Abstract: A gas laser 10 has a gas-field enclosure 12 in which electrodes 14, 16 are operable to excite the gas within the enclosure to emit laser radiation. The region 20 between the electrodes 14, 16 contains a plasma which emits the laser radiation. At one end of the enclosure 12, there is a plasma-free region 22 undivided from the region 20. A microphone 24 is located in the plasma-free region 22. This detects pressure waves occurring in the plasma-free region when laser radiation is absorbed. The signal from the microphone is used to control a feedback circuit 26 to stabilize the frequency of the emitted laser radiation.

Abstract: A system for generating a stable optical frequency from a laser signal having inherent frequency fluctuations. The signal from an injection-controlled pulsed laser is divided into two parts. One part is mixed with the signal from a stable CW laser to generate beat frequencies. These signals are amplified and recombined with the pulsed laser signal in an output modulator. In one embodiment, the difference frequency between the pulsed laser and the reference signal is less than 1000 MHz. The beat frequencies are increased by an X-band mixer to the microwave range where they can be readily amplified in an available broad band amplifier. In another embodiment, the transmitter laser and the reference laser operate at a difference frequency in the microwave range, say, above 5,000 MHz. The beat frequencies are obtained by a high frequency mixer such as a bulk crystal in a waveguide or cavity. In still another embodiment, two independent transmitter lasers generate pulses that occur with a significant time delay.

Abstract: There are disclosed a method and apparatus for stabilizing an oscillation frequency separation among a plurality of laser devices wherein a plurality of laser devices are controlled to radiate output lights each having a predetermined frequency so that a frequency separation is stabilized. Reference pulses are produced in an optical resonator which has periodic resonant frequencies and receives a frequency sweep signal, and beat signals are produced in accordance with the combination of the frequency sweep signal and oscillation frequencies of the plurality of laser devices. The reference signals and beat signals thus produced are processed to produce error signals which are time differences between the producing times of the both signals. The plurality of laser devices are controlled to be driven such that the error signals become a predetermined value.

Abstract: There are disclosed a method and apparatus for producing laser pulses at two wavelengths alternately by switching the oscillations of a distributed feedback semiconductor laser of the continuous grating type back and forth across the stop band. The necessary shaping of the gain or index of refraction characteristic along the path of the oscillations is accomplished in part by two top electrodes, one of which is longer than the other along that path, and by varying the current supplied to at least one of those electrodes in the appropriate sense. Applications for optical communication and for optical logic are disclosed, the preferred embodiment being a transmitter for an optical communication system with minimal chirp of the optical pulses, in which pulses at one of the wavelengths are modulated at a bit rate exceeding 1 Gigabit by direct-modulation control of the switching of the laser, and the pulses at the other of the two wavelengths are discarded.

Abstract: This invention relates to an improved method for producing pulsed trains of light within a cavity which comprises repeatedly incrementally increasing the frequency of a constant wave of light circulating within the cavity and combining the frequency-shifted beams to produce at least one pulsed train output thereof. This can be done in either a passive or active cavity.

Abstract: A light modulator for modulating data signal to high frequency light signal includes a semiconductor laser diode having an input for receiving the data signal and an output for producing a laser beam, a light detector for receiving the laser beam and producing an electric signal representing the laser beam, and an electric passage between the light detector and the input of the semiconductor laser diode so as to define a positive feedback circuit for feeding the output of the semiconductor laser diode to the input of the same, whereby an oscillation at a resonance frequency is effected in the semiconductor laser diode to generate a light modulated high frequency laser signal from the semiconductor laser diode.

Abstract: A low-laser-noise semiconductor driver device is provided for use in an optical information processing device which is recordable or erasable and which oscillates a semiconductor laser with a high output when it is recorded or erased. A semiconductor is generally oscillated with a rated maximum output during a recording and erasing operation. Therefore, when high frequency superposition is made in such a high output oscillation state, an oscillation output exceeds the rated output, which badly influences the life of the laser. To obviate this drawback, the high frequency superposition is stopped at the mode of recording or erasing in which the high output oscillation is made by a switching circuit which is controlled by a mode control signal. This reduces the laser noise at the mode of reproducing and also lengthens the life of the semiconductor laser.

