Charles C. Zhou

Waveguide-hologram-based wavelength-multiplexed pseudoanalog true-time-delay module for wideband phased-array antennas

A pseudoanalog true-time-delay (TTD) module based on substrate-guided waves and wavelength-division multiplexing is presented. A 1-to-32 (5-bit) even fan-out is demonstrated by use of a two-dimensional waveguide hologram array. This module has a packing density of 2.5 lines/cm(2) and very compact packaging (8 cm x 4 cm x 8 mm). It also reduces TTD system complexity by providing continuously tuned delay signals to parallel-control the whole phased-array antenna system. The device has a measured bandwidth of as high as 2.4 THz. The delay signal can range from tens of picoseconds to several nanoseconds.

Dispersion correction of surface-normal optical interconnection using two compensated holograms

Optical interconnects have advantages over electrical interconnects in applications where low transmission loss, electromagnetic interference immunity, low power budget, and high bandwidth requirements are critical. 1‐3 The need for optically-interconnected memories and processors in multichip modules is imperative due to the rapid increase of clock speed and of data throughput. Free-space interconnects must overcome packaging vulnerability in order to be practical. Guided-wave interconnects based on silica or polymeric thin films attract more attention since they can be fabricated in two-dimensional arrays using a standard very large scale integrated ~VLSI! microfabrication process. Coupling light into and out of waveguides efficiently becomes more important. Coupling methods using gratings, end-face joints, and prisms have been reported. 4,5 Surface-normal transmission holographic gratings are widely used to couple light into and out of waveguides due to their high diffraction efficiency and planarized packaging. In this letter, we investigate the light dispersion of a surface-normal input volume holographic grating. Experimental data of grating dispersion characteristics are obtained using a mode-locked femtosecond laser. A compensation method is developed to eliminate the wavelength-induced dispersion, and we demonstrate surface-normal input and output optical interconnect structures which automatically correct the dispersion resulting from the laser wavelength chirping and therefore greatly enhance the interconnection bandwidth. The basic structure of a surface-normal input and output optical interconnect using volume holographic gratings and substrate-guided waves is shown in Fig. 1. The grating structure induced by the refractive index modulation is slanted, having a tilt angle f. The grating spacing is L. Due to the high diffraction efficiency of the volume hologram and the low propagation loss due to total internal reflection, the surface-normal optical interconnect configuration is useful in photonics applications such as backplane buses, computer clock signal distribution, and waveguide-based wavelength

Axial-graded-index (AGRIN) lens-based eight-channel wavelength division demultiplexer for multimode fiber-optic systems

We have designed and fabricated the first multimode wavelength division multiplexer (WDM) and demultiplexer (WDDM) based on axial graded index (AGRIN) lenses in conjunction with a volume holographic grating. The demonstration is made using a multimode fiber with a 50-/spl mu/m core size. The diffraction-limited AGRIN lenses employed significantly increase the output coupling efficiency and reduce crosstalk when compared with the best homogeneous lens solutions previously reported. The volume holographic grating has a maximum diffraction efficiency of 92% at the center wavelength of 780 nm. An eight-channel WDDM device with a center wavelength of 780 nm and a channel separation of 4 nm is designed and demonstrated. The end-to-end insertion loss for each channel is between 2.8 and 3.8 dB. The maximum channel-to-channel crosstalk is -25 dB.

Surface-normal 4 x 4 nonblocking wavelength-selective optical crossbar interconnect using polymer-based volume holograms and substrate-guided waves

We present a 4/spl times/4 surface-normal wavelength-selective nonblocking crossbar using polymer-based volume holograms and substrate-guided waves. A prototype device is demonstrated using the center wavelengths of 750, 780, 810, and 840 nm. The employment of wavelength-division multiplexer and of address coding reduce the required 16 wavelengths to four while maintaining the 4/spl times/4 interconnects. Diffraction efficiencies of 85%, 83%, 79%, and 82% are experimentally confirmed for randomly polarized light at 750, 780, 810, and 840 mm, respectively. The measured crosstalk is less than -24 dB.

Four-channel multimode wavelength-division-demultiplexer (WDM) system based on surface-normal volume holographic gratings and substrate-guided waves

We demonstrate a four channel integrated wavelength division multiplexer (WDM) and demultiplexer (WDDM) based on volume holographic gratings and substrate-guided waves at near IR wavelengths. The four operating wavelengths are centered at 750, 780, 810 and 840 nm respectively. The WDM and WDDM are demonstrated using 50/125 multimode fibers. The channel-to- channel crosstalk level is measured to be less than -40 dB. The system insertion losses are -23 dB, -21 dB, -20 dB, -22 dB respectively for 750 nm, 780 nm, 810 nm and 840 nm.

