By using only two input signals of A and B, an all-optical half adder that utilizes a cross gain modulation in
semiconductor optical amplifiers is demonstrated at 10 Gbps. The half adder utilizes two logic functions of SUM
and CARRY, which can be demonstrated by using the XOR gate and the AND gate, respectively. The extinction
ratios of SUM and CARRY are approximately 6.1 dB. No additional input beam such as clock signal or
continuous wave light, which is required in many other all-optical logic gates, is used in this design concept.
Using the cross-gain modulation (XGM) characteristics of semiconductor optical amplifiers (SOAs), multi-functional
all-optical logic gates including XOR, AND, and OR gates are successfully demonstrated at 10 Gbps by using VPI
component makerTM simulation tool. Multi-quantum well (MQW) SOA is used for the simulation of all-optical logic
system. Our suggested system is composed of four MQW SOAs, SOA-1 and SOA-2 for XOR logic operation and SOA-
3 and SOA-4 for AND logic operation. By the addition of two output signals XOR and AND, all-optical OR logic can
be obtained.
KEYWORDS: Logic, Semiconductor optical amplifiers, Modulation, Logic devices, Clocks, Electrons, Signal processing, Optical signal processing, Signal generators, Computing systems
By using cross gain modulation in semiconductor optical amplifiers, basic logics for all-optical computing
and signal processing are successfully demonstrated at 10Gbps. These functions will bring up the increased
speed and capacity of telecommunication systems, basic or complex optical computing, and many other optical
signal processing systems.
Requirements for suitable communication systems with large capacity and high speed processing of information are rapidly on increase. Fiber-optic communication systems are presented for these requirements today. Modulation is one of the most important part in these system. Although many optical modulators already has been existed, for more high speed and performance we are interested in design of traveling-wave type electro-optic modulator which can be used for wide-band applications. Quantum dots(QDs) have long been expected to improve the performance of optical devices. Since their density of states due to the three-dimensional (3-D) carrier confinement behave as delta function, thus, QDs have the characteristics such as enhanced differential gain, suppressed thermal distribution of carriers, and a nearly zero alpha parameter at the peak gain. In this paper, we fabricated electro optic modulator using InAs/InGaAs columnar QD. The height of one QD is 4 nm and 10 periods of QDs are stacked including InGaAs capping layer. The peak wavelength of photoluminescence is 1260 nm at room temperature. The electrode of QD modulator is designed as Traveling-wave Mach-Zehnder type for high speed operation. And the microwave characteristics are simulated to design Traveling-wave QD modulator using Finite Difference-Time Domain method. Using simulation results, we fabricated Traveling-wave type quantum dot electro-optic modulator with varying the length of modulation region.
An all-optical full adder using semiconductor optical amplifiers has been demonstrated at 10 Gbps for the first time. The full adder consisted of XOR and NOR gates only utilizes the mechanism of cross-gain modulation. The full adder utilize two logic functions of SUM and CARRY, which can be demonstrated by using two XOR gates and four NOR gates, respectively. By passing signal A as probe signal and signal B as pump signal into SOA-1, Boolean A NOT B can be obtained. Also, by changing the role of signals A and B for SOA-2, Boolean NOT A B can be acquired. Addition of Boolean A NOT B and NOT A B results in NOT A B + A NOT B , which is Boolean expression of logic XOR. By passing this XOR signal and signal C into the second XOR gate with the same principle, SUM signal of the full adder can be obtained. The Boolean expression of SUM can be expressed as A # B # C . With the first three NOR gates, Boolean NOT(A+B), NOT(B+C), and NOT(C+A) can be obtained. With the addition of these outputs, Boolean NOT(A+B) + NOT(B+C) + NOT(C+A) can be formed. By injecting these outputs through the last NOR gate with clock signal, CARRY signal of the full adder can be realized. The Boolean expression of CARRY can be expressed as AB +BC +CA. The extinction ratio is about 6.1dB.
By using gain nonlinearity characteristics of semiconductor optical amplifier, an all-optical binary half adder at 10 Gbps is demonstrated. The half adder operates in single mechanism, which is XGM. The half adder utilizes two logic functions of SUM and CARRY, which can be demonstrated by using the XOR gate and the AND gate, respectively. In the XOR (A NOT B + NOT A B) gate, Boolean A NOT B is obtained by using signal A as a probe beam and signal B as a pump beam in SOA-1. Also, Boolean NOT A B is obtained by using signal B as a probe beam and signal A as a pump beam in SOA-2. By adding two outputs from SOA-1 and SOA-2, Boolean A NOT B + NOT A B (logic XOR) can be obtained. In the AND (AB ) gate, Boolean NOT B is firstly obtained by using signal B as a pump beam and clock signal as a probe beam in SOA-3. By passing signal A as a probe beam and NOT B as a pump beam through SOA-4, Boolean AB is acquired. By achieving this experiment, we also explored the possibilities for the enhanced complex logic operation and higher chances for multiple logic integration.
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