Abstract:
A method for fabricating ion exchange waveguides, such as lithium niobate or lithium tantalate waveguides in optical modulators includes ion exchanging the crystalline substrate (102) with a source of ions and annealing the substrate by pressurizing a gas atmosphere containing the lithium niobate or lithium tantalate substrate above normal atmospheric pressure, heating the substrate to a temperature ranging from about 150 degrees Celsius to about 1000 degrees Celsius, maintaining pressure and temperature to effect greater ion diffusion and limit exchange, and cooling the structure to an ambient temperature at an appropriate ramp down rate. In another aspect of the invention a powder (110) of the same chemical composition as the crystalline substrate (102) is introduced into the anneal process chamber (100) to limit the crystalline substrate from outgassing alkaline earth metal oxide during the anneal period. In yet another aspect of the invention an anneal container (100) is provided that allows for crystalline substrates (102) to be annealed in the presence of powder (110) without contaminating the substrate with the powder during the anneal process. Waveguides manufactured in accordance with the method exhibit superior drift performance.
Abstract:
Apparatus for processing one or more optical signals to produce a desired polarisation transformation on a Poincaré sphere has particular application in a receiver for a coherent communication system. One or more birefringent elements (11) receive a polarised optical signal from a local oscillator (12), and vary the state of polarisation of the local optical signal in order to match it to a received optical signal from a remote source on a line (13). The transformed local signal is fed on a line (14) to a directional coupler (15) which compares the local and remote optical signals. A receiver (16) extracts data by interference between the two signals in the directional coupler (15), and feeds data out at a line (17). A level detector (18) detects the level of the output signal (17) and supplies a feed-back signal to a polarisation controller (19), which controls the birefringent element or elements (11). The birefringent device (11) is adapted to provide a variable rotation on a Poincaré sphere about an axis of rotation which itself may be varied in direction. The control means (19) varies the amount of rotation on the Poincaré sphere produced by the birefringent device, and varies the direction of the axis about which the rotation takes place, so as to achieve the desired polarisation transformation. A preferred form of the birefringent device (11) comprises a waveguide (20) of electro-optic material, and means (22, 23) for producing in the electro-optic material an electric field of variable strength and variable orientation wherby required polarisation transformation can take place. Preferably the electro-optic material is lithium niobate.
Abstract:
An opto-electronic modulator includes a Mach-Zehrader structure that comprises p + in + -diodes in both arms of the Mach-Zehrader structure. The Mach-Zehrader structure is formed by waveguides so as to confine an optical mode in the opto-electronic modulator.
Abstract:
An optical delay generator comprises a first waveguide made from electro-optically active material resonantly coupled to a second non-electro-optically active waveguide. The first waveguide contains a chirped distributed Bragg reflector structure which reflects optical signals at a specific wavelength at a specific reflection point within the structure. An electric field applied to the first waveguide changes the refractive index of the electro-optically activematerial and thus shifts the reflection point. Optical signals reflecting from the reflection points are resonantly coupled into the second waveguide, and are thus not affected by the electric field applied to the first waveguide. The controllable optical delay applied to the optical signals results from control over the reflection point and the round-trip travel time for an optical signal forward propagating in the first waveguide, being reflected at the reflection point, and backward propagating in the second waveguide.
Abstract:
A light modulator of waveguide type (40) comprises electrooptic substrate (1), an optical waveguide (2) for guiding light wave, a traveling wave type signal electrode (3) for controlling the guided light, and a grounding electrode (4). A buffer layer (6), having a width W greater than the width omega of the traveling wave type signal electrode (3), is formed only under traveling wave type signal electrode (3), and the buffer layer is buried at least in part into the surface portion of the substrate (1).