A new channel drop filters (CDFs) configuration based on a single line-defect resonator (LDR) is presented. The proposed structure is composed of a bus waveguide, a LDR and a u-shaped output waveguide. The bandgap structure and filter characteristics of the filter are investigated by using the plane wave expansion (PWE) method and finite difference time domain (FDTD) method in a square lattice dielectric rod photonic crystal structure respectively. Though this novel resonator, the two wavelengths at 1531nm and 1551nm are dropped from the two ports of the u-shaped output waveguide with high dropping efficiency. This is very well meeting the requirement of ITU-T G.694.2 standard. The proposed CDF can play important role in optical communication networks and photonic integrated circuits.
Based on reverse recursion algorithm, the one-dimensional photonic crystal containing a Kerr nonlinear medium layer (AB)MD(BA)N is investigated to realize the unidirectional transmission function of all-optical diode by introducing additional dielectric layers. Results show that when a single-dielectric-layer (for example, dielectric layer A) or a doubledielectric-layer with different refractive index (for example, dielectric layer AB) is introduced in the outside of the structure, the bistable curve of the input and output light intensity for the forward and backward incident is separated, and the unidirectional transmission characteristics appear. Increasing the period of the double-dielectric-layer introduced in the structure, the unidirectional transmission wavelength range and the transmittance are both improved for the same intensity of incident light. Based on the analysis we present an optimized structure (AB)6 D(BA)8 (AB)2 . Numerical simulations demonstrate that the structure exhibit ideal unidirectional transmission characteristics. Besides, the wavelength range of unidirectional transmission is also extended with the increasing of the intensity of incident light. When the intensity of incident light is 1.48MW/m2 , the wavelength range of the unidirectional transmission is 1564.7nm1574nm with transmittance greater than 0.8. Compared with the results in available literatures, the proposed all-optical diode structure has the prominent characteristics of simple structure, wider wavelength range, and greatly reduced the intensity of incident light. The results are of great significance for the design of all-optical diode and other unidirectional transmission devices.
Based on digital signal processing theory, a novel and simple method is proposed to design asymmetrical film-microcavity interleaver filters (FMCIF) with arbitrary duty cycles. The transmission spectrums obtained have the characteristics of high isolation, great rectangular degree and wide flat passband. Design examples of different duty cycles are given and the influence of some key parameters on the spectral performance is discussed. The proposed method is simpler and more efficient than existing methods.
Based on sublayer division and backward recursion algorithm, the nonlinear reflection spectra at normal and oblique incidence for one-dimensional photonic crystal (1DPC) with one Kerr nonlinear defect are investigated. When incident intensity is higher than the incident intensity threshold, the defect mode appears inclined curved multiple-valued features at certain wavelengths. Compared with the circumstances of normal incidence, the full width at half maximum (FWHM) of the TE wave becomes smaller and that of the TM wave becomes greater. The change of FWHM also arouses the change of the incident intensity threshold. For the 1DPC with third-order nonlinear coefficient χ(3)>0, the defect mode position would be determined by the incident angle and incident intensity together and the minimal separation angle of TE wave and TM wave is decreased with increasing the incident intensity. While for the 1DPC with third-order nonlinear coefficient χ(3)<0, the defect mode moves towards shortwave direction when increasing incident intensity or incident angle. Besides, the minimal separation angle of TE wave and TM wave is increased with increasing the incident intensity. This research provides a valuable reference to the design and application of polarization filters, optical sensors, tunable filters and so on.
A terahertz (THz) polarization filter based on liquid crystal cavities is designed. The P and S polarized light are both
transmitted and the minimum transmittance of P and S polarized light at pass-band is higher than 99.5%.The P polarized
light and S polarized light can be both separated distinctly at a small angle. We discuss the influence of each structural
parameter on spectral performance, such as rectangle degree, duty cycle, spectral period etc systematically. The results
show that the refractive index of the thin-film layers mainly influences the rectangle degrees and duty cycle. The liquid
crystal cavities are inversely proportional to the spectral period. The center-frequency tunable characteristics can be
realized by changing the incident angle with small angle.
A centrosymmetric structure containing anisotropic medium is proposed. The polarization filtering property of the
structure is studied systematically by the transfer matrix method. The results demonstrate that transmittance, isolation
and FWHM of transmission spectra are influenced by period N. FWHM is also influenced by incident angle. In addition,
center frequency and frequency spacing are determined by incident angle and thickness of medium cavity. On this basis,
a detailed design example is given. Isolations of transmission spectra of TM-polarized light and TE-polarized light
respectively are 40.46dB and 42.37dB.Transmittances of them respectively are higher than 99.209% and 97.594%. Their
center frequencies of transmittance windows accord with the ITU standard. The structure is very simple and transmission
spectra of TM and TE polarized lights are completely separated. It is easy to be accomplished and will have worthiness
in practical application.
