U.S. patent application number 11/466000 was filed with the patent office on 2008-02-21 for optical frequency mixer and method for the same.
This patent application is currently assigned to HC PHOTONICS CORP.. Invention is credited to Ming-Hsien Chou, Borwen Yu.
Application Number | 20080043320 11/466000 |
Document ID | / |
Family ID | 39031487 |
Filed Date | 2008-02-21 |
United States Patent
Application |
20080043320 |
Kind Code |
A1 |
Yu; Borwen ; et al. |
February 21, 2008 |
OPTICAL FREQUENCY MIXER AND METHOD FOR THE SAME
Abstract
An optical frequency mixer according to one embodiment of the
present invention comprises a V-shaped resonant cavity including a
first reflective surface, a second reflective surface and an output
coupler, a pumping unit configured to emit a pumping wave to the
laser gain medium to generate a resonating wave in the resonant
cavity, a nonlinear crystal positioned on an optical path of the
resonating wave in the resonant cavity, and an input interface
configured to emit a mixing wave into the resonant cavity.
Preferably, the output coupler can be a plano-concave lens having a
concave surface configured to reflect the resonating wave and to
focus the resonating wave such that the spot size of the resonating
wave is matched the spot size of the pumping wave. Particularly,
the nonlinear crystal is positioned between the output coupler and
the input interface.
Inventors: |
Yu; Borwen; (Hsinchu,
TW) ; Chou; Ming-Hsien; (Hsinchu, TW) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
1875 EYE STREET, N.W., SUITE 1100
WASHINGTON
DC
20036
US
|
Assignee: |
HC PHOTONICS CORP.
Hsinchu
TW
|
Family ID: |
39031487 |
Appl. No.: |
11/466000 |
Filed: |
August 21, 2006 |
Current U.S.
Class: |
359/330 |
Current CPC
Class: |
G02F 1/3775 20130101;
G02F 1/3548 20210101; G02F 1/3534 20130101; G02F 1/3542
20210101 |
Class at
Publication: |
359/330 |
International
Class: |
G02F 1/35 20060101
G02F001/35 |
Claims
1. An optical frequency mixer, comprising: a resonant cavity
including a first reflective surface, a second reflective surface
and an output coupler; a pumping unit configured to emit a pumping
wave to the laser gain medium to generate a resonating wave in the
resonant cavity; a nonlinear crystal positioned on an optical path
of the resonating wave in the resonant cavity, wherein the
nonlinear crystal includes a plurality of domains having
alternating polarity and the widths of the domains are the same
along a propagation of the resonating wave; and an input interface
configured to emit a mixing wave into the resonant cavity.
2. The optical frequency mixer of claim 1, wherein the resonant
cavity is configured in a V-shaped manner.
3. The optical frequency mixer of claim 1, wherein the pumping unit
includes a laser diode capable of generating the pumping wave and a
pump-coupling lens configured to couple the pumping wave to the
laser gain medium.
4. The optical frequency mixer of claim 1, wherein the output
coupler is a plano-concave lens having a concave surface configured
to reflect the resonating wave.
5. The optical frequency mixer of claim 1, wherein the output
coupler is a dichroic mirror.
6. The optical frequency mixer of claim 1, wherein the spot size of
the resonating wave is matched with the spot size of the pumping
wave.
7-9. (canceled)
10. The optical frequency mixer of claim 1, wherein the
longitudinal widths of the domains along a propagation direction of
the resonating wave varies along a direction perpendicular to the
propagation direction.
11. The optical frequency mixer of claim 1, wherein the nonlinear
crystal includes: a first poling portion having a plurality of
first domains having alternating polarity; and a second poling
portion having a plurality of second domains having alternating
polarity, wherein the widths of the first domains is different from
the widths of the second domains along a propagation direction of
the resonating wave.
12. The optical frequency mixer of claim 11, wherein the first
poling portion is positioned in parallel to the second poling
portion with respect to a propagation direction of the resonating
wave.
