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Newport Nirvana™ 自動(dòng)平衡光接收器

為了消除與手動(dòng)平衡參考和信號(hào)光束相關(guān)的問(wèn)題，Nirvana 自動(dòng)平衡光接收器具有內(nèi)置的低頻反饋回路，可控制其中一個(gè)接收器的電子增益，并保持信號(hào)臂和參考臂之間的自動(dòng)平衡。您可以有效消除激光強(qiáng)度噪聲，并且在不使用鎖相放大器和光學(xué)斬波器的情況下進(jìn)行限制散粒噪聲的測(cè)量。

可將共模噪聲降低 50 dB

保持參考臂和信號(hào)臂之間的自動(dòng)直流平衡

自動(dòng)平衡或手動(dòng)平衡模式

增益和帶寬

非常適用于光譜分析

對(duì)比	型號(hào)
	1837 GHz Nirvana 自動(dòng)平衡光接收器，900-1650 nm
	2007 Nirvana 自動(dòng)平衡光接收器，400-1070 nm，125 kHz，8-32/M4
	2017 Nirvana 自動(dòng)平衡光接收器，800-1700 nm，125 kHz，8-32/M4

Newport Nirvana™ 自動(dòng)平衡光接收器產(chǎn)品規(guī)格

型號(hào)	1837	2007	2017
光輸入	FC/APC	FC and Free Space	FC and Free Space
探測(cè)器直徑		2.5 mm	1 mm
探測(cè)器類(lèi)型	PIN	PIN	PIN
波長(zhǎng)范圍	900-1650 nm	400-1070 nm	800-1700 nm
3 dB 帶寬	100 kHz to 300 MHz	DC to 125 KHz	DC to 125 KHz
共模抑制	25 dB	50 dB	50 dB
上升時(shí)間	1 ns	3 µ s	3 µ s
大轉(zhuǎn)換增益	30,000 V/W	5.2 x 105 V/W	1 x 106 V/W
大跨阻抗增益	40,000 V/A	1x106 V/A	1x106 V/A
大射頻功率	20 dB THD @ 100 MHz	+12 dBm bei 50 Ω	+12 dBm bei 50 Ω
NEP	15 pW/√Hz	3 pW/√Hz	3 pW/√Hz
峰值響應(yīng)度	0.75 A/W	0.5 A/W	1.0 A/W
飽和功率	1 mW	1 mW	0.5 mW
大光功率		4 mW	4 mW
輸出接頭	SMB	Male BNC	Male BNC
輸出阻抗	50 Ω	100 Ω	100 Ω
螺紋類(lèi)型	8-32	8-32	8-32

特征

可將共模噪聲降低 50 dB

Nirvana 的zhuan利電路除去了參考和信號(hào)光電流，進(jìn)而消除了這兩個(gè)通道常有的噪聲信號(hào)。與單光束實(shí)驗(yàn)相比，這使您測(cè)量信號(hào)功率時(shí)，對(duì)于 125 kHz 模型，噪聲減少了 50 dB；對(duì)于 1 GHz 模型，噪聲減少了 25 dB。

保持參考臂和信號(hào)臂之間的自動(dòng)直流平衡

與傳統(tǒng)的平衡接收器不同，即便兩個(gè)探測(cè)器上的平均光強(qiáng)度不同且會(huì)隨時(shí)間變化，Nirvana 的電子增益補(bǔ)償也可自動(dòng)實(shí)現(xiàn)平衡探測(cè)。自動(dòng)平衡技術(shù)可以消除來(lái)自動(dòng)態(tài)變化系統(tǒng)中的背景噪聲，包括熱漂移和波長(zhǎng)依賴性，實(shí)現(xiàn)參考光束和信號(hào)光束之間的*功率平衡。

400-1070 nm 或 800-1700 nm 版本

我們提供兩個(gè) Nirvana 光接收器，涵蓋 400-1070 nm 或 800-1700 nm 光譜范圍。

自動(dòng)平衡或手動(dòng)平衡模式

Nirvana 光接收器可在信號(hào)模式、平衡模式或自動(dòng)平衡模式下工作。光電探測(cè)器 (A) 的輸出可以表示為 A=(IS – g x IR) x Rf。在這里，IS 是信號(hào)光電二極管電流，IR 是參考光電二極管電流，Rf 是反饋電阻的值，g 是電流分流比，用于表示參考電流有多少來(lái)自消除節(jié)點(diǎn) (Isub)，有多少來(lái)自地面。在信號(hào)模式下，g 為零，沒(méi)有參考光電流來(lái)自消除節(jié)點(diǎn)。這里，輸出 A 僅僅是放大的信號(hào)電流。在平衡模式下，g 等于 1，所有參考光電流來(lái)自消除節(jié)點(diǎn)。在該模式下，A=(IS–IR)•Rf，光電探測(cè)器作為普通的平衡光接收器，如果直流光電流相等，則消除激光噪聲。在自動(dòng)平衡模式下，g 由低頻反饋回路以電子方式控制，以保持相等的直流光電流，抵消激光噪聲，而與光電流的大小無(wú)關(guān)。

