Abstract: An optical phase detector comprising coupling means for receiving two optical inputs and for producing two combined optical outputs, means for detecting the two combined optical outputs and producing two corresponding electrical signals, and means for measuring the difference between the two electrical signals and generating an output difference signal which may be used to provide an indication of the phase difference between the two optical inputs. The optical phase detector comprises a voltage-tuneable electro-optic phase modulator for modulating the phase of an optical input to the optical phase detector to provide a linearized response. In this arrangement the output difference signal may be maintained at a constant level by varying the voltage applied to the electro-optic phase modulator, the applied voltage providing an indication of the phase difference between the two optical inputs. Applications include frequency discriminators, various sensors, and a laser stabilization apparatus.

Abstract: There are disclosed a wavelength monitoring device of tunable laser sources and a method thereof. A Fabry-Perot etalon is provided to detect the wavelength drift, and furthermore, a Fabry-Perot laser diode or a light emitting diode is provided to recognize the channel of the wavelength. The wavelength drift is used to determine the junction voltage of each corresponding channel in advance. Then, the actually detected junction voltage of the diode is used to determine the channel of the wavelength, thereby accurately detecting the actual channel wavelength.

Abstract: A laser oscillation apparatus includes a wavelength change unit for driving a wavelength selection element in a band-narrowing module and changing the oscillation wavelength of a laser beam to a target value, and an oscillation history memory for storing the oscillation state of the laser beam as an oscillation history. The wavelength change unit drives the wavelength selection element on the basis of the oscillation history and changes the oscillation wavelength of the laser beam to the target value.

Abstract: The present invention provides a generator of a CS-RZ optical clock signal at a predetermined clock frequency. The generator contains a first laser source and a second laser source which respectively produce first and second continuous lightwaves, where the laser frequency of at least one of the sources is adjustable. The generator also contains a coupler disposed to receive the first and second lightwaves and forms optical beats at a beat frequency. An opto-electronic feedback is used to servo-control the adjustable-frequency laser source(s) in such a manner that the beat frequency, which is equal to the difference between the laser frequencies, is substantially equal to the clock frequency.

Abstract: A high power diode laser system utilizes an external cavity to narrow the spectral width of a high power multimode diode laser to change the output power normally produced by the diode from a broad spectrum to a very narrow spectrum. The power output of the laser system is concentrated over a narrow spectral range which falls within the useable range for particular applications, such as optical pumping of noble gas samples for magnetic resonance imaging. The output of the diode is received by a collimating element which directs the light on a beam path to a diffraction grating which is oriented at an angle to the incident beam. A portion of the beam may be directed from the diffraction grating to provide useable output light, and a portion of the light incident on the grating is directed back to be focused on the diode to provide feedback to cause the diode to preferentially lase at the wavelength of the light that is fed back.

Abstract: An optical servo writer system including a laser subsystem to generate a multiplicity of light beams, a lens positioned to receive and focus the light beams and a spatial filter positioned in the system so as to allow a subset of the light beams to pass through the filter. The multiplicity of light beams includes the subset that contains the desired beams, or the servo beams, and also the undesired beams, called the ghost beams. The system further includes a digital linear tape positioned adjacent the spatial filter with the spatial filter allowing the subset of light beams to hit the digital linear tape and produce servo marks. The spatial filter includes openings positioned to allow the subset of light beams to pass through the filter. The openings may be staggered relative to the digital linear tape to prevent debris generated by the marking process from clogging the openings.

Abstract: A method and apparatus are provided for generating short (e.g., picosecond) pulses using a 2 section 1553 nm DBR laser without gain switching nor external modulation. The center wavelength of the DBR section is modulated at 0.5 GHz to generate a constant amplitude frequency modulated optical wave Large group velocity dispersion is then applied with a chirped fiber Bragg grating to convert the FM signal to a pulse stream.

Abstract: Conventionally, in the wavelength locking optical system, the wavelength as detected is deviated from a targeted range owing to the change of the peripheral temperature resulting from the temperature characteristics of the wavelength error detection device. To solve this prior issue, it is arranged such that a portion of the wavelength error detection device, through which portion light-beams passes, contacts a material of high heat conductivity.