13. The optical frequency mixer of claim 11, wherein the first
poling portion is positioned in cascade to the second poling
portion along a propagation direction of the resonating wave.
14. The optical frequency mixer of claim 1, wherein the second
reflective surface is positioned on a mirror positioned between the
nonlinear crystal and the input interface.
15. The optical frequency mixer of claim 1, wherein the second
reflective surface is positioned on an end surface of the nonlinear
crystal close to the input interface.
16. The optical frequency mixer of claim 1, wherein the second
reflective surface is a concave surface of a plano-concave
lens.
17. The optical frequency mixer of claim 1, wherein the input
interface includes an optical connector configured to receive a
mixing unit including a laser diode capable of generating the
mixing wave and a mix-coupling lens configured to couple the mixing
wave to the nonlinear crystal.
18. The optical frequency mixer of claim 17, wherein the mixing
unit further includes a pulsing device, and the mixing wave is a
series of pulses.
19. The optical frequency mixer of claim 17, wherein the mixing
wave is a continuous wave.
20. The optical frequency mixer of claim 1, wherein the nonlinear
crystal is positioned between the output coupler and the input
interface.
21. A method for frequency mixing, comprising the steps of:
generating a resonating wave in a resonant cavity having a
nonlinear crystal; and emitting a mixing wave into the resonating
cavity such that the resonating wave interacts with the mixing wave
in the nonlinear crystal to generate an output wave having a
wavelength different from those of the resonating wave and the
mixing wave, wherein the resonating wave interacts with the mixing
wave in the nonlinear crystal to generate the output wave through a
nonlinear frequency mixing process selected from the group
consisting of sum frequency generation process, difference
frequency generation process, second harmonic generation process
and combinations thereof.
22. The method for frequency mixing of claim 21, further comprising
a step of changing the spot size of the resonating wave.
23. The method for frequency mixing of claim 22, wherein the spot
size of the resonating wave is changed by a plano-concave lens
having a concave surface for focusing the resonating wave.
24. The method for frequency mixing of claim 21, further comprising
a step of separating the output wave from the resonating wave by an
output coupler.
25. (canceled)
26. The method for frequency mixing of claim 21, further comprising
a step of matching phases of the resonating wave and the mixing
wave by periodically poled domains having alternating polarity in
the nonlinear crystal.
27. An optical frequency mixer, comprising: a resonant cavity
including a first reflective surface, a second reflective surface
and an output coupler; a pumping unit configured to emit a pumping
wave to the laser gain medium to generate a resonating wave in the
resonant cavity; a nonlinear crystal positioned on an optical path
of the resonating wave in the resonant cavity, wherein the spot
size of the resonating wave is matched with the spot size of the
pumping wave and the widths of the domains vary along a propagation
direction of the resonating wave; and an input interface configured
to emit a mixing wave into the resonant cavity.
28. An optical frequency mixer, comprising: a resonant cavity
including a first reflective surface, a second reflective surface
and an output coupler; a pumping unit configured to emit a pumping
wave to the laser gain medium to generate a resonating wave in the
resonant cavity; a nonlinear crystal positioned on an optical path
of the resonating wave in the resonant cavity, wherein the
nonlinear crystal includes a plurality of domains having
alternating polarity and the widths of the domains vary along a
propagation direction of the resonating wave; and an input
interface configured to emit a mixing wave into the resonant
cavity.
Description
BACKGROUND OF THE INVENTION
[0001] (A) Field of the Invention
[0002] The present invention relates to an optical frequency mixer
and method for the same, and more particularly, to an optical
frequency mixer using a resonant cavity having a nonlinear crystal
to generate a wavelength shifting through a nonlinear frequency
mixing process and the method for the same.
[0003] (B) Description of the Related Art
[0004] Nonlinear crystal, including periodically poled domains on a
ferroelectric single crystal such as lithium niobate, may be widely
used in technical fields such as optical storage, optical
measurement and optical communication. Particularly, nonlinear
optical crystals are also proposed to be used for optical frequency
mixing to generate a laser beam having a certain wavelength from at
least one source beam through a nonlinear frequency mixing
process.
