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;   N lasers provided on the substrate;   2N modulators provided on the substrate, each of first N modulators of the 2N modulators respectively modulating a first portion of light generated by a respective one of the N lasers, each of second N modulators of the 2N modulators respectively modulating a second portion of light generated by a respective one the N lasers;   first N waveguides, each of which being optically coupled to a respective one of the first N modulators, each of the first N waveguides extending to an edge of the substrate and supplying a corresponding one of first N modulated optical signals;   second N waveguides, each of which being optically coupled to a respective one of the second N modulators, each of the second N waveguides extending to an edge of the substrate and supplying a corresponding one of second N modulated optical signals, each of the first N modulated optical signals and each of the second N modulated optical signals including an in-phase component and a quadrature component, the first and second waveguides 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 modulated optical signals and the second N modulated 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 the first N modulated optical signals and a respective one of the second N modulated optical signals, each of the first N modulated optical signals having a polarization that is rotated relative to a corresponding one of the first N modulated optical signals.   
     
     
         2 . An optical device in accordance with  claim 1 , wherein each of the first N modulators includes a nested modulator, the nested modulator including a first Mach-Zehnder modulator and a second Mach-Zehnder modulator, the first Mach-Zehnder modulator supplying the in-phase component of each of the first N modulated optical signals and the second Mach-Zehnder modulator supplying the quadrature component of each of the first N modulated optical signals. 
     
     
         3 . An optical device in accordance with  claim 3 , wherein each said first Mach-Zehnder modulator and each said second Mach-Zehnder modulator includes first and second arms, the optical device further including:
 a phase adjuster provided in at least one of the first and second arms of each said first Mach-Zehnder modulator and each said second Mach-Zehnder modulator.   
     
     
         4 . An optical device in accordance with  claim 3 , the optical device further including:
 an amplitude adjuster provided in at least one of the first and second arms of each said first Mach-Zehnder modulator and each said second Mach-Zehnder modulator.   
     
     
         5 . An optical device in accordance with  claim 3 , the optical device further including:
 an electrode coupled to at least one of the first and second arms of each said first Mach-Zehnder modulator and each said second Mach-Zehnder modulator, the electrode being configured to receive radio frequency (RF) signals.   
     
     
         6 . An optical device in accordance with  claim 1 , wherein each of the first N waveguides is coupled to a corresponding one of first N amplifiers and each of the second N waveguides is coupled to second N optical amplifiers. 
     
     
         7 . An optical device in accordance with  claim 6 , wherein each of the first N optical amplifiers and each of the second N optical amplifiers is an erbium doped fiber amplifier. 
     
     
         8 . An optical device in accordance with  claim 6 , wherein each of the first N optical amplifiers and each of the second optical N amplifiers is provided on the substrate. 
     
     
         9 . An optical device in accordance with  claim 8 , wherein each of the first N optical amplifiers and each of the second N optical amplifiers is a semiconductor optical amplifier. 
     
     
         10 . 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.   
     
     
         11 . 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 modulated optical signals; and   second N lenses, each of which receiving a corresponding one of the second N modulated optical signals.   
     
     
         12 . An optical device in accordance with  claim 11 , wherein each of the first N lenses collimates a corresponding one of the first N modulated optical signals, and each of the second N lenses collimates a corresponding one of the second N modulated optical signals. 
     
     
         13 . An optical device in accordance with  claim 1 , further including:
 N lenses that focus said respective one of the first N modulated optical signals and said respective one of the second N modulated optical signals onto a corresponding one of the N fibers.   
     
     
         14 . An optical device in accordance with  claim 11 , wherein each of the first N lenses and each of the second N lenses are provided in an array. 
     
     
         15 . 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 first N modulated optical signals and providing said corresponding one the polarization-rotated first N modulated optical signals. 
     
     
         16 . An optical device in accordance with  claim 15 , wherein the at least one optical element further includes N polarization combiners, each of which receiving a respective one of the polarization rotated first N modulated optical signals and a respective one of the second N modulated optical signals. 
     
     
         17 . An optical device in accordance with  claim 16 , wherein the N polarization rotators are arranged in a first array and the N polarization combiners are arranged in a second array. 
     
