Kar Pong Lor

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.

UV-written long-period gratings on polymer waveguides

We report an ultraviolet (UV)-writing technique for the fabrication of a long-period waveguide grating on a benzocyclobutene ridge waveguide coated with epoxy (UV 11-3), where the grating is formed by exposing the waveguide to 248-nm UV pulses emitted from a KrF excimer laser through an amplitude mask. The UV pulses produce both index modulation and corrugation on the epoxy cladding, and their combined effect gives rise to the observed transmission spectrum. We also highlight the effects of UV-induced nonuniformity along the grating by simulation and measure the temperature sensitivity of the resonance wavelength of the grating.

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.

Widely tunable long-period waveguide grating couplers

We demonstrate experimentally two widely tunable optical couplers formed with parallel long-period polymer waveguide gratings. One of the couplers consists of two parallel gratings and shows a peak coupling efficiency of ~34%. The resonance wavelength of the coupler can be tuned thermally with a sensitivity of 4.7 nm/ degrees C. The experimental results agree well with the coupled-mode analysis. The other coupler consists of an array of ten widely separated gratings. A peak coupling efficiency of ~11% is obtained between the two best matched gratings in the array and the resonance wavelength can be tuned thermally with a sensitivity of -3.8 nm/ degrees C. These couplers have the potential to be further developed into practical broadband add/drop multiplexers and signal dividers.

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 gratings in polymer ridge waveguides

We report the design and fabrication of long-period waveguide gratings (LPWGs) in benzocyclobutene (BCB) ridge waveguides. We apply an accurate perturbation theory to analyze the LPWGs. In particular, the phase-matching condition, the coupling coefficients, the temperature dependence of the resonance wavelength, the bandwidth, and the polarization dependence of the resonance wavelength are discussed. Several LPWGs in BCB ridge waveguides are fabricated by a UV-writing technique using a KrF excimer laser. The transmission spectra of the gratings are measured and discussed. An LPWG with a polarization-insensitive resonance wavelength at a specific temperature is demonstrated. Experimental results agree well with the theory. Our results are useful for the design of LPWG-based devices for various applications.

Condition for the realization of a temperature-insensitive long-period waveguide grating

We analyze the condition for achieving a temperature-insensitive resonance wavelength of a long-period grating formed in a channel waveguide. We find that by controlling the waveguide cladding thickness, zero temperature sensitivity can be achieved with core and cladding materials that have significantly different thermo-optic coefficients. To verify our finding, we design a polymer long-period waveguide grating (LPWG) according to the zero-sensitivity condition, where the thermo-optic coefficient of the core is twice that of the cladding. The temperature sensitivity of the fabricated grating is within +/-0.15 nm/ degrees C over a temperature range of approximately 15 degrees C, which is more than an order of magnitude lower than those of previously reported LPWGs fabricated with the same materials.

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.

Refractive-Index Profiling of Buried Planar Waveguides by an Inverse Wentzel–Kramer–Brillouin Method

We propose an inverse Wentzel-Kramer-Brillouin (WKB) method for the construction of the refractive-index profiles of buried graded-index planar waveguides from the measured effective indexes of the guided modes. Our method involves experimental determination of the location of the peak index in the buried profile, measurement of the effective indexes in air, and an index-matching liquid, and application of a searching algorithm to find the best-fit profile through inverting the WKB equations. We present numerical examples and experimental results to demonstrate the performance of the method.

Tailoring the transmission characteristics of polymer long-period waveguide gratings by UV irradiation

We propose a simple technique of realizing complicated yet controllable transmission spectra from a uniform polymer long-period waveguide grating. The technique is based on varying the waveguide parameters along the grating by exposing the grating to a controlled distribution of ultraviolet (UV) irradiation. To demonstrate the idea, we produce transmission spectra that mimic those of a phase-shifted grating and a chirped grating by using a step-wise and a linear 248-nm UV distribution, respectively. The experimental results agree well with the simulation results. The UV process allows real-time monitoring of the change in the transmission spectrum. Furthermore, the resultant spectrum can be tuned thermally over the entire C+L-band with a temperature control of only /spl sim/20/spl deg/C. The proposed technique provides an effective means of achieving widely tunable complicated filter characteristics.