Injection locking properties of a semiconductor laser have been analyzed, taking into account the injected carrier density dependent refractive index in the active region. It has been found that this dependence significantly affects the injection locking properties, giving rise to a peculiar asymmetric tuning curve and dynamic instability. The instability originates from the intermode interaction via the modulation in the injected carrier density caused by intensity beat. The detuning dependence of the direct modulation response characteristics inside and outside of the locking range have also been examined.

Injection locking properties of a semiconductor laser

Direct frequency modulation characteristics in three different AlGaAs lasers-a channeled-substrate planar (CSP) laser, a buried-heterostructure (BH) laser, and a transverse-junction-stripe (TJS) laserare studied theoretically and experimentally. Experimental FM responses are measured by using the Fabry-Perot interferometer and birefringent optical filters in the 0-5.2 GHz modulation frequency region. Experimental FM response dependences on modulation frequency, dc bias level, and stripe structure are successfully explained by the theoretical analyses considering both the carrier density modulation effect and the temperature change effect. FM response in the low modulation frequency regin from 0 to 10 MHz, gradually decreasing with the modulation frequency, stems from the thermal effect. FM response in the high modulation frequency region from 10 MHz to 5.2 GHz is caused by the carrier effect. A flat FM response of several hundred MHz per 1 mA is observed in the CSP and TJS lasers, but a V-shaped FM response is obtained in the BH laser. Resonance peak due to relaxation oscillation and cutoff characteristics are observed in several gigahertz regions. Weak lateral mode confinement, strong vertical mode confinement, carrier injection outside the effective core region, and p-side down mounts are effective ways to achieve a flat and efficient FM response with a small spurious intensity modulation.

Direct frequency modulation in AlGaAs semiconductor lasers

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.

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

The main bandwidth bottleneck in today's networks is in the access segment. To address that bottleneck, broadband fiber access technologies such as passive optical networks (PONs) are an indispensable solution. The industry has selected time-division multiplexing (TDM) for current PON deployments. To satisfy future bandwidth demands, however, next-generation PON systems are being investigated to provide even higher performance. In this paper, we first review current TDM-PONs; we designate them as generation C. Next, we review next-generation PON systems, which we categorize into C+1 and C+2 generations. We expect C+1 systems to provide economic near-term bandwidth upgrade by overlaying new services on current TDM-PONs. For the long term, C+2 systems will provide more dramatic system improvement using wavelength division multiplexing technologies. Some C+2 architectures require new infrastructures and/or equipment, whereas others employ a more evolutionary approach. We also review key enabling components and technologies for C+1 and C+2 generations and point out important topics for future research.

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Next-Generation Optical Access Networks

It is anticipated that more than 75 Mb/s per subscriber is required for the convergence service such as triple-play service (TPS) Among several types of high-speed access network technologies, wavelength-division-multiplexing passive optical network (WDM-PON) is the most favorable for the required bandwidth in the near future Furthermore, WDM technologies, such as athermal arrayed-waveguide grating (AWG) and low-cost light source, have matured enough to be applied in the access network In this paper, the authors propose and implement a WDM-PON system as a platform for TPS The system employs an amplified spontaneous emission (ASE)-injected Fabry-Pe/spl acute/rot laser diode scheme It has 32 channels of 125 Mb/s and adopts Ethernet as Layer 2 Multicast and virtual local area network features are used for the integration of services such as Internet protocol high-definition broadcast, voice-over Internet protocol, video on demand, and video telephone The services were demonstrated using the WDM-PON system

Fiber-to-the-home services based on wavelength-division-multiplexing passive optical network

Single-mode operation of an AlGaAs double heterostructure semiconductor laser directly modulated at 500 Mbit/s data rate was realised by injection locking. The power ratio of central injected mode to total spectrum power was 94%.

Single-mode operation of 500 Mbit/s modulated AlGaAs semiconductor laser by injection locking

Optical frequency. modulation index suppression in FM signal amplification and FM signal generation in an injection locked semiconductor laser are experimentally studied by injecting coherent FM signals and CW light, respectively. Experimental results are in good agreement with a simple theory using the van der Pol equation with an external signal term. The FM noise accumulation in cascade injection locked amplifiers is calculated and an optimum design for an injection locked repeater system is discussed.

Optical FM signal amplification and FM noise reduction in an injection locked AlGaAs semiconductor laser

Optical frequency spectra of directly frequency modulated AlGaAs semiconductor laser in the 0?5.2 GHz range were measured by using a Fabry-Perot interferometer and a birefringent optical filter. The frequency deviation is linearly proportional to the RF modulation current. The measured modulation frequency characteristics for the frequency deviation show that the thermal effect is predominant in the frequency below 10 MHz. It has a resonance peak which behaves just like the peak observed in the modulation. Experimental results agreed well with theoretical values calculated by considering thermal effect and carrier-dependent refractive index variation.

Modulation frequency characteristics of directly optical frequency modulated AlGaAs semiconductor laser

A new UV-curable primary coating material, polybutadiene acrylate (PBA), has been developed. The new acrylate has much lower modulus at low temperature than epoxy and urethane acrylates. The transmission loss increase at low temperature for coated fibres is related to the modulus value for coatings.

Tomohiro Kimura

Papers

Single-mode operation of 500 Mbit/s modulated AlGaAs semiconductor laser by injection locking

Optical FM signal amplification and FM noise reduction in an injection locked AlGaAs semiconductor laser

Modulation frequency characteristics of directly optical frequency modulated AlGaAs semiconductor laser

New UV-curable primary coating material for optical fibre