D.H. Chang

Recent advances in electrooptic polymer modulators incorporating highly nonlinear chromophore

Based on a nonlinear optical polymer with a highly nonlinear chromophore (CLD) dispersed in an amorphous polycarbonate (APC), we have developed electrooptic (EO) polymer modulators operating at 1550-nm wavelength with low loss and good thermal stability. By incorporating polymer insulation layer, push-pull poling was successfully performed without film damages. We also demonstrated that the propagation loss of the EO polymer waveguide could be reduced as low as 1.2 dB/cm at 1550 nm when the large core waveguide structure was incorporated. The long-term reliabilities of the EO polymer modulator made of CLD/APC polymer were investigated. When the modulator was hermetically sealed in an inert gas, the V/sub /spl pi// change of a Mach-Zehnder modulator was negligible over 30 d of operation with 20-mW exposure to the waveguide input. In the thermal stability measurement, 25% V/sub /spl pi// increase was observed from the sample heated to 60/spl deg/C over 40 d, though the sample left at room temperature showed no decay of nonlinearity.

Push–pull electro-optic polymer modulators with low half-wave voltage and low loss at both 1310 and 1550 nm

Push–pull polymeric electro-optic Mach–Zehnder (MZ) modulators with Vπ of 1.2 and 1.8 V at 1310 and 1550 nm, respectively, with an interaction length of 2 cm are demonstrated. These devices were made from second-order nonlinear optic guest–host polymers that consisted of a phenyltetraene bridged high μβ chromophore guest and an amorphous polycarbonate host. Poling was done in N2 atmosphere to avoid chromophore bleaching by oxidation. A MZ-like two-arm microstrip line was used as the driving electrode in these devices. The optical response dropped 3 dB electrical from 2 to 20 GHz. These 3 cm long devices have 5 dB total chip loss at both wavelengths and good thermal stability.

Demonstration of a photonically controlled RF phase shifter

Integrated photonic radio frequency (RF) phase shifters with dc voltage control have been realized using a nested dual Mach-Zehnder modulator configuration in a new nonlinear optical polymer, CLD2-ISX. These modulators have a V/sub /spl pi// of 10.8 V and exhibit excellent frequency performance measured up to 20 GHz. A near linear phase shift exceeding 108/spl deg/ was obtained for a 16-GHz microwave signal by tuning the dc control voltage over a 7.8-V range. It is expected that these integrated polymer phase shifters will find widespread applications in new types of lightweight optically controlled phased array systems.

Electrooptic polymer modulators with an inverted-rib waveguide structure

Polymeric APC-CPW electrooptic modulators incorporating an inverted-rib waveguide structure were fabricated and tested for the first time. The inverted structure greatly simplifies fabrication procedures, and additionally improves propagation loss performance. Mach-Zehnder electrooptic modulators fabricated using this structure exhibited 6 dB of fiber-to-fiber insertion loss for 2.3-cm length and 6 V of driving voltage for a one-arm micro-strip electrode of 1.5-cm interaction length, at a wavelength of 1.55 /spl mu/m.

39-GHz optoelectronic oscillator using broad-band polymer electrooptic modulator

An optoelectronic oscillator (OEO) producing a 39-GHz microwave signal has been demonstrated using a novel electrode-poled push-pull polymer modulator. This is the highest reported OEO operating frequency to date. Preliminary measurement of the phase noise shows performance in the range of commercial synthesizers and behavior with respect to cavity length in accordance with theory. It is also observed that dispersion penalty is a significant factor at this high frequency.

Time stretching of 102-GHz millimeter waves using novel 1.55 μm polymer electrooptic modulator

Millimeter (MM)-wave signals at frequencies up to 102 GHz have been time stretched down to 11 GHz using a new wide-band traveling-wave polymer modulator. This is the first application of electrooptic modulators fabricated using the new polymer material PC-CLD, which has demonstrated good optical loss and high nonlinearity at 1.55 /spl mu/m.

Vertical adiabatic transition between a silica planar waveguide and an electro-optic polymer fabricated with gray-scale lithography

We report on a vertical adiabatic transition between silica planar waveguides and electro-optic (EO) polymer. Gray-scale lithography was used to pattern a polymer transition with an exponential profile. Excess losses of the order of 1 dB were measured, and good mode matching to simulation was observed. This configuration, which married the advantages of both silica and EO-polymer planar-optic technologies, demonstrates a new technique for fabricating hybrid active devices with high modulation speed, low insertion loss, and complex geometries.

High speed polymer electro-optic modulators

We have used this polymer technology to fabricate modulators with balanced outputs by including a 3 dB coupler on the output and incorporated them in a digital time delay array. Arrays of RF photonic phase shifter operating at 20 GHz has also been demonstrated. For more complex integrated optical circuits, it will be important to use low loss passive polymers to interconnect the active polymer devices.

Frequency conversion for WDM applications using polymer traveling-wave electro-optic devices

Frequency conversion of optical waves as a result of refraction through a moving interface in traveling-wave electro-optic phase modulators is analyzed. Two configurations of a device performing conversion are proposed, and their operating requirements are determined.

Time stretched millimeter waves using novel 1.55 /spl mu/m broadband polymer modulators

Summary form only given. Time stretching of electrical signals as described in has been identified as a possible solution to the limited bandwidth of electronic analog to digital converters (ADCs). However, the use of LiNbO/sub 3/ modulators in these systems has limited the maximum frequency of the signal to be stretched to approximately 12 GHz. Polymer traveling-wave modulators have demonstrated outstanding performance in terms of bandwidth and have begun to be implemented in critical photonic functions. Using their superior speed, these modulators can significantly enhance the overall lime stretch system bandwidth. To demonstrate this we have fabricated traveling-wave polymer Mach-Zehnder modulators from a new material, PC/CLD, which has exhibited reduced optical losses at 1.55 /spl mu/m together with increased optical nonlinearity. Sinusoids ranging in frequency from 3 3 to 61.8 GHz were stretched into the band ranging from 8.5 to 13 GHz. These results represent a significant extension of the input bandwidth of time stretchers and offers major extensions of optical ADCs.