JPS62252982A - Variable wavelength light source - Google Patents

Abstract

PURPOSE:To know oscillating wavelengths over a wide band, by marking the wavelength of the output light of a variable wavelength laser light source by the output light, which is generated by a marker light source at a specified wavelength interval. CONSTITUTION:Part of output light from a variable wavelength laser light source 11 is transmitted through a half mirror 14 and becomes the output light. The other part is reflected and inputted to a half mirror 15. The light is interfered with output light from a marker light source 12 after said output light is transmitted through the half mirror 15. The resultant light is inputted to a light detector 17. The light detector 17 converts the light into an electric signal, which has the difference frequency between both light beams. A part of the electric output from the light detector 17 passes the bandpass characteristic part of a filter 18. Variable wavelength laser light (a) and merker light (b) are displayed on an electric spectrum analyzer 21. The other part of the light, which is transmitted through the half mirror 15, is interfered with output light of a reference light source 13. Said output light is tranmitted through a half mirror 16. The resultant light is inputted to a light detector 19. The variable wavelength laser light (a) and reference light (c) are displayed on an electric spectrum analyzer 22 through a filter 20.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in the characteristics and functionality of tunable wavelength laser light sources.

(Prior Art) FIG. 10 is a block diagram showing an example of a conventional variable wavelength light source. The output light of the semiconductor laser LDI enters the diffraction grating DG via the condenser lens LS2, and becomes the first-order diffracted light P1.
returns to the semiconductor laser LD1. Pl is the 0th order diffracted light. When the diffraction grating DG is rotated, the wavelength of the first-order diffracted light that returns to the semiconductor laser LDI changes, so the oscillation wavelength can be controlled. For output to the outside, the output light from the other end of the semiconductor laser LD1 is taken out via the lens LS1.

(Problem to be Solved by the Invention) However, in a tunable wavelength light source with such a configuration, when trying to correlate the rotation angle of the diffraction grating with the wavelength of the output light, it is difficult to use a reference light source with a clear wavelength such as a He Ne laser. There was a problem that only one or a few points could be calibrated using the .

The relationship between the diffraction angle θ and the wavelength λ is λ−ksinθ (1) (k is a proportionality constant). That is, since there is no proportional relationship between the rotation angle and the wavelength, there is a problem in that the error is small near the calibration point, but becomes large at a distance.

The present invention was made to solve these problems, and therefore, it is an object of the present invention to provide a tunable wavelength light source whose oscillation wavelength can be accurately determined over a wide band.

(Means for Solving the Problems) A tunable wavelength light source according to the present invention includes a tunable wavelength laser light source whose output light wavelength changes in response to an input signal, and a marker light source that outputs multimode oscillation laser light. The present invention is characterized in that the wavelength of the output light of the variable wavelength laser light source is scaled by the output light generated at predetermined wavelength intervals of the marker light source.

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

FIG. 1 is a block diagram showing an embodiment of a variable wavelength light source according to the present invention. In the variable wavelength light source 1, 11 is a variable wavelength laser light source that outputs light of a wavelength corresponding to an input signal, and 12 is an optical frequency marker light IT! that outputs marker light at constant wavelength intervals. (hereinafter referred to as a marker light source), 13 is a reference wavelength laser light source (hereinafter referred to as reference light source) that outputs light with a constant wavelength, and 14 is an input light output from the variable wavelength laser light source 11 and separates it into two directions. A half mirror 115 receives the reflected light from this half mirror 14 and the marker light source 1.
A half mirror 116 receives the output light from the half mirror 15 and a half mirror 117 receives the output light from the reference light source 13. The half mirror 117 includes a PIN photodiode, an avalanche photodiode, etc. A photodetector 18 inputs the light and the transmitted light, a bandpass amplifier 18 inputs the electrical output of the photodetector 17, and one photodetector similar to 17 inputs the reflected light and transmitted light of the half mirror 16. 20 is a bandpass amplifier that inputs the electrical output of this photodetector 19. In the signal processing section 2, reference numerals 2'1 and 22 denote electrical spectrum analyzers to which the outputs of the bandpass amplifiers 18 and 20 are respectively input.

