George T. Harvey

Harmonically mode-locked fiber ring laser with an internal Fabry–Perot stabilizer for soliton transmission

We describe a modulator-driven, erbium-fiber ring laser that produces chirp-free pulses with width adjustable over the range of 5 to 100 ps. A high-finesse Fabry-Perot étalon with a free spectral range equal to the 2.5-GHz laser repetition rate eliminates unwanted laser ring modes and stabilizes the pulse amplitude. Using this laser, we have extended the error-free distance of a series of soliton transmission experiments by 2000-3000 km over previous results with a mode-locked semiconductor laser.

Timing-jitter stabilization of a colliding-pulse mode-locked laser by active control of the cavity length

Colliding-pulse mode-locked lasers are an excellent source of ultrashort pulses but exhibit timing jitter that can seriously degrade the temporal resolution in experiments that require synchronization to an external source. We describe a method that synchronizes the colliding-pulse mode-locked laser to a high-stability external oscillator by actively controlling the cavity length of the laser and reduces the absolute timing jitter from ~25 ps rms to only 1.7 ps over the 1-kHz bandwidth, which contains most of the laser phase noise. By using this method, the repetition rate of the laser pulses is held constant at 100 MHz.

First dispersion-flattened transpacific undersea system: from design to terabit/s field trial

The 8991-km-long transpacific segment of the Tyco Global Network (TGN) [TGN is a trademark of Tyco Telecommunications, Eatontown, NJ 07724 USA], connecting Hillsboro, Oregon, USA to Toyohashi, Japan, is the first installed dispersion-flattened dense wavelength division multiplexed (DWDM) system. In this paper, we describe the development path bringing this system from the computer design stage to a field trial, which confirms that the installed segment can support the design capacity of 96/spl times/10 Gb/s customer channels per fiber pair. Commercial channels have been provisioned on this segment with satisfactory system margins. Exploratory transmission results at 128/spl times/12.3 Gb/s over this segment are also reported here. The experimental results agree well with our expectations based on the results from our system design simulator.

Timing jitter and pump-induced amplitude modulation in the colliding-pulse mode-locked (CPM) laser

The timing jitter and spurious amplitude modulation of colliding-pulse mode-locked (CPM) lasers were measured. The absolute jitter (the jitter of the laser alone) varied between 5 and 10 ps RMS in a 50-500-Hz bandwidth. The smallest measured relative jitter (timing fluctuations between the CPM and a radio-frequency (RF) synthesizer synchronized to the CPM) was 1.8 ps RMS in a 2-Hz to 1-kHz bandwidth. Separate from the jitter, spurious modulation in the CW pump laser mixes with the CPM pulse train to produce a set of discrete amplitude-modulated sidebands in the power spectrum of the CPM output. The frequencies of these sidebands change with cavity length, and the sidebands can be eliminated by operating the pump laser in a single longitudinal mode. >

A four-channel lightwave subsystem using wavelength division multiplexing

A four-channel multimode transmission subsystem employing wavelength division multiplexing (WDM) was assembled and optically evaluated. Diffraction grating devices with identical fibers for inputs and outputs were used for both multiplexing and demultiplexing. The 1-dB full width of the passbands was ∼4 nm thus there was a requirement for wavelength selection and temperature tuning of the corresponding laser sources. A temperature excursion of 7°C from the optimum resulted in 1 dB of additional attenuation. Insertion losses for the multiplexer/demultiplexer (Mux/Demux) pair were 3.7, 3.6, 4.7, and 7.3 dB at 812, 830, 867, and 885 nm, respectively. The higher losses at 867 and 885 nm were due to chromatic abberation. The channel spacing of 18 nm is smaller than could be achieved with state-of-the-art filter devices. For unidirectional transmission the out of band rejection exceeded 40 dB in all channels.

Electro‐optic sampling of high‐speed silicon integrated circuits using a GaAs probe tip

Electro‐optic sampling is performed on a high‐speed silicon multiplexer integrated circuit using a gain‐switched semiconductor laser and an external probe tip fabricated from GaAs. An approximate electrostatic model is used to calculate the dependence of the electro‐optic modulation on the height of the probe tip above the circuit, the geometry of the circuit, and the dielectric constants of the probe tip material and the passivation layer (if any) on the circuit. The measured variation of the electro‐optic modulation with probe tip height is in good agreement with the prediction of the model.

Amplitude noise reduction of 50 dB in colliding-pulse mode-locking dye lasers

Spurious sidebands observed in the noise spectrum of colliding-pulse mode-locking dye lasers result from coupling of the longitudinal mode beating modulations of the (argon-ion) pump laser with the dye laser. We achieve a 50-dB amplitude noise reduction at the mixing frequencies by inserting a single-frequency étalon in the argon-laser cavity. Furthermore, we find the amplitude noise of the colliding-pulse mode-locking laser to be entirely dominated by the (plasma discharge) noise of the argon laser.

Guest Editorial Special Issue on the Optical Fiber Communications Conference (OFC 2005)

The twenty-eight papers in this special section were presented at the 2005 Optical Fiber Communications Conference held in Anaheim, CA, in March 2005.

Special Issue on the Optical Fiber Communications Conference/National Fiber Optic Engineers Conference (OFC/NFOEC 2007)

The 26 papers in this special issue represent a broad overview of advances in the science and technology of optical communications.

Performance tests of angled fiber 3 dB couplers made with drawn silica substrates

A report is presented on a series of tests performed on angled-fiber-type optical couplers fabricated with drawn silica substrates. The couplers use a multilayer dielectric coating, applied directly on an angled fiber interface. Measured performance of the device shows an average near-end crosstalk of -48 and an excess of 0.46 dB. The use of an all silica design for the substrate holding the fiber results in good environmental performance. The simple design and compact nature of the coupler lend themselves to the economical replacement of separate splitters and detectors in single-mode bidirectional systems. >