ABSTRACT
Integrated-optic acousto-optic filters have large asymmetric sidelobes that have not been explained in previous publications. We show that this is caused by waveguide birefringence nonuniformity. For the devices described here, the dominant cause of the nonuniformity is a thermal gradient associated with the generation and absorption of the surface acoustic wave. When the thermal birefringence gradient is included in the coupled-mode model, asymmetric sidelobes in good agreement with observations are predicted. In addition, we show that waveguide inhomogeneities also lead to birefringence nonuniformity and can be used to tailor the birefringence to supress sidelobes in a two-section acousto-optic filter.
ABSTRACT
A two-section integrated acousto-optic tunable filter with significantly reduced sidelobes has been fabricated. The sidelobe reduction was achieved with birefringence apodization in the form of variable-width Ti-stripe waveguides. The design and fabrication of the device, which includes integrated proton-exchanged TE and TM-pass polarizers, are described. Experimental tuning curves for each filter section and the overall device are presented and compared with calculated results. The largest sidelobes were found to be 24 dB below the peak transmission, which represents a 5.3-dB improvement over an ideal filter without birefringence apodization. The FWHM of the filter is 1.36 nm, which is only 16% larger than predicted for its interaction length of 17 mm/section.
ABSTRACT
A reset-free polarization controllsynthesis system is described. The desired polarization state can be selected by keyboard control with no insertion or rearrangement of optical components.
ABSTRACT
An incoherent, frequency modulated continuous wave optical reflectomer is described which utilizes a broadband LiNbO(3) electrooptic modulator and slow photodiode for optical downconversion and detection, and a waveform recorder for digital spectrum analysis of the incoming signal. A two-point resolution of 6.8 cm in fiber is achieved. The dynamic range, defined as the location of the system noise floor relative to the maximum producible signal, is 50-dB optical.
ABSTRACT
Optical nonlinear interactions may be made broadband while maintaining a high conversion efficiency by applying spread-spectrum pseudorandom spatial modulation.
ABSTRACT
We have characterized the intermodulation distortion and compression properties of an integrated optical modulator at microwave frequencies by measuring the third-order intercept and 1-dB compression points. Values of +30.0 and +21.4 dBm, respectively, were measured and agree well with theory. When operated in the shot-noise-limited regime, these devices can have spurious free dynamic ranges in excess of 100 dB, making them attractive as potential alternatives to conventional diode mixers in special applications.