The operation of the variable wavelength light source configured as described above will be explained below. A part of the output light from the variable wavelength laser light source 11 passes through the half mirror 14 and becomes output light, and the other part is reflected and enters the half mirror 15.

A portion of this light is reflected by the half mirror 15, interferes with the output light of the marker light source 12 that has passed through the half mirror 15, and enters the photodetector 17. The photodetector 17 uses heterodyne detection to convert the two lights into an electrical signal having a difference in frequency. Part of the electrical output of the photodetector al 117 passes through the bandpass characteristic of the filter 18, and the electrical spectrum analyzer 21 displays the variable wavelength laser beam a and the marker beam.

The other part of the light (light from the variable wavelength light source) that has passed through the half mirror 15 is reflected by the half mirror 16, interferes with the output light of the reference light source 13 that passes through the half mirror 16, and enters the photodetector 19. do. The photodetector 19 uses heterodyne detection to convert both lights into an electrical signal having a difference in frequency.

A part of the electrical output of the photodetector 19 passes through the bandpass characteristic of the filter 20 and is output to the electrical spectrum analyzer 22.
The variable wavelength laser beam a and the reference beam C are displayed.

The frequency interval of the marker light and the frequency interval between the marker light and the variable wavelength light can be accurately known from the display screen of the electric spectrum analyzer 21, and the frequency interval of the variable wavelength light can be determined from the relationship with the reference light on the display screen of the electric spectrum analyzer 22. You can know the frequency accurately. For example, if the beat signal is O on the display screen of the electrical spectrum analyzer 22,
Hz, the wavelength of the variable wavelength laser and the wavelength of the reference wavelength laser are equal.

In the apparatus shown in FIG. 1, the variable wavelength laser light source 11 is one that changes the wavelength by changing the injected current of a semiconductor laser. A grating that changes the wavelength by changing its rotation angle, and various other types can be used.

FIG. 2 is a block diagram showing an embodiment of the variable wavelength laser light source 11. As shown in FIG. In the figure, LD2 is a semiconductor laser,
ARI and AR2 are anti-reflection coated parts provided at both ends of this semiconductor laser LD2, and LS3 is this anti-reflection coated part △
A lens that converts the light emitted from R1 into parallel light, BSl is a beam splitter that reflects the light that has passed through this lens LS3 and outputs the resonant light to the outside, and LS4 converts the light that is emitted from anti-reflection coating AR2. A lens for parallelizing light, UMl is the first ultrasonic modulator into which the light passing through this lens LS4 is incident, and UM2 is this ultrasonic modulator UMI.
Ml is a mirror that reflects the light emitted from the ultrasonic modulator UM2, and DRl is a second ultrasonic modulator into which the output light from the ultrasonic modulator UM1 is incident. UM2 to frequency F
It is an oscillator that is excited by The light emitted from the non-reflection coated portion ΔR1 of the semiconductor laser LD2 is reflected by the simulated beam splitter BS1 which is converted into parallel light by the lens LS3, and the reflected light returns along the optical path and enters the semiconductor laser LD2 again. Frequency fo+ emitted from anti-reflection coating part AR2
The light is made into parallel light by the lens LS4, and is incident on the first ultrasonic modulator UM1.

The wavelength of light that satisfies specific incident and exit angles with respect to a diffraction grating formed by ultrasonic waves changes as the wavelength of the ultrasonic waves changes. The incident light undergoes a Doppler shift due to the ultrasonic wave during diffraction, and the frequency of the +1st order diffracted light (the direction of the ultrasonic wave is the same as the diffracted direction) becomes fo++F.

The light emitted from the ultrasonic modulator tJM1 is the ultrasonic modulator UM.
It is diffracted again at 2. In the ultrasonic modulator 1@UM2, the relationship between the ultrasonic traveling wave and the diffracted light is opposite to that in the ultrasonic modulator UMI, and it becomes -1st order diffracted light, so the Doppler shift amount is -F, and the relationship between the ultrasonic traveling wave and the diffracted light is opposite to that in the ultrasonic modulator UMI. The frequency of the output light is f
or + FF-for. Ultrasonic modulator U
After the output light of M2 is reflected by the mirror M1, it undergoes a Doppler shift by the ultrasonic modulator UM2, and the frequency becomes fo + F.
After that, the ultrasonic modulator tJM1 converts fo + F+
The frequency becomes F-fo+ and returns to the original frequency fo+ to the semiconductor laser LD2, so that the resonance state continues. By changing the wavelength (frequency F) of the ultrasonic wave in such a configuration, it is possible to sweep the wavelength of light that is in common. The resonant light is output to the outside via the beam splitter BS1.

