We report on optical components for parallel transmit and receive module, operating at 850nm, designed for short haul optical multimode fiber networks. The component is realized by flip-chip bonding of arrayed optoelectronic devices, i.e., VCSEL and PIN detector array, onto ultra-thin silicon- on-sapphire (UTSi) substrate, which is optically transparent and electrically insulated. Flip-chipped assemblies provide several advantages over conventional wire bond techniques, such as extremely low interconnection parasitics that enable high data rates at low power. Using UTSi technology further improves performance by minimizing crosstalk through its insulating substrate while providing the means for a reliable, low cost optical assembly directly onto the substrate. In addition, applying UTSi technology to optical modules allows a higher degree of functional integration within the module. The insulating substrate provides excellent isolation between mixed signal circuitry, enabling the integration of high performance transmitters, receivers and other sensitive analog circuits with digital circuitry on the same substrate. Furthermore, the integration of VCSEL and photodetector array with UTSi circuits for parallel optical interconnects yields several packaging advantages, such as parallelism, scalability, compactness and simplicity.
A mode-locked erbium-ytterbium fiber laser operating at 1550 nm using multiple quantum well (MQW) saturable absorbers was developed. The laser was constructed in a Fabry-Perot configuration using a fiber Bragg grating as a front reflector and a fiber chirped Bragg grating output as a back reflector of the laser cavity. The laser can either produce Q-switched or CW passively mode-locked pulse trains by simply changing the location of the saturable absorber with respect to a focal plane. The pulse train of laser Q- switching operates at an 85-KHz repetition rate when the position of the absorber is near the focus. Peak power of the Q-switching pulses is about thirty times higher than for the CW mode locking which occurs when the absorber is placed exactly at the focal plane. The CW passively mode-locked pulse trains have a 19-MHz repetition rate with 2.6-mW average output power.
A novel mode-locked erbium-ytterbium fiber laser operating at 1550 nm using multiple quantum well (MQW) saturable absorbers was developed. The laser was constructed in a Fabry-Perot configuration using a fiber Bragg grating as a front reflector and a fiber Bragg grating output as a back reflector of the laser cavity. The passive mode-locking element placed inside the laser cavity is a 75 period InGaAs/InAlAs MQW saturable absorber grown lattice matched on an InP substrate. The output of the laser was taken through the other available port of a wavelength-division demultiplexer. The laser produced mode-locked output pulse trains at 16.67-MHz repetition rate and 10 mW of average output power.
Bacteriorhodopsin (BR) is a light transducing photochromic protein in the purple membrane of a salt-loving microorganism that inhabits salt marshes. It has strong absorption in a broad region of the visible spectrum. The B- state in the photocycle can be considered to be the ground state, which has absorption maxima at 570 nm. Perhaps, the most intriguing features of this organic photopolymer are its extraordinary stability in the chemical, thermal and photochemical sense, its large optical nonlinearity, dynamic nature, durability, real-time holographic recording capabilities, and information storage potential. Furthermore, BR-doped polymer film can be fabricated for a large-scale application, whereas photorefractive crystals like BSO or KNSBM cannot be grown easily to the same dimension as BR. Hence, BR's potential in optical system includes transient dynamic applications of an M-type hologram and 3D optical memories of a branched photocycle that shows a great promise for data storage and retrieval due to its high capacity. The major advantages of this organic photopolymer include high density, low cost, low weight and portability which are a projected requirement for the Air Force and commercial applications.
A novel three-laser-beam technique that can be used to investigate holographic diffraction characteristics of an M- type and a transient dynamic hologram of a hydrated D96N mutant bacteriorhodopsin (BR) film is described in this paper. The method in both experiments is to build up molar concentrations in the M-state before holographic gratings are written. Note that the commonality between these two holograms is the M-state holographic gratings. Hence, a B-state absorption light source, a 532-nm doubled Nd:YAD laser, pumps BR molecules from the B-state to the excited M-state, then the M-state absorption beam, a 413-nm wavelength from a Krypton Ion laser, is used to write holographic gratings in that state. Writing with an M-state absorption laser induces a direct phototransition from the excited M-state to the B-state (ground state). This concept capitalizes on the bilevel BR system, i.e., depleting the ground state with a B-state absorption laser creates molar concentrations in the excited M-state, and vice versa. The reading is done with a 680-nm laser, which is far away from the absorption bands to ensure a negligible erasing effect on the gratings written in the film, resulting a pure phase hologram with high efficiency. The experimental results have shown that response times are in the order of milliseconds, and Bragg diffraction efficiency is close to 7% for this sample. Note that this CW holographic technique is a nondegenerate four-wave mixing.
