Showing papers on "Injection locking published in 1997"

Phase noise in coupled oscillators: theory and experiment

Abstract: Phase noise in mutually synchronized oscillator systems is analyzed for arbitrary coupling and injection-locking topologies, neglecting amplitude noise, and amplitude modulation (AM) to phase modulation (PM) conversion. When the coupling phase is chosen properly (depending on the oscillator model), the near-carrier phase noise is reduced to 1/N that of a single oscillator, provided the coupling network is reciprocal. This is proved In general, and illustrated with specific cases of globally coupled and nearest-neighbor coupled oscillator chains. A slight noise degradation is found for unilaterally coupled (nonreciprocal) chains. The 1/N reduction for reciprocal coupling applies over nearly the entire range of free-running frequency distributions required for beam-scanning, and is verified experimentally using a linear chain of coupled GaAs MESFET voltage-controlled oscillators (VCOs) operating at X-band. The effect of a nonoptimum coupling phase on the phase noise of the system is also studied. As the coupling phase deviates from the optimum value, the phase noise increases significantly near the locking range edge for noise offset frequency near the carrier.

Dual microwave and optical oscillator.

Abstract: We describe and demonstrate a novel device in which a microwave oscillation and an optical oscillation are generated and directly coupled with each other. With the mutual influence between the microwave and the optical oscillations, we project that this device is capable of simultaneously generating stable optical pulses down to the subpicosecond level and spectrally pure microwave signals at frequencies greater than 70 GHz.

Modulation bandwidth, noise, and stability of a semiconductor laser subject to strong injection locking

Abstract: Operating conditions for modulation bandwidth enhancement, noise reduction, and stable locking to be simultaneously fulfilled in a semiconductor laser subject to strong optical injection are investigated. When the strength of the injection signal is fixed, the optimum detuning of the injection frequency exists as a tradeoff between bandwidth enhancement and noise reduction. When the laser is injection-locked at a given value of frequency detuning in the stable locking region, both bandwidth enhancement and noise reduction are improved as the injection parameter is increased over a wide range.

Absolute value of the d 36 nonlinear coefficient of AgGaS 2 : prospect for a low-threshold doubly resonant oscillator-based 3:1 frequency divider

Abstract: We report the measurement of the absolute d36 nonlinear coefficient of silver gallium sulfide (AgGaS2) from three phase-matched nonlinear interactions spanning from 10.2 to 0.78 µm: the sum-frequency of a CO2 laser (10.2 µm) and a near-IR AlGaAs diode laser (0.842 µm), the second-harmonic generation of a KCl:Li color-center laser (2.53 µm), and the noncritically phase-matched 3ω-ω→2ω difference frequency between the AlGaAs diode laser and the KCl:Li laser to generate 1.265 µm. From the theoretical evaluation of the Gaussian-beam aperture functions for these type I interactions with arbitrary focusing parameters, beam-waist locations, and absorption losses, we have deduced from the three processes the same consistent value d36=13 (±2) pm/V for AgGaS2. Our value is independent of the growth origin of the material. In light of the trustworthy value of d36 measured from our experiments we analyze the feasibility of a continuous-wave doubly resonant parametric oscillator-(DRO-)based 3:1 frequency divider pumped by a near-IR diode laser. The predicted pump power threshold for the ring-resonator DRO lies in the range of 70–140 mW for a 14–18-mm-long sample with an absorption loss near the level of 1% cm-1 at the output frequencies.

Phase noise in externally injection-locked oscillator arrays

Abstract: Previous investigations of noise in mutually synchronized coupled-oscillator systems are extended to include the effects of phase noise introduced by externally injected signals. The analysis is developed for arbitrarily coupled arrays and an arbitrary collection of coherent injected signals, and is illustrated with the specific case of linear chains of nearest neighbor coupled oscillators either globally locked (locking signal applied to each array element) or with the locking signal applied to a single-array element. It is shown that the general behavior is qualitatively similar to a single injection-locked oscillator, with the output noise tracking the injected noise near the carrier, and returning to the free-running array noise far from the carrier, with intermediate behavior significantly influenced by the number of array elements and injection strength. The theory is validated using a five-element GaAs MESFET oscillator array operating at S-band.

