JP2003222644A - Optical sampling waveform observing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sampling waveform observing apparatus capable of multiplexing a high-sensitive signal light, which is measured, with a sampling pulse light even if wavelength of the signal light differs much from that of the sampling pulse light, regardless of being first kind phase matching or second kind phase matching. <P>SOLUTION: The optical sampling waveform observing apparatus analyzes the waveform of the signal light, which is to be measured, by sampling the signal light using sampling pulse light. It is provided with a single multiplexing means 18 which has the characteristics of both polarized wave dependent filter and a multiplexer as a means for multiplexing the signal light with the sampling pulse light. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sampling waveform observing device for observing an optical signal waveform to be measured by sampling the signal light to be measured with sampling light, and particularly, in a multiplexer, there is no polarization dependence. The present invention relates to a high-efficiency multiplexer.

[0002]

2. Description of the Related Art As a device for observing the waveform of an optical signal,
Conventionally, an optical sampling waveform observation device has been known.
This optical sampling waveform observation apparatus generates a sum frequency light (ω1 + ω2) of an optical signal under measurement (angular frequency ω1) and a sampling pulse optical signal (angular frequency ω2) having a narrower pulse width than that in a nonlinear optical crystal. (Sun-Frequency-
Generatio: hereinafter referred to as "SFG"), the optical sampling is performed, the photoelectric conversion element converts the signal into an electric signal, and the waveform of the measured optical signal is observed.

Further, in order to generate the sum frequency light (ω1 + ω2) by the nonlinear optical crystal, it is necessary to perform phase matching. For phase matching, the first-order phase matching, in which the polarization states of the sampling pulse light and the signal light to be measured are incident in the same direction, and the linear polarization in which the polarization states of the sampling pulse light and the signal light to be measured are orthogonal, are incident. There is the second type phase matching.

As the nonlinear optical crystal used for the first type phase matching, there is a PPLN crystal (periodically poled LiNbO ₃ crystal) or the like. Further, as the nonlinear optical crystal used for the second type phase matching, there is a KTP crystal (KTiOPO ₄ crystal) or the like, but the sum frequency light generation efficiency is low and the sensitivity is deteriorated as compared with the case of the PPLN crystal.

Next, an example of a conventional optical sampling waveform observation apparatus using the second type phase matching will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes an electric signal source (SG1) for generating a signal light to be measured (for example, 10 GHz), and the electric signal (fsi
g) is applied to a 10-GHz MLFRL (mode-locked fiber ring laser) indicated by 2 to generate a repetitive optical pulse train of 10 GHz.

This optical pulse train is given to a light intensity modulator (LN-mod) shown by 3 together with a data (deta) signal from a pulse pattern generator shown by 5, and an optical signal train of 10 Gb / s is given. Then, data is modulated, and the signal is optically amplified by the optical amplifier shown by 4 to obtain the optical signal to be measured. The portions 1 to 5 in FIG. 1 are portions for obtaining the signal light to be measured having a repetition frequency of fsig, and this portion may be omitted and the signal light to be measured may be directly applied to the device.

Reference numeral 13 is an electric signal source (SG2) for generating sampling pulsed light, and has a repetition period of (fsig /
n−Δf) (for example, 50MHz-100Hz) electric signal
It is generated in synchronization with the output of fsig. This electrical signal (fsig
/ n-Δf) is given to the pulse light source shown by 14 to be converted into an optical pulse, which is optically amplified by the optical amplifier shown by 15 to obtain sampling pulsed light.

Reference numerals 6 and 16 denote polarization controllers for varying the polarization states of the signal light under measurement and the sampling pulse light, and the signal light under measurement and the sampling pulse light whose polarization states are adjusted by the polarization controller. Is applied to a polarization beam splitter (PBS) indicated by 7 and multiplexed.

The signal light to be measured and the sampling pulse light multiplexed by the polarization beam splitter are applied to a nonlinear optical crystal (KTP) 8 to generate sum frequency light (ω1 + ω2), and the sum frequency light (ω1 + ω2) is generated. Only the sum frequency light is selected through the band pass filter (BPF) and the optoelectronic converter (Si-A
PD) to convert to electrical signals. The sum frequency light (ω1 + ω2) converted into an electric signal is converted into a digital signal by an analog-digital converter (A / D) indicated by 11 and input to a computer indicated by 12 to be measured optical signal. Analyze the waveform of.

