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Experiment and Theory of an Active Optical Filter

Figure 1

Figure 1
Network diagram of the 2-D active lattice filter fabricated and demonstrated herein. At the center is a four-port coupler. Attached to each port is the equivalent of a Fabry-Perot stage comprising both gain and delay.

Figure 2

Figure 2
Optical micrograph of an exemplary 2-D active lattice filter. These are four independently addressable semiconductor optical amplifiers that meet at the four-port coupler in the center of the micrograph.

Figure 3

Figure 3
SEM micrograph of the center of the 2-D active lattice filter showing the four-port nanophotonic coupler with metal contacts.

Figure 4

Figure 4
Cross-sectional SEM image of the nanophotonic coupler structure. (a) Vertical, deep, high aspect ratio trench dry etched with HBr-based ICP. (b) Trench filled with alumina using atomic layer deposition.

Figure 5

Figure 5
Main processing steps for the fabrication of devices, such as that shown in Fig. 2.

Figure 6

Figure 6
Custom designed submount and circuit board assembly used to mount the device under test.

Figure 7

Figure 7
Near-field mode intensity profiles through the four-port nanophotonic coupler from an external light source. Light from (a) port 1 transmitted to port 3, (b) port 4 reflected to port 3, and (c) port 4 reflected to port 1.

Figure 8

Figure 8
Schematic setup for cross-correlation measurements of the filter device (BPF: band pass filter, PC: polarization controller, EDFA: erbium-doped fiber amplifier, DUT: device under test, LDD: laser diode driver, TECC: thermoelectric cooler controller, ODL: optical delay line, CORR: cross-correlator). Inset shows a typical CC trace of an interrogation pulse.

Figure 9

Figure 9
Cross-correlation traces of pulse trains measured at port 4 of the filter device for three cases. The injection of driving current is provided through contact pads to produce optical gain. (a) Case 1: without any driving current, 0 mA. (b) Case 2: total driving current of 230 mA. (c) Case 3: total driving current of 380 mA. An input ultra-short pulse is coupled into port 1 for each case.

Figure 10

Figure 10
Impulse responses, h[n], extrapolated from corresponding cross-correlation traces and a comparison between experimental magnitude responses according to h[n] and simulated magnitude responses with the ARX model for three cases. (a) Case 1: without any driving current, 0 mA. (b) Case 2: total driving current of 230 mA. (c) Case 3: total driving current of 380 mA.

Figure 11

Figure 11
Poles and zeros of the filter response for which transfer functions are given according to the ARX model for cases 1–3. The zeros are denoted “Formula$\bigcirc$,” “□,” and “Formula$\vartriangle$” the poles are denoted “×,” “+,” and “Formula${\ast}$,” for each case respectively.

Figure 12

Figure 12
Theoretical fitting of experimental magnitude responses for cases 1–3 using the model with Formula$z$-transform technique: (a) Case 1: without any driving current, 0 mA. (b) Case 2: total driving current of 230 mA. (c) Case 3: total driving current of 380 mA.

Figure 13

Figure 13
Poles and zeros of system response of the filter for which transfer functions are given based on the filter model with Formula$z$-transform technique. The zeros are denoted “Formula$\bigcirc$,” “□,” and “Formula$\vartriangle$” the poles are denoted “×,” “+,” and “∗,” for cases 1–3, respectively.