Large-signal analysis of all-optical wavelength conversion using two-mode injection-locking in semiconductor lasers

Abstract: A large-signal analysis is presented for a DC-biased Fabry-Perot laser locked by simultaneous strong optical injection of a CW signal and a modulated signal into different modes. The model is based on the description of injection-locking by Lang (1982) which is shown to hold even under the condition of strong injection and large detuning of the input signals. The following results are obtained: the configuration allows all-optical wavelength conversion in the multigigabit range, and both logically noninverting and inverting conversion is possible. In both operation modes, the conversion mechanism is mainly attributed to dispersive switching which is shown to be very fast above threshold due to injection-locking. Operation up to data rates of 20 Gb/s is possible with reasonable output extinction ratio. The bandwidth is determined by the relaxation oscillation frequency of the laser. It will be extended by decreasing the resonator length, increasing the injected current, and increasing the injected optical power. The output signal is nearly chirp-free. The model is able to explain the main results of previously published experiments.

Interference-free broadband television tuner

Abstract: An interference free local oscillator circuit is disclosed A first local oscillator signal is generated in a first phase locked loop A second local oscillator signal is generated in a second phase locked loop Third and fourth phase locked loops provide inputs to the second phase locked loop to control the second local oscillator frequency The operating frequencies of the first and second local oscillator signals are selected so that spurious signals generated in the phase locked loops do not interfere with a received RF signal in a conversion circuit

Injection-locked semiconductor lasers with delayed optoelectronic feedback

Abstract: Optical injection and optoelectronic feedback are efficient techniques to externally control the spectral characteristics of a semiconductor laser. This paper presents theoretical and experimental results about the effects of a delayed optoelectronic feedback loop on the stability of an optically injected diode laser. In particular, negative feedback configurations (out-of-phase carrier reinjection) are shown to widen the injection-locking domain of the laser and reduce its unstable region. On the contrary, in positive feedback configurations (in-phase carrier reinjection), the laser diode generates a modulation with tunable multigigahertz frequency.

Injection-locked oscillator chain: a possible solution to millimeter-wave MMIC synthesizers

Abstract: An injection-locked oscillator (ILO) monolithic-microwave integrated-circuit (MMIC) chain-a cascade of low- and high-frequency-band ILOs-is proposed for simple and cost-effective millimeter-wave local oscillators and synthesizers. Primary 5, 20, and 50 GHz-band ILO MMICs are designed and fabricated as an ILO-chain chip set. Improvements made to the active combiner/dividers (A-C/D's), the heart of the MMIC, in the external feedback path for an amplifier to suppress spurs at the output port of 5 and 20 GHz band ILOs, and enhance the loop gain and layout flexibility at millimeter-wave frequencies. Fabricated 5 and 20 GHz-band ILO MMICs are chain-connected to confirm the design techniques. The ILO chain provides a 20 GHz-band output signal for an injection signal of 571 MHz, as well as a very low level of spurs of less than -45 dBc around the output signal. The measured results show that the proposed ILO chain is extremely suitable for developing full millimeter-wave MMIC frequency synthesizers.

Linewidth narrowing and optical phase control of mode-locked semiconductor ring laser employing optical injection locking

Abstract: The linewidth of the individual modes of an actively mode-locked extended-ring-cavity semiconductor laser is reduced from a free running linewidth of over 200-20 kHz by the injection of a narrow linewidth continuous-wave (CW) light. The optical phase of the injection-locked pulses can be controlled by adjusting the free-running optical frequency of the semiconductor ring laser. The variation in the optical phase of the output pulses versus the change of the free-running optical frequency is evaluated to be 0.57/spl pi/ radians within the locking range of about 96 MHz by observing temporal shape of the beat signal formed between output pulses and CW injection light.

Injection-locking properties of self pulsation in semiconductor lasers

Abstract: The injection-locking properties of self pulsation in semiconductor lasers are studied, using a phenomenological approach, based on an analogy with laser models. It has been found that the locking range is directly proportional to the input power, rather than to the square root of the input power as in injection-locked microwaves or laser oscillators; the locking range is symmetric with respect to the self-pulsation frequency in the free-running case; in the locking state, the spectral linewidth of the self-pulsation peak is equal to that of the incoming signal. These theoretical results agree very well with experimental ones, obtained on a distributed feedback three-section laser.

