Abstract:
A method of producing a modulated light source including the steps of providing a modulator, fiberlessly coupling a laser diode light source to the modulator and enclosing the modulator and the laser diode light source within a housing together with output optics operative to direct modulated light from the modulator into an optical fiber extending outwardly from the housing.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to light modulators generally.  
         BACKGROUND OF THE INVENTION  
         [0002]    Various types of light modulators are known. These include, for example, Mach-Zehnder type modulators and electroabsorption modulators. The following literature references describe various Mach-Zehnder type modulators:  
           [0003]    High-Speed Electrooptic Modulation in GaAs/GaAlAs Waveguide Devices, by Robert G. Walker, Journal of Lightwave Technology, Vol LT-5, No. 10, pp 1444-1453, October, 1987 and the references therein;  
           [0004]    Broadband Y-branch electro-optic GaAs waveguide interferometer for 1.3 micrometers, by P. Buchmann et al, Applied Physics Letters, Vol 46, No. 5, pp 462-464 (1985);  
           [0005]    Broad-Band Guided-Wave Electrooptic Modulators, by Richard A. Becker, The Journal of Quantum Electronics, Vol. QE20, No. 7, July, 1984, pp 723-727;  
           [0006]    The following product publications describe what is believed to be the state Mach-Zehnder optical modulators:  
           [0007]    LC1000 Series GaAs Optical Modulators for D.C. to 50 GHz, GEC-Marconi, Materials Technology, Caswell Towcester, Northamptonshire, U.K. 2.5 GHz,  8  &amp; 18 GHz Integrated Optical Amplitude Modulators, GEC Advanced Optical Products, West Hanningfield Road, Great Baddow, Chelmsford, Essex, U.K.  
           [0008]    The following reference shows an optical switch which employs a multimode interference coupler:  
           [0009]    Novel 1×N and N×N integrated optical switches using self-imaging multimode GaAs/AlGaAs waveguides by R. M. Jenkins et al., Applied Physics Letters, Vol 64 (6), 7 February, 1994, pp. 684-686.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention seeks to provide an improved and exceedingly cost effective optical coupler.  
           [0011]    There is thus provided in accordance with a preferred embodiment of the present invention a modulated light source module including a modulator disposed in a housing, a laser diode light source disposed in the housing and fiberlessly coupled to the modulator, and output optics operative to direct modulated light from the modulator into an optical fiber extending outwardly from the housing.  
           [0012]    Further in accordance with a preferred embodiment of the present invention the modulator includes an input multi-mode interference coupler; an output multi-mode interference coupler, and first and second waveguides interconnecting the input multimode interference coupler and the output multi-mode interference coupler, the first and second waveguides having associated therewith electrodes for the application of voltage thereacross, thereby to vary the phase of light passing therealong.  
           [0013]    Still further in accordance with a preferred embodiment of the present invention the modulator includes an input Y-junction splitter, an output Y-junction combiner, and first and second waveguides interconnecting the Y-junction splitter and the output Y-junction combiner, the first and second waveguides having associated therewith electrodes for the application of voltage thereacross, thereby to vary the phase of light passing therealong.  
           [0014]    Additionally in accordance with a preferred embodiment of the present invention the laser diode light source is monolithically integrated with the modulator.  
           [0015]    Preferably the laser diode light source is monolithically integrated with the modulator and occupy different regions of at least some of identical epitaxial layers.  
           [0016]    Additionally or alternatively in accordance with a preferred embodiment of the present invention the laser diode light source is a discrete element which is mechanically mounted in a desired position with respect to said modulator.  
           [0017]    Still further in accordance with a preferred embodiment of the present invention the laser diode light source is butted against an input to the modulator.  
           [0018]    Alternatively the laser diode light source is coupled to an input to the modulator via a discrete lens.  
           [0019]    Additionally in accordance with a preferred embodiment of the present invention the each of the laser diode light source and the modulator are mounted on parallel surface mountings, the parallel surface mountings include mutually facing surfaces which lie in parallel planes which are perpendicular to an optical axis of a light beam propagating from the laser diode light source towards the modulator via the lens.  
