JPS62198723A - Variable wavelength light source - Google Patents

Abstract

PURPOSE:To make wavelength measurement with high accuracy over a wide band by providing a wavelength selector which is inputted with the output light of a variable wavelength laser light source and generates light output at prescribed wavelength intervals. CONSTITUTION:A resonator FP1 consists of a Fabry-Perot etalon to be inputted with the transmitted light of a beam splitter BS1 to constitute the wavelength selector. The variable wavelength laser light source 2 generates the output light of the wavelength corresponding to a signal Ei and part thereof is reflected by a splitter BS1 form variable wavelength output light Rv. The other part transmits the splitter and is inputted to the resonator EP1. The resonator EP 1 changes the equiv. resonator intervals by the effect of an electrooptic element EO1 existing on the optical path. The output light Rm of the resonator FP1, therefore, has the peak value at the wavelength intervals corresponding to the output of the signal source E1. The photodetector PD1 of the resonator EP1 converts the output light Rm to an electric signal and outputs a marker signal Em from a terminal 3.

Description

Detailed Description of the Invention 3. AT of the Invention (Industrial Field of Application) The present invention relates to improvements in a variable wavelength light source that is used in optical spectrum analyzers and the like to enable precise wavelength measurement. .

(Prior Art) Conventionally, when measuring wavelength characteristics or spectral characteristics using an optical spectrum analyzer, a spectrometer, or the like, a light source that serves as a wavelength reference is required to increase the precision.

(Problems to be Solved by the Invention) However, there is a drawback that the error increases when measuring a band far from the wavelength of the reference wavelength light source.

In addition, if a variable wavelength light source is used as the male wavelength light source,
Although the wavelength range can be wide, it is not easy to accurately match the input and oscillation wavelength of the tunable wavelength light source.

The present invention was made to solve these problems, and an object of the present invention is to realize a variable wavelength light source that enables highly accurate wavelength measurement 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 tunable wavelength laser light source that inputs the output light of the tunable wavelength laser light source and generates a predetermined signal. a resonator that generates an optical output having peaks at wavelength intervals; and a base 1 that generates an optical output of a constant wavelength within the output horn band of the variable wavelength laser light source.
It is characterized by being equipped with a long-lenah light source.

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

FIG. 1 is a conjunctive block diagram showing an embodiment of a variable wavelength light source according to the present invention. J3 is in the variable wavelength light source 10, and 1
is an input terminal to which an input electric signal (No. 13) Et for controlling the wavelength is added, 2 is a variable wavelength laser light source to which the electrical signal Ei is input via this input terminal 1, and BS1 is an input terminal for the output light of this variable wavelength laser light source 2. A beam splitter that enters the beam and separates it into two directions, FPl is a resonator consisting of a Fabry-Bello etalon that inputs the transmitted light of this beam splitter BS1, and constitutes a wavelength selection device. An electro-optical element provided on the optical axis, El is a signal source that drives this electro-optical element EOI, PDI is a light receiving element that roughly divides the output light of the resonator FP1 and converts it into an electrical signal, 4 is a constant wavelength This is a highly stable and highly accurate reference wavelength laser light source that generates an output light of .

The operation of the variable wavelength light source configured as described above will be explained next. A variable wavelength laser light source 2 is applied via the input terminal 1 (
The output light with a wavelength corresponding to No. Fj "1" is JIE. A part of this output light is reflected by the beam splitter BS1 and becomes the variable wavelength output light Rυ, and the other part is transmitted and enters the resonator FPI. The equivalent resonator spacing can be changed by the action of the electro-optical element EO1 present on the optical path of the resonator Pll. Therefore, the output light RWL of the resonator FP1 is equal to the output (voltage) of the signal source E1. The light receiving element PCI has a peak value at a wavelength interval corresponding to the output light R.
m is converted into an electric signal and a marker signal @E electric signal is output from terminal 3. FIG. 2 is a spectrum chart showing this marker signal Ex in the frequency domain. The reference wavelength laser light source 4 generates output light R6 of a constant wavelength within the output band of the variable wavelength laser light source 2.

