Optical multiplexer

Abstract

An optical multiplexer includes a substrate into which are integrated a polarization rotator and a polarization coupler. The polarization coupler and the polarization rotator are in optical communication with each other.

What is claimed is:  
     
         1 . A multiplexer comprising: 
 a substrate;    a polarization rotator integrated into the substrate; and    a polarization coupler integrated into the substrate, the polarization coupler being in optical communication with the polarization rotator.    
     
     
         2 . The multiplexer of  claim 1 , further comprising a laser integrated into the substrate, the laser diode in optical communication with one of the polarization rotator and the polarization coupler.  
     
     
         3 . The multiplexer of  claim 1 , further comprising a lens coupling system in optical communication with the substrate for coupling light into the substrate.  
     
     
         4 . The multiplexer of  claim 3 , further comprising a laser source in optical communication with the lens coupling system.  
     
     
         5 . The multiplexer of  claim 4 , further comprising a controller in communication with a laser source, the controller being configured to control the output of the laser source.  
     
     
         6 . The multiplexer of  claim 4 , wherein the controller is configured to receive a feedback signal indicative of the output of the laser source and to generate a control signal for controlling the laser source, the control signal depending, at least in part, on the feedback signal.  
     
     
         7 . The multiplexer of  claim 1 , further comprising a tap formed in the substrate for providing a feedback signal for controlling light entering the substrate.  
     
     
         8 . The multiplexer of  claim 1 , further comprising: 
 a plurality of laser sources in optical communication with the substrate,    a controller in communication with each of the laser sources for controlling the output of each of the laser sources, the controller being configured 
 to receive a feedback signal indicative of the output of each laser source, and  
 to implement a gain flattening algorithm for controlling each of the laser sources  
   
     
     
         9 . The multiplexer of  claim 1 , further comprising an output tap formed in the substrate, the output tap being disposed to detect reflected light at an output of the substrate.  
     
     
         10 . The multiplexer of  claim 7 , further comprising a controller in communication with an input laser source and with the output tap, the controller being configured to control the input laser source on the basis of detecting a signal on the output tap indicative of reflected light at an output of the substrate.  
     
     
         11 . A Raman amplifier comprising a multiplexer as recited in  claim 1 .  
     
     
         12 . An erbium-doped fiber amplifier comprising a multiplexer as recited in  claim 1 .  
     
     
         13 . An optical imaging system comprising a multiplexer as recited in  claim 1 .  
     
     
         14 . An optical transport system comprising a multiplexer as recited in  claim 1 .  
     
     
         15 . An illumination system comprising a multiplexer as recited in  claim 1 .  
     
     
         16 . Optical test equipment comprising a multiplexer as recited in  claim 1 .  
     
     
         17 . Optical measurement equipment comprising a multiplexer as recited in  claim 1 .  
     
     
         18 . The multiplexer of  claim 1 , further comprising a waveguide extending between the polarization rotator and the polarization coupler.  
     
     
         19 . The multiplexer of  claim 1 , further comprising a wavelength coupler disposed on an optical path extending between the polarization coupler and the polarization rotator.  
     
     
         20 . The multiplexer of  claim 1 , further comprising: 
 a feeder waveguide in optical communication with the polarization coupler for guiding a beam having a first polarization state to the polarization coupler; and    a main waveguide in optical communication with the polarization coupler for receiving the first beam from the polarization coupler.    
     
     
         21 . The multiplexer of  claim 1 , wherein the polarization rotator comprises: 
 a stress-inducing element disposed to generate a stress-field in the substrate; and    a waveguide having a portion that passes through the stress-field.    
     
     
         22 . The multiplexer of  claim 21 , wherein the stress-inducing element comprises a strip bonded to the substrate, the strip having a coefficient of expansion different from the coefficient of expansion of the substrate.  
     
     
         23 . The multiplexer of  claim 21 , wherein the stress-inducing element comprises walls forming a trench in the substrate.  
     
     
         24 . The multiplexer of  claim 21 , wherein the stress-inducing element comprises walls forming a ledge in the substrate.  
     
