Channel-switched tunable laser for DWDM communications
First Claim
1. A thermally tuned laser source with an athermal resonator comprising:
- a laser gain medium, an intracavity waveguide segment optically coupled to said gain medium, and thermo-optic feedback means for defining a resonant laser cavity including said gain medium and intracavity waveguide segment, said thermo-optic feedback means including heating means for tuning a frequency of operation of said laser cavity, wherein said gain medium is characterized by a positive refractive index change with increase in temperature and said intracavity waveguide segment is characterized by a negative refractive index change with increases in temperature, said gain medium and intracavity waveguide segments having optical path lengths chosen such that a round trip optical path in said cavity has a substantially net zero optical length change with increase of temperature profile of said optical path.
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Abstract
Laser source including materials with negative index of refraction dependence on temperature and with temperature independent coincidence between cavity modes and a set of specified frequencies such as DWDM channels in telecommunications applications. The free spectral range may be adjusted to equal a rational fraction of the specified frequency interval. The operating frequency may be defined by a frequency selective feedback element that is thermo-optically tuned by the application of heat from an actuator without substantially tuning the cavity modes. The operating frequency may be induced to hop digitally between the specified frequencies. In a particular embodiment, semiconductor amplifier and polymer waveguide segments form a linear resonator with a thermo-optically tuned grating reflector. In a further embodiment, an amplifier and two waveguides from a tunable grating assisted coupler form a ring resonator. Tuning may also be accomplished by means of applying an electric field across a liquid crystal portion of the waveguide structure within the grating.
138 Citations
63 Claims
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1. A thermally tuned laser source with an athermal resonator comprising:
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a laser gain medium, an intracavity waveguide segment optically coupled to said gain medium, and thermo-optic feedback means for defining a resonant laser cavity including said gain medium and intracavity waveguide segment, said thermo-optic feedback means including heating means for tuning a frequency of operation of said laser cavity, wherein said gain medium is characterized by a positive refractive index change with increase in temperature and said intracavity waveguide segment is characterized by a negative refractive index change with increases in temperature, said gain medium and intracavity waveguide segments having optical path lengths chosen such that a round trip optical path in said cavity has a substantially net zero optical length change with increase of temperature profile of said optical path. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A tunable laser source comprising:
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a laser gain medium, an intracavity waveguide segment optically coupled to said gain medium, and electro-optic feedback means for defining a resonant laser cavity including said gain medium and intracavity waveguide segment, said electro-optic feedback means including electrode means for tuning a frequency of operation of said laser cavity, wherein said gain medium is characterized by a positive refractive index change with increase in temperature and said intracavity waveguide segment is characterized by a negative refractive index change with increases in temperature, said gain medium and intracavity waveguide segments having optical path lengths chosen such that a round trip optical path in said resonant cavity has an optical length that is substantially independent of ambient temperature over a specified ambient temperature range. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
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33. An athermal laser source comprising:
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a laser gain medium, an intracavity waveguide segment optically coupled to said gain medium, and frequency selective feedback means having a feedback bandwidth and defining a resonant laser cavity including said gain medium and intracavity waveguide segment, said feedback bandwidth being sufficiently narrow compared to the free spectral range of said cavity so that only one of the longitudinal modes of said cavity is substantially excited by said gain medium, wherein said gain medium is characterized by a positive refractive index change with increase in temperature and said intracavity waveguide segment is characterized by a negative refractive index change with increases in temperature, said gain medium and intracavity waveguide segments having optical path lengths chosen such that a round trip optical path in said resonant cavity has an optical length that is substantially independent of ambient temperature over a specified ambient temperature range. - View Dependent Claims (34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49)
a heating means disposed in said frequency selective feedback means, for tuning a frequency of operation of said laser cavity wherein said grating structure is formed on a second waveguide segment coupled to said optical path in said cavity, said second waveguide segment having a temperature dependent refractive index, and wherein said heating means changes the temperature in said second waveguide segment. -
40. The source of claim 39 wherein said second waveguide segment comprises a polymer structure, said polymer structure having said temperature dependent refractive index.
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41. The source of claim 33 wherein said resonant laser cavity is a bidirectional resonator.
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42. The source of claim 41 wherein said bidirectional resonator contains a grating assisted coupler.
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43. The source of claim 33 wherein said optical path in said cavity has a length that defines a free spectral range of said resonant cavity that is a rational fraction of a specified communication frequency channel spacing within an optical frequency band corresponding to said gain medium.
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44. The source of claim 33 wherein said optical path in said cavity has a length that defines longitudinal modes of said resonant cavity and said tuning comprises switching said frequency of operation between said longitudinal modes.
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45. The source of claim 33 wherein said resonant laser cavity is a ring resonator.
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46. The source of claim 33 wherein in another portion of its structure said intracavity waveguide segment is characterized by a positive refractive index change with increase in temperature.
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47. The source of claim 33 wherein said frequency selective feedback means is substantially independent of temperature.
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48. The source of claim 47 wherein said frequency selective feedback means comprises an electro-optical feedback element, and an electrode actuator for applying an electric field in said feedback element to produce a change in refractive index of said feedback element for tuning said feedback bandwidth.
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49. The source of claim 33 wherein said frequency selective feedback means comprises a thermo-optical feedback element, and a thermal actuator for heating said feedback element to produce a change in refractive index of said feedback element for tuning said feedback bandwidth.
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50. A ring laser apparatus comprising:
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a laser gain medium, first and second waveguide segments optically coupled to said laser gain medium; and
a frequency selective means for coupling optical energy between said first and second waveguide segments and also coupling a portion of said optical energy out of at least one of said waveguide segments to form an optical output, wherein said laser gain medium and said optically coupled first and second waveguide segments form a ring resonator having a round trip optical path characterized by a round trip optical length, at least one of said waveguide segments characterized by a negative refractive index change with increases in temperature and having a length chosen such that the round trip optical length is athermal. - View Dependent Claims (51, 52, 53, 54, 55, 56, 57, 58, 59)
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60. An athermal ring laser source comprising:
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a laser gain medium, an first intracavity waveguide segment optically coupled to said gain medium, an second intracavity waveguide segment optically coupled to said gain medium, and frequency selective feedback means disposed to couple optical energy between said first and second waveguide segments having a feedback bandwidth and defining a resonant ring cavity including said gain medium and said first and second intracavity waveguide segments, wherein said gain medium is characterized by a positive refractive index change with increase in temperature and said first intracavity waveguide segment is characterized by a negative refractive index change with increases in temperature, said gain medium and first intracavity waveguide segments having optical path lengths chosen such that a round trip optical path in said resonant ring cavity has an optical length that is substantially independent of ambient temperature over a specified ambient temperature range. - View Dependent Claims (61, 62, 63)
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Specification