Abstract: A split-band amplifying apparatus that has a first section for amplifying a long wavelength band of an optical signal and a second section equipped with a fiber amplifier for amplifying a short wavelength band of the optical signal. The fiber amplifier in the second section uses a short-pass fiber with a depressed cladding cross-section and core doped with an active material, e.g., Erbium, and pumped to a high relative inversion D. The split-band amplifying apparatus can be used to amplify signals whose short wavelength band includes at least a portion of the S-band and whose long wavelength band includes at least a portion of the C- and/or L-band.

Abstract: A frequency-converted laser may be made with a non-linear material having a surface coated with an anti-reflection coating by measuring an absorbance of the anti-refection coating, and using the non-linear crystal for frequency conversion in the laser if the absorbance measured is less than a rejection threshold of about 100 parts-per-million or less.

Abstract: Methods and apparatus for managing thermal loads on a laser gain medium and for boosting the output power of a diode pumped laser are disclosed. The short-term average pumping power to the gain medium is increased, to provide a burst of pumping energy to the laser gain medium. A subsequent short-term reduction in the average pumping power then allows the gain medium to cool to a desired state steady level. The average pumping power is then increased to maintain this steady state level until the next burst is desired. For example, a pulse of current may be applied to a laser diode at a first current level I1 for a first time interval ?t1, where I1 exceeds a nominal current value Inom by an amount ?I1. The current to the laser diode is reduced to a second current level I2 for a second time interval ?t2, where Inom exceeds I2 by an amount ?I2. To balance the thermal load on the diode an integral of ?I1 over the time ?t1 is approximately equal in magnitude to an integral of ?I2 over the time ?t2.

Abstract: A fiber amplifier in which the active core is surrounded by a cladding and coupling of radiation between a core mode and cladding modes is suppressed to minimize cladding mode losses in a short wavelength range. An index profile is established in the active core and in the cladding such that the core exhibits a loss above a cutoff wavelength ?c and positive gains in the short wavelength range below the cutoff wavelength ?c. Suppression of cladding mode losses is achieved by an arrangement for suppressing the coupling of radiation in the short wavelength range between a core mode supported the active core and a cladding mode supported by the cladding. The arrangement for suppressing can include an absorbing material or a scattering material distributed in the cladding. The arrangement for suppressing can include a non-phase-matched length section of the fiber amplifier in which the core mode and the cladding modes are not phase matched.

Abstract: A fiber amplifier in a depressed cladding or W-profile fiber. The fiber has a core doped with the active material and defined by a core cross-section and a refractive index no. A depressed cladding of index n1 surrounds the core and a secondary cladding of index n2 surrounds the depressed cladding. The fiber amplifier is pumped to a level of high relative inversion, such that the active material exhibits positive gains in a short wavelength band and high gains in a long wavelength band. The core cross-section, the depressed cladding cross-section and the refractive indices no, n1, and n2 are selected to obtain a roll-off loss curve about a cutoff wavelength ?c. The roll-off loss curve yields losses at least comparable to the high gains in the long wavelength band and losses substantially smaller than the positive gains in the short wavelength band.

Abstract: Methods and apparatus for controlling a passively Q-switched laser (PQSL) that use a Q-switched laser as a voltage controlled oscillator (VCO) in a phase-locked loop control circuit are disclosed. The PQSL may be optically coupled to a detector. The detector may be coupled to a an input of a phase lock loop controller. A reference oscillator may be coupled to a reference input of the phase lock loop controller. An output of the phase lock loop controller may be coupled to an integrator. The integrator may be coupled to a means for controlling an amount of power provided to the PQSL.

Abstract: An optical communication system such as a Wavelength-Division-Multiplexed (WDM) or Dense Wavelength-Division-Multiplexed (DWDM) communication system using Erbium doped fiber amplifiers (EDFAs) for amplifying signals in the S-band. The fiber amplifier has a core doped with Erbium and defined by a core cross-section and a refractive index n0. The fiber amplifier has a depressed cladding surrounding the core and a secondary cladding surrounding the depressed cladding. The depressed cladding has a depressed cladding cross-section and a refractive index n1, and the secondary cladding has a secondary cladding cross-section and a refractive index n2. The fiber amplifier has a pump source for pumping the Erbium to a level of high relative inversion D such that the Erbium exhibits positive gains in the S-band and high gains in a long wavelength band longer than the S-band, i.e., in the C- and L-Bands.