           [0020]    Preferably the laser diode light source and the modulator are aligned by relative movement thereof in the parallel planes and are fixed in desired alignment by fixing the mutually facing surfaces together.  
           [0021]    Further in accordance with a preferred embodiment of the present invention at least one of the laser diode light source and the modulator are mounted onto a support element by means of side mounting blocks which are fixed in position upon precise mutual alignment of the laser diode light source and the modulator.  
           [0022]    Preferably the modulator is implemented in gallium arsenide.  
           [0023]    There is also provided in accordance with a preferred embodiment of the present invention a method of producing a modulated light source including the steps of providing lator, fiberlessly coupling a laser diode light source to the modulator, and enclosing the modulator and the laser diode light source within a housing together with output optics operative to direct modulated light from the modulator into an optical fiber extending outwardly from the housing.  
           [0024]    Further in accordance with a preferred embodiment of the present invention the step of fiberlessly coupling a laser diode light source to the modulator includes the steps of using at least one external manipulator, manipulating at least one of the modulator and the laser diode light source relative to the other such that the output beam of the laser diode enters the modulator with relatively low light loss, and fixing the modulator and the laser diode light source in desired relative positions independently of the external manipulator, and disengaging the at least one external manipulator from the modulated light source.  
           [0025]    Still further in accordance with a preferred embodiment of the present invention the step of fixing the modulator and the laser diode light source in desired relative positions comprises fixedly attaching parallel surfaces attached to the modulator and to the laser diode light source to each other in desired relative orientations.  
           [0026]    Preferably the step of fixing the modulator and the laser diode light source in desired relative positions includes employing side mounting blocks to fix at least one of the laser diode light source and the modulator in position upon precise mutual alignment of the laser diode light source and the modulator.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:  
         [0028]    [0028]FIG. 1A is a simplified sectional illustration of a modulated light source module constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0029]    [0029]FIG. 1B is a simplified sectional illustration of a modulated light source module constructed and operative in accordance with another preferred embodiment of the present invention;  
         [0030]    [0030]FIGS. 2A and 2B are simplified, partially cut-away pictorial illustrations of alignment and fixing of a Mach-Zender type modulator and a laser diode light source arranged in a housing in the manner shown in FIG. 1A in accordance with one embodiment of the present invention; and  
         [0031]    [0031]FIGS. 3A and 3B are simplified, partially cut-away pictorial illustrations of alignment and fixing of a Mach-Zender type modulator and a laser diode light source arranged in a housing in the manner shown in FIG. 1B in accordance with one embodiment of the present invention;  
         [0032]    [0032]FIGS. 4A, 4B,  4 C,  4 D &amp;  4 E are simplified pictorial illustrations of various steps in the alignment and fixing of a Mach-Zender type modulator and a laser diode light source arranged in a housing in accordance with another embodiment of the present invention; and  
         [0033]    [0033]FIGS. 5A, 5B,  5 C,  5 D &amp;  5 E are simplified pictorial illustrations of various steps in the alignment and fixing of a Mach-Zender type modulator and a laser diode light source arranged in a housing in accordance with yet another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0034]    Reference is now made to FIG. 1A, which is a simplified sectional illustration of a modulated light source module constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0035]    The modulated light source of FIG. 1A preferably comprises a generally cylindrical housing  10 , typically having a rectangular cross section and preferably having mounting surfaces, such as end flanges  12  and  14  at respective opposite ends thereof. Housing  10  is typically formed of metal, but may be formed of any suitable material, such as a plastic material.  
         [0036]    A laser diode light source assembly  16  is mounted at one end of housing  10  and secured thereto at flange  12 . Typically the laser diode light source assembly  16  comprises a base element  18 , which is attached to flange  12 . A laser diode  20 , typically an 1310 nm or 1550 nm laser diode, is mounted on base element  18  and arranged to direct a beam of laser radiation along an optical axis  22 , which is preferably coaxial with the longitudinal axis of cylindrical housing  10 .  
