Manik Attygalle

Analysis of optical carrier-to-sideband ratio for improving transmission performance in fiber-radio links

In this paper, we investigate the optimum carrier-to-sideband ratio (CSR) for maximizing the transmission performance of an optically modulated millimeter-wave signal in a fiber-wireless system via experiment, theory, and simulation. We present a simple analytical model to assess the performance enhancement resulting from optical CSR variations. The model is capable of analyzing systems incorporating binary phase-shift keyed and quaternary phase-shift keyed modulation formats. We quantify the optical CSR of a point-to-point fiber-radio link and establish that the performance of the fiber-wireless links can be significantly improved when the optical signal is transmitted at the optimum CSR of 0 dB. The analysis further shows that the optimum optical CSR is independent of transmission bit rates.

Transmission improvement in fiber wireless links using fiber Bragg gratings

We demonstrate a simple, passive technique for significant improvement of transmission performance in fiber wireless links through the application of a narrow-band fiber Bragg grating. The grating is used to optimize the optical modulation depth in the transmitted signal by reducing the power of the optical carrier. We present experimental measurements that show improvements in receiver sensitivity (at bit-error rate =10/sup -9/) of up to 7 dB for both double- and single-sideband modulation schemes. The scheme is applicable to a wide range of radio frequencies and modulation depths.

Extending optical transmission distance in fiber wireless links using passive filtering in conjunction with optimized modulation

The authors demonstrate a simple passive technique for increasing the transmission distance in fiber wireless links through the application of a narrowband fiber Bragg grating (FBG) with high reflectivity (90-99%). They are applied in a conventional downstream link and also for the upstream in a wavelength-reused scheme. In the conventional nonwavelength-reused system, the grating is used to optimize the optical modulation depth and, hence, the receiver sensitivity in the downstream transmitted signal by reducing the power of the optical carrier before fiber transmission. In the wavelength-reused systems, the highly reflective FBGs can be effectively used at the base stations to recover a major portion of the optical carrier (as high as 99% of the downlink carrier) for uplink transmission from a weakly modulated downstream signal. In the latter case, the penalty in the downstream signal due to the large extraction of carrier power is partially offset by the sensitivity enhancement obtained in the filtering process. The authors present experimental results for the increased transmission performance for both the nonwavelength-reused and wavelength-reused scenarios. The increase in the sensitivity (at biterrorrate=10/sup -9/) in the nonwavelength-reused scheme for a given launch channel power that facilitates the increased transmission distance can be as large as 7 dB. The relative increase in the power margin for the upstream signal can be up to 4 dB in the wavelength-reused scheme. This would more than double the currently demonstrated transmission distances in such wavelength-reused systems without any optical amplification. The scheme is applicable to a wide range of radio frequencies and modulation depths.

On the merging of millimeter-wave fiber-radio backbone with 25-GHz WDM ring networks

We present an optical modulation and distribution scheme that incorporates subcarrier-multiplexed (SCM) transport with remote local oscillator (LO) delivery for a millimeter-wave (mm-wave) fiber-radio backbone driving a sectorized antenna interface. The proposed method is compatible with a standard wavelength-division multiplexing infrastructure with a 25-GHz channel spacing. We also characterize the profiles and bandwidths of the optical filters, which are essential for the adding and dropping of the 25-GHz signal block and the optical extraction of the LO signal. The placement of the LO signal within the 25-GHz band is investigated and its effect on the filter bandwidth requirements and system performance quantified. The performance of a ring incorporating the distribution scheme is evaluated via simulation. It is established that a compromise must be made between the feasibility of the required filters and the incurred penalty due to intermodulation distortions from adjacent blocks.

Improved Photonic Technique for Broadband Radio-Frequency Measurement

We propose a photonic technique for the measurement of frequency information in radar signal processing applications that has the potential to cover a frequency range of 40 GHz. This technique compares the radio-frequency power response functions generated within a low dispersion element of two complementary double sideband optical signals. The technique eliminates measurement ambiguities over the entire operating range along with reduced sensitivity to dispersion errors. The scheme is experimentally demonstrated over the frequency range of 4-19 GHz.