The feedback loop in the Nirvana™ photoreceiver splits the reference photodetector current, IR, to generate the cancellation photocurrent, Isub. When the DC value of Isub equals the signal current, IS, the laser-amplitude noise is cancelled.

Femtosecond Ultrasonics Application Example

The optical components of improved laser-based acoustic set-up for thin film and microstructure metrology.

One example associated with the balanced photodetection technique is femtosecond ultrasonics wherein a femtosecond laser pulse is used to excite an acoustic wave in a material. The length of mechanical (acoustic) wave determines the resolution of ultrasound. Depending upon the materials for test, the velocity of sound, propagating through the media, has a magnitude in the order of 103
m/s. The acoustic wavelength employed in classical ultrasonics locates at around 0.1–10 mm, depending on materials and frequencies. A growing demand of computer chip manufacturers for non-destructive testing of microstructures and thin films has pushed the wavelength scope down to 10–20 nm.

Piezoelectric devices used for production and echo detection of acoustic waves in the macroscopic scale are too rigid in order to resolve signals within time scales of a few picoseconds and corresponding frequencies of 0.30.6 THz. In 1987, researchers at Brown University
proposed the use of laser-generated ultrasound for film thickness measurements. The performance of the laser-based acoustic method has been further improved recently by means of double-frequency modulation, cross-polarization, and balanced photodetection techniques. Shown above
is an improved pump-probe laser-based ultrasonic set-up as it is realized at the Center of Mechanics, Swiss Federal Institute of Technology in Zürich. The specimens (DUTs) consist of aluminum film
on a sapphire substrate.

A Ti:sapphire laser is used in this event to create short laser pulses having durations of less than 70 fs (1015
s) and a wavelength of 810 nm at a repetition rate of 81 MHz. The laser beam is split into a pump beam (carrying 90% of the energy) and a weaker probe beam by a beamsplitter. The short pump pulse hits perpendicular to the surface of the film specimen, and is absorbed within a thin surface layer (less than 10 nm deep). A mechanical stress is generated, which then excites thermo-elastically an acoustic pulse. When the bulk wave propagates and hits a discontinuity of the acoustic impedance (note: the film substrate border represents a strong discontinuity of the acoustic impedance), an echo occurs which is heading back to the surface of the film. Reaching the surface, the echo causes a slight change of the optical reflectivity.

The purpose of the probe pulse is to scan the optical reflectivity at the thin film surface versus time. Therefore, the experiments are constantly repeated at a repetition rate of 81 MHz, while the length of the optical path of the pump beam is varied. This means that the relative time shift between the pump pulse and the probe pulse is varied, and the optical reflectivity at the surface is scanned versus this relative time shift.

Frequency Modulation Spectroscopy Application Example

Diode-laser-based trace gas sensor configuration for continuous NH3 concentration measurements at 1.53 µm.6

In order to interrogate the spectral absorption profile of a sample (such as a noble gas),
frequency modulation spectroscopy
takes advantage of the change in optical absorption as a function of the frequency (wavelength) of light passed through the sample. A tunable laser can be used to generate a beam whose wavelength is time-varying. This beam is then split into two beams for balanced detection, one passing through the sample, and the other going directly into the reference photodiode. This differential measurement is the basis of FM
spectroscopy. Since the time axis of the observed signal is directly related to the optical frequency, the observed signal can easily be couched in terms of optical frequency (hence the name frequency modulation spectroscopy). By using a balanced photoreceiver, any fluctuations of the laser's intensity can be directly eliminated. In addition, the small percentage fluctuations on the DC optical signal due to the time-varying absorption of the sample can be detected with greatly enhanced signal-to-noise by employing a balanced photoreceiver. Light scattering spectroscopy (LSS) detects the scattered electric field interferometrically. It is very sensitive to phase front variations in the scattered wave.