Starting from the theory of one-dimensional photonic crystal, a flat-top polarization interleaver filter composed of
cascaded thin-film glass cavities is proposed. A detailed design example with three cascaded thin-film glass cavities is
given in the paper. The minimum transmissivity of P polarized light at passband is higher than 99.6% and the
maximum transmissivity of S polarized light is about 0.1%. The center-frequencies of the transmissivity of P polarized
light accord with the ITU standard. The proposed interleaver filter not only has the characteristics of very simple
structure, easy to accomplish, but also has high transmittance for P polarized light and good cut-off characteristic for S
polarized light. When rotating the cascaded thin-film glass cavities in the horizontal plane with small angle, the filter
has the center-frequency tunability characteristic as well.
Based on digital signal processing theory, a novel method of designing optical notch filter is presented for Michelson
interferometer with Gires-Tournois Etalon. The method is not only effective and simple, but also can be used to
implement the designing of the optical notch filter which has arbitrary numbers of notch points in one free spectrum
range. As a designing example, the optical notch filter with one notch point is given in the paper. The change of output
intensity spectrum is also investigated for the reflection coefficient of the mirror and the distance between the mirrors
deviating from the ideal value, finally the tuning characteristics of the notch filter is discussed.
Based on digital signal processing theory, a simple method of designing interleavers is proposed for MZI with fiber ring
coupled structure. The results of different coupled structures, including no-ring, single ring coupled on one arm of MZI,
single ring coupled on each arm of MZI, two rings coupled on one arm of MZI while one ring coupled on another arm
and two rings coupled on the both arms of MZI structures are given and analyzed. The proposed method is not only
simple but also effective. At last, take two vertically cascaded rings coupled on one arm and one ring coupled on another
arm for instance, the change of spectral transmittance is investigated for each design parameters deviating from ideal
value and the tuning characteristics are discussed as well.
Based on the theory of one-dimensional photonic crystal, an asymmetrical interleaver filter is proposed. It is composed
of cascaded thin-film glass cavities. Each thin-film glass cavity is formed by evaporating several layers of reflecting
films on two surfaces of glass medium. Compared with other proposed structures, the proposed interleaver structure is
not only very simple but also easy to accomplish. Moreover, flat passband and stopband can be obtained by the
interleaver. A design example of a 50 GHz interleaver filter with duty cycle of 1:5 is presented. The influence of each
structural parameter on spectral performance, especially for the duty cycles is discussed. On this basis, design results of
interleaver filters with duty cycle of 1:3 and 1:4 are shown and analyzed. A design example of an interleaver filter with
five cascaded cavities is given at last.
A novel and simple design method based on pole-zero diagram is proposed for optical interleaver based on Michelson
Gires-Tournois interferometer (MGTI) with arbitrary cascaded reflectors. Digital filter model which is equivalent to the
MGTI optical interleaver is derived firstly. Then on the basis of it, the transfer functions of two output ports of the
interleaver are simplified and all the design parameters of the interleaver can be obtained conveniently by the use of the
mature design principle of elliptic filter and pole values. The two output spectrums obtained has the wide flat passband
(and stopband) width and high isolation simultaneously. Compared with other existing design methods, the proposed
method is simpler and more efficient, especially for interleavers with GTE composed of much more reflectors. Design
examples of the interleaver with different cascaded G-T etalon structure are given.
This paper aims at bridging the gap between the academic research and practical application in water environment
monitoring by remote sensing. It mainly focuses on how to rapidly construct the Inland and coastal Water Environment
Remote Sensing Monitoring System (IWERSMS) in a software perspective. In this paper, the remote sensed data
processing framework, dataflow and product levels are designed based on the retrieval algorithms of water quality
parameters. The prototype is four-tier architecture and modules are designed elaborately. The paper subsequently
analyzes the strategy and key technology of conglutinating hybrid components, adopting semantic metafiles and tiling
image during rapid construction of prototype. Finally, the paper introduces the successful application to 2008 Qingdao
enteromorpha prolifra disaster emergency monitoring in Olympics Sailing Match fields. The solution can also fit other
domains in remote sensing and especially it provides a clue for researchers who are in an attempt to establish a prototype
to apply research fruits to practical applications.