     
         25 . The multiplexer of  claim 20 , wherein the polarization coupler comprises 
 a stress-inducing element disposed to generate a stress-field in the substrate;    a first periodic structure in optical communication with a portion of the main waveguide, the portion of the main waveguide being disposed to pass through the stress-field; and    a second periodic structure in optical communication with a portion of the feeder waveguide and with the first periodic structure, the portion of the feeder waveguide being disposed to pass through the stress-field.    
     
     
         26 . The multiplexer of  claim 25 , wherein the stress-inducing element comprises a strip bonded to the substrate, the strip having a coefficient of expansion different from the coefficient of expansion of the substrate.  
     
     
         27 . The multiplexer of  claim 25 , wherein the stress-inducing element comprises walls forming a trench in the substrate.  
     
     
         28 . The multiplexer of  claim 25 , wherein the stress-inducing element comprises walls forming a ledge in the substrate.  
     
     
         29 . A multiplexer comprising: 
 a substrate;    a polarization coupler integrated into the substrate; and    a first and second laser in optical communication with the substrate.    
     
     
         30 . The multiplexer of  claim 29 , wherein the substrate comprises: 
 a first waveguide in optical communication with the first laser; and    a second waveguide in optical communication with the second laser.    
     
     
         31 . The multiplexer of  claim 29 , wherein the first and second lasers are rotated relative to each other such that a first beam from the first laser and a second beam from the second laser enter the substrate with different polarizations.  
     
     
         32 . The multiplexer of  claim 29 , wherein the first and second lasers are rotated relative to each other such that a first beam from the first laser and a second beam from the second laser enter the substrate with orthogonal polarizations.  
     
     
         33 . The multiplexer of  claim 29 , wherein at least one of the first and second lasers is integrated into the substrate.  
     
     
         34 . The multiplexer of  claim 29 , further comprising a polarization rotator disposed on an optical path between the first laser and the substrate.  
     
     
         35 . A multiplexer comprising: 
 a substrate;    a polarization coupler integrated into the substrate; and    a polarization rotator disposed to intercept a beam entering the substrate.    
     
     
         36 . The multiplexer of  claim 35 , wherein the polarization rotator is configured to orthogonally rotate a beam entering the substrate.  
     
     
         37 . The multiplexer of  claim 35 , wherein the polarization rotator comprises a quarter-wave plate.  
     
     
         38 . A multiplexer comprising: 
 a substrate;    a polarization rotator integrated into the substrate, the polarization rotator comprising: 
 an input for receiving a wave having a first polarization, and  
 an output for transmitting a wave having a second polarization;  
   a polarization coupler integrated into the substrate, the polarization coupler comprising: 
 a first waveguide coupled to a first input for receiving a wave having a first polarization,  
 a second waveguide coupled to a second input for receiving a wave having a second polarization, the first and second waveguides having portions in proximity to each other to allow coupling of the waves to an output to transmit a wave having both the first polarization and the second polarization, with the polarization coupler being in optical communication with the output of the polarization rotator; and  
 an optical path between the output of the polarization rotator and the second input of the polarization coupler.  
   
     
     
         39 . The multiplexer of  claim 38 , wherein the polarization rotator is configured to provide, at its output, a wave having a polarization that is in quadrature with a polarization of a wave presented at its input.  
     
     
         40 . The multiplexer of  claim 38 , wherein the optical path comprises a waveguide extending between the polarization rotator and the polarization coupler.  
     
     
         41 . The multiplexer of  claim 38 , wherein the optical path comprises: 
 a wavelength coupler;    a first waveguide extending between the polarization rotator and the wavelength coupler, and    a second waveguide extending between the wavelength coupler and the polarization rotator.    
     
     
         42 . The multiplexer of  claim 38 , wherein the polarization rotator comprises: 
 a stress-inducing element disposed to generate a stress-field in the substrate; and    a waveguide having a portion that passes through the stress-field.    
     
     
         43 . The multiplexer of  claim 42 , wherein the stress-inducing element comprises a strip bonded to the substrate, the strip having a coefficient of expansion different from the coefficient of expansion of the substrate.  
     
