Showing papers on "Injection locking published in 1990"

Optical synchronization of millimeter-wave oscillators for distributed architecture

Abstract: A review of various methods of phase and frequency synchronization of active MMIC based transmit/receive modules is presented, and particular emphasis is placed on the synchronization of oscillators through the use of an indirect subharmonic optical injection locking technique. In this approach, the nonlinear behavior of large-signal modulated laser diodes and solid-state oscillators is exploited to extend the bandwidth of the synchronizing link to the millimeter-wave frequency range. Experimental results of the phase and frequency coherency of two 21.5 GHz FET oscillators are reported. Optimum performance is achieved at a subharmonic factor of 1/4, with a locking range of 84 MHz and a phase noise degradation of only 14 dB. The phase coherency measurement of two injection-locked oscillators points to a phase shift, which is introduced as a result of the frequency detuning between the slave and master oscillator signals. A scheme to correct for this phase error is presented. >

Nonlinear injection locking dynamics and the onset of coherence collapse in external cavity lasers

Abstract: A theoretical analysis is presented of the experimentally observed collapse of coherence in semiconductor lasers exposed to moderate optical feedback. A main point in the analysis is, that coherence collapse in the delayed-feedback (DFB) system shows up as bistability in a much simpler model which corresponds to an injection locking system. Based on this, the authors derive a simple analytical expression, valid for DFB as well as Fabry-Perot lasers, for the critical feedback level at which coherence collapse sets in. Simulations of the nonlinear injection locking model reveal the presence of complicated nonlinear dynamics with period-doubling bifurcations and coexisting attractors even inside what is normally denoted the stable locking range. >

Novel measurement technique of α factor in DFB semiconductor lasers by injection locking

Abstract: A simple and accurate method to measure the linewidth enhancement factor a in DFB semiconductor lasers is proposed. This method, based on the principle of external optical injection locking, does not require the knowledge of the absolute value of optical injection level.

A periodic planar Gunn diode power combining oscillator

Abstract: Several planar periodic power combining oscillators containing two to six Gunn diodes operating in the X-band region are discussed. The maximum power combining efficiency, 126.7% was obtained from the three-diode oscillator. The frequency dependence of all the power combiners on the bias voltage variation seemed to be independent of the number of diodes. Injection locking was maintained over a large variation of the bias voltage. >

Subharmonic injection locking phenomena in synchronous oscillators

Abstract: Subharmonic locking behaviour of a synchronous oscillator has been demonstrated. It is shown that the oscillator can be locked using all subharmonics down to the tenth. Locking behaviour is similar to that observed for IMPATT diode and Gunn microwave injection locked oscillators.

Phase control of optically injection locked oscillators for phased arrays

Abstract: The most suitable architecture for millimeter-wave frequencies is based on the transmit/receiver (T/R)-level data mixing architecture, where a frequency reference is provided to local oscillators in the subarrays to have them frequency and phase synchronized. The indirect subharmonic optical injection locking has the benefit of a high degree of frequency synchronization up to millimeter-wave frequencies; however, the local oscillators suffer from phase inaccuracy over the locking range, first formulated by R. Adler (1946). A scheme is proposed to measure this phase error and correct for it by adjusting the free-running oscillation frequency of a voltage controlled oscillator (VCO). Experiments supporting this approach are reported for two optically injection locked oscillators at 18 GHz, where controlled phase shifts over -90 degrees to 78 degrees are achieved by adjusting the bias current to a yttrium-iron-garnet (YIG) tuned VCO. >

Quantum noise properties of an injection-locked laser oscillator with pump-noise suppression and squeezed injection

Abstract: The quantum noise properties of injection-locked semiconductor laser oscillators are investigated. Included in the analysis are pump-noise suppression and squeezing of the injection signal. It is shown that the main effect of injection locking is the reduction of the phase noise of the outgoing laser light field. The influence that squeezing of the injection signal state has on the output state is shown to be strongly dependent on the value of the linewidth enhancement factor. In general, little or no noise reduction stands to be gained by squeezing the injection signal. It is also shown that under idealized conditions, the spectral uncertainty product of the outgoing field will approach, but never go below, the minimum uncertainty value given by the Heisenberg uncertainty relation.