         [0037]    The laser diode  20  typically receives electrical power and control inputs from an external driver (not shown). A lens  24  is preferably mounted on an internal mounting cylinder  26 , fixed to base element  18  and is located within housing  10  for receiving the beam of laser radiation from laser diode  20  and directing it onto an radiation input location  28  in a modulator assembly  30 .  
         [0038]    Alternatively the internal mounting cylinder  26  may also be fixed to the housing  10  instead of being fixed to the base element  18 .  
         [0039]    It is a particular feature of the present invention that the optical connection between the laser diode  20  and the modulator assembly  30  is a fiberless connection. This feature greatly simplifies manufacture of the modulated light source and provides much more efficient coupling between the laser diode  20  and the modulator assembly  30  than was possible in the prior art which employs fiber connections.  
         [0040]    The modulator assembly  30  is preferably a Mach-Zehnder type modulator, although any other suitable type of modulator can be employed. Modulator assembly  30  preferably comprises a substrate  32 , preferably Gallium Arsenide (GaAs), onto which is formed, preferably by conventional semiconductor fabrication techniques, an input waveguide  34  which leads to a splitter  36 .  
         [0041]    A pair of generally parallel waveguides  38  and  40  extend from splitter  36  to a combiner  42  which terminates in an output waveguide  44 . Radiation input location  28  is preferably at an end of input waveguide  34 .  
         [0042]    Output waveguide  44  preferably defines a radiation output location  48  which provides a modulated beam which can be coupled to an output fiber  50  by any suitable pigtailing technique. One such pigtailing technique employs the structure shown in FIG. 1A, namely a fiber mounting assembly  52  which includes a base element  54  onto which is mounted a fiber support  56 . Base element  54  is preferably mounted onto flange  14  and also includes a lens  58 , which is mounted via an internal mounting cylinder  60 , fixed to base element  54 . Lens  58  preferably directs light from radiation output location  48  onto an end of fiber  50  mounted on fiber support  56 .  
         [0043]    Alternatively the lens  58  does not have to be part of the fiber mounting assembly  52 , rather the internal mounting cylinder  60  may be fixed directly to the housing  10  instead of being fixed to the base element  54 .  
         [0044]    It is appreciated that alternatively input and output waveguides  34  and  44  may be obviated. In such a case, light is directed directly to and from the splitter  36  and the combiner  42  respectively.  
         [0045]    Modulator  30 , which is typically a Mach-Zehnder modulator as shown in FIG. 1A, preferably includes multiple signal inputs  62  which supply suitable electrical signals from an external signal source (not shown) to waveguides  38  and  40  for varying the relative phase of the radiation passing therethrough, thereby to modulate the output intensity by radiation interference in the combiner  42  in a known manner.  
         [0046]    Reference is now made to FIG. 1B, which is a simplified sectional illustration of a modulated light source module constructed and operative in accordance with another preferred embodiment of the present invention.  
         [0047]    The modulated light source of FIG. 1B preferably comprises a generally cylindrical housing  110 , typically having a rectangular cross section and preferably having mounting surfaces, such as end flanges  112  and  114  at respective opposite ends thereof. Housing  110  is typically formed of metal, but may be formed of any suitable material, such as a plastic material.  
         [0048]    A laser diode light source assembly  116  is mounted at one end of housing  110  and secured thereto at flange  112 . Typically the laser diode light source assembly  116  comprises a base element  118 , which is attached to flange  112 . A laser diode  120 , typically an 1310 nm or 1550 nm laser diode, is mounted on base element  118  and arranged to direct a beam of laser radiation directly to a radiation input location  128  of a modulator  130  which is butted against laser diode  120 .  
         [0049]    The laser diode  120  typically receives electrical power and control inputs from an external driver (not shown).  
         [0050]    As noted above, it is a particular feature of the present invention that the optical connection between the laser diode  120  and the modulator assembly  130  is a fiberless connection, such as in this example, a butted optical connection. This feature greatly simplifies manufacture of the modulated light source and provides much more efficient coupling between the laser diode  120  and the modulator assembly  130  than was possible in the prior art which employs fiber connections.  