Abstract: A system for generating a stable optical frequency from a laser signal having inherent frequency fluctuations. The signal from a injection-controlled pulsed laser is divided into two parts. One part is mixed with the signal from a stable CW laser to generate beat frequencies. These signals are amplified and recombined with the pulsed laser signal in an output modulator. In one embodiment, the difference frequency between the pulsed laser and the reference signal is less than 1000 MHz. The beat frequencies are increased by an X-band mixer to the microwave range where they can be readily amplified in an available broad band amplifier. In another embodiment, the transmitter laser and the reference laser operate at a different frequency in the micorwave range, say, above 5,000 MHz. The beat frequencies are obtained by a high frequency mixer such as a bulk crystal in a waveguide or cavity. In still another embodiment, two independent transmitter lasers generate pulses that occur with a significant time delay.

Abstract: A method and apparatus for monitoring and/or controlling the frequency of a beam of coherent radiation. The apparatus comprises a reference source (1) which is controlled to generate reference radiation beam with a frequency which is repeatedly swept through a range of operating frequencies. This reference beam is combined with a beam of coherent radiation from a test source and the combined beams are fed to a photodiode (9). The output of the photodiode (9) can be displayed so that the upper and lower beat frequencies can be determined enabling the variation of the average of the upper and lower beat frequencies with time to be monitored. Alternatively, the average beat frequency can be fed back as a control signal to control the test beam source (8). In this latter case, the frequency of the test beam will be locked.

Abstract: The present invention provides a laser device comprising a substrate; an active layer; a multi-quantum-well layer disposed on one side of the active layer and optically coupled therewith; a diffraction grating layer disposed on a side of the active layer and optically coupled therewith; and a device for applying a reverse voltage to the multi-quantum-well layer. The laser device can generate a light output, with its wavelength being controlled electrically for a 350 .ANG. range at a 1.55 .mu.m wavelength.

Abstract: A system for generating a stable optical frequency from a laser signal having inherent frequency fluctuations. The signal from an injection-controlled pulsed laser is divided into two parts. One part is mixed with the signal from a stable CW laser to generate beat frequencies. These signals are amplified and recombined with the pulsed laser signal in an output modulator. In one embodiement, the difference frequency between the pulsed laser and the reference signal is less than 1000 MHZ. The beat frequencies are increased by an X-band mixer to the microwave range where they can be readily amplified in an available broad band amplifier. In another embodiment, the transmitter laser and the reference laser operate at a difference frequency in the microwave range, say, above 5,000 MHZ. The beat frequencies are obtained by a high frequency mixer such as a bulk crystal in a waveguide or cavity. In still another embodiment, two independent transmitter lasers generate pulses that occur with a significant time delay.

Abstract: Spatial modulation representing digital information is imposed on a pump laser beam, and differing modulation representing different digital information is imposed on a second light beam which has a frequency equal to the pump beam less the nonlinear optical Stokes frequency shift. All the digital information on the two beams is logically combined simultaneously in a single waveguide containing the corresponding nonlinear optical (e.g. Brillouin) material with the result of the logical operations recorded on the wavefront of the second light beam.

Abstract: At the receiving end or point at which a data or information carrying seed laser beam is to be received after traveling through a medium, a pump laser beam is propagated through the medium to the sending end of the medium at which point the now aberrated pump laser beam may be amplified if necessary and directed to and propagated through a waveguide composed of a suitable third order optically nonlinear medium. The data carrying seed laser beam is directed to and through the waveguide where it is phase conjugated and then through the medium in the direction opposite to that of the pump laser and arrives at the receiving end as an unaberrated laser beam. The data carrying laser beam and the pump laser beam have a frequency difference equal to the Stokes frequency shift of the waveguide material.

Abstract: A dual-wavelength laser apparatus includes a laser emitting a laser beam consisting of two wavelength components, a methane cell for controlling and equalizing gains of the two wavelength components, a cavity length modulator including a piezoelectric element for periodically modulating the cavity length of the laser, and a feedback circuit for controlling the modulation center such that the sum of outputs of the two modulated wavelength components is kept substantially constant. The feedback circuit includes a detector for detecting a laser output, a lock-in amplifier for detecting and amplifying an output from the detector, an integrator for integrating an output from the lock-in amplifier, and a high-voltage amplifier for generating a bias voltage set by the integrator.

Abstract: An acousto-optical isolator for isolating unwanted, backwardly propagating laser beams. The isolator includes a first Bragg cell to shift the frequency of a desired, forwardly propagating beam by a first step, a second Bragg cell to shift the frequency by a second, converse step back to its original value, and an attenuator between the two Bragg cells. The frequency of a backwardly propagating beam is shifted by the second step in the second cell and then is shifted back to its original value in the first cell. The attenuator attenuates a signal having a frequency equal to the original beam frequency shifted by the second step. Accordingly, the backwardly propagating beam is attenuated but the forwardly propagating one is not. Using dual-transducer Bragg cells, the preferred direction of propagation can rapidly be reversed.

