Wavelength Division Multiplexing Filters Research Articles

Holographic recording in LiNbO3 using various polarized lights

Holographic recordings in a LiNbO3 crystal using ordinary and extraordinary light in transmission-type geometry were performed. The system parameters of storage capacity (M/#), sensitivity, and signal-to-noise ratio were measured. Although extraordinary light will induce stronger fanning light (nonlinear enhanced scattered light) in LiNbO3, our experimental results indicate that the system using extraordinary light is superior to that using ordinary light. Our demonstrations and results can help to optimize the holographic recording in some applications of volume holographic optical element (VHOE), such as wavelength division multiplexing (WDM) filters in optical communication.

Design of optical filters for coarse wavelength division multiplexing by using down binary number sequence multilayer structures

Design of optical filters for coarse wavelength division multiplexed optical communication wavelengths by using new down binary number sequence multilayer structures are suggested. These new down binary number sequence multilayer filters are smaller in size, cheaper in cost, and easier to fabricate as compared to optical filter designs previously suggested by researchers.

On triplexer design for next generation Ethernet passive optical network systems

The standardisation effort targeting 10 Gbit/s EPON systems, together with the requirement for coexistence with the legacy IEEE 802.3ah compliant equipment, impose a set of very tight requirements in terms of wavelength allocation plan for future EPON systems and significant limitations in terms of triplexer design for optical network unit (ONU) modules, where two wavelength channels (or three, when an analogue video overlay is used on the downstream) must be properly separated with minimum power and quality loss, providing also a high quality transmission window for the upstream 1310 nm signal. In this paper, we look closer at the possible triplexer and filter design for emerging 10 Gbit/s EPON systems in the light of current IEEE 802.av Task Force activities and technical limitations of the wavelength division multiplexing (WDM) filter design process.

622-Mb/s Bidirectional SFP Optical Transceiver Using an Integrated WDM Optical Subassembly

The 1.3/1.55-mum bidirectional small form pluggable (SFP) optical transceiver with an integrated wavelength division multiplexing (WDM) subassembly using accurate ceramic blocks has been developed. The WDM subassembly on which a laser diode, a receiver photodiode, a WDM filter, and two microlenses are integrated is only 2.0 times 2.1 times 0.6 mm3 in size and inserted in a TO-CAN package. The SFP transceiver coupled with single-mode fiber has been operated at a 622-Mb/s data rate. The transmitted optical output power is -2.8 dBm and the measured value of sensitivity is -32 dBm at 10-10 bit-error rate.

A bidirectional module integrated on a planar lightwave circuit with a coated WDM filter

We have developed a cost-effective 2.5 Gb s−1 wavelength-division multiplexing (WDM) bidirectional module using two integrated optical subassemblies, which are composed of a planar lightwave circuit (PLC) platform for upstream operation and a silicon optical bench (SiOB) platform for downstream operation. The module is constructed by employing a flip-chip bonding method with passive alignment using a distributed feedback laser diode (DFB-LD) with a monitoring waveguide photodiode (PD) on a PLC platform and a receiver with a PIN-PD on an SiOB platform. We investigated the optical performance of the transmitter based on the PLC platform and the receiver subassembly module based on the SiOB platform, respectively.

Thin WDM filters for low-cost optical triplexers on silicon optical benches

A cost-effective optical triplexer using thin wavelength-division multiplexing (WDM) filters and lensed fibres on a silicon optical bench is proposed. The wavelength demultiplexing of the triplexer was performed using two 60 µm-thick WDM thin-film filters (TFFs). The fibre-to-fibre insertion losses were less than 1.2 dB. The thermal stability of the triplexer was also investigated. The variations of power at the 1.31/1.49/1.55 µm ports were less than 0.8 dB within the bandwidth required by ITU-T G.983.3 at a substrate temperature of 100°C.

Germanium photodetectors enable scalable silicon photonics

Silicon photonics—the fabrication of optical components and systems in silicon chips by leveraging cost-effective silicon integrated circuit manufacturing—has seen considerable activity over the last few years, with major breakthroughs in modulation, fiber-to-chip coupling, and wavelength-division multiplexing filters. These components have been integrated into complex systems together with custom designed CMOS circuitry.1, 2 On the other hand, the generation and detection of light remains a much more challenging problem. Silicon, being an indirect bandgap semiconductor, does not provide an efficient platform for light generation, and its vanishing absorption coefficient at wavelengths longer than 1μm hinders its use for photodetection in the near-infrared optical communication wavelengths (1.3 and 1.55μm). Given the importance of an integrated source for a CMOS optical transceiver, several attempts have beenmade to enhance the light emission properties of silicon, but even the best results lag behind the performance of a typical III-V laser source.When it comes to near-infrared photodetection, however, high-performance CMOS-based devices relying on the high absorption coefficient of germanium have been achieved.3 Today, optical communication receivers use high-performance, discrete, InGaAs photodiodes, with several drawbacks arising from the hybrid nature of the technology. The full receiver chain cannot be tested waferscale, which results in yield fall-out after complete assembly. Furthermore, these devices are difficult to scale to multiple channel applications, as each channel requires a separate, expensive, and large component. Significant financial benefits may be achieved through the use of embedded photodetectors.4 Embedding the photodetectors directly on the wafer will eliminate the costs associated with the assembly and testing of multiple components. This technology will allow a very large number of photodetectors to be grown directly Figure 1. A typical germanium-on-silicon waveguide photodetector. SOI: silicon on insulator.