Next, the principle of optical sampling in the optical sampling waveform observation apparatus of FIG. 1 will be described with reference to FIG.
In FIG. 5, the signal light to be measured having a repetition period (fsig) (this angular frequency is ω1) and a repetition period (fsig / n−) lower than an integer fraction of the fsig by about several hundred Hz or several kHz. Sampling pulsed light having Δf) (this angular frequency is ω2) and a nonlinear optical crystal (KTP)
Incident on.

In the nonlinear optical crystal, the sum frequency light (ω1 + ω2) occurs only when both the signal light to be measured and the sampling pulse light are simultaneously incident due to the nonlinear optical effect by the incident signal light to be measured and sampling pulse light. (SCIENCE FICTION
Light) etc. At this time, the pulse width of the sampling pulse light is made sufficiently narrower than the pulse width of the signal light under measurement, so that the signal light under measurement is sampled according to the principle of sampling. The waveform of the signal light to be measured can be observed by converting the sampled signal into an electric signal and analyzing it by a computer.

FIG. 6 shows the relationship among the wavelengths of the incident signal light to be measured, the sampling pulse light, and the sum frequency light (SF light) in the optical sampling waveform observation apparatus in FIG. In FIG. 6, the horizontal axis represents wavelength and the vertical axis represents optical power. FIG. 6 shows that the sampling pulse light in the 1500 nm band and the signal light to be measured generate sum frequency light and second harmonic light in the 780 nm band due to the nonlinear optical effect.

The prior application No. 2001-25 of the present applicant
As No. 8008, there is an optical sampling waveform observation device (reference example) using Raman shift light shown in FIG. This optical sampling waveform observation device is characterized in that Raman shift light is used as the sampling pulse generating means.

The Raman-shifted light propagates in the fiber when an ultrashort pulsed light is incident on the optical fiber, and due to the Raman effect which is a kind of nonlinear optical effect, the Raman-shifted light has a wavelength on the long-wave side in addition to the incident pulse. It is an ultrashort pulsed light generated by shifting.

An optical sampling waveform observation apparatus using Raman shift light, which is a reference example, will be described with reference to FIG. In FIG. 3, reference numeral 1 denotes an electric signal source (SG1) for generating an optical signal under measurement (eg, 10 GHz), and the electric signal (fsi
g) is applied to a 10-GHz MLFRL (mode-locked fiber ring laser) indicated by 2 to generate a repetitive optical pulse train of 10 GHz.

This optical pulse train is given to a light intensity modulator (LN-mod) shown by 3 together with a data (deta) signal from a pulse pattern generator (shown by 5) to give an optical signal train of 10 Gb / s. Then, data modulation is performed, and the signal is optically amplified by the optical amplifier shown by 4 to obtain the measured optical signal. The portions 1 to 5 in FIG. 3 are portions for obtaining the signal light to be measured having a repetition frequency of fsig, and this portion may be omitted and the signal light to be measured may be directly applied to the device.

Reference numeral 13 is an electric signal source (SG2) for generating sampling pulse light, and has a repetition period of (fsig /
n−Δf) (for example, 50MHz-100Hz) electric signal
It is generated in synchronization with the output of fsig. This electrical signal (fsig
/ n−Δf) is applied to the pulse light source indicated by 14 and converted into an optical pulse, which is optically amplified by the optical amplifier indicated by 15 and is incident on the Raman shift optical fiber indicated by 20, and is converted by the pulse light source. The Raman shift light having a wavelength different from that of the pulsed light is generated.

The output light of this Raman shift optical fiber is
Only Raman-shifted light is selected through the fundamental-wave removing bandpass filter 21 to obtain sampling pulsed light (Raman-shifted light).

Reference numerals 6 and 16 denote polarization controllers for varying the polarization states of the signal light to be measured and the sampling pulse light, and the signal light to be measured and Raman shift light whose polarization states are adjusted by the polarization controller. Is applied to the multiplexer indicated by 7 and multiplexed.

