Coherent light generators – Particular beam control device – Nonlinear device
Reexamination Certificate
2001-02-27
2004-08-10
Wong, Don (Department: 2828)
Coherent light generators
Particular beam control device
Nonlinear device
C372S023000
Reexamination Certificate
active
06775307
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light wavelength conversion module. More precisely, the present invention relates to a light wavelength conversion module which includes a semiconductor laser having an external resonator provided with a wavelength selecting element, and a light wavelength conversion element for converting a laser beam emitted from the semiconductor laser to a second harmonic wave or the like.
2. Description of the Related Art
Conventionally, various types of light wavelength conversion devices which convert a laser beam emitted from a semiconductor laser to a second harmonic wave or the like have been proposed, and have been used as a blue laser light source and/or a green laser light source. For example, a light wavelength conversion module is disclosed in Japanese Patent Laid-Open (JP-A) No. 10-254001. The light wavelength conversion module illustrated in
FIG. 9
in this publication (JP-A No. 10-254001) includes a semiconductor laser which is provided with an external resonator and a wavelength selecting element such as a narrow band-pass filter or the like provided in the external resonator, and a light wavelength conversion element which is composed of a waveguide type second harmonic generation (SHG) element having a periodic domain reversing structure, wherein the semiconductor laser and the light wavelength conversion element are optically coupled directly with each other. In the light wavelength conversion module, a wavelength can be locked to a central transmitted wavelength of the narrow band-pass filter provided in the external resonator, and an oscillation wavelength of the semiconductor laser can be locked to a certain wavelength corresponding to a rotation angle of the narrow band-pass filter by rotating the filter.
A general semiconductor laser can oscillate a laser beam even without an external resonator since it has a resonator structure provided in an element thereof. However, the oscillation wavelength of the semiconductor laser prior to the locking of the wavelength fluctuates within a range of a few nanometers, and shifts toward the longer wavelength side as the driving current increases. For example, in a case in which the electric current is changed from 50 to 200 mA when a semiconductor laser having several longitudinal modes at intervals of about 0.2 nm is used, the central oscillation wavelength shifts about 5 nm toward the longer wavelength side due to heat generation of the semiconductor laser itself, as shown in
FIG. 9
of the present application.
Therefore, when a semiconductor laser is optically coupled with an SHG element without locking the wavelength, the oscillation wavelength of the semiconductor laser does not coincide with a wavelength at which the wavelength conversion efficiency of the SHG element is maximized, i.e., does not coincide with a wavelength which phase-matches with the SHG element. The output light amount of the second harmonic wave fluctuates, resulting in almost no output of second harmonic waves. In order to solve this problem, in the light wavelength conversion module disclosed in JP-A No. 10-254001, an external resonator is provided, and an oscillation wavelength of the semiconductor laser is locked to a wavelength which phase-matches with the SHG element to thereby stabilize the outputted light amount of the second harmonic wave light.
However, even if the above-described locking of the wavelength is carried out, there still exists the following problem. The output light amount of the semiconductor laser itself increases linearly as the driving current of the semiconductor laser increases as shown in
FIG. 10A
when a threshold current (I
op
) is exceeded. In contrast, the output light amount of the SHG element does not increase monotonically as the driving current of the semiconductor laser increases, but increases while repeatedly increasing and decreasing as shown in
FIG. 10B
, when the same semiconductor laser and SHG element are optically coupled to generate a second harmonic wave. That is, the IL characteristic (current vs. output characteristic) which expresses the relationship between the driving current of the semiconductor laser and the output light amount of the SHG element repeatedly increases and decreases.
When such increasing and decreasing of the output light amount occurs, there is a problem in that automatic power control (APC) for stabilizing the output light amount of the SHG element cannot be carried out properly when used. Moreover, there is another problem in that it is difficult to control the output light amount to a desirable amount when the output light of the SHG element is modulated by increasing and decreasing the driving current, since the output light amount of the SHG element does not increase monotonically as the driving current of the semiconductor laser increases.
SUMMARY OF THE INVENTION
The present invention is provided so as to solve the aforementioned problems, and an object of the present invention is to provide a light wavelength conversion module in which the output light amount of a light wavelength conversion element increases monotonically as the driving current of a semiconductor laser increases.
In order to solve the aforementioned problems, a first aspect of the present invention is a light wavelength conversion module including: (a) a light wavelength conversion element having a wavelength band, which when the light wavelength conversion element receives light within the wavelength band, emits light having a different wavelength; and (b) a semiconductor laser having an external resonator provided with a wavelength selecting element, the semiconductor laser being disposed for communicating light to the light wavelength conversion element and operable for producing light of a fundamental wavelength including a plurality of longitudinal mode spectra within the wavelength band of the light wavelength conversion element.
A second aspect of the present invention is a light wavelength conversion module including: (a) a light wavelength conversion element having a wavelength band, which when the light wavelength conversion element receives light within the wavelength band, emits light having a different wavelength; and (b) a semiconductor laser having opposite emitting end surfaces and an external resonator, the semiconductor laser being operable for producing light of a fundamental wavelength including a plurality of longitudinal mode spectra within the wavelength band of the light wavelength conversion element, which is disposed for receiving light from one emitting end surface of the semiconductor laser, and the external resonator being disposed for receiving light from the other emitting end surface, the external resonator including a wavelength selecting element and a reflecting member disposed on an optical path for receiving the light, with the reflecting member disposed on the optical path opposite the wavelength selecting element from the semiconductor laser.
A third aspect of the present invention is a light wavelength conversion module according to either of the first and second aspects, wherein the wavelength band has a length &Dgr;&lgr;, and a wavelength interval of the longitudinal mode spectra of the semiconductor laser is &Dgr;&lgr;
m
, and the number of the longitudinal mode spectra is N
max
, which is an integer part of the quotient of &Dgr;&lgr;/&Dgr;&lgr;
m
or less.
A fourth aspect of the present invention is a light wavelength conversion module according to either of the first and second aspects, wherein the light wavelength conversion element and the semiconductor laser are optically coupled directly to each other.
A fifth aspect of the present invention is a light wavelength conversion module according to either of the first and second aspects, wherein the light wavelength conversion element is a quasi-phase matching type light wavelength conversion element which performs wavelength conversion by quasi-phase matching.
A sixth aspect of the present invention is a light wavelength
Fuji Photo Film Co. , Ltd.
Nguyen Tuan N.
Stroock & Stroock & Lavan LLP
Wong Don
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