Birefringent optical multiplexer with flattened bandpass

• US 4,685,773 A
• Filed: 10/28/1985
• Issued: 08/11/1987
• Est. Priority Date: 09/13/1984
• Status: Expired due to Term

• Current Assignee: GTE Laboratories Incorporated (Lumen Technologies, Inc.)
• Original Assignee: GTE Laboratories Incorporated (Lumen Technologies, Inc.)
• Inventors: Melman, Paul, Carlsen, W. John
• Primary Examiner(s): Arnold, Bruce Y.
• Application Number:
  US06/791,820
• Time in Patent Office: 652 Days
• Field of Search: 350/401, 350/403, 370/2, 455/616
• US Class Current: 359/489.09
• CPC Class Codes: G02B 27/283 used for beam splitting or combining
• CPC Class Codes: G02B 27/288 Filters employing polarising elements, e.g. Lyot or Solc filters G02B5/3016 takes precedence
• CPC Class Codes: G02B 6/105 having optical polarisation effects
• CPC Class Codes: G02B 6/272 comprising polarisation means for beam splitting and combining
• CPC Class Codes: G02B 6/2773 Polarisation splitting or combining
• CPC Class Codes: G02B 6/2817 using reflective elements to split or combine optical signals
• CPC Class Codes: G02B 6/29302 based on birefringence or polarisation, e.g. wavelength dependent birefringence, polarisation interferometers
• CPC Class Codes: G02B 6/2938 for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM

Abstract

A birefringent optical wavelength multiplexer/demultiplexer includes a first polarization beam-splitter, a first reflector, a plurality of birefringent elements, a second reflector, and a second polarization beam-splitter. The plurality of birefringent elements are so oriented that each element introduces an additional sinusoidal component to the transfer function of the device that tends to effectuate a flattened transfer function.

Claims

1. A birefringent optical wavelength multiplexer/demultiplexer comprising

first polarization beam splitting means for splitting an applied collimated beam of light into a first pair of linearly polarized beams whose directions of propagation are perpendicular to one another;

first reflecting means for reflecting one of said linearly polarized beams parallel to the other polarized beam;

a plurality of birefringent elements, each said element having a pair of opposed surfaces, one of said surfaces of one of said elements being parallel to and in adjacent relationship with another of said elements, each of said elements having a respective optical axis oriented nominally parallel to said surfaces of the respective element, said elements being oriented with said parallel surfaces perpendicular to the direction of propagation of said linearly polarized beams, said respective optical axis being oriented at specific angles with respect to said first polarization beam splitting means,

one electric field component of each of the two beams incident upon an element being parallel to the "extraordinary" axis of that element and propagating at different velocity, dependent upon the material of that element, from the other electric field component which is parallel to the "ordinary" axis of that element;

said plurality of birefringent elements being so oriented that each element introduces an additional sinusoidal component to the transfer function of the device, tending to effectuate a flattened transfer function;

second reflecting means for reflecting the other of said linearly polarized beams, following propagation of said other beam through said elements, in a direction perpendicular to that of said one of said polarized beams following propagation of said one polarized beam through said elements; and

second polarization beam splitting means oriented to receive both said reflected other beam and the propagated one beam, wherein

(1) when the propagated other beam and the propagated one beam have polarization states which are linearly polarized parallel to the polarization directions of said respective first pair of polarized beams, said reflected other beam is transmitted by said second polarization beam splitting means, and said propagated one beam is reflected by said second polarization beam splitting means, whereby said reflected other beam and said propagated one beam are combined and transmitted outwardly from a first port; and

(2) when the propagated other beam and the propagated one beam have polarization states which are linearly polarized perpendicular to the polarization directions of said respective first pair of polarized beams, said reflected other beam is reflected by said second polarization beam splitting means, and said propagated one beam is transmitted by said second polarization beam splitting means, whereby said reflected other beam and said propagated one beam are combined and transmitted outwardly from a second port.

