JPS62172777A - Variable wavelength laser light source - Google Patents

Abstract

PURPOSE:To perform a variable wavelength laser light source having narrow oscillating spectral width with good responsiveness and high ageing change resistance by diffracting a light plural times in acoustic-optical means and cancelling the influence due to a Doppler shift occurring due to diffraction. CONSTITUTION:A light emitted from a nonreflecting coating 11 of a semiconductor laser LD1 becomes a parallel light by a lens LS1, and is reflected on a mirror M1. The reflected light from the mirror M1 is returned through an optical path to the original position, and is again incident to the laser LD1. The light emitted from a nonreflecting coating 12 becomes parallel light by a lens LS2, and is incident to a first acoustic-optical element UM1. In this case, it is diffracted while receiving a Doppler shift by an ultrasonic wave 21. The light emitted from the element UM1 is again diffracted by an acoustic optical element UM2. Here, it is affected by a Doppler shift by ultrasonic wave 22, the light emitted from the element UM2 is reflected on a mirror M2, returned in the original optical path, and is again incident to the laser LD1. Thus, since the Doppler shift due to the diffraction is cancelled, the resonance is stable, and the spectral beam width can be narrowed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvement of a variable wavelength laser light source that can change the oscillation wavelength of laser light.

(Prior Art) Conventional tunable wavelength laser light sources include the following.

A1 What rotates the diffraction grating (Figure 4) Optical amplification unit LD
The output light enters the diffraction grating DG via the condenser lens LS, and the first-order diffracted light 41 returns to the optical amplification section LD. 42 is O-th order diffracted light. When the diffraction grating DG is rotated, the optical amplification section LD
Since the wavelength of the first-order diffracted light that returns to changes, the oscillation wavelength can be controlled.

(Fig. 5) Instead of rotating the diffraction grating as in A, fl, IJQI optical element UM is used.
The oscillation wavelength is controlled σO by avoiding a change in the incidence β on the diffraction grating DG.

(Problems to be Solved by the Invention) However, the variable wavelength laser light source configured as described above has the following problems.

Since the diffraction grating is mechanically moved, it is difficult to make the viscosity become heavy.
f1il, has poor response and is sensitive to changes over time.

Since the wavelength of the light returning to the optical amplification section is slightly shifted due to Doppler shift, stable oscillation is delayed by 1q, and the oscillation spectrum width becomes wider.

The present invention has been made to solve these problems, and aims to realize a tunable wavelength laser light source that has good response, is resistant to changes over time, and has a narrow oscillation spectrum width.

(Means for Solving the Problems) A tunable wavelength laser light source according to the present invention includes an acousto-optic means into which light related to the output light of the optical amplification section enters into a laser resonator, and an acousto-optic means in which light output from the acousto-optic means is input. and an optical means that returns to the blind tube optical means, and diffracts light a plurality of times in the acousto-optical means so as to cancel out the influence of Doppler shift caused by the diffraction.

(Example) The present invention will be explained in detail below using the drawings.

FIG. M1 is a configuration block diagram of an embodiment of a variable wavelength laser light source according to the present invention. L D 1 is a semiconductor laser constituting the optical amplification section, 11.12 is this semiconductor laser °
The non-reflective coated portions provided on both ends of the LD1, the LSI are lenses that convert the light emitted from the non-reflective coated portions 11 into 100 nm light, and the Ml converts the light that has passed through this lens LSI into reflective light.
1s2 is a lens that converts the light emitted from the anti-reflection coating section 12 into parallel light, UMI is a first acousto-optic element into which the light emitted from this lens LS2 enters, and UM2 is an output tA from this acousto-optic element UM1. The second acousto-optic element M2, into which the acousto-optic light is incident, reflects the light emitted from the acousto-optic element UM2, and between the mirror M1 and the mirror M1, the laser resonator R1 is connected to the acousto-optic element UM1. UM2 to frequency F
It is an oscillator that is excited by Acousto-optic cable UM1゜UM2
constitutes an acousto-optic means, and the mirror M2 constitutes an optical means.

The operation of the apparatus configured as described above will be described in detail below.

FIG. 2 is an operation explanatory diagram for explaining the operation of the apparatus shown in FIG. Anti-reflection coating portion 11 of semiconductor laser LD 1
The light emitted from the lens LSI becomes parallel light and is reflected by the mirror M1. The reflected light from the mirror M1 returns along the optical path and enters the semiconductor ray If L D 1 again.

