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We have proposed and experimentally demonstrated a 6 × 40-Gb/s long reach dense wavelength division multiplexed passive optical network downlink system operating over 80 km of standard single mode fiber. The six optical channels with 20 GHz spacing are generated by an externally injected gain switched optical comb source. Each comb line is imposed with a 6-GBd polarization division multiplexed quadrature amplitude modulation, which included a 20% overhead for forward error correction. A worst case channel sensitivity of -35.6 dBm (54 photons/bit) at a bit error rate of 1.5×10-2 was achieved, yielding a system loss budget of 40 dB.

We report on a wavelength division multiplexed-orthogonal frequency division multiplexed-passive optical network (WDM-OFDM-PON), for downstream transmission, based on a tunable mode locked comb source. The 12.75 Gb/s compatible single side-band (SSB) OFDM signal is used to modulate 10 comb tones separated by 10 GHz. Net spectral efficiencies of 1.12 and 1 bit/s/Hz were achieved in conjunction with the use of low complexity electronics. Transmission over 50 and 87 km of standard single mode fiber was successfully demonstrated. The incurred penalty after transmission over 50 km was at a bit error rate (BER) of 3×10-3, relative to the back-to-back case. All channels after 87 km transmission achieved performance below the 20% forward error correction (FEC) limit.

Experimental and simulation work, presented in this letter, demonstrates for the first time how the monolithic integration of two single-mode lasers in a master-slave configuration, can substantially increase the achievable bit rate of a direct modulation adaptively modulated optical orthogonal frequency-division multiplexing (AMO-OFDM) system. The Levin-Campello algorithm is applied to select the OFDM bit and power loading scheme used for each system configuration. Improvement in terms of data throughput due to injection is measured for several transmission distances with the improvement in performance presented in terms of error vector magnitude per OFDM subcarrier.

This letter describes a dynamic linewidth characterization method using an optical quadrature front end. The phase noise of the laser is recorded using a real-time oscilloscope in the time domain and the linewidth of the laser can be estimated statistically offline. The major advantage of this technique compared with conventional linewidth measurements in the frequency domain, is that this method enables the dynamic phase noise characterization which is increasingly important for fast wavelength tunable and switched networks employing advanced modulation formats. The dynamic linewidth of an sampled grating distributed Bragg reflector (SG-DBR) laser is characterized by using this method.

We propose and experimentally demonstrate a novel technique for optical generation of modulated millimeter-wave (mm-wave) by using a gain switched laser (GSL) that is externally injected with a modulated light source. The GSL generates a stream of optical pulses, and these pulses exhibit a small shift in the time domain when the GSL is injected with an on-off keyed (OOK) optical data signal. This time shift can produce a phase modulated mm-wave signal at 60 GHz by suitable optical filtering of the GSL laser output. The system performance was analyzed for data streams at 1.25 Gb/s by using bit-error-rate (BER) measurements for back-to-back (BTB) and 3-km fiber transmission.

A two-photon absorption microcavity-based technique for monitoring in-band optical signal-to-noise ratio (OSNR) in nonreturn-to-zero phase-shift-keying systems is presented. Experiments using a 10-Gb/s differential phase-shift-keying system showed that accurate measurements (±1 dB) were possible for OSNRs in excess of 20 dB.

The authors demonstrate a compensation scheme to reduce the frequency chirp associated with directly modulated sampled grating distributed Bragg reflector tunable lasers. Experimental results obtained show that the direct modulation of the laser's gain section results in a large frequency chirp of 25 GHz. However, by simultaneous modulation of the laser's phase section this large frequency chirp can be significantly reduced.

The authors demonstrate the drift in frequency of a static sampled-grating distributed Bragg reflector (SG DBR) laser module when it is subjected to direct modulation. The magnitude of drift and its settling time is characterized as a function of the index of modulation. Results show that when the directly modulated SG DBR is optically filtered, as in a dense wavelength- division- multiplexed system, a power penalty of 6.7 dB is incurred in comparison to the unfiltered case.