A novel flat-top and low dispersion optical interleaver using ring cavities (RCs) in a Mach-Zehnder interferometer is
proposed. It is composed of eight mirrors and two nested prism pairs. Each prism and two mirrors behave as a RC. The
phase shift of RC is periodic function of the frequency of the input light which acts as phase dispersive mirror. The two
phase shifts needed to achieve a flat-top spectral passband is provided by the Fresnel reflectivities at the prism-air
interface of the two RCs. The optimum interface reflectivities for flat passband, high isolation and low dispersion can be
obtained only by choosing the appropriate material of the prism in each RC. The proposed novel interleaver in a 25GHz
channel spacing application exhibits a 0.5dB passband larger than 24 GHz (96% of the spacing), a 30 dB stopband
greater than 21.2 GHz (84.8% of the spacing), a channel isolation higher than 32 dB and chromatic dispersion ±50 ps/nm
within center-frequency ± 2GHz ITU passband. It's the best result demonstrated at the present time.
A novel optical interleaver scheme based on nested optical glass pairs is proposed. The assembly of pairs behaves as a cascaded Mach-Zehnder interferometer. The interleaver, with simple structure, low cost, and compact size, can be easily implemented with inexpensive material and mature preparation technology. Small channel spacing (50 GHz), high isolation (<–30 dB), a wide, flat passband and stop band (>2/11 period), and center-frequency tunability can be obtained simultaneously. An optimum design of a 50-GHz tunable interleaver based on this structure is given as an example. Its environmental temperature sensitivity and fabrication tolerance are also analyzed.
Tunable interleaver filters are very important in DWDM applications. To be effective, it is required that the filters must possess wide passband (or stopband) width, high isolation, small channel spacing, high tuning speed an so on simultaneously. Whereas, for the small birefringence of all the natural crystals and synthesized crystals, it is quite difficult for the available birefringent interleavers to have the channel spacing smaller than 50GHz and other properties mentioned above simultaneously. This paper proposes a novel electro-optically tunable birefringent interleaver filter, which solves the problem successfully. It is based on cascaded analog birefringent structures. The filter of this configuration can achieve small channel spacing (≤50GHz), wide passband and stopband width (>1/5 period) and high isolation (<-30dB). When voltage is applied on electro-optical crystal plates in analog birefringent structures, the filter also possesses the function of high-speed (submicrosecond) center-frequency tunability simultaneously. A most efficient electro-optic configuration, which needs the lowest operating voltage and has not walk-off effect of extraordinary ray in the crystals, is proposed and analyzed. A prototypical experiment verifies the electro-optic tunability of this filter as well.
External electric field has great effect on grating formation via additional carrier drift during nonvolatile holographic recording. The photorefractive properties of doubly doped LiNbO3:Fe:Mn crystals are theoretically investigated by jointly solving the two-center material equations with nonzero external electric field and the coupled-wave equations. The external electric field dependence of the refractive-index changes n1, the diffraction efficiency η as well as the photorefractive sensitivity S are studied for oxidized LiNbO3:Fe:Mn crystals. Significant improvement of the photorefractive performance has been revealed by applying external electric fields to oxidized LiNbO3:Fe:Mn. The enhanced material performance under external electric field improves the applicability of doubly doped LN crystals.
Integration of optical systems is important in practical applications for enhanced compactness and stability, particularly for optical switch. In the previous reports, 1×N electro-optic switches were constructed by the assembling of discrete E-O elements. The aim of this paper is to develop a 1×N switch integrated in a single slab of LiNbO3, which consists of an array of electro-optic polarization modulators between the interfaces for total-internal reflection. Due to the double refraction effect, the ordinary ray and the extraordinary ray have different reflections. From different switching states of modulators, the internally double reflection along the sequential interfaces of a crystal can lead to different directions of the output beam. On this basis, a 1×N optical switch is designed, which is a crystal slab of 2 refractive interfaces for beam input and output, 4 reflective interfaces for total-internally double reflection, and N-1 E-O modulators with pairs of electrodes. A voltage on the n pair of electrodes will induce output beam onto the n angular position. The suggested 1×N switch is simple and compact in construction, low in loss and insensitive to environment. An experimental 1×4 switch is demonstrated, too.