Ring cavity laser device

Abstract: A ring cavity laser device includes a slave laser placed in a ring cavity. The injection locking of a beam emitted by a master laser is achieved by a non-linear material in which interference occurs between the master laser beam and the beam circulating in the ring.

Short pulse injection seeding of Q-switched Nd:glass laser oscillators-theory and experiment

Abstract: A 0.5-GW-peak-power solid-state laser source that is based on injection seeding a Q-switched Nd:Glass laser is discussed. In the first experimental demonstration, a Q-switched oscillator producing 101 mJ was seeded by a train of 11-ps pulses from a CW (continuous-wave) mode-locked laser to produce injection-mode-locked pulses under a 91-ns envelope. A theoretical analysis of injection seeding of a high-gain Q-switched oscillator by the output of a mode-locked oscillator is presented. The numerical analysis predicts the minimum signal power required for injection mode locking and the temporal shape of the output pulse. The experimental results agree well with the theoretical predictions. The amplification demonstrated by this technique is 104.4 dB, which is much greater than that demonstrated by a multipass or regenerative amplifier. The experimental advantages of injection mode locking include greater than 100 dB of effective amplification and noncritical cavity length adjustment of the seed resonator. >

Equilibrium and stability of free-running, phase-locked, and mode-locked quasi-optical gyrotrons

Abstract: Equilibria and stability (both single-mode and sideband) are calculated and contrasted for free-running, phase-locked, and mode-locked oscillator configurations in a quasi-optical gyrotron. The oscillator can be phase locked by direct injection of radiation into the oscillator cavity. The equilibrium and stability properties are not greatly affected at low injection power levels. Alternatively, the oscillator could be phase locked by prebunching the beam. If the beam is prebunched, there are dramatic effects on both equilibrium and stability. The transverse efficiency can be considerably enhanced by prebunching the beam. This prebunching can be done on either a phase-locked (using an external RF source) or mode-locked (using the oscillator output) configuration. The stable locking bandwidth turns out to be about half the omega /Q linewidth of the mode. >

The effect of electronic feedback on semiconductor lasers

Abstract: Negative electronic feedback (EFB) has a strong effect on the performance of a bistable laser diode amplifier and on injection-locked lasers. Negative EFB drastically reduces the switching-up input power level and the hysteresis in the input-output power characteristic and in the tuning curves of the bistable laser amplifier. Furthermore, negative EFB leads to a reduction in the time delay associated with optical switching in diode laser amplifiers. This provides a means of enhancing the versatility of the proposed system in some potential applications. For an injected-locked laser, negative EFB achieves a broadening in the locking bandwidth and its dynamically stable region. >

Demodulation of multi-gigahertz frequency-modulated optical signals in an injection-locked distributed feedback laser oscillator

Abstract: A new type of wavelength selective optical receiver that allows the demodulation of multi-gigaHertz frequency modulated (FM) optical signals is demonstrated by detecting FM light-induced changes in the forward voltage of an optically injection-locked distributed feedback semiconductor laser operating at far above the lasing threshold. A bandwidth as wide as 2 GHz is reported together with an FM demodulation efficiency of 52 mu V/GHz. >

Two-stage injection locking of high-power semiconductor arrays.

Abstract: A new multistage diode-array injection-locking technique is demonstrated. This approach permits higher power extraction or higher overall gain to be achieved than possible with single-stage designs. Using two antireflection-coated 40-stripe multiple-quantum-well diode arrays, we characterize the amplifier small-signal and saturated gain performance. More than 500 mW of power is achieved with single frequency and narrow linewidth in a nearly diffraction-limited far-field lobe. With small-signal inputs, an overall gain of 25 dB with 290-mW locked output is obtained.

Logic inverter based on side mode injection locking in semiconductor lasers

Abstract: The performance of a logic inverter based on injection locking in laser diodes is presented. The fast commutation rise and fall times (5 and 2 ns, respectively) allow a 150 MHz repetition rate. Due to the gain existing in laser diodes, low optical switching energies (50 fJ) and large fan‐out rates (30) are also obtained, making such an inverter attractive for the purpose of parallel optical computing, particularly if semiconductor laser arrays are used in place of single laser diodes.