Surface‐normal 3×3 non‐blocking wavelength‐selective crossbar using polymer‐based volume holograms

We present a 3×3 surface‐normal wavelength‐selective crossbar using polymer‐based volume holograms. A prototype device is demonstrated using the center wavelength of 775 nm and Δλ=10 nm. Employment of 1/4‐pitch graded‐index rod lenses reduces the required nine wavelengths to three while maintaining the 3×3 interconnects. The diffraction efficiencies of 75%, 83%, and 75% are experimentally confirmed for wavelength 765, 775, and 785 nm, respectively. Surface‐normal configuration eliminates the conventional edge‐coupling scheme which is vulnerable in a harsh environment. A 3×3 crossbar is demonstrated with a two‐way system insertion loss less than 3 dB and channel‐to‐channel cross talk less than 20 dB.

Multimode WDM using holographic gratings and substrate-guided waves

Wavelength division multiplexing and demultiplexing (WDDM) techniques are the two key technologies for upgrading optical communication system bandwidth. The use of WDM technologies not only provides high speed optical communication links, but also provide advantages such as higher data rates, format transparency, and self-routing. Over the past twenty years, many kinds of WDDM device technologies have been developed and demonstrated. WDDM devices using dispersive photopolymer or dichromated gelatin volume holographic gratings have been recently reported. In this paper, we report an integrated four-channel multimode fiber compatible WDDM system with four semiconductor lasers operating at 750, 780, 810 and 840 nm, respectively. The device is demonstrated using the combination of graded index lenses, photopolymer based holographic gratings and substrate-guided waves.

Polymer-Based Volume Holograms for a Surface-Normal 3×3 Non-Blocking Wavelength-Selective Crossbar

In this paper, we present a 3x3 non-blocking crossbar for network applications. This device is pivotal for the realization for a computer-to-computer interconnect network where both wavelength division multiplexing and space division multiplexing are employed to enhance the transmission bandwidth. We report the formation of a surface -normal wavelength selective non-blocking crossbar using photopolymer-based volume holograms in conjugation with graded index (GRIN) lenses. The elimination of edge-coupling significantly enhances the packaging reliability. Furthermore, such a configuration is compatible with the implementation of vertical cavity surface-emitting lasers where the characteristic of azimuthal symmetry is maintained in the waveguiding substrate. The prototype polymer-based volume hologram for a multiple-wavelength 3x3 crossbar is experimentally demonstrated at 755, 765, and 775 nm. The unique beam routing property of GRIN lens reduced nine wavelengths to three wavelengths while maintaining the required nine (3x3) individual interconnects. Realizing the fact that the wavelength-switching speed of semiconductor lasers is as fast as 1 nsec, we expect to build a fully packaged system with much less system latency.

Polymer-based volume holograms for multiple wavelength network applications

Wavelength division multiplexing (WDM) and demultiplexing (WDDM) devices are considered to be two of the key elements for enhancing the transmission bandwidth of optical communications and sensor systems. During the past 20 years, various type of WDMs and WDDMs have been proposed and demonstrated. Recently the technique for producing spatially multiplexed phase grating based on polymer-based waveguide holograms for WDDM applications has been reported. We report the formation of a surface-normal WDDM using photopolymer-based volume holograms in conjugation with graded index lenses. The elimination of edge-coupling significantly enhances the packaging reliability and the time reversal of the beam propagation automatically results in the required WDM. Furthermore, such a configuration is compatible with the implementation of vertical cavity surface-emitting lasers where the characteristic of azimuthal symmetry is maintained in the waveguiding substrate. In this paper, we present two devices for network applications. The first is an 8 channel surface-normal WDM with a center channel wavelength of 772 nm and a wavelength separation of 4 nm. The second is a 3 X 3 wavelength selective crossbar with a center wavelength of 765 nm and a channel separation of 10 nm. These devices are pivotal for the realization of such a computer-to-computer interconnect network where both WDM and space division multiplexing are employed to enhance the transmission bandwidth. The switching device can be realized using the wavelength-selective crossbar to be presented in this paper.