniform wavelength period.

We have realized a first optical filter composed of optical delay lines and couplers that has a periodic response with respect to wavelength, whereas a conventional optical filter is known to have a periodic response to relative optical frequency. This new filter can be constructed by using a phase-generating coupler (PGC) that supplies the optical delay lines with a wavelength-dependent nonlinear phase. The PGC, which is also composed of optical delay lines and couplers, can simultaneously provide a desired phase and an arbitrary amplitude coupling ratio. We applied our transformation method to a conventional Mach-Zehnder interferometer (MZI) as an example of an optical frequency filter and converted it to an optical wavelength filter. We fabricated the designed MZI on a silica-based planar lightwave circuit and successfully realized what is believed to be the first MZI with a uniform wavelength period.