WDM-PON Architectures With a Single Shared Interferometric Filter for Carrier-Reuse Upstream Transmission

We propose two novel wavelength-division-multiplexed passive-optical-network (WDM-PON) architectures where subcarriers are employed to transmit downstream data and optical carriers are reused for upstream transmission. Architecture I is designed for the situation where two short distribution fibers are available between the remote node (RN) and each optical network unit (ONU), whereas Architecture II is devised for the case where there is only one distribution fiber between the RN and each ONU. Both architectures use only one interferometric filter located at the RN to simultaneously separate all downlink optical carriers and subcarriers, leading to a considerable cost reduction in the implementation of the WDM-PONs. Separated optical carriers are then reused and injected into reflective semiconductor optical amplifiers as the uplink light sources, which eliminates the necessity of specific wavelength sources at the ONUs. The downstream subcarrier signals are directly detected using baseband receivers. Two multichannel upstream and downstream transmission experiments are carried out at 1.25 Gb/s using the proposed schemes. The impact of optical carrier-to-subcarrier ratio of downlink signal, Rayleigh-backscattering noise, and wavelength mismatch between laser source and filter on system performance is also investigated.

Protection switching and local area network emulation in passive optical networks

This paper proposes and experimentally demonstrates an automatic-protection-switching (APS) mechanism against distribution fiber breaks in passive optical networks (PONs). The protection of optical-network units (ONUs) that are located at the customer premises is carried out by monitoring the distribution fiber using the traffic that is transported among the customers in the PON. This configuration emulates a local area network (LAN) over the existing PON while facilitating the switching of signal transmissions to a predetermined protection path in an event of a distribution fiber break. As failure detection and APS are performed independently by each ONU in a distributed manner, the processing complexities and delays are reduced at the central office (CO). The restoration of the traffic transported between the CO and an ONU in the event of the distribution fiber break is performed by interconnecting adjacent ONUs and carrying out signal transmissions via an independent but interconnected ONU. Such a protection mechanism enables multiple adjacent ONUs to be simultaneously protected by a single ONU utilizing its maximum available bandwidth. This paper experimentally verifies the feasibility of the proposed protection mechanism in conjunction with two different LAN-emulation schemes with a 1.25-Gb/s upstream baseband transmission to the CO and a 155-Mb/s LAN data transmission on a radio-frequency carrier. The experimental results obtained from both schemes are compared, and the power budgets are calculated to analyze the scalability of each scheme.

Novel schemes for local area network emulation in passive optical networks with RF subcarrier multiplexed customer traffic

This paper proposes two novel optical layer schemes for intercommunication between customers in a passive optical network (PON). The proposed schemes use radio frequency (RF) subcarrier multiplexed transmission for intercommunication between customers in conjunction with upstream access to the central office (CO) at baseband. One scheme employs a narrowband fiber Bragg grating (FBG) placed close to the star coupler in the feeder fiber of the PON, while the other uses an additional short-length distribution fiber from the star coupler to each customer unit for the redirection of customer traffic. In both schemes, only one optical transmitter is required at each optical network unit (ONU) for the transmission of customer traffic and upstream access traffic. Moreover, downstream bandwidth is not consumed by customer traffic unlike in previously reported techniques. The authors experimentally verify the feasibility of both schemes with 1.25 Gb/s upstream baseband transmission to the CO and 155 Mb/s customer data transmission on the RF carrier. The experimental results obtained from both schemes are compared, and the power budgets are calculated to analyze the scalability of each scheme. Further, the proposed schemes were discussed in terms of upgradability of the transmission bit rates for the upstream access traffic, bandwidth requirements at the customer premises, dispersion tolerance, and stability issues for the practical implementations of the network.

A novel local area network emulation technique on passive optical networks

An optical layer solution for intercommunication between customers in a passive optical network by placing a narrow-band fiber Bragg grating close to the star coupler in the feeder fiber is proposed. The local area network (LAN) emulation technique is experimentally demonstrated with 1.25-Gb/s upstream transmission to the central office and with 155 Mb/s customer data transmission that is multiplexed on a 5-GHz radio frequency carrier. Experimental results show that this technique has the potential to support high data rate LAN traffic while imposing minimal penalty on downstream and upstream transmissions.

WDM passive optical network with subcarrier transmission and baseband detection scheme for laser-free optical network units

We demonstrate a new scheme to achieve source-free optical network units (ONUs) in a wavelength-division-multiplexed passive optical network. The scheme utilizes subcarrier downlink transmission that enables penalty-free remodulation of the downstream signal for upstream transmission. The downstream data can be recovered at baseband either using an optical or electrical technique. In the optical scheme, the downstream signal is passed through a delay interferometer (DI) at the ONUs. A single variety of the DI is applicable to all ONUs that eliminates location-specific devices. Alternatively, the baseband data can be detected using a high-speed photodiode, a dc block, and a rectifier without any optical filter or phase locked loop for down-conversion. The upstream data is also detected at baseband without any modification to conventional receivers. We present experimental and simulation results for the scheme at 2-Gb/s downstream and upstream transmission over 20 km of fiber