     
         44 . The multiplexer of  claim 38 , wherein the polarization coupler comprises 
 a stress-inducing element disposed to generate a stress-field in the substrate;    a first periodic structure in optical communication with a portion of a first waveguide, the portion of the first waveguide being disposed to pass through the stress-field; and    a second periodic structure in optical communication with a portion of a second waveguide and with the first periodic structure, the portion of the second waveguide being disposed to pass through the stress-field.    
     
     
         45 . The multiplexer of  claim 44 , wherein the stress-inducing element comprises a strip bonded to the substrate, the strip having a coefficient of expansion different from the coefficient of expansion of the substrate.  
     
     
         46 . The multiplexer of  claim 44 , wherein the stress-inducing element comprises walls forming a trench in the substrate.  
     
     
         47 . The multiplexer of  claim 44 , wherein the stress-inducing element comprises walls forming a ledge in the substrate.  
     
     
         48 . A Raman pump module comprising: 
 first and second sources for generating first and second pump beams at a particular wavelength;    a substrate; 
 a polarization rotator integrated into the substrate, the polarization rotator being configured to provide a rotated pump beam by rotating a polarization of an input pump beam;  
 a polarization coupler in optical communication with the polarization rotator, the polarization coupler having 
 a first input for receiving the second pump beam,  
 a second input for receiving a rotated pump beam from the polarization rotator, and  
 an output for providing an output pump beam that includes a superposition of the second pump beam and the rotated pump beam; and  
 an optical path extending between the polarization coupler and the polarization rotator for guiding the rotated pump beam to the polarization coupler.  
 
   
     
     
         49 . The Raman pump module of  claim 48 , further comprising an output waveguide for guiding the output pump beam, the output waveguide extending along an optical path that includes the output of the polarization coupler.  
     
     
         50 . The Raman pump module of  claim 49 , further comprising a wavelength division multiplexer having a first input in optical communication with the output waveguide and a second input for receiving a signal beam, the wavelength division multiplexer being configured to combine the signal beam with the output pump beam guided by the output waveguide.  
     
     
         51 . The Raman pump module of  claim 48 , wherein the polarization rotator is configured to provide a rotated pump having a polarization orthogonal to a polarization of the input pump beam.  
     
     
         52 . A method for combining first and second orthogonally polarized beams, the method comprising: 
 guiding the first beam along a feeder waveguide to a polarization coupler integrated into a substrate;    guiding the second beam along a main waveguide to the polarization coupler;    coupling the first beam from the feeder waveguide to the main waveguide.    
     
     
         53 . The method of  claim 52 , further comprising rotating the polarization of the first beam at a polarization rotator integrated into the substrate.  
     
     
         54 . The method of  claim 52 , further comprising: 
 providing a first laser to generate the first beam polarized along a first principal axis;    providing a second laser to generate the second beam, the second beam being polarized along the first principal axis; and    rotating the first and second lasers relative to each other.    
     
     
         55 . The method of  claim 52 , further comprising: 
 providing a first laser to generate the first beam polarized along a first principal axis;    providing a second laser to generate the second beam, the second beam being polarized along the first principal axis; and    passing the second beam through a birefringent film to rotate the polarization thereof.    
     
     
         56 . The method of  claim 53 , wherein rotating the polarization of the first beam comprises: 
 inducing birefringence in a selected region of the substrate; and    guiding the first beam through the selected region.    
     
     
         57 . The method of  claim 56 , wherein inducing birefringence comprises imposing a stress field in the selected region of the substrate.  
     
     
         58 . The method of  claim 52 , wherein coupling the first beam from the feeder waveguide to the main waveguide comprises: 
 providing a first grating in optical communication with the feeder waveguide;    providing a second grating in optical communication with the main waveguide and with the first grating; and    inducing birefringence in a selected portion of the substrate, the selected portion including the first and second grating.    
     
     
         59 . The method of  claim 58 , wherein inducing birefringence comprises imposing a stress field in the selected region of the substrate.