         [0051]    The modulator assembly  130  is preferably a Mach-Zehnder type modulator, although any other suitable type of modulator can be employed. Modulator assembly  130  preferably comprises a substrate  132 , preferably Gallium Arsenide (GaAs), onto which is formed, preferably by conventional semiconductor fabrication techniques, an input waveguide  134  which leads to a splitter  136 .  
         [0052]    A pair of generally parallel waveguides  138  and  140  extend from splitter  136  to a combiner  142  which terminates in an output waveguide  144 . Radiation input location  128  is preferably at an end of input waveguide  134 .  
         [0053]    Output waveguide  144  preferably defines a radiation output location  148  which provides a modulated beam which can be coupled to an output fiber  150  by any suitable pigtailing technique. One such pigtailing technique employs the structure shown in FIG. 1B, namely a fiber mounting assembly  152  which includes a base element  154  onto which is mounted a fiber support  156 . Base element  154  is preferably mounted onto flange  114  and also includes a lens  158 , which is mounted via an internal mounting cylinder  160 , fixed to base element  154 . Lens  158  preferably directs light from radiation output location  148  onto an end of fiber  150  mounted on fiber support  156 .  
         [0054]    It is appreciated that alternatively input and output waveguides  134  and  144  may be obviated. In such a case, light is directed directly to and from the splitter  136  and the combiner  142  respectively.  
         [0055]    Modulator  130 , which is typically a Mach-Zehnder modulator as shown in FIG. 1B, preferably includes multiple signal inputs  162  which supply suitable electrical signals from an external signal source (not shown) to waveguides  138  and  140  for varying the relative phase of the radiation passing therethrough, thereby to modulate the output intensity by radiation interference in the combiner  142  in a known manner.  
         [0056]    Reference is now made to FIGS. 2A and 2B, which are simplified, partially cut-away pictorial illustrations of alignment and fixing of a Mach-Zender type modulator and a laser diode light source in a housing in accordance with one embodiment of the present invention. For the sake of clarity and conciseness, all of the structural elements of the modulated light source appearing in FIGS. 2A and 2B are identified by the corresponding reference numerals used to designate them in FIG. 1A.  
         [0057]    [0057]FIG. 2A shows that the laser diode light source assembly  16  has multiple degrees of freedom in positioning relative to flange  12 . The relative positioning show in FIG. 2A is seen to be less than optimal, in that the radiation output of laser diode  20  is being focussed by lens  24  onto a location  200  which is offset from the radiation input location  28  defined on input waveguide  34 . FIG. 2B illustrates that by suitable repositioning of base element  18  of assembly  16  relative to flange  12 , location  200  is caused to be at the radiation input location  28 , as desired and a desired rotational orientation of the laser diode is provided so that a desired orientation of the polarization of the beam is realized.  
         [0058]    When the relative positions of the laser diode light source assembly  16  and flange  12  are as shown in FIG. 2B, the base element  18  is preferably bonded onto flange  12 , preferably using a thin layer of UV curable adhesive  204  which does not involve significant shrinkage during curing, as by use of a UV light source  202 , so that the relative position shown in FIG. 2B is preserved. Alternatively, any other suitable fixing technique or technology may be employed, such as, for example, laser welding or soldering.  
         [0059]    Reference is now made to FIGS. 3A and 3B, which are simplified, partially cut-away pictorial illustrations of alignment and fixing of a Mach-Zender type modulator and a laser diode light source in a housing in accordance with another embodiment of the present invention. It is noted that the methodology of FIGS. 3A and 3B is generally identical to that of FIGS. 2A and 2B, notwithstanding that FIGS. 2A and 2B relate to the structure of FIG. 1A while FIGS. 3A and 3B relate to the structure of FIG. 1B.  
         [0060]    For the sake of clarity and conciseness, all of the structural elements of the modulated light source appearing in FIGS. 3A and 3B are identified by the corresponding reference numerals used to designate them in FIG. 1B.  