Abstract: Methods and apparatus for aligning a lens with respect to an axis of beam propagation are disclosed. A position of the lens is adjusted with respect to the axis along one or more directions that lie substantially parallel to a surface of a bulkhead connector. The surface of the bulkhead connector is substantially not parallel to the axis of beam propagation. A position of the lens is adjusted along a direction substantially parallel to the axis of beam propagation. After adjustment, the position of the lens is fixed with respect to the surface. An example of a lens aligning apparatus includes a lens mount configured to receive the lens, a bulkhead connector having a surface, wherein the axis of beam propagation intersects a plane of the surface, means for fixing a position of the lens mount with respect to the surface; and means for fixing a position of the lens with respect to the lens mount.

Abstract: A Thulium-doped silica fiber normally has its strongest gain at 1.9 microns and thus is not suitable for communication use. By engineering a W-profile or depressed cladding fiber with an appropriate index profile having a fundamental mode cut-off between 1.9 microns and the shorter wavelength of desired operation, an optical amplifier based on the W-profile Thulium-doped silica fiber operates at wavelengths shorter than conventional amplifiers, just above what is currently called the Erbium L-band. In a preferred embodiment, the cut-off wavelength is at or near 1.7 ?m, eliminating longer wavelengths from the fiber. Amplifiers engineered according to the principles and techniques of the present invention can operate in the wavelength range between about 1.6 to 1.8 microns, which is particularly useful for telecommunications.

Abstract: A laser apparatus is disclosed. The apparatus includes a Neodymium-doped lasing material having first and second surfaces and a passive Q-switch optically coupled to the second surface. The first-surface is substantially transparent to a pump radiation and substantially reflective to laser radiation generated by an interaction between the pump radiation and the Neodymium-doped lasing material. The laser radiation is characterized by a vacuum wavelength corresponding to an atomic transition from the 4F3/2 level to the 4I9/2 level of Neodymium in the lasing material. The second surface transmits at least a portion of the laser radiation. The lasing material and Q-switch are configured to produce pulses of the laser radiation characterized by a pulse length of greater than zero and less than about 1.5 nanoseconds and a pulse repetition rate greater than about 100 kHz. A PQSL laser, an apparatus for generating blue light and a display system based on the laser apparatus are also disclosed.

Abstract: The use of <100>-oriented crystals as gain media in lasers and optical amplifiers is disclosed. In a laser, a substantially <100>-oriented crystal, such as <100> YAG can be disposed within an optical cavity as a gain medium. The crystal is orientated such that a <100> plane is substantially perpendicular to a direction of beam propagation within the crystal. A pump source provides pumping energy to a pumped region of the crystal. The use of a substantially <100>-oriented crystal can reduce depolarization loss and thermal lens effects if an absorbed power of the pumping energy is less than or equal to about 1000 watts of pumping radiation and/or a cross-sectional overlap between a beam of radiation propagating through the crystal and the pumped region is greater than about 20% of a cross-sectional area of the pumped region.

Abstract: A heterodyne modulated optical signal that includes two or more beat notes is produced. A portion of the heterodyne modulated optical signal is coupled to a device under test (DUT). This portion includes modulation at least at two of the beat note frequencies. The output of the DUT includes signals corresponding to two of the beat notes. These signals are mixed to produce a mixed output signal having the same frequency as an additional beat note but a phase that depends on the phase response of the DUT at one or more of the two beat note frequencies. The phase of the mixed output signal is measured with respect to a reference signal having the same frequency and a known phase with respect to the additional beat note. The resulting phase measurement represents the dispersion of the DUT with respect to modulation frequency.

Abstract: A source that employs an Erbium-Doped Fiber Amplifier (EDFA) for generating light in an S-band of wavelengths. The EDFA uses a fiber having a core with a core cross section surrounded by a depressed cladding with a depressed cladding cross section and a secondary cladding with a secondary cladding cross section. A pump source is provided for pumping the Erbium contained in the core of the fiber to a high relative inversion D, such that the Erbium exhibits positive gains in the S-band and high gains in a long wavelength band longer than the S-band. The core cross-section, the depressed cladding cross-section, and the refractive indices no, n1, and n2 are selected to produce losses at least comparable to the high gains in the long wavelength band and losses substantially smaller than the positive gains in the S-band.

Abstract: A Saturable Reflector apparatus comprises a substrate having a first and second surfaces, and a reflector having a saturable absorber layer, attached to the first surface. At least one of the first and second surfaces has been modified to enhance an etalon effect of the substrate due to interference of light reflecting from the first and second surfaces. Either or both of the surfaces may be modified, for example, by polishing or coating. The apparatus may also include means for adjusting an optical thickness of the substrate to tune the etalon effect. Such means may comprise a temperature control element, such as a heater, coupled to a temperature controller. The inventive apparatus may be incorporated into a mode-locked laser. The etalon tuning optimizes a relation between temporal and frequency domains of radiation incident on the saturable reflector.

Abstract: Co-doping the gain medium of a diode-pumped infrared laser to make the laser resistant to long-term degradation from high-intensity internal infrared radiation is disclosed. Co-doping the gain medium with ions such as Cr3+ and Ce3+ that make the gain medium resistant to external ionizing radiation solves problems of long-term degradation of the gain medium.

Abstract: Methods and apparatus for calibrating a frequency difference between two or more lasers over an extended frequency range as well as optical signal generators that employ such an apparatus or method are disclosed. The lasers are tuned in coordination with respect to one or more readily characterized narrow frequency ranges to characterize one or more tuning parameters of each of the lasers over the extended frequency range. The apparatus may include first and second tuning controllers respectively coupled to the first and second lasers, an optical coupler optically coupled to the first laser and the second laser, a frequency detector coupled to the optical coupler and a controller coupled to the frequency detector and the temperature controllers. The controller may include a processor and a memory containing processor executable instructions for calibrating the two lasers in accordance with the method described above.

Abstract: A system and method for using pulses of laser light delivered in a non-overlapping sequence of first pulses at a green wavelength, second pulses at a blue wavelength and semi-continuous pulses at a red wavelength to illuminate a color generation unit for generating a color. Typically, the color generating unit is an image generating unit for producing color images and is equipped with transmissive or reflective pixels which are adjusted to select portions of the laser light generated at the green, blue and red wavelengths to obtain a desired output color. The first and second pulses preferably have a narrow pulse width and an interpulse separation equal to at least 100 times the narrow pulse width, while the semi-continuous pulses at the red wavelength have a wide pulse width equal to at least 100 times the narrow pulse width.

Abstract: A method for tuning nonlinear optical frequency converters including devices such as optical parametric amplifiers and optical parametric oscillators through degeneracy. The nonlinear conversion process is driven by a pump beam at an original pump wavelength and the tuning is accomplished by setting a passband around a first wavelength generated by the optical frequency converter and thereby generating a passband image around a second wavelength. Once the passband and passband image are within a critical range the original pump wavelength is adjusted to an adjusted pump wavelength and tuning continues by moving the passband which the adjusted pump wavelength is either held constant or further adjusted. In particular, the passband can now be moved through the resonant wavelength which corresponds to a point of degeneracy at the original pump wavelength.

Abstract: A tunable light source equipped with an optical parametric amplifier (OPA) placed in a cavity for performing an optical parametric oscillation (OPO) driven by a pump beam at a pump frequency selected within a certain range such that the OPO is driven near degeneracy. An adjustment mechanism adjusts the pump frequency within a wavelength tuning range to select a gain spectrum of the OPO and a spectral control mechanism sets a resonant frequency of the cavity within that gain spectrum. Thus, only one of the idler and signal beams within the passband set by the narrowband tuner is supported inside the cavity. Other nonlinear frequency conversion operations can also be performed within the cavity in conjunction with the OPO. The light source can be operated in cw, near-cw and pulsed operation modes as a broadly tunable narrowband source covering a wavelength window of 250 nm.

Abstract: A light source is disclosed having a pulsed laser, a fiber amplifier optically coupled to the pulsed laser, and a nonlinear frequency converting element optically coupled to the fiber amplifier. The pulsed laser, e.g., a passively Q-switched laser, is configured to generate light pulses characterized by a pulse length of less than about 1.7 nsec and sufficiently large that a frequency bandwidth of the pulses after they emerge from the fiber amplifier is less than an acceptance bandwidth of the nonlinear frequency converting element. The laser is pulsed at a pulse repetition rate sufficiently large that the fiber amplifier does not spontaneously emit radiation between pulses. In such a source, the fiber amplifier is substantially free of stimulated Brillouin scattering and self-phase modulation may be held to a level that does not reduce conversion of infrared radiation to visible radiation. Such a light source can be combined with an image generator and a scanner in an image projection system.