JP2863564B2 - Ultra-wideband and high coherent optical sweep generator from infrared to ultraviolet - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sweep generator that generates an ultra-wide band and high coherent light from infrared to ultraviolet by frequency sweeping.

[Conventional technology]

In the field of physical measurement such as coherent light measurement and spectroscopic measurement, a variable frequency laser light source is an essential device. For example, if the laser frequency can be continuously swept over 100 THz, the performance of the spectroscopic measurement system for unknown atoms and molecules will be dramatically improved, thereby providing a wealth of new knowledge on the structure of atoms and molecules. Furthermore, coherent optical communication,
In an optical application field such as an optical computer, in particular, in frequency multiplexing optical communication, a semiconductor laser light source capable of performing frequency sweep with high accuracy over a range of 100 THz or more is required.

Conventionally, devices that can improve the structure of the semiconductor laser itself and perform frequency sweep over a relatively wide band have been devised.
An optical oscillator capable of continuously sweeping a wide frequency range of 0 THz or more has not yet been realized. The reason for this is that the technology for integrating both frequency conversion between different types of lasers and frequency synchronization has not been developed. The former requires an optical mixing technology utilizing the nonlinear optical effect, and the latter requires an electrical control technology mediated by microwaves, but there has been no example of using both simultaneously. This is due to the fact that conventionally high frequency stable lasers generally have low optical power, so that there was no nonlinear optical crystal suitable for this, and the frequency controllability of conventional lasers was insufficient.

[Problems to be solved by the invention]

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a novel optical sweep generator that generates an ultra-wide band and high coherent light ranging from infrared to ultraviolet by frequency sweeping. It is.

[Means for solving the problem]

The ultra-wideband and high coherent optical sweep generator ranging from infrared to ultraviolet of the present invention has an oscillation frequency of one semiconductor laser or a harmonic frequency due to the nonlinear optical effect thereof and a harmonic frequency due to the nonlinear optical effect of the other semiconductor laser. At least one pair of semiconductor lasers whose oscillation frequencies are different from each other can be matched, the frequencies of light from one or both semiconductor lasers are converted and matched using the nonlinear optical effect, and the vicinity of the matched frequency is adjusted. Light having the same frequency from both semiconductor lasers is made incident on a gas cell having a resonance frequency, and the oscillation wavelengths of both semiconductor lasers are fixed to each other by using the optical double resonance of the gas cell. At least one pair of light having a fixed frequency is incident on two nonlinear waveguides at an angle to each other. Converted into light having a frequency between both the incident light by a linear optical effect to generate a beat causes interference light mutual exiting the two nonlinear waveguide,
This beat is photoelectrically converted and compared with a reference frequency from a microwave oscillator, and an angle of one of the two nonlinear waveguides with respect to the incident light or a pair of incident light into this waveguide is obtained by the obtained error signal. The angle formed between the lights is adjusted so that the error signal becomes zero, the reference frequency from the microwave oscillator is configured to be sweepable, and the frequency of the light emitted from the one nonlinear waveguide is adjusted. It is characterized by being configured to be capable of sweeping.

In this optical sweep generator, a harmonic is generated by a nonlinear optical effect of at least one light having a fixed frequency using optical double resonance, and the harmonic and the light having a fixed frequency are converted into two nonlinear waveguides. The light may be incident at an angle to each other, and may be converted into light having a frequency between the two incident lights by a nonlinear optical effect.

In addition, two pairs of semiconductor lasers having different oscillation frequencies at which the oscillation frequency of one semiconductor laser or the harmonic frequency due to the non-linear optical effect thereof and the harmonic frequency due to the non-linear optical effect of the other semiconductor laser can coincide. It can also be used.

In the above, the nonlinear waveguide has a shape of a planar waveguide formed by pouring and crystallizing an organic nonlinear material between an upper flat glass and a lower flat glass having a lattice perpendicular to one incident light on the lower surface. It is desirable that