In the apparatus shown in FIG. 1, the variable wavelength light source 2 is one that changes the wavelength by changing the injection current or temperature of a semiconductor laser;
It is possible to use a diffraction grating that uses one mirror of the external resonator and change the wavelength by changing the rotation angle, or other types of various types.

FIG. 3 is a block diagram showing an embodiment of the variable wavelength laser beam source 2. As shown in FIG. In the figure, LDl should be a conductor laser,
a and b are anti-reflection coating parts provided at both ends of this semiconductor laser LD1, LSI is a lens that converts the light emitted from this anti-reflection coating part a into parallel light, and BS2 is this lens 1.
LS2 is a lens that converts the light emitted from the non-reflective core into parallel light, and LIMI is the light that passes through this lens LS2. UM2 is a second ultrasonic modulator into which the output light from the ultrasonic modulator ii1iUM1 is incident, Ml is a mirror that reflects the light emitted from the ultrasonic modulator LJM2, D
I (1 is the ultrasonic modulation: brown UMI.

This is an oscillator that excites UM2 at frequency F. The light emitted from the non-reflection coating part a of the semiconductor laser LDI is transmitted through the lens 1.
After being converted into parallel light at 81, it is reflected at a beam splitter 882, and the reflected light returns to the original optical path and enters the semiconductor laser LD again.
1. Frequency f emitted from the non-reflection coating part
The oI light is made into parallel light by the lens L S 2 and enters the first ultrasonic modulator UM1. The nine wavelengths that satisfy specific incident and exit angles for the diffraction grating produced by the ultrasound vary as the wavelength of the ultrasound 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 for +F. Ultrasonic modulator UM
The emitted light from 1 is diffracted again by the ultrasonic modulator UM2.

In the ultrasonic 'a' modulator LJM2, the relationship between the ultrasonic traveling wave and the diffracted light is opposite to the JJi combination in the ultrasonic modulator UM1.
-Since it is the first-order diffracted light, Dopplash I-ffl is -
F, and the frequency of the output light of ultrasonic modulation nuM2 is ".

, +F−F==f. It becomes l. The output light of the ultrasonic modulator UM2 is reflected by the mirror M1, and then undergoes a Doppler shift in the ultrasonic modulator UM2, so that the frequency becomes foIF, and then the ultrasonic modulator allLJM1 converts it into f'or −F+F−.
for r, and returns to the original frequency f'o+ to the semiconductor laser 'J'LD1, 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 the resonant light. The resonant light is output to the outside via the beam splitter BS2.

FIG. 4 is a block diagram showing a second embodiment of the variable wavelength laser light source 2. In FIG. The same parts as in FIG. 3 are given the same symbols and their explanation will be omitted. BS3 is a beam splitter that separates the light emitted from the lens LS2 into two directions, EO2 is an electro-optical element that receives the light transmitted through this beam splitter 883, and vl is a signal source that controls this electro-optical element EO2, Ml is a mirror that reflects the light emitted from the electro-optical element EO2, and EO3 is the beam splitter BS3.
M2 is a mirror that reflects the light emitted from the electro-optical element EO3, and v2 is a signal source that controls the electro-optical element EO3. The lengths of electro-optical elements EO2 and EO3 in the optical path direction are each Q+
+92, refractive index nI r n2 , beam splitter 1382. The distance e along the optical path between Ml, excluding e, is l-1, and the beam splitter 882. vF′! When distance is L2 and Q is an integer, the oscillation frequency Co2 in this case is f'o2 = q-c/21 (I-+
lln+ (V+ >R+)-
(L2 +nz (V2) 9
2) It becomes l. In other words, the electric field strength 1 of the electro-optical element EO2 or EO3 is increased by the signal source 1 or v2.
By changing the refractive index n or n2, the oscillation frequency f02 can be subtracted by 1 over a wide range.

