Abstract: The present invention provides a wide band optical modulator comprising an optical waveguide which is provided on a substrate and comprises a substance having electrooptic effects, a laminate which is provided on the optical waveguide and comprises a substance having a refractive index smaller than that of the optical waveguide, and two traveling-wave electrodes which are provided opposite to each other on the parallel side surfaces of the laminate in the traveling direction of light so as to hold the laminate therebetween. When the laminate provided on the optical waveguide is replaced by a gap, similar effects to those of the above-described optical modulator can be obtained.

Abstract: A system for producing spectrally pure optical pumping light at a resonant frequency is disclosed for molecular species and atomic isotopes. A Faraday filter is used as a transmission filter, and the frequency overlap between the output of a light source containing the atomic or molecular material and the spectrum of the Faraday filter allows optically pure pumping light to emanate from the filter. Cross-polarizers are used to further reduce background noise.

Abstract: Gaseous flux laser generator of the nitrogen and carbon dioxyde type. The dimensions of the enclosure and the conditions of injection of the nitrogen and those of the electrical supply are chosen to set up a luminescent discharge in a swirling flow.

Abstract: An amplifier for use with fiber optic systems comprises a neodymium YAG crystal placed in series with a signal-carrying optical fiber. The ND:YAG crystal is supplied by the optical fiber with both the signal to be amplified, and pumping illumination. The pumping illumination is coupled onto the optical fiber by a multiplexing coupler which is used to combine the signal to be amplified and illumination from a pumping illumination source onto a single optical fiber. The pumping illumination inverts the neodymium ions within the ND:YAG crystal. The signal to be amplified propagates through this crystal to stimulate emission of coherent light from the neodymium ions, resulting in amplification of the signal.

Abstract: A method and apparatus are disclosed for providing a laser beam that is automatically aligned with a substantially rigid, stabilized platform or frame that can be oriented over a wide angular range, such as by the gimbals of a laser pointing and tracking system. A single-transverse-mode master laser oscillator 12 is mounted on the stabilized platform 13 which is part of the inner gimbal, which can be rotated about an elevation axis 16, and a multipass laser amplifier 21 with a phase conjugation mirror 22 and an optional nonlinear frequency-conversion device 20 are located off the inner gimbal. An outer gimbal or pedestal mount permits rotation about an azimuthal axis 17. The laser oscillator 12 and laser amplifier 21 are coupled by means of a beamsplitter 15 and two reflecting elements 18 and 19. The laser media used for the oscillator 12 and amplifier 21 are either the same, or compatible media having the same 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 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: An optical resonant assembly which has at least two stable light transmittance values dependent on incident light beams. The assembly consists of a pair of parallel partially transmission mirrors with a photochromic layer placed therebetween which has a refractive index dependent upon the intensity of incident light beams. The parallel mirrors constitute a Fabry-Perot type resonator. The incident light beams have the effect of "couloring" or "bleaching" the photochromatic material.

Abstract: A device for steering a wavefront of electromagnetic radiation comprising a pumping means for coherently pumping a plurality of phase conjugate mirrors with a monochromatic coherent beam having a wavelength substantially the same as the wavelength of the wavefront. The device further comprises an array of phase conjugate mirrors wherein the acceptance of each phase conjugate mirror, for conjugate reflection of the wavefront, is pointing in substantially the same direction, and the phase conjugate mirrors are composed of material responsive to the beam wavelength. The device further comprises a Fourier transform lens, a control reflector positioned such that the reflected beam from the reflector back to the lens is within the acceptance angle of the ray, and a beam splitter positioned between the array and the control reflector for extracting a steered beam. Each phase conjugate mirror may provide amplification of the wavefront, or amplifying lasers may be used.