         [0061]    [0061]FIG. 3A shows that the laser diode light source assembly  116  has multiple degrees of freedom in positioning relative to flange  112 . The relative positioning show in FIG. 3A is seen to be less than optimal, in that the radiation output of laser diode  120  is located at a location  300  which is offset from the radiation input location  128  defined on input waveguide  134 . FIG. 3B illustrates that by suitable repositioning of base element  118  of assembly  116  relative to flange  112 , location  300  is caused to be at the radiation input location  128 , as desired and a desired rotational orientation of the laser diode is provided so that a desired orientation of the polarization of the laser diode radiation is realized.  
         [0062]    When the relative positions of the laser diode light source assembly  116  and flange  112  are as shown in FIG. 3B, the base element  118  is preferably bonded onto flange  112 , preferably using a thin layer of UV curable adhesive  304  which does not involve significant shrinkage during curing, as by use of a UV light source  302 , so that the relative position shown in FIG. 3B is preserved. Alternatively, any other suitable fixing technique or technology may be employed, such as, for example, laser welding or soldering.  
         [0063]    Reference is now made to FIGS. 4A, 4B,  4 C,  4 D &amp;  4 E, which are simplified illustrations of various steps in the alignment and fixing of a Mach-Zender type modulator and a laser diode light source in a housing in accordance with another embodiment of the present invention.  
         [0064]    In the embodiment of FIGS.  4 A- 4 E, there is shown a preferred technique for precise alignment and assembly of a modulated light source including a modulator assembly  430 , which preferably comprises a substrate  432 , preferably Gallium Arsenide (GaAs), onto which is formed, preferably by conventional semiconductor fabrication techniques, an input waveguide  434  which leads to a splitter  436 .  
         [0065]    As seen in FIG. 4A, a pair of generally parallel waveguides  438  and  440  extend from splitter  436  to a combiner  442  which terminates in an output waveguide  444 . Radiation input location  428  is preferably at an end of input waveguide  434 .  
         [0066]    Output waveguide  444  preferably defines a radiation output location  448  which provides a modulated beam which can be coupled to an output fiber (not shown) by any suitable pigtailing technique. One such pigtailing technique employs the structure shown in FIG. 1A, namely a fiber mounting assembly  52  which includes a base element  54  onto which is mounted a fiber support  56 . It is appreciated that, alternatively, input and output waveguides  434  and  444  may be obviated. In such a case, light is directed directly to and from the splitter  436  and the combiner  442  respectively.  
         [0067]    Modulator  430 , which is typically a Mach-Zehnder modulator as shown in FIG. 1A, preferably is provided with multiple signal inputs (not shown) supply suitable electrical signals from an external signal source (not shown) to waveguides  438  and  440  for varying the relative phase of the radiation passing therethrough, thereby to modulate the output intensity by radiation interference in the combiner  442  in a known manner.  
         [0068]    An input lens  450  is preferably precisely mounted onto a substrate  452 , typically formed of glass, ceramic or any other suitable material, and which also supports substrate  432 .  
         [0069]    As seen in FIG. 4A, a laser diode light source assembly  466 , typically comprises a base element  468 , which is supported during assembly as by a vacuum holder  470  for selectable positioning with multiple degrees of freedom relative to substrate  452 . A laser diode  472 , typically an 1310 nm or 1550 nm laser diode, is fixedly mounted to base element  468 .  
         [0070]    As seen in FIG. 4B, the laser diode light source assembly  466  is precisely positioned so as to direct a beam of laser radiation via lens  450  onto radiation input location  428  of modulator  430  and such that a desired rotational orientation of the laser diode is provided so that a desired orientation of the polarization of the beam is realized. The laser diode  472  typically receives electrical power and control inputs from an external driver (not shown).  
         [0071]    As noted above, it is a particular feature of the present invention that the optical connection between the laser diode  472  and the modulator assembly  430  is a fiberless connection. This feature greatly simplifies manufacture of the modulated light source and provides much more efficient coupling between the laser diode  472  and the modulator assembly  430  than was possible in the prior art which employs fiber connections.  
