Optical modules having an improved optical signal to noise ratio

Abstract

Consistent with the present disclosure, a photonic integrated circuit (PIC) is provided that has 2 N channels (N being an integer). The PIC is optically coupled to N optical fibers, such that each of N polarization multiplexed optical signals are transmitted over a respective one of the N optical fibers. In another example, each of the N optical fibers supply a respective one of N polarization multiplexed optical signals to the PIC for coherent detection and processing. A multiplexer and demultiplexer may be omitted from the PIC, such that the optical signals are not combined on the PIC. As a result, the transmitted and received optical signals incur less loss and amplified spontaneous emission (ASE) noise. In addition, optical taps may be more readily employed on the PIC to measure outputs of the lasers, such as widely tunable lasers (WTLs), without crossing waveguides.

What is claimed is: 
     
         1 . An optical device, comprising:
 a substrate;   2N inputs on the substrate, N being an integer, each of the 2N inputs including a respective one of 2N waveguides, each of which extending to an edge of the substrate, and each of the 2N waveguides carrying a respective one of 2N optical signals, each of the 2N optical signals including an in-phase component and a quadrature component;   N lasers provided on the substrate;   first N optical hybrid circuits, each of which receiving a respective one of first N optical signals of the 2N optical signals from a corresponding one of first N waveguides of the 2N waveguides and a first portion of light output from a respective one of the N lasers, each of the first N optical hybrid circuits providing a respective one of first N groups of mixing products; and   second N optical hybrid circuits, each of which receiving a respective one of second N optical signals from a corresponding one of second N waveguides and a second portion of the light output from a respective one of the N lasers, each of the second N optical hybrid circuits providing a respective one of second N groups of mixing products, the first N and second pluralities of optical hybrid circuits being provided on the substrate; and   at least one optical element that collimates, focuses, rotates a polarization of at least one of, or combines the first N optical signals and the second N optical signals, said at least one optical element being configured to be coupled to N optical fibers, such that each of the N optical fibers carries a respective one of N polarization multiplexed optical signals, each of which including a respective one of the first N optical signals and a respective one of the second N optical signals, each of the second N optical signals having a polarization that is rotated relative to a corresponding one of the first N optical signal.   
     
     
         2 . An optical device in accordance with  claim 1 , wherein each of the N lasers is tunable. 
     
     
         3 . An optical device in accordance with  claim 1 , wherein the substrate includes a Group III-V material. 
     
     
         4 . An optical device in accordance with  claim 1 , further comprising:
 N optical splitters provided on the substrate, each of the N optical splitters being coupled to a respective one of the N lasers;   wherein the first portion of the light output from a respective one of the N lasers is supplied from a first output of a corresponding one of the N optical splitters, and the second portion of the light output from a respective one of the N lasers is supplied from a second output of a corresponding one of the N optical splitters.   
     
     
         5 . An optical device in accordance with  claim 1 , wherein each of the first N waveguides is coupled to a corresponding one of N optical amplifiers. 
     
     
         6 . An optical device in accordance with  claim 5 , wherein each of the N optical amplifiers is an erbium doped fiber amplifier. 
     
     
         7 . An optical device in accordance with  claim 5 , wherein each of the N optical amplifiers is provided on the substrate. 
     
     
         8 . An optical device in accordance with  claim 7 , wherein each of the N optical amplifiers is a semiconductor optical amplifier. 
     
     
         9 . An optical device in accordance with  claim 1 , further including:
 first N spot size converters included in a respective end portion of each of the first N waveguides adjacent the edge of the substrate; and   second N spot size converters included in a respective end portion of each of the second N waveguides adjacent the edge of the substrate.   
     
     
         10 . An optical device in accordance with  claim 1 , wherein the at least one optical element includes:
 first N lenses, each of which receiving a corresponding one of the first N optical signals; and   second N lenses, each of which receiving a corresponding one of the second N optical signals.   
     
     
         11 . An optical device in accordance with  claim 11 , wherein each of the first N lenses collimates a corresponding one of the first N optical signals, and each of the second N lenses collimates a corresponding one of the second N optical signals. 
     