Injection-locking technique for heterodyne optical phase locking of a diode laser.

Abstract: A novel technique is demonstrated for heterodyne optical phase locking of a diode laser to a single-frequency source by injection seeding. By modulation of the drive current of the diode laser at as much as several gigahertz, FM sidebands are imposed upon the output. We demonstrate that it is possible to phase lock either sideband to an injected beam. The carrier of the diode laser output is therefore locked in phase with the injected light but with a frequency difference given by the modulation of the drive current. The phase fluctuations between the lasers are analyzed, and the variance is found to be (4.4( degrees ))(2) , corresponding to 99.4% of the diode carrier light locked to the injected beam.

Microwave generation for bidirectional broadband mobile communications using optical sideband injection locking

Abstract: Bidirectional 140 Mbit/s OQPSK-signal transmission with remotely generated microwaves applying optical heterodyning is reported. Two microwave carriers in the 18-20 GHz band are generated: one modulated by the downlink data, the other unmodulated and used as the local oscillator signal for the uplink mixer in the base station.

Active SIMMWIC-antenna for automotive applications

Abstract: An active SIMMWIC-Antenna (Silicon Monolithic Millimeterwave Integrated Circuit) for vehicular technology in the frequency range around 76.5 GHz is presented. This active antenna acts as a transceiver and is well suited for low-cost integrated sensor systems for automotive applications. The monolithic active antenna embedded in a synchronization network requires only 3.2/spl times/2.6 mm/sup 2/ chip size. Using subharmonic injection locking frequency tuning and stabilization is realized. With an injection power of 0 dBm we measured a tuning range of 300 MHz. To our knowledge, this is the first synchronizable monolithic integrated active antenna suited for automotive applications in the frequency band around 76.5 GHz.

Frequency dynamics of gain-switched injection-locked semiconductor lasers

Abstract: The frequency dynamics of gain-switched single-mode semiconductor lasers subject to optical injection is investigated. The requirements for low time jitter and reduced frequency chirp operation are studied as a function of the frequency mismatch between the master and slave lasers. Suppression of the power overshoot, typical during gain-switched operation, can be achieved for selected frequency detunings.

Coherent optical CDMA with limited phase excursion

Abstract: We examine the bit error rate (BER) of the conventional matched-filter detector for an optical code division multiple access (CDMA) system employing coherent homodyne detection. We assume a phase shift keying (PSK) modulation format where the phase is modulated by one of two methods: (1) an external phase modulator or (2) injection locking. Phase excursion is limited to /spl plusmn/0.42 /spl pi/ when using injection locking. We examine the bit error rate performance for both external modulation and modulation of the injection current and find only a moderate penalty (0.55 dB) associated with the limited phase excursion.

Method and apparatus for reducing radiated electromagnetic emissions from harmonic frequencies for electronic equipment

Abstract: A system of spreading the energy of higher harmonic frequencies in digital circuits to lower the interference to bandpass receivers is disclosed. A set of passive, impedance-regulated circuits, preferably housed in a standard enclosure, comprises a power restoring unit, a modulating signal generator, an internal oscillator and an impedance spreading unit. The circuits are equivalent to passive resonators such as crystal resonators used in standard oscillators. Any existing standard oscillator that uses common crystal resonators can be transformed into a spectrum-spread oscillator by replacing the crystal resonator with the disclosed circuit, whereby a tightly controlled small frequency spreading occurs in the fundamental clock frequency. Further an active oscillator is disclosed wherein a spreading circuit spreads the frequency of the clock signal originally generated by the oscillator based on a sequence of processing the original clock signal. The processing includes the use of a plurality of delay elements based on a certain topology, the comparisons between the clock signal and a set of predefine parameters so as to create a frequency offset. The spreading circuit, without using additional clocking sources, spreads the frequency of the clock signal with respect to the comparisons.

Wideband and high frequency stabilization of an injection-locked Nd:YAG laser to a high-finesse Fabry Perot cavity.