High-Performance and Low-Cost 10-Gb/s Bidirectional Optical Subassembly Modules

High-performance and low-cost 10-Gb/s bidirectional optical subassembly (BOSA) modules that are obtained by adopting low-cost transistor outline (TO)-Can materials and processes are proposed and demonstrated. The BOSA module consists of an uncooled 1.3-mum distributed-feedback laser diode and a 1.5-mum p-i-n/transimpedance amplifier receiver (Rx), which integrate a 45deg tilted thin-film wavelength-division multiplexing filter to transmit a 1.3-mum light into the fiber and reflect a 1.55-mum light into the Rx. The matching resistor and low parasitic inductance packages are applied with the TO-Can laser diode to enable 10-Gb/s operation. A modulation bandwidth of 11.86 GHz and an OC-192 eye diagram of a 19% mask margin are obtained from the transmitter side. After a 10-km single-mode fiber (SMF) transmission, the mask margin for the OC-192 eye diagram decreases to 11%. For the Rx, an OC-192 eye diagram of a 31% mask margin is obtained under back-to-back connections. The mask margin is maintained at 29% after a 10-km SMF transmission. The measured crosstalk penalty is 0.9 d 15 at the Rx side. These results indicate that the BOSA module is capable of a 10-Gb/s bidirectional transmission. This unique high-performance 10-Gb/s BOSA module not only demonstrates the feasibility of a 10-Gb/s bidirectional transmission on an SMF for fiber-to-the-home applications but also shows the low-cost possibility to ensure the success of next-generation 10-Gb/s access networks.

The Improvement of the Backward Cladding–Core Coupling in a Tilted Fiber Grating by Two Acoustic Flexural Waves

The cladding modes of a tilted fiber grating can be coupled back to the core modes by acoustooptic interactions. However, the coupling of high-order diffractions by acoustic-optic interaction is not apparent, owing to the insufficiency of acoustic power. In this paper, we will demonstrate that as two acoustic flexural waves with appropriate frequency are launched to a tilted fiber Bragg grating, high-order harmonic acoustic waves can be superposed to improve the coupling efficiency between the backward cladding modes and core modes. This phenomenon may be applied to induce several optical channels for multichannel laser and wavelength-division multiplexing filters.

1 × N add–drop filter structures using one dense wavelength division multiplexing thin-film filter

This paper proposes 1 × N add–drop filter structures in which only one thin-film filter (TF) is used. Our key idea is based on a combination of an angle-multiplexing concept and the flexibility of the optical fiber to allow a multiwavelength optical beam hit the TF several times, each time at a different angle but same position. Due to the TF angle sensitivity, the desired wavelength optical beam corresponding to the incident angle is therefore spatially isolated from the main optical beam. Our first TF-based 1 × N add–drop filter structure is arranged in a reflective design in which N wavelength optical beams can be dropped out from the main channel. For our transmissive architecture, N − 2 channels are directed to their associated output terminals while the remaining λ N−1 and λ N wavelength optical beams are sent out at the same port. Experimental proof of concept for our reflective TF-based 1 × 3 add–drop filter using one off-the-shelf TF, a triple fiber-optic collimator, and an optical circulator separates two wavelength optical beams with their channel spacing of 0.8 nm from the main channel. In this case, measured optical losses of 0.67 dB, 1.66 dB, and 2.59 dB are obtained for the first, the second, and the remaining dropped wavelength optical beams, respectively. Optical crosstalk and polarization dependent loss of <−18 dB and <0.08 dB are also investigated, respectively.

Effect of Linear Crosstalk of WDM Filters on Multilevel Modulation

The effect of the crosstalk of wavelength-division-multiplexing (WDM) optical filters on the performance of WDM transmission systems that use multilevel modulation formats are examined and it is found that the currently common specification of -30 dBm is not adequate when more than eight signal levels are used. Also, the systems using coherent detectors and those using direct detection receivers are compared

Exact solution of resonant modes in a rectangular resonator

The resonant modes of rectangular two-dimensional optical resonators were analyzed exactly. Based on the characteristics of the Bessel function, the resonant frequencies of the rectangular microcavities are expressed in a simple way. In addition, a simple rule to judge when the finite length of a rectangular resonator can be considered infinite is given in realistic applications. The solution that is presented should be useful in possible applications of the rectangular resonators as filters for dense wavelength-division multiplexing.