     
         12 . An optical device in accordance with  claim 11 , wherein each of the first N lenses focuses a corresponding one of the first N optical signals, and each of the second N lenses focuses a corresponding one of the second N optical signals. 
     
     
         13 . An optical device in accordance with  claim 12 , wherein each of the first N lenses and each of the second N lenses are arranged in an array. 
     
     
         14 . An optical device in accordance with  claim 1 , wherein the at least one optical element includes N polarization splitters, each of which receiving the respective N optical signals. 
     
     
         15 . An optical device in accordance with  claim 1 , wherein the at least one optical element further includes N polarization rotators, each of which receiving a corresponding one of the first N optical signals from a corresponding one of the N polarization splitters, each of the N polarization rotators further rotating a polarization of said corresponding one of the first N optical signals. 
     
     
         16 . An optical device in accordance with  claim 15 , wherein the N polarization rotators are arranged in a first array and the N polarization splitters are arranged in a second array. 
     
     
         17 . An optical device in accordance with  claim 15 , wherein the substrate is a first substrate, the optical device further including:
 a second substrate, each of the N polarization rotators and each of the N polarization splitters being provided on the second substrate.   
     
     
         18 . An optical device in accordance with  claim 1 , wherein the at least one optical element is a plurality of optical elements, adjacent ones of the plurality of optical elements being separated from one another by a distance that is less than or equal to 1 mm. 
     
     
         19 . An optical device in accordance with  claim 1 , further including:
 first N optical isolators, each of which receiving a corresponding one of the first N optical signals; and   second N optical isolators, each of which receiving a corresponding one of the second N optical signals.   
     
     
         20 . An optical device in accordance with  claim 1 , further including a bulk optical isolator that receives the first N optical signals and the second N optical signals. 
     
     
         21 . An optical device in accordance with  claim 1 , wherein the at least one optical element includes:
 first N lenses, each of which receiving a corresponding one of the N polarization multiplexed optical signals, each of the first N lenses being configured to collimate a corresponding one of the first N optical signals and a corresponding one of the second N optical signals;   second N lenses each of which focusing said corresponding one of the first N optical signals for transmission on a corresponding one of the first N waveguides; and   third N lenses each of which focusing said corresponding one of the second N optical signals for transmission on a corresponding one of the second N waveguides.   
     
     
         22 . An optical device in accordance with  claim 21 , wherein the second N lenses and the third N lenses are arranged in an array that extends parallel to a facet of the substrate. 
     
     
         23 . An optical device in accordance with  claim 1 , wherein the substrate is a first substrate, the at least one optical element is provided on a second substrate. 
     
     
         24 . An optical device in accordance with  claim 1 , wherein the at least one optical elements is provided in a planar lightwave circuit (PLC). 
     
     
         25 . An optical device in accordance with  claim 1 , wherein the substrate is a first substrate, the optical device further including:
 a second substrate, a planar lightwave circuit (PLC) provided on the second substrate;   first N spot size converters included in the PLC, each of the first N spot size converters receiving a corresponding one of the first N optical signals; and   second N spot size converters included in the PLC, each of the second N spot size converters receiving a corresponding one of the second N optical signals.   
     
     
         26 . An optical device in accordance with  claim 25 , wherein the at least one optical element constitutes a plurality of silicon photonics devices. 
     
     
         27 . An optical device in accordance with  claim 23 , wherein the second substrate is attached to the first substrate. 
     
     
         28 . An optical device in accordance with  claim 25 , further including a layer of epoxy, wherein the second substrate is attached to the first substrate via the layer of epoxy. 
     
     
         29 . An optical device in accordance with  claim 1 , further including a pump laser that supplies pump light to at least one of the N optical fibers, said pump light having a wavelength corresponding to a pump wavelength of a doped fiber amplifier optically coupled to the at least one of the N optical fibers. 
     
     
         30 . An optical device in accordance with  claim 1 , wherein the substrate is a first substrate, the optical device further including an alignment laser, the alignment laser being provided on the first substrate and being configured supply light that it is detected by at least one photodiode provided on a second substrate or the first substrate, such that each of the N lasers is tuned based on one or more electrical signals generated by said at least one photodiode. 
     