Specifically, the semiconductor lasers are 1.56 μm and 1.
It consists of four devices that oscillate light with wavelengths of 34 μm, 0.78 μm, and 0.67 μm, and one that oscillates light with a wavelength of 1.56 μm.
A set that oscillates light with a wavelength of 0.78 μm is
The other group that oscillates light with a wavelength of 1.34 μm and the one that oscillates light with a wavelength of 0.67 μm generates a second harmonic of light from a semiconductor laser that oscillates light with a wavelength of 1.56 μm. Therefore, the light having a wavelength of 0.78 μm is incident on the rubidium cell together with the light from the semiconductor laser that oscillates, and the oscillation wavelengths of both semiconductor lasers are fixed to each other using the optical double resonance of the rubidium cell. By generating the second harmonic of light from a semiconductor laser that oscillates light at a wavelength of 1.34 μm,
A light having a wavelength of 0.67 μm can be incident on a lithium cell together with light from a semiconductor laser that oscillates, and the oscillation wavelengths of both semiconductor lasers can be fixed to each other by using optical double resonance of the lithium cell. it can.

In this case, a second harmonic of light having a wavelength of 0.67 μm having a fixed wavelength is generated, and the harmonic and the light having a wavelength of 0.67 μm having the fixed wavelength are mutually angled into two nonlinear waveguides. It is preferable that the light is made incident on the light source so that the light is converted into light having a frequency between the two incident lights by the nonlinear optical effect.

[Action]

Since the frequency of at least two semiconductor lasers is an integral multiple of the common frequency, the oscillation frequencies of both can be fixed to a high coherent frequency having a narrow spectral range by utilizing optical double resonance. Or between one of them and another light of a fixed frequency as well, which can be converted to light having a frequency between the two incident lights by the nonlinear optical effect of the nonlinear waveguide. Can be tuned to a predetermined frequency by comparing the emitted light with a reference frequency from a microwave oscillator, and sweeping the frequency of light emitted from a nonlinear waveguide by sweeping the reference frequency from the microwave oscillator. Can be.

Embodiment First, the basic concept of the sweep generator of the present invention will be described. At present, one of the semiconductor lasers that can be obtained relatively easily is one having four oscillation wavelengths as shown in FIG. That is, 1.56 μm for communication, 1.
34 μm, 0.78 μm for CD, and 0.67 μm for emitting red light. Looking at the relationship between these wavelengths, 1.56 μm is 0.78
μm is just twice as large, and 1.34 μm is just twice as large as 0.67 μm. Therefore, taking the second harmonic of 1.56 μm,
Equivalent to 78 μm, and taking the second harmonic of 1.34 μm,
It is equal to 0.67 μm. Therefore, in the present invention, utilizing this relationship, a 1.56 μm semiconductor laser and a 0.1 μm semiconductor laser are used.
The oscillation wavelength of the semiconductor laser of 78 μm is mutually fixed using the optical double resonance described later. Similarly, 1.34 μm
And the semiconductor laser of 0.67 μm are mutually fixed in oscillation wavelength using optical double resonance. In this manner, four light sources having fixed wavelengths are obtained. The wavelength between these wavelengths is swept using a non-linear waveguide described later, and light having a wavelength between those wavelengths is tunable. Generated by In addition, a second harmonic of 0.67 μm is generated to obtain light of 0.34 μm, and light of a variable wavelength is similarly generated between these wavelengths. Therefore, 1.56μm to 0.34μm
, Ie, an ultra-wide band light ranging from infrared to ultraviolet. The above is the basic principle of the ultra-wideband and high coherent optical sweep generator from infrared to ultraviolet according to the present invention.

FIG. 2 shows an apparatus for mutually fixing the oscillation wavelength of a 1.56 μm semiconductor laser and a 0.78 μm semiconductor laser using optical double resonance. In this apparatus, light from the semiconductor laser 1 of 0.78 μm is made incident on the rubidium cell 3 via the half mirror 2, the passing light is reflected by the reflecting mirror 4, and the light passes through the cell 3 again (the light must be passed twice). The light is photoelectrically converted by the detector 5 and the signal is fed back to the injection current of the semiconductor laser 1 to stabilize the oscillation wavelength of the semiconductor laser 1 (the oscillation wavelength of the semiconductor laser is controlled by the injection current. Changes). At this time, a signal of a predetermined frequency from the oscillator 6 is applied to the injection current to frequency-modulate the oscillation wavelength of the semiconductor laser 1, and the signal from the detector 5 is detected by the lock-in amplifier 7 at the frequency from the oscillator 6. The oscillation wavelength of the semiconductor laser 1 is
It is fixed at the absorption wavelength (resonance wavelength) of rubidium, and a light with a narrow spectral width and high coherency can be obtained. This light is extracted from, for example, a half mirror 8 disposed immediately before the semiconductor laser 1. On the other hand, the 1.56 μm light from the semiconductor laser 9 is converted by the nonlinear optical crystal 10 into light having a wavelength of 0.78 μm as the second harmonic, enters the rubidium cell 3 and undergoes photoelectric conversion at the detector 11. . The signal is detected by the lock-in amplifier 12 at the frequency from the oscillator 6 and fed back to the semiconductor laser 9. The oscillation wavelength of the semiconductor laser 9 is fixed to twice the absorption wavelength of rubidium, and the spectral width is narrow and the coherency is low. High light can be obtained. This light is extracted from, for example, a half mirror 13 disposed immediately before the semiconductor laser 9. The details of this principle can be found in the IEEE Journal of Quantum Electronic
s, Vol. 24, No. 12, pp. 2392-2399. Similarly, using a lithium cell instead of the rubidium cell,
And the semiconductor laser of 0.67 μm can mutually fix the oscillation wavelength using the optical double resonance. Thus, four light sources with fixed wavelengths are obtained.