[0005] U.S. Pat. No. 6,762,876 discloses an optical converter with
a designated output wavelength. The optical converter includes an
optical sum frequency generator (SFG) and an optical difference
frequency generator (DFG). The SFG receives part of both an input
beam carrying information and a continuous-wave (CW) optical pump
beam, while the DFG receives part of the input beam as well as the
output of the SFG. The output of the DFG represents the signal of
the input beam modulated on a beam having the frequency of the pump
beam.
[0006] U.S. Pat. No. 6,697,391 discloses an optical fourth-harmonic
generation system including a V-shaped resonant cavity configured
to support an electromagnetic radiation of a fundamental frequency
and a fourth-harmonic generator (FHG) disposed within the resonant
cavity to produce an electromagnetic radiation of a fourth-harmonic
frequency by an interaction with the electromagnetic radiation of
the fundamental frequency. The fundamental radiation is
characterized by a p-polarization that is complementary to an
s-polarization that characterizes the fourth-harmonic radiation.
The fourth-harmonic generator has an output facet oriented
substantially at a Brewster's angle with respect to the fundamental
radiation to separate the fundamental radiation from the
fourth-harmonic radiation as they emerge from the output facet.
[0007] U.S. Pat. No. 6,726,763 discloses a nonlinear crystal having
an increased spectral acceptance. The nonlinear crystal includes a
plurality of domains arranged serially across the nonlinear
crystal, and has alternating polarity. The poling periods of the
domains are varied across the nonlinear crystal so as to provide
nonuniform chirping of phase matching of focused optical signals
propagated through the nonlinear crystal.
SUMMARY OF THE INVENTION
[0008] One aspect of the present invention provides an optical
frequency mixer using a resonant cavity having a nonlinear crystal
to generate a wavelength shifting through a nonlinear frequency
mixing process and the method for the same.
[0009] An optical frequency mixer according to this aspect of the
present invention comprises a V-shaped resonant cavity including a
first reflective surface, a second reflective surface and an output
coupler, a pumping unit configured to emit a pumping wave to the
laser gain medium to generate a resonating wave in the resonant
cavity, a nonlinear crystal positioned on an optical path of the
resonating wave in the resonant cavity, and an input interface
configured to emit a mixing wave into the resonant cavity.
Preferably, the output coupler can be a dichroic mirror such as a
plano-concave lens having a concave surface configured to reflect
the resonating wave and to focus the resonating wave such that the
spot size of the resonating wave is matched with the spot size of
the pumping wave. Particularly, the nonlinear crystal is positioned
between the output coupler and the input interface.
[0010] The nonlinear crystal includes a plurality of periodically
poled domains having alternating polarity orientation, and the
widths of the domains may be the same or vary along the propagation
direction of the resonating wave. In addition, the longitudinal
widths of the domains along the propagation direction of the
resonating wave varies along a lateral direction perpendicular to
the propagation direction. Further, the nonlinear crystal may
include a first poling portion having a plurality of first domains
and a second poling portion having a plurality of second domains,
and the widths of the first domains is different from the widths of
the second domains along the propagation direction of the
resonating wave. The first poling portion may be positioned in
parallel or in cascade to the second poling portion with respect to
the propagation direction of the resonating wave.
[0011] Another aspect of the present invention provides a method
for frequency mixing comprising the steps of generating a
resonating wave in a resonant cavity having a nonlinear crystal and
emitting a mixing wave into the resonating cavity such that the
resonating wave interacts with the mixing wave in the nonlinear
crystal to generate an output wave having a wavelength different
from those of the resonating wave and the mixing wave. The method
may further comprise a step of changing the spot size of the
resonating wave by a plano-concave lens having a concave surface
for focusing the resonating wave.