Abstract: A modulation control system is used in fiber optic data transmission and fiber optic test equipment. A modulation controller includes a plurality of function generators that are linked by a switching mechanics, to a rail system that drives a plurality of laser source cards. The switching mechanism for each rail is capable of driving the rail at the function-generated waveform or switching to an external source waveform. The laser source cards are intelligent in the sense that they can be programmably controlled by switching to select waveforms from a selected one of the rails.

Abstract: A tuned optical resonator having a substrate and an input waveguide and an optical resonator waveguide formed on the substrate. The optical resonator waveguide has a resonant frequency, exhibits a first index of refraction, temporarily exhibits a second index of refraction responsive to application of laser energy, and temporarily resonates at the resonant frequency while the laser energy is being applied.

Abstract: A laser, including a grating structure consisting of two or more gratings generating a plurality of different wavelength peaks for reflection of optical radiation therefrom. The laser also includes a semiconductor device having a gain region which is operative to amplify the optical radiation, and a wavelength tunable filter (WTF) region which is adapted to filter the optical radiation. The device is optically coupled to the grating structure so as to define a laser cavity having a plurality of cavity modes. The cavity modes are selected by tuning a wavelength pass-band of the WTF region to overlap with one of the wavelength peaks of the grating structure.

Abstract: An optical frequency converter that can use a low-amplitude, high-frequency signal for converting a wide range of optical frequencies. The optical frequency converter includes a device for modulating a lightwave of a preset frequency with a modulation signal to generate a group of sidebands thereof, a device for selecting sidebands from among the group of sidebands, and a device for changing modulation signal frequencies and selecting specific sidebands.

Abstract: A discontinuous phase element (86, 204) is disposed between the reflector (20, 23) elements of an optical resonator in order to suppress unwanted modes propagating within the cavity, and to preferentially allow the existence of preferred modes within the cavity. The discontinuous phase element (204) operates by producing sharp changes in the phase distribution of the undesirable modes, so that their propagation losses are sufficiently high prevent their build-up. This is achieved by introducing a discontinuous phase change to these modes at locations where they have high intensity. At the same time, the desired modes suffer 0 or 2&pgr; phase change, or have low intensity at the discontinuity, and so are unaffected by the discontinuous phase element. Such elements can be used in a single element or a double element configuration, and can be used in passive cavities or active cavities, such as lasers.

Abstract: An optical frequency synthesizer controls a tunable laser to output signals having specific wavelengths. The synthesizer includes a wavelength discriminating device, a wavelength tuning device and a phase locked loop (PLL) circuit. The wavelength discriminating device receives a sample of the signals outputted by the tunable laser, processes the sample signals and passes the processed sample signals to the PLL circuit. Based on the processed sample signals, the PLL circuit controls the wavelength tuning device to tune the laser to output the signals having specific wavelengths.

Abstract: A virtual coherent signal controlled laser oscillator for use in optical phase locked coherent receivers. The present invention employs a fixed laser oscillator in combination with a signal controlled microwave oscillator. A single sideband mixer processes the signals output by the laser oscillator and microwave oscillator to generate a single controlled optical frequency signal.

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 hybridized optoelectronic device having a multi-section laser and a wavelength measuring component such that stable operational characteristics remote from mode boundaries may be determined and stored in a look-up table. A fast means of characterizing the device using sampling techniques is also disclosed. The device may incorporate a frequency-locking component to enable the laser to emit radiation at predetermined frequencies.

Abstract: A light frequency locker (10) able to accept a light beam (14) generated by a controllable light source (12) into a light diverter (16) and impart to it a transverse displacement characteristic which can be detected in a light detection unit (20) connected to a processor (22). The processor (22) then controls the light source (12). Optionally, a light diverger (18) may be provided to enhance angular resolution. The light diverter (16) and the light diverger (18) may either transmit or reflect the light. The light diverter (16) may particularly include a diffraction grating (116, 156), Fabry-Perot interferometer (216), multiple slit plate (316), or an acousto-optical unit (416).

Abstract: A frequency modulated laser comprises a laser cavity in which the gain section of the laser cavity is imbedded within a phase modulation section of the cavity. The laser cavity further comprises electrically-sensitive material, so that an electric field applied across the laser cavity changes the index of refraction within the laser cavity according to the magnitude of the change in the electric field. Uniformly and simultaneously changing the index of refraction along the laser cavity length modulates the frequency of the laser light produced within the laser cavity. The upper bound of the frequency modulation is limited by the propagation time for the electric field to cross the laser cavity.

