Km Of Single-mode Fiber Research Articles

Signal-induced noise in fiber-optic links using directly modulated Fabry-Perot and distributed-feedback laser diodes

A quantitative comparison has been made, both theoretically and experimentally, of signal-induced noise in high-frequency, single-mode fiber-optic links using directly modulated multimode (Fabry-Perot) and single-frequency (distributed-feedback, DFB) lasers. It is shown that the common procedure of evaluating the signal-to-noise (S/N) performance in a typical fiber-optic link by treating the various sources of noise as additive quantities that are independent of the modulation signal is inadequate. This is due to the presence of signal-induced noise, which concentrates at low frequencies, so that a casual observation might lead to the erroneous conclusion that it is of no relevance to high-frequency transmission systems. It is shown that, for Fabry-Perot lasers, signal-induced noise arising from translation of low-frequency noise to high frequencies causes significant degradation in S/N performance in transmission of 6-GHz signals over only 1 km of single-mode fiber. With DFB lasers, signal-induced noise due to interferometric phase arrow intensity conversion is present, but does not become significant even for transmission at 10 GHz up to 20 km.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Broadband dispersion compensation by using the higher-order spatial mode in a two-mode fiber

A fiber-optic technique for compensating both first- and second-order group-velocity dispersion in single-mode fiber spans is demonstrated by using the large waveguide dispersion that occurs for the higher-order (LP11) spatial mode in a two-mode fiber near cutoff. Complete restoration of 7-ps pulses that had been dispersed by a factor of 10 in 5 km of single-mode fiber is demonstrated over a 20-nm-wavelength window. First-order dispersion as large as −228 ps/(nm km) is observed for the LP11 mode at 1560 nm in the two-mode fiber.

8-Gb/s-130 km transmission experiment using Er-doped fiber preamplifier and optical dispersion equalization

The authors report an 8-Gb/s lightwave transmission system operating at 1.53- mu m wavelength through 130 km of single-mode fiber having a chromatic dispersion of zero at 1.3- mu m wavelength. A receiver sensitivity of -34.2 dBm (365 photons/bit) was achieved using an erbium-doped fiber preamplifier pumped at 980-nm wavelength. A sensitivity of -31.9 dBm (620 photons/bit) was reached by a preamplifier pumped at a 1480-nm wavelength. By employing a Ti:LiNbO/sub 3/ external modulator and a fiber Gires-Tournois interferometer to equalize fiber chromatic dispersion, the penalty for 130 km transmission was held to only 0.9 dB. >

Polarisation-insensitive optical coherent SCM system using mixed lightwave transmission of signal and local laser light

An optical coherent transmission and distribution system using subcarrier multiplexing (SCM) techniques is proposed in which the local LD is set in the transmitter and the signal and local light are mixed before transmission. The feasibility of the system was experimentally confirmed, using three-electrode DFB-LDs, with an optical FM by two-channel 560 Mbit/s ASK-SCM signal and a heterodyne transmission through 25.7 km of single mode fibre. This system was insensitive to the state of polarisation in the transmission fibre. It was shown that more than 1000 subscribers could be served with Er3+-doped fibre amplifiers.

Optical FM and heterodyne detection of 2-channel 560 Mbit/s subcarrier multiplexed ASK signal using 3-electrode DFB-LDs

An optical carrier was frequency-modulated by directly modulating a three-electrode DFB laser diode using two-channel 560 Mbit/s subcarrier multiplexed ASK signals, and was transmitted through 122•3 km of single-mode fibre. Both channels were heterodyne-detected and selected simultaneously by a bandpass filter. A receiver sensitivity of −32•4 dBm was obtained and a crosstalk penalty was less than 0•8 dB with channel spacing of 1•8 GHz

An FDDI overview: Some questions answered

The Fiber Distributed Data Interface, a standard specially designed for use with fiber optic media, is based on the X3T9.5 ANSI standard. The FDDI network uses a dual counter rotating ring topology which guarantees reliability, availability, and security. Transmitting over fiber optic media, FDDI provides a throughput of 100 Mb/s and allows a large distance between the two nodes; up to 12 km in multimode fibers and 20 km in single mode fiber. FDDI allows backbone applications where computers and workstations connected to medium speed LANs can exchange data with other LANs or LAN segments in an FDDI extended network configuration. FDDI allows also back-end and front-end applications. Bridging methods such as encapsulation, translation, etc. are currently valid, and must be used for specific applications that need the corresponding technique. Today's FDDI prices will be dramatically reduced within the coming years by a factor of 20–30% per year.

