We added a control electrode to a phase-shifted Bragg grating filter in an electro-optic polymer waveguide to obtained voltage tunability. The waveguide grating transmission spectrum near 1.3 microns featured a 5 GHz passband with a peak transmission of 32% within a 2 nm wide, 12 dB deep blocking band. With the waveguide grating sandwiched between gold layers separated by ~10 microns, we were able to shift the transmission spectrum at a rate of 0.1 GHz/volt. Such filter tunability may be used in ultradense WDM channel selection or to compensate for detuning by environmental factors.
Recent developments in electro-optic polymer materials and devices have led to new opportunities for integrated optic devices in numerous applications. The results of numerous tests have indicated that polymer materials have many properties that are suitable for use in high-speed communications systems, various sensor systems, and space applications. These result coupled with recent advances in device and material technology will allow very large bandwidth modulators and switches with low drive voltages, improved loss, long-term stabilty, and integration with other microelectronic deices such as MEMS. Low drive voltage devices are very important for space applications where power consumption scales as the square of the modulator half-wave voltage. In addition, we have demonstrated novel dual polymer modulators for mixing RF signals to produce sum and difference frequency modulation on an optical beam. This novel approach allows the suppression of the modulation at the two input RF signals and only the mixing signals remain superimposed on the optical beam. The dual modulator can be used for various encoding and frequency conversion schemes that are frequently used for both terrestrial and space communcations. Another application of polymer integrated optics is in the field of optical sensing for high frequency electric field.
We report a simplified version of a mm-wave generator employing the sideband filtering technique which uses a single optical sideband filter. Instead of using a Mach- Zehnder-like fiber network to select a pair of sidebands, we employ a single Fabry-Perot fiber Bragg grating with a pair of passbands separated by the mm-wave frequency. Using a single filter, eliminated the need for polarization control and pathlength matching that was required by the former interferometer-like arrangement. We describe a 30 GHz generator design and present its mm-wave signal spectrum showing an instrument limited linewidth of approximately 20 Hz. The generation of such an extremely narrow signal spectrum from a laser with a 1 MHz linewidth demonstrates the remarkable laser frequency nosie cancellation property of the sideband filtering technique.
We have developed an optical key distribution scheme where communicators are able to generate identical binary keys from a wideband optical phase-noise-bearing lightwave. In our scheme, a phase-noise-bearing lightwave is distributed among the communicators via optical fiber, and then converted an intensity modulation by an unequal path length interferometer and converted to a binary stream by a comparator. The use of a broadband noisewave (>100GHz, ~0.8nm at 1550 nm), precludes the possibility of an eavesdropper recording the signal in enough detail to analyze the noise in conjunction with the encrypted data processing. Corresponding intensity modulations are produced if both interferometers have the same pathlength inequality to within a certain tolerance. We have demonstrated identical key generation by two independent terminals receiving a distributed optical noisewave for bit positions designated with a good validity bit. A separate Ethernet link between the terminals was used to assess the quality of the binary key generation. The system uses three WDM optical channels to transmit the noisewave at 1550 nm, data at 1310 and a probe signal for interferometer stabilization at 1530nm.
We generated a low phase noise 16 GHz electrical signal of 20 Hz linewidth from a single 1 MHz linewidth diode laser. At 36 Ghz, our frequency angle mm-wave generator produced an electrical signal with an instrument resolution limited linewidth of < 1 kHz. Our approach uses a relatively low frequency (4-8 GHz) phase modulator to generate a multiline sideband spectrum from a single mode laser, which is filtered to pass or select a pair of spectral lines. Interference between the lines on the active area of a photodetector produces an electrical signal that can be set between 4 and 60 Ghz. B y controlling the phase modulator frequency and amplitude we set the sideband frequency spacing between 4 and 8 Ghz, and efficiently couple optical power into sidebands up to the fourth order. Rapid transitioning between sideband spectra best suited for a particular mm-wave frequency could be made in a few milliseconds using a programmable synthesizer and RF amplifier. Two- sideband selection was obtained by splitting the signal between two legs of a filter network and using ultra-narrowband fiber Bragg grating (FBG) fiber filters to select single lines. We controlled the fiber filter strain to tune the filters rapidly, setting the tension using PZT actuators. The generator prototype was packaged as a pair of portable twin rack modules under PC control.
We generated low phase noise mm-wave electrical signals of sub-kHz linewidth from a single 1550 nm diode laser with a linewidth in excess of 1 MHz. Our approach uses a phase modulator to generate a multiline spectrum from a single mode laser, which is filtered to pass only a pair of spectral lines. Interference between the lines on the active area of a photodetector produces an electrical signal that can be set between 4 and 60 GHz. This technique has the advantage that the electrical linewidth can be much narrower than the laser linewidth due to common mode rejection of frequency noise between the interfering sidebands, and that relatively low frequency electronics can be used to generate the sideband spectrum.