We demonstrate the first SOA-integrated CW-DFB laser at 1.3 µm with kink-free and stable single-mode operation over 100 mW at up to 80 ºC. We also achieved reliable operation over 700 hours at 80 ºC.
Waveleiigth-division multiplexing (WDM) networks using optical adddrop multiplexers and optical switches are effective for increasing not only capabilities but also transparency, survivability against fiber cuts, etc."* In systems employing erbium-doped fiber amplifiers (EDFAs), the per-channel output power control by a wavelength monitor is an important function, because a change in the number of channels caused by network reconfigurations or faults may bring a power transition in EDFA output.A wavelength monitor3 for an optical amplifier with cascaded fiber gratings and delay lines of optical fibers has been reported, but the number of channels that can be detected is limited because of the fu;ed wavelength of the fiber gratings. We have recently developed an EDFA repeater for WDM networks that has a wavelength monitor for arbitrary wavelength and uses an acousto-optic tunable filter (AOTF).4 This repeater keeps the per-wavelength power constant when the number of channels changes. Figure 1 shows the wavelength monitor used for EDFA gain control. The monitor uses a polarization-independent AOTF that operates over a wide tunable wavelength range (> 110 nm), with a high extinction ratio -Tuning acoustic frequency (MHz) J85.0 1788 173.1 -Time Wavelength,(&) 5 -30 /I450 1500 1550 WDM signal input TuEl characteristics. AOTF: acousto-optic tunable filter; PD: photo diode.Fig. 1. Block diagram for wavelength monitor and measured AOTF TuElBlock diagram for a dynamic gain-controlled EDFA repeater. AOTF: acousto-optic tunable filter; PD: photo diode; CPL optical coupler; ALC automatic level controller. Fig. 2. detected WDM pulses 1 detected WDM pulses -.-E c a time (10msIdiv) TuEl EDFA.Fig. 3. Detected WDM pulses from AOTF and output waveforms from(>15 dB). The AOTF is driven by the pulses sweeping frequencies from 172-178 MHz (from 1530-1570 nm). A WDM signal is converted to separate pulses (in time) corresponding to the wavelength. The channel number, wavelength band, and power for each wavelength are obtained from the number, position, and level of the detected pulses, respectively. The AOTF selects wavelength continuously, so that the wavelength monitor can detect any wavelength. Figure 2 shows the block diagram of the dynamic gain-controlled EDFA repeater. The repeater consists of a wavelength monitor circuit, a gain control circuit, and a wideband EDFA with a high aluminum codoped EDF pumped by a 0.98 p m laser diode (LD) (forward) and a 1.48 p m LD (backward). To keep per-channel output power constant, the gain of the EDFA repeater was controlled by tuning the pump LD current according to the number of channels detected. To maintain the quality of service on surviving channels, it is also important to suppress the power transient overshoot5 that occurs in the surviving channels' waveform after a change in number of channels. A frequency equalizer is connected to the LD drive circuit to increase response speed for EDFA gain control and limit the overshoot.
Four directly modulated DFB lasers with 1.3-μm CWDM range demonstrated 106-Gb/s PAM4 operation for transmission over 2-km SMF. Dispersion penalties of the lasers were less than 0.8 dB after 2-km transmission up to 70ºC.
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