560 Mb/s optical PSK synchronous heterodyne experiment

A phase-locked optical heterodyne receiver constructed using a 1320-nm diode-pumped miniature Nd:YAG ring laser is discussed. Using this receiver and a transmitter based on another Nd:YAG laser, a 560-Mb/s phase-shift keying (PSK) synchronous heterodyne transmission was demonstrated over 78 km of single-mode fiber. With an optical phase-locked loop (PLL) natural frequency of 32 kHz and a damping factor of 1.46, the receiver sensitivity, measured at the output of the transmission link, was -48.7 dBm, or 159 photons/b. The corresponding detected sensitivity, measured on the surface of the p-i-n diode, was -51.8 dBm or 78 photons/b. This result suggests that the receiver sensitivity would have been about 82 photons/b if a balanced receiver with 0.2-dB excess coupler loss had been used. The impact of the finite intermediate frequency (IF) on heterodyne system performance was investigated; it was found that an IF of at least twice the bit rate is needed for a negligibly small penalty.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An optical PSK homodyne transmission experiment using 1320 nm diode-pumped Nd:YAG lasers

A second-order optical phase-locked loop was constructed using 1320-nm diode-pumped miniature Nd:YAG ring lasers. Using the loop, a 140-Mb/s PSK homodyne transmission experiment was demonstrated over 28.6 km of single-mode fiber. With a loop natural frequency of 13 kHz and a damping factor of 0.6, the receiver sensitivity was -62.8 dBm, or 25 photons/bit. The authors believe this is the highest sensitivity obtained to date with any optical communication system. >

5 Gbit/s, 233 km optical fiber transmission experiment employing five semiconductor laser amplifiers

A directly modulated 1.519- mu m distributed-feedback laser signal was transmitted over 233 km of single-mode fiber consisting of dispersion shifted fiber and conventional step-index fiber to minimize the dispersion penalty. The power penalty after the transmission was 0.25 dB. The results show the effectiveness of an optical amplifier repeater system for high-speed long-haul fiber optic transmission.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical time-division multiplexed transmission at 8 Gbit/s using single laser and semiconductor optical power amplifier

We report transmission over 57 km of single-mode fibre in a two-channel, 8 Gbit/s optical time-division multiplexed system experiment using a transmitter with a single laser and a semiconductor optical power amplifier at the transmitter output. The amplifier operates with a net gain of 11.5 dB, which corresponds to 0.8 dB gain compression, and a fibre coupled output power of +6 dBm. The amplifier facet output power for which the gain is compressed by 3 dB is +13 dBm. The experimental system uses neither an isolator nor an optical filter.

Wavelength-tunable 16 optical channel transmission experiment at 2 Gbit/s and 600 Mbit/s for broadband subscriber distribution

We report a 16 optical-channel single-mode fibre transmission experiment based on dense-WDM and tunable-etalon channel selection. Experiments at 2 Gbit/s and 600 Mbit/s over 10 km of single-mode fibre show little crosstalk penalty when the optical channel spacing is 2 nm. The system architecture is useful for high-capacity broadband subscriber distribution.

Multigigabit-per-second optical baseband transmission system

Optical transmission baseband technology for multigigabit-per-second transmission is discussed. It is shown that a laser diode direct modulation scheme for multigigabit-per-second transmission is an extremely efficient approach to transform limited pulse transmission. The return to zero (RZ) format is effective for this approach. By the application of multigigabit-per-second monolithic IC technology, an 8-Gb/s optical regenerator and transmission experiment was successfully conducted through dispersive fiber. The experiment suggests that there is no degradation of transmission characteristics through more than 100 km of single-mode fiber within the wavelength region between zero and weak normal dispersion. >

WDM experiment using 1300/1500 nm dual-wavelength LED for single-mode fibre transmission systems

A wavelength-division-multiplexing transmission experiment using a 1300/1500 nm dual-wavelength LED modulated at 140/560 Mbit/s over 10 km of single-mode fibre has been demonstrated. This dual-LED device has a 9 μm emitter spacing between the active facets with a coupling loss of 2.3 dB through a lens/fibre coupler. The chromatic dispersion penalty for the 1500 nm channel at 560 Mbit/s was about 6-5 dB and the electrical crosstalk penalty was 2.5 dB.