We propose a novel method that allows continuous repetition rate tuning of a self-seeded gain-switched Fabry-Perot laser without the need for change in cavity length. This is achieved by employing a linearly chirped fiber Bragg grating with a large dispersion parameter. The dispersed pulses overlap to produce a continuous-wave-like feedback into the gain-switched laser cavity. By using the proposed experimental setup, we demonstrate pulses portraying sidemode suppression ratios of at least 30 dB and widths of about 30 ps over the entire repetition rate tuning range of 2.5-10 GHz.

peer-reviewed The authors investigate the propagation of picosecond pulses through semiconductor optical amplifiers using the measurement technique of frequency resolved optical gating. The work shows the generation of significant pulse pedestals and frequency chirp across the optical pulses, which initially have a duration of 2 ps. As the input peak power of the optical pulses is increased from 2.4 to 80 mW, the pulse pedestals increased by 20 dB and the chirp became significantly more nonlinear. The generated pedestals and the nonlinear output chirp may cause serious degradation in high-speed communications systems employing wavelength-division-multiplexing and optical time-division-multiplexing techniques.

The authors demonstrate the generation of short optical pulses, which display spectral sidemode suppression ratio, and temporal pedestal suppression ratio, well in excess of 30 dB. The exceptional spectral and temporal characteristics exhibited by these pulses are attained by employing a novel technology, based on an externally injected gain-switched laser in conjunction with a nonlinearly chirped grating. Using this technique, near transform limited 7-ps optical pulses, exhibiting a time bandwidth product of 0.49, are generated.

The authors demonstrate a procedure of generating picosecond optical pulses that are tunable over a wide wavelength range (65 nm) and have very high spectral purity side-mode suppression ratio [(SMSR)>60 dB]. The large tuning range is obtained by employing external injection into a gain-switched source containing two Fabry-Pe/spl acute/rot lasers. The use of a widely tunable Bragg grating at the output improves the SMSR such that it exceeds 60 dB over the entire tuning range.

A radio over fiber distribution system incorporating both sub-carrier multiplexing (SCM) and wavelength division multiplexing (WDM) technologies is presented. The SCM signal contains five 155-Mbit/s data channels, centered around 18.5 GHz with 450 MHz spacing. This signal is directly modulated onto three high-speed lasers with emission frequencies spaced by 50 GHz. Bragg filters are employed at the receiver base-station in order to both demultiplex the required optical channel and ensure that the detected signal is single sideband (in order to overcome dispersion limitations on the link). Our results show negligible degradation in system performance for the demultiplexing of the WDM signal compared with the back-to-back performance curves.

The authors demonstrate the generation of nearly transform-limited optical pulses that are wavelength tunable over almost 50 nm. The wide tuning range is obtained by self-seeding a gain-switched source containing two Fabry-Perot lasers, and employing a widely tunable Bragg grating in the feedback loop. The generated pulses exhibit Side-mode suppression ratios of 50 dB above and across the full tuning range.

A self-pulsating laser is used to generate a multicarrier (five radio frequency (RF) channels) microwave optical signal for use in a hybrid radio/fiber system. The self-pulsation is achieved by external light injection into the laser diode. By varying the RF channel spacing, we have been able to estimate the degradation in system performance due to intermodulation distortion (caused by the nonlinear dynamic response of the laser). The power penalty on the central RF channel is found to be 3.2 dB for operation at the RF band around the laser self-pulsation frequency of 18.5 GHz. We have also characterized the performance of the multicarrier hybrid radio/fiber system in the frequency band corresponding to the inherent relaxation frequency of the laser.

Bit-error-rate measurements have been carried out on a four-channel wavelength division multiplexed setup using tunable self-seeded gain-switched pulse sources. These measurements demonstrate the degradation in overall system performance, due to mode partition noise, as the sidemode suppression ratio of the self-seeded gain-switched optical pulse sources is reduced. The results also show that the constraints on the minimum sidemode suppression ratio required increase with the number of channels in the system.

We demonstrate that by using strong external-injection seeding of gain-switched Fabry-Perot (FP) lasers, it is possible to generate optical pulses at repetition rates far in excess of the laser bandwidth. Experimental results illustrate the generation of optical pulses at frequencies up to 20 GHz from a FP laser with a 3-dB bandwidth of only 8 GHz. The optical pulses generated have a duration around 12 ps, and a spectral width of 40 GHz.