Abstract: Systems and methods are described for laser array synchronization using master laser injection of broad area lasers. A method, includes: master laser injecting a plurality of broad area lasers; and externally cavity coupling the plurality of broad area lasers. A method, includes: master laser injecting a plurality of broad area lasers; and externally Q switch coupling the plurality of broad area lasers. A method, includes: injection synchronizing a plurality of pulsed broad area lasers using a signal source; modulating the plurality of pulsed broad area lasers using the signal source; and externally coupling the plurality of pulsed broad area lasers.

Abstract: An object of the invention is to provide a wavelength locker which has a wider locking range than that of the wavelength locker in the prior art and which can cope with a plurality of wavelengths. The aforementioned objects are achieved by a wavelength locker, which comprises a periodic filter, a detecting part for detecting the intensity of a laser beam through the periodic filter, and a controlling part for controlling the wavelength of the laser beam to a desired wavelength in accordance with the output of the detecting part. In this wavelength locker, the FSR of the periodical filter is controlled according to space between the wavelengths, and refers to the number of wavelength to be locked, so that the characteristics corresponding to output wavelengths that vary in every period twice the space of wavelengths and are complementary to each other, can be obtained, and the locking range will become wider.

Abstract: A frequency modulated (FM) vertical cavity surface emitting laser (VCSEL). The frequency modulated VCSEL includes a mirror region that has an active region. The frequency modulated VCSEL also includes a phase adjustment region for use in altering the characteristics of the VCSEL. For example, by changing the index of refraction in the phase adjustment region, the wavelength of the VCSEL can be changed, resulting in frequency modulation.

Abstract: A multi-wavelength laser array has a group of multiple lasers, each of the lasers in the group being constructed to emit at a specified wavelength within a range, the specified wavelength of one laser being different from the specified wavelength of the other lasers in the group. The lasers in the group are individually selectable so that, when emission at a particular wavelength is called for, a laser capable of providing the particular wavelength will be selected.

Abstract: A method for recording an image on a photosensitive surface, comprising: producing a primary pulsed light beam; converting the primary light beam, in a light wavelength converter separate from the pulsed light source, to an ultraviolet pulsed light beam; modulating the ultraviolet pulsed beam; and scanning the ultraviolet pulsed light over the surface to record an image on the photosensitive surface.

Abstract: A method and device for the nonlinear combination of laser light which produces a beam of uniform intensity, high spatial purity, and high conversion efficiency. The method includes emitting a laser light from a tunable distributed feedback fiber laser having both thermal and piezoelectric control elements which produces a laser light at a given frequency, wavelength, and intensity; converting the laser light in a nonlinear resonator which uses a nonlinear optical crystal for frequency conversion or mixing; and measuring the resonant frequency of the nonlinear resonator and adjusting the laser light frequency using both the thermal and piezoelectric elements of the fiber laser light source to match the resonant frequency conditions within the nonlinear resonator.

Abstract: A semiconductor optical modulator having an electroabsorptive layer and a pair of modulating voltage electrodes also has a direct-current voltage electrode, from which an unmodulated electric field can be applied to the electroabsorptive layer to adjust the output optical power level. The output optical power level can thus be adjusted without the need for an external attenuator, and without shifting the modulating voltage away from the part of the extinction ratio characteristic having the best linearity. An optical multiplexing module using semiconductor optical modulators of this type can generate a multiplexed output signal with a uniform optical power level simply by controlling the direct-current voltages applied to the semiconductor optical modulators.

Abstract: Apparatus and method for stabilizing the wavelength of a tunable laser to a target wavelength, by correspondingly adjusting the electrooptical performance of the laser's gain medium, whereby to eliminate the frequency shift due to vibrational factors. The electrooptical performance of the laser's gain medium is adjusted, in the case of an electrically pumped laser, by changing the injection current used to pump the laser; and the electrical performance of the laser's gain medium is adjusted, in the case of an optically pumped laser, by changing the intensity of the pump laser used to energize the laser. The system is implemented with a feedback mechanism.