Propagation equation based theory of intermodal injection locking in semiconductor lasers

Abstract: Intermodal injection locking is analyzed theoretically through the use of propagation equations inside the amplifying semiconductor medium and the boundary conditions on the laser facets. In particular, the stability analysis is performed by considering the oscillation threshold of sideband waves generated inside the laser via intracavity nearly degenerate four-wave mixing processes. This study of injection locking is performed by taking into account the dispersion relationship of both the optical gain and linewidth enhancement factor. As a consequence, in intermodal injection locking, the injected-locked power is shown to be, in certain cases, lower than that of the free-running laser, and the frequency zones of stable injection locking broader than those obtained in the intramodal injection-locking case usually considered. >

Mutual injection-locking properties of monolithically-integrated surface-emitting multiple-quantum-well distributed feedback lasers

Abstract: The mutual injection-locking properties of a coupled pair of multiple-quantum-well distributed-feedback lasers with grating output couplers were investigated experimentally and theoretically. When the mutual injection locking occurred, the output of one laser decreased while that of the other increased. The locking curve was asymmetric, and a stable and an unstable locking region existed. From the theoretical analysis, it was found that the phase delay with which the electric field emitted from each laser to the other laser significantly influences the locking characteristics. The increase and decrease of the locked output power are caused by the phase delay. It is also shown that the laser which receives the larger optical injection behaves like a slave laser and the laser which has less optical injection behaves like a master laser, and the shape of the locking curve is determined by the balance between the alpha parameter and the thermal resistance. >

Injection‐locking characteristics of gain‐guided diode laser arrays with an ‘‘on‐chip’’ master laser

Abstract: We report measurements of the injection‐locking characteristics of a high‐power continuous‐wave diode laser array with an on‐chip independently controlled master laser. This integrated injection‐locked array emits a near‐diffraction‐limited single‐lobed output beam at cw power levels up to 220 mW/facet. By controlling the current to the master laser, the single‐lobed output beam can be electronically steered over a far‐field angle of >1.7°. We also report preliminary studies of the coupling interaction in these integrated devices.

Efficient amplification of a single-mode laser diode by photorefractive beam combination using an injection-locked diode-laser array pump.

Abstract: Powers in excess of 100 mW have been obtained in a near-diffraction-limited, single-mode laser-diode output by photorefractive two-beam coupling in BaTiO3, using an injection-locked 1-W diode-laser array as the pump source. Signal gains of as much as 8.1 are obtained, corresponding to pump transfer efficiencies of 49%. Calculations suggest that powers as high as 225 mW should be obtainable, given suitably antireflection-coated optics.

Theoretical performance of multigigabit-per-second lightwave systems using injection-locked semiconductor lasers

Abstract: The locking conditions for multigigabit-per-second modulation are examined, and the dependence of the receiver sensitivity on the fiber dispersion coefficient-length product is investigated. With a 4.8-Gb/s NRZ (nonreturn-to-zero) modulation, a 1-dB penalty in receiver sensitivity occurs for a transmission distance of 68 km. The injected power is 0.4 mW and the frequency detuning is -35 GHz. With 10-Gb/s NRZ modulation, the allowable transmission distance is 12.5 km for an injected power of 1.0 mW and a frequency detuning of -35 GHz. These results represent increases in the transmission distances obtained with a solitary laser by factors of 3.7 at 4.8 Gb/s and 2.7 at 10 Gb/s. >

Optical techniques for microwave generation, transmission and control

Abstract: Techniques for optical generation of microwave signals to 35 GHz, including direct laser diode modulation, FM sideband injection locking of laser diodes, and offset frequency phase locking of solid-state lasers, are reviewed. Optical methods for controlling microwave devices, including phased array radar and oscillators, are described. Recent advances in optical transmission of microwave signal are examined. >

