Showing papers on "Injection locking published in 1985"

Locking conditions and stability properties for a semiconductor laser with external light injection

Abstract: We present a theoretical and experimental investigation of injection locking of semiconductor lasers. The theoretical analysis takes into account the dependence of refractive index on the carrier density expressed by the linewidth enhancement factor α. Locking conditions and dynamic stability are analyzed. The nonzero value of α results in an increased locking bandwidth, where only part of the range corresponds to a dynamically stable state. Asymmetric characteristics are obtained for the locked power and phase as a function of frequency detuning between the master and slave laser. Outside the stable range, light injection gives rise to beat phenomena and intensity pulsations. The theoretical results were confirmed by experiments on 830 nm CSP lasers and 1.3 μm BH lasers. The experiments include the first measurements of locking bandwidth characteristics reported for 1.3 μm lasers. Power spectra are recorded under locked and near-locked conditions and compared with theory. The 1.3 μm lasers are found to have a better dynamic stability than 830 nm lasers. Even so, the stability problems may exclude the particular application of injection locking where phase modulation is generated for coherent transmission.

Injection locking of coupled‐stripe diode laser arrays

Abstract: The control of the far‐field beam pattern and the spectrum of 10‐element laser diode array by injection locking to a single‐mode master laser are described. With less than 3 mW of injected power an array output of 105 mW at a single frequency with a 0.5° wide far‐field lobe is obtained. Similar results are observed when the entire array is illuminated by the master laser beam, or when only one of the stripes is illuminated. The narrow lobe contains 60–70% of the total power and is centered at an angle of about 4° relative to the normal of the array facet.

35 GHz microwave signal generation with an injection-locked laser diode

Abstract: A new technique for sinusoidal intensity modulation of light, based on injection-locking of two longitudinal modes of a single laser to FM sidebands of another laser, is described. A 35 GHz microwave signal with a linewidth of less than 10 Hz was generated.

Contribution of spontaneous emission to the linewidth of an injection-locked semiconductor laser

Abstract: We show that the spontaneous emission inside an injection-locked semiconductor laser does not alter the lasing field. For injection at the free-running frequency, the linewidth is only governed by the injected-field phase noise and may no longer follow the Schawlow-Townes dependence on emitted optical power.

Chirp-free transmission over 82.5 km of single mode fibers at 2 Gbit/s with injection locked DFB semiconductor lasers

Abstract: The spectral and modulation characteristics of injection locked distributed feedback lasers operating at 1.5-μm wavelength have been investigated. The total elimination of excess chirp in directly modulated lasers by the injection locking technique has allowed us to perform transmission experiments over 82.5 km of single mode fibers at 2 Gbit/s without any measurable penalty related to dispersion. Device design parameters for efficient chirp suppression are also given.

Single‐channel injection locking of a diode‐laser array with a cw dye laser

Abstract: We report injection‐locking studies on a gain‐guided diode‐laser array using a single‐frequency cw tunable dye laser master oscillator. By injecting a single end element, both the spatial and spectral emission characteristics of the entire ten‐element array could be controlled. The injection‐locked array produced over 100 mW output in a single‐lobed far‐field beam ( 60 GHz wide. Furthermore, by varying the injection frequency, the far‐field emission angle of the array could be continuously scanned over several degrees at a rate of 2.3×10−2 deg/GHz.

FM noise suppression and linewidth reduction in an injection-locked semiconductor laser

Abstract: An expression is derived for the FM noise spectrum of an injection-locked semiconductor laser. For increasing injection level the FM noise spectrum and the lineshape change gradually from those of the slave laser to those of the master laser. The ultimate linewidth reduction is obtained if the locking bandwidth is large enough to accommodate the frequency fluctuations and if the detuning is controlled carefully.

Influence of amplitude-phase coupling on the injection locking bandwidth of a semiconductor laser

Abstract: The strong amplitude-phase coupling in a semiconductor laser is well known to induce an enhancement linewidth factor (1 + α2) It is shown that it also produces an enhancement of the injection locking bandwidth proportional to (1 + α2)1/2. The connection with the usual locking bandwidth derived from Adler's equation is pointed out by considering the carrier dependence of the injected cavity resonance frequency.

Monolithically integrated thermoelectric controlled laser diode

Abstract: The fabrication and performance characteristics of a monolithically integrated thermoelectric controlled laser diode are described. The thermoelectric element is the n‐InP substrate. The lasers (λ∼1.51 μm InGaAsP) have threshold currents of ∼20 mA and operate kink free to >10 mW/facet. A variation of active region temperature of ± 2.5 °C has been achieved using 50 mA of thermoelectric controller current. The observed frequency tuning rate associated with this temperature shift is ∼0.5 GHz/mA. The device is useful for applications that require a high degree of frequency stability or small frequency tuning. Some potential lightwave system applications are in single‐frequency transmission systems, coherent transmission systems, optical amplifiers, resonant external cavity modulators, and injection locking.

