Jason C. Fan

Dynamic range of coherent analog fiber-optic links

We investigate the performance of coherent analog optical links employing amplitude modulation (AM), phase modulation (PM), and frequency modulation (FM). The performance of these coherent links is compared to that of AM direct-detection (DD) links. The signal-to-noise ratios, nonlinearities, and-spurious-free dynamic ranges (SFDRs) of the foregoing links are evaluated. We calculate the SFDR for links using DFB and Nd:YAG lasers with typical linewidths of 10 MHz and 5 kHz, respectively. The performance of PM and FM links is dominated by phase noise above a critical value of received optical power. For a linewidth of 10 MHz, and SFDRs of PM and FM links are 30 and 31 dB, respectively, for a received optical power above -27 dBm in a 1 GHz bandwidth. For a linewidth of 5 kHz, the corresponding SFDRs above a received power level of 0 dBm are 51 and 53 dB. The performance of DD and AM links is dominated by RIN above a critical value of received optical power. For a RIN level of -155 dB/Hz, the SFDRs of DD and AM links are 49 and 47 dB, respectively, for a received optical power of 10 dBm in a 1 GHz bandwidth. The SFDRs of the DD and coherent links used for transmission of subcarrier-multiplexed (SCM) signals are also derived. We evaluate target laser parameters needed by a number of different applications. For AM video and antenna remoting applications, linewidths of >

Dynamic range requirements for microcellular personal communication systems using analog fiber-optic links

Fiber infrastructures in future personal communication systems (PCSs) must minimize remote antenna size and cost, and facilitate system maintenance and upgradeability. These goals can be met by a centralized PCS infrastructure using analog fiber-optic links. It is essential that the relationship between optical-link quality in terms of spurious-free dynamic range (SFDR) and PCS quality of service be accurately quantified so that optical device and other infrastructure design requirements can be determined. This paper presents a comprehensive wireless/optical simulation model which combines wireless system characteristics (such as fading, cochannel interference, diversity, and power control) with the noise and nonlinearities of fiber-optic links. Results of the simulation indicate that representative SFDR requirements for fiber infrastructures in PCS systems are in the 72-83 dB/spl middot/Hz/sup 2/3/ range. The impact of varying environmental characteristics as quantified by distance loss and shadowing variance is between 7-10 dB. A larger distance loss or lower shadowing variance result in lower SFDR requirements. The required automatic gain control (AGC) accuracy decreases as the SFDR increases. These results indicate that either distributed feedback (DFB) or Fabry-Perot (FP) semiconductor laser diodes can be used in the implementation of PCS infrastructures.

A novel analog optical link with high dynamic range

A heterodyne interferometric phase modulated link, a new analog optical link, is described. This link, based on phase modulation using an external modulator, has high linearity and suppresses the impact of laser relative intensity noise. The link increases the spurious-free dynamic range by 21 dB as compared to a conventional externally modulated AM link for 10 mW of received optical power, relative intensity noise of -130 dB/Hz, and a 15-GHz intermediate frequency.<<ETX>>

Performance optimization of directly modulated FM-SCM systems with optical discriminator

Theoretical models were developed to accurately describe the behavior of directly modulated communication systems with a predetection optical frequency discriminator. A ten-channel 100-Mb/s subcarrier multiplexed (SCM) system with a DFB laser light source and fiber Fabry-Perot discriminator was built. For an input optical power of -17 dBm a system with a 67-GHz Fabry-Perot filter achieved an optimal CNR of 23 dB at a frequency modulation index ( beta ) of 0.5, compared to optimal CNR of 17 dB at beta approximately=0.3 for a system with a 10-GHz discriminator. System performance demonstrated excellent agreement with the theoretical predictions.<<ETX>>

Design and analysis of a novel fiber-based PCS optical network

We propose a passive antenna remote unit (PARU) architecture which can be used in future optical fiber-based PCS networks. This system is robust, easy to maintain, and upgradeable to multi-GHz frequencies. By using externally modulated Nd:YAG lasers and coherent detection on the uplink, the system is far more efficient than for a direct detection (DD) uplink in terms of subcarrier multiplexed (SCM) voice and video channels per laser, meeting an spurious-free dynamic range (SFDR) requirement of 55 dB. For voice channels, a coherent FM uplink, a coherent AM uplink, and a DD uplink support, per laser with 200 mW optical power, over 1600 channels, 352 channels, and 96 channels, respectively. For moderate quality video, a coherent FM uplink supports over 1000 channels but a coherent AM uplink and a DD uplink cannot achieve the required SFDR due to the Brillouin threshold.