Next, wavelength sweeping using a nonlinear waveguide will be described. As shown in FIG. 3, a thin deposited film of SiO ₂ or the like is interposed as a spacer 18 between an upper flat glass 15 and a lower flat glass 17 having a lattice 16 perpendicular to a pump light 20 described later on the lower surface. In the meantime, for example, an organic nonlinear material MNA (C ₆ H
₄ NH ₂ NO ₂ ), PCA and the like 19 are poured and crystallized, and the organic nonlinear material region 19 is used as a flat waveguide. When a pump light 20 having a frequency ω _p and a signal light 21 having a frequency ω _s are incident on such a planar waveguide in the plane of the waveguide so as to form an angle θ with each other as shown in FIG. The idler light 22 of ω _i is emitted from the opposite end face. Idler light
The frequency ω _{i at} 22 is the angle at which the waveguide rotates about a rotation axis 23 perpendicular to the waveguide plane, or the pump light 20
And the signal light 21 to change between the frequencies ω _p and ω _s . That is, the wavelength can be swept by changing any of these parameters. The mechanism capable of sweeping the wavelength in this way is modeled as shown in FIG. That is, the relationship of the wave vector as shown by the solid line first is the pump light 2
0, signal light 21, when present between idler light 22, when rotating the waveguide around the rotation axis 23, or changing the angle θ between the pump light 20 and the signal light 21,
Since the refractive index of the nonlinear optical material changes depending on the direction,
This relationship does not hold anymore, and does not hold unless the idler light is divided into two (k _i1 and k _i2 ). And one idler light (k _i1 ) divided in this way
The sum of the frequencies (ω _s + ω _i1 ) occurs between the signal and the signal light, and this light goes out as the idler light 22 (dotted line. In this case, the idler light has a phase matching condition with the pump light). Must be satisfied). This frequency ω _i1
Varies within the range from ω _p to ω _s depending on the rotation angle or the angle between them, the wavelength of the idler light is ω _p and ω
_s . The grating provided on the lower surface of the upper flat glass 15 acts as a resonator for pump light and signal light, and serves to enhance the electric field strength of the pump light and signal light in the waveguide and enhance the above-described nonlinear action. Things,
The period of this grating is half the effective wavelength of the pump light or an integral multiple thereof.