[0012] Preferably, the resonating wave interacts with the mixing
wave in the nonlinear crystal to generate the output wave through a
nonlinear frequency mixing process selected from the group
consisting of sum frequency generation process, difference
frequency generation process, second harmonic generation process
and combinations thereof. In addition, the method may further
comprise a step of matching phases of the resonating wave and the
mixing wave in the nonlinear crystal by periodically poled domains
having alternating polarity orientation in the nonlinear
crystal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The objectives and advantages of the present invention will
become apparent upon reading the following description and upon
reference to the accompanying drawings in which:
[0014] FIG. 1 illustrates an optical frequency mixer according to
one embodiment of the present invention;
[0015] FIG. 2 shows the theoretical simulation of the circulation
power of the resonating wave in the resonant cavity according to
the present invention;
[0016] FIG. 3 shows the relation between the output powers of the
output wave and the resonating wave according to the present
invention;
[0017] FIG. 4(a) to FIG. 4(e) illustrate the structure of the
nonlinear crystal according to one embodiment of the present
invention;
[0018] FIG. 5 shows the variation of the spot size of the
resonating wave with respect to the lateral position in the
resonant cavity according to one embodiment of the present
invention;
[0019] FIG. 6(a) and FIG. 6(b) illustrate the modulation of the
output wave by the mixing wave in pulses or in a continuous form,
respectively;
[0020] FIG. 7(a) and FIG. 7(b) illustrate the broadband operation
range of optical frequency mixer in temperature and in wavelength,
respectively;
[0021] FIG. 8 illustrates the relation between the output power of
the resonating wave and the output power of the output wave with
respect to the pumping power of the pumping wave;
[0022] FIG. 9 and FIG. 10 illustrate two optical frequency mixers
according to other embodiments of the present invention,
respectively;
[0023] FIG. 11 and FIG. 12 illustrate an optical frequency mixers
60 and the variation of the spot size of the resonating wave 24
with respect to the lateral position in the resonant cavity 12
according to another embodiments of the present invention; and
[0024] FIG. 13 and FIG. 14 illustrate an optical frequency mixers
60' and the variation of the spot size of the resonating wave 24
with respect to the lateral position in the resonant cavity 12
according to another embodiments of the present invention,
respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0025] FIG. 1 illustrates an optical frequency mixer 10 according
to one embodiment of the present invention. The optical frequency
mixer 10 comprises a resonant cavity 12 including a first
reflective surface 14A on a laser gain medium 16, a second
reflective surface 14B on a mirror 18 and an output coupler 20, a
pumping unit 30 configured to emit a pumping wave 22 to the laser
gain medium 16 to generate a resonating wave 24 in the resonant
cavity 12, a nonlinear crystal 40 positioned on an optical path of
the resonating wave 24 in the resonant cavity 12, and an input
interface 50 configured to emit a mixing wave 26 into the resonant
cavity 12. The laser gain medium 16 can be solid state crystals
such as Nd:YVO.sub.4, Nd:YAG, or Nd:GdVO.sub.4, semiconductors such
as AlGaInP/GaAs, InGaAs/GaAs, or AlGaAs/GaAs. The nonlinear crystal
40 includes a plurality of periodically poled domains 42 having
alternating polarity orientation.
[0026] Preferably, the output coupler 20 is a plano-concave lens
having a concave surface 20A configured to reflect and focus the
resonating wave 24 such that the spot size of the resonating wave
24 can match with the spot size of the pumping wave 22.
Particularly, the nonlinear crystal 40 is positioned between the
output coupler 20 and the input interface 50. The pumping unit 30
includes a laser diode 32 capable of generating the pumping wave 22
and a pump-coupling lens 34 configured to couple the pumping wave
22 to the laser gain medium 16. The input interface 50 includes an
optical connector 52 configured to receive a mixing unit including
an external laser source 62 such as a laser diode capable of
generating the mixing wave 26 such as a continuous wave and a
mix-coupling lens 54 configured to couple the mixing wave 26 to the
nonlinear crystal 40. The mixing unit may further include a pulsing
device, and the mixing wave 26 is a series of pulses.
