Small packaged tunable laser transmitter

Abstract

A tunable laser transmitter configured in a small package subassembly coupled to a printed circuit board. The tunable laser transmitter includes a housing with a volume formed by exterior walls. An electrical input interface is positioned at the first end of the housing. A first and a second optical output interface is positioned at the second end of the housing, the first output being configured to transmit a modulated optical beam, and the second output configured to transmit a cw beam to the local oscillator of an external receiver.

1 . A small, packaged tunable optical transmitter comprising:
 a first housing;   an electrical input interface positioned at the first end of a first housing, the electrical input interface configured to receive an information-containing electrical signal;   an optical first output interface positioned at the second end of the first housing, the optical output interface configured to transmit a modulated optical communication beam;   a tunable semiconductor laser disposed within a rectangular second housing having a volume of less than 0.6 cubic centimeters, the second housing being disposed in the interior space of the first housing, the second housing having six planar exterior walls including a bottom, a top, opposing first and second ends, and opposing sidewalls, the exterior walls forming a hermetically sealed interior space and operable to emit a laser beam having a selectable wavelength; and   a semiconductor-based modulator positioned in the interior space of the first housing along an optical path of the laser beam, the semiconductor-based modulator configured to impart I and Q modulation respectively to the laser beam corresponding to the information-containing electrical signal received through the electrical input interface.   
     
     
         2 . The tunable optical transmitter of  claim 1 , wherein the modulator includes first and second discrete semiconductor-based modulators positioned in the interior space of the first housing is configured to impart X and Y polarization, respective to the laser beam corresponding to the information-containing electrical signal received through the electrical input interface, and each of the first and second modulators is configured to impart both I and Q modulation respectively to the laser beam corresponding to the information-containing electrical signal received through the electrical input interface. 
     
     
         3 . The tunable optical transmitter of  claim 1 , wherein the tunable semiconductor laser is an external cavity laser that includes a tunable filter that comprises a Vernier tuning mechanism including respective first and second optical filters having respective sets of transmission peaks having slightly different free spectral ranges and similar finesses, and wherein tuning is performed by shifting the set of transmission peaks of the second optical filter relative to the set of transmission peaks of the first optical filter to align a single transmission peak of each of the first and second sets of transmission peaks. 
     
     
         4 . The tunable optical transmitter of  claim 1 , further comprising a base in the interior of the second housing; a structure operatively coupled to the base, having a front facet and a substantially non-reflective rear facet optically coupled via a waveguide passing there through, the structure further including a gain section to emit a plurality of photons in response to a first electrical input, and having a facet defining the rear facet of the structure. 
     
     
         5 . The tunable optical transmitter of  claim 1 , further comprising a ferrule having an entry aperture disposed adjacent to the coupling optics, wherein the entry aperture has a planar face which is inclined at an angle of from five to seven degrees from a plane which is normal to the incoming central beam from the coupling optics so as to prevent reflections of the incoming beam from the surface of the planar entry end face from going back into the coupling optics. 
     
     
         6 . The tunable optical transmitter of  claim 3 , further including a cavity length actuator positioned in the interior space of the second housing along an optical path of the beam downstream from the first optical filter and along the optical path of the beam emitted from the first optical filter and functioning to adjust and lock an optical pathlength of the external cavity tunable laser. 
     
     
         7 . The tunable optical transmitter of  claim 6 , wherein the cavity length actuator is a block of silicon having a planar surface tilted with respect to the optical axis to prevent the incoming light from the laser from reflecting back into the cavity of the laser. 
     
     
         8 . The tunable optical transmitter of  claim 3 , further comprising a cavity length actuator disposed in the second housing between the first and second optical filters of the Vernier tuning mechanism, and further including an anti-reflection coating on its planar surface. 
     
     
         9 . The tunable optical transmitter of  claim 4 , further including a thermoelectric cooler positioned within the interior space of the second housing between the bottom of the second housing and at least one of the tunable semiconductor laser and the coupling optics. 
     
     
         10 . The tunable optical transmitter of  claim 1 , wherein the electrical input interface includes a row of pins extending from the housing to enable an electrical connector to be coupled thereto. 
     
     
         11 . The transmitter of  claim 3 , further including a cavity length actuator positioned in the interior space along an optical path of the beam from the first optical filter to adjust and lock an optical path length of the external cavity tunable laser. 
     
     
         12 . The transmitter of  claim 11 , wherein the cavity length actuator is a block of silicon having a planar surface tilted with respect to the optical axis to prevent the incoming light from the laser from reflecting back into the cavity of the laser. 
     
     
         13 . The transmitter of  claim 3 , further comprising a cavity length actuator disposed between the first and second optical filters of the Vernier tuning mechanism along an optical path of the beam from the first optical filter, and further including an anti-reflection coating on its planar surface. 
     
     
         14 . The transmitter of  claim 3 , wherein the external cavity laser further includes a cavity length actuator to adjust an optical pathlength of the external cavity tunable laser. 
     
     
         15 . The transmitter of  claim 2 , wherein the output of the tunable laser is coupled to the first and second modulators by free space. 
     
     
         16 . The transmitter of  claim 1 , wherein the coupling optics are positioned in the interior space along the optical path between the external cavity laser and the focusing lens assembly, the coupling optics including a pair of coupling lenses and an isolator. 
     
     
         17 . The transmitter of  claim 2 , wherein the first and second semiconductor-based modulators are disposed in elongated housings that are positioned in the interior space substantially orthogonal to the outgoing optical path of the laser beam from the tunable laser, and further comprising first and second optical reflectors in the optical path of the laser beam from the tunable laser to direct the laser beam to the optical input interface of the first and second semiconductor-based modulators respectively. 
     
     
         18 . The transmitter of  claim 2 , wherein the first and second semiconductor-based modulators are positioned parallel to one another in the interior space, with the one of the modulators being positioned offset from the other modulator, and further comprising a one piece third optical reflector being disposed at the output ends of the first and second semiconductor-based modulators so that the modulated output beams from the first and second semiconductor-based modulators are combined to produce a composite output beam. 
     
     
         19 . The transmitter of  claim 1 , further comprising an optical second output interface positioned at the second end of the first housing, and further comprising fourth and fifth optical reflectors in the optical path of the laser beam from the tunable laser to direct the laser beam to the optical second output interface. 
     
     
         20 . The transmitter of  claim 1 , wherein the first housing conforms to either the CFP, CFP2 or CFP4 Multi-Source Agreement.