Optically Controlled Microwave Devices and Circuits

Abstract: There is a growing interest in optically controlled microwave devices and systems. This paper is concerned with two experiments in this emerging area. The first describes the design, fabrication and application of optically controlled microwave PIN diodes. The utilization of these devices for phase-shifting and switching at X-band was demonstrated. The second experiment involved the optical tuning and indirect optical injection locking of a X-band dielectric resonator oscillator. A locking range of 400 KHz was achieved utilizing a third harmonic.

Generation and control of bandwidth-limited, single-mode picosecond optical pulses by strong RF modulation of a distributed feedback InGaAsP diode laser

Abstract: Bandwidth-limited, single-mode ultrashort optical pulses with excellent coherency were generated for the first time from an InGaAsP DC-PBH distributed feedback (DFB) diode laser oscillating at 1.3 μm. It was achieved only by the laser diode itself through the most feasible and reliable method of strong RF modulation superimposed on the dc bias current. This method appears to be practically superior over the other techniques such as modelocking and injection locking because the simplest configuration with no requirement of any other optical elements and external cavity other than a laser diode as well as careful alignment and precise control. The measurement of second-order intensity auto- and cross-correlation demonstrated to be their traces completely free from noise spikes, with the contrast ratio of almost three. The time-bandwidth products of generated coherent picosecond pulses measured at different RF modulation frequencies and positive and negative dc bias current levels gave almost the values between 0.32 and 0.44 for Lorentzian pulse shape, and this fact proves definitely the bandwidth limited or coherent character. The pulsewidth was demonstrated to be continuously controllable over a range of approximately twice to three times depending upon the modulation frequency by changing the dc bias current from positive to negative. Also, the strong sinusoidal RF current superimposed on the negative dc bias current was found to be effective for high peak power operation for this InGaAsP DFB-DC-PBH diode laser. The theoretical analysis using the single-mode rate equations provides quantitatively the good agreement with the experimental results presented in this paper.

Injection locking a xenon chloride laser at 308.4 nm

Abstract: A method for injection locking a xenon chloride laser at 308.4 nm. Neon (Ne) is used as a diluent in the laser to shift slightly the gain profile of the laser towards the longer wavelengths and towards 308.4 nm. The laser is operated at a lower level of gain than is used in the prior art by using a lower level of electrical discharge than was used in the prior art. The lowered gain reduces the numerical magnitude of the difference in the gain of the laser at 308.4 nm and its gain at the highest gain modes of operation. Either a low level signal at 308.4 nm is injected into the laser to mode lock the lowered gain laser at 308.4 nm. or a frequency selection device such as etalons is inserted within the laser cavity to restrict operation to 308.4 nm. The period of the electrical discharge also is lengthened from that typically used in the prior art so as to obtain saturation of the output at 308.4 nm.

Observations of Phase Locking in a Single-Cavity Gyrotron Oscillator

Abstract: Observations of phase locking in a single-cavity gyrotron oscillator operating at 35 GHz are reported. Injection of the locking power was made via a circulator into the gyrotron output guide. Locking was observed with input power levels as low as 35 dB below the gyrotron power. For low input powers, good agreement is found with theory based on lumped-element circuit modeling and a new distributed oscillator model.

Coherent lightwave transmitters

Abstract: A coherent lightwave transmitter includes a relatively low power, single frequency laser which provides an injection locking signal to a plurality of higher power lasers located in separate, parallel optical paths. A modulator is interposed between the single frequency laser and the higher power lasers, and the outputs of the latter are added constructively to form a high power transmitter output. Feedback control of the optical path lengths to maintain constructive interference is also described.

Differential phase shift keying receiver

Abstract: A receiver for demodulating differential phase shift keying data, the data having bit values dependent upon whether the phase of a carrier is inverted or not inverted during a bit interval, the receiver having a phase locked loop oscillator for locking up with the phase of the carrier, a phase detector for sensing differences in phases between the oscillator signal and the incoming data, an oscillator controller for controlling the output phase of the oscillator in response to the phase detector, a phase sense detector which detects whether or not the carrier has been inverted, a data clock responsive to the oscillator and to the phase sense detector for providing a data clock signal defining a bit interval, and a bit detector responsive to the phase sense detector, the data clock and the oscillator for integrating the incoming data.

Injection locking and saturation intensity of a cadmium iodide laser.

Abstract: A discharge-pumped cadmium monoiodide (CdI) laser utilizing isotopically pure CdI2 (114CdI2) has been injection locked with a flashlamp-pumped dye laser having a linewidth of 0.3 cm−1. Complete locking of the slave oscillator occurs for wavelengths between 655 and 660 nm and for injection intensities of ∼5 W cm−2. The saturation intensity for the B → X band of CdI has been directly measured with an excimer-pumped dye laser to be (125 ± 60) kW cm−2.

Measurements of the injection-locking influence on the frequency noise spectrum of single-mode semiconductor lasers

Abstract: The power spectral density of the instantaneous oscillation frequency of single-mode semiconductor lasers under the influence of an external optical driving signal is directly measured for the first time to our knowledge. The experimental results show how the frequency noise of the slave is influenced by the value of the injected power and by the difference between the emission frequencies of the master and slave optical cavities and how it is correlated to the noise properties of both the master and the free-running slave.