The light with the frequency f0 emitted from the anti-reflection coated part 12 is converted into a flattened light by the lens LS2, and then passed through the first @acoustic optical element (JM
incident on l. At this time, from the diffraction conditions, the incident angle θII to the diffraction grating 23 generated by the ultrasonic wave 21 + the output angle θ01 after diffraction. There is a relationship between the wavelength λ0 of light and the wavelength Δ0 of ultrasonic waves as shown in the following equation (Figure 2)・sinθL, +s
inθo1−λ0/Δ0...(1) S'j IFI et al. Specific incident angle θL1 and exit angle θo
J that satisfies 1, the wavelength of the light passing through the optical path λ0 changes to the wavelength of the ultrasonic wave if 〇 changes. The emitted light is subjected to a Doppler shift 1- by the ultrasonic wave, and in this case, it is +1st order diffracted light (the direction of the ultrasonic wave is the same as the diffracted direction), so its frequency becomes fo+F. The light emitted from the acousto-optic element UM1 is diffracted again by the sonic optical water element UM2. Same as above, super? The following relationship exists between the incident angle θ to the diffraction grating 2+ caused by the first wave 22, the exit angle θ021 after the 21st diffraction, the wavelength λo of the light, 1 and the wavelength of the ultrasonic wave.

sin θ12+sin θ02−λ0/Δ0 (2) However, in equation 2), the change in λ0 due to the Doppler shift of the acousto-optic cable UM1 is ignored because it is small. Here, the relationship between the ultrasonic traveling wave 22 and the diffracted light is opposite to that in the acousto-optic element LIM1, and it becomes -1st-order diffracted light, so the Doppler shift angle becomes -F, and the acousto-optic element UM
The frequency of the second emitted light is fo+F−F=f'o. The emitted light from the acousto-optic probe UM2 is reflected by the mirror M2, then reverses its original optical path and enters the semiconductor laser LD1 again)
Do 1.

When going backwards, the frequency of the output light of tJM2 becomes fo F due to the Doppler shift, and the frequency of the output light of LJMl becomes fo F 1 F = f 6 and the original frequency f
o and returns to the semiconductor laser #fLD1, so the resonance state continues. In addition, in order to increase the diffraction efficiency, the Bragg incidence condition is satisfied, and the incident angle θ is adjusted to the ultrasonic wavelength.
．． Output tJ4 angle θOI + incident angle θ, 2OJ, and output angle θo
The following relationship is established between the two.

OL+ = θOI = θi2 - θ02 With this configuration, the wavelength of the ultrasonic wave is △. If you change θLI+
θO++ θ, 2. The wavelength λ0 of the light that resonates while satisfying θo2 is swept as shown in the following equation.

sinθ7. ±sinθo1=(λ0+Δλ)/(to 80+Δ) From the Shallow-Towns equation, the spectral linewidth of the output light of the tunable wavelength laser light source configured as above becomes 2 " = π hvV Cnsp/Pc. However, r c = c (β L −1n R) /
2 π n l-h blank constant C: Laser wavelength Pc: Oscillation power nsp: Carrier density of spontaneous emission C: Speed of light β: Loss coefficient L in the resonator: Resonator length R: Anti-IA rate n of the mirror :Refractive index Therefore, compared to the L of a single semiconductor laser, which is approximately 0.3 mm, the above configuration allows L to be greater than 100 mm.
The oscillation spectrum linewidth can be easily reduced.
.

Furthermore, since the Doppler shift due to diffraction is canceled out, resonance is stable and the spectral linewidth can be narrowed.

Also, since it uses an acousto-optic effect, M! electrical #1t
ll, the response is fast, and there is little change over time.

In the above embodiment, two acousto-optic elements are used as the acousto-optic means, but the present invention is not limited to this, and any even number of acousto-optic elements can be used.

Further, in the above embodiment, the Doppler shift caused by the +1st-order diffracted light and the 11st-order diffracted light is canceled out, but the present invention is not limited to this, and diffracted light of any order with opposite signs can be used.

Further, a diffraction grating may be used instead of the mirror M2.

