Hernan Erlig

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.

Electro-optic polymer modulators for 1.55 μm wavelength using phenyltetraene bridged chromophore in polycarbonate

Electro-optic polymer modulators operating at 1550 nm are demonstrated based on a nonlinear optical polymer of a phenyltetraene bridged chromophore in polycarbonate. It has a large electro-optic coefficient (r33=55 pm/V at 1550 nm), good thermal stability (90 °C), and low loss (1.7 dB/cm). A thin protective layer was used in the fabrication of ridge waveguides on the nonlinear polymer. We measured Vπ of 2.4 and 3.7 V at 1300 and 1550 nm, respectively. The chip loss of the modulator at both wavelengths was 5 dB, not including fiber coupling losses.

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.

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.

Multiple output photonic RF phase shifter using a novel polymer technology

Photonic RF phase shifters with independent multiple outputs have been fabricated using our novel polymer modulator technology. These integrated planar devices incorporated low crosstalk optical waveguide crossings, which were critical to the independent operation of RF phase outputs. The measured RF phase shift characteristics at 20 GHz were approximately linear up to /spl sim/150/spl deg/ with respect to do control voltages. In addition, the optical single-sideband (SSB) modulators, which were part of the phase shifters, were characterized and SSB modulation was confirmed.

Group velocity dispersion cancellation and additive group delays by cascaded fiber Bragg gratings in transmission

We have demonstrated that cascaded fiber Bragg gratings can provide delays of propagating pulses with minimal pulse reshaping. The grating pair used exhibited an overlap transmission region centered at 1551.05 nm, where both gratings contribute to the group delay and the group velocity dispersion (GVD) was canceled. Using wavelength tunable pulses spectrally sliced from a mode-locked fiber laser, the measurement was performed in the time domain with single picosecond resolution. Both gratings were 3 mm long and a maximum group delay of 15 ps was measured for the cascaded sequence. This compound grating configuration can be implemented as encoders and decoders in spread spectrum CDMA systems.

High-power high-frequency traveling-wave heterojunction phototransistors with integrated polyimide waveguide

A high-power high-speed phototransistor has been demonstrated using a traveling-wave (TW) structure with an integrated polyimide optical waveguide. In our configuration, optical power transfer is distributed along the length of the device via leaky mode coupling of light from the polyimide waveguide to the active region of the phototransistor. The TW electrode design allows for an electrically long structure while maintaining high bandwidths. Due to the increased absorption volume, the optical power handling capabilities of the TW-heterojunction phototransistors (TW-HPTs) are improved over that of conventional lumped-element HPT detectors. The experimental results show no saturation of the fundamental at 60 GHz up to 50 mA of DC photocurrent.

Electrical tuning of the kinetic inductance of high temperature superconductors

A current controlled delay in the time of flight of electrical picosecond pulses in a YBa2Cu3O7 spiral delay line has been investigated using optoelectronic sampling techniques. The transmission line is a microwave stripline on the LaAlO3 substrate and is passivated with the contact pads open. The measured delay time clearly shows a squared dependence on the applied current, in good agreement with Ginzburg–Landau theory for the case of a uniform current density through a thin film.