Abstract: A tunable dye laser has been found particularly suited to selective photothermolysis. A longer pulse duration which makes the system suitable for a wider range of applications is obtained by modifying the laser to generate a spatially noncoherent beam. The optical system at each end of the laser cell, which may include a lens or spherical mirror, refocuses the aperture of the dye cell near to itself so that substantially all light emanating from the dye cell is returned to the dye cell until the light passes through one of the optic systems as a noncoherent laser beam. A tunable intracavity element tunes the laser across the gain curve of the dye solution. The pulse duration of the laser beam can be selected from a range of durations up to about one millisecond.

Abstract: A solid state radar transmitter pulse modulator system capable of generating high power operating pulses having pulse width and pulse repetition rate agility and being programmable for output pulse current over a substantial range of peak current values to produce corresponding values of transmitter output power. A multi-stage cascade cross-field amplifier (CFA RF chain) is employed, each stage having its own pulse modulator comprised of one or more standard modules paralleled at the output to drive the corresponding CFA stage provides fail-soft operation. Means are included for protecting solid state circuits in the event of CFA or other component failures, for dynamically matching CFA and pulse transformer impedances, and for preventing BH curve "walk-up" during operation.

Abstract: Microwave oscillators and amplifiers which utilize a superconducting slow-wave circuit. The slow circuit is made from materials which exhibit superconductivity at relatively high critical temperatures. The slow wave circuit is integral with the device's vacuum housing. Coolant exterior to the vacuum housing maintains the circuit in the superconducting state. The slow-wave circuit, which protrudes into the vacuum housing provides modulation of an electron beam which traverses the interior of the vacuum housing. Output power is ultimately extracted from the slow wave circuit.

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 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: A bistable laser for realizing a waveshaping function, having a drive current which during normalcy biases the bistable laser to the middle point of the hysteresis region thereof. When input light exceeds a threshold level, the bistable laser is switched into the lasing state, and even when the input light thereafter disappears, the laser emits light of fixed intensity. A detector having detected this lasing state decreases the drive current temporarily after a predetermined period of time, to switch the bistable laser into the non-lasing state, whereby not only the amplification but also the shaping of an optical pulse signal is achieved.

Abstract: A laser diode circuit has a photodiode which monitors the light output which is outputted by the laser diode and generates a photovoltaic current that corresponds to the level of the light output, a reference current selection device which selects a required reference current by switching among a plurality of reference current sources that are set to values of mutually different current values, and an amplifying apparatus which, by receiving a signal that corresponds to the photovoltaic current, controls the forward current of the laser diode so as to bring the photovoltaic current to a selected reference current.

Abstract: A glass bead laser amplifier which is designed to operate efficiently at relatively high optical power outputs, and which is designed to be easily manufactured and scaled up in size to produce high power laser beams. The laser amplifier cavity if filled with doped glass lasing beads or elements which are packed therein to be in contiguous contact with each other. The shape of each glass element preferably provides a relatively large ratio of the external area to volume of the glass lasing element, to provide for efficient cooling thereof. A cooling system is provided for the laser amplifier cavity in which a coolant fluid circulates through the laser cavity around and between the contiguous glass lasing elements for cooling thereof. The cooling fluid is selected to have an index of refraction substantially matching that of the glass lasing elements to substantially reduce scattering of light passing through the glass/cooling fluid interfaces in the laser amplifier cavity.

Abstract: Apparatus and a related method for generating a uniphase reference beam from a weak and aberrated input probe beam in an optical system. A portion of the input probe beam is split off and injected into the cavity of a laser, such as a semiconductor diode laser, where four-wave mixing takes place and an amplified input wave or its phase conjugate is output. Because the laser cavity is selected to provide single-mode operation, the laser provides not only amplification but an output that includes a uniphase wave, which may be interfered with the original aberrated input probe beam for purposes of obtaining wavefront information.

