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Abstract

A zigzag waveguide device-based apparatus and method for achieving or maintaining wavelength lock for a tunable laser designed to generate light at a selected one of a plurality of target wavelengths. The apparatus has a reflectively coupled zigzag waveguide device for receiving a portion of light output by the tunable laser, the zigzag waveguide device having a plurality of filters, each having a passband centered at a respective one of the plurality of target wavelengths, whereby said zigzag waveguide device produces a plurality of filtered light outputs. A plurality of photosensors is provided, one for each of said plurality of filters, each said filter positioned to receive a respective one of the plurality of filtered light outputs, each said filter producing a filter output signal related to the intensity of said portion of light in the passband of the corresponding filter. A processor generates, in response to the plurality of filter output signals, a control signal to adjust the lasing wavelength of the tunable laser to achieve or maintain said selected one of the target wavelengths. In one embodiment, the zigzag waveguide device includes a first waveguide that is coupled to the laser to receive light output. A first wavelength filter is coupled to the first waveguide to receive light therefrom. The first wavelength filter transmits a band of wavelengths and reflecting one or more bands of wavelengths. A second waveguide is coupled to the first wavelength filter and receives light reflected from the first wavelength filter. A mirror is coupled to the second waveguide and receives light from the second waveguide. A third waveguide is coupled to the mirror to receive light reflected from the mirror. A second wavelength filter is coupled to the third waveguide to receive light therefrom. The second wavelength filter transmits a band of wavelengths different from the band of wavelengths transmitted by the first wavelength filter and reflects one or more bands of wavelengths. A first photodiode is coupled to receive light transmitted by the first wavelength filter. A second photodiode is coupled to receive light transmitted by the second wavelength filter. A laser wavelength controller is coupled to the tunable laser and is capable of modifying the wavelength of the tunable laser based at least in part on an output of one of the first and second photodiodes.

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First Claim