FIG. 5 shows a conceptual diagram of an actual optical sweep generator. In the figure, the wavelength range is 0.34 ~ 0.67μm, 0.78 ~ 1.34μ
m, the sweeping mechanism in the range of 1.34 to 1.56 μm is not shown, but is the same as the mechanism in the range of 0.67 to 0.78 μm shown (however, in the range of 0.34 to 0.67 μm, as the material of the nonlinear waveguide, LiNbO ₃ , PCA instead of MNA
Is used). The light from the 1.56 μm semiconductor laser 31 and the light from the 0.78 μm semiconductor laser 32 are fixed to the absorption wavelength with a narrow spectral width of the rubidium cell 35 by the apparatus shown in FIG. 2, and the 1.34 μm semiconductor laser 33 and the 0.67 μm The light from the semiconductor laser 34 is fixed to an absorption wavelength having a narrow spectral width of the lithium cell 36 by a device similar to the device shown in FIG. Among them, 0.78 from semiconductor laser 32
The light of .mu.m and the light of 0.67 .mu.m from the semiconductor laser 34 are separated into two and made to enter the nonlinear waveguides 37 and 38 shown in FIG. 3 as pump light and signal light. The nonlinear waveguide 38 is
It is for emitting light that is a reference for wavelengths between 0.78 μm and 0.67 μm, and is fixed. On the other hand, the nonlinear waveguide 37 is for sweeping the wavelength between 0.78 μm and 0.67 μm, and is rotated around its rotation axis by a feedback signal, or the angle between incident lights is changed. be changed. Light irradiated as idler light from the nonlinear waveguides 37 and 38 is multiplexed by the multiplexer 39 to generate a beat having a difference between the two frequencies. The beat is converted into an electric signal by the detector 40, and is multiplied by the signal from the microwave reference oscillator 41 in the multiplier 42. If there is a difference between the two frequencies, a signal of the difference is fed back, and the output light from the nonlinear waveguides 37 and 38 is adjusted by rotating the nonlinear waveguide 37 or by adjusting the angle between the incident lights. The frequency difference between them can be made to match the frequency of the microwave from the reference oscillator 41. Therefore, when the oscillation frequency of the microwave reference oscillator 41 is swept, the frequency of light emitted from the nonlinear waveguide 37 is also swept. By outputting this light from the half mirror 44 disposed in front of the waveguide 37, the light can be used. As above, 0.34 to 0.67 μm, 0.
Light having a wavelength in the range of 78 to 1.34 μm and 1.34 to 1.56 μm can be output.

The above is only one embodiment of the present invention, and various modifications are possible. For example, the light from the semiconductor laser to be incident on the gas cell 3 in FIG. 2 may be a harmonic converted by a nonlinear optical element. Further, both the pump light 20 and the signal light 21 to be incident on the nonlinear waveguide of FIG. 3 may be harmonics converted by the nonlinear optical element.

〔The invention's effect〕

According to the present invention, a plurality of infrared semiconductor lasers and visible semiconductor lasers whose frequencies are fixed to the resonance frequency of a specific gas or an integer multiple thereof using optical double resonance are used, and further, a nonlinear waveguide is used to perform frequency synchronization. , Conversion and sweep can realize an optical sweep generator (sweep range reaches 1 petahertz) capable of high-precision, ultra-broadband continuous frequency sweep over the infrared to ultraviolet range. Using this optical sweep generator, new knowledge on the structure of various types of atoms and molecules can be obtained by high-precision physical measurement, especially spectroscopic measurement, which enables new materials for communication and computer systems,
New materials can be developed. Furthermore, in communications, the characteristics of laser light as an ultrahigh-frequency coherent lightwave can be utilized, so that the frequency can be swept or fixed over a wide range, and voice, image, and data information can be added to each frequency, making it extremely useful. Such information can be transmitted simultaneously on many channels. In this way, it is possible to increase the capacity of communication that was impossible with a conventional microwave. On the other hand, in the field of optical computers, which are next-generation computers, if information is stored in each frequency channel of such a light source capable of frequency sweeping, application to a large-capacity optical storage device becomes possible. As described above, the present invention has a high contribution to improving the performance of a system in the fields of physical measurement, optical communication, and optical computer.

[Brief description of the drawings]

FIG. 1 is a view for explaining the basic concept of the sweep generator of the present invention, FIG. 2 is an explanatory view of an apparatus for mutually fixing the oscillation wavelength using optical double resonance, and FIG. FIG. 4 is a view for explaining a wavelength sweeping mechanism of a nonlinear waveguide, and FIG. 5 is a conceptual diagram of an actual optical sweep generator. 1: 0.78 μm semiconductor laser, 2: half mirror, 3: rubidium cell, 4: reflector, 5: detector, 6: oscillator, 7: lock-in amplifier, 8: half mirror, 9: 1.56 μm semiconductor laser , 10: nonlinear optical crystal, 11: detector, 12: lock-in amplifier, 13: half mirror, 15: upper flat glass, 16: lattice, 17: lower flat glass, 18: spacer, 19: organic nonlinear material ( MNA), 20: pump light, 21: signal light, 22: idler light, 23: rotation axis, 31: 1.56 μm semiconductor laser, 32:
0.78 μm semiconductor laser, 33: 1.34 μm semiconductor laser, 34: 0.67 μm semiconductor laser, 35: rubidium cell,
36: lithium cell, 37, 38: nonlinear waveguide, 39: multiplexer, 4
0: detector, 41: microwave reference oscillator, 42: multiplier, 43:
Rotating mechanism, 44: half mirror