Abstract: Apparatus, and a corresponding method for its use, for producing a phased array of high-energy laser beams from multiple laser amplifiers. A reference beam produced by a master oscillator senses phase and piston errors in a primary mirror array, and is divided into multiple probe beams, each of which makes multiple passes of its own laser amplifier. The multiple probe beams are together focused into a single phase conjugation cell, which not only produces phase-conjugated reflected beams, to effect compensation for various phase aberrations, but also locks all of the reflected beams together in phase. An arrangement of a birefringent wedge and a quaterwave plate for each of the beams prevents the reflected beams from returning to the master oscillator and facilitates combining of the reflected beams for output as a cophasal array.

Abstract: The present invention relates to an optical upconverting or downconverting gain or loss modulating mixer and a receiver for subcarrier optical communication systems using this mixer. The optical mixer can be formed, for example, from an optical amplifier including a semiconductor laser chip comprising a p-n junction with an active region channel formed along the junction. An optical signal received from the communication system is directed into one end of the channel, and a combination of a D-C bias signal and a local oscillator signal is concurrently impressed on the chip to gain-modulate the received optical signal and produce an upconverted or downconverted output signal. In the receiver, the upconverted or downconverted output signal from the gain-modulated optical amplifier is detected by a photodetector, amplified if necessary, filtered and then demodulated before transmission to the output utilization device.

Abstract: The broadband semiconductor optical amplifier fabricated in accordance with the teachings of the present invention comprises first and second active semiconductor regions (50, 51) disposed in tandem with each other, and means for injecting current (I.sub.1,I.sub.2) into the first and second active semiconductor regions to provide gain distributions over wavelength regions in the two active semiconductor regions which partially overlap to form a combined gain distribution over a wider range of wavelengths. Anti-reflection coatings (54, 55) are disposed on the extreme ends of the combined structure. Tuneable wavelength selective amplification over the wider range is achieved in various embodiments by including a tunable optical bandpass filter (53) or by including various tunable auxiliary light guiding structures (115, 116; 140; or 450) to which and from which light power is coupled from and to the active semiconductor regions of the amplifier, respectively.

Abstract: An optical amplifier takes the form of a semiconductor laser with coatings on its two facets. The coating takes the form of an anti-reflective coating, e.g. an oxide of Y, Gd, Nd, or La, to reduce the reflectivity and a thin interlayer, e.g. Al.sub.2 O.sub.3, to enhance compatibility between the laser and the anti-reflective coating.

Abstract: An apparatus 10 and method for producing a high-energy laser beam 14'". A low-power, good quality, input laser beam 14 is produced by master oscillator 12. The low-power beam 14 is focused at an input focal point 20 and reflected from turning flat 22 to a power amplifier 24 where it is amplified to a moderate power level. It is then transmitted through a polarization beam splitter 28 and its optical path length adjusted by adjustment means 30,32,34,36 prior to being directed to a phase conjugator 44. A quarter-wave plate 40 causes the phase conjugated returning beam 14" to be orthogonally polarized thereby reflecting it from polarization beam splitters 38,28. Beam 14" is then passed through the power amplifier 24 and focused at an output focal point 50 in a vacuum. The resultant high-power output beam 14'" is produced without significant degradation in the beam quality.

Abstract: An unstable optical resonator having a gain region that has an elliptic or other non-circular cross section still has the benefits of a total collimated cavity Fresnel number that is azimuthally symmetric by the combination of several cavity regions of azimuthally non-uniform Fresnel number of appropriate size.

Abstract: An optical system comprises a low coherence light-emitting device and a mirror. The mirror is positioned adjacent an end face of the device such that light emitted from the end face may be redirected back into the device. Radiation having low coherence, which is emitted from an opposing end face, is amplified greatly due to the radiation which reenters the device.

Abstract: Means including a single comparatively low-power laser and cooperative optics are disclosed for both designating and boresighting a comparatively high-power laser with an intended target object.

Abstract: A low diffraction-feedback high-energy laser system includes an injection laser, and a master power amplifier (MOPA). The master oscillator power amplifier preferably includes a convex and a concave cavity reflector. A sensor mounted to the convex reflector is operative to provide a signal indication of cavity turbulence.