The Phase Noise Characteristics of a Driven SAW Oscillator in the Threshold Vicinity for Injection Locking

Abstract: Studies have been conducted on the phase noise of a driven 674 MHz SAW oscillator in the threshold vicinity for injection locking. An automated frequency stability analyzer was used to characterize phase noise and Allan variance, while a low-noise f requency synthesizer was used for injection. 1 Hz 5 fF 5 10 kHz was used for close-in phase noise measurements, while Allan variance U~(N,T,T) was computed over times 0.0001 i T 5 100s. In the l ocked state, it was found experimentally that the SAW oscillator adopted the close-in phase noise characteristics of the low-level (-30 dB down) injection source. This result is explained with reference to the theory of beat spectra in a driven unlocked oscillator. A Fourier frequency fF range

Mathematical Expression of the Loading Characteristics of Microwave Oscillators and Injection-Locking Characteristics (Short Paper)

Abstract: Most of the studies concerning microwave oscillators have so far been based on the Van der Pol oscillator model. However, this model is too simple to obtain good agreement between observation and theory. Our previous paper proposed a new mathematical model which describes the loading characteristics of oscillators more accurately than the Van der Pol model does. In this paper, we have investigated injection-locked microwave oscillators using the mathematical model to find out the relation between the loading and injection-locking characteristics.

Injection locking of ArF excimer lasers

Abstract: Injection-locking characteristics of an ArF excimer oscillator-amplifier laser are described including the use of stable-unstable optical cavities. Output intensities of 1 MW cm−2 have been produced with 3 mJ output energy, a spectral linewidth better than 5×10−3 nm and an injection locking efficiency of 0.9.

Injection-Locking and Self-Injection-Locking of Pulsed Single-Longitudinal Mode Alexandrite Lasers

Abstract: We will describe our results in obtaining high power single-longitudinal mode operation with alexandrite by two injection-locking techniques, conventional injection-locking and a novel self-injection-locking method which requires only a single laser cavity. An alexandrite laser for water vapor DIAL investigations near 727 nm, designed using this self-injection-locking technique, will also be described.

Locking Behavior of a Microwave Multiple-Device Ladder Oscillator

Abstract: This paper presents a detailed discussion on the injection-Iocking property of a microwave ladder oscillator which is essentially an array of diode mount-pairs in a rectangular waveguide cavity. It is shown both analytically and experimentally that the use of a ladder structure is advantageous both in obtaining a large locking figure of merit (i.e., 2Q/sub ex//sup -1/) and in rapidity of the transient response to the PSK signal injection.

Injection locked RF oscillator with control hoop

Abstract: An injection locked RF oscillator comprises a variable frequency RF source 12 having a Gunn diode 20 and a varactor 22, and a frequency stable reference oscillator 14 whose output fi is injected into the source to cause injection locking of the source. The output of a low frequency perturbation oscillator 30 is applied to the varactor and the resultant variation in the current consumption Io of the Gunn diode detected by amplifier 28 and filter 36 to provide a control signal which is effective to shift the resonant frequency fo of the source 12 towards the frequency fi of the reference oscillator, or a harmonic thereof. A sweep-and-lock circuit 44 is provided to acquire injection locking upon switch-on.

Millimeter-Visible Injection Locking and Testing

Abstract: A Visible-Millimeter Wave mixing system for testing high frequency devices has been set up with all components operating satisfactorily and locked to stabilized cavities. Using this system, mixing has been obtained, with frequency separations ranging to 100 GHz, in a number of GaAs and GaAs/AlGaAs devices. These devices include commercial FETs, state of the art industrial FETs as well as modulation doped HEMT structures and Heterojunction bi-polar transistors.

Tunable LC oscillator comprising a voltage-controlled reactance.

Abstract: Signal-processing phase-locked loops for generating carrier signals normally use varactor oscillator circuits as voltage-controlled oscillators. In the frequency range from a few hundred kHz down to a few MHz, when varactors are used, including those with the so-called hyper-abrupt p-n junction, it is not possible to obtain sufficiently linear control characteristics. In accordance with the invention therefore an oscillator is proposed, the voltage-controlled reactance of which contains a current-balancing circuit. Oscillators of this kind can be used with advantage in all cases where a particularly linear control characteristic is required at frequencies in the specified frequency range.

Suppression of Timing and Energy Fluctuations in a Modelocked Semiconductor Laser by cw-Injection

Abstract: Active modelocking of semiconductor lasers in an external cavity is a simple and useful technique for generation of short optical pulses in the wavelength region of interest for optical communications. Up to now, most attention has been paid to the time-averaged behaviour of pulse width, optical spectrum and time-bandwidth product, although noise, both at baseband and optical frequencies, is of major importance in communication and logic applications. In this paper, we investigate the noise behaviour of a modelocked GaAlAs laser and demonstrate a partial suppression by cw injection locking. A similar technique has previously been demonstrated with CO2 lasers [1].