Richard Gross

Multichannel coherent FSK experiments using subcarrier multiplexing techniques

The results for coherent digital subcarrier multiplexed (SCM) lightwave system experiments are described. A total of 20 frequency-shift-keyed (FSK) channels at 100 Mb/s each were transmitted on one optical carrier using microwave subcarriers in a multioctave configuration. A complete description of the system performance, including carrier-to-noise ratio, crosstalk, intermodulation distortion, and receiver sensitivity, is given. With a phase modulation index of beta =0.13, a receiver sensitivity of -27 dBm was obtained, representing a 14-dB improvement over a 20-channel direct detection SCM system. Crosstalk due to adjacent channels is negligible with a channel spacing of twice the data rate (200 MHz). Theoretical and experimental results are compared, and conditions for optimal performance as a function of channel number and phase modulation index are discussed. >

Subcarrier multiplexed coherent lightwave systems for video distribution

The application of subcarrier multiplexing techniques to coherent lightwave systems designed for video transmission is described. The theory of the intrinsic receiver sensitivity of multichannel coherent SCM (subcarrier multiplexing) systems is presented. Specific implementations of SCM coherent systems transmitting 60 FM video channels and 20 100 Mb/s FSK (frequency shift keying) channels are described. It is shown that a simple phase noise canceling circuit can be implemented, which allows these systems to be built with wide-linewidth DFB (distributed feedback) lasers. Several applications of multichannel coherent SCM systems to video distribution networks are proposed. >

Coherent FM-SCM system using DFB lasers and a phase noise cancellation circuit

A multichannel coherent subcarrier multiplexing (SCM) system using standard distributed-feedback lasers is discussed. A simple phase noise canceling circuit yields excellent quality FM video transmission (SNR=56 dB), even though the 50-MHz IF linewidth exceeds the 30-MHz signal bandwidth.<<ETX>>

Optical DQPSK video system with heterodyne detection

An optical heterodyne subcarrier-multiplexed (SCM) quadrature-phase-shift keying (QPSK) system is described that employs differential encoding to transmit multiple video channels. With this differential encoding scheme, only a simple delay-and-multiply demodulator is necessary, considerably reducing the signal processing complexity. The demodulators reproduce the data in a parallel fashion so no baseband demultiplexing or four-level decision circuit is required. This approach also avoids the complications of implementing a carrier recovery circuit (CRC) and a phase-locked loop associated with coherent microwave demodulation schemes. In addition to bandwidth efficiency and simplicity, differential QPSK also provides very good receiver sensitivity. With heterodyne detection, a receiver sensitivity of -41 dBm is achieved.<<ETX>>

Subcarrier multiplexed broad-band service network: a flexible platform for broad-band subscriber services

The concept of the subcarrier multiplexed broadband service network (SCM-BSN) has been developed in response to the need to provide low-cost integrated broad-band services in the local loop. The SCM-BSN architecture incorporates three elements which have been identified over the past few years as key cost-saving features: passive optical splitting, fiber-to-the-curb, and subcarrier multiplexing of video signals. This paper introduces the SCM-BSN concept, describes a prototype system that has been built at GTE Laboratories, and describes some possible evolutionary scenarios to integrated digital services. While the SCM-BSN prototype system has been designed to provide voice, data, and switched video services using FM-video modulation, the BSN design has been structured to provide for a graceful evolution to other broad-band services including HDTV, digital video, and integrated broad-band services based on ATM transmission. Because of its potentially low-cost and flexibility, SCM-BSN is attractive for local loop services.

Characteristics of a compact three cavity laser configuration

Experimental and theoretical results on the characteristics of a compact three cavity transmitter configuration are presented. The configuration consists of a 1.3-μm semiconductor laser with external resonators on each side. One resonator is a spherical reflector positioned at the rear facet for sidemode suppression to about 30 dB. The other resonator at the front facet is a semitransparently gold coated grin-rod lens for linewidth reduction to about 1 MHz. The whole configuration has a length of less than 2 cm.

20 channel coherent FSK system using subcarrier multiplexing

A 20-channel multioctave coherent frequency shift keying (FSK) system using subcarrier multiplexing techniques is described. The microwave subcarriers range from 2.1 to 5.9 GHz with a 200-MHz channel spacing. The receiver consists of a p-i-n photodiode, electrical isolator, low-noise amplifier, and bandpass filter to provide channel selection. The channels are modulated at 100 Mb/s, corresponding to one digitized video channel. Results for the optimal phase modulation index and degradation due to second- and third-order intermodulation distortion are discussed. For the worst-case channel, a receiver sensitivity of -27 dBm was achieved.<<ETX>>

Five-channel coherent heterodyne subcarrier multiplexed system

Results of a coherent digital-subcarrier multiplexed (SCM) lightwave system are described. Five frequency-shift-keyed channels at 100 Mb/s each were transmitted using microwave subcarriers. With a phase modulation index of beta =0.19, a bit error rate of 10/sup -9/ was achieved with a detected optical power of -33 dBm. This is a 14-dB improvement in receiver sensitivity over a comparable direct-detection SCM system.<<ETX>>

Heterodyne video distribution systems sharing transmitter and local oscillator lasers

The authors present theoretical and experimental results for coherent subcarrier multiplexed (SCM) systems using a novel architecture that shares both the transmitter and local oscillator (LO) laser among multiple optoelectronic receivers. The ability to share both lasers significantly reduces the cost and complexity compared to a multichannel coherent frequency division multiplexed (FDM) system. Experimental results confirm that the system performance can be greatly enhanced by inserting an inline optical amplifier so that many receivers can share one transmitter and LO laser. For example, with an amplifier chip gain of 24 dB, increasing the optical power at the input to the amplifier by 3 dB from -27.6 to -24.5 dBm, the number of receivers can be increased from 2 to 32. >

Coherent transmission of 60 FM-SCM video channels

A fiber-optic 60-channel FM video system using coherent subcarrier multiplexing (SCM) is described. Two receiver implementations were studied. For the 60-channel coherent experiment, a carrier-to-noise ratio of 17 dB and a corresponding signal-to-noise ratio of 56 db was achieved with a detected optical power of -32 dBm and a phase modulation index of beta -0.07. This represents a 15.2-dB improvement over a similar 60-channel direct-detection FM-SCM system and a 5.6 dB improvement compared to the performance of the system when a semiconductor optical preamplifier was used.<<ETX>>