2. The multiplexer/demultiplexer as recited in claim 1 further comprising means for uniformly varying the temperature of said birefringent elements.

3. A birefringent optical wavelength multiplexer/demultiplexer comprising

first polarization beam splitting means for splitting an applied collimated beam of light into a first pair of linearly polarized beams whose directions of propagation are at an angle with one another;

first reflecting means for reflecting one of said linearly polarized beams parallel to the other polarized beam;

a plurality of birefringent elements, each said element having a pair of opposed surfaces, one of said surfaces of one of said elements being parallel to and in adjacent relationship with another of said elements, each of said elements having a responsive optical axis oriented nominally parallel to said surfaces of the respective element, said elements being oriented with said parallel surfaces perpendicular to the direction of propagation of said linearly polarized beams, each said respective optical axis being oriented at a specific angle with respect to the first polarization beam splitting means,

one electric field component of each of the two beams incident upon an element being parallel to the "extraordinary" axis of that element and propagating at different velocity, dependent upon the material of that element, from the other electric field component which is parallel to the "ordinary" axis of that element;

said plurality of birefringent elements being so oriented that each said element introduces an additional sinusoidal component to the transfer function of the device tending to effectuate a flattened transfer function;

second reflecting means for reflecting the other of said polarized beams, following propagation of said other beam through said elements, in a direction perpendicular to that of said one of said polarized beams following propagation of said one polarized beam through said elements; and

second polarization beam splitting means oriented to receive both said reflected other beam and the propagated one beam, wherein

(1) when the propagated other beam and the propagated one beam have polarization states which are linearly polarized parallel to the polarization directions of said respective first pair of polarized beams, said reflected other beam is transmitted by said second polarization beam splitting means, and said propagated one beam is reflected by said second polarization beam splitting means, whereby said reflected other beam and said propagated one beam are combined and transmitted outwardly from a first port; and

(2) when the propagated other beam and the propagated one beam have polarization states which are linearly polarized perpendicular to the polarization directions of said respective first pair of polarized beams, said reflected other beam is reflected by said second polarization beam splitting means, and said propagated one beam is transmitted by said second polarization beam splitting means, whereby said reflected other beam and said propagated one beam are combined and transmitted outwardly from a second port.

4. The multiplexer/demultiplexer as recited in claim 3 further comprising means for uniformly varying the temperature of said birefringent elements.

5. A birefringent optical wavelength multiplexer/demultiplexer comprising

first polarization beam splitting means for splitting a first applied collimated beam of light into a first pair of linearly polarized beams whose directions of propagation are perpendicular to one another, and for splitting a second applied collimated beam of light into a second pair of linearly polarized beams whose directions of propagations are perpendicular, one polarized beam from said first collimated beam being directed along a first common path as one polarized beam of said second collimated beam, and the other polarized beam from said first collimated beam being directed along a second common path as the other polarized beam of said second collimated beam;

first reflecting means for reflecting said one polarized beams of said both collimated beams to a third path parallel to said second common path;

a plurality of birefringent elements, each said element having a pair of opposed parallel surfaces, with a respective optical axis oriented nominally parallel to said surfaces of the respective element, said elements being oriented with said parallel surfaces perpendicular to said third path and said second common path, each said respective optical axis being oriented at specific angles with respect to said first polarization beam splitting means,

those components of those polarized beams incident upon an element being parallel to the "extraordinary" axis of that element and propagating at different velocity, dependent upon the material of said element, from the other polarized components which are parallel to the "ordinary" axis of that element;

said plurality of birefringent elements being so oriented that each element introduces an additional sinusoidal component to the transfer function of the device tending to effectuate a flattened transfer function;

second reflecting means for reflecting said other polarized beams that have traversed said second common path to a direction perpendicular to said third path; and

second polarization beam splitting means oriented to receive the one polarized beams from both collimated beams that have traversed said third path, and said other polarized beams from both collimated beams that have traversed said second common path, wherein