Preamplifier ASK system performance with incomplete ASK modulation: influence of ASE and laser phase noise

Present extensions of the rigorous model of Jacobsen and Garrett and of the Gaussian approximation of Tonguz and Kazovsky for the performance of optically amplified direct detection ASK receivers. These new models take into account incomplete ASK modulation, nonzero laser linewidth, and spontaneous emission noise from the optical amplifier in both polarization control (PC) and polarization diversity (PD) receiver configurations. The penalty associated with the polarization diversity configuration is shown to be consistently under 1 dB for a wide range of ASK modulation depths. The penalty due to the noise in the orthogonal polarization decreases with ASK modulation depth. We find optimum optical filter bandwidths and linewidth-induced performance penalties as a function of ASK modulation depth and linewidth. We provide detailed tables of optimum filter bandwidths for bath PC and PD receivers using both the rigorous method and the Gaussian approximation; the Gaussian approximation frequently underestimates the optimum bandwidth values. A linewidth-induced floor in the minimum usable ASK modulation depth is found for nonzero linewidth and a fixed optical filter bandwidth. Though the Gaussian approximation is found to be accurate within 1.5 dB in all computed cases for optimum optical filter bandwidths, it does not predict the floor accurately in the case of a nonoptimum filter bandwidth. >

Sensitivity optimization of WDMA networks with subcarrier control channels

In this paper, we analyzed and optimized different receivers used in WDMA networks with subcarrier control channels. For the first time, APD/APD and APD/PIN receivers are suggested and analyzed. The results show that for a reasonable number of stations, the new receivers will give 6 dB to 10 dB performance improvement over a conventional PIN/PIN receiver.

Noise analysis of subcarrier-multiplexed coherent optical video transmission systems using direct frequency modulation of semiconductor lasers

The authors present a noise analysis of an analog subcarrier-multiplexing coherent optical system for video transmission using direct frequency modulation of semiconductor lasers. Receiver sensitivity using the FM subcarrier modulation format is analyzed for realistic values of receiver thermal noise (3.31*10/sup -22/ A/sup 2//Hz), laser linewidth (up to 100 MHz), relative intensity noise (RIN) (-130 to -170 dB/Hz), and optical bandwidth (20 GHz). Linewidth-induced performance degradation is negligible for up to 50 channels, and RIN-induced performance degradation becomes dominant as RIN increases above -140 dB/Hz. A sensitivity floor of about -40 dBm (for RIN=-160 dB/Hz) exists for small numbers of channels (up to 50) due to the FM threshold effect at the IF demodulator.<<ETX>>

A comparison of three analog optical links for high dynamic range applications

A new heterodyne interferometric phase modulation (HIPM) link and a new subcarrier frequency modulation with direct detection (SFM-DD) link are proposed. To generate angle-modulated signals at the receiver, the HIPM system utilize a novel external modulator, while the SFM-DD system uses electronic preprocessing. The spurious free dynamic ranges (SFDR) of the SFM-DD and HIPM systems are larger than that of the amplitude modulation with direct detection (AMDD) system; when relative intensity noise (RIN) is dominant, these two systems can show 26 dB and 28 dB advantages with respect to the AMDD system, respectively.<<ETX>>

Dynamic range improvement using a novel phase-modulated analog optical link

We propose and analyze a new analog optical link which we refer to as the heterodyne interferometric phase modulated (HIPM) link. The HIPM link phase modulation uses a novel three leg external modulator, has high linearity and suppresses laser relative intensity noise. The link increases the spurious-free dynamic range by 21 dB as compared to a conventional externally modulated AM link for 10 mW of received optical power, relative intensity noise of -130 dB/Hz, and a 15 GHz intermediate frequency.