The measured optical signal and the sampling pulse light multiplexed by the multiplexer are applied to a nonlinear optical crystal (PPLN) indicated by 19 to generate sum frequency light (ω1 + ω2),
Only the sum frequency light is selected through the band pass filter (BPF) 9 and converted into an electric signal by the photoelectric converter (Si-APD) 10. Sum frequency light (ω1
+ ω2) is converted into a digital signal by an analog-to-digital converter (A / D) indicated by 11 and a computer (compute
Input to r) and analyze the waveform of the measured optical signal.

FIG. 7 shows the relationship between the wavelengths of the signal light to be measured, the sampling pulse light, and the sum frequency light (SF light) that are incident on the optical sampling waveform observation apparatus using the Raman shift light in FIG. In FIG. 7, the horizontal axis represents wavelength and the vertical axis represents optical power. FIG. 7 shows that the signal light to be measured (signal light) in the 1550 nm band and the sampling pulse light in the 2000 nm band generate sum frequency light in the 780 nm band and second harmonic light in the 1000 nm band due to the nonlinear optical effect. ing.

[0022]

As described above, in the conventional optical sampling waveform observing apparatus using the second type phase matching shown in FIG. 1, the polarization beam splitter ( However, in the case of Phase I phase matching, the signal light to be measured and the sampling pulsed light must be combined with the same linear polarization, so a polarization beam splitter (PBS) is used. It could not be used. In this case, an ordinary beam splitter is used, but in that case, there is a problem that both the signal light to be measured and the sampling pulse light receive a large loss and the sensitivity deteriorates.

Also, in the case of the optical sampling waveform observing apparatus using the type II phase matching shown in FIG. 1, when the wavelengths of the signal light to be measured and the sampling pulse light are significantly different, the wavelength dependence of the polarization beam splitter is used. Depending on the characteristics, there is a problem that both or one of the signal light to be measured and the sampling pulsed light is largely lost and the sensitivity is deteriorated.

In the optical sampling waveform observation apparatus using Raman shift light which is the reference example shown in FIG. 3, since two optical elements (optical fiber for Raman shift and bandpass filter for removing fundamental wave) are used, Raman is used. The loss of the shift light increases and the alignment becomes complicated, which is also disadvantageous in terms of cost.

An object (object) of the present invention is to provide a highly sensitive signal to be measured even when the wavelengths of the signal light to be measured and the sampling pulsed light are largely different, regardless of the first type phase matching and the second type phase matching. An object of the present invention is to provide an optical sampling waveform observation device capable of multiplexing light and sampling pulse light.

[0026]

In order to solve the above problems, in an optical sampling waveform observing device for sampling a signal light to be measured with a sampling pulse light and analyzing the waveform of the signal light to be measured, As a means for combining the sampling pulsed light and the sampling pulsed light, a single combining means having the characteristics of the polarization independent filter and the combiner is provided.
(Claim 1)

As the sampling pulse light,
The configuration uses Raman shift light. (Claim 2) Further, a cold filter is used as the multiplexing means. (Claim 3) Further, a cold mirror is used as the multiplexing means.
(Claim 4) The optical sampling waveform observation apparatus according to claim 1 or 2, characterized in that. In addition, the wavelengths of the signal light to be measured and the sampling pulsed light have values that greatly differ from each other.
(Claim 5)

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical sampling waveform observing device using a multiplexing means having a polarization independent filter and a multiplexer, which is a first embodiment of the present invention, will be described with reference to FIG. explain. In FIG. 2, reference numeral 1 denotes an electric signal source (SG1) for generating a signal light to be measured (for example, 10 GHz),
The electric signal (fsig) is applied to a 10-GHz MLFRL (mode-lock fiber ring laser) indicated by 2 to generate a repetitive optical pulse train of 10 GHz.

This optical pulse train is given to the light intensity modulator (LN-mod) shown by 3 together with the data (deta) signal from the pulse pattern generator (pulse-pattern-genrator) shown by 5, and an optical signal train of 10 Gb / s is given. Then, data is modulated, and the signal is optically amplified by the optical amplifier shown by 4 to obtain the optical signal to be measured. The portions 1 to 5 shown in FIG. 2 are portions for obtaining the signal light to be measured having a repetition frequency of fsig, and this portion may be omitted and the signal light to be measured may be directly applied to the device.