     
         18 . An optical device in accordance with  claim 16 , 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 combiners being provided on the second substrate.   
     
     
         19 . An optical device in accordance with  claim 1 , wherein the at least one optical element is configured to provide a respective one of the first N modulated optical signals and a respective one of the second N modulated optical signals to a corresponding one of N optical fibers, wherein each of the first N modulated optical signals are polarization rotated relative to each of the second N modulated optical signals. 
     
     
         20 . 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. 
     
     
         21 . 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 modulated optical signals; and   second N optical isolators, each of which receiving a corresponding one of the second N modulated optical signals.   
     
     
         22 . An optical device in accordance with  claim 1 , further including a bulk optical isolator that receives the first N modulated optical signals and the second N modulated optical signals. 
     
     
         23 . An optical device in accordance with  claim 1 , wherein the at least one optical element includes first N lenses and second N lenses, each of the first N lenses being configured to collimate a corresponding one of the first N modulated optical signals and each of the second N lenses being configured to focus said collimated corresponding one of the first N modulated optical signals. 
     
     
         24 . An optical device in accordance with  claim 1 , wherein the at least one optical element includes first N lenses and second N lenses, each of the first N lenses receiving a corresponding one of the first N modulated optical signals and each of the second N lenses receiving a corresponding one of the second N modulated optical signals,
 the first N lenses and the second N lenses being provided in an array that extends parallel to a facet of the substrate, each of the first N lenses and each of the second N lenses being aligned such that each of the first N lenses collimating a respective one of the first N modulated optical signals and each of the second N lenses collimating a respective one of the second N modulated optical signals   
     
     
         25 . 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. 
     
     
         26 . An optical device in accordance with  claim 1 , wherein the at least one optical elements is provided in a planar lightwave circuit (PLC). 
     
     
         27 . 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 modulated 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 modulated optical signals.   
     
     
         28 . An optical device in accordance with  claim 25 , wherein the at least one optical element constitutes a plurality of silicon photonics devices. 
     
     
         29 . An optical device in accordance with  claim 25 , wherein the second substrate is attached to the first substrate. 
     
     
         30 . 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. 
     
     
         31 . An optical device in accordance with  claim 1 , wherein each of the first N modulated optical signals has a corresponding one of N wavelengths and each of the second N modulated optical signals has a respective one of the N wavelengths, the optical device further including:
 first N optical filters, each of the first N optical filters receiving a corresponding one of the first N modulated optical signals and having a passband that includes a respective one of the N wavelengths; and   a second plurality of optical filters, each of the second plurality of optical filters receiving a corresponding one of the second N modulated optical signals and having the passband that includes a corresponding one of the N wavelengths.   
     
     
         32 . An optical device in accordance with  claim 1 , wherein the at least one optical element includes N polarization rotators and N polarization combiners, each of the N polarization rotators receiving a corresponding one of the first N modulated optical signals and providing a corresponding one of the polarization rotated first N modulated optical signals, and
 each of the N polarization combiners provides a corresponding one of N polarization multiplexed outputs, each of which including a respective one of the polarization rotated first N modulated optical signals and a respective one of the second N modulated optical signals, and   each of the first N modulated optical signals has a corresponding one of N wavelengths and each of the second N modulated optical signals has a respective one of the N wavelengths, the optical device further including:   N tunable optical filters, each of which receiving a corresponding one of the polarization multiplexed outputs, each of the N optical filters has a passband that includes a respective one of the N wavelengths.   
     
     
         33 . An optical device in accordance with  claim 1 , wherein each of the first N modulated optical signals has a corresponding one of N wavelengths and each of the second N modulated optical signals has a respective one of the N wavelengths, the optical device further including:
 N tunable optical filters, each of which being coupled to a corresponding one of the N optical fibers, each of the N optical filters has a passband that includes a respective one of the N wavelengths.   
     
     
         34 . 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 that receives the N polarization multiplexed outputs. 
     
     
         35 . An optical device in accordance with  claim 32 , further including:
 a coupler optically coupled to receive an output of at least one of the N tunable optical filters; and   a pump laser that supplies pump light to the coupler, the pump light having a wavelength corresponding to a pump wavelength of a doped fiber amplifier optically coupled to one of the N optical fibers.   
     