FIG. 3 is a block diagram showing a second embodiment of the variable wavelength laser light source 11. In FIG. The same parts as in FIG. 2 are given the same symbols and their explanations will be omitted. BS2 is a beam splitter, Eol, that separates the light emitted from lens LS4 into two directions.
is an electro-optical element that receives the light transmitted through this beam splitter 882, 1 is a signal source that controls this electro-optic element EO1, Ml is a mirror that reflects the light emitted from the electro-optic element EO1, and EO2 is the beam An electro-optical element receives the light reflected by the splitter 882, M2 is a mirror that reflects the light emitted from the electro-optical element EO2, and 2 is a signal source that controls the electro-optical element EO2. The quality of the optical path direction of electro-optical elements EO1 and EO2 is Q＋＊Q, respectively.
2, refractive index nl+02, beam splitter 881. Let the distance excluding ρ along the optical path between Ml +
Beam splitter 381. If we take the distance along the optical path between M2 excluding Q2 and 2%q to be the number of m, then the oscillation frequency fO□ of this ringing is fo 2-Q -C/21 (L+ +n+
(V+)ffi+ >(L2 +n2
(V2) R2) l -<2). That is, the oscillation frequency fo2 can be swept over a wide range by changing the 1il field strength of the electro-optical element EOI or EO2 using the signal source 1 or 2 to change the refractive index n1 or n2.

FIG. 4 is a block diagram showing an embodiment of the marker light source 12 of the apparatus shown in FIG. In the marker light source 12a, L
D3 is a semiconductor laser whose both ends are AR co-coated (non-reflective coating), LS5 and LS6 are collimator lenses that convert the output light of this semiconductor laser LD3 into parallel light, and HMl and 8M2 are lenses LS5. LS6
The semi-transmissive mirror A forming the external resonator on the outside of the semi-transmissive mirror LS6 is an attenuator through which the light output from the semi-transmissive mirror LS6 passes. The output light that has passed through the semi-transparent mirror 1-I M 1 is condensed by a lens LS7, and is converted into an APD (Aval
It is detected by a photodetector PD1 consisting of an anche photodiode. The output electrical signal of the photodetector PD1 is amplified by the amplifier A1 and then sent to the spectrum analyzer SA.
The waveform is monitored.

The operation of the apparatus shown in FIG. 4 will be explained below. semiconductor laser LD
The spontaneous emission light gain curve of the output light of No. 3 is shown by the dotted line d in Fig. 5.
become that way. The light output from both end faces of the semiconductor laser LD3 is passed through the lens LS5. Each becomes parallel light at LS6, and resonates between the semi-transmissive mirrors 1-:Ml and 8M2. The resonator length (distance 11t of semi-transparent mirrors HM1 and HM2) is 1
If 1 light speed is 01 and refractive index is n, then the Fries vector range of the external resonator is determined by C/2 n L, and as shown by the dotted line e in FIG. 3, Q increases every C/2111.

As a result, the marker output light output from the attenuator 8T becomes as shown by the solid line f in FIG. 5 (multimode oscillation). The wavelength interval λχ of the marker output light is the electronus vector analyzer) J
'SA can be accurately read as the frequency interval νχ. By changing the resonator length, the wavelength interval λ of the marker output can be changed.
χ can be changed.

For example, when L-10 mm, the frequency interval νχ is χ=c
/2m-15GHz. Furthermore, if necessary, an external resonator can be placed in a thermostatic oven or the like to maintain a stable frequency interval.

FIG. 6 is a block diagram showing one embodiment of the reference wavelength laser light source 13. As shown in FIG. In the figure, LD4 is a semiconductor laser, BS3 is a beam splitter into which the output light of this semiconductor laser LD4 enters, and CLI is this beam splitter BS.
an absorption cell filled with a standard substance that receives the reflected light from step 3;
PD2 is a light receiving element into which the output light of this absorption cell CL1 is incident, LΔ1 is a lock-in amplifier that inputs the electrical output of this light receiving element PD2 and controls the current of the semiconductor laser LD4 with the corresponding output. The semiconductor laser L
This is an oscillator that frequency modulates the current of D4 and supplies the phase detection frequency of the lock-in amplifier LA1.