Reference numeral 13 is an electric signal source (SG2) for generating sampling pulsed light, and has a repetition period of (fsig /
n−Δf) (for example, 50MHz-100Hz) electric signal
It is generated in synchronization with the output of fsig. This electrical signal (fsig
/ n-Δf) is given to the pulse light source shown by 14 to be converted into an optical pulse, which is optically amplified by the optical amplifier shown by 15 to obtain sampling pulsed light.

Reference numerals 6 and 16 denote polarization controllers for changing the polarization states of the signal light under measurement and the sampling pulse light, and the signal light under measurement and the sampling pulse light whose polarization states are adjusted by the polarization controller. (17) is applied to the combining means having the characteristics of the polarization independent filter and the combiner to combine the signals.

A non-linear optical crystal (KTP or PPLN) indicated by 18 shows the signal light to be measured and the sampling pulsed light, which are combined by the combining means having the characteristics of the polarization independent filter and the combiner. Generates the sum frequency light (ω1 + ω2), selects only the sum frequency light through the band pass filter (BPF) 9 and selects the photoelectric converter (Si-APD) 10
Is converted into an electric signal with. An analog-digital converter (A that indicates the sum frequency light (ω1 + ω2) converted into an electric signal at 11
Computer (c
input to the computer) and analyze the waveform of the measured optical signal.

In the optical sampling waveform observing device using the multiplexing means having both the polarization independent filter and the multiplexer shown in FIG. 2, even in the case of the signal light to be measured and the sampling pulsed light whose wavelengths are greatly different from each other. It becomes possible to observe the signal waveform under measurement with high sensitivity. As a nonlinear optical crystal, KTP
Or, either PPLN can be applied.

Next, an optical sampling waveform observing device using Raman shift light, which is a second embodiment of the present invention, will be described with reference to FIG. In FIG. 4, reference numeral 1 denotes an electric signal source (SG1) for generating a signal light to be measured (eg, 10 GHz), and the electric signal (fsig) is indicated by 2 in the 10-GHz MLFRL.
(Mode-lock fiber ring laser), give 10GH
Generate a repetitive optical pulse train of z.

This optical pulse train is given to the light intensity modulator (LN-mod) shown by 3 together with the data (deta) signal from the pulse pattern generator (pulse-pattern-genrator) shown by 5, and an optical signal train of 10 Gb / s is given. Then, data modulation is performed, and the signal light to be measured is obtained by optical amplification by the optical amplifier shown by 4. The portions 1 to 5 shown in FIG. 4 are portions for obtaining the signal light to be measured having a repetition frequency of fsig, and this portion may be omitted and the signal light to be measured may be directly applied to the device.

Reference numeral 13 is an electric signal source (SG2) for generating sampling pulsed light, and has a repetition period of (fsig /
n−Δf) (for example, 50MHz-100Hz) electric signal
It is generated in synchronization with the output of fsig. This electrical signal (fsig
/ n−Δf) is given to the pulse light source shown by 14 to be converted into an optical pulse, amplified by the optical amplifier shown by 15 and incident on the Raman shift optical fiber shown by 20, and converted by the pulse light source. Raman shift light having a wavelength different from that of the pulsed light is generated.

Reference numerals 6 and 16 denote polarization controllers for changing the polarization states of the signal light under measurement and the sampling pulse light, and the signal light under measurement and the sampling pulse light whose polarization states are adjusted by the polarization controller. 17 is applied to a combining means having the characteristics of a polarization-independent filter and a combiner to select only Raman-shifted light and combine with the signal light to be measured.

A nonlinear optical crystal (PPLN) indicated by 19 for the signal light to be measured and Raman shift light multiplexed by the multiplexing means having the characteristics of the polarization independent filter and the multiplexer.
To generate the sum frequency light (ω1 + ω2), select only the sum frequency light through the bandpass filter (BPF) 9 and convert the electrical power with the photoelectric converter (Si-APD) 10 Convert to signal. Sum frequency light (ω1 + ω2) converted into an electrical signal
Is converted into a digital signal by an analog-to-digital converter (A / D) indicated by 11 and is input to a computer indicated by 12 to analyze the waveform of the measured optical signal.

