Optical Control Signal Research Articles

Analysis of erasable fiber loop optical buffer

In this paper, we propose a model of a fiber loop buffer, which incorporates a semiconductor laser amplifier (SLA) as nonlinear element controlled by an optical control signal. The impact of the accumulated and amplified spontaneous emission noise of the SLA and data pattern dependent gain saturation effect in the SLA on the properties of the buffer is taken into account to give the optimum operation conditions theoretically.

A BASIC STUDY ON OPTIMAL DESIGN OF OPTO-PNEUMATIC SERVO SYSTEM

An optical servo system is a new control system which can be used in hazardous environments where electromagnetic noises and radiations exist. In our previous study, we have realized an opto-pneumatic control system which executed a cart positioning using optical control signals instead of electric signals in ahazardous area. However, the response of the system was slower than a usual electro-pneumatic control system, because the response time of the optical servo valve which converted optical signal to pneumatic fluid power was longer. In the next step, we have proposed an analytical model of the valve in order to improve the dynamics of the valve. In order to design the valve, it is necessary to analyze the characteristics of moving rubber membranes in the valve in detail. In this paper, we propose an analytical model of the membranes. And we investigate the relation between design parameters of the valve, such as an equivalent spring constant, damping coefficient and so on, and structural parameters of the membranes, such as a diameter and thickness.

Spatial mode filters realized with multimode interference couplers

Spatial mode filters based on multimode interference couplers (MMI's) that offer the possibility of splitting off antisymmetric from symmetric modes are presented, and realizations of these filters in InGaAsP/InP are demonstrated. Measured suppression of the antisymmetric first-order modes at the output for the symmetric mode is better than 18 dB. Such MMI's are useful for monolithically integrating mode filters with all-optical devices, which are controlled through an antisymmetric first-order mode. The filtering out of optical control signals is necessary for cascading all-optical devices. Another application is the improvement of on-off ratios in optical switches.

Studies on Opto-Pneumatic Servo System. 1st Report. Development of servo System in which Optical Control Signal is Fed Back Directly or Indirectly.

Present electrical servo systems are sensitive to environmental hazards such as electromagnetic noise and radiation. To avoid such influences, it is effective to use laser beams and optical fibers. Our purpose is to develop an optical servo system in which an optical signal is used as a control signal in part or all of the system. In this paper, we describe the development of two types of optical servo system which consist of a photo-fluidic interface, two tested double-acting booster amplifiers, a pneumatic cylinder and an opto-optical encoder. One type is the cart position control system in which the optical signal is fed back directly, and the other type is that in which the optical signal is fed back indirectly. As the result of experiments on these systems, it is shown that the cart positioning in which an optical control signal is fed back directly can be realized by using dither generated in a booster amplifier. In the tested servo system in which an optical signal is fed back indirectly, the position control performance can be improved using a P-controller to compensate the friction, compared with the direct feedback type.

Optically controlled spatial modulation of (sub-)millimeter waves using nipi-doped semiconductors

The use of a molecular beam epitaxy engineered InGaAs/GaAs semiconductor structure to quasioptically modulate a millimeter wave Gaussian beam using an optical control signal has been demonstrated. The RF transmission is modulated spatially by the optically generated excess carrier density. Low optical intensities are sufficient due to the long recombination lifetime achieved in the nipi-doped structure used. A modulation depth of more than 15 dB in transmission mode has been obtained at 100 GHz. Modulation has been measured up to 5 THz using a Fourier transform spectrometer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance analysis of an all-optical gate using a multisection travelling wave amplifier

The paper outlines a model for an all-optical gate and presents results concerning its static and dynamic characteristics. The gate is an inhomogeneously pumped travelling wave amplifier operating with an optical information signal and an optical control signal. Optical gates with two and three homogeneously pumped regions are analysed. The model takes into account the longitudinal variation of photon flux and carrier density, and adopts a multiwavelength approach to consideration of the optical pumping due to spontaneous emission. It is extended to consider also the switching characteristics with applied electrical pulses. Criteria are introduced for the evaluation of the device performance, and, through numerical simulations, the trade-off between the desired static and dynamic characteristics is shown. It is found that, although the switch-on time can be strongly enhanced, the switch-off time is limited by the dynamics of the free carriers for the all-optical operation. Finally, it is verified that electrical switching can substantially improve the performance for the switch-off transient.

All-optical multistage demultiplexers operated by logical permutations of control pulses

An all-optical multistage demultiplexer is proposed which enables 2/sup M/ time-division-multiplexed optical signals to be separately assigned to arbitrary output ports by logical permutations of M sets of optical control signals. Demultiplexing at 30 Gb/s was successfully demonstrated in a two-stage configuration composed of optical Kerr switches with two control inputs. The application of this device to various high-speed processing schemes is briefly discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

All-optical remote gain switching in Er-doped fibre amplifiers

A novel, all-optical feedback scheme that allows remote optical gain switching in Er-doped fibre amplifiers is demonstrated. A selected wavelength of the amplified spontaneous emission (ASE) at the output of the amplifier is fed back to the input through an unpumped Er-doped fibre acting as a saturable absorber. Off and on switching of ring lasing (and hence, respectively, on and off switching of the amplifier gain) is achieved by remotely injecting optical control signals at appropriate wavelengths over the transmission fibre. A gain bistability (on–off ratio) of 26 dB at 1530 nm is demonstrated. A switching time of 10–50 ms was observed, inherent to the erbium fluorescence lifetime. This scheme could be useful in directing traffic flow in optical networks.

Semiconductor-laser amplifier as an optically controlled switch

The application of a semiconductor-laser amplifier with reduced facet reflectivity as all-optical switch is described. An optical data signal is switched on and off with an extinction ratio of 10 dB when an optical control signal is turned on and off. The two optical signals are polarized perpendicularly to each other. The device was operated up to 100 MHz.

Photofluidic Interface

A device that transduces optical control signals to pneumatic control pressures was assembled and tested. This photofluidic interface uses no electronic components and requires no electrical power. The interface employs the photoacoustic effect and fluidic signal processing techniques. The pressure output from the interface can be controlled by modulating the input optical signal in any one of four different ways (amplitude modulation, frequency modulation, pulse width modulation, and gate width modulation). Results of performance tests are reported. There is also a discussion of the physical parameters involved in the conversion of optical signals to fluidic signals.

Optically controlled two-component heterojunction laser

Hard switching-on and bistable operation were observed when an optical signal was applied to a weakly injected region of a two-component (GaAl) As heterojunction laser in a state close to the self-excitation threshold under continuous pumping conditions. A purely optical flip-flop operating regime with switching fronts of about 1 nsec duration and 4 mW amplitude, as well as a regime of generation of subnanosecond optical single pulses, were realized. The amplitude of the optical control signal was estimated to be below 0.1 mW.

Proposals for logical optical operators

Logical operators can be implemented by optical filtering and quadratic detection. For the logical signal representations we choose the input amplitude and output intensity. Using finite dynamic range and a reference input, the three fundamental operators can be realized, with the same logical convention. We finally propose a programmable operator consisting of a unique filter whose logical operation depends on input optical control signals.