Abstract: An all-optical device containing saturable gain, saturable loss and unsaturable loss regions which functions to transform weak, distorted optical pulses into uniform standard-shape pulses. The device performs thresholding, amplification and pulse shaping as required from an optical repeater, and may be implemented in semiconductor technology.

Abstract: An improved unstable optical cavity for optical amplifiers or laser oscillators is made effectively single mode by altering the central Fresnel zone of the back mirror in order to provide constructive interference at the plane of the output aperture.

Abstract: A low diffraction-feedback high-energy laser system includes an injection laser, a master oscillator power amplifier (MOPA), and means for aligning the injection laser to the MOPA. A composite sensor for providing a dual-sensing capability is disclosed including a mosaic array and a superposed quad sensor.

Abstract: A low diffraction-feedback high-energy laser system includes an injection laser, a master oscillator power amplifier (MOPA), and means for aligning the injection laser to the MOPA. The alignment means includes a relay mirror and sensor array cooperative to center the injection laser externally of the cavity, and the alignment means further includes a relay mirror and cooperative optics and sensor to center the injection laser interiorly of the cavity. The master oscillator power amplifier preferably includes a convex and a concave cavity. reflector. In one embodiment, an intracavity laser separator is disclosed for providing alignment of the injection laser, and in a further embodiment an extracavity laser separator is disclosed for providing injection laser alignment.

Abstract: A light induced unidirectional light switch is described wherein a unidirectionally emitting medium is obtained using the method of Doppler compensation by light-induced velocity-dependent light shifts. The emission in the emitting medium can be switched on by a pulse of laser light which acts as a light induced light switch.

Abstract: A unidirectional light amplifier is described wherein laser light is utilized to create an anisotropic medium in which light is fully amplified in only one direction and fully absorbed in the opposite direction. It is analogous to the way in which a junction diode conducts electrical current more easily in one direction than in the other direction.

Abstract: A laser apparatus (10) has a coherent master oscillator radiation source (30) for driving a plurality of laser gain elements (20) positioned in a operationally parallel configuration so as to receive unamplified radiation (40) from master oscillator (30) and transmitting amplified radiation (44). Input means (60) couples portion of radiation (40) from master oscillator to each of said gain elements (20). Phase conjugate reflector means (80) operatively coupled to gain elements (20) reflects the phase conjugate of amplified radiation (44) back into the gain elements (20) where it is further amplified. Output coupling means (90) couples amplified radiation from the plurality of gain elements (20) out of the laser apparatus as a single coherent output beam of radiation.

Abstract: In a method and apparatus for amplifying and/or generating electromagnetic wave radiation, a gas plasma region having a non-Maxwellian electron distribution is produced by effecting collisions between scattering particles in the gas with free electrons which have been accelerated to an energy level which is greater than that providing maximum probability of collision of the electrons with scattering particles in said gas; and the electromagnetic wave radiation is subjected to the plasma region such as to produce amplification of the radiation by stimulated emission of Bremstrahlung from scattered free electrons in the plasma region.

Abstract: The input signal to a TWT amplifier is predistorted in amplitude and phase to the inverse of the amplifier transfer characteristic by an adjustable circuit including a phase linearizing section and an amplitude linearizing section, both in series with the input signal and amplifier. Each section includes two pairs of back-to-front Schottky diodes. Preferably an additional diode is in series with one pair for the amplitude section. The diodes of each pair are of like polarity and opposite to the diodes of the other pair of the section. Additional diodes are connected between the pair junctions and ground, and adjustable D.C. bias fed into these junctions. Additional resistors and capacitors bridge the pairs, and are arranged into a phase delay network in one of the sections.