Abstract: A laser irradiation apparatus includes a laser light generation element, a splitting element for splitting laser light generated from the laser light generation element, a light interference element for causing a first beam and a second beam of the laser light split by the splitting element to interfere with each other to form a periodic light pattern, and a phase shifting element for electro-optically shifting the phase of the first beam. The laser light generation element is a pulse oscillation laser based on laser diode excitation.

Abstract: A solid-state light source apparatus includes a first excitation laser light source for outputting a laser beam of a first wavelength, a second excitation laser light source for outputting a laser beam of a second wavelength, a difference frequency between the laser beam of the first wavelength and the laser beam of the second wavelength being in a terahertz band, and a semiconductor pseudo phase matching device which is disposed at a place where a first optical axis of the laser beam of the first wavelength overlaps with a second optical axis of the laser beam of the second wavelength, and generates a terahertz beam in a direction coaxial with the first and second optical axes on the basis of irradiation of the laser beams of the first and second wavelengths. Thus, high output and high efficiency terahertz wave generation can be easily and certainly realized while a narrow line width characteristic is maintained.

Abstract: An optical alignment system for controlling the position of a laser beam through an optical train. The optical alignment system includes a semiconductor laser source for the generation of an alignment beam, and a beam steering device to manipulate the position of the alignment beam on a multi-element detector. The semiconductor laser is driven to mode hop at a frequency greater than the upper frequency limit of the multi-element detector. Driving the semiconductor laser to mode hop at a frequency greater than the upper frequency limit of the multi-element detector results in a more uniform alignment beam as seen by the detector, as the alignment beam becomes an average of all the operational modes of the semiconductor laser. A more uniform alignment beam results in improved accuracy of the alignment system.

Abstract: A method for generating radiation with stabilized frequency, comprises the steps of providing laser light pulses with a repetition frequency fR, said pulses comprising a plurality of N frequency components fn with fn=n fR+f0, wherein f0 represents an offset frequency with n=1 , . . . , N, said frequency components forming a comb with first and second different frequency portions, and generating a primary light output with at least one output frequency component corresponding to the difference of frequencies of said first and second frequency portions.

Abstract: A tunable optical resonator whose resonance frequency is determined by a light signal introduced into the resonator. The resonator includes an optical cavity having a first mirror and a second mirror. The first mirror and second mirror are supported relative to one another such that the distance between the first and second mirrors may be altered by applying a force to said second mirror thereby altering the resonance frequency of said cavity. The resonator includes a light input port for receiving a tuning light signal, and a light signal generator for generating the tuning light source. The tuning light signal is introduced into the optical cavity such that the tuning light signal is reflected between the first and second mirrors. In the absence of the tuning light signal, the resonator has a resonance characterized by a resonance response curve centered at &lgr;0.

Abstract: The present invention provides a system and method for dynamically increasing the numeric gain applied to the temperature loop in a DBR laser control system in response to the anticipated wavelength change that occurs as a tuning current ramp is in progress. In accordance with a preferred embodiment of the invention, the feedback control signal to the laser's TEC is overcompensated for, and as a result, the system is forced to respond much faster, thermally, to the anticipated wavelength shift, thus providing improved real time wavelength stabilization to the control system. The implementation of the increased numeric gain can be carried out through software and/or firmware.

Abstract: An optical fourth-harmonic generation system includes a resonant cavity configured to support electromagnetic radiation of a fundamental frequency and a fourth-harmonic generator disposed within the resonant cavity produces electromagnetic radiation of a fourth-harmonic frequency by an interaction with radiation of the fundamental frequency. The fundamental radiation is characterized by a p polarization that is complementary to an s polarization that characterizes the fourth-harmonic radiation. The fourth-harmonic generator has an output facet oriented substantially at a Brewster's angle with respect to the fundamental radiation to separate the fundamental radiation from the fourth-harmonic radiation as they emerge from the output facet.

