US 6,674,968 B1 · Passive thermal stabilization for an optical mux/demux

Abstract

A method and apparatus for multiplexing/de-multiplexing optical signals is disclosed. The method and apparatus are applicable to a range of optical multiplexing techniques including, but not limited to: wavelength division multiplexing (WDM), dense wavelength division multiplexing (DWDM) and frequency division multiple accessing (FDMA). The disclosed devices do not require active components. The disclosed devices may be implemented with fiber or fiberless optical communication systems including telecommunications systems. The devices may be used on their own or as part of a larger system such as a multi-stage mux/demux, an optical switch, or router. Additionally, the devices are passively thermally stabilized with the result that their tuning is substantially invariant across a wide temperature range. The optical device includes a linear polarizer, at least one wave plate and a beam displacer/combiner. The wave plate optically couples to the linear polarizer and rotates both odd and even channel components of an optical beam between a linear and an orthogonal relationship depending on the propagation direction. The wave plate includes a primary and a compensating birefringent element with respective first and second lengths and first and second indices of refraction. The first and second lengths and the first and second indices of refraction together determinative both of a free spectral range for the at least one wave plate corresponding to a spacing between adjacent gridlines of the selected wavelength grid, and of a combined optical pathlength difference for the wave plate substantially invariant with temperature.

Claims32

Dependent claims

An optical device for operating upon optical signals between a first port communicating odd channels and even channels and a second port communicating the odd channels together with a third port communicating the even channels, and adjacent orders of the odd and even channels evenly spaced apart and each centered on a corresponding gridline of a selected wavelength grid;

and said optical device comprising;
a linear polarizer coupled to the first port for linearly polarizing optical signals;
at least one wave plate with a first and a second I/O interface, and the at least one wave plate optically coupled at a first I/O interface to the linear polarizer, and the at least one wave plate rotating both odd and even channel components of an optical beam between a linear and an orthogonal relationship depending on the propagation direction, and the at least one wave plate including:
a) a primary birefringent element with a selected first length L1 and first indices no1, ne1 of refraction;
and
b) a compensating birefringent element with a selected second length L2 and a second indices no2, ne2 of refraction distinct from the first indices of refraction, and
the first length, the second length, the first indices of refraction and the second indices of refraction together determinative both of a free spectral range for the at least one wave plate corresponding to a spacing between adjacent gridlines of the selected wavelength grid, and determinative as well as of a combined optical pathlength difference for the wave plate substantially invariant with respect to temperature;
and
a beam displacer/combiner, optically coupling the second I/O interface of the at least one wave plate with both the second port and the third port, and the beam displacer/combiner displacing and combining orthogonally polarized odd and even channel components of an optical beam depending on a propagation direction.

6 more elements

A method for splitting/combining odd and even channels of an optical beam between a first port communicating odd channels and even channels and a second port communicating the odd channels together with a third port communicating the even channels, and adjacent orders of the odd and even channels evenly spaced apart and each centered on a corresponding gridline of a selected wavelength grid;

and said method for splitting/combining comprising;
linearly polarizing the optical beam at the first port;
relatively retarding an e-ray and an o-ray component of the optical beam by a primary amount and a compensating amount and a sum of the primary amount and the compensating amount substantially invariant with respect to temperature, and the sum corresponding to an integer multiple of 2π of a one of the odd channels and the even channels and to odd integer multiples of π for an other of the odd channels and the even channels, both at a free spectral range corresponding to the spacing between gridlines of the selected wavelength grid, to rotate odd and even channel components of the optical beam between a linear and an orthogonal relationship depending on the propagation direction;
and
displacing and combining orthogonally polarized odd and even channel components of an optical beam depending on a propagation direction.

2 more elements

An optical device for operating upon optical signals including odd and even channels, and adjacent orders of the odd and even channels evenly spaced apart and each centered on a corresponding gridline of a selected wavelength grid;

and said optical device comprising;
at least one wave plate with a first and a second I/O interface, and the at least one wave plate, and the at least one wave plate to rotate both odd and even channel components of an optical beam between a linear and an orthogonal relationship depending on the propagation direction, and the at least one wave plate including:
a) a primary birefringent element with a selected first length L1 and first indices no1, ne1 of refraction;
and
b) a compensating birefringent element with a selected second length L2 and a no2, ne2 second indices of refraction distinct from the first indices of refraction, and
the first length, the second length, the first indices of refraction and the second indices of refraction together determinative both of a free spectral range for the at least one wave plate corresponding to a spacing between adjacent gridlines of the selected wavelength grid, and determinative as well as of a combined optical path length difference for the wave plate substantially invariant with respect to temperature.

3 more elements

Dependencies are inferred from the claim text.

Passive thermal stabilization for an optical mux/demux

Life of this patent

Passive thermal stabilization for an optical mux/demux

Life of this patent

Abstract

Claims32