Johan Backlund

Multifunctional grating couplers for bidirectional incoupling into planar waveguides

A novel type of grating coupler for coupling light from free space into a planar waveguide was designed. Compared to a conventional grating coupler which can couple light into one main direction, this new design enables simultaneous coupling into two opposite main directions. This leads to increased flexibility in integrated optics design and may also increase the overall coupling efficiency. We demonstrate experimentally devices for bidirectional incoupling with additional beam splitting and focusing capabilities.

Input waveguide grating couplers designed for a desired wavelength and polarization response

Input grating couplers are used to couple light from free space into a waveguide and can provide additional functions such as focusing and beam splitting of the light into arbitrary desired positions in the waveguide. We show that it is possible to design the couplers so that they perform different desired functions depending on the polarization or wavelength of the incident light. We demonstrate experimentally a number of couplers that may be of interest, e.g., in optical fiber communications. Examples are polarization-independent couplers, designed to have the same response for two orthogonal polarizations of the incident light, and couplers for demultiplexing in wavelength division multiplexing applications, designed to separate and focus different input wavelengths to different positions in the waveguide.

Incoupling waveguide holograms for simultaneous focusing into multiple arbitrary positions

A design method is presented that enables the realization of a novel type of incoupling waveguide hologram (IWGH) that simultaneously focuses the incoupled light to any desired positions in the waveguide. IWGHs, or grating couplers, are gratinglike structures etched into the waveguide surface. They couple the light incident from free space into the waveguide. The grating lines can be dislocated with respect to each other to provide phase modulation of the incoupled light. By use of this phase modulation, novel beam splitting and focusing functions can be built into the IWGHs. The new design algorithm is based on a model that assumes a simple relation between the incident light wave and the locally excited guided wave. This model is used to obtain an efficient formulation of the optimization problem. Four different IWGHs were designed and fabricated in InP for light at 1550-nm wavelength. Experiments confirm that these IWGHs are capable of incoupling the incident wave and simultaneously splitting and focusing the guided wave into multiple positions in the waveguide at different distances from the IWGH.

Waveguide input grating coupler for wavelength-division multiplexing and wavelength encoding

We demonstrate the wavelength-division multiplexing (WDM) and wavelength-encoding capability of input waveguide grating couplers. The couplers are designed to have a predetermined wavelength response in addition to their conventional function of coupling an incident beam from, e.g., an optical fiber into a planar waveguide. The first example shows the WDM function: separating each of four input wavelengths into a different focus position in the waveguide. The second example shows wavelength encoding: translating a certain wavelength into a desired configuration of focus positions that is different for four different input wavelengths. The couplers were fabricated in an InP waveguide for /spl sim/1550-nm wavelength and the separation between the wavelengths was 10 nm. A WDM coupler with a narrower channel separation of 2 nm was also fabricated and successfully demonstrated.

Multifunctional gratings for surface-emitting lasers: design and implementation.

We experimentally demonstrate the use of two different multifunctional grating couplers in surface-emitting lasers for improved beam quality and advanced beam profiles. The lasers used for the demonstration are grating-based unstable resonator lasers, each with a grating coupler for surface emission and beam shaping. The new design method, described in detail, allows for simultaneous optimization of arbitrary feedback and outcoupling characteristics of the grating coupler. The first coupler is designed to reduce feedback to the resonator that would otherwise disturb the operation of the laser and lower the beam quality and to produce an output beam focused to four spots. The second coupler is designed to provide the feedback needed to support the unstable resonator, eliminating one feedback grating, and simultaneously focus the output beam to a single spot. As far as we know, this is the first time such multifunctional couplers are used in grating-coupled surface-emitting lasers. The couplers provide near-diffraction-limited spots that are a considerable improvement compared with previous lasers with no feedback control in the couplers.

Effects of feedback from collimating, focusing, and spot-array generating outcoupler gratings in surface-emitting semiconductor lasers.

We experimentally demonstrate that a grating outcoupler used for complex beam shaping (spot-array generation) can produce unintentional optical feedback that severely disturbs the integrated in-plane laser that illuminates the coupler. Simulations show that these outcouplers, in contrast to conventional collimating or focusing outcouplers, tend to produce high levels of feedback in spite of the detuning used to suppress feedback. Further, this feedback is focused to high intensity in the laser gain medium. This focused light acts as a seed for the nonlinear self-focusing that causes wave-front distortion and filamentation, which degrades the beam quality.

Waveguide hologram for outcoupling and simultaneous focusing into multiple arbitrary positions

Outcoupling waveguide holograms are gratings with locally dislocated grating lines etched into the waveguide surface. They couple light out of the waveguide into air and simultaneously provide focusing capabilities. Here, we present a waveguide hologram that focuses light into spots in any desired three-dimensional configuration. The hologram is fabricated on an InGaAsP-InP waveguide for 1550-nm optical wavelength. In an experiment we obtained simultaneously focused spot patterns at 1.5, 3 and 40 mm distance from the waveguide surface. The uniformity error was 23%, 8%, and 16%, respectively, for the three patterns and the diffraction efficiency was 40%.

Progress in diffractive integrated optics

Exploiting the wave nature of light to create new compact components is the goal of Diffractive Integrated Optics (DIO). So far DIOs have been only partly successful and in the next generation DIOs the diffractive, coupling, and waveguiding functions will be more indistinguishable.

Incoupling waveguide hologram with reduced polarization sensitivity

An incoupling waveguide hologram (IWGH) with significantly reduced polarization sensitivity was designed and fabricated in InP for 1550 nm wavelength. The IWGH couples the light from an optical fiber, irrespectively of the state of polarization, into the InP waveguide and simultaneously focuses it to a desired position in the waveguide. Conventional IWGHs are strongly polarization sensitive with a measured 19 dB difference in the incoupling efficiency between the TE and TM mode. In contrast, although some design parameters turned out to be slightly in error, the fabricated IWGHs designed for reduced polarization sensitivity exhibited a 3.1 dB difference in the incoupling efficiency between the TE and TM modes.

Diffractive optics at the surface of light-emitting/receiving semiconductor components

Abstract Semiconductor components that emit or receive light can use diffractive surface structures to increase the functionality and reduce the number of additional optical components needed in the system. The diffractive structure couples the light out of, or into, the semiconductor material; it splits the light and directs it into one focus or several foci at any desired position. Further, the diffractive optics can be designed so that the function of the device is largely insensitive to the polarization of the light. In this survey, we briefly discuss design and fabrication issues, and show simulated and measured results, for a few different types of components.