60-channel FM video subcarrier multiplexed optical communication system

A subcarrier multiplexed (SCM) optical communication system is described which transmits 60 frequency-modulated (FM) video channels over 18 km of single-mode fibre with a 56 dB weighted signal/noise ratio.

Optical time-division multiplexed transmission system experiment at 8 Gbit/s

We describe the design and performance of an experimental two-channel optical time-division multiplexed fibre transmission system operating at a wavelength of 1.3 μm and a bit rate of 8 Gbit/s. Transmission over 8 km of single-mode fibre with low crosstalk and transmission error rates as low as 10 -10 is demonstrated.

Transmission at 1 Gbit/s over 7.4 km of single-mode fibre using an edge-emitting LED and PINFET receiver

Transmission at 1 Gbit/s over 7.4 km of 1300 nm optimised single-mode fibre has been demonstrated using a standard, 1300 nm edge-emitting LED with 150 MHz 3 dB bandwidth and a PINFET receiver. Computer simulation was used to accurately assess each of the system degradations: LED rise/fall, extinction ratio, dispersion penalty and receiver noise.

FSK heterodyne transmission experiments at 560 Mbit/s and 1 Gbit/s

Optical frequency-shift-keying (FSK) signals are obtained from directly modulated distributed feedback (DFB) semiconductor lasers. Experimental studies of the direct frequency modulation (FM) characteristics of the DFB lasers show a nonuniform FM response due to the competing effects of thermal modulation of the laser active region and carrier density modulation. Equalization of the signal current to the laser is employed to produce a flat FM response from 30 kHz to 1 GHz. Optical FSK transmission and heterodyne detection experiments at 560-Mbit/s and 1-Gbit/s are conducted at a wavelength of 1497 nm. Receiver sensitivities of -39 dBm at 560 Mbit/s and -37 dBm at 1 Gbit/s are obtained. Transmission through 100 km of single-mode fiber at 1 Gbit/s is achieved with no degradation in receiver sensitivity.

A 2-Gbit/s optical FSK heterodyne transmission experiment using a 1520-nm DFB laser transmitter

Optical FSK transmission at 2 Gbit/s using a directly modulated DFB laser at 1520-nm wavelength is reported. A receiver sensitivity of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\bar{P} = -36.7</tex> dBm ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\eta\bar{P} = -39.2</tex> dBm) at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> BER was achieved for transmission over 101 km of single-mode fiber with no additional penalty attributable to the fiber. The effect of the nonlinear phase of the transmitter FM response, and the system performance for discriminator demodulation, including the impact of laser phase noise, is analyzed and compared with experimental results.

Polarisation-dependent gain spectrum of a 1.5 μm travelling-wave optical amplifier

We present high-resolution gain spectra measurements of a 1.5 μm near-travelling-wave amplifier for both TE and TM polarisation. We use 49km of single-mode fibre at the amplifier input to demonstrate a reduction in the effective bandwidth of the amplifier caused by a combination of dichroism in the amplifier and the polarisation dispersion present in long lengths of fibre.

Ge0.6Si0.4 rib waveguide avalanche photodetectors for 1.3 μm operation

Performance of strained-layer superlattice Ge0.6Si0.4 waveguide avalanche photodetectors is evaluated for optical fiber applications at 1.3 μm. These devices are grown on Si substrates by molecular beam epitaxy. Waveguiding is accomplished by means of a 1.5–1.8-μm-thick Si rib waveguide which provides an effective index step of δn=8×10−3. The detector response bandwidth exceeds 8 GHz at a gain of 6. A receiver sensitivity of ηP̄=−29.4 dBm has been obtained at the data rate of 800 Mb/s with the corresponding error-free transmission over 45 km of single mode fiber.