Abstract: A narrow linewidth semiconductor laser device has a semiconductor laser and a low noise current source operatively connected to the laser with the current source being adapted to prevent degradation of the laser's frequency noise spectrum. An optical frequency discriminator provides an error signal representative of the laser's optical frequency and a control circuit has a feedback network that provides a frequency feedback signal that is adapted to the frequency noise spectrum of the frequency discriminator and to the laser's frequency noise spectrum and tuning response. The control circuit also has a sequencer to automatically enable frequency locking of the laser on the frequency reference of the optical frequency discriminator. An enclosure encloses the frequency discriminator to isolate the frequency discriminator from external perturbations.

Abstract: There is provided a narrow linewidth semiconductor laser device comprising a semiconductor laser and a low noise current source operatively connected to the laser for supplying current thereto, the current source being particularly adapted to prevent a significant degradation of the frequency noise spectrum of the laser. The laser device also has an optical frequency discriminator providing an error signal representative of the optical frequency of the laser. The laser device also has control means having a feedback network for providing a frequency feedback signal. The feedback network is particularly adapted to the frequency noise spectrum of the frequency discriminator, the frequency noise spectrum of the laser and the tuning response of the laser. The control means is also provided with sequencing means for allowing to automatically enable frequency locking of the laser on the frequency reference of the optical frequency discriminator.

Abstract: An athermally packaged optical fiber device, such as a Bragg grating, is provided. The device includes a hollow structure, and a free and a threaded member projecting in the hollow structure from both ends. The optical fiber is mounted in tension inside the hollow structure through longitudinal fiber-receiving bores in both members, and has an anchor point affixed to each member with the grating therebetween. The anchor point of the threaded member is provided outside of the hollow structure, making the device more compact. The free and threaded members are rotatable together to adjust the resonant wavelength of the grating, and a nut may be provided to allow a fine-tuning. The hollow structure, free member and threaded member have a coefficient of thermal expansion selected so that they together compensate for the temperature dependency of the Bragg wavelength.

Abstract: The invention is the novel use of dispersion compensation in a long haul wavelength division multiplexed high capacity optical transport system which has very many channels packed extremely closely together, in order to greatly reduce the deleterious effects of four-wave mixing. Four-wave mixing is an exchange of energy between nominally independent channels, arising from the fundamental fibre non-linearity, which has the effect of degrading transmission quality. Conventional systems make use of fibre dispersion compensating modules to overcome the effects of fibre dispersion. In such systems, it has been discovered that the exact distribution of fibre dispersion along the optical link (the ‘dispersion map’) strongly influences the degree of four-wave mixing, and hence the degradation in transmission quality.

Abstract: An athermally packaged optical fiber device, such as a Bragg grating, is provided. The device includes a hollow structure, and a free and a threaded member projecting in the hollow structure from both ends. The optical fiber is mounted in tension inside the hollow structure through longitudinal fiber-receiving bores in both members, and has an anchor point affixed to each member with the grating therebetween. The anchor point of the threaded member is provided outside of the hollow structure, making the device more compact. The free and threaded members are rotatable together to adjust the resonant wavelength of the grating, and a nut may be provided to allow a fine-tuning. The hollow structure, free member and threaded member have a coefficient of thermal expansion selected so that they together compensate for the temperature dependency of the Bragg wavelength.

Abstract: A method and an apparatus to photoinduce a grating or other type of modulated refractive index change in a photosensitive optical medium such as optical fiber. The resulting grating has a variable and controllable intensity profile and average value of the index change. The modulated refractive index change is photoimprinted in the medium in a series of writing steps, each comprising exposing a segment of the medium to a writing beam for a predetermined exposure time. To change the modulation intensity from step to step, the angle of incidence of the writing beam is dithered for an appropriate fraction of the exposure time at each step. This allows to control the amount of incident light on the medium for each step. If the exposure time is the same for each writing step, the average value of the index change may be kept constant avoiding undesired structure in the grating frequency response.

Abstract: The amplifier is a two-stage amplifier in which dispersion compensation and WDM channel equalization are carried out using a plurality of in-waveguide Bragg gratings placed between the two stages. The first stage has a gain able to raise the intensity of WDM optical communications signals to a high enough level that after dispersion compensation and equalization, the signals fed into the second stage nearly or substantially saturate the second stage amplifier. The noise figure signal-to-noise ratio is thereby of good quality since there are no significant losses at the signal input of the signal into the optical amplifier. Erbium-doped optically pumped fiber amplifiers are used for the two stages. An add/drop filter can be appended to the end of the conditioning Bragg gratings. Residual optical signal from the fiber Bragg grating may be used to optically pump another amplifier for amplifying longer wavelength optical signals.