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We have systematically designed and realized the optical feedforward transmitter using microwave circuit model of distributed-feedback laser diode (DFB LD) based on rate equations. Through the system-level simulation for the optical feedforward method, the nonlinearity of DFB-LD is analyzed, and the optimized characteristics of the RF components in the system are confirmed by using a microwave simulator. The experimental and simulated results show the reduced distortion products and enhanced spurious-free dynamic ranges are in good agreement at 2.4 GHz. These results are analyzed as the evaluation parameters for the miniaturization and optimization of the feedforward compensation method in radio-over-fiber systems. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 192–195, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24007

We demonstrate an interference cancellation technique of optical AND gate receiver using optical thyristor for fiber-optic code division multiple access (FO-CDMA) systems. In particular, we fabricate the optical thyristor operating as optical hard-limiter and evaluate that the optical AND gate receiver using fabricated optical thyristor excludes the peaks of side-lobe and cross-correlation result in the system performance degradation. It found that the optical AND gate receiver using optical thyristor excludes the intensity of interference signal resulting in that the peaks of side-lobe and cross-correlation can be fully eliminated for any two users. Therefore, the optical AND gate receiver using optical thyristor is shown to be effective to accommodate more simultaneous users.

We demonstrate the optical thyristor operating as optical hard-limiter (OHL) in the optical channel and AND gate logic element (AGLE). The oxidized PnpN vertical-cavity laser (VCL)–depleted optical thyristor (DOT) clearly shows the nonlinear s-shaped current-voltage and lasing characteristics. A switching voltage of 5.24 V, a holding voltage of 1.50 V, and a threshold current of 0.65 mA is measured, making these devices attractive for optical processing applications. The VCL–DOT operating as OHL would enhance the system performance because it would exclude some combinations of interference patterns from causing errors as in all previous works. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2779–2780, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22850

We propose novel correlator receiver architecture with a PnpN optical thyristor operating as optical hard-limiter, and demonstrate a multiple-access interference rejection of the proposed correlator receiver. The proposed correlator receiver is composed of the 1×2 splitter, optical delay line, 2×1 combiner, and fabricated PnpN optical thyristor. The proposed correlator receiver enhances the system performance because it excludes some combinations of multiple-access interference patterns from causing errors as in optical code-division multiple access systems with conventional optical receiver shown in all previous works. It is found that the proposed correlator receiver can fully reject the interference signals generated by decoding processing and multiple access for two simultaneous users.

We propose a novel optical decoder for a fiber-optic code-division multiple-access communication system. In particular, we discuss a means of reducing the effective multiple-access interference signal by inserting an optical hard limiter (optical thyristor). The optical decoder employs an AND gate logic element (AGLE) composed of a 1×M splitter, optical delay lines, an M×1 combiner, and the optical hard limiter. It is found that the AGLE suppresses the interference signal, so that the autocorrelation sidelobe and the cross-correlation peaks can be fully eliminated for any two users.