Abstract: A phase-matched resonant waveguide modulator suitable for very high frequency modulation and applications such as FM laser spectroscopy is described. The width of a crystal modulator section of the waveguide is chosen so that the operating frequency is just above cut-off to achieve optical and RF phase velocity matching at high frequencies such as 10 GHz by virtue of the dispersion of the waveguide near cut-off. The waveguide contains air in opposite end sections so that those sections are below cut-off and the microwave is evanescent, with the result that the end sections preferably are open for ease of optical coupling to the waveguide.

Abstract: A semiconductor light emitting element is disclosed, which is provided with a light emitting region having a diffraction grating formed by periodic corrugations, a modulation region having an external waveguide layer optically connected directly to the light emitting region and a pn junction separated from a pn junction of the light emitting region and a window region formed of a semiconductor having a larger energy gap than that of a light emitting layer of the light emitting region and extending from at least one end of the light emitting region and the external waveguide layer. The refractive index of the external waveguide is varied through utilization of the electrooptic effect so that the frequency or phase of light stably oscillating at a single wavelength is precisely controlled or modulated.

Abstract: Apparatus is provided for rapidly switching among discrete wavelengths within the output spectrum of a gas laser. A portion of the radiation in a primary optical cavity of a laser is transmitted by a partially reflective surface into a secondary cavity which includes a reflector element and one or more Bragg deflector cells. The Bragg cells are positioned between the primary cavity and reflector element, and frequency shift radiation passing between the primary cavity and reflector element. Each Bragg cell is selectably driven by an RF driver to enhance radiation of a predetermined wavelength within the range of the laser spectrum. Consequently, radiation injected back into the primary cavity from the secondary cavity is essentially of the predetermined wavelength.

Abstract: A laser which discriminates against a high gain transition in laser materials allowing a low gain transition to oscillate is provided by using more than two mirrors in the laser cavity which are highly reflective at the frequency of the high gain transition.

Abstract: In an FSK laser transmitting apparatus, a light source can change the output light frequency. A driver performs FSK of the light source with a plurality of values. A beam splitter splits the output light from the light source into two split beams. A delay circuit delays one of the two split beams with respect to the other. A beam coupler combines delayed and nondelayed beams as the two split beams from the beam splitter. A controller detects the beat frequency of combined light from the beam coupler and supplies a control signal to the driver so as to set the beat frequency to be a predetermined value.

Abstract: A laser radar system employing a linear FM chirp laser followed by post detection pulse compression by a surface acoustic wave (SAW) device. The system includes an FM chirp modulator that provides the needed tuning range and linearity for pulse compression. This modulation is accomplished by using a high-pressure CO.sub.2 laser with an intracavity electro-optic modulator of CdTe. The frequency of the transmitter laser is accurately controlled through the application of high linearity, high frequency, sawtooth voltages to the two plates of the CdTe crystal, with the voltage waveform applied to one plate being out of phase with that applied to the other crystal plate. With the performance the system offers, absolute radar ranges can be measured to 0.22 m and velocities to 0.37 m/sec.

Abstract: A chirp laser system includes an intracavity electro-optical crystal modulated at a relatively high frequency, for example 250 kilohertz, to sweep the frequency of the transmitter laser above and below its nominal center frequency. One of the mirrors of the laser transmitter is adjustable to vary the length of the cavity and to shift the frequency of the transmitter laser. When the frequency of the transmitter laser is shifted, the output amplitude of the laser changes. With the center frequency of the laser at a maximum gain point, the amplitude of the output signals during positive and negative frequency excursions of the transmitter laser will be substantially symmetrical. However, if thermal or other effects cause the frequency of the laser to shift away from the maximum gain point, the output during positive and negative excursions will be asymmetrical.

Abstract: A miniaturized inert gas ion laser is proposed whose discharge column has a diameter between 6.times.10.sup.-3 cm and 8.times.10.sup.-2 cm. In a preferred embodiment, a BeO plate is enclosed by two metal parts which lie against one of the base areas of the plate. One metal part is a copper sheet functioning as anode and the other metal part forms a cavity in which the cathode is situated. The BeO plate is provided with a longitudinal bore which is terminated at both sides by mirrors and communicates via plate perforations with the anode and the cathode space. The bore is 0.1 mm in size and 30 mm long; the discharge occurs on a path of 10 mm; discharge current, discharge voltage and filling pressure lie at 200 mA, 130 V and 5 Torr; the output power amounts to about 1 mW. This type of laser is extremely compact; it is particularly suitable as a stable frequency signal generator and can be simply amplitude-modulated and/or frequency-modulated.