Quantum-well SEED optical oscillators

Abstract: Oscillation at 110 MHz in a GaAs-GaAlAs quantum-well SEED (self-electrooptic effect device) optical oscillator is considered. Optimization of device length and optical pump wavelength for high-frequency oscillation is discussed. Frequency tuning is obtained by adjusting the oscillator bias voltage or optical pump power, and the oscillator can be injection locked to modulated optical signals. Frequency fluctuations caused by perturbative Gaussian noise and 1/f frequency noise are observed; the 1/f noise in an 8.5-MHz oscillator limited the minimum frequency variance to 230 Hz/sup 2/. >

Two-Frequency Operation of a Hybrid TEA CO2 Laser and Its Application to Two-Frequency Pulse Injection Locking

Abstract: Simultaneous two-frequency oscillation of a hybrid TEA CO2 laser is exhibited when the cw section is operated in a "below threshold" state. The output of the hybrid laser thus obtained is injected into a main TEA CO2 laser to obtain a power-modulated, long-pulse output with a well suppressed gain-switched spike.

Pulse injection-locked TEA CO2 laser for long pulse operation with feedback stabilization

Abstract: Stable, long pulse operation of a TEA CO2 laser is achieved with a pulse injection locking system using a hybrid CO2 laser as an injection source. With feedback stabilization loops incorporated, both single-longitudinal- mode and two-longitudinal-mode oscillations are realized. The optimum condition for the synchronization between the injection pulse and the initiation of the discharge of the main TEA CO2 laser is investigated. The effect of the detuning angle on the long pulse operation is also studied.

An Injection Locking Method for Multiple FET Oscillators Suitable for Active Phased Arrays and Quasi-Optical Power Combining

Abstract: In this paper we present a new method for the mutual injection locking of large numbers of FET oscillators. This is accomplished by taking advantage of the non-reciprocal nature of the FET, using the gate of the device as the locking signal injection port, and extracting the rf power from the drain port, which is relatively insensitive to an injected signal. This method is attractive for injection locked phased arrays and quasi-optical power combining schemes, where each oscillator is associated with an individual radiating element Results for a five element phased array prototype circuit operating at 6 GHz are reported.

Experimental results of power combining and phase-locking magnetrons for accelerator applications

Abstract: It is demonstrated that injection-locked magnetrons can be used to drive a moderate Q cavity without a circulator with excellent interpulse phase coherency. A 3-dB hybrid coupler provides the avenue for both injection locking and power combining of magnetron pairs. Better intrapulse phase coherency than has been demonstrated is anticipated when lower Q magnetrons or lower gains are used. The cavity transient impedance does not preclude the magnetrons from filling the cavity, at least when the cavity fill time is less than the magnetron phase lock time. >

Optical homodyne detection with an injection-locked Er-doped-fiber ring laser.

Abstract: Optical homodyne detection is demonstrated with an injection-locked Er-doped-fiber ring laser. A 3-MHz phase-modulated optical signal is successfully demodulated.

Phase jitter in an injection-locked semiconductor laser.

Abstract: An expression for the mean-square phase jitter of an injection-locked semiconductor laser is derived. It leads to the determination of the power spectrum of the locked laser. The theoretical results are in good agreement with experimental results reported previously [IEEE J. Quantum Electron. 24, 148 (1988)].

An equivalent circuit model of a multimode semiconductor laser

Abstract: It is shown how equivalent circuit modelling techniques can be expanded to cover the simulation of multimode lasers. The topics covered include: the single resonance model; representation of photons as classical pulses; the multiple resonance model; results from the double resonance model including mode competition; and injection locking with the single resonance model.

Coupling strength dependence of phase locking of Ar-ion lasers.

Abstract: An experiment was performed using two cw Ar-ion lasers in Fabry-Perot resonators configured in a U-shaped cavity and coupled through a common end mirror to examine the effect of coupling strength on phase locking. The near field fringe visibilities were measured while varying the reflectivity of the common end mirror from 10 to 90%. The total multiline and single line visibilities during multiline coupling along with the visibility during single line coupling were measured. The optimal coupling strength for phase-locked operation for the Ar-ion lasers used in this experiment was found to be ~25%.