Claims (6)

(57) [Claims] At least one pair of oscillation frequencies at which the oscillation frequency of one semiconductor laser or the harmonic frequency due to the nonlinear optical effect thereof and the harmonic frequency due to the non-linear optical effect of the other semiconductor laser coincide with each other. Using different semiconductor lasers, using the nonlinear optical effect to convert and match the frequency of light from one or both semiconductor lasers,
The light having the same frequency from both semiconductor lasers is incident on a gas cell having a resonance frequency in the vicinity of the matched frequency, and the oscillation wavelengths of the two semiconductor lasers are mutually adjusted using the optical double resonance of the gas cell. A light having a frequency between the two incident lights by a non-linear optical effect by fixing at least one pair of lights whose frequencies are fixed in this way and entering the two nonlinear waveguides at an angle to each other. And a beat is generated by interfering the light emitted from the two nonlinear waveguides with each other, and the beat is photoelectrically converted and compared with a reference frequency from a microwave oscillator. Angle of one of the nonlinear waveguides with respect to the incident light, or 1 which is incident on this waveguide.
The angle formed between the pair of light beams is adjusted so that the error signal becomes zero, and the reference frequency from the microwave oscillator can be swept so that the light emitted from the one non-linear waveguide can be swept. An ultra-wideband and high coherent optical sweep generator from infrared to ultraviolet, characterized in that the frequency can be swept. 2. A method for generating harmonics due to a nonlinear optical effect of at least one light having a fixed frequency using optical double resonance, and converting the harmonics and the light having a fixed frequency into two nonlinear waveguides. 2. An infrared-ultraviolet light according to claim 1, wherein the light is incident at an angle to each other and converted into light having a frequency between the two incident lights by a nonlinear optical effect. Broadband and high coherent optical sweep generator. 3. The two pairs of oscillation frequencies at which the oscillation frequency of one semiconductor laser or the frequency of the harmonics due to the non-linear optical effect thereof and the frequency of the harmonics due to the non-linear optical effect of the other semiconductor laser coincide with each other are different from each other. 3. An ultra-wideband and high coherent optical sweep generator from infrared to ultraviolet according to claim 1 or 2, wherein a semiconductor laser is used. 4. A planar waveguide formed by pouring and crystallizing an organic nonlinear material between an upper flat glass and a lower flat glass having a lattice perpendicular to one of the incident light on the lower surface. 2. The method according to claim 1, wherein
4. An ultra-wide band and high coherent optical sweep generator from infrared to ultraviolet according to any one of items 1 to 3. 5. The semiconductor laser according to claim 1, wherein said semiconductor lasers are 1.56 μm,
μm, 0.78 μm, and 0.67 μm wavelength light.
One that oscillates light with a wavelength of 78 μm is a set of 1.
The other group that oscillates light with a wavelength of 34 μm and the one that oscillates light with a wavelength of 0.67 μm generates the second harmonic of light from a semiconductor laser that oscillates light with a wavelength of 1.56 μm. Together with light from a semiconductor laser that oscillates light having a wavelength of 0.78 μm, the light is incident on a rubidium cell, and the oscillation wavelengths of both semiconductor lasers are fixed to each other using the optical double resonance of the rubidium cell. A second harmonic of light from a semiconductor laser that oscillates light having a wavelength of μm is generated.
Light of 67μm wavelength is incident on the lithium cell together with the light from the oscillating semiconductor laser, and the oscillation wavelengths of both semiconductor lasers are fixed to each other using the optical double resonance of the lithium cell. Claim 3 or 4
Ultra-wideband and high coherent optical sweep generator from infrared to ultraviolet as described. 6. A second harmonic of light having a wavelength of 0.67 μm having a fixed wavelength is generated, and this harmonic and the light having a wavelength of 0.67 μm having a fixed wavelength are transmitted to two nonlinear waveguides. 6. An ultra-wide band from infrared to ultraviolet according to claim 5, wherein the light is incident at an angle to the light and converted into light having a frequency between the two incident lights by a nonlinear optical effect. And high coherent optical sweep generator.