Abstract: An extended laser sensor including a laser with an opticla gain lasing medium optically coupled to an optical resonant cavity including reference and sensor arms. Optical path length variations in the sensor arm induced by an incident physical field modulate the operating parameters of the laser. The field is sensed by monitoring these modulated operating parameters.

Abstract: A semiconductor laser is frequency modulated and the output is put through an FM to IM converter. Intensity modulation is obtained at high frequency with the use of low switching current and minimal chirping oscillations.

Abstract: A device is provided for fast frequency modulating the output spectrum of multimode lasers and single frequency lasers that are not actively stabilized. A piezoelectric transducer attached to a laser cavity mirror is driven in an unconventional manner to excite resonance vibration of the transducer to rapidly, cyclicly change the laser cavity length. The result is a cyclic sweeping of the output wavelength sufficient to fill the gaps in the laser output frequency spectrum. When such a laser is used to excite atoms or molecules, complete absorption line coverage is made possible.

Abstract: A frequency control system for a laser for compensating for thermally-induced laser resonator length changes. The frequency control loop comprises a frequency reference for producing an error signal and electrical means to move a length-controlling transducer in response thereto. The transducer has one of the laser mirrors attached thereto. The effective travel of the transducer is multiplied severalfold by circuitry for sensing when the transducer is running out of extension and in response thereto rapidly moving the transducer and its attached mirror toward its midrange position.

Abstract: Method and apparatus for modulating coherent radiation generated by an orotron in accordance with a low voltage control signal applied to the diffraction grating to vary the grating-to-cathode voltage from the cathode-to-collector voltage over a selected voltage range determined by the maximum and minimum values of the control voltage. For amplitude modulation, the grating-to-cathode voltage is varied within a voltage range between a lower voltage at which the orotron output power starts to fall abruptly and a cutoff voltage at which coherent radiation ceases. For frequency modulation, the grating-to-cathode voltage is varied within a voltage range, including the point of maximum power output, where there is a minimum change of output power with a change in the grating-to-cathode voltage.

Abstract: A method and apparatus are disclosed for precisely stabilizing a laser to a sub-Doppler resonance of an absorbing gas contained in a cell located external to the laser resonator. Stabilization is based on the detection of modulation transferred onto a previously unmodulated probe beam by the non-linear interactions of the absorbing gas located in a cell which is subject to a counter-running, frequency-modulated saturation beam. Alternatively, the further modulation of the saturation beam can be detected.

Abstract: A frequency shifted cavity apparatus for electromagnetic radiation. The cavity filters electromagnetic radiation wherein the instantaneous frequency increases and changes non-linearly in time. The cavity can optionally include an optical amplifier with sufficient gain to cause oscillation of at least one cavity mode.

Abstract: An analog-to-digital converter using a frequency tunable laser having output radiation of a frequency determined by the input voltage to the laser is described.

Abstract: A light beam modulating and deflecting system comprising a stationary electrode secured to a stationary body, and a rotatable electrode secured to a rotating body, on which a light source is mounted, and opposed in slightly spaced relation to the stationary electrode to form a capacitor together with the stationary electrode. A high frequency signal modulated with a light modulating signal is applied to the stationary electrode, thereby to feed the light modulating signal from the stationary electrode to the rotatable electrode. The system may comprise a plurality of light sources, stationary electrodes and rotatable electrodes, and high frequency signals modulated with various light modulating signals may be applied to the respective stationary electrodes, thereby to independently modulate the light sources via the rotatable electrodes.

Abstract: A light source comprises a semiconductor laser and a gas laser. The semiconductor laser is injection locked using the highly coherent output from the gas laser. The output from the semiconductor laser has a narrow linewidth and a high stability.The invention has a major application in optical fibre communications systems.

Abstract: A method of modulating the output of a solid state diode laser by directly straining the laser chip. The chip is mechanically coupled to a transducer such as a piezoelectric crystal in such a manner that a dimensional variation in the transducer is translated into a corresponding variation in the chip. It is contemplated that the modulated output will have application in communication systems and in particular a hydrophone system.