FIG. 5 is a block diagram showing one embodiment of the reference wavelength laser light source 4. As shown in FIG. In the figure, LD2 is a semiconductor laser,
884 is a beam splitter into which the output light of this semiconductor laser LD2 enters, and CLl is this beam splitter B.
An absorption cell sealed with a standard substance into which the reflected light of S4 enters; PO2 is a light receiving element into which the output light of this absorption cell CL1 enters; 1. ,, A1 inputs the electric output of this light receiving element PD2 and outputs the semiconductor laser D with the corresponding output.
A lock-in amplifier DR2 that controls the current of the semiconductor laser LD2 is an oscillator that frequency-modulates the current of the semiconductor laser LD2 and supplies a phase detection frequency of the lock-in amplifier LAI. The transmitted light of the beam splitter 13S4 becomes the output light of this reference wavelength Rade light source. Standard substances include Cs, Rb, NH3, I-! Any material such as 20 can be used.

The output light of the semiconductor laser LD2 is sent to the beam splitter 834.
It is reflected by IJ'JL and enters the absorption cell CLI, where it is absorbed by the standard substance in the absorption cell CL1.

The amount of absorption is detected by the light receiving element PD2, and the lock-in amplifier L
The current is fed back to the semiconductor radar 1-D2 via Δ1.

Since the output wavelength of the semiconductor laser LD2 is locked to the absorption spectrum line of the standard material, a highly stable and highly accurate reference wavelength light source can be realized.

In the embodiment shown in FIG. 1 above, Fabry-Perot
If the spacing between the resonators of the etalon can be freely changed, the electro-optical element EOI is not necessary.

Also, as the resonator FP1, a Michelson interference "1" as shown in FIG. 6 may be used instead of the 77-noble bellow etalon. In the figure, the light incident from the Rade light source LD3 is separated into two directions by the beam splitter 884. The light reflected by the beam splitter BS4 and the light transmitted through the beam splitter BS4, which is reflected by the mirror M3 and then reflected by the beam splitter BS4 and the mirror 4, interfere with the light transmitted through the beam splitter [3S4.This result Output light having peaks at regular wavelength intervals can be generated.

In addition, the fifth light source shown as an embodiment of the reference wavelength Rade light source 4
The method shown in the figure is called the linear absorption method, and the absorption spectrum becomes relatively thick due to the Doppler shift.
Kaida, Kitano, Yabusaki, Koyo: Frequency stabilization of semiconductor lasers using saturation single-spectrum spectroscopy, IEICE Technical Report 0QE82-11
6>, by detecting the absorption line of the ultrafine structure hidden by the Doppler shift, and locking the oscillation wavelength of the semiconductor laser LD2 to this, it is possible to achieve a high degree of stability.

FIG. 7 is a block diagram illustrating a modification of the apparatus shown in FIG. 1. The same parts as in FIG. 1 are given the same symbols and the explanation is omitted. BS5 is a beam splitter that is provided in the output optical path of the reference wavelength laser light source 4 and makes the reflected light enter the beam splitter 881, 1-△2 is a lock-in amplifier that inputs the output of the photodetector PD1, and E2 is a lock-in amplifier of this lock-in amplifier. This is a bias signal source that is applied to the electro-optical element EO1 in combination with the output. A part of the output light from the reference wavelength laser light source 4 is reflected by the beam splitter BS5 and enters the resonator F P 1 via the beam splitter 881. The marker light and the reference wavelength can be matched by controlling the distance between the resonances of the resonator Fl)1 so that the reference wavelength component is maximized in the feedback loop including the lock-in amplifier LA2. .

FIG. 8 is a configuration block diagram showing an optical spectrum analyzer which is an application example of the variable wavelength light source according to the present invention.

Band-shaped arrows indicate the flow of optical signals, and solid arrows indicate the flow of electrical signals. Reference numeral 11 denotes a light control section using a pneumatic effect crystal (YIG, lead glass, etc.) into which the light to be measured is incident, 12 a light amplification section into which the output light of the polarization control section 11 is input; 1 is a suspension signal generator; Wavelength light Rs and variable wavelength) Hi1
The half mirror 1l-IMI which synthesizes 15 is an optical heterodyne detection section which inputs the output light of M1, 15 is a filter section which inputs and amplifies the electric power of the optical heterodyne detection section 14 and has a bandpass characteristic, and 16 is a filter section which has a bandpass characteristic. A detection section 17 receives the electrical output of the filter section 15, and a signal processing/display section 17 receives the electrical output of the detection section 16. The optical amplifying section 12 is G
aA I As laser (780nm band) and 1uGa
It is composed of an AsP laser (1500 nm band), and the following three types can be used.