         [0072]    Once desired positioning of the laser diode light source assembly  466  has been achieved, side mounting blocks  480  and  482  are carefully positioned alongside base element  468  (FIG. 4C) and are bonded thereto and to substrate  452 , preferably using a thin layer of UV curable adhesive (not shown) which does not involve significant shrinkage during curing, as by use of a UV light source  402 , so that the relative position shown in FIG. 4C is preserved, as seen in FIG. 4D.  
         [0073]    The finished, suitably aligned modulated light source is shown in FIG. 4E.  
         [0074]    Reference is now made to FIGS. 5A, 5B,  5 C,  5 D &amp;  5 E, which are simplified illustrations of various steps in the alignment and fixing of a Mach-Zender type modulator and a laser diode light source in a housing in accordance with yet another embodiment of the present invention.  
         [0075]    In the embodiment of FIGS.  5 A- 5 E, there is shown a preferred technique for precise alignment and assembly of a modulated light source including a modulator assembly  530 , which preferably comprises a substrate  532 , preferably Gallium Arsenide (GaAs), onto which is formed, preferably by conventional semiconductor fabrication techniques, an input waveguide  534  which leads to a splitter  536 .  
         [0076]    As seen in FIG. 5A, a pair of generally parallel waveguides  538  and  540  extend from splitter  536  to a combiner  542  which terminates in an output waveguide  544 . Radiation input location  528  is preferably at an end of input waveguide  534 .  
         [0077]    Output waveguide  544  preferably defines a radiation output location  548  which provides a modulated beam which can be coupled to an output fiber (not shown) by any suitable pigtailing technique. One such pigtailing technique employs the structure shown in FIG. 1B, namely a fiber mounting assembly  152  which includes a base element- 154  onto which is mounted a fiber support  156 . It is appreciated that, alternatively, input and output waveguides  534  and  544  may be obviated. In such a case, light is directed directly to and from the splitter  536  and the combiner  542  respectively.  
         [0078]    Modulator  530 , which is typically a Mach-Zehnder modulator as shown in FIG. 1B, preferably is provided with multiple signal inputs (not shown) supply suitable electrical signals from an external signal source (not shown) to waveguides  538  and  540  for varying the relative phase of the radiation passing therethrough, thereby to modulate the output intensity by radiation interference in the combiner  542  in a known manner. A substrate  550 , typically formed of glass, ceramic or any other suitable material supports substrate  532 .  
         [0079]    As seen in FIG. 5A, a laser diode light source assembly  566 , typically comprises a base element  568 , which is supported during assembly as by a vacuum holder  570  for selectable positioning with multiple degrees of freedom relative to substrate  532 . A laser diode  572 , typically an 1310 nm or 1550 nm laser diode, is fixedly mounted to base element  568 .  
         [0080]    As seen in FIG. 5B, the laser diode light source assembly  566  is precisely positioned so as to direct a beam of laser radiation directly to a radiation input location  528  of modulator  530  which is butted against laser diode  570  and such that a desired rotational orientation of the laser diode is provided so that a desired orientation of the polarization of the laser diode radiation is realized. The laser diode  572  typically receives electrical power and control inputs from an external driver (not shown).  
         [0081]    As noted above, it is a particular feature of the present invention that the optical connection between the laser diode  572  and the modulator assembly  530  is a fiberless connection. This feature greatly simplifies manufacture of the modulated light source and provides much more efficient coupling between the laser diode  572  and the modulator assembly  530  than was possible in the prior art which employs fiber connections.  
         [0082]    Once desired positioning of the laser diode light source assembly  566  has been achieved, side mounting blocks  580  and  582  are carefully positioned alongside base element  568  and are bonded thereto and to substrate  552  (FIG. 5C), preferably using a thin layer of UV curable adhesive (not shown) which does not involve significant shrinkage during curing, as by use of a UV light source  502 , so that the relative position shown in FIG. 5B is preserved, as seen in FIG. 5D.  
         [0083]    The finished, suitably aligned modulated light source is shown in FIG. 5E.  
         [0084]    It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. The present invention also includes combinations and subcombinations of the various features described hereinabove as well as modifications and variations thereof as would occur to a person of ordinary skill in the art upon reading the foregoing description and which are not in the prior art.