     
         31 . An optical device in accordance with  claim 1 , wherein a third portion of the light output from each of the N lasers is provided to a corresponding one of N variable optical attenuators provided on the first substrate, each of the N variable optical attenuators being configured to selectively supply the third portion of the light to an optical receiver. 
     
     
         32 . An optical device in accordance with  claim 1 , further including:
 a wedge-shaped block provided adjacent the substrate, the at least one optical element being provided on the wedge-shaped block in an optical path of at least one of the first N modulated optical signals or one of the second N modulated optical signals, such that a propagation direction of said at least one of the first N modulated optical signals or said one of the second N modulated optical signals is changed.   
     
     
         33 . An optical device in accordance with  claim 1 , wherein the at least one optical element includes N polarization rotators, each of which receiving a corresponding one of the polarization rotated split first N optical signals from a polarization splitter block, each of the N polarization rotators further rotating a polarization of said corresponding one of the first N optical signals. 
     
     
         34 . An optical device in accordance with  claim 13 , wherein the first N lenses and the second N lenses constitute a plurality of lenses, each lens in the plurality of lenses being attached to one another. 
     
     
         35 . An optical device in accordance with  claim 13 , wherein the first N lenses and the second N lenses constitute a plurality of lenses that are provided as an integral unit. 
     
     
         36 . An optical device in accordance with  claim 13 , wherein the first N lenses and the second N lenses constitute a plurality of lenses that constitute a complex lens. 
     
     
         37 . An optical device in accordance with  claim 18 , wherein said adjacent ones of the plurality of optical elements are separated from one another by a distance that is less than or equal to 600 μm. 
     
     
         38 . An optical device in accordance with  claim 15 , wherein each of the N polarization rotators and a corresponding one of the N polarization splitters are provided in a respective one of N groupings, the N groupings be provided in an array. 
     
     
         39 . An optical device in accordance with  claim 1 , wherein the N fibers are provided in an array. 
     
     
         40 . An optical device, comprising:
 a substrate;   2N inputs on the substrate, N being an integer, each of the 2N inputs including a respective one of 2N waveguides, each of which extending to an edge of the substrate, and each of the 2N waveguides carrying a respective one of 2N optical signals, each of the 2N optical signals including an in-phase component and a quadrature component;   N lasers provided on the substrate;   first N optical hybrid circuits, each of which receiving a respective one of first N optical signals of the 2N optical signals from a corresponding one of first N waveguides of the 2N waveguides and a first portion of light output from a respective one of the N lasers, each of the first N optical hybrid circuits providing a respective one of first N groups of mixing products; and   second N optical hybrid circuits, each of which receiving a respective one of second N optical signals from a corresponding one of second N waveguides and a second portion of the light output from a respective one of the N lasers, each of the second N optical hybrid circuits providing a respective one of second N groups of mixing products, the first N and second pluralities of optical hybrid circuits being provided on the substrate; and   at least one optical element that collimates, focuses, rotates a polarization of at least one of, or combines the first N optical signals and the second N optical signals, said at least one optical element being configured to be coupled to M optical fibers, where M is an integer less than N.   
     
     
         41 . An optical device, comprising:
 a substrate;   2N inputs on the substrate, N being an integer, each of the 2N inputs including a respective one of 2N waveguides, each of which extending to an edge of the substrate, and each of the 2N waveguides carrying a respective one of 2N optical signals, each of the 2N optical signals including an in-phase component and a quadrature component;   N lasers provided on the substrate;   first N optical hybrid circuits, each of which receiving a respective one of first N optical signals of the 2N optical signals from a corresponding one of first N waveguides of the 2N waveguides and a first portion of light output from a respective one of the N lasers, each of the first N optical hybrid circuits providing a respective one of first N groups of mixing products; and   second N optical hybrid circuits, each of which receiving a respective one of second N optical signals from a corresponding one of second N waveguides and a second portion of the light output from a respective one of the N lasers, each of the second N optical hybrid circuits providing a respective one of second N groups of mixing products, the first N and second pluralities of optical hybrid circuits being provided on the substrate; and   at least one optical element that collimates, focuses, rotates a polarization of at least one of, or combines the first N optical signals and the second N optical signals, said at least one optical element being configured to be coupled to M optical fibers, where M is an integer greater than N.