[0027] In brief, the operation of the frequency mixer 10 comprises
the steps of generating the resonating wave 24 in the resonant
cavity 12 having the nonlinear crystal 40, emitting the mixing wave
26 into the resonating cavity 12 such that the resonating wave 24
interacts with the mixing wave 26 in the nonlinear crystal 40 to
generate an output wave 28 having a wavelength different from those
of the resonating wave 24 and the mixing wave 26, and separating
the output wave 28 from the resonating wave 24 by the output
coupler 20. In addition, the spot size of the resonating wave 24 is
changed by the output coupler 20 of the plano-concave lens serving
to focus and reflect the resonating wave 24, and the periodically
poled domains 42 having alternating polarity in the nonlinear
crystal 40 is used for phase matching of the resonating wave 24 and
the mixing wave 26.
[0028] FIG. 2 shows the theoretical simulation of the circulation
power of the resonating wave 24 in the resonant cavity 12 in
relation to the pump power of the pumping wave 22, and FIG. 3 shows
the relation between the output powers of the output wave 28 and
the resonating wave 24 according to the present invention.
Nd:YVO.sub.4 solid state crystal is used as the laser gain medium
16 and pumped by the pumping wave 22 having a wavelength of 808 nm
to generate the resonating wave 24 having a wavelength of 1064 nm,
the mixing wave has a wavelength of 905 nm and 200 mW, and the
nonlinear frequency process occurring in the nonlinear crystal 40
is sum frequency generation (SFG). When the output power of the
output wave 28 reaches the maximum of approximately 0.37 W, the
circulation power of the resonating wave 24 is about 37 W.
Accordingly, the pumping power of the pumping wave 22 is less than
1 W. The optical frequency mixer 10 possesses the advantage of
highly efficient generation of new wavelength by mixing different
wavelengths and nonlinear crystals.
[0029] FIG. 4(a) to FIG. 4(e) illustrate the structure of the
nonlinear crystal 40 according to one embodiment of the present
invention. The nonlinear crystal 40 includes a plurality of
periodically poled domains 42 having alternating polarity
orientation, and the longitudinal widths (W) of the domains 42 and
the poling period (.LAMBDA.) is the same along the propagation
direction (x) of the resonating wave 24, i.e., known as quasi-phase
matching (QPM), as shown in FIG. 4(a). In addition, the
longitudinal widths (W) of the domains 42 and the poling period
(.LAMBDA.) may vary along the propagation direction (x) of the
resonating wave 24, i.e., known as chirped quasi-phase matching, as
shown in FIG. 4(b). In addition, the longitudinal widths (W) of the
domains 42 along the propagation direction (x) of the resonating
wave 24 may vary along a lateral direction (y) perpendicular to the
propagation direction (x), as shown in FIG. 4(c). In other words,
the poling period (.LAMBDA.) of nonlinear crystal 40 can be
designed to compensate the group velocity delay of pulse laser
mixed in the optical frequency mixer 40. As a result, the generated
pulse width can be narrowed down.
[0030] Furthermore, the nonlinear crystal 40 may include a first
poling portion 44 having a plurality of first domains 44A and a
second poling portion 46 having a plurality of second domains 46A,
and the widths (W1) of the first domains 44A is different from the
widths (W2) of the second domains 46A along the propagation
direction (x) of the resonating wave 24. The first poling portion
46 may be positioned in parallel or in cascade to the second poling
portion 44 with respect to the propagation direction (x) of the
resonating wave 24, as shown in FIG. 4(d) and FIG. 4(e),
respectively. In other words, the nonlinear crystal 40 can be
manufactured in multiple channels, i.e., two poling portions in
parallel, and the nonlinear crystal 40 can be adjusted by
translation function to allow the optical frequency mixer 10 to be
usable for at least two mixing wavelengths.
[0031] The resonating wave 24 interacts with the mixing wave 26 in
the nonlinear crystal 40 to generate the output wave 28 through a
nonlinear frequency mixing process including sum frequency
generation (SFG) process, difference frequency generation (DFG)
process, second harmonic generation (SHG) process or combinations
thereof. Particularly, the phase matching of the resonating wave 24
and the mixing wave 26 are achieved in the nonlinear crystal 40 by
the periodically poled domains 42 having alternating polarity
orientation in the nonlinear crystal 40.