A cold filter and a cold mirror are suitable as the multiplexing means having the characteristics of the polarization independent filter and the multiplexer used in the present invention. A cold filter is a wavelength selection filter for the infrared region (heat rays) in which heat-absorbing glass is coated with dielectric substances with different refractive indexes alternately in multiple layers. It transmits visible light and reflects near-infrared light. Absorb. A cold mirror is a wavelength selection mirror for the infrared region (heat rays) in which dielectric materials with different refractive indexes are alternately coated on white plate glass and reflects 90% or more of visible light (400 to 700 nm). , Transmits 80% or more of near infrared light.

[0040]

According to the invention described in claim 1, in the optical sampling waveform observing device for sampling the signal light to be measured with the sampling pulse light and analyzing the waveform of the signal light to be measured, the signal light to be measured and the sampling pulse are As a means for combining light, by providing a single combining means that combines the characteristics of a polarization-independent filter and a combiner, regardless of the type 1 phase matching and the type 2 phase matching It is possible to obtain an optical sampling waveform observing device capable of multiplexing the highly sensitive signal light to be measured and the sampling pulse light even when the wavelengths of the signal light to be measured and the sampling pulse light are largely different.

According to the second aspect of the present invention, the Raman shift light is used as the sampling pulse light, so that it is necessary to remove the fundamental wave, which has conventionally been required to be installed in the subsequent stage for Raman shift. The bandpass filter can be omitted. In the inventions according to claims 3 and 4,
The device can be configured by using a commercially available cold filter and cold mirror as the multiplexing means. Further, in the invention according to claim 5, even when the wavelengths of the signal light to be measured and the sampling pulsed light are set to values greatly different from each other, the loss of the optical signal can be minimized and the deterioration of the sensitivity can be prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a conventional optical sampling waveform observing apparatus using second type phase matching.

FIG. 2 is a diagram showing a configuration of an optical sampling waveform observing device using a multiplexing means having the characteristics of a polarization-independent filter and a multiplexer of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional optical sampling waveform observation apparatus using Raman shift light.

FIG. 4 is a diagram showing a configuration of an optical sampling waveform observation device using Raman shift light according to the present invention.

FIG. 5 is a diagram for explaining the principle of optical sampling.

FIG. 6 is a diagram showing a relationship of wavelengths of optical signals of the optical sampling waveform observation device of FIG.

7 is a diagram showing a relationship of wavelengths of optical signals of the optical sampling waveform observation device of FIG.

[Explanation of symbols]

1 signal source for generating signal light to be measured 2 mode-locked fiber ring laser (electrical-optical conversion means) 3 optical intensity modulator 4 optical amplifier 5 pulse pattern generator 6 polarization controller 7 polarization beam splitter 8 nonlinear optical crystal (KTP) 9 band Pass filter (BPF) 10 Optical-electrical conversion means 11 Analog-digital conversion means 12 Computer 13 Sampling pulse light generation signal source 14 Pulse light source 15 Optical amplifier 16 Polarization controller 17 Multiplexing means (polarization independent filter + 18 Nonlinear optical crystal (KTP or PPLN) 19 Nonlinear optical crystal (PPLN) 20 Optical fiber for Raman shift 21 Bandpass filter for fundamental wave removal

Claims (5)

[Claims] 1. An optical sampling waveform observing device for analyzing a waveform of a signal light under measurement by sampling the signal light under measurement with a sampling pulse light, comprising: An optical sampling waveform observing device comprising a single multiplexing means having the characteristics of a wave independent filter and a multiplexer. 2. The optical sampling waveform observing device according to claim 1, wherein Raman shift light is used as the sampling pulse light. 3. The optical sampling waveform observing device according to claim 1, wherein a cold filter is used as the multiplexing means. 4. The optical sampling waveform observing apparatus according to claim 1, wherein a cold mirror is used as the multiplexing means. 5. The optical sampling waveform observing device according to claim 1, wherein the wavelengths of the signal light to be measured and the sampling pulsed light are values that are significantly different from each other.