Abstract: A directly modulatable laser comprising an active medium inside a laser cavity formed by a resonator mirror and an out-coupling mirror, and a pump light source exciting the active medium. It is characterized in that the active medium generates radiation of two wavelengths (&lgr;1 and &lgr;2) and the resonator mirror is constructed as a controllable reflector by which the reflectivity is controllable for each of the two wavelengths (&lgr;1 and &lgr;2) and the controllable reflector is connected with a control unit, wherein the reflection factor is controlled in such a way that the inversion density of the electrons which is generated in the active medium is constant and the light output of one of the wavelengths ((&lgr;1) is controllable between a minimum value and a maximum value according to an applied control signal, wherein the control of the two wavelengths ((&lgr;1 and &lgr;2) is carried out in push-pull.

Abstract: A third harmonic laser system includes a fundamental wave resonator for generating fundamental laser beam, a second harmonic laser generator for converting fundamental laser beam to a second harmonic laser beam, and a third harmonic laser generator for mixing the second harmonic laser beam with the fundamental laser beam so as to produce a third harmonic laser beam. Multi-pass tripling is used for producing the third harmonic laser beam by means of reflecting and polarizing mirrors, and that the outputted third harmonic laser beam has a high efficiency of about 51% and a high power up to 8.6 W.

Abstract: An apparatus including a cavity optical length actuator to vary a cavity optical path length of a laser in response to an excitation signal having varying frequencies. The cavity optical length actuator induces intensity perturbations in an optical beam of the laser corresponding to the excitation signal. A sensor senses the intensity perturbations in the optical beam and generates a response signal corresponding to the intensity perturbations. A combiner combines the excitation signal and the response signal to generate an error signal.

Abstract: A seed laser apparatus is disclosed. It comprises a distributed feedback laser system for transmitting a dithered optical signal having a frequency versus time characteristic that is represented by a triangular waveform and an optical medium including a plurality of optical signal paths, each path including an optical fiber and a fiber amplifier. The optical medium is characterized by stimulated Brillouin scattering (SBS) having a response time, whereby the period of the triangular waveform is equal to the round-trip transit time in the fiber or shorter than the response time of the SBS.

Abstract: The present invention has applications in high-bandwidth communications systems and other applications that utilize modulated optical energy. In one aspect of the invention, a short cavity diode-pumped laser generates optical energy that may be modulated over a wide range of frequencies. In one embodiment, the short cavity diode-pumped laser may be modulated at rates up to 15 GHz. The short cavity diode-pumped laser may include a laser diode modulator and a laser coupled to the laser diode modulator having a cavity lifetime of less than about 100 picoseconds.

Abstract: Method and apparatus for producing a laser output having stimulated Brillouin scattering (SBS) suppression characteristics. An excitation signal is provided to an optical path length adjustment element in an external cavity laser to modulate the optical path length of the cavity. This produces a laser output having a wavelength modulation frequency and line width that are a function of the frequency and amplitude of the excitation signal. Under appropriate modulation frequency and line width combinations, the laser output comprises an optical signal with SBS suppression characteristics, thus enabling a higher power signal to be launched into a fiber link since the SBS suppression characteristics raise the SBS threshold of the link. The optical path length modulation also produces an intensity (amplitude) modulation in the laser output. A detector is employed to produce a feedback signal indicative of the intensity modulation that is used for tuning the laser in accordance with a wavelength locking servo loop.

Abstract: A servo technique for concurrently providing wavelength locking and stimulated Brillouin scattering (SBS) suppression in an external cavity laser. Respective wavelength locking and SBS suppression signals are generated by a controller and combined into a composite drive signal. The composite drive signal is used to drive an optical path length adjustment element to modulate the optical path length of the laser cavity. The wavelength locking and SBS suppression portions of the drive signals produce concurrent modulations of the laser optical path length having different modulation frequencies and causing different frequency (wavelength) excursions. These modulations produce corresponding wavelength and intensity amplitude modulations in the laser's output. A feedback signal indicative of the intensity amplitude modulations is filtered to attenuate the portion of the signal due to the SBS suppression modulation, and is received as a tuning feedback signal by the controller.

Abstract: A novel and efficient system and method for providing an output beam of collimated energy in the 8-12 micron range. The solid state system includes a pump laser (210) for providing an input beam and an OPO (250) using an x-cut potassium titanyl arsenate crystal for shifting the input beam from the first wavelength to a second wavelength. A second optical parametric oscillator (271) is included for shifting the beam from a second wavelength to a third wavelength. The second optical parametric oscillator (271) uses a cadmium selenide crystal. A tuning mechanism with an associated controller is provided to tune the oscillator as needed for a particular application.