The transmitted light of the beam splitter BS3 becomes the output light of this reference wavelength laser light source. Standard materials include Cs, Rb, and N.
Any substance such as H3 or H2O can be used.

The output light of the semiconductor laser LD4 is sent to the beam splitter BS3.
It is reflected by the absorption cell CLI and enters the absorption cell CLI.
absorbance by the standard substance of 1.

The absorption wave is detected by the light receiving element PD2, and the lock-in amplifier L
The current is fed back to the semiconductor laser LD4 via A1. Since the output wavelength of the semiconductor laser LD4 is locked to the absorption spectrum line of the standard material, a highly stable and highly accurate reference wavelength light source can be realized.

The method used in the device shown in Figure 6 is called the linear absorption method, which produces a relatively thick absorption spectrum due to the Doppler shift. Frequency stabilization of semiconductor lasers, IEICE Technical Report 0QE82-116) detects absorption lines in the ultrafine structure hidden by Doppler shift, and locks the oscillation wavelength of D4 with a semiconductor laser to achieve even higher stability. be able to.

In addition, as the reference light source in FIG. 1, a laser with a known wavelength, such as a He Ne laser, can be used.

According to the variable wavelength light source with such a configuration, by adding a marker light source and a reference light source to the variable wavelength laser light source,
The oscillation wavelength of the tunable laser can be accurately determined over a wide range.

Furthermore, by using an electrical spectrum analyzer, the oscillation wavelength can be determined as a frequency with high precision and high resolution.

Although the above embodiment uses an electric spectrum analyzer, it is also possible to approximate the variable wavelength using an optical spectrum analyzer as described below. i
FIG. 17 is an explanatory diagram showing a display screen when each output light of the variable wavelength laser light source, marker light source, and reference wavelength light source of the apparatus shown in FIG. 1 is observed by an optical spectrum analyzer.

In the figure, the wavelength AO of the reference light 9 and the wavelength interval λ3 of the marker light are accurately known in advance. The lengths V2 and V3 of each part corresponding to the position of the reference light on the display screen, and the length y of each part corresponding to the position of the variable wavelength light.

Using y4, the wavelength λχ of the variable wavelength light can be approximately calculated as follows.

λe-λ, +22. +22+λ0 1λ3V3/V2+2λ3 +λko V4/V! +λ.

=23 (Yko /V2 +2+'/4 /V+
) +λ.・
(3) FIG. 8 is a block diagram showing another example of the structure of the marker light source 12 of the apparatus shown in FIG. 1. Marker light @12b
LS7 and LS8 are rod lenses that convert the output light of the semiconductor laser LD4 into parallel lights, M3 is a mirror provided at one end of the rod lens LS7, and EO3 is an electro-optic crystal that receives the output light of the rod lens LS8.
3 is a control signal source connected to the electrode of the electro-optic crystal E3, and HM3 is a semi-transparent mirror that reflects the output light of the electro-optic crystal EO3.

In the device with the above configuration, the mirror M3 and the semi-transparent mirror HM3 constitute a resonator on both sides of the semiconductor laser LD4, and the co-optical length thereof changes equivalently when the refractive index of the electro-optic crystal Eo3 changes depending on the applied voltage. Therefore, the wavelength interval of the marker output light can be easily changed by the output of the control signal source v3.

Note that a single semiconductor laser that oscillates in multiple modes may be used as the marker light source 12 of the apparatus shown in FIG.

In this case, the wavelength interval of the markers can be changed by changing the temperature and current of the semiconductor laser.

Further, in the apparatus shown in FIG. 1, each part is synthesized in real time using a half mirror, but the display is not limited to this, and display may be performed by switching in a time-sharing manner using a switch or the like.