[0032] The sum frequency generation (SFG) process results in a
short wavelength. For example, the resonating wave 24 in the
resonating cavity 12 has a wavelength of 1064 nm and the mixing
wave 26 has different wavelengths, and the mixed results for the
SFG process can be 1064 nm+635 nm.fwdarw.3397 nm, 1064 nm+808
nm.fwdarw.459 nm, or 1064 nm+532 nm.fwdarw.4355 nm. The mixing
output ranges from visible to ultraviolet bands, and the grating
period of the nonlinear crystal 40 is preferably less than 6 um. In
contrast, the difference frequency generation (DFG) process results
in longer wavelength. For example, the resonating wave 24 still has
a wavelength of 1064 nm and the mixing wave 26 is different, and
the mixed results for the DFG process can be 1064 nm+1550
nm.fwdarw.43.391 .mu.m or 1064 nm+1300 nm.fwdarw.45.86 .mu.m. The
mixing output is extended from middle IR to sub-millimeter wave,
and the grating period is preferably longer than 20 .mu.m. As to
the cascaded SHG/SFG or SHG/DFG processes, SHG occurs first to
double the input frequency, 1064 nm.fwdarw.(SHG) 532 nm for
instance, and then partial energy of 1064 nm can be mixed with 532
nm to generate UV-wavelength in the subsequent SFG process, 1064
nm+532 nm.fwdarw.355 nm.
[0033] FIG. 5 shows the variation of the spot size of the
resonating wave 24 with respect to the lateral position in the
resonant cavity 12 according to one embodiment of the present
invention. The lateral position starts from the first reflective
surface 14A to the second reflective surface 14B. One design rule
for the frequency mixer 10 is that the higher intensity of the
resonating wave 24, the better efficiency of the nonlinear
frequency mixing. With the utilization of the plano-concave lens at
a lateral position of 28 mm around the middle of the V-shaped
resonant cavity 12, the focusing ability of the concave surface of
the plano-concave lens decreases the spot size of the resonating
wave 24 propagating toward the nonlinear crystal 40 at a lateral
position of 42 mm from 0.14 mm to about 0.035 mm, which is
contributory to nonlinear frequency mixing efficiency, i.e., to
optimize the optical-to-optical transformation.
[0034] FIG. 6(a) and FIG. 6(b) illustrate the modulation of the
output wave 28 mixed by the mixing wave 26 in pulses or in a
continuous form, respectively. The mixing wave 26 may carry
information, or be amplitude-modulated with information in pulse
form, and the nonlinear frequency mixing of the mixing wave 26 and
the resonating wave 24 in the nonlinear crystal 40 results in an
output wave 28 carrying the information in pulses. In addition, the
resonating wave 24 can be modulated by the mixing wave 26 in a
continuous form, as shown in FIG. 6(b). The new wavelength
generation of the optical frequency mixer 10 is based on photonic
conversion, such as the SFG or DFG processes in the nonlinear
crystal 40. Therefore, the response time can be up to ultra-fast
(pico-second or femto-second) and achieve a high frequency
repetition rate without oscillation delay in the optical frequency
mixer 10. In other words, the optical frequency mixer 10 can be
modulated by ultra-fast or high frequency signal of the mixing wave
26 from the input interface 50 to perform all optical
modulation.
[0035] FIG. 7(a) and FIG. 7(b) illustrate the broadband operation
range of the optical frequency mixer in temperature and in
wavelength, respectively. The nonlinear frequency mixing efficiency
is proportional to "effective d coefficient" shown on the vertical
axis in FIG. 7(a) and FIG. 7(b). The bandwidth is defined as the
full width half maximum (FWHM), and bandwidth of the optical
frequency mixer 10 is around 70.degree. C. in temperature and
around 3 nm in wavelength.