Configurable coarse wavelength division demultiplexers based on planar reflective gratings

Configurable coarse wavelength division multiplexing filters were realized using a planar reflective grating architecture utilizing small diffraction angles. The novel architecture yielded a 10-fold reduction in the chip size compared to previously reported filter configurations. The proposed design was manufactured using a standard silica-on-silicon process with a waveguide refractive index contrast of 0.82%. Polarization dependent losses of less than 0.2 dB were achieved without any post-processing steps. Fabricated filters showed insertion losses of 2.4 dB and remarkably broad free spectral ranges of more than 500 nm. The combination of single-mode input and multi-mode output guides resulted in box-like passband responses with bandwidth of 14.2 nm. Applications of the filters for integrated coarse wavelength division receivers and monitors are discussed.

Optically Modulated MEMS scanning endoscope

This letter presents a novel configuration of a microelectrical-mechanical system (MEMS) scanning endoscope that is actuated by external optical modulation. Light at a wavelength in the 1550-nm range is used to modulate a scanning MEMS mirror. The instrument also provides for the delivery of a second beam at a wavelength of 1310 nm, commonly used for medical diagnostic applications such as optical coherence tomography. The two wavelengths are combined with using a wavelength-division multiplexing filter and launched into a single-mode fiber. This novel approach provides for the operation of a scanning endoscope without the need for directly powering up the scanning element. In this way a less hazardous apparatus for in vivo diagnosis is possible. The design of the module and MEMS scanning mirror is discussed. A fabricated module is demonstrated in which a MEMS mirror scans at the resonant frequency of 350 Hz, generating an optical scanning angle of 8/spl deg/.

Packaging for a FP-LD hybrid transceiver using filter-integrated PLC platform with PD insertion trench

We present the packaging of a 1.25-Gb/s bidirectional transceiver using a filter-integrated planar lightwave circuit (PLC) platform for passive optical networks. A simple packaging for a hybrid transceiver is successfully demonstrated by using a PLC platform with the trench for photodiode (PD) insertion and the adiabatic wavelength division multiplexing (WDM) filter. This transceiver exhibited full-duplex operation of 1.25 Gb/s with a minimum optical sensitivity of −26.5 dBm under an output power of 0 dBm. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 489–491, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21387

High accuracy measurement of the residual air gap thickness of thin-film and solid-spaced filters assembled by optical contacting

Optical contacting is a powerful tool for assembling solid-spaced filters in order to form a wavelength division multiplexing (WDM) multiple-cavity filter. In this article, we propose a method able to characterize the optical quality of such assembling with a high accuracy. We use localized spectral transmittance measurements to map the thickness of the residual air gap existing at the adhesion interface with a few nanometers precision. Tests on thick (2mm) and thin (100μm) substrates coated by Dual Ion Beam Sputtering are performed. Thus, we show that our 25mm-diameter samples are strictly contacted over more than 80% of their surface, with no detectable residual air gap.

Stresses and Temperature Stability of Dense Wavelength Division Multiplexing Filters Prepared by Reactive Ion-Assisted E-Gun Evaporation

In this paper, we report the in situ measurement of the temperature stability of narrow-band-pass filters on different types of substrate, for dense wavelength division multiplexing (DWDM) filters in optical-fiber transmission systems. The DWDM filters were designed as all-dielectric Fabry–Perot filters and fabricated by reactive ion-assisted deposition. Ta2O5 and SiO2 were used as high- and low-refractive-index layers, respectively, for constructing the DWDM filters. The accuracy and stability of the coating process were evaluated for fabricating the DWDM filters for the temperature stability of the center wavelength. The center wavelength shift was determined to be greatly dependent on the coefficient of thermal expansion of the substrate on which the filter is deposited.

Coating uniformity improvement for a dense-wavelength-division-multiplexing filter by use of the etching effect

The uniformity of optical narrow-bandpass filters for dense wavelength division multiplexing (DWDM) has been improved by control of the coating parameters of electron guns and the ion source. The optical film was deposited by the electron gun and was etched by the ion source during the ion-assisted deposition process. The uniformity of the coating of a 100 GHz DWDM filter is better than +/- 0.003% over a circular area of 50 mm in diameter when such an etching process is used.

Wide-range tunable Fabry–Perot array filter for wavelength-division multiplexing applications

A new design for a Fabry-Perot-based array filter for wavelength-division multiplexing (WDM) applications is proposed. The device is composed of two partially reflective mirrors; the surface of one of the mirrors is stepwise. Not only does the configuration of multiple air-gap cavities into a single unit provide wavelength tunability but the channel numbers can be expanded. A four-channel multiplexer has been demonstrated. The results revealed that a compact and cost-effective WDM device should be easily attainable.

Tunable double-cavity solid-spaced bandpass filter

In this paper, we introduce the principle and demonstrate the feasibility of a tunable multiple-cavity solid-spaced bandpass filter for WDM (Wavelength Division Multiplexing) applications, which uses a vernier effect since the two cavities have different thermal sensitivities. A set of specific wavelengths can be addressed in the whole C-Band by using temperature changes less than 100 degrees C. This result corresponds to a gain factor in sensitivity about 5 with respect to alternative standard thin-film configurations.