Abstract: An anomalous intensification of the infrared emission from n-InSb having a central wavelength almost equal to the energy gap has been observed, as a result of the cooperation of the magnetoconcentration effect and the photo-excitation, in the temperature range from 80.degree. to 300.degree. K. This suggests that a light amplifier which operates at room temperature can be realized through the process for photons with a wavelength corresponding to the energy gap of the semiconductor material forming the light amplifier concerned. Also the cooperation of the magneto-concentration with the photo-excitation has another useful application as a tunable light source controlled by varying the applied magnetic field through the interband Landau-level transitions at liquid helium temperatures.

Abstract: A semiconductor amplifying device 1 comprises, a substrate 2, a first optical waveguide 7 on the substrate 2 for transmitting an optical signal, a second optical waveguide 8 on the substrate 2, a third optical waveguide 11 on the substrate 2 forming an optical coupling with the first optical waveguide 7 along an interaction length and constructed as a semiconductor optical amplifier 11 that receives and amplifies at least a portion of the optical signal to the first waveguide 7, and antireflective means 16 covering light emitting edges 7a, 8a, 11a, 3a at corresponding ends of the respective waveguides 7, 8, 11 and an optical transmitting medium 3, the second optical coupling having a phase mismatch selected for a wavelength of the optical signal to provide for a power gain in the first optical waveguide 7 attributed to an amplified portion of the same wavelength of the optical signal coupled back from the amplifier 11.

Abstract: A circuit arrangement protects against thermal overload as a consequence of impermissible operating conditions in traveling wave tube amplifiers having multi-collector traveling wave tubes. At least one measuring device is provided for measuring the collector current at at least one collector of the traveling wave tube and, in response to measuring a prescribed current threshold, the cathode current of the traveling wave tube is regulated back by way of a control device or is disconnected by way of a control logic circuit.

Abstract: The invention relates to an optical amplification device (10) with noise filter function. A body, composed of a plurality of layers (11-15) of different materials has electrodes (16) on its opposing sides. A first (12) and a second (14) of these layers is light wave conductive and forms a directional coupler with an interaction length (2L) consisting of two coupling lengths. The other (14) of the light wave conductive layers is a travelling wave amplifier which is pumped by an electric current (I) between the electrodes (16). The dispersion of the light wave conductors varies according to different relationships, and the effective refractive index has a common value (N.sub.eff0) for the wavelength intended for amplification. A light signal (I.sub.s, I.sub.b) in the first waveguide (12) migrates transversely over to the second waveguide (14), where it is amplified and migrates back again to the first waveguide (12). At the same time there is noise filtration of the signal (I.sub.s, I.sub.

Abstract: An optical signal pulse to be amplified and a pump signal pulse are launched consecutively into one end of an optical fiber, which may comprise a separate fibre or part of a transmission line. The pulses differ in wavelength by one or more Stokes shift and the order of launch is determined by the relative group velocities in the fibre. Owing to dispersion in the fibre the pulses overlap and overtake one another while they are transmitted along the fibre, the signal pulse being amplified as a result of Raman stimulated emission and compressed as a result of power depletion from the pump pulse, thus increasing the bandwidth of the transmission line.

Abstract: Light is amplified in a semiconductor laser structure through which a current is passed and (a) the wavelength of the light is greater than the wavelength of maximum gain of the laser structure, or (b) injection locking is avoided, or (c) the current is controlled so as at least partly to compensate for the decrease in the monitored light output at a wavelength or over a wavelength range distinct from that of the emitted amplified signal.In this way relatively high input powers can be amplified.

Abstract: A relatively low-power but high-quality laser oscillator is coupled to a high-power laser amplifier. The amplifier includes a rectangular slab of laser active material, and a phase-conjugate end mirror.

Abstract: An amplifier for use with fiber optic systems comprises a neodymium YAG crystal placed in series with a signal-carrying optical fiber. The ND:YAG crystal is supplied by the optical fiber with both the signal to be amplified, and pumping illumination. The pumping illumination is coupled onto the optical fiber by a multiplexing coupler which is used to combine the signal to be amplified and illumination from a pumping illumination source onto a single optical fiber. The pumping illumination inverts the neodymium ions within the ND:YAG crystal. The signal to be amplified propagates through this crystal to stimulate emission of coherent light from the neodymium ions, resulting in amplification of the signal.

