The Michelson interferometer-based interleaver is widely used in wavelength-division multiplexing (WDM) systems. A performance comparison for a 10-gigabit/s WDM system with a Michelson interferometer-based interleaver of different designs is presented. The trade-off between the designs that improve the passband bandwidth and reduce chromatic dispersion is discussed. It is concluded that a comprehensive design, including analysis at both the component and system levels, is necessary.
Inter-channel crosstalk for a liquid crystal-based dynamic channel blocker/equalizer has been experimentally studied.
With the optimal interpixel width, a 32-channel, 100-GHz channel-spacing sample is fabricated and characterized. The
maximum insertion loss (IL) of 5 dB and the polarization dependent loss (PDL) of 0.5 dB within the ITU ± 14 GHz are
achieved. The 45 dB extinction ratio is obtained. The variations of the IL and PDL within the temperature range from - 5°C to 65°C cross the C-band are less than 1 dB and 0.4 dB respectively.
The effect of an interpixel gap on light leakage in a free-space liquid-crystal-based dynamic channel blocker/equalizer is studied. The electric field components along the driving electric field within the liquid crystal interpixel gap are numerically calculated. The results show nonuniform distributions in both width and thickness. The numeric results on the relation between gap width and electric field distribution are also presented. A 20-channel, 200-GHz channel-spacing blocker/equalizer on the C band with flat tops and a 40-dB extinction ratio is fabricated and examined.
The effect of an imperfect antireflection (AR) coating on a birefringent interleaver (an important optical communication component) and on an optical communications system containing such a birefringent interleaver is investigated. We demonstrate how the imperfect AR coating on the rhomb surfaces affects the birefringent interleaver's intensity spectrum and generates undesirable chromatic dispersion (CD) ripples for an interleaver that should be dispersion-free by design. Our results show that a rhomb with a close-to-perfect AR surface coating (T=99.8%) can still generate a ±30-ps/nm CD ripple, causing a nonnegligible power penalty in an optical communications system. We also demonstrate a simple and practical approach to reduce the CD ripple caused by the imperfect AR coating.
Wavelength interleaver is an important component of dense wavelength division multiplexing systems. Various
techniques are proposed to implement the wavelength interleaver. Among these approaches, the one based on the
birefringent crystal might be the first ever been proposed and manufactured. The birefringent wavelength interleaver has
a de facto standard structure consisting of n pieces of birefringent crystal with designed rotation angles. One important
yet often overlooked issue regarding this structure is worthy of discussion. It is well known that the lossless finite
impulse response (FIR) filter pair can be used to model the "standard" birefringent interleaver without material loss, and
a "standard" interleaver consisting of n pieces of birefringent crystals implements nth-order Z-transform transfer
functions. However, it is seldom mentioned that, this popular birefringent interleaver diagram can not represent arbitrary
nth-order Z-transform functions of a lossless FIR filter pair. In other words, for an nth-order lossless FIR filter whose
transfer function is derived from signal processing theory, it might not be feasible with the standard birefringent
wavelength interleaver diagram. This fact makes it difficult to apply signal processing techniques to birefringent
wavelength interleaver design. In this article, we present an alternative birefringent wavelength interleaver diagram to
solve this problem.
The Michelson interferometer based interleaver has been widely used in dense wavelength-division multiplexing (DWDM) systems. It possesses advantages such as compact size, low material costs, etc. However, the Michelson interferometer based interleaver can not be designed as a constant group delay filter due to its infinite impulse response filter nature. In this article, a Michelson interferometer design algorithm based on all-pass filter phase approximation is proposed. It is demonstrated that, with the proposed algorithm, it is straightforward to design an interleaver with respect to different requirements such as bandwidth utilization, isolation, etc. More importantly, it is also demonstrated that, with the proposed algorithm, the group delay variation of the Michelson interferometer based interleaver can be minimized while given magnitude spectrum specifications are satisfied.
In this article, two application examples of signal processing for optical interleaver design are presented. The optical interleaver has become an important building block of the dense wavelength division multiplexing (DWDM) system. Numerous design diagrams have been proposed for the optical interleaver, and, among these diagrams, the Mach-Zehnder interferometer type interleaver and the Michelson interferometer type interleaver might be the most popular ones. The Mach-Zehnder interferometer is a special case of the finite impulse response (FIR) filter, and the Michelson interferometer belongs to the category of the infinite impulse response (IIR) filter. In this article, we demonstrate how signal processing techniques could be applied to design the Mach-Zehnder interferometer type interleaver and the Michelson interferometer type interleaver. Detailed Z-domain transfer functions of these two types of interferometers are presented. The two case studies presented in this article demonstrate how signal processing has become a great enabling technology for optical device design.
A wavelength interleaver structure with asymmetrical output spectra, an important yet seldom investigated device, is presented. The interleaver has become an important fiber optics communication component. Numerous interleaver designs have been proposed and studied. However, most interleavers are designed for symmetrical spectrum splicing, so they cannot be very useful in applications where only a few channels among multiples need to be added or dropped. As a result, the design capability of network engineers is severely limited by the nature of the symmetrical interleaver. In this work, an asymmetrical interleaver structure based on the modified Michelson interferometer is proposed and investigated. The asymmetrical interleaver implemented with the lattice filter approach is also investigated for comparison. The proposed structure has better performance compared to other asymmetrical interleaver structures such as the lattice filter approach, and it also has advantages of compact size and low material costs. With an asymmetrical interleaver, network engineers could enjoy great design flexibility they would not possess otherwise.
A novel bandwidth- and center-wavelength-tunable interleaver structure based on birefringent materials is proposed. This device can provide network designers more flexibility in their design work and reduce system upgrading and modification costs. Since the proposed structure is a kind of finite-impulse-response filter, the interleaver can be designed to be dispersion-free. Moreover, it can be implemented without moving parts to increase reliability. These two features make the proposed device attractive for increasing design flexibility and network efficiency. Simulation and experimental results are presented to verify the fundamental idea.
The impact of cascaded spectral Slicers on network performance is investigated in this paper. For a dispersive spectral Slicer, its dispersion is inversely proportional to the square of its channel spacing. When many narrow-band spectral Slicers are cascaded together, the total dispersion can cause significant penalty on system performance. We demonstrated the deleterious effects on system performance caused by the dispersion of cascaded spectral Slicers. To solve this problem, we applied a signal processing technique to design theoretically dispersion-free spectral Slicers. The design principle and simulation results of dispersion-free spectral Slicers are presented. Based on this signal processing technique, six dispersion-free 50-GHz Slicers were made and cascaded together. The total group delay ripples across spectrum within ±12GHz around center frequencies are less than ±0.8ps, which are much less than the group delay variation of ±14ps within the same bandwidth for dispersive Slicers. The power penalty of cascade dispersion-free Slicers is investigated by deploying them in a 16-channel OC-192 WDM (wavelength-multiplexing division) link. The measurement result shows no noticeable power penalty.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.