Abstract: A slave pulsed laser stabilizes the frequency by using the master laser frequency to stabilize a cavity in the slave pulsed laser. The slave pulsed laser includes an optical modulator, a cavity, a cavity modifier, and an output generator. The cavity includes an end reflector, a laser generator, an optical injector, and an output coupler. The optical modulator receives a continuous wave laser signal that includes a carrier frequency. The optical modulator then modulates the continuous wave laser signal to generate two sidebands around the carrier frequency. The laser generator generates a first laser signal in the cavity. The optical injector then injects the continuous wave laser signal with the first laser signal. The output generator generates an output signal based on the continuous wave laser signal. The cavity modifier then modifies a length of the cavity based on the output signal wherein the cavity is in resonance with the frequency of the continuous wave laser signal.

Abstract: An arrayed-waveguide grating (AWG) is provided in a tunable mode-locked laser resonator where when a clock signal corresponding to a predetermined wavelength is input, the arrayed-waveguide grating (AWG) generates an output signal having an oscillation wavelength which has an arbitrary wavelength interval independent of the wavelength of said clock signal and a different propagation delay for each wavelength. Furthermore, a transmitter and a wavelength converter is provided that uses a tunable mode-locked laser where the frequency of the clock signal determines the wavelength and where a transmitted data signal at a fixed data rate is generated by setting the clock signal frequency sufficiently higher than the data rate. Furthermore, a wavelength converter and wavelength router is provided that uses said tunable mode-locked laser and in which the output wavelength is determined by extracting said clock signal from the input data signal.

Abstract: A tunable laser source changes the resonator length of an external resonator, which is constituted including a laser diode and a diffraction grating, by a driver controlled by a drive control section, to continuously or intermittently vary the wavelength of an emitted light from a start wavelength to a stop wavelength that are desired. A point wavelength information setting section sets the point wavelength information representing the positional information of the driver that corresponds to each resonator length of the external resonator regarding the start wavelength, the stop wavelength and a plurality of the wavelengths obtained by dividing a period between the start wavelength and the stop wavelength into arbitrary steps. An emitted wavelength information detecting section detects emitted wavelength information corresponding to the wavelength of the emitted light from the tunable laser source.

Abstract: Microwaves are generated by heterodyning the outputs of two or more optical lasers which have differing central frequencies to produce beat frequencies in the microwave range. One of the beat frequencies is used to modulate the output of at least one of the lasers so as to produce sidebands which differ from the central frequency by an integral number of the sideband frequency. Each laser is connected to one of the other lasers by a weak optical link to optically injection lock the laser to the sideband of the other laser.

Abstract: A method of delivering a seed-pulse to a regenerative amplifier includes generating an ultrashort optical pulse. The ultrashort optical pulse is delivered to a single-mode optical fiber configured to generate a continuum. A portion of the continuum generated by the optical fiber is selected by a pulse stretcher and converted into the seed pulse. The pulse stretcher can be tuned to provide seed pulses of selectively variable wavelength.

Abstract: A dynamic change detecting apparatus allows canceling the influence of environmental change or an individual difference between a plurality of laser elements so as to perform a stable detection.

Abstract: A Q-switched solid state laser is disclosed comprising a pump radiation source, whose pump radiation is focused through focusing elements in the laser crystal, a resonator formed by reflecting surfaces in which at least one laser crystal, an acousto-optic switch for Q-switching, and, if desired, a freqency-doubling crystal (KTP) are arranged. The acousto-optic Q-switch is connected with an electronic unit generating a high-frequency wave which can be modulated. The Q-switch is controlled by the high-frequency wave in such a way that laser pulses with pulse lengths on the order of magnitude of several microseconds (&mgr;s) and with an energy content on the order of magnitude of several millijoules can be generated by controlling the steepness of the edge of the modulation function of the high-frequency wave.

Abstract: An acousto-optic scanning system, which relies on two counter propagating acoustic waves with the same frequency modulation. This scheme completely suppresses the linear frequency chirp, and thus enables the generation of fast non-linear scans and non-constant linear scans. By changing the phase between the modulating signals, this scheme also provides fast longitudinal scans of the focal point.