Abstract: Use is made of stimulated Raman emission to induce gain in an optical signal (13) of a first wavelength. The optical signal (13) and a pump signal (14) are synchronously coupled to a length of optical fibre (15). The pump signal is at a second wavelength. The first wavelength corresponds to one Stokes shift from the pump signal. The pump signal is generated by a semiconductor laser (11) and thus only relatively low pump powers are involved in comparison with the conventional use of YAG lasers as the pumps, however significant gain is achieved despite the low pump powers. Preferably the optical fibre (15) has a high Raman cross-section and a low transmission loss, for example GeO.sub.2 doped SiO.sub.2 or pure GeO.sub.2.

Abstract: An optical amplifier particularly suitable for use in amplifying signals carried on optical fiber in a select communication band. The amplifier comprises a resonant optical waveguide cavity which has a core containing an active gain material with given absorption and fluorescence spectrums. The gain material is of the type that preferably has at least two different emission bands originating from the same energy level with one of the emission bands encompassing the select communication band. The cavity is structured to resonate wavelengths in both emission bands, but with a higher combination of cavity Q and gain coefficient per excited ion for wavelengths in the emission band not corresponding to the select communication band so that, when pumped, the cavity first lases at this band.

Abstract: A method and apparatus are disclosed for regulating the operation of a TWT. The TWT regulation is achieved by detecting the operating condition of the TWT, e.g., by measuring dynamic gain, and regulating feedback of the TWT output in response to the TWT operating condition. The invention is preferably implemented so as to augment the TWT input drive from an exciter source to induce the TWT to drive itself into saturation. The inventive technique comprises determining whether the TWT is operating in a desired operating condition, e.g., saturation, feeding back to the TWT input a portion of the TWT output power to the TWT input, and regulating the feedback signal to keep the TWT operating in the desired condition. Determination of whether the TWT is operating in a saturation condition may be affected through measurement of the TWT dynamic gain. The invention permits dynamic management of the feedback to accommodate variations in gain of the TWT, e.g.

Abstract: This application discloses light amplification apparatus in which population inversion is created in which energized particles collide with a lasing medium to create a population inversion. In the preferred embodiment the energized particles are atoms, ions, or molecules different than the lasing medium which are excited to a long-lived state above the ground state. Various materials usable in such light amplification apparatus are disclosed as well as means for passing light through an amplification region.

Abstract: A traveling wave tube transmission amplifier arrangement, including the series connection of a predistortion circuit, a preamplifier with limiter circuit and a traveling wave tube amplifier, which is provided with several stabilizing circuits. To limit the output power, a signal which is a measure of the output power of the traveling wave tube, e.g., a signal proportional to the collector current of the traveling wave tube, is fed to a threshold controller which governs a variable attenuator provided at the input of the transmission amplifier arrangement. Moreover, to provide compensation for aging effects, a remote control signal, which is determined on the basis of an intermodulation measurement, is fed to the preamplifier with limiter circuit.

Abstract: Two or more distributed amplifiers are paralleled to increase the available output power. Phase shifters are coupled to the amplifiers as necessary to maximize output power at a frequency. With this phase adjustment, the amplifiers may have effective electrical lengths which differ one from another by N (360.degree.), where N is zero or an integer. Values of N other than zero undesirably reduce the instantaneous bandwidth of the paralleled amplifiers. The bandwidth is maximized by the addition of sufficient delays to reduce N to zero.

Abstract: A system for linearly amplifying an optical analog signal by backward stimulated Raman scattering comprises a laser source for generating a pump pulse; and an optic fiber having two opposed apertures, a first aperture for receiving the pump pulse and a second aperture for receiving the optical analog signal, wherein the optical analog signal is linearly amplified to an amplified optical analog signal.