(1) when both polarized beams from said first collimated beam combine to yield a polarization state which is linearly polarized parallel to the polarization directions of said first applied collimated beam, the reflected other beam of said first collimated beam is transmitted by said second polarization beam splitting means, and said propagated one beam of said first applied collimated beam is reflected by said second polarization beam splitting means, whereby said reflected other beam and said propagated one beam of said first collimated beam are combined and transmitted outwardly from a first port;

(2) when both polarized beams from said second collimated beam combine to yield a polarization state which is linearly polarized perpendicular to the polarization directions of said second applied collimated beam, the reflected other beam of said second collimated beam is transmitted by said second polarization beam splitting means, and said propagated one beam of said second collimated beam is reflected by said second polarization beam splitting means, whereby said reflected other beam and said propagated one beam of said second collimated beam are combined and transmitted outwardly from said first port;

(3) when both polarized beams from said first collimated beam combine to yield a polarization state which is linearly polarized perpendicular to said first applied collimated beam, the reflected other beam of said first collimated beam is reflected by said second polarization beam splitting means, and said propagated one beam of said first applied collimated beam is transmitted by said second polarization beam splitting means, whereby said reflected other beam and said propagated one beam of said first collimated beam are combined and transmitted outwardly from a second port; and

(4) when both polarized beams from said second collimated beam combine to yield a polarization state which is linearly polarized parallel to said second applied collimated beam, the reflected other beam of said second collimated beam is reflected by said second polarization beam splitting means, and said propagated one beam of said second collimated beam is transmitted by said second polarization beam splitting means, whereby said reflected other beam and said propagated one beam of said second collimated beam are combined and transmitted outwardly from said second port.

6. A comb filter unit comprising

a plurality of birefringent elements, each said element having a pair of parallel opposite sides, one of said sides of one of said elements being parallel to and in adjacent relationship with another of said elements,

said plurality of birefringent elements being so oriented that each element introduces an additional sinusoidal component tending to effectuate a flattened transfer function;

a first polarization beam splitter for splitting a collimated beam of light into two linearly polarized beams whose directions of propagations are at an angle to one another,

a first reflecting surface for reflecting one of said polarized beams along a path parallel to the other of said polarized beams,

both said other polarized beam and said reflected beam being incident upon one of said parallel sides of one of said elements, for transmission through all of said elements,

a second reflecting surface for reflecting the other of said polarized beams following its transmission through all of said elements, and

a second polarization beam splitter for combining said reflected other beam and said reflected one beam and transmitting the combined light through one of two ports.

7. A mechanically tunable optical wavelength multiplexer including a comb filter unit comprising

a plurality of birefringent elements, each said element being a pair of parallel opposite sides, one of said sides of one of said elements being parallel to and in adjacent relationship with another of said elements,

said plurality of birefringent elements being so oriented that each element introduces an additional sinusoidal component tending to effectuate a flatened transfer function;

a first polarization beam splitter for splitting a collimated beam of light at a wavelength λ

into two linearly polarized beams whose directions of propagations are at an angle to one another,

a first reflecting surface for reflecting one of said polarized beams along a path parallel to the other of said polarized beams,

both said other polarized beam and said reflected beam being incident upon one of said parallel sides of said elements for transmission through all said elements,

a second reflecting surface for reflecting the other of said polarized beams following its transmission through all of said elements, and

a second polarization beam splitter for combining said reflected other beam and said reflected one beam and transmitting the combined light through one of two ports,

at least one of said birefringent elements including a pair of wedges of birefringent material, arranged such that moving one relative to the other changes the effective thickness of the material through which the light propagates, and thus varies the overall retardation

whereby, a continuous change in both said wavelength λ and

in channel spacing Δ

λ

is provided, so that in a 2-channel system, said unit can be tuned precisely to the wavelengths of two signals to be multiplexed.