     
         36 . 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 to 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. 
     
     
         37 . An optical device in accordance with  claim 1 , further including:
 a plurality of splitters, each of which being configured to be coupled to a respective one of the first N waveguides, each of the plurality of splitters supplying a power split portion of each of the first N optical signals, each of the plurality of splitters being provided on the first substrate; and   a plurality of variable optical attenuators provided on the first substrate, each of the plurality of variable optical attenuators being configured to selectively supply the power split portion of said each of the first plurality of optical signals to an optical receiver.   
     
     
         38 . 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.   
     
     
         39 . An optical device in accordance with  claim 4 , wherein the amplitude adjuster includes a variable optical attenuator. 
     
     
         40 . An optical device in accordance with  claim 1 , 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. 
     
     
         41 . An optical device in accordance with  claim 1 , wherein the N fibers are provided in an array. 
     
     
         42 . An optical device, comprising:
 a substrate;   N lasers provided on the substrate;   2N modulators provided on the substrate, each of first N modulators of the 2N modulators respectively modulating a first portion of light generated by a respective one of the N lasers, each of second N modulators of the 2N modulators respectively modulating a second portion of light generated by a respective one the N lasers;   first N waveguides, each of which being optically coupled to a respective one of the first N modulators, each of the first N waveguides extending to an edge of the substrate and supplying a corresponding one of first N modulated optical signals;   second N waveguides, each of which being optically coupled to a respective one of the second N modulators, each of the second N waveguides extending to an edge of the substrate and supplying a corresponding one of second N modulated optical signals, each of the first N modulated optical signals and each of the second N modulated optical signals including an in-phase component and a quadrature component, the first and second waveguides 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 modulated optical signals and the second N modulated optical signals, said at least one optical element being configured to be coupled to M optical fibers, where M is an integer less than M.   
     
     
         43 . An optical device, comprising:
 a substrate;   N lasers provided on the substrate;   2N modulators provided on the substrate, each of first N modulators of the 2N modulators respectively modulating a first portion of light generated by a respective one of the N lasers, each of second N modulators of the 2N modulators respectively modulating a second portion of light generated by a respective one the N lasers;   first N waveguides, each of which being optically coupled to a respective one of the first N modulators, each of the first N waveguides extending to an edge of the substrate and supplying a corresponding one of first N modulated optical signals;   second N waveguides, each of which being optically coupled to a respective one of the second N modulators, each of the second N waveguides extending to an edge of the substrate and supplying a corresponding one of second N modulated optical signals, each of the first N modulated optical signals and each of the second N modulated optical signals including an in-phase component and a quadrature component, the first and second waveguides 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 modulated optical signals and the second N modulated optical signals, said at least one optical element being configured to be coupled to M optical fibers, where M is an integer greater than M.   
     
     
         44 . An optical device in accordance with  claim 1 , wherein the at least one optical element includes N optical rotators and N optical combiners. 
     
     
         45 . An optical device in accordance with  claim 16 , wherein each of the N polarization rotators and a corresponding one of the N polarization combiners are provided in a respective one of N groupings, the N groupings be provided in an array. 
     
     
         46 . An optical device in accordance with  claim 11 , 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. 
     
     
         47 . An optical device in accordance with  claim 11 , wherein the first N lenses and the second N lenses constitute a plurality of lenses that are provided as an integral unit. 
     
     
         48 . An optical device in accordance with  claim 11 , wherein the first N lenses and the second N lenses constitute a plurality of lenses that constitute a complex lens. 
     
     
         49 . An optical device in accordance with  claim 24 , wherein an end portion of each of the first N waveguides extends perpendicular to a facet of the substrate and an end portion of each of the second N waveguides extends perpendicular to a facet of the substrate. 
     
     
         50 . An optical device in accordance with  claim 24 , wherein an end portion of each of the first N waveguides is tilted at a first non-perpendicular angle relative to a facet of the substrate and an end portion of each of the second N waveguides is tilted at a second non-perpendicular to a facet of the substrate, the first and second non-perpendicular angles being the same or different from one another.