FIG. 3 is a block diagram showing a second embodiment of the present invention. The same parts as in FIG. 1 are given the same symbols and their explanations will be omitted. R1,, 1 is a rod lens that converts the light emitted from the non-reflection coated part 11 into parallel light, M3 is a mirror coating part provided at one end of this rod lens RLI and reflects the parallel light, R(-2 is a non-reflection coat part 1
A rod lens (J
M3 is a Raman-Nath type acousto-optic element into which the light passing through the rod lens RL2 is incident, RL3 is a rod lens into which the +1st-order diffracted light from this acousto-optic element U M3 is incident, and RL4 is the 11st-order diffracted light. Incoming light is incident on the 1st lens (FB1 is the light that connects the rod lenses RL3 and 1114 and forms a laser resonator with the mirror M3). The acousto-optic element UM3 constitutes an acousto-optic means, and the rod lens RL3. RL4 and the optical fiber I31 constitute optical means.

Top 1. The operation of the device configured as shown in C will now be described.

The light emitted from the non-reflection coating part 11 of the semiconductor laser 1-Dl becomes parallel light by the lens RL1, and is reflected by the mirror coding part M3. The reflected light from the mirror coating part M3 returns to the original optical path and enters the semiconductor laser LD again.
1. Light with a frequency f emitted from the anti-reflection coating portion 12 is converted into parallel light by the lens RL2, and enters the acousto-optic element UM3 rAff. In a Raman Nass type acousto-optic element, high-order diffraction occurs simultaneously on both sides of the incident light direction. The +1st-order diffracted light whose frequency has been Doppler-shifted by 10F enters the rod lens R1-3, propagates through the optical fiber FB1, and returns from the rod lens RL4 to the acousto-optic cable LJ.
After entering M3, the frequency is shifted by -F Doppler and returns to the original frequency fo"r" optical amplification section LD1. Similarly, the first-order diffracted light whose frequency has been Doppler-shifted by -F enters the rod lens RL4, propagates through the optical fiber FB1, and returns from the rod lens Ri-3 to the acousto-optic cable UM.
3, the frequency is Doppler shifted by 10F and returns to the original frequency of 1゛o. As a result of the above, the influence of the Doppler shift is canceled out, and the oscillating state of the frequency f continues stably. As in the case of FIG. 1, the resonant frequency f can be adjusted by changing the ultrasonic frequency F. can be changed.

The variable wavelength laser light source having such a configuration has the same features as the first embodiment.

In the above embodiment, the Doppler shift caused by the +1st-order diffracted light and the 11th-order diffracted light that occurs in the Raman-Nath type optical element is canceled out, but this is not limited to this, and diffracted light of any order with the opposite sign can be used. You may.

Further, in the above embodiment, a mirror coach ink may be applied to the left end surface of the optical amplification section LD1, and in this case, the rod lens RL 1 J5 and the mirror M3 can be made unnecessary.

Further, the optical means may be constructed by combining a mirror instead of a rod lens and a fiber.

Further, although each of the above embodiments is constructed using individual elements, a monolithic construction can be easily achieved by using diffraction of light in a guiding waveguide using an optical waveguide or a surface acoustic wave.

(Effects of the Invention) As described above, according to the present invention, it is possible to realize a tunable wavelength laser light source that has good response, is resistant to changes over time, and has a narrow oscillation spectrum width with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing one embodiment of the present invention, and FIG.
Figure 1 is an operation explanatory diagram for explaining the operation of the device, Figure 3 is a block diagram showing a second embodiment of the present invention, and Figures 4 and 5 are diagrams showing a conventional tunable wavelength laser light source. Hara yJ for showing! It is an explanatory diagram. LDl... optical amplification section, UMl, UM2. UM3...
Acousto-optic means, M2. RL3. RL4. FBI...optical means.

Claims (3)

[Claims] (1) An acousto-optic means into which light related to the output light of the optical amplification section enters into a laser resonator, and an acousto-optic means into which light emitted from the acousto-optic means enters and returns it to the acousto-optic means; A variable wavelength laser light source characterized in that the means is configured to diffract light multiple times to cancel out the influence of Doppler shift caused by the diffraction. (2) The tunable wavelength laser light source according to claim 1, wherein the acousto-optic means is constituted by a plurality of acousto-optic elements, and the optical means is constituted by a mirror. (3) A tunable wavelength laser light source according to claim 1, wherein diffracted lights of opposite signs generated by an acousto-optic means are connected by an optical means.