[0036] FIG. 8 illustrates the relation between the circulation
power of the resonating wave 24 and the output power of the output
wave 28 with respect to the pumping power of the pumping wave 22.
The optical frequency mixer 10 uses 0.5%-Nd:YVO4, 5 mm-long as the
laser gain medium 16; 808 nm LD 5 W as the pumping source;
HR>99.9% @1064 nm; PP MgO:LN (periodically poled MgO:LiNbO3) 10
mm-long with 5.3 .mu.m grating period as the nonlinear crystal 40;
and 200 mW, 905 nm as the mixing wave 26 to generate the output
wave 28 of 488 nm.
[0037] The resonating wave 24 having a wavelength of 1064 nm is
generated from the pumping wave 22 having a wavelength of 808 nm
pumping the laser gain medium 16 of Nd:YVO.sub.4 crystal. The
output power of the resonating wave 24 is saturated at pumping
power 4.7 W pump, induced by thermal perturbation in a resonator.
The power can also be estimated for circulation power based on
fixed reflective ratio on the output coupler 20. Therefore, the
1064 nm-circulation power will be saturated at 4.7 W pump (808 nm)
and its estimated power is 30.about.40 W for 99.93% HR at 1064
nm.
[0038] The poling period of the nonlinear crystal 40 is 5.3 .mu.m
and the mixing wave 26 of 905 nm is mixed with the resonating wave
24 of 1064 nm through the nonlinear crystal 40 to generate the
output wave 28 having a wavelength of 488 nm. The output power of
the output wave 28 is saturated at pumping power of 4.5 W (4.5 W
pump). The power level (4.5 W-pump) is less than that of 1064
nm-power (4.7 W-pump). That means the power saturation of the
output wave 28 of 488 nm is due to nonlinear transformation but
1064 nm-power supplement, i.e., the resonant intra-cavity 12 can
supply sufficient 1064 nm-power until output power of the output
wave 28 cannot be increased with more 1064 nm power.
[0039] FIG. 9 and FIG. 10 illustrate two optical frequency mixers
10', 10'' according to other embodiments of the present invention,
respectively. In comparison with the optical frequency mixers 10 in
FIG. 1, the optical frequency mixer 10' in FIG. 9 uses a
plano-concave lens 18' having a concave surface as the second
reflective surface 14B instead of the mirror 18. As to the optical
frequency mixer 10'' in FIG. 10, the second reflective surface 14B
is positioned on an end surface of the nonlinear crystal 40 close
to the input interface 50.
[0040] FIG. 11 and FIG. 12 illustrate an optical frequency mixer 70
and the variation of the spot size of the resonating wave 24 with
respect to the lateral position in the resonant cavity 12 according
to another embodiments of the present invention, respectively. In
comparison with the optical frequency mixers 10 in FIG. 1, the
optical frequency mixer 72 in FIG. 11 uses a first reflective
surface 76 positioned on a plano-concave lens 74 and a dichroic
mirror 72 as the output coupler 20. The variation of the spot size
of the resonating wave 24 increases as the lateral position of the
resonate cavity 12, and the lateral position starts from the second
reflective surface 14B to the first reflective surface 76, as shown
in FIG. 12.
[0041] FIG. 13 and FIG. 14 illustrate an optical frequency mixer 80
and the variation of the spot size of the resonating wave 24 with
respect to the lateral position in the resonant cavity 12 according
to another embodiments of the present invention, respectively. In
comparison with the optical frequency mixers 10 in FIG. 1, the
optical frequency mixer 80 in FIG. 13 uses a second reflective
surface 84 positioned on a plano-concave lens 82 and a dichroic
mirror 72 as the output coupler 20. The variation of the spot size
of the resonating wave 24 increases as the lateral position of the
resonate cavity 12, and the lateral position starts from the first
reflective surface 14A to the second reflective surface 84, as
shown in FIG. 14.
[0042] The above-described embodiments of the present invention are
intended to be illustrative only. Numerous alternative embodiments
may be devised by those skilled in the art without departing from
the scope of the following claims.
* * * * *