(a) This is called a resonator type semiconductor laser amplifier, which performs linear optical amplification through stimulated emission by passing a bias current near the oscillation threshold and inputting signal light into a laser diode.

([1) Optical injection-locked amplifier, which controls the optical frequency a and phase of the oscillated light by inputting signal light into the emitting laser diode.

(c) This is called a traveling wave laser amplifier, and it amplifies light only by passing signal light through non-reflective two-pieces on both end faces of a laser diode chip.

The operation of the optical spectrum 1-ram 7-narrow zoomer configured as described above will be explained in detail below. When the measured light of frequency ω is incident on the polarization control unit 11, the polarization plane of the incident light is changed to the output light of the half mirror 1-1M2 by controlling the applied magnetic field using the optical rotation of the magneto-optic effect crystal. The light output from the polarization control unit 11 is amplified by the optical amplification unit 12, and then combined with the output light at the frequency ω of the variable wavelength light source 10 by the half mirror 1”Ml, and the light output from the polarization control unit 11 is The optical heterodyne detection section 14 converts the image frequency difference into an electrical signal having a frequency of ω0 - ω1' (in this case, ω,' - ω,). A part of the characteristic passes through and is extracted as power by the detection section 16.The signal processing/display section 17 inputs the signal related to The subtraction from the h3 subtraction signal generator 13 as a frequency axis signal, and outputs the signal to the detection section 16. The electrical output is input as a power signal to display the spectrum of the light to be measured 18 and the reference light 19, and the power signal output from the variable wavelength light IfA 10 is input to display the marker 20.

An example of optical frequency operation in this application example is shown below.

Wavelength of reference wavelength light Rs: 780 nm (tuning the wavelength of the laser diode to the absorption line of Rb) Variable wavelength light R
o wave 1: 780nm + 50nm ω1 wavelength: 78
0nm±5Qnm In FIG. 8, a pulse synchronization signal is applied to the insertion signal generator 13 in order to show the case where pulsed light is used as the light to be measured and its spectrum is measured. A bird synchronized with the pulsed light to be measured inputs a signal to the sweep signal generator 13, and in synchronization with this, the frequency of the variable wavelength light Rυ of the variable wavelength light source 10 is swept in steps. At the same time, a signal corresponding to the step frequency is sent to the communication/display section 17. As a result, the power spectrum of one frequency point is measured for each pulsed light, and after sweeping, the entire spectrum of the pulsed light can be output.

According to the configuration described in the embodiment shown in FIG. 8, the frequency resolution of the optical spectrum analyzer is as follows:
The spectral width of the variable wavelength output light Rυ and the filter section 15
determined by the bandwidth of The spectral width of the variable wavelength output Rυ is determined by the variable wavelength laser light source 2.
By using an external cavity laser diode such as the one shown in FIG.

Note that in the above application example, a bandpass filter is used as the filter section 15, but the present invention is not limited to this, and a lowpass filter may be used.

FIG. 9 shows a second application example of the variable wavelength light source according to the present invention,
FIG. 2 is a block diagram showing the configuration of a conventional optical spectrum analyzer (or spectrometer, hereinafter the same) used as a light source.The marker light output Rm of the variable wavelength light source 10 is reflected by a mirror M3 and becomes the reference wavelength light output Rs. 5 by beam splitter BS6, beam splitter 887
The optical spectrum analyzer 2 is added to the light to be measured.
Enter 1. The moonlight signal from the optical spectrum analyzer 21 becomes the wavelength variable power E of the variable wavelength light source 10. With such a configuration, the light to be measured 22.
The spectra of the reference light 23 and marker light 24 appear.

