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.
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.
External electric field has great effect on grating formation via additional carrier drift during nonvolatile holographic recording. The photorefractive properties of doubly doped LiNbO<sub>3</sub>: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 n<sub>1</sub>, the diffraction efficiency η as well as the photorefractive sensitivity S are studied for oxidized LiNbO<sub>3</sub>:Fe:Mn crystals. Significant improvement of the photorefractive performance has been revealed by applying external electric fields to oxidized LiNbO<sub>3</sub>:Fe:Mn. The enhanced material performance under external electric field improves the applicability of doubly doped LN crystals.
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.
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 LiNbO<sub>3</sub> 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 LiNbO<sub>3</sub> 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.
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 LiNbO<sub>3</sub>, 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 <i>n</i> pair of electrodes will induce output beam onto the <i>n</i> 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.
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 LiNbO<sub>3</sub>: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 LiNbO<sub>3</sub>:Fe:Mn.
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.
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.