FIG. 9 is a block diagram showing a coherent optical spectrum analyzer which is an example of application of the variable wavelength light source according to the present invention. The same parts as those in the apparatus shown in FIG. 1 are given the same symbols and the explanation will be omitted. 1a is a variable wavelength light source; 31 is a half mirror 132, which receives output light from the variable wavelength light source 1a from one side and enters the light to be measured from the other; a PIN photodiode, an avalanche photodiode, etc., and the output of the half mirror 31; 33 is a filter circuit which has a bandpass characteristic and inputs the electrical output of the photodetector 32; 34 is an amplifier which inputs the output of this filter circuit 33; A signal processing/display unit 36 into which the output of the amplifier 34 is input is a sweep signal source that controls the sweeping of the signal processing/display unit 35 and the variable wavelength laser light source 11 of the variable wavelength light source 1a.

The operation of the optical spectrum analyzer configured as described above will be explained next. The variable wavelength light source 1a includes a variable wavelength laser light source 11 whose wavelength is controlled by a sweep signal source 36. The output lights of the marker light source 12 and the reference light af13 are combined by the half mirrors 14, 15 and 16, and then enter the half mirror 31 from the half mirror 14. The light to be measured is combined with the output light of the variable wavelength light source 1a by the half mirror 31, and converted by the photodetector 32 into an electrical signal having a frequency that is the difference between the image frequencies. A part of the electrical output of the photodetector 32 passes through the bandpass characteristic of the filter circuit 33 and is transmitted to the amplifier 3.
4 is taken out as power.

The signal processing/display unit 35 inputs the control signal from the sweep signal source 36 as a frequency axis signal, inputs the electrical output of the amplification unit 34 as a power signal, and converts the measured light j, the reference light, and the marker light 1 into spectra. indicate.

Note that in the above application example, a bandpass filter is used as the filter circuit 33, but the present invention is not limited to this, and a lowpass filter may be used.

According to the above application example, the reference light and marker light are displayed (or recorded) along with the measurement data, so the wavelength can be easily found by counting the number of intervals between marker lights from the wavelength of the reference light and performing interpolation. be able to.

(Effects of the Invention) As described above, according to the present invention, a variable wavelength light source whose oscillation wavelength can be accurately determined over a wide band can be realized with a simple configuration.

Further, since precision is not required in the relationship between the input signal of the tunable wavelength laser light source and the oscillation wavelength, the configuration of the tunable wavelength laser light source is simple.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing one embodiment of a variable wavelength light source according to the present invention, FIGS. 2 to 4, and FIG. 6 are partial configuration block diagrams for explaining a part of the device shown in FIG. Fig. 5 is a characteristic curve diagram for explaining the operation of the device shown in Fig. 4;
1 is a characteristic curve diagram for explaining the operation of the device, FIG. 8 is a block diagram showing another configuration example of a part of the device in FIG. 1, and FIG. 9 is a variable wavelength according to the present invention. FIG. 10 is a block diagram showing a conventional variable wavelength light source. 1.1a... variable wavelength light source, 11.11a, 11b-
... Variable wavelength laser light source, 12.12a, 12b...
Marker light source, λ3...Wavelength interval, 13.13a...
Reference wavelength laser light source. Figure 3 Figure 4 Figure q

Claims (6)

[Claims] (1) Equipped with a tunable wavelength laser light source whose output light wavelength changes in response to an input signal and a marker light source that outputs multimode oscillation laser light, the wavelength of the output light of the tunable wavelength laser light source is set to a predetermined wavelength of the marker light source. A variable wavelength light source characterized in that it is configured to be graduated with output light generated at wavelength intervals of . (2) A tunable wavelength light source according to claim 1, wherein the marker light source is constructed by combining a semiconductor laser and an external resonator. (3) The variable wavelength light source according to claim 2, wherein the wavelength interval of the marker light source output is changed by changing the external resonator length. (4) The tunable wavelength light source according to claim 2, which is configured to electrically change the equivalent resonator length by inserting an electro-optical element into the external resonator. (5) The tunable wavelength light source according to claim 1, further comprising a reference wavelength laser light source that generates an optical output of a constant wavelength within the output band of the tunable wavelength laser light source. (6) By interfering the variable wavelength laser light source output with the marker light source output and the reference wavelength laser light source output, performing heterodyne detection and passing through a band pass filter, a variable optical electrical signal, a marker electrical signal, and a reference electrical signal are obtained. A tunable wavelength light source according to claim 5, which is constructed as follows.