FIG. 10 is a configuration block diagram showing an optical network analyzer which is a third application example of the variable wavelength light source according to the present invention. The variable wavelength output light Rυ of the variable wavelength light source 10 is incident on the object to be measured 22, the output light is detected by the light receiving element PD3, and the output is converted to XY and is set as the first Y-axis input Y1 of the 25. The marker light output Rm and the reference wavelength light output Rs from the variable wavelength light source 10 also enter the light receiving element PD4 via the mirror M3 and the beam splitter BS6, where they are converted into electrical signals and sent to the second Y-axis input Y2 of the XY recorder 25. becomes. The output of the lamp generator 29 is the output of the variable wavelength light source 10.
It serves as the wavelength variable manual output and the X-axis input of the XY recorder 25. As a result, the spectral characteristics 26 are displayed on the XY recorder 25.
At the same time, reference light 27 and marker light 28 are recorded.

According to each of the above application examples, the reference light and marker light are displayed or recorded together with the measurement data, so the wavelength can be easily determined by counting the number of intervals between marker lights from the wavelength of the reference light and performing interpolation. I can do it.

(Effects of the Invention) As described above, according to the present invention, since marker signals at regular intervals are output together with the reference wavelength, it is possible to realize a variable wavelength light source that enables highly accurate wavelength measurement over a wide band. can. Furthermore, since precision is not required for the relationship between the input signal of the tunable wavelength laser +r light source and the oscillation wavelength, the configuration of the tunable wavelength laser light source is I! ! ! It's inside.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing one embodiment of the variable wavelength light source according to the present invention, FIG. 2 is a time chart for explaining the operation of the device shown in FIG. 1, and FIGS. 3 to 6 are the same as those shown in FIG. 1. A configuration block diagram showing an example of each component of the device, FIG.
8 is a principle explanatory diagram showing a modification of the device; FIG. 8 is a configuration block diagram showing one application example of the variable wavelength light source according to the present invention; FIG.
FIG. 10 is a block diagram showing a second application example of the variable wavelength light source according to the present invention, and FIG. 10 is a block diagram showing a third application example of the variable wavelength light source according to the present invention. 2... Variable wavelength laser light source, 4... Reference wavelength laser light source, 10... Variable wavelength light source, E+... Input signal,
"Pl...Wavelength selection device. ' = Mi a ν - Figure 4 Figure 5 Mu foil diagram Figure 7 A2

Claims (10)

[Claims] (1) Equipped with a tunable wavelength laser light source whose output light wavelength changes in accordance with an input signal, and a wavelength selection device which inputs the output light of the tunable wavelength laser light source and generates optical output at predetermined wavelength intervals. A variable wavelength light source characterized by: (2) 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. (3) The tunable wavelength light source according to claim 1, which uses a Fabry-Perot etalon as a wavelength selection device. (4) The tunable wavelength light source according to claim 2, which uses a Fabry-Perot etalon as a wavelength selection device. (5) A tunable wavelength light source according to claim 1, which uses an interferometer that passes only light at predetermined wavelength intervals as a wavelength selection device. (6) The tunable wavelength light source according to claim 1, further comprising a light-receiving element that inputs transmitted light of the wavelength selection device and converts it into an electrical signal, and the output of the light-receiving element is a marker signal output. (7) The tunable wavelength light source according to claim 3, wherein the wavelength interval of the marker light is changed by changing the resonator interval of the Fabry-Perot etalon. (8) The tunable wavelength light source according to claim 3, wherein an electro-optical element is provided in the Fabry-Perot etalon, and the equivalent resonator spacing is changed by an electric signal. (9) The tunable wavelength light source according to claim 4, wherein the Fabry-Perot etalon is provided with an electro-optical element, and the equivalent resonator spacing is changed by an electric signal. (10) By inputting a part of the output light of the reference wavelength laser light source into the Fabry-Perot etalon and controlling the electro-optical element so that the transmitted light of the reference wavelength component is maximized,
10. The variable wavelength light source according to claim 9, wherein one of the marker lights is configured to match a reference wavelength.