Compact, low operating voltage, high-speed bypass-exchange switches are major elements in optical interconnection networks. Conventionally, a bypass-exchange switch consists of a controllable half-wave plate sandwiched between two polarizing beam displacers. In this paper, an integrated optical bypass-exchange switch is designed in a single block of LiNbO3 crystal. The switch is polarization based and consists of only one birefringent crystal slab with electro-optic property. Based on both the phenomena of double refraction and internally double reflection, and the electro-optic effect in a crystal, an electro-optic modulator, a beam combiner and a beam splitter are integrated in a single block of LiNbO3 crystal. The polarization states of the two input signals are both linear and perpendicular to each other. First the two signal beams are combined into a single channel with two orthogonal polarization directions by double refraction and internally double reflection. The signal couple propagates along the optical axis of the crystal. When a half-wave voltage is applied on the direction normal to the incident plane, the polarization directions of the two beams in a single channel will be exchanged. Last the signal couple is divided separately with the same deflection as that of the two input beams by double refraction and internally double reflection again. The experimental results show that the switch is low operating voltage, low cross talk, low energy loss, fast-speed, and insensitive to environment disturbance. The switch may be applied to the nodes of various multistage interconnection networks.
Birefringent interleaving filters are very useful in DWDM, but it is quite difficult to design the birefringent interleavers with the frequency spacing smaller than 50GHz. Because of the small birefringence of all the natural and synthesized crystals, the sizes of birefringent plates in this use become impossible large. This paper proposes an analog birefringence structure, which is suitable for such a task. The structure consists of a pair of double-refraction plates for splitting and combination, respectively, and in between a set of two optical plates of different indices of refraction. An incident beam is first divided into two separated beams by the first plate, which then pass through the individual plates to delay with different refraction. Finally the two delayed beams are combined spatially into a single beam by the second plate. It can be understood that this structure has the function just the same as a birefringent plate. The difference of the refractive indices of the two optical plates can be very large (up to 0.8), so that the analog birefringence structure is not only practically possible but also very compact. As usual, a cascade of analog birefringence structures will form a flat-passband interleaver. The detailed designs are given. The experiment on an analog birefringence structure is demonstrated as well.
The time-space dynamics of the recording and fixing of photorefractive holograms in doubly-doped LiNbO3:Fe:Mn crystals are analyzed by jointly and numerically solving the set of time-differential two-center material equations and the set of space-differential coupled-wave equations. In the formulation, the absorption of both the recording light and the sensitizing light is included. The results for optimizing the holographic recording are similar to those obtained by the previous steady-state solving. In this paper, therefore, a special attention is paid on the time-space evolution of the intensity and phase distributions of the induced space-charge fields and the exciting interference pattern of the two beams for recording or the readout and diffracted beams for coherent erasing. It is interesting to find that during the time development of hologram there is a spatially changed direction of energy transferring between the two-coupled beams, which depends spatially on the relative phase difference between the induced space-charge field and the exciting interference pattern. The energy transferring direction will be reversed as the relative phase difference becomes opposite in the sign. As a result, the spatial figures of the isophase and the recording or recorded holographic fringes are depicted, which gives a full understanding for the formation of photorefractive hologram in LiNbO3:Fe:Mn.
Birefringent filters in which several unequal-length birefringent crystal plates are located between two polarizing devices are used to flatten the gain spectrum of erbium-doped fiber amplifiers. The intensity transmission function of birefringent filter is a cosine series containing a finite number of terms. Because the desire intensity function can be transform into a cosine Fourier series which is truncated after an appropriate number of terms, the thickness and the relative rotation angles of each element can be acquired by comparing the intensity transmission function with the cosine expanding series of the desire function. Since the rotation angles of each element are easy to control, the desired function can be realized accurately. With this device, an amplifier can be given with <0.1dB gain variation in 1550nm-1562nm spectrum band. Furthermore, the use of a polarization beam-splitter and a polarization beam-combiner makes this device polarization-independent.
A new method to produce flattening spectral transmittance for birefringent chain filter based on the interference of polarized light is presented. In previous publications, each birefringent crystal must be of equal thickness and only one group of azimuth angles of the crystals was obtained. Besides, the shape of spectral transmittance is not enough flat and the flatness width of the passband and the stopband is not wide enough. Our method is more advantageous than that of the previous publications. It is based on Fourier transform. The thickness of each crystal can be different. We can obtain all the numerical solutions of the azimuth angles of the crystals when ripples are relative small in both the relative wide passband and stopband. In this paper, three birefringent crystals are used and all the azimuth angles of the crystals are obtained when ripples are limited to a uniform 0.1% in both the passband and the stopband with the widths of greater than 2/11 period. The influence of the change of the azimuth angles and thickness of the crystals on the spectral transmittance of the system is discussed as well.