Abstract: High frequency stabilization of a 2.2-W injection-locked laser-diode-pumped Nd:YAG laser to a high-finesse optical cavity has been realized by frequency control of the master laser. With the help of an external electro-optical modulator, the feedback bandwidth was extended to 1 MHz and the frequency noise relative to the reference cavity was suppressed to 3×10-4 Hz/Hz1/2 below 1 kHz. This feedback laser system is an ideal laser source for gravitational wave detectors, which require both ultralow frequency noise and high output power.

A new approach for optical millimeter wave generation utilizing locking techniques

Abstract: A new approach is presented for the optical generation of millimeter waves. Instead of the millimeter wave signal, one of its subharmonics is optically transmitted and the millimeter wave signal is generated utilizing the subharmonic signal as a reference. This way the optical components become much simpler and cheaper. In this procedure a crucial point is the frequency division at millimeter wave frequencies. For this purpose a new method is introduced: the superharmonic injection locking of oscillators. The main advantage of the new approach is that it is applicable even for frequencies at shorter millimeter waves.

Diode lasers locked to noisy injection

Abstract: We have analyzed the behavior of a diode laser with low-amplitude optical injection. The noisy injection field has phase fluctuations only, with a linewidth larger than both the free-running slave laser linewidth and the locking range. Simulations show that the laser output spectrum can be much narrower than the injection spectrum and may have a dip at the free-running laser frequency. A model describing these features is based on linear superposition of the stationary responses to monochromatic injection. The mechanism of line narrowing is that the response to injection outside the locking range lies mainly inside.

Longitudinal-mode-partition noise and amplitude squeezing in semiconductor lasers

Abstract: We have measured the longitudinal-mode-partition noise of free-running, grating-feedback external-cavity and injection-locked semiconductor lasers, using a nonsymmetric Mach–Zehnder interferometer. For an external-cavity laser operated at a high pumping level, the contribution of the longitudinal-mode-partition noise to the total intensity noise was negligible, and 0.9 dB of amplitude squeezing was observed. On the other hand, injection locking suppressed the longitudinal-mode-partition noise by 34 dB, and 1.9 dB of amplitude squeezing was observed when the locking bandwidth was 5 GHz. A further increase in the locking bandwidth reduced the suppression of the longitudinal-mode-partition noise and degraded the amplitude squeezing.

A 20-GHz-band subharmonically injection-locked oscillator MMIC with wide locking range

Abstract: A monolithic subharmonically injection-locked oscillator (ILO) with wide frequency tuning range using a shunted varactor diode inserted to the oscillation loop is presented. A 20-GHz-band ILO is fabricated that achieves the wide injection locking range of more than 700 MHz at each subharmonic factor up to 32. In addition, the phase-noise degradation rate of the ILO against the subharmonic factor is close to 6 db/oct. The ILO configuration is extremely suitable for realizing low cost and low-phase-noise millimeter-wave monolithic microwave integrated circuit (MMIC) sources.

Millimeter-wave HBT MMIC synthesizers using subharmonically injection-locked oscillators

Abstract: A subharmonically injection-locked MMIC harmonic VCO for use as a synthesized local oscillator in the 60 GHz band has been experimentally investigated. The designs using HBT MMICs are based on the use of 2nd subharmonic injection locking of the harmonic VCOs to upconvert to millimeter-wave frequency and broaden the locking range. The use of the 4th harmonic signal from the VCOs allows a factor of eight increase in the locking range. The transmission type injection-locked MMIC VCO with the refractive type load circuit increases not only the locking range, but also the high-order harmonic output power in the locked VCO output.

Polarisation-diversity phase-encoded patch-antenna transponder

Abstract: Application of phase encoding to a received RF signal, and retransmission of the signal phase encoded at the same frequency using polarisation diversity, is used to design a simple two-port microstrip patch antenna which will permit single-frequency polarisation-diversity operation. The antenna is characterised in terms of its far-field radiation pattern and its two-port scattering parameters. An injection-locked oscillator is coupled to an adapted passive quasicirculator to perform the phase-encoding function. Here control of the direct tuning voltage to the injection-locked oscillator effects the degree of phase change obtained. The operation of this circuit is discussed and its inclusion with the dual-port patch antenna to form a phase-encoding transponder is described.

