C. K. Chow

Widely tunable long-period gratings fabricated in polymer-clad ion-exchanged glass waveguides

Long-period-grating filters were fabricated in polymer-clad ion-exchanged BK7 glass waveguides. The transmission spectra of the filters exhibited strong polarization dependence. A contrast as high as 25 dB at the resonance wavelength was obtained. The temperature sensitivity of the filters was measured to be /spl sim/9.0 nm//spl deg/C, which allows potential wavelength tuning over the entire S+C+L band of /spl sim/180 nm with a temperature control over a range of /spl sim/20/spl deg/C.

Temperature sensitivity of a long-period waveguide grating in a channel waveguide

We present a simulation of the temperature sensitivity of the resonance wavelength of a long-period waveguide grating (LPWG). We find that the temperature sensitivity of an LPWG in a channel waveguide is proportional to a modal dispersion factor that depends sensitively on the size of the core of the waveguide. Measurements with experimental polymer LPWGs agree well with the simulation results. The dimension of the waveguide core is an effective parameter for the control of the thermal characteristics of an LPWG in a channel waveguide.

Band-rejection filter with widely tunable center wavelength and contrast using metal long-period grating on polymer waveguide

We demonstrate a widely tunable band-rejection filter using a metal long-period grating deposited directly on the cladding of a polymer waveguide. The contrast of the rejection band can be tuned by 28 dB with /spl sim/45-mW electric power applied to the metal grating and the center wavelength can be tuned over the C+L-band with a temperature control of /spl sim/40/spl deg/C. The device can find applications as a tunable notch filter, a polarization-dependent loss compensator, or a variable attenuator.

Long-Period Waveguide Gratings

In this paper, we review our research efforts in the development of long-period waveguide gratings (LPWGs). We describe LPWGs fabricated in slab and channel waveguides with polymer and glass by conventional photolithography and reactive ion etching to demonstrate the flexibility of the technology, which leads to many advantages of LPWGs, compared with long-period fiber gratings. In particular, we show that an LPWG can function as a widely tunable filter and it is possible to control its wavelength tunability and polarization sensitivity by controlling the dimensions of the waveguide cladding. We also present an LPWG written in a polymer-clad waveguide by a UV technique. Furthermore, we illustrate experimentally the principle of light coupling among an array of parallel waveguides with identical LPWGs. LPWGs can serve as building blocks for the realization of a wide range of integrated optic devices.

A wide-angle X-junction polymeric thermooptic digital switch with low crosstalk

We present our recent design of a wide-angle asymmetric X-junction for the implementation of a digital-optical switch. The simulated crosstalk in the OFF and ON states are -28 and -26 dB, respectively, at an X-branching angle of 1/spl deg/. Polymeric material benzocyclobutene was used to fabricate our design and its switching property was demonstrated using the thermooptic effect. The measured crosstalk is approximately -24 dB in both states with rise-time and fall-time 140 and 210 /spl mu/s, respectively.

A wide-angle X-junction in polymer using truncated-structural branches (TSB)

We present a detailed design and characterization for a compact X-junction we proposed recently. Even at a wide full-branching angle of 1.4/spl deg/, simulation predicts the crosstalk and insertion loss to be -20.1 and 0.2 dB, respectively; the wavelength bandwidth is 230 nm (1390-1620 nm). Devices made in polymer realize -16.1-dB crosstalk and 0.3-dB loss.

Lithium–Niobate Channel Waveguide for the Realization of Long-Period Gratings

We propose a special lithium-niobate (LiNbO3) single-mode waveguide for the realization of long-period gratings, which consists of a channel core embedded in a thin slab cladding. We fabricated the waveguide on a z-cut LiNbO3 substrate with a two-step proton-exchange process and demonstrated its suitability for grating application with a number of removable photoresist long-period gratings deposited on the waveguide surface. The waveguide fabrication process and the LiNbO3 waveguide structure could be further explored for the development of electrooptic gratings for high-speed applications.

Electro-Optic Long-Period Grating on Lithium-Niobate Waveguide

We report an experimental electro-optic long-period grating, which was formed on a lithium-niobate waveguide fabricated by a two-step proton-exchange process. This grating is a promising structure for the realization of high-speed dynamic filters and modulators.

UV-written long-period waveguide grating coupler

We present a UV-written polymer long-period waveguide grating coupler, which can be tuned over a wavelength range of 100 nm with a temperature control of 22 degC. Its coupling efficiency varies between 57% and 80%.

Experimental investigation of electro-optic long-period gratings on lithium-niobate waveguides

Using several electro-optic long-period grating s fabricated on LiNbO3 wave guides, we demonstrate the effects of the cladding modes and the waveguide structure on the grating performance. We obtain a 25-dB rejection band at 95-V driving voltage.