We report the first demonstration of all-optical address recognition and self-routing of photonic packets for a case where the packet bit period is only 4 ps, corresponding to a 0.25- Tb/s bandwidth optical network. An ultrafast all-optical devices, known as a terahertz optical asymmetric demultiplexer (TOAD), was used to read the address information encoded in a packet header, which in turn was used to route the packet. The bit-error rate at the switch output was measured to be less than 10-9.
We report on the development of a transparent optical node at 1.3 micrometers wavelength for an ATM packet switch operating at 1.24416 Gbit/s header recognition rates. The node takes advantage of the high-speed performance of optoelectronic components to alleviate potential bottlenecks resulting from optical to electrical conversion experience in nontransparent packet switching architectures. The node is intended for use in two-connected, slotted networks, is self-clocking, and has drop/add multiplexing, buffering, and routing capabilities.
We have measured the performance of a new demultiplexing device, known as a Terahertz Optical Asymmetric Demultiplexer, while operating it in an optical time division multiplexed system with an aggregate bandwidth of 50 Gbits/s. These measurements also illustrate the device's adjustable tolerance to jitter.
We demonstrate a simple method to modulate a pulse train of arbitrarily narrow optical pulses using off-the-shelf components. The method makes use of the Sagnac loop fiber interferometer only several meters in circumference.
A semi-conductor TWLA provides the gain medium for an external cavity laser source at 1.32 microns for compatibility with single mode fiber optic systems. The active layer of the waveguide is InGaAsP in an angle stripe geometry. Parameters for CW lasing are established. Pulsed operation is then achieved by two methods: direct RF modulation of the bias current, and regenerative feedback of the converted optical output signal. Both methods yield short pulses of different frequency noise characteristics. The mode-locked rate can be adjusted over a wide range for different applications by varying the cavity length. Wavelength tuning is achieved by replacing the cavity end mirror with a grating the use of an all fiber cavity is examined.
Optical Kerr effect were applied to an all-optical switching device in the form of nonlinear waveguide directional couplers. The nonlinear directional coupler had a nonsymmetrical waveguide whose structure consists of a quartz thin gap between two Corning 7059 guided layers on the pyrex substrate with ion-milled grating and organic thin film as a top layer. The vacuum-deposited polydioacetylene film was used as an organic nonlinear material. Switching phenomena in this nonlinear directional coupler were confirmed for 10 ns pulse Nd:YAG laser and 150 fs pulse duration of mode-locked Ti:Sapphire laser.
We summarize our ultrafast switching results in GaAs multiple quantum well directional couplers and report on coherent pulse propagation in single strip-loaded GaAs multiple quantum well waveguides. The transmitted pulse shape is measured by sum frequency generation cross-correlation and compared with calculations based on the coupled semiconductor Bloch and Maxwell's equations.
Modified fabrication technique has been developed to improve the performance of GaAs/A1GaAs
MQW nonlinear directional couplers for all-optical picosecond and subpicosecond switching and
A nonlinear directional coupler (NLDC) capable of switching data streams and demultiplexing signals
could be an important component in switching networks. Reliable and reproducible performance depends
on the proper technique used to fabricate these devices. Previously, we demonstrated all-optical
switching in GaAs/AlGaAs multiple quantum well (MQW) nonlinear directional couplers using 10 ps
pulses1 where the origin of the nonlinearities was due to photo-excited real carriers. The contrast of the
PS switching was from 1 : 3 to 3 : 1 . We have also observed subpicosecond all-optical modulation in the
same device using 150 fs pulses2 where the origin of such ultrafast modulation is attributed o optical
Stark effect3. The contrast of the fs modulation was from 1 :2.3 to 1 : 1 .2. Recently, we improved the
fabrication procedures. This results in improved performances in both the picosecond and subpicosecond
The MQW waveguide structure was designed to sustain a single planar mode for wavelength close to
the absorption edge using a four-layer waveguide model. The effective index method4 was then used to
model the strip-loaded waveguide performance to ensure single mode operation. The sample is grown by
molecular beam epitaxy (MBE) and has 1 .2 am thick guiding region which consists of 60 periods of
alternating 100 GaAs wells/lOO Al023Ga72As barriers. The guiding in the direction perpendicular
to the MQW is provided by the AlGaAs layers above and below the MQW region whereas the
confinement in the horizontal direction is facilitated by the 2 ,am wide ridge etched into the top
AlGaAs layer. The ridge structures are formed by first patterning the sample through contact-print
photolithography using positive photoresist (KTI 820), and then reactive ion etching the top AlGaAs
layer with photoresist mask. The etch process uses pure BC!3 as an etching gas flowing at 25 sccm
with a pressure of 45 mTorr. The power density delivered is 0.43 W/cm2 and the self bias potential is
1 82 V. A Si wafer is laid on the bottom electrode on top of which the sample is placed. After etching,
the couplers are cleaved on both ends to allow light to be end-fire coupled into the guides.
We have since improved the fabrication procedures. First, previous studies show that
photolithography is a problem when the guide separation is only 1 m whereas a guide separation of 4
m is too large for efficient coupling. A mask is thus made that consists only of guides separated by 2
or 3 'am. Second, more care is taken to prevent dust from falling on the sample during the
photolithographic process in our non-clean lab environment. Third, a new cleaving device is assembled
using a phonographic needle and an x-y-z translation stage. With the help of a stereo microscope,
devices as short as 100 1am can be cleaved with high-quality end surfaces. See Fig. 1. These
improvements not only enhance our yield so that nonlinear coupling behavior is observed in almost
every pair of guides but also allows the light to be coupled into each guide with ease, greatly
shortening the alignment time.