A three-laser-beam technique is developed to study the transient diffraction efficiency of M-state dynamic phase holograms in a D96N mutant bacteriorohodopsin film (BR). A CW beam from 532 nm doubled Nd:YAD laser is used to pump BR molecules from B-state to photoexcited M-state. Then the M- state absorption laser 413-nm wavelength from a Krypton Ion laser is used to write holographic gratings in the excited M- state. The writing process also depletes M-molar concentrations. This process offers the advantages of better modulation and faster response. The reading is done with a 680 nm laser, which is far away from the absorption bands to ensure a negligible erasing effect on the gratings written in the film, resulting a pure phase hologram with high efficiency. A maximized transient peak diffraction efficiency approaches a saturated value when the ratio of write to pump intensity is approximately unity.
A novel bacteriorhodopsin based photonic crossbar system for broadband communications is proposed. This free-space dynamically reconfigurable N X N crossbar switch utilizes an intelligent holographic system for routing and switching by dynamically reconfigurable gratings of bacteriorhodopsin, which has high write/read photocyclicity that is greater than 106. The major advantages of the system include large interconnectivity density, transparent data redistribution, and fiber optic bandwidth capacity. In addition, the switching device resolves optical-to-electronic and electronic-to- optical conversion bottlenecks and reduces signal-to-noise degradation which is due to the conversions. This crossbar design is completely free of internal blocking which is one of the major drawbacks of guided optical crossbars. The system takes advantage of the parallelism and multidimensionality inherent in optics and can be scaled to a large capacity of N X N, while it maintains a low weight and portability which are a projected requirement for future broadband communications.
Gaussian-beam propagation in the bio-optical material bacteriorhodopsin is studied with the consideration of the material's intensity-dependent absorption and refractive index modulation. The beam focusing size, focusing position and their dependence on the incident beam parameters are simulated.
Existing manned airborne platforms are becoming increasingly loaded with additional mission performance
requirements. These requirements severely stress weight, mission performance, size and electromagnetic
interference (EM!) constraints. In addition, as platforms are reduced in size - such as space-based platforms - these
limitations become extremely critical.
Optical fiber-based systems can be used to provide both data and RF signal distribution for sensors and
avionics. These photonic-based systems are lighter weight, smaller in size, lower in loss, and reduce or
eliminate signal interference as compared to existing metallic-based signal distribution systems. These fiber
based systems apply to both RF and data transmission in manned and unmanned space-based and airborne
platforms as well as ground based applications.
Photonics also provides non-frequency dependent true time delay RF signal distribution. This results in the
additional benefit of improved interferometric direction finding and beam nulling through software applications in
sensor and avionics systems.
This paper will discuss research which is underway at Rome Laboratory to develop actively reconfigurable
photonic-based signal distribution systems, using either all optical techniques - including optical switching - or
through a combination of optics and electronics, to meet the future requirements for avionics and sensors in
airborne and space-based platforms.
This paper reports on the novelty of the bacteriorhodopsin photonic crossbar system for broadband communications. A free- space dynamically reconfigurable bacteriorhodopsin holographic crossbar provides a large interconnectivity density, transparent data redistribution, and fiber optic bandwidth capacity. This switching device resolves optical-to-electronic and electronic-to-optical conversion bottleneck and reduces signal-to-noise degradation which is due to the conversions. This crossbar design is completely free of internal blocking which is one of the major drawbacks of guided optical crossbars. This system takes advantage of the parallelism and multidimensionality inherent in optics and can be scaled to a large capacity of NXN while it maintains a low weight and portability which are a projected requirement for future broadband communications. This NXN crossbar is an intelligent holographic system for routing and switching by dynamically reconfigurable grating of bacteriorhodopsin which has high write/read photocyclicity that is greater than 106.
The effective optical nonlinearity n2 of a Ce-doped KNSBN crystal is measured by using the Z-scan method. The dependence of n2 on the illumination wavelength and polarization is characterized. An optical limiter for strong cw illumination is demonstrated, based on self-focusing and spatial self-phase-modulation.
A novel concept for a high-speed signal routing holographic switching system for long-haul communications is proposed. A 1 X 2 optical switch is used to split transmitting optical signals so that part of it can be used to control the state of the photonic switches after it had been converted to the electrical domain. The routing controller then matches a given address to a specific frequency that is used to modulate a spatial light modulator (SLM). As a result, a reference beam is produced that in turn is used to write a grating on a transmission volume hologram. Meanwhile the information remains in the optical domain where it travels through the optical delay line and priority sorter. The delay time is equivalent to the total processing time of the holographic grating. The grating is changed by changing wavelengths. This wavelength tunability provides a method for free-space reconfigurable optical interconnections with high connection density.
An integrated-optic parallel directional coupler waveguide modulator is the subject of this paper. The device consists of two directional coupler modulators in parallel so that a single laser can be used as a source. Advantages of one laser source are to minimize a relative frequency drift difference and allow for high speed communications on separate channels. Applications include television and videophone where audio and video signals can be transmitted simultaneously. A feedback phase shift noise reduction scheme will be investigated for high speed information flow with high fidelity and high linearity. As the result, the parallel modulation technique approaches transparent transmission which will increase the dynamic range and minimize signal distortions.
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