An optimization procedure for spatial mode multiplexing from individual single-mode fibers into a three-mode fiber based on a spatial aperture sampling concept has been developed. By placing space-variant imaging elements between the single-mode and few-mode fibers, each beam aperture can be shaped for lower loss coupling and low mode-dependent losses. The optimization achieves a record theoretical −1.5-dB insertion loss, improving on the previous theoretical −2-dB record.
We propose and demonstrate a compact tunable optical dispersion compensation (TODC) device with a 100 GHz free spectral range capable of mitigating chromatic dispersion impairments. The TODC is based on longitudinal movement of a waveguide grating router, resulting in chromatic dispersion compensation of 1000 ps/nm. We employed our TODC device for compensating 42.8 Gbit/sec differential phase-shifting keying signal, transmitted over 50km fiber with a −2 dB power penalty at 10−9.
We analyze the performance of a spatial fiber switching system when using a pixelized mirror, such as a LCoS or MEMS spatial light modulator, in place of a large tilting micromirror. Our findings demonstrate the dependence of insertion losses on tilt angles or fiber counts, and the dependence of the crosstalk in the number of phase quantization levels and random phase errors. The former effects can be minimized by satisfying a relationship between the tilt angle to a fiber, the pitch of the array, and the optical wavelength.
We propose and demonstrate a photonic spectral processor for applying arbitrary spectral phase and amplitude at high resolution with a 100-GHz free-spectral range for colorless wavelength-division-multiplexing adaptive filtering applications. The system employs free-space optics for projecting the dispersed light coming out of a planar-lightwave circuit onto a phase spatial-light modulator. The processor achieves 3-GHz optical resolution over 75-GHz usable bandwidth, with 557-MHz addressable granularity.
Optical communication systems are the premier conduit for providing broadband data across continents, nations, cities, neighborhoods, and are now starting to penetrate into private homes. This spectacular achievement is the culmination of years of research and development efforts in diverse fields. Recently we are witnessing the evolution of these communication systems towards optical networking. The advent of optical networking has been enabled by a suite of complementary optical subsystems that are pivotal to the operation and management of these networks. These optical microsystems directly interact with the optical signal and-through functionality afforded by design-are able to filter, switch, attenuate, and adapt the optical communication channels carried by the network. In this talk I will review a sampling of these enabling devices and focus on the MEMS technology required for its implementation.
A novel tunable dispersion compensator (TDC) with ±500-ps/nm tuning range and bandwidth support for 40-Gb/s signals is described. The TDC is constructed from a waveguide grating router (WGR) that provides very high spatial dispersion and a deformable cylindrical mirror for applying quadratic spatial phase across the dispersed wavefront. The WGR’s 100-GHz free-spectral range (FSR) allows the device to simultaneously apply the same dispersion to all wavelength-division multiplexing (WDM) channels.
The design and performance of several generations of wavelength-selective 1 X K switches are reviewed. These optical subsystems combine the functionality of a demultiplexer, per-wavelength switch, and multiplexer in a single, low-loss unit. Free-space optics is utilized for spatially separating the constituent wavelength division multiplexing (WDM) channels as well as for space-division switching from an input optical fiber to one of K output fibers (1 X K functionality) on a channel-by-channel basis using a microelectromechanical system (MEMS) micromirror array. The switches are designed to provide wide and flat pass- bands for minimal signal distortion. They can also provide spectral equalization and channel blocking functionality, making them well suited for use in transparent WDM optical mesh networks.
This paper describes a continuously variable and independently addressable channelized dispersion compensator. The optical system is a free-space grating-based system used in a four-pass configuration to ensure flat passbands. The variable dispersion is produced by an array of thermally adaptable curvature micromechanical mirrors. A per-channel variable dispersion greater than +/-400 ps/nm has been demonstrated, with 58 GHz +/-0.4 dB flat passband on 85 GHz spacing. The group delay ripple is less than 7 ps and the penalty with 40 Gb/s CSRZ is 0.7 dB.
We introduce a general concept for the design of all-optical wavelength converters with pulse reformatting functionality. The novel wavelength converters are based on a single semiconductor optical amplifier followed by an optical filter. A microelectromechanical system-based realization is shown and simultaneous 40 Gb/s wavelength conversion, switching and signal format conversion is demonstrated. The new pulse reformatting optical filter device outperforms current schemes with respect to input-power requirements, input-power dynamic range and signal quality.
Free-space-based channelized dynamic spectral equalizers are theoretically investigated by solving the temporal-frequency-dependent power-coupling integral for commonly used active device technologies: liquid-crystal modulators, tilting micromirror arrays, and deformable gratings. Channel-filter characteristics, such as bandwidth and interchannel transition, are found to depend on the different attenuation mechanisms provided by the active devices. Such information is required for choosing the proper device parameters in designing channel equalizers and similar free-space spatially dispersed subsystems.
In part I, we proposed and investigated a hybrid pulse position modulation/ultrashort light pulse code-division multiple-access (PPM/ULP-CDMA) system for ultrafast optical communication networks. In this scheme, the large bandwidth of a ULP is efficiently utilized by virtue of the very high time resolution of a time-space processor. More detailed analysis and discussion on the receiver scheme using the time-space processor is now presented; nonideal performance of the time-space processor, including the reference pulse realization problem, as well as amplifier and detector noise, are taken into account. Discussions on physically achievable ranges of the system parameters that determine the performance of the proposed PPM/ULP-CDMA system are also made based upon current, state of the art technology. As remedies to overcome the physical limitations on the system parameters, two modified modulation/demodulation schemes are proposed and investigated to enhance the performance of the hybrid PPM/ULP-CDMA system.
A new approach is presented for fabricating monolithic crystalline silicon tilting-mirror microoptoelectromechanical systems (MOEMS) devices. The activation electrodes, etched from a thick silicon layer deposited over insulating oxide onto the top surface of a silicon-on-insulator (SOI) wafer, are displaced from the mirrors and interact with these tilting elements via electrostatic fringing fields. In contrast to the more usual parallel-plate activation, the rotation angle saturates at high voltages. This paper discusses concept, design, and processing, and also compares modeling and measured performance of a specific 9 tilt range device array.