Theory of modulation of an injection-locked semiconductor diode laser with applications to laser characterization and communications

Abstract: The current-modulation properties of an injection-locked semiconductor diode laser are investigated, with focus on the two values of detuning at which the intensity or the phase-modulation sensitivity of the slave laser is a minimum. The master laser’s frequency for minimum AM modulation is located near the lower edge of the locking band, and the condition for minimum FM response is just that of synchronization before injection, a stable operating point at 2% injection level that coincides with the point of maximum modulation bandwidth. The relaxation-oscillation resonance in the modulation spectrum can be largely removed by passage through a dispersive medium such as an optical fiber so that instead of deteriorating by fiber dispersion, the combined bandwidth of a properly designed system, in which the fiber length is limited only by loss, can exceed that of the injection-locked laser alone. In another application an accurate determination of the line-broadening factor, α, from the solitary-laser output power and the power at the two mentioned operating points is shown possible. The harmonic distortion is also evaluated, as relevant to α measurement and high-bandwidth modulation.

Progress in the realization of a frequency standard at 192.1 THz (1560.5 nm) using /sup 87/Rb D/sub 2/-line and second harmonic generation

Abstract: Second harmonic generation of a 192.1 THz semiconductor distributed feedback (DFB) laser is achieved using a KNbO/sub 3/ crystal in a resonant ring cavity. Optical feedback from this cavity is used to stabilize the laser frequency and reduce its linewidth. A second harmonic power of 5.5 /spl mu/W is generated with 38 mW incident on the cavity. We use the second harmonic signal to observe saturated absorption lines and orientation signals in rubidium vapor. Injection-locking of a 780 nm Fabry-Perot laser using the second harmonic signal is also demonstrated. With this scheme, we observe saturated absorption lines in rubidium.

Stable injection locking of diode lasers through a phase-modulated double phase-conjugate mirror

Abstract: The stable injection locking of 0.8-µm diode lasers with a double phase-conjugate mirror (DPCM) was achieved. Phase modulation by piezoelectric transducers allowed us to keep two input beams of the DPCM mutually incoherent during locking. We preserved the high performance of the DPCM and retained stable locking for more than an hour.

Reduced-radiation radio signal receivers

Abstract: A radio receiver with isolation between an antenna and a regenerative oscillator/detector. The isolation is provided by periodically (at the receiver's quench frequency) uncoupling the antenna from the regenerative oscillator/detector. The receiver preferably includes an antenna, a super-regenerative oscillator/detector, a clock that indicates the quench frequency, a timing circuit coupled to the clock, and a switch coupled to the antenna, to the oscillator/detector, and to the timing circuit. The timing circuit specifies a first part and a second part of each clock period. During the first part of each clock period, the switch at least partially couples the antenna to the oscillator/detector on the nominal reception frequency. During the second part of each clock period, the switch at least partially uncouples these two elements on the nominal reception frequency. The timing circuit determines the first and second parts of each clock period so that the first part corresponds to a phase of sensitivity for the oscillator/detector, and so that the second part corresponds to phases in which oscillations in the oscillator/detector rise in amplitude, and/or have an increased amplitude, and/or decay in amplitude. Thus, the inadvertent emission of electromagnetic radiation from the regenerative oscillator/detector at the nominal reception frequency is attenuated or suppressed at least during the second part of each clock period.

Multimode effects on the evolution and long-term stability of a passively mode-locked laser under pulsed injection locking

Abstract: A multidimensional extension of the injection locking of CW lasers has been recently presented and experimentally verified when both a passively and an actively mode-locked laser were locked to injected coherent pulse trains. Harmonic injection locking of a passively mode-locked laser, where a subset of the laser cavity modes were locked to the injected signal, was also recently realized in a fiber laser to yield trains of 6-ps pulses at rates of up to 40 GHz. In this paper, the multimode injection-locking process is addressed with an emphasis on the long-term dynamics of the laser, pulse buildup under injection locking, memory effects, noise mechanism as well as potential applications, e.g., optical signal regeneration. Using a recently introduced formalism for describing passively mode-locked lasers, the experimental results are compared to numerical simulations.