Abstract: A laser radar transmitter (2) has, associated with a single active lasing region (11) and preferably in the same laser cavity (1) therewith, an amplitude modulator (21) and a frequency modulator (25), which may simultaneously place continuous AM and continuous FM on a single output beam (7). Amplitude modulator (21) is preferably an EO crystal having a high EO coefficient, low loss, and field-induced birefringence. Frequency modulator (25) is preferably an EO crystal having a high EO coefficient, low loss, and a field-induced index change. Applying a d.c. driving voltage to the AM crystal (21) and an a.c. driving voltage to the FM crystal (25) produces an output beam (7) having FM. Applying an a.c. driving voltage to the AM crystal (21) produces an output beam (7) having AM, independently of whether FM is added by means of applying an a.c. driving voltage to the FM crystal (25).

Abstract: A waveguide laser having a square bore and an external modulator has its power doubled by proper relationship of a coupled cavity external to a cavity in the waveguide medium.

Abstract: An injection laser is provided with a modulator which includes an external resonator cavity including a lithium niobate crystal and a spherical mirror closely coupled to the rear end of the laser with a source of bias voltage for selectively tuning the resonator for high frequency modulating the laser.

Abstract: A laser control apparatus for use with a laser having output radiation including an intermodal beat frequency and electric signal responsive means for controlling the light frequency from the laser; radiation responsive electric signal means adapted for association with said radiation for providing an electric signal having a frequency as a function of said beat frequency; and means for sensing changes in phase of the aforementioned signal and providing a second electric signal varying as a function thereof and being adapted for connection to the electric signal responsive means. The apparatus also includes a phase comparator and circuitry providing a phase lock of the first-named and reference signals.

Abstract: A control system for a laser-intensity-modulator system to maintain the modulated component of the output beam at a constant amplitude. The electro-optical modulator has a resonant driving circuit supplied by a voltage controlled oscillator. A portion of the output beam is detected and a control signal representative of the amplitude of the modulated component is derived and supplied to the oscillator in addition to the normal bias voltage which sets the nominal frequency. This stabilizes the amplitude of the modulated component in the output beam.

Abstract: Continuous offset tuning of a frequency stabilized cw gas laser (10) is achieved by using a spectrophone (14) filled with the same gas as the laser for sensing a dither modulation, detecting a first or second derivative of the spectrophone output with a lock-in amplifier (28), the detected output of which is integrated (36), and applying the integrator output as a correction signal through a circuit (24) which adds to the dither signal from an oscillator (22) a dc offset (B1) that is adjusted with a potentiometer (26) to a frequency offset from the absorption line center of the gas, but within the spectral linewidth of the gas. Tuning about that offset frequency is achieved by adding a dc value (B2) to the detected output of the dither modulation before integration using a potentiometer (30).

Abstract: A method and apparatus for operating a dual-frequency gas laser so as to controllably switch between frequencies makes use of a cavity so tuned that the comb of resonant frequencies is not commensurate with the frequency difference between the laser operating frequencies, and, in a preferred embodiment, with one of the resonant frequencies tuned to coincide with one of the operating frequencies. The cavity length and overall gain at each frequency are so selected that the spacing between resonant frequencies is greater than the breadth above unity gain of the individual peaks of the gain vs. frequency curve. The active material is subjected to a magnetic field which may be varied in a controlled manner. In a preferred embodiment, this field is applied normal to the optical axis of the resonant cavity, and an optical element within the cavity is arranged to act as a plane polarizer with its plane of polarization normal to the magnetic field.

Abstract: A laser apparatus including first and second frequency sweeping laser devices, the sweep frequency range of each being different. The output laser beams of the first and second laser devices are multiplexed by a multiplexer. The output laser beam of the multiplexer is transmitted to a photodetector for detecting the difference in frequency between those of the first and second laser devices. A frequency monitor, coupled to the photodetector, provides a signal to a control circuit which causes the first and second laser devices to sequentially sweep their respective sweep frequency ranges.

Abstract: A single electro-optic device is provided for simultaneously mode-locking and chirping the output of a laser by simultaneously applying to the electrodes of the electro-optic device a periodic signal superimposed on a voltage ramp. The electro-optic device in general utilizes a crystal of the type which changes refractive index in accordance with an applied voltage. As a result, FM mode-locking is achieved through the use of the periodic signal, whereas mode lines are displaced or shifted